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Assessment of TBC systems failure mechanisms using a fracture mechanics approach
Failure of thermal barrier coating (TBC) systems under thermomechanical loading is very complicated, as it is influenced by many factors, such as thermal mismatch, oxidation, interface roughness, creep, sintering, which have to be more or less taken into account. Determination of the residual stress fields induced yields information about the critical areas for crack nucleation in a first step and
J. Aktaa; K. Sfar; D. Munz
Numerical investigation of residual stress fields and crack behavior in TBC systems
Due to thermal expansion mismatch and bond coat (BC) oxidation, high residual stresses are induced in the thermal barrier coating (TBC), leading to failure by spalling and delamination. Using the finite element method (FEM), an analysis of the stress distributions in TBC systems, which is a prerequisite for the understanding of failure mechanisms, was performed. As cracking usually occurs at
K Sfar; J Aktaa; D Munz
Effect of Bond Coat Creep and Oxidation on TBC (Thermal Barrier Coating) Integrity.
National Technical Information Service (NTIS)
The potential of thermal barrier coatings (TBCs) on high-pressure turbine (HPT) nozzles and blades is limited at present by the inability to quantitatively predict TBC life for these components. The goal is to isolate the major TBC failure mechanisms, whi...
E. C. Duderstadt B. H. Pilsner
Modelling of TBC system failure: Stress distribution as a function of TGO thickness and thermal expansion mismatch
Advances in gas turbine technology place an increasing demand on thermal protection systems of nickel-base superalloys in turbine blades. Current strategies for performance improvements are focused on thermal barrier coatings (TBC). Typical current TBC system are composed of: top coat (TC), an yttria stabilised zirconia outer layer that provides thermal insulation; a bond coat (BC) layer, aluminium rich, supplying oxidation
M. Martena; D. Botto; P. Fino; S. Sabbadini; M. M. Gola; C. Badini
Mechanics of damage initiation and growth in a TBC\\/superalloy system
Creep analysis was used to estimate stresses in different layers especially in bond coat and the thermally grown oxide (TGO) layer to determine the role of creep on damage initiation in the TBC system. Microcracks were observed to initiate near the bond coat\\/TGO interface after only a few thermal cycles. The origin of these microcracks can be attributed to the
M. Y. Ali; S. Q. Nusier; G. M. Newaz
MEMS components by their very nature have different and unique failure mechanisms than their macroscopic counterparts. This paper discusses failure mechanisms observed in various MEMS components and technologies. MEMS devices fabricated using bulk and surface micromachining process technologies are emphasized. MEMS devices offer uniqueness in their application, fabrication, and functionality. Their uniqueness creates various failure mechanisms not typically found in their bulk or IC counterparts. In ICs, electrical precautions are taken to mitigate failure. In MEMS, both electrical and mechanical precautions must be enacted to reduce the risk of failure and increased reliability. Unlike ICs, many MEMS components are designed to interact with their environment, making the fabrication, testing, and packaging processes critical for the success of the device.
Walraven, Jeremy Allen
Study of the performance of TBC under thermal cycling conditions using an acoustic emission rig
An experimental rig based on the use of infrared quartz lamps has been developed to monitor the degradation mechanisms causing\\u000a failure of thermal barrier coatings (TBC) under thermal-cycling conditions. An acoustic emission (AE) technique monitored\\u000a these degradation mechanisms, and advanced signals processing identified the key parameters that classify the AE signals according\\u000a to the long-term behavior of the TBC. The
J. Voyer; F. Gitzhofer; M. I. Boulos
Oxidation-induced failure of EB-PVD thermal barrier coatings
Oxidation-induced failure of EB-PVD thermal barrier coatings (TBC) deposited on a single-crystal superalloy with a platinum aluminide bond coat has been studied in order to determine the specific mechanisms leading to TBC spallation. Cyclic oxidation tests performed at 1150�C show that failure of the TBC occurs when the alumina scale, growing at the bond coat�TBC interface, attains its critical thickness.
V. K Tolpygo; D. R Clarke; K. S Murphy
TBC-domain GAPs for Rab GTPases accelerate GTP hydrolysis by a dual-finger mechanism
Rab GTPases regulate membrane trafficking by cycling between inactive (GDP-bound) and active (GTP-bound) conformations. The duration of the active state is limited by GTPase-activating proteins (GAPs), which accelerate the slow intrinsic rate of GTP hydrolysis. Proteins containing TBC (Tre-2, Bub2 and Cdc16) domains are broadly conserved in eukaryotic organisms and function as GAPs for Rab GTPases as well as GTPases
Xiaojing Pan; Sudharshan Eathiraj; Mary Munson; David G. Lambright
Degradation Mechanisms of an Advanced Jet Engine Service-Retired TBC Component
Current use of TBCs is subjected to premature spallation failure mainly due to the formation of thermally grown oxides (TGOs). Although extensive research has been carried out to gain better understanding of the thermo - mechanical and -chemical characteristics of TBCs, laboratory-scale studies and simulation tests are often carried out in conditions significantly differed from the complex and extreme environment
Rudder T. Wu; Makoto Osawa; Tadaharu Yokokawa; Kyoko Kawagishi; Hiroshi Harada
Two simplistic models using fracture mechanics considerations are used to advance understanding of the failure conditions in TBC system. One model assumes isostrain behavior prior to the onset of crack initiation and is based on elastic energy balance approach. The other model is used for crack propagation behavior. The analysis for crack initiation suggests that the crack tip driving force,
Amar N. Kumar; Amiya Nayak; Alok R. Patnaik; Xijia Wu; Prakash C. Patnaik
Failure mechanisms of thermal barrier systems
NASA Astrophysics Data System (ADS)
Thermal barrier coatings (TBCs) are widely used in turbines for propulsion and power generation. The benefit results from their ability to sustain high thermal gradients in the presence of adequate backside cooling. Lowering the temperature of the metal substrate prolongs the life of the component: whether from environmental attack, creep rupture, or fatigue. Thermal barrier systems exhibit multiple failure mechanisms, depends on the deposition methods of the TBCs, chemical composition of the bond coats, and their working environments. Some of the most prevalent are studied in this thesis. There are two types of thermal barrier systems based on the chemical composition of the bond coats: Pt-aluminide and NiCoCrAlY bond coats. Ratcheting happens the most in the systems with Pt-aluminide bond coats; while edge delamination is considered a possible failure mechanism for the systems with NiCoCrAlY bond coats. Ratcheting is motivated by displacement instability in the thermally grown oxide (TGO). Interactions between cracks induced in TBCs upon thermal cycling have been calculated. Cracks that converge from neighboring imperfections exhibit a minimum energy release rate prior to coalescence. Equating this minimum to the toughness of the TBC provides a criterion for coalescence and failure. Imposing this criterion allows the change in crack length upon cycling and the number of cycles to failure to be ascertained. This simulation capability is used to explore various influences on durability. Samples with NiCoCrAlY bond coat are studied after subjected to thermal cycling in a burner rig. In each case, a dominant delamination has been identified, that extends primarily along the interface between the TGO and the bond coat. Calculations of the delamination energy release rate, upon comparison with the interface toughness, reveals a critical TGO thickness, (h tgo)c ? 3mum, comparable to that found experimentally.
Xu, Tao
TBC experience in land based gas turbines
NASA Technical Reports Server (NTRS)
Prior and on-going machine evaluations of TBC coatings for power generation applications are summarized. Rainbow testing of various TBC's on turbine nozzles, shrouds and buckets are described along with one test on combustor liners. GEPG has conducted over 15 machine tests with TBC coated turbine nozzles of various coatings. Rainbow test times generally range between 10,000 to 24,000 hours. TBC performance has been quite good and additional testing, including TBC's on shrouds and buckets is continuing. The results show that TBC's have the capability of surviving in power generation machines for the times required. The earlier rainbow tests which evaluated various top coat compositions resulted in confirmation of the superiority of YSZ and especially the 6-8 YSZ composition. On-going tests are more focused on TBC process and property variations. The prevalent failure modes seen thus far in the various rainbow tests are erosion, foreign object damage and buildup of deposits. Additional post test analysis is required to investigate bond coat oxidation and other time/temperature dependent changes to the system.
Nelson, W. A.; Orenstein, R. M.
Failure rate estimation of known failure mechanisms of electronic packages
Product reliability is one of the key factors for a successful product launch. However, electronic components can still fail in various stages of applications due to certain failure mechanisms. A constant failure rate typically describes a majority of non-solder joint related package failures in the accelerated testing or the field application. Historically, the failure rate for a constant failure phenomenon
Liyu Yang; Joseph B. Bernstein
Ubiquitination and degradation of the hominoid-specific oncoprotein TBC1D3 is regulated by protein palmitoylation
Highlights: �Hominoid-specific oncogene TBC1D3 is targeted to plasma membrane by palmitoylation. �TBC1D3 is palmitoylated on two cysteine residues: 318 and 325. �TBC1D3 palmitoylation governs growth factors-induced TBC1D3 degradation. �Post-translational modifications may regulate oncogenic properties of TBC1D3. -- Abstract: Expression of the hominoid-specific oncoprotein TBC1D3 promotes enhanced cell growth and proliferation by increased activation of signal transduction through several growth factors. Recently we documented the role of CUL7 E3 ligase in growth factors-induced ubiquitination and degradation of TBC1D3. Here we expanded our study to discover additional molecular mechanisms that control TBC1D3 protein turnover. We report that TBC1D3 is palmitoylated on two cysteine residues: 318 and 325. The expression of double palmitoylation mutant TBC1D3:C318/325S resulted in protein mislocalization and enhanced growth factors-induced TBC1D3 degradation. Moreover, ubiquitination of TBC1D3 via CUL7 E3 ligase complex was increased by mutating the palmitoylation sites, suggesting that depalmitoylation of TBC1D3 makes the protein more available for ubiquitination and degradation. The results reported here provide novel insights into the molecular mechanisms that govern TBC1D3 protein degradation. Dysregulation of these mechanisms in vivo could potentially result in aberrant TBC1D3 expression and promote oncogenesis.
Kong, Chen; Lange, Jeffrey J.; Samovski, Dmitri [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States); Su, Xiong [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States); Liu, Jialiu [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States); Sundaresan, Sinju [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States); Stahl, Philip D., E-mail: firstname.lastname@example.com [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States)
Stress state and failure mechanisms of thermal barrier coatings: role of creep in thermally grown oxide
The mechanical loading of the thermal barrier coating (TBC)\\/thermally grown oxide (TGO)\\/bond coat interface region is calculated for a TBC coated superalloy specimen using a finite element model. It is shown that the evolving stress state depends crucially on the ratio of the loading rate caused by growth and swelling of the oxide layer and the unloading rate by creep
J. R�sler; M. B�ker; M. Volgmann
Metabolic Mechanisms in Heart Failure
Although neurohumoral antagonism has successfully reduced heart failure morbidity and mortality, the residual disability and death rate remains unacceptably high. Though abnormalities of myocardial metabolism are associated with heart failure, recent data suggest that heart failure may itself promote metabolic changes such as insulin resistance, in part through neurohumoral activation. A detrimental self-perpetuating cycle (heart failure 3 altered metabolism 3
Houman Ashrafian; Michael P. Frenneaux; Lionel H. Opie
TBC experience in land based gas turbines
NASA Technical Reports Server (NTRS)
This paper summarizes prior and on-going machine evaluations of TBC coatings for power generation applications. Rainbow testing of TBC's on turbine nozzles, shrouds, and buckets are described along with a test on combustor liners. GEPG has conducted over 15 machine tests with TBC coated turbine nozzles of various coatings. TBC performance has been quite good and additional testing, including TBC's on shrouds and buckets, is continuing. Included is a brief comparison of TBC requirements for power generation and aircraft turbines.
Nelson, Warren A.; Orenstein, Robert M.
Two test bed concentrators (TBCs) were designed to provide high-performance test beds for advanced solar receivers and converters. However, the second-surface silvered-glass mirror facets on the TBCs, which were originally manufactured by the Jet Propulsion Laboratory, have experienced severe silver corrosion. To restore reflectance, TBC-2 was refurbished with a lustering technique developed at Sandia National Laboratories. In the lustering technique, second-surface silvered thin-glass mirrors were applied over the corroded facets, thereby increasing the dish reflectivity and raising the available power of TBC-2 from approximately 70 to 78 kW{sub t}. Degradation of the original optical accuracy of the TBC facets was determined to be minimal. Lustering was chosen over facet replacement because of the lower cost, the anticipated improvement in corrosion resistance, and the shorter project duration. This report includes background information, details of the lustering process, and test results from TBC-2 characterization, both before and after lustering.
Diver, R.B.; Jones, S.; Robb, S.; Mahoney, A.R.
Failure Mode/Mechanism Distributions.
National Technical Information Service (NTIS)
The intent of this document is to present failure mode distributions to be used in support of reliability analysis such a FMEAs and FMECAs when used in conjunction with accepted reliability prediction techniques such as MIL-HDBK-21 along with RACs Nonelec...
G. Chandler M. J. Rossi R. Wanner W. K. Denson
Field failure mechanisms for photovoltaic modules
NASA Technical Reports Server (NTRS)
Beginning in 1976, Department of Energy field centers have installed and monitored a number of field tests and application experiments using current state-of-the-art photovoltaic modules. On-site observations of module physical and electrical degradation, together with in-depth laboratory analysis of failed modules, permits an overall assessment of the nature and causes of early field failures. Data on failure rates are presented, and key failure mechanisms are analyzed with respect to origin, effect, and prospects for correction. It is concluded that all failure modes identified to date are avoidable or controllable through sound design and production practices.
Dumas, L. N.; Shumka, A.
Microstructural investigations of plasma-sprayed yttria partially stabilized zirconia TBC (in relation to thermomechanical resistance and high-temperature oxidation mechanisms)
This study deals with microstructural investigations of plasma-sprayed yttria partially stabilized zirconia thermal barrier coatings, performed by classical and analytical transmission electron microscopy. The aim of the study was to determine eventual relationships between coating microstructure and toughness. The ceramic\\/metal interface, which plays an important role during TBC thermomechanical solicitation, has also been studied. In the 6--8 wt. percent Y[sub
S. Alperine; L. Lelait
To the mechanisms of failure wave
NASA Astrophysics Data System (ADS)
Results of shock-wave experiments with free and prestressed samples of K8 and K14 crown glasses are presented. Controlled confinement pressure on the specimen of around 200 MPa was provided by installing a shrink-fit metal sleeve on the lateral surface of the sample disk. Results of measurements of the free surface velocity histories show that prestressing leads to earlier stopping of the failure wave. Thus, the compressive transverse stress increases the failure threshold that is in agreement with existing criteria of compressive fracture. However, sensitivity of the failure threshold to the confinement stress value is not as high as it could be expected. Measurements of the refractive indexes for the particles from the failure wave zone of recovered glass samples have shown their small increase whereas no index change for particles from the residual zone was found. It has been concluded that irreversible densification makes essential contribution to the mechanism of failure of glasses.
Kanel, G. I.; Bless, S. J.; Savinykh, A. S.; Razorenov, S. V.; Chen, T.; Rajendran, A.
Failure mechanisms in wire ropes
The inevitable attrition of wire rope in service is discussed with an overview of the consequences in terms of inspection and replacement criteria. Details are presented of specific degradation mechanisms observed in three different applications: a mine hoist rope operating on a drum winder, a mooring rope for an offshore structure and a spin-resistant single-fall offshore crane rope. In each
C. R. Chaplin
Failure of thermal barrier coating systems under cyclic thermomechanical loading
The failure mechanisms of thermal barrier coating (TBC) systems applied on gas turbine blades and vanes are investigated using thermomechanical fatigue (TMF) tests and finite element (FE) modeling. TMF tests were performed at two levels of applied mechanical strain, namely five times and three times the critical in-service mechanical strain of an industrial gas turbine. TMF testing under the higher
E Tzimas; H M�llejans; S. D Peteves; J Bressers; W Stamm
Cytoplasmic Retention of a Nucleocytoplasmic Protein TBC1D3 by Microtubule Network Is Required for Enhanced EGFR Signaling
The hominoid oncogene TBC1D3 enhances epidermal growth factor receptor (EGFR) signaling and induces cell transformation. However, little is known regarding its spatio-temporal regulation and mechanism of tumorigenesis. In the current study, we identified the microtubule subunit ?-tubulin as a potential interaction partner for TBC1D3 using affinity purification combined with mass spectrometry analysis. The interaction between TBC1D3 and ?-tubulin was confirmed by co-immunoprecipitation. Using the same method, we also revealed that TBC1D3 co-precipitated with endogenous ?-tubulin, another subunit of the microtubule. In agreement with these results, microtubule cosedimentation assays showed that TBC1D3 associated with the microtubule network. The ?-tubulin-interacting site of TBC1D3 was mapped to amino acids 286?353 near the C-terminus of the TBC domain. Deletion mutation within these amino acids was shown to abolish the interaction of TBC1D3 with ?-tubulin. Interestingly, the deletion mutation caused a complete loss of TBC1D3 from the cytoplasmic filamentous and punctate structures, and TBC1D3 instead appeared in the nucleus. Consistent with this, wild-type TBC1D3 exhibited the same nucleocytoplasmic distribution in cells treated with the microtubule depolymerizing agent nocodazole, suggesting that the microtubule network associates with and retains TBC1D3 in the cytoplasm. We further found that deficiency in ?-tubulin-interacting resulted in TBC1D3's inability to inhibit c-Cbl recruitment and EGFR ubiquitination, ultimately leading to dysregulation of EGFR degradation and signaling. Taken together, these studies indicate a novel model by which the microtubule network regulates EGFR stability and signaling through tubulin dimer/oligomer interaction with the nucleocytoplasmic protein TBC1D3.
Guo, Dan; Wu, Huijuan; Chen, Yang; Zhang, Yongchen; Wan, Qing; Zhao, Huzi; Wang, Congyang; Shen, Hongjing; Zhao, Lei; Bu, Xiaodong; Wan, Meiling; Shen, Chuanlu
Failure mechanisms of thermal barrier systems
Thermal barrier coatings (TBCs) are widely used in turbines for propulsion and power generation. The benefit results from their ability to sustain high thermal gradients in the presence of adequate backside cooling. Lowering the temperature of the metal substrate prolongs the life of the component: whether from environmental attack, creep rupture, or fatigue. Thermal barrier systems exhibit multiple failure mechanisms,
Tao Xu
Failure mechanisms and mechanisms-based life predictions for electron beam physical vapor deposition thermal barrier coatings
NASA Astrophysics Data System (ADS)
This research is designed to define failure mechanisms and to develop and experimentally validate non-destructive life prediction methodologies for electron beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs). It is shown that for the two TBCs of this study ((Ni,Pt)Al and NiCoCrAlY bond coated TBCs) different failure mechanisms are exhibited, and therefore, the selected life prediction methodologies are accordingly different. For the (Ni,Pt)Al bond coated TBC tested at three temperatures, progressive rumpling of the thermally grown oxide (TGO) and bond coat interface is responsible for the failure at a critical rumpling value. Rumpling is a single value function of TGO thickness, suggesting that TGO growth strains are critical to rumpling, and the TGO growth controls rumpling, which in turn controls spallation life. Associated with rumpling, the TGO stress, as measured by the Photoluminescence Piezospectroscopy (PLPS) technique, decreases linearly with thermal cycles. Longer life specimens exhibit shallower slopes. The relationships among rumpling rate, stress relaxation rate and spallation life are defined: as temperature increases, rumpling and stress relaxation rates increase, and spallation life decreases. The rumpling of the TGO provides a physical basis for use of TGO stress measurements as a non-destructive method for TBC damage initiation, progression and life prediction. Temperature-blind remaining life predictions were made successfully using regression and neural network methods based on only TGO stress measurements at three temperatures. The lowest root mean square error for the prediction using neural networks and regression methods was 6.6% and 14.7%, respectively. Bimodal luminescence spectra, obtained using PLPS, are shown to be related to TGO cracking. The degree of cracking increases initially as theta- transforms to alpha-Al2O3, then decreases as the cracks heal, and then increases again prior to spallation. Area stress maps, based on the bimodal luminescence and average fraction of bimodal spectra with cycles, show damage progression and have the potential for non-destructive prediction of spallation failure. For NiCoCrAlY bond coated TBCs, damage initiates at localized debonds at the TGO/bond coat interface due to an increasing out-of-plane tensile stress. The spallation of the coating is driven by the strain energy stored in the TGO. (Abstract shortened by UMI.)
Wen, Mei
Sulfur and Moisture Effects on Alumina Scale and TBC Spallation
NASA Technical Reports Server (NTRS)
It has been well established that a few ppmw sulfur impurity may segregate to the interface of thermally grown alumina scales and the underlying substrate, resulting in bond degradation and premature spallation. This has been shown for NiAl and NiCrAl-based alloys, bare single crystal superalloys, or coated superalloys. The role of reactive elements (especially Y) has been to getter the sulfur in the bulk and preclude interfacial segregation. Pt additions are also very beneficial, however a similar thermodynamic explanation does not apply. The purpose of the present discussion is to highlight some observations of these effects on Rene'142, Rene'N5, PWA1480, and PWA1484. For PWA1480, we have mapped cyclic oxidation and spallation in terms of potential sulfur interfacial layers and found that a cumulative amount of about one monolayer is sufficient to degrade long term adhesion. Depending on substrate thickness, optimum performance occurs if sulfur is reduced below about 0.2-0.5 ppmw. This is accomplished in the laboratory by hydrogen annealing or commercially by melt-fluxing. Excellent 1150 C cyclic oxidation is thus demonstrated for desulfurized Rene'142, Rene'N5, and PWA1484. Alternatively, a series of N5 alloys provided by GE-AE have shown that as little as 15 ppmw of Y dopant was effective in providing remarkable scale adhesion. In support of a Y-S gettering mechanism, hydrogen annealing was unable to desulfurize these alloys from their initial level of 5 ppmw S. This impurity and critical doping level corresponds closely to YS or Y2S3 stoichiometry. In many cases, Y-doped alloys or alloys with marginal sulfur levels exhibit an oxidative sensitivity to the ambient humidity called Moisture-Induced Delayed Spallation (MIDS). After substantial scale growth, coupled with damage from repeated cycling, cold samples may spall after a period of time, breathing on them, or immersing them in water. While stress corrosion arguments may apply, we propose that the underlying cause is related to a hydrogen embrittlement reaction: Al alloy + 3 H2O = Al(OH)3 + 3H(+) + 3e(-). This mechanism is derived from an analogous moisture-induced hydrogen embrittlement mechanism originally shown for Ni3Al and FeAl intermetallics. Consequently, a cathodic hydrogen charging technique was used to demonstrate that electrolytic de-scaling occurs for these otherwise adherent alumina scales formed on Y-doped Rene'N5, in support of hydrogen effects. Finally, some TBC observations are discussed in light of all of the above. Plasma sprayed 8YSZ coatings, produced on PWA1484 without a bond coat, were found to survive more than 1000 1-hr cycles at 1100 C when desulfurized to below 0.1 ppmw. At higher sulfur (1.2 ppmw) levels, moisture sensitivity and delayed TBC failure, referred to as Desk Top Spallation, occurred at just 200 hr. Despite a large degree of scatter, a factor of 5 in life improvement is indicated for desulfurized samples in cyclic furnace tests, confirming the beneficial effect of low sulfur alloys on model TBC systems. (DTS and moisture effects are also observed on commercially applied PVD 7YSZ coatings on Rene'N5+Y with Pt-aluminide bond coats). These types of catastrophic failure were subverted on the model system by segmenting the substrate into a network of 0.010 high ribs, spaced in. apart, prior to plasma spraying. No failures occurred after 1000 cycles at 1150 C or after 2000 cycles at 1100 C, even after water immersion. The benefit is described in terms of elasticity models and a critical buckling stress.
Smialek, James L.
�ber Glyk�mie bei chronischer Tbc
Zusammenfassung 1.Es ist nicht richtig, da� Lungen-Tbc. immer von Abnahme des Blutzuckergehaltes begleitet wird.2.In Hinsicht des Blutzuckergehaltes k�nnen alle Tuberkul�sen in 2 Gruppen geteilt werden: a) mit herabgesetztem Zuckergehalt und b) mit normalem oder etwas erh�htem Zuckergehalt.3.Die Grenze zwischen diesen beiden Gruppen bildet ein Zuckergehalt von 0,07�0,08 mg.4.Herabgehen des Zuckers unter diese Norm ist charakteristisch f�r F�lle mit deutlich ung�nstiger
M. Borock; P. Wowsi; G. Banzmann
Assessment of Cyclic Lifetime of NiCoCrAlY/ZrO2-Based EB-PVD TBC Systems via Reactive Element Enrichment in the Mixed Zone of the TGO Scale
NASA Astrophysics Data System (ADS)
The chemical composition of the alumina-zirconia mixed zone (MZ) of an electron beam physical vapor deposited thermal barrier coating (EB-PVD TBC) system is affected by service conditions and by the interdiffusion of elements from the substrate alloy below and the zirconia top coat. Three NiCoCrAlY bond-coated Ni-base substrates with YPSZ or CeSZ EB-PVD TBCs were subjected to a cyclic furnace oxidation test (FCT) at 1373 K (1100 �C) in order to provide experimental evidence of a link between chemistry of the MZ, the substrate alloy, the ceramic top coat, and the time in the FCT. Energy dispersive spectroscopy of the MZ revealed preferred accumulation of Cr, Zr, Y, and Ce. The concentration of the reactive elements (RE = Ce + Y + Zr) was related to the respective average lifetimes of the TBC systems at 1373 K (1100 �C). The RE content in the MZ turned out to be a life-limiting parameter for YPSZ and CeSZ TBC systems which can be utilized to predict their relative lifetimes on the individual substrates. Conversely, the TBC failure mechanisms of YPSZ and CeSZ TBC systems are dissimilar.
Fritscher, Klaus; Braue, Wolfgang; Schulz, Uwe
Compression failure mechanisms of composite structures
NASA Technical Reports Server (NTRS)
An experimental and analytical study was conducted to delineate the compression failure mechanisms of composite structures. The present report summarizes further results on kink band formation in unidirectional composites. In order to assess the compressive strengths and failure modes of fibers them selves, a fiber bundle was embedded in epoxy casting and tested in compression. A total of six different fibers were used together with two resins of different stiffnesses. The failure of highly anisotropic fibers such as Kevlar 49 and P-75 graphite was due to kinking of fibrils. However, the remaining fibers--T300 and T700 graphite, E-glass, and alumina--failed by localized microbuckling. Compressive strengths of the latter group of fibers were not fully utilized in their respective composite. In addition, acoustic emission monitoring revealed that fiber-matrix debonding did not occur gradually but suddenly at final failure. The kink band formation in unidirectional composites under compression was studied analytically and through microscopy. The material combinations selected include seven graphite/epoxy composites, two graphite/thermoplastic resin composites, one Kevlar 49/epoxy composite and one S-glass/epoxy composite.
Hahn, H. T.; Sohi, M.; Moon, S.
Role of failure-mechanism identification in accelerated testing
NASA Technical Reports Server (NTRS)
Accelerated life testing techniques provide a short-cut method to investigate the reliability of electronic devices with respect to certain dominant failure mechanisms that occur under normal operating conditions. However, accelerated tests have often been conducted without knowledge of the failure mechanisms and without ensuring that the test accelerated the same mechanism as that observed under normal operating conditions. This paper summarizes common failure mechanisms in electronic devices and packages and investigates possible failure mechanism shifting during accelerated testing.
Hu, J. M.; Barker, D.; Dasgupta, A.; Arora, A.
Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion
NASA Technical Reports Server (NTRS)
Alumina scale adhesion to high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for TBC s, culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylation of aluminum from the alloy interface appears to be the relevant basic reaction.
Smialek, James L.
Structure-sensitive mechanism of nanographene failure
The quantum-mechanochemical-reaction-coordinate approach has disclosed atomically matched peculiarities that accompany the deformation-failure-rupture process occurring in nanographenes. The high stiffness of the graphene body is provided by the benzenoid unit. The anisotropy of the unit mechanical behavior in combination with different configurations of the unit packing with respect to the body C-C bond chains forms the ground for the structure-sensitive mechanism of the mechanical behavior that is drastically different for two different deformation modes. The zig-zag deformation mode is particularly manifested with the formation of one-atom chains. The approach allows tracing a deformation-stimulated change in the chemical reactivity of both the nanographene body and its individual atoms.
Sheka, E. F., E-mail: firstname.lastname@example.com; Popova, N. A.; Popova, V. A.; Nikitina, E. A.; Shaymardanova, L. H. [Peoples' Friendship University of Russia (Russian Federation)
Validation of a mechanical component constant failure rate database
This paper reports on our successful efforts to validate statistically certain constant failure rate data in a mechanical component constant failure rate and failure mode database. To accomplish this, we use a Failure Modes, Effects, and Diagnostic Analysis (FMEDA) to predict the constant failure rate, lambdaD, for the fail-to-open condition of a particular series of pressure relief valves (PRV) using
Julia V. Bukowski; William M. Goble
PVD TBC experience on GE aircraft engines
NASA Technical Reports Server (NTRS)
The higher performance levels of modern gas turbine engines present significant challenges in the reliability of materials in the turbine. The increased engine temperatures required to achieve the higher performance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of thermal barrier coatings (TBC's) have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the physical vapor deposition (PVD) process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 micron (0.005 in) PVD TBC have demonstrated component operating temperatures of 56-83 C (100-150 F) lower than non-PVD TBC components. Engine testing has also revealed the TBC is susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues, the TBC erodes away in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area, however a significant temperature reduction was realized over an airfoil without TBC.
Maricocchi, Antonio; Bartz, Andi; Wortman, David
Mechanism of Hyperlipidemia in Chronic Renal Failure.
National Technical Information Service (NTIS)
The authors investigated whether the hyperlipidemia of chronic renal failure is associated with altered hepatic lipogenesis or carbohydrate metabolism. The rates of lipogenesis were measured in animals with chronic renal failure both in vivo and in the is...
L. M. Lowenstein D. Phil
Mesh convergence differences based on failure mechanisms
Material properties affect the deformation and failure modes in structural parts. When performing finite element analyses to compare response for different materials, different levels of mesh discretization may be necessary for each analyses because the failure mode changes, even through the part geometry and loading remain the same. Take, for example, strain localization, a material dependent phenomenon. When localization occurs, the mesh needs to be much finer to capture the steep strain gradients in the region of localization than in a case where localization does not occur. Although this requirement is almost intuitive once stated, it is often not used in practice because the effects are less pronounced when failure is not present, and also because failure modes are difficult to anticipate. The lack of availability of constitutive models for failure prediction is also a contributing factor. This paper describes a recent study regarding the effect of mesh refinement on failure prediction in a part modeled with two different materials.
Pilat, K.R. [Cornell Univ., Ithaca, NY (United States); Revelli, V.D. [Sandia National Labs., Livermore, CA (United States)
Failure mechanisms of load-sharing complex systems
NASA Astrophysics Data System (ADS)
We investigate the failure mechanisms of load-sharing complex systems. The system is composed of multiple nodes or components whose failures are determined based on the interaction of their respective strengths and loads (or capacity and demand, respectively) as well as the ability of a component to share its load with its neighbors when needed. We focus on two distinct mechanisms to model the interaction between components' strengths and loads. The failure mechanisms of these two models demonstrate temporal scaling phenomena, phase transitions, and multiple distinct failure modes excited by extremal dynamics. For critical ranges of parameters the models demonstrate power-law and exponential failure patterns. We identify the similarities and differences between the two mechanisms and the implications of our results for the failure mechanisms of complex systems in the real world.
Siddique, Shahnewaz; Volovoi, Vitali
TBC experience in land- based gas turbines
This paper summarizes prior and on-going machine evaluations of thermal barrier coatings (TBC) for power generation, that\\u000a is large industrial gas turbine applications. Rainbow testing of TBCs on turbine nozzles, shrouds, and buckets are described\\u000a along with a test of combustor liners. General Electric Power Generation has conducted more than IS machine tests on TBC turbine\\u000a nozzles with various coatings.
W. A. Nelson; R. M. Orenstein
Electro-Thermomigration as an Electrical Overstress Failure Mechanism.
National Technical Information Service (NTIS)
A critical review of electro-thermomigration as an EOS/ESD failure mechanism is presented. The paper focuses on the physical basis of the failure mechanism, the strength of the driving forces, and the effects of pulse attributes such as polarity on electr...
D. G. Pierce
Electro-thermomigration as an electrical overstress failure mechanism
NASA Astrophysics Data System (ADS)
A critical review of electrothermomigration as an EOS/ESD failure mechanism is presented. The paper focuses on the physical basis of the failure mechanism, the strength of the driving forces, and the effects of pulse attributes such as polarity on electrothermomigration. Recommendations or experiments to better understand this phenomenon are given.
Pierce, D. G.
Failure Mechanics of Cohesive-Frictional Materials.
National Technical Information Service (NTIS)
Cohesive-frictional materials are known to exhibit strong coupling between the volumetric and deviatoric behavior. The Reynolds effect is responsible for inelastic dilatancy which leads to localized failure modes which vary between tensile decohesion and ...
K. J. William
Moisture-Induced TBC Spallation on Turbine Blade Samples
NASA Technical Reports Server (NTRS)
Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. The weekend effect or DeskTop Spallation (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schuetze), and CNRS Toulouse/SNECMA (Deneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond coat are reported. Cut sections were intermittently oxidized at 1100, 1150, and 1200 C and monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers. The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that embrittle the interface. A negative synergistic effect with interfacial sulfur is also invoked.
Smialek, James
Moisture-Induced TBC Spallation on Turbine Blade Samples
NASA Technical Reports Server (NTRS)
Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. "The weekend effect" or "DeskTop Spallation" (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schuetze), and CNRS Toulouse/SNECMA (Deneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers. The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that 'embrittle' the interface. A negative synergistic effect with interfacial sulfur is also invoked.
Smialek, James L.
Failure mechanism characterization of platinum alloy
NASA Technical Reports Server (NTRS)
This article describes procedures and results of testing performed on a platinum/10-percent rhodium, thin-wall tubular product. The purpose of the testing was to develop exemplar SEM fractographs to be used to characterize failures under various environmental conditions. Conditions evaluated for the platinum alloys included high temperature, hydrogen environment, braze metal contamination, and cyclic loading.
Rosen, J. M.; Mcfarlen, W. T.
Sandwich construction is of particular interest and widely used, because the concept is very suitable and amenable to the development of lightweight structures with high in-plane and flexural stiffness. Sandwich panels consist typically of two thin face sheets (or facings, or skins) and a lightweight thicker core. They display various failure modes under general bending, shear and in-plane loading. The
E. E Gdoutos
Thesaurus of terms for information on mechanics of structural failure
NASA Technical Reports Server (NTRS)
A Thesaurus of approximately 700 subject terms used to describe the six problem areas in the mechanics of structural failure is presented. The initial criteria for the selection of terms are their significance and frequency of use in the literature describing the mechanics of structural failure. The purpose of the Thesaurus is to provide the Aerospace Safety Research and Data Institute a list of key works and identifiers that afford effective retrieval of information regarding failure modes and mechanisms for aerospace structures. The Thesaurus includes both a conventional listing of subject terms and a Key Words In Context (KWIC) listing.
Carpenter, J. L., Jr.; Moya, N.
Failure mechanisms in lithium-ion batteries
NASA Astrophysics Data System (ADS)
Lithium-ion batteries have become one of the leading candidates for energy storage in electric and hybrid-electric vehicles due to their high energy and power densities. However, the life of this class of rechargeable cells is limited, and is usually considerably shorter than the requirement for an economically feasible alternative to the internal combustion engine. The goal of this research is to explore specific mechanisms for cell failure via mathematical modeling of phenomena that occur in a broad assortment of lithium-ion cells. The theoretical framework of the models presented here is general enough to be applicable to most lithium-ion cells and even electrochemical cells that fall outside the realm of lithium-ion technology, but the properties and parameters that are used are specific enough that quantitative predictions can be made. Specifically, models for passive-film growth at the electrode/electrolyte interface and for particle fracture are presented. In addition, we discuss a framework for describing and understanding various types of capacity fade. Finally, we optimize the design of a lithium-titanate based cell using an existing full-cell model and compare its performance to that of a graphite based cell. The passive-film model indicates that the extent of film growth and impedance rise in a cell should depend strongly upon the state of charge (SOC) at which a battery is stored. We further show that current efficiency increases with the rate at which a cell is charged, although the cycling range of the cell decreases as the current is raised due to the impedance of the film. The particle-fracture model elucidates the conditions under which both graphitic and lithium-manganese-oxide particles surpass their yield strength, at which point cracking is initiated and particle fragmentation may occur. Higher rates of charge and larger particle size generally lead to a higher likelihood of fracture, although this dependence is absent in materials that undergo a two-phase transition. Pressure diffusion and nonidealities embodied in solid-state diffusion and the kinetics of lithium insertion are included in the model, and are shown to have significant impact on the results. Variations in the thermodynamic factor with lithium content result in local SOCs at which the stress in the material is much higher than would be predicted for an ideal solution. The implications of these variations, including the possibility of selecting SOC windows for battery operation that minimize stress, are examined in detail. The high-rate performance of cells with lithium-titanate negative electrodes can be enhanced, relative to cells with graphitic negative electrodes, through the selection of active material of small particle size. The high potential of the lithium-titanate electrode prevents many of the undesirable side reactions that occur in graphitic electrodes, including passive-film formation and lithium deposition. We conclude that the lithium-titanate electrode is probably the more attractive candidate for hybrid-electric-vehicle and other high-power applications.
Christensen, John Francis
Indentation Analysis of a Multi-Layered Hollow Cylinder for the Measurement of Interfacial Toughness in TBC Systems
Summary This paper addresses the mechanics of indentation-induced delamination of a coating on a multi-layered hollow cylinder, for application to toughness testing of thermal barrier coating (TBC) systems. An electron-beam physical vapor depo- sition (EB-PVD) TBC system has been analyzed through a contact finite element model usingastandardconical indenterimpressed verticallyon thetop ofthecylin- der. Two cylinder sizes used in thermal-mechanical fatigue tests
Q. Ma; J. L. Beuth; G. H. Meier; F. S. Pettit
Ultimate Strength and Failure Mechanism of Anthropoid Knee Joints.
National Technical Information Service (NTIS)
Testing of the anthropoid knee in three point loading indicates a progressive failure mechanism in an anterior loading situation. This phenomenon is investigated and is shown to be due to the failure of the connective tissue of the knee region as loading ...
C. H. Jacobs J. O. Outwater R. W. Castle
Prevent boiler tube failures -- Part 2: Waterside mechanisms
Boiler tubes can fail due to problems on either the fire-side or the water-side of the tube. Part 1 of this article discussed fire-side failure mechanisms and measures for preventing failures. Here the author focuses on the tubes' water-side. The term water-side mechanisms'' refers to damage on the water side of the boiler tube (as opposed to the fire side).
Failure mechanisms of fibrin-based surgical tissue adhesives
NASA Astrophysics Data System (ADS)
A series of studies was performed to investigate the potential impact of heterogeneity in the matrix of multiple-component fibrin-based tissue adhesives upon their mechanical and biomechanical properties both in vivo and in vitro. Investigations into the failure mechanisms by stereological techniques demonstrated that heterogeneity could be measured quantitatively and that the variation in heterogeneity could be altered both by the means of component mixing and delivery and by the formulation of the sealant. Ex vivo tensile adhesive strength was found to be inversely proportional to the amount of heterogeneity. In contrast, in vivo tensile wound-closure strength was found to be relatively unaffected by the degree of heterogeneity, while in vivo parenchymal organ hemostasis in rabbits was found to be affected: greater heterogeneity appeared to correlate with an increase in hemostasis time and amount of sealant necessary to effect hemostasis. Tensile testing of the bulk sealant showed that mechanical parameters were proportional to fibrin concentration and that the physical characteristics of the failure supported a ductile mechanism. Strain hardening as a function of percentage of strain, and strain rate was observed for both concentrations, and syneresis was observed at low strain rates for the lower fibrin concentration. Blister testing demonstrated that burst pressure and failure energy were proportional to fibrin concentration and decreased with increasing flow rate. Higher fibrin concentration demonstrated predominately compact morphology debonds with cohesive failure loci, demonstrating shear or viscous failure in a viscoelastic rubbery adhesive. The lower fibrin concentration sealant exhibited predominately fractal morphology debonds with cohesive failure loci, supporting an elastoviscous material condition. The failure mechanism for these was hypothesized and shown to be flow-induced ductile fracture. Based on these findings, the failure mechanism was stochastic in nature because the mean failure energy and burst pressure values were not predictive of locus and morphology. Instead, flow rate and fibrin concentration showed the most predictive value, with the outcome best described as a probability distribution rather than a specific deterministic outcome.
Sierra, David Hugh
Die Tbc.-Serologie in der Kinderheilkunde
Die Aktivit�tsdiagnose der kindlichen Tuberkulose st��t oft auf Schwierigkeiten. Deshalb versuchten wir, mit Hilfe eines neuen Tbc.-Antigens den Antik�rpernachweis im Blutserum daf�r zu verwerten. Die bisherigen Vorstellungen �ber die Serumantik�rper sind u. E. revisionsbed�rftig, da sie zu falschen Schlu�folgerungen f�hren.
Werner Herrmann; Albert Massenberg
The Hominoid-specific Oncogene TBC1D3 Activates Ras and Modulates Epidermal Growth Factor Receptor Signaling and Trafficking*S?
Hominoid- and human-specific genes may have evolved to modulate signaling pathways of a higher order of complexity. TBC1D3 is a hominoid-specific oncogene encoded by a cluster of eight paralogs on chromosome 17. Initial work indicates that TBC1D3 is widely expressed in human tissues (Hodzic, D., Kong, C., Wainszelbaum, M. J., Charron, A. J., Su, X., and Stahl, P. D. (2006) Genomics 88,731 -73616863688). In this study, we show that TBC1D3 expression has a powerful effect on cell proliferation that is further enhanced by epidermal growth factor (EGF) in both human and mouse cell lines. EGF activation of the Erk and protein kinase B/Akt pathways is enhanced, both in amplitude and duration, by TBC1D3 expression, whereas RNA interference silencing of TBC1D3 suppresses the activation. Light microscopy and Western blot experiments demonstrate that increased signaling in response to EGF is coupled with a significant delay in EGF receptor (EGFR) trafficking and degradation, which significantly extends the life span of EGFR. Moreover, TBC1D3 suppresses polyubiquitination of the EGFR and the recruitment of c-Cbl. Using the Ras binding domain of Raf1 to monitor GTP-Ras we show that TBC1D3 expression enhances Ras activation in quiescent cells, which is further increased by EGF treatment. We speculate that TBC1D3 may alter Ras GTP loading. We conclude that the expression of TBC1D3 generates a delay in EGFR degradation, a decrease in ubiquitination, and a failure to recruit adapter proteins that ultimately dysregulate EGFR signal transduction and enhance cell proliferation. Altered growth factor receptor trafficking and GTP-Ras turnover may be sites where recently evolved genes such as TBC1D3 selectively modulate signaling in hominoids and humans. PMID:16863688
Wainszelbaum, Marisa J.; Charron, Audra J.; Kong, Chen; Kirkpatrick, Donald S.; Srikanth, Priya; Barbieri, M. Alejandro; Gygi, Steven P.; Stahl, Philip D.
Failure mechanism study of GaAs technology
NASA Astrophysics Data System (ADS)
In this report we have discussed the characterization of the power FETs procured for this program and failure analysis of low noise devices, including wire bonding failures and environmental stress test failures. A method of etching gold while leaving the underlying refractory metals relatively unaffected was explained. An analysis of the Type A-6 low noise FET was given, in which a failure mode was discussed that involved possible channel doping compensation. Results were then presented on device failures from high and medium temperature stress tests on low noise FETs. A number of medium power devices were received from RADC for analysis. These were packaged FETs that had been subjected to various stresses at Texas Instruments on a RADC/TI reliability contract. Typically, the devices had failed during deliberate stressing to the maximum electrical limits or in temperature stress tests. Failure mechanism studies of two different ohmic contact metallizations showed that both fabrication procedures produced reliable contacts. Constant elevated temperature tests of gold-based gate diode FETs from two different manufacturers showed that one device type was considerably less prone to gate diode failure than the other, indicating the necessity of additional work on the gold gate versus aluminum gate reliability question. Failures were investigated that involve problems associated with gold contact pads overlaying aluminum gate pads with a refractory metal interface. Finally, temperature-accelerated studies of the resistance of aluminum gates were carried out.
Bowman, L. S.; Tarn, W.
Mechanisms of fatigue failure in thermal spray coatings
NASA Astrophysics Data System (ADS)
The aim of this experimental study was to ascertain the fatigue failure modes of thermal spray coatings in rolling/sliding contact. These failure modes outline the design requirements of thermal spray coatings for high-stress tribological applications including impact and point or line contact loading. Recently, a number of scientific studies have addressed the fatigue performance and durability of thermal spray coatings in rolling/sliding contact, but investigations on the mechanisms of these failures are seldom reported. The understanding of such failure mechanisms is, however, critical in optimizing the generic design of these overlay coatings. This study takes a holistic approach to summarize the results of ongoing research on various cermet (WC-Co) and ceramic (Al2O3) coatings deposited by detonation gun (D-Gun), high-velocity oxyfuel (HVOF), and high-velocity plasma spraying (HVPS) techniques, in a range of coating thickness (20-250 �m) on various steel substrates to deliver an overview of the various competing failure modes. Results indicate four distinct modes of fatigue failure in thermal spray cermet and ceramic coatings: abrasion, delamination, bulk failure, and spalling. The influences of coating process, thickness, materials, properties of substrate materials, and prespray conditions on these fatigue failure modes are also discussed. A modified four-ball machine was used to investigate these failure modes under various tribological conditions of contact stress and lubrication regimes in conventional steel and hybrid ceramic contact configurations. Results are discussed in terms of pre- and post-test surface examination of rolling elements using scanning electron microscopy (SEM), electron probe microscopy analysis (EPMA), and surface interferometry, as well as subsurface observations using x-ray diffraction (XRD), residual stress analysis, and dye-penetrant investigations.
Ahmed, R.; Hadfield, M.
Survey on Failure Modes and Failure Mechanisms in Digital Components and Systems
This paper presents the preliminary results of a survey on the operating experience of a broad range of digital components and systems deployed in various industries. The primary objective of this survey is to identify principal modes and mechanisms of failure in field-deployed digital systems. Earlier works have sought to determine the failure rates of various classes of digital devices with the intent to integrate this information into the risk analysis calculations though still immature for such systems. Failure rates of individual components or systems are not taken into account in this evaluation; only failure modes and their respective probabilistic distribution are considered. Preliminary results from two data sources, SPIDR and FARADIP, are presented.
Cetiner, Mustafa Sacit [ORNL; Korsah, Kofi [ORNL; Muhlheim, Michael David [ORNL
Rockfall failure mechanisms in Yosemite Valley, California (USA)
NASA Astrophysics Data System (ADS)
Rockfall hazard is especially high in Yosemite Valley, with tens of rockfalls inventoried every year. A rockfall on 5 October 2013 from Ahwiyah Point consisted of a volume of 740 cubic meters and occurred within the perimeter of a larger event on 28 March 2009 that released 25'400 cubic meters of rock (Zimmer et al., 2012). In both events (2009 and 2013), the initial rockfall volumes dislodged a second one approximately equivalent in size by impacting the cliff below the source area during the fall. Rock fragments of up to several cubic meters were deposited on the talus slope, damaging a heavily used and recently reconstructed hiking path. We performed extensive mapping of structural features for several cliffs of Yosemite Valley to improve the assessment of the most susceptible rockfall areas. In particular we mapped and characterized the main brittle structures, the exfoliation joints and the failure mechanisms of the past rockfalls. Several failure mechanisms exist in Yosemite including the propagation of brittle structures that may lead to tensile, planar sliding, wedge sliding or toppling failures. Frequently, topographically-parallel exfoliation joints and topographically-oblique discontinuities coexist, resulting in complex failures. We also developed a methodology to examine how the distribution of joints within the cliff faces of Yosemite Valley affects overall stability with respect to the identified failure mechanisms. For these analyses, we used terrestrial laser scanning (TLS) to collect high resolution point clouds of the vertical and overhanging rock faces throughout the Valley. This provided the necessary 3D data to identify the main joint sets, perform spacing and trace length measurements, and calculate volumes of previous and potential rockfalls. We integrated this information with stability calculations to identify the likely failure mechanisms for each area of cliff and to obtain the number of potential failures per square meter of cliff face. The areas of a cliff with the highest number of potential failures per cliff surface are considered to be the most susceptible to rockfalls. We then compared these areas to field observations displaying the most visually unstable compartments by considering the following factors: 1) the compartment's degree of isolation due to bounding fractures, 2) the existence of basal steep, sliding prone discontinuities, 3) the opening of cracks, 4) the persistence of cracks, 5) the existence of overhangs, 6) the surrounding rockfall activity, 7) the water seepage along the limiting cracks, 8) the proximity to very fractured layers, 9) the proximity to geologic limits. Our preliminary results show a link between the type of failure mechanism, the persistence of discontinuities and the volume of analyzed rockfalls. Generally, planar or wedge sliding isolate larger unstable compartments compared to tensile failures along exfoliation joints.
Matasci, Battista; Guerin, Antoine; Carrea, Dario; Stock, Greg M.; Jaboyedoff, Michel; Collins, Brian
Mechanical failure probability of glasses in Earth orbit
NASA Technical Reports Server (NTRS)
Results of five years of earth-orbital exposure on mechanical properties of glasses indicate that radiation effects on mechanical properties of glasses, for the glasses examined, are less than the probable error of measurement. During the 5 year exposure, seven micrometeorite or space debris impacts occurred on the samples examined. These impacts were located in locations which were not subjected to effective mechanical testing, hence limited information on their influence upon mechanical strength was obtained. Combination of these results with micrometeorite and space debris impact frequency obtained by other experiments permits estimates of the failure probability of glasses exposed to mechanical loading under earth-orbit conditions. This probabilistic failure prediction is described and illustrated with examples.
Kinser, Donald L.; Wiedlocher, David E.
Prevent boiler tube failures -- Part 2: Water-side mechanisms
Boiler tubes can fail due to problems on either the fire-side or the water-side of the tube. Part 1 of this article discussed fire-side failure mechanisms and measures for preventing failures. Here the author focuses on the tubes' water-side. The term water-side mechanisms'' refers to damage on the water side of the boiler tube (as opposed to the fire side). However, the water itself is often not the culprit. Water-side corrosion mechanisms may be classified into two major categories: physical and chemical. Physical mechanisms include steam blanketing and overheating. Chemical mechanisms include: deposition; caustic, acidic, and chelant corrosion; oxidation; and hydrogen embrittlement.
Colannino, J. (Colannino Consultants, Oceanside, CA (United States))
IMPERMEABLE THIN Al2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES
In order to improve the hot corrosion resistance of conventional YSZ TBC system (YSZ/CoNiCrAlY/Inconel 601), an overlay Al{sub 2}O{sub 3} was sprayed on the surface of TBC samples by high velocity oxy-fuel (HVOF) spray techniques. The TBC preparation in Japan was based on our technical requirement by plasma spray. Bond coat CoNiCrAlY and the YSZ was produced by low-pressure plasma spray and air plasma spray respectively. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC reacted with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. Al{sub 2}O{sub 3} overlay coating sprayed by HVOF was dense, continues and adherent to the TBC even after exposure to the molten salts. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and arrest the penetration of salts into the YSZ along porous and cracks in the YSZ TBC. Accordingly, the amount of M-phase formed in TBC with Al{sub 2}O{sub 3} overlay was significantly lower than that in conventional YSZ TBC system. In the next period, the hot corrosion tests of TBC with EB-PVD Al{sub 2}O{sub 3} coating under Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5} will be again performed at 950 C. However before hot corrosion tests, the post-annealing will be carried at 1273K for 1h in order to transform the as-sputtered {gamma}-Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay. In addition, the effect of coating thickness on corrosion resistance and the mechanisms of cracking of EB-PVD alumina layer during hot corrosion will be also investigated.
Scott X. Mao
Mechanical Failure Rate Data for Low Demand Applications
The use of IEC 61508 (1) and IEC 61511 (2) has increased rapidly in the past several years. Along with the adoption of the standards has come an increase in the need for accurate reliability data for devices used in Safety Instrumented Systems (SIS), both electronic and mechanical. While the methodology of determining failure rates for electronic equipment is fairly
Chris O'Brien
[Respiratory failure in mitochondrial myopathy treated with noninvasive mechanical ventilation].
Young man suffering from mitochondrial myopathy was admitted to our Institute due to severe hypercapnic respiratory failure. Noninvasive mechanical ventilation (NWM) during sleep using nasal mask was instituted with positive results. Diurnal blood gases breathing air also ameliorated suggesting improvement of respiratory muscles function. PMID:10391964
Biele?, P; Sliwi?ski, P; Kami?ski, D; Zieli?ski, J
Numerical assessment of failure mechanisms in fibre metal laminates
In this contribution numerical models are discussed for describing failure mechanisms in fibre metal laminates. Fibre metal laminates form a new class of materials which are considered for a possible application to the fuselage of future aircraft generations. The intensive experimental analyses of these materials are focused on the assessment of their residual strength and on the assessment of new
F. Hashagen; R. De Borst
Mechanics of snow slab failure from a geotechnical perspective
Field observations and measurements show that all snow slab failures have some common features. The physical mechanisms governing the release can differ greatly depending on the character of the deformation in the weak layer or interface beneath the slab where the release process initiates. Here two prototypes for slab avalanche initiation are considered: I. release of dry slab avalanches where
D. M. McCLUNG
Research on Tool Failure Mechanism of PRMMCs with Ultrasonic Assistance
In this paper, the experimental research on the tool failure mechanism using YG6 and PCD tool cutting Particular Reinforced Metal Matrix Composites (PRMMCs) with ultrasonic cutting and common cutting was carried out, and it was discovered that: (1) the tool wear of ultrasonic cutting is less than that of common cutting, the cutting speed and feed speed have greater effect
Xiao Ma; Xueli Cheng
Register of experts for information on mechanics of structural failure
NASA Technical Reports Server (NTRS)
This register is comprised of a list of approximately 300 experts from approximately 90 organizations who have published results of theoretical and/or experimental research related to six problem areas in the mechanics of structural failure: (1) life prediction for structural materials, (2) fracture toughness testing, (3) fracture mechanics analysis; (4) hydrogen embrittlement; (5) protective coatings; and (6) composite materials. The criteria for the selection of names for the register are recent contributions to the literature, participation in or support of relevant research programs, and referral by peers. Each author included is listed by organizational affiliation, address, and principal field of expertise. The purpose of the register is to present, in easy reference form, sources for dependable information regarding failure modes and mechanisms of aerospace structures. The register includes two indexes; an alphabetical listing of the experts and an alphabetical listing of the organizations with whom they are affiliated.
Carpenter, J. L., Jr.; Stuhrke, W. F.
Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature
OAK B188 Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature. This summary refers to work done in approximately the twelve months to the present in our contract ''Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature,'' which commenced in August, 1997. Our activities have consisted mainly of measurements of creep-controlled crack growth in ceramic matrix composites (CMCS) at high temperature; imaging of deformation fields in textile CMCS; the assessment of mechanisms of damage in textile composites, especially those with through-thickness reinforcement; the formulation of models of delamination crack growth under fatigue in textile composites; analytical models of the bridging traction law for creeping fibers in a CMC at high temperature; and an analytical model of a bridging fiber tow in a textile composite.
Cox, Brian
On the role of imperfections in the failure of a thermal barrier coating made by electron beam deposition
An impression test has been used to explore the remnant toughness and the delamination characteristics of thermal barrier coatings (TBCs) after extended thermal exposure. The delamination trajectory is found to change as the thermally grown oxide (TGO) thickens. At small thicknesses, delamination occurs predominantly within the TGO and TBC. With a thicker TGO, developed after 100 h exposure at 1,100 C, the delamination extends predominantly along the TGO/bond coat interface, but with small oxide domains remaining embedded in the bond coat. The changes in the interface adhesion and the mechanics responsible for this transition are addressed, along with a discussion of the role of morphological imperfections in the TGO in failure nucleation. A method for determining the effective in-plane modulus of the TBC from the curvature of decohered TGO/TBC bilayers is also presented.
Mumm, D.R.; Evans, A.G.
Assessing mechanical vulnerability in water distribution networks under multiple failures
NASA Astrophysics Data System (ADS)
mechanical vulnerability of water distribution networks (WDN) is of direct relevance for water utilities since it entails two different purposes. On the one hand, it might support the identification of severe failure scenarios due to external causes (e.g., natural or intentional events) which result into the most critical consequences on WDN supply capacity. On the other hand, it aims at figure out the WDN portions which are more prone to be affected by asset disruptions. The complexity of such analysis stems from the number of possible scenarios with single and multiple simultaneous shutdowns of asset elements leading to modifications of network topology and insufficient water supply to customers. In this work, the search for the most disruptive combinations of multiple asset failure events is formulated and solved as a multiobjective optimization problem. The higher vulnerability failure scenarios are detected as those causing the lower supplied demand due to the lower number of simultaneous failures. The automatic detection of WDN topology, subsequent to the detachments of failed elements, is combined with pressure-driven analysis. The methodology is demonstrated on a real water distribution network. Results show that, besides the failures causing the detachment of reservoirs, tanks, or pumps, there are other different topological modifications which may cause severe WDN service disruptions. Such information is of direct relevance to support planning asset enhancement works and improve the preparedness to extreme events.
Berardi, Luigi; Ugarelli, Rita; R�stum, Jon; Giustolisi, Orazio
Register of experts for information on mechanics of structural failure
NASA Technical Reports Server (NTRS)
A list of approximately 150 experts from approximately 60 organizations who have published results of theoretical and/or experimental research related to six problem areas in the mechanics of structural failure is presented. Each author included is listed by organizational affiliation, address and principal field of expertise. The initial criteria for the selection of names for the register are recent contributions to the literature, participation in or support of relevant research programs, and referral by peers. The purpose of the register is to present, in easy reference form, sources for dependable information regarding failure modes and mechanisms of aerospace structures. The Register includes two indexes: an alphabetical listing of the experts and an alphabetical listing of the organizations with whom they are affiliated.
Carpenter, J. L., Jr.; Moya, N.
Bibliography of information on mechanics of structural failure
NASA Technical Reports Server (NTRS)
A bibliography of approximately 1500 reference citations related to six problem areas in the mechanics of failure in aerospace structures is presented. The bibliography represents a search of the literature published in the ten year period 1962-1972 and is largely limited to documents published in the United States. Listings are subdivided into the six problem areas: (1) life prediction of structural materials; (2) fracture toughness data; (3) fracture mechanics analysis; (4) hydrogen embrittlement; (5) protective coatings; and (6) composite materials. An author index is included.
Carpenter, J. L., Jr.; Moya, N.; Shaffer, R. A.; Smith, D. M.
Methods of failure and reliability assessment for mechanical heart pumps.
Artificial blood pumps are today's most promising bridge-to-recovery (BTR), bridge-to-transplant (BTT), and destination therapy solutions for patients suffering from intractable congestive heart failure (CHF). Due to an increased need for effective, reliable, and safe long-term artificial blood pumps, each new design must undergo failure and reliability testing, an important step prior to approval from the United States Food and Drug Administration (FDA), for clinical testing and commercial use. The FDA has established no specific standards or protocols for these testing procedures and there are only limited recommendations provided by the scientific community when testing an overall blood pump system and individual system components. Product development of any medical device must follow a systematic and logical approach. As the most critical aspects of the design phase, failure and reliability assessments aid in the successful evaluation and preparation of medical devices prior to clinical application. The extent of testing, associated costs, and lengthy time durations to execute these experiments justify the need for an early evaluation of failure and reliability. During the design stages of blood pump development, a failure modes and effects analysis (FMEA) should be completed to provide a concise evaluation of the occurrence and frequency of failures and their effects on the overall support system. Following this analysis, testing of any pump typically involves four sequential processes: performance and reliability testing in simple hydraulic or mock circulatory loops, acute and chronic animal experiments, human error analysis, and ultimately, clinical testing. This article presents recommendations for failure and reliability testing based on the National Institutes of Health (NIH), Society for Thoracic Surgeons (STS) and American Society for Artificial Internal Organs (ASAIO), American National Standards Institute (ANSI), the Association for Advancement of Medical Instrumentation (AAMI), and the Bethesda Conference. It further discusses studies that evaluate the failure, reliability, and safety of artificial blood pumps including in vitro and in vivo testing. A descriptive summary of mechanical and human error studies and methods of artificial blood pumps is detailed. PMID:15644079
Patel, Sonna M; Allaire, Paul E; Wood, Houston G; Throckmorton, Amy L; Tribble, Curt G; Olsen, Don B
Mechanical performance of a dental composite: probabilistic failure prediction.
In clinical situations, the mechanical performances of dental structures--for example, composite restorations--depend on many factors. Most of them have a probabilistic character. Because composites are brittle materials, their strength should also be considered as a probabilistic quantity. For successful prediction of mechanical failure of structures consisting of these materials, a probabilistic approach is indispensable, and a suitable definition of equivalent stress must be introduced. An equivalent stress facilitates the transfer of strength data of laboratory specimens to situations where the stress state is much more complicated. The tensile and compressive strengths of composites differ considerably. Of two equivalent stress definitions that potentially describe this experimental fact (the Dr�cker-Prager and the Modified von Mises equivalent stress), the predictive capacity was investigated for a microfine composite. In a probabilistic approach to failure, use of the Dr�cker-Prager equivalent stress appeared to be superior, because the average failure load of notched beams was predicted with an error smaller than 8%. PMID:8360371
van der Varst, P G; Brekelmans, W A; de Vree, J H; de Groot, R
Degradation of a TBC with HVOF-CoNiCrAlY Bond Coat
NASA Astrophysics Data System (ADS)
Thermal barrier coatings (TBCs) provide both thermal insulation and oxidation and corrosion protection to the substrate metal, and their durability is influenced by delamination near the interface between the ceramic topcoat and the metallic bond coat, where a layer of thermally grown oxide (TGO) forms during service exposure. In the present work, the degradation process of a TBC with an air-plasma-spray ZrO2-8 wt.%Y2O3 topcoat and a high-velocity oxy-fuel CoNiCrAlY bond coat was studied, in terms of TGO growth kinetics and aluminum depletion in the bond coat, as well as cracking behavior. The results show that the TGO growth kinetics can be described by a transient oxidation stage with ?3 = k 1 t followed by a steady-state oxidation stage with ?2 = c + k 2 t. Significant aluminum depletion was observed in the bond coat after extended thermal exposure; however, chemical failure of the bond coat did not occur even after the aluminum content near the TGO/CoNiCrAlY interface decreased to 4.5 at.%. A power-law relationship between the maximum crack length in the TBC and the TGO thickness was observed, which may serve as the basis for TBC life prediction.
Chen, Weijie R.
Degradation of a TBC with HVOF-CoNiCrAlY Bond Coat
NASA Astrophysics Data System (ADS)
Thermal barrier coatings (TBCs) provide both thermal insulation and oxidation and corrosion protection to the substrate metal, and their durability is influenced by delamination near the interface between the ceramic topcoat and the metallic bond coat, where a layer of thermally grown oxide (TGO) forms during service exposure. In the present work, the degradation process of a TBC with an air-plasma-spray ZrO2-8 wt.%Y2O3 topcoat and a high-velocity oxy-fuel CoNiCrAlY bond coat was studied, in terms of TGO growth kinetics and aluminum depletion in the bond coat, as well as cracking behavior. The results show that the TGO growth kinetics can be described by a transient oxidation stage with ?3 = k 1 t followed by a steady-state oxidation stage with ?2 = c + k 2 t. Significant aluminum depletion was observed in the bond coat after extended thermal exposure; however, chemical failure of the bond coat did not occur even after the aluminum content near the TGO/CoNiCrAlY interface decreased to 4.5 at.%. A power-law relationship between the maximum crack length in the TBC and the TGO thickness was observed, which may serve as the basis for TBC life prediction.
Chen, Weijie R.
Mechanical properties testing and results for thermal barrier coatings
NASA Technical Reports Server (NTRS)
Thermal Barrier Coatings (TBC's) provide a significant challenge in the evaluation of their mechanical properties in ways that provide data that is not specimen dependent. The paper reviews various developments of the principal author over the past several years for both plasma sprayed and physical vapor deposited (PVD) materials, as well as new data on the fatigue behavior of one material system. The test methods that have been employed address tensile and compressive modulus and ultimate strength, tensile and compressive fatigue strength, and interfacial strength. This testing is now underway. Property testing is especially difficult for TBC's owing to the limitation on fabrication thickness of the coating. Bending tests are not used as these tests do not provide sufficiently uniform states of strain for property evaluations. Test specimens with uniform states of axial stress have been devised for each material system. The results show that the material property results between various experimenters and experimental methods are not yet consistent. However, the results provide critical design data at a suitable level of accuracy for life prediction. The paper will review both tensile and compressive mechanical testing of uniaxial specimens showing property dependencies on material density and temperatures for both material systems. Successful test results for both tensile and compressive fatigue loadings will be given. The test data shows that the fatigue strength of the TBC's is highly stress dependent in both loading conditions and is likely to depend on stress range and not mean stress. The fatigue strength of the plasma sprayed TBC's appears to increase with elevated temperatures in a range of temperatures below the creep activation temperature for the materials. The plasma sprayed TBC materials have been confirmed to have cyclic hysteresis at all temperature levels down to room temperature. Limited failure analysis data for various specimens suggest that the failure modes are driven by normal geometric discontinuities in the TBC's.
Cruse, T. A.; Johnsen, B. P.
In order to improve the hot corrosion resistance of conventional YSZ TBC system, the overlay of Al{sub 2}O{sub 3} coating was deposited on the TBC by EB-PVD techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. Al{sub 2}O{sub 3} overlay coating deposited by EB-PVD was dense, continues and adherent to the TBC. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and arrest the penetration of salts into the YSZ along porous and cracks in the YSZ TBC, although there were some cracks in overlay Al{sub 2}O{sub 3} coating and at the interface between alumina and zirconia formed during hot corrosion tests due to the presence of tensile stress in the alumina coating. In the next reporting period, we will study the mechanisms of cracking of the overlay Al{sub 2}O{sub 3} layer and finish the hot corrosion tests of TBC with Al{sub 2}O{sub 3} coating deposited by high velocity oxy-fuel (HVOF) technique. The hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, a post-annealing will be carried out in vacuum (residual pressure 10{sup -3} Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay.
Scott X. Mao
Evaluation of thickness, porosity and pore shape of plasma sprayed TBC by electrochemical impedance spectroscopy
An equivalent circuit of electrochemical impedance spectroscopy (EIS) was suggested to model the morphological structure of nonexposure thermal barrier coating (TBC). The morphological properties of as-coated air plasma sprayed (APS) TBC were correlated with the EIS parameters. A linear relationship between TBC topcoat thickness, Dc, and ceramic resistance, Rc, has been found particularly when the TBC have the same porosity.
J. Zhang; V. Desai
The role of microstructure and phase distribution in the failure mechanisms and life prediction model for PSZ coatings
NASA Technical Reports Server (NTRS)
Partially Stabilized Zirconia (PSZ) may become widely used for Thermal Barrier Coatings (TBC). Failure of these coatings can occur due to thermal fatigue in oxidizing atmospheres. The failure is due to the strains that develop due to thermal gradients, differences in thermal expansion coefficients, and oxidation of the bond coating. The role of microstructure and the cubic, tetragonal, and monoclinic phase distribution in the strain development and subsequent failure will be discussed. An X-ray diffraction technique for accurate determination of the fraction of each phase in PSZ will be applied to understanding the phase transformations and strain development. These results will be discussed in terms of developing a model for life prediction in PSZ coatings during thermal cycling.
Sisson, R. D., Jr.; Sone, Ichiro; Biederman, R. R.
Mechanisms and pathways of growth failure in primordial dwarfism
The greatest difference between species is size; however, the developmental mechanisms determining organism growth remain poorly understood. Primordial dwarfism is a group of human single-gene disorders with extreme global growth failure (which includes Seckel syndrome, microcephalic osteodysplastic primordial dwarfism I [MOPD] types I and II, and Meier-Gorlin syndrome). Ten genes have now been identified for microcephalic primordial dwarfism, encoding proteins involved in fundamental cellular processes including genome replication (ORC1 [origin recognition complex 1], ORC4, ORC6, CDT1, and CDC6), DNA damage response (ATR [ataxia-telangiectasia and Rad3-related]), mRNA splicing (U4atac), and centrosome function (CEP152, PCNT, and CPAP). Here, we review the cellular and developmental mechanisms underlying the pathogenesis of these conditions and address whether further study of these genes could provide novel insight into the physiological regulation of organism growth.
Klingseisen, Anna; Jackson, Andrew P.
Knowledge Discovery Process for Characterization of Materials Failure Mechanism
NASA Technical Reports Server (NTRS)
It is the intent of this project to provide a platform to visualize the various data collected from stress-strain testing of composite ceramic matrix materials. The data collected from the stress-strain tests are acoustic emissions (AE). As a material is subjected to a stress-strain test, various failure mechanisms occur in the material. The recorded sounds emitted during the test may correspond to various failure mechanisms. This project, thus, will give a possible way to visualize the data and data derived from the recorded AE. The stress-strain testing was performed on several composite matrix material combinations. Each of these tests produced anywhere from 1000 to 10,000+ AE events. For each AE event recorded, several characteristics in both the time and frequency domains are created. This project has two goals. First, this project will provide a summation page for a selected waveform. This page will include all of the characteristics determined from the AE event waveform along with graphs of the AE event waveform and its corresponding Power Spectrum. The other function of this project is to retrieve and display selected AE event waveforms for comparison.
Cios, Krzysztof J.
An investigation of mechanical behavior and failure mechanisms of composite T-joints with transverse stitching
NASA Astrophysics Data System (ADS)
A new low cost damage tolerant method of joining load-bearing composite structures using two-dimensional dry fabric preforms with transverse stitching and a novel fiber insertion process with resin transfer molding has recently been developed, however, knowledge of strength prediction and failure mechanisms is not well understood. In this investigation, fundamental knowledge of T-joint mechanical behavior was developed through detailed experimental, numerical, and post failure analyses. Experiments were conducted under flexure, tension, and shear loads and failed specimens were examined to discern failure modes. T-joint constituent elastic and strength properties were experimentally determined. Elastic properties were used as input to the finite element analysis and strength properties were used as limiting values in the T-joint failure analysis. Linear elastic, nonlinear elastic, and progressive damage finite element models were developed under each load condition. T-joint numerical models are shown to predict experimental behavior through ultimate load. Damage accumulation was characterized based on experimental, numerical, and post failure analyses. A parametric finite element analysis was conducted and design curves were derived to demonstrate the effect of varying key T-joint interface parameters on mechanical behavior under each load condition. Results of this research enable the application of T-joints with transverse stitching to future products and predictive finite element models developed herein reduce the structural testing required to validate these designs.
Stickler, Patrick Bickford
Thermal fatigue failure induced by delamination in thermal barrier coating
The paper presents the experimental and theoretical investigation on the thermal fatigue failure induced by delamination in thermal barrier coating system. Laser heating method was used to simulate the operating state of TBC (thermal barrier coating) system. The non-destructive evaluation such as acoustic emission (AE) detect was used to study the evolution of TBC system damage. Micro-observation and AE detect
Y. C. Zhou; T. Hashida
The present paper describes a simulation model for the operation of an automotive air conditioning system subjected to typical mechanical failures. A review identified the most common mechanical failures in automotive A\\/C systems. Simple mathematical models of two of the most common of these failures were developed and introduced in a simulation model of the vapor compression cycle. Simulated components
Sergio Libanio Campos; Jos� Luiz Fernandes; Jos� Alberto Reis Parise
[Chronic respiratory failure: the role of home mechanical ventilation].
While negative pressure ventilation using cuirass respirators or iron-lung machines was prevailing in the first part of the 20th century, the polio epidemic in Copenhagen 1952 marks the turning point at which positive pressure ventilation following tracheotomy was started. Furthermore, following the introduction of facial masks and starting 1985 in Germany non-invasive positive pressure ventilation has meanwhile been developed as a routine procedure for the long-term treatment of patients with chronic ventilatory failure today. The current article provides an overview of these developments and also outlines the role of two particular national societies: "Deutsche Gesellschaft f�r Pneumologie und Beatmungsmedizin (DGP) e.?V." (German Medical Association of Pneumology and Ventilatory Support) and "Deutsche Interdisziplin�re Gesellschaft f�r au�erklinische Beatmung (DIGAB) e.?V." (German Interdisciplinary Society for Home Mechanical Ventilation). PMID:20827646
Windisch, W
Mechanisms of compressive failure in woven composites and stitched laminates
NASA Technical Reports Server (NTRS)
Stitched laminates and angle interlock woven composites have been studied in uniaxial, in-plane, monotonic compression. Failure mechanisms have been found to depend strongly on both the reinforcement architecture and the degree of constraint imposed by the loading grips. Stitched laminates show higher compressive strength, but are brittle, possessing no load bearing capacity beyond the strain for peak load. Post-mortem inspection shows a localized shear band of buckled and broken fibers, which is evidently the product of an unstably propagating kink band. Similar shear bands are found in the woven composites if the constraint of lateral displacements is weak; but, under strong constraint, damage is not localized but distributed throughout the gauge section. While the woven composites tested are weaker than the stitched laminates, they continue to bear significant loads to compressive strains of approx. 15 percent, even when most damage is confined to a shear band.
Cox, B. N.; Dadkhah, M. S.; Inman, R. V.; Morris, W. L.; Schroeder, S.
Emerging mechanisms of T-tubule remodelling in heart failure
Cardiac excitation�contraction coupling occurs primarily at the sites of transverse (T)-tubule/sarcoplasmic reticulum junctions. The orderly T-tubule network guarantees the instantaneous excitation and synchronous activation of nearly all Ca2+ release sites throughout the large ventricular myocyte. Because of the critical roles played by T-tubules and the array of channels and transporters localized to the T-tubule membrane network, T-tubule architecture has recently become an area of considerable research interest in the cardiovascular field. This review will focus on the current knowledge regarding normal T-tubule structure and function in the heart, T-tubule remodelling in the transition from compensated hypertrophy to heart failure, and the impact of T-tubule remodelling on myocyte Ca2+ handling function. In the last section, we discuss the molecular mechanisms underlying T-tubule remodelling in heart disease.
Guo, Ang; Zhang, Caimei; Wei, Sheng; Chen, Biyi; Song, Long-Sheng
Mechanisms of renal hyporesponsiveness to ANP in heart failure.
The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure. PMID:12925036
Charloux, A; Piquard, F; Doutreleau, S; Brandenberger, G; Geny, B
Failure mechanisms of flip chip DCA assembly using eutectic solder
Reliability performance is still the major concern for flip chip interconnection. While solder fatigue is believed to be the contributing factor for packaging failure and is the most widely studied for flip chip soldering, experimental work in this study find out solder fatigue itself is seldom the driving force for early failure. With the introduction of underfill, failures solely due
Qing Tan; Rebecca Cole; Addi Mistry; Craig Beddingfield
Simulated Hail Ice Mechanical Properties and Failure Mechanism at Quasi-Static Strain Rates
NASA Astrophysics Data System (ADS)
Hail is a significant threat to aircraft both on the ground and in the air. Aeronautical engineers are interested in better understanding the properties of hail to improve the safety of new aircraft. However, the failure mechanism and mechanical properties of hail, as opposed to clear ice, are not well understood. A literature review identifies basic mechanical properties of ice and a failure mechanism based upon the state of stress within an ice sphere is proposed. To better understand the properties of Simulated Hail Ice (SHI), several tests were conducted using both clear and cotton fiber reinforced ice. Pictures were taken to show the internal crystal structure of SHI. SHI crush tests were conducted to identify the overall force-displacement trends at various quasi-static strain rates. High speed photography was also used to visually track the failure mechanism of spherical SHI. Compression tests were done to measure the compression strength of SHI and results were compared to literature data. Fracture toughness tests were conducted to identify the crack resistance of SHI. Results from testing clear ice samples were successfully compared to previously published literature data to instill confidence in the testing methods. The methods were subsequently used to test and characterize the cotton fiber reinforced ice.
Swift, Jonathan M.
Failure mechanisms in composite panels subjected to underwater impulsive loads
NASA Astrophysics Data System (ADS)
This work examines the performance of composite panels when subjected to underwater impulsive loads. The scaled fluid-structure experimental methodology developed by Espinosa and co-workers was employed. Failure modes, damage mechanisms and their distributions were identified and quantified for composite monolithic and sandwich panels subjected to typical blast loadings. The temporal evolutions of panel deflection and center deflection histories were obtained from shadow Moir� fringes acquired in real time by means of high speed photography. A linear relationship of zero intercept between peak center deflections versus applied impulse per areal mass was obtained for composite monolithic panels. For composite sandwich panels, the relationship between maximum center deflection versus applied impulse per areal mass was found to be approximately bilinear but with a higher slope. Performance improvement of sandwich versus monolithic composite panels was, therefore, established specially at sufficiently high impulses per areal mass ( I0/ M�>170 m s -1). Severe failure was observed in solid panels subjected to impulses per areal mass larger than 300 m s -1. Extensive fiber fracture occurred in the center of the panels, where cracks formed a cross pattern through the plate thickness and delamination was very extensive on the sample edges due to bending effects. Similar levels of damage were observed in sandwich panels but at much higher impulses per areal mass. The experimental work reported in this paper encompasses not only characterization of the dynamic performance of monolithic and sandwich panels but also post-mortem characterization by means of both non-destructive and microscopy techniques. The spatial distribution of delamination and matrix cracking were quantified, as a function of applied impulse, in both monolithic and sandwich panels. The extent of core crushing was also quantified in the case of sandwich panels. The quantified variables represent ideal metrics against which model predictive capabilities can be assessed.
Latourte, F�lix; Gr�goire, David; Zenkert, Dan; Wei, Xiaoding; Espinosa, Horacio D.
Application of fracture mechanics in electrical/mechanical failures of dielectrics
NASA Astrophysics Data System (ADS)
Theoretical and experimental study of the mechanical/electrical fracture behavior of dielectric materials, piezoelectric ceramics PZT 8, PZT 4, and polymeric material poly vinyl chloride (PVC), was made in this work. The charge-free zone (CFZ) model proposed by Zhang et al. for the failure of conductive cracks in dielectrics, which was well verified by the experimental results of depoled piezoelectric ceramics PZT 4, was extended to predict the failure behavior of conductive cracks in piezoelectric ceramics. Piezoelectric ceramics were treated as mechanically brittle and electrically ductile materials in the charge-free zone model. The failure criterion, developed from the CFZ model, for conductive cracks in piezoelectric ceramics under mechanical and/or electrical loading has an elliptic shape in terms of the normalized electric intensity factor and the normalized stress intensity factor. To verify the theoretical prediction from the CFZ model for piezoelectric ceramics, experiment was conducted to study the failure behavior of electrically conductive cracks (deep notches) in poled lead zirconate titanate PZT-8 ceramics. When the critical stress intensity factor was normalized by the critical stress intensity factor under purely mechanical loading and the critical electric intensity factor was normalized by the critical electric intensity factor under purely electric loading, the experimental results revealed that the failure behavior of the conductive cracks in the ceramics was described by an elliptic function of the normalized electric intensity factor versus the normalized stress intensity factor under combined mechanical and electric loading. The experimental results verified well the theoretical predictions from the CFZ model. The relationship between strain (deformation) and electric field (voltage) is linear when electric fled (voltage) is low. The relationship becomes nonlinear at high electric field (voltage). In order to adopt the linear constitutive equations which have simple forms, and to cover the actual applying procedure at the same time, a novel concept of secant piezoelectric constant was introduced to refine the CFZ model. In addition, the concepts of fracture mechanics, which were successfully applied in the study of poled PZT 4, PZT 8 and depoled PZT 4, were introduced to study the electrical failure behavior of polymeric material poly vinyl chloride (PVC). Two kinds of samples, compact tensile (CT) samples and the double notched samples, were used to obtain the electrical fracture toughnesses. The electrical fracture toughnesses obtained from CT samples were higher than those obtained from the double notched samples. This showed that for polymers, electrical fracture toughnesses were not only related to the tested materials, but also related to the conditions of how the notch tips were electrically biased.
Liu, Guoning
Investigation of Interface States and Failure Mechanisms in Mnos Devices
NASA Astrophysics Data System (ADS)
The objective of this dissertation is to conduct a quantitative study of the interface state characteristics at Si-SiO(,2) interface and the failure mechanisms in the silicon MNOS nonvolatile memory devices under different write/erase (W/E) cycling conditions. The main thrust of this research is to quantitatively characterize the interface states in MNOS devices and to correlate the results of the measurements to the failure mechanisms in the exercised MNOS devices for W/E cycles up to 1 x 10('11) cycles. The Constant-Capacitance Deep Level Transient Spectroscopy (CC-DLTS) technique is employed for the first time to characterize the interface states in the MNOS device. The existing theory for the CC-DLTS technique is modified to analyze the interface state density and electron capture cross sections of the trap states at Si-SiO(,2) interface. An exact equivalent circuit model for the p('+)-gridded MNOS capacitors is developed to predict the high frequency C -V behavior in the exercised MNOS devices. The results show little change in the interface state density was observed for W/E cycles less than 1 x 10('7) and increased rapidly for W/E cycles greater than 1 x 10('7). For W/E cycles greater than 5 x 10('9), a gradual increase in interface state density with W/E cyclings was observed. The negative shift of threshold voltage in the exercised MNOS devices can be attributed to the creation of interface states for W/E cycles less than 10('9) and primarily due to the generation of interface states for W/E cycles exceeding 1 x 10('9). The increase in interface state densities and the degradation of the thin oxide layer after prolonged W/E cycling increase the back tunneling current which results in the increase of retention decay rate. Furthermore, mobility degradation in the inversion layer was observed in the MNOS transistors for W/E cycling exceeds 10('9). This is attributed to the generation of surface state densities. Improvement in retention and endurance of the MNOS transistors may be achieved by altering NH(,3)/SiH(,4) ratio, oxide thickness and annealing conditions. The scale-down Metal-Oxide-Nitride-Oxide-Silicon (MONOS) structure may enhance the performance of MNOS nonvolatile memory devices.
Lu, Hsing-Liang
The use of fracture mechanics in failure analysis in the offshore diamond mining industry
This paper considers two major failures of offshore diamond mining equipment, which should not have occurred had both fracture mechanics aspects and materials behaviour been more fully understood. The two case studies include (a) failure of a wire rope swivel, and (b) failure of a load cell (used for monitoring rope load). In case (a) the swivel shank had failed
R. B. Tait; C. Emslie
Failure mechanism of the all-polyethylene glenoid implant
Fixation failure of glenoid components is the main cause of unsuccessful total shoulder arthroplasties. The characteristics of these failures are still not well understood, hence, attempts at improving the implant fixation are somewhat blind and the failure rate remains high. This lack of understanding is largely due to the fundamental problem that direct observations of failure are impossible as the fixation is inherently embedded within the bone. Twenty custom made implants, reflecting various common fixation designs, and a specimen set-up was prepared to enable direct observation of failure when the specimens were exposed to cyclic superior loads during laboratory experiments. Finite element analyses of the laboratory tests were also carried out to explain the observed failure scenarios. All implants, irrespective of the particular fixation design, failed at the implant�cement interface and failure initiated at the inferior part of the component fixation. Finite element analyses indicated that this failure scenario was caused by a weak and brittle implant�cement interface and tensile stresses in the inferior region possibly worsened by a stress raiser effect at the inferior rim. The results of this study indicate that glenoid failure can be delayed or prevented by improving the implant/cement interface strength. Also any design features that reduce the geometrical stress raiser and the inferior tensile stresses in general should delay implant loosening.
Sarah, Junaid; Sanjay, Gupta; Sanjay, Sanghavi; Carolyn, Anglin; Emery, Roger; Andrew, Amis; Ulrich, Hansen
Failure mechanism of the all-polyethylene glenoid implant.
Fixation failure of glenoid components is the main cause of unsuccessful total shoulder arthroplasties. The characteristics of these failures are still not well understood, hence, attempts at improving the implant fixation are somewhat blind and the failure rate remains high. This lack of understanding is largely due to the fundamental problem that direct observations of failure are impossible as the fixation is inherently embedded within the bone. Twenty custom made implants, reflecting various common fixation designs, and a specimen set-up was prepared to enable direct observation of failure when the specimens were exposed to cyclic superior loads during laboratory experiments. Finite element analyses of the laboratory tests were also carried out to explain the observed failure scenarios. All implants, irrespective of the particular fixation design, failed at the implant-cement interface and failure initiated at the inferior part of the component fixation. Finite element analyses indicated that this failure scenario was caused by a weak and brittle implant-cement interface and tensile stresses in the inferior region possibly worsened by a stress raiser effect at the inferior rim. The results of this study indicate that glenoid failure can be delayed or prevented by improving the implant/cement interface strength. Also any design features that reduce the geometrical stress raiser and the inferior tensile stresses in general should delay implant loosening. PMID:19939390
Sarah, Junaid; Sanjay, Gupta; Sanjay, Sanghavi; Carolyn, Anglin; Emery, Roger; Andrew, Amis; Ulrich, Hansen
Mechanisms of star fruit-induced acute renal failure.
We have previously discovered that star fruit can induce oliguric acute renal failure. To investigate the mechanisms of star fruit-associated acute oxalate nephropathy, the nephrotoxic effect of star fruit was examined in both cellular experiments and animal models. We evaluated renal function, pathological changes in kidney tissues and apoptotic effects using terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) assay in four groups of rats -- a control group (CG), fed with tap water (1); a star fruit group (SG), fed with star fruit juice naturally containing 0.2M oxalate (2); and oxalate groups (OxG), fed with 0.2M (3) or 0.4M (4) oxalate solution. The effects of both star fruit juice and oxalate on MDCK cells were also analyzed by flow cytometry. We found that the mean creatinine clearance was significantly lower in the SG, 0.2M OxG and 0.4M OxG. Dose-dependent apoptotic effects were evident from the TUNEL assay, and flow cytometry analysis of treated MDCK cells showed dose- and time-dependent effects. Our findings suggest that star fruit juice produces acute renal injury, not only through the obstructive effect of calcium oxalate crystals, but also by inducing apoptosis of renal epithelial cells, which may be caused by the levels of oxalate in the fruit. PMID:18294746
Fang, Hua-Chang; Lee, Po-Tsang; Lu, Pei-Jung; Chen, Chien-Liang; Chang, Tsu-Yuan; Hsu, Chih-Yang; Chung, Hsiao-Min; Chou, Kang-Ju
Mechanisms of bee venom-induced acute renal failure.
The spread of Africanized bees in the American continent has increased the number of severe envenomation after swarm attacks. Acute renal failure (ARF) is one of the major hazards in surviving patients. To assess the mechanisms of bee venom-induced ARF, rats were evaluated before, up to 70 min and 24h after 0.5mg/kg of venom injection. Control rats received saline. Bee venom caused an early and significant reduction in glomerular filtration rate (GFR, inulin clearance, 0.84+/-0.05 to 0.40+/-0.08 ml/min/100g, p<0.0001) and renal blood flow (RBF, laser Doppler flowmetry), which was more severe in the cortical (-72%) than in the medullary area (-48%), without systemic blood pressure decrease. Creatine phosphokinase, lactic dehydrogenase (LDH) and serum glutamic oxaloacetic transaminase increased significantly, pointing to rhabdomyolysis, whereas serum glutamic pyruvic transaminase and hematocrit remained stable. Twenty-four hours after venom, RBF recovered but GFR remained significantly impaired. Renal histology showed acute tubular injury and a massive tubular deposition of myoglobin. Venom was added to isolated rat proximal tubules (PT) suspension subjected to normoxia and hypoxia/reoxygenation (H/R) for direct nephrotoxicity evaluation. After 60 min of incubation, 0.1, 2 and 10 microg of venom induced significant increases in LDH release: 47%, 64% and 86%, respectively, vs. 21% in control PT while 2 microg of venom enhanced H/R injury (85% vs. 55%, p<0.01). These results indicate that vasoconstriction, direct nephrotoxicity and rhabdomyolysis are important mechanisms in the installation of bee venom-induced ARF that may occur even without hemolysis or hypotension. PMID:16774771
Grisotto, Luciana S D; Mendes, Gl�ria E; Castro, Isac; Baptista, Maria A S F; Alves, Venancio A; Yu, Luis; Burdmann, Emmanuel A
The project started on September 1, 2001. During last 4 months, one post-doctor has been hired for this project. We have received TBC samples (YSZ/CoNiCrAlY/ Inconel 601) from Tohoku University, Japan, while processing of the TBC samples was delayed in GE Corp. Research and Development. The TBC preparation in Japan was based on our technical requirement by plasma spray. Bond coat CoNiCrAlY and the YSZ was produced by low-pressure plasma spray and air plasma spray respectively. The morphology of the surface and the microstructure of cross-section of the sample was observed and analyzed by SEM and EDX. XRD was also used to detect the phases in the YSZ. Currently we are processing the overlay Al{sub 2}O{sub 3} on the TBC samples by EB-PVD and high velocity oxy-fuel (HVOF) spray techniques in collaboration with Penn State University and State University of New York at Stony Brook. We will finish comparing the hot corrosion behavior of the Al{sub 2}O{sub 3}/YSZ/CoNiCrAlY/superalloy system with the YSZ/CoNiCrAlY/superalloy system. The mechanism of hot corrosion will be investigated. The processing-structure-properties relationship of the overlays will be determined.
Scott X. Mao
Design and Environmental Factors Contributing to the Failure of Thermal Barrier Coating Systems
NASA Astrophysics Data System (ADS)
Gas turbine engines are a staple of 21st century air and sea propulsion systems and are also a critical component in large-scale electricity generation. The hot-section components of these engines are protected by a complex ceramic and metal multi-layer coating called a thermal barrier coating (TBC) system. The failure of TBC systems occurs as a result of both thermo-chemical and thermo-mechanical degradation. This research involves exploring both of these mechanisms for two distinctly different issues. The United States Navy is currently making a push to implement the use of alternative fuels by 2012, but the use of these fuels (syngas, high hydrogen content, and alternatives to JP-8) presents significant materials durability challenges. Initial data suggests that high water vapor levels, high sulfur concentrations, and ash deposits from fuel impurities lead to unique, and severe, degradation modes. This research is aimed at addressing the effects of differing combustion environment characteristics on the corrosion and oxidation of TBC systems. On the industrial front, there is a constant driver to better understand and predict coating failure, particularly in air-plasma sprayed (APS) TBC systems. The morphology of the metal-ceramic interface is known to play a key role in the generation of compressive and tensile stresses that eventually cause coating failure in typical engine environments. Experimental evidence and field experience have shown that a tortuous interface is generally beneficial to coating lifetime. Nevertheless, for the past 40 years engineers have struggled to find a functional correlation between BC topology and coating system lifetime. This document also addresses the progress that has been made toward the establishment of this functional correlation.
Weeks, Matthew David
Evolution of Tre-2/Bub2/Cdc16 (TBC) Rab GTPase-activating proteins.
Rab GTPases serve as major control elements in the coordination and definition of specific trafficking steps and intracellular compartments. Rab activity is modulated in part by GTPase-activating proteins (GAPs), and many RabGAPs share a Tre-2/Bub2/Cdc16 (TBC)-domain architecture, although the majority of TBC proteins are poorly characterized. We reconstruct the evolutionary history of the TBC family using ScrollSaw, a method for the phylogenetic analysis of pan-eukaryotic data sets, and find a sophisticated, ancient TBC complement of at least 10 members. Significantly, the TBC complement is nearly always smaller than the Rab cohort in any individual genome but also suggests Rab/TBC coevolution. Further, TBC-domain architecture has been well conserved in modern eukaryotes. The reconstruction also shows conservation of ancestral TBC subfamilies, continuing evolution of new TBCs, and frequent secondary losses. These patterns give additional insights into the sculpting of the endomembrane system. PMID:23485563
Gabernet-Castello, Carme; O'Reilly, Amanda J; Dacks, Joel B; Field, Mark C
Fracture surface analysis to understand the failure mechanisms of collagen degraded bone
Fracture surface analysis is a powerful technique to investigate bone failure mechanisms. Previously, emu tibiae were endocortically\\u000a treated with 1�M potassium hydroxide (KOH) solution for 14�days. This treatment caused in situ collagen degradation rather\\u000a than removal, with no differences in geometrical parameters, but with significant changes in mechanical properties. KOH-treated\\u000a tibiae showed significant decreases in failure stress and increased failure
Lisa Wise-Milestone; Sidney Omelon; Zhirui Wang; Marc Grynpas
Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions.
National Technical Information Service (NTIS)
A critical assessment is carried out of the microstructural changes in respect of the associated reductions in material mechanical properties and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found...
A. Arakere B. Pandurangan B. A. Cheeseman C. Yen M. Grujicic
Properties and failure mechanisms of pinned composite lap joints in monotonic and cyclic tension
The effect of through-thickness reinforcement by fibrous pins on the static tensile strength, fatigue life and failure mechanisms of single lap joints made of carbon\\/epoxy composite is investigated. Pinning is highly effective in increasing the ultimate strength, elongation limit and fatigue life. Improvements to the monotonic and fatigue properties are attributed to transitions in the failure mechanisms, from unstable joint
P. Chang; A. P. Mouritz; B. N. Cox
This paper describes an application of data on cracking, leak and rupture events from nuclear power plant operating experience to estimate failure frequencies for piping components that had been previously evaluated using the PROLOCA and PRAISE probabilistic fracture mechanics (PFM) computer codes. The calculations had addressed the failure mechanisms of stress corrosion cracking, intergranular stress corrosion cracking and fatigue for
Fredric A. Simonen; Stephen R. Gosselin; Bengt O. Lydell; David L. Rudland; Gery M. Wilkowski
High-voltage failure mechanisms in liquid-filled, Fluorinert FC-40, capacitors
NASA Astrophysics Data System (ADS)
The high-voltage electrical failure of a liquid-filled, FC-40 Fluorinert, capacitor occurred during a system random vibration test. This failure occurred between 1 and 5 hours of random vibration of the system in the longitudinal axis of the capacitor. The previous five hours of random vibration in the transverse direction left the capacitor functioning as designed. Similar failures were observed during component random vibration testing under high-voltage. This paper will describe the investigation of the above mentioned failures. The design and processing of this type of capacitor technology will also be reviewed. Both electrical and mechanical data will be provided. The results of this investigation revealed the cause of the above failures and the procedures necessary for avoiding such failures in the future. The interaction of the mechanical system, piece-part designs and the bellows temperature compensation system will be explained in connection with the electrical failures. Suggestions for future improved designs will be included.
McBrayer, J. D.; Richardson, C. B.; Jojola, A. A.; Pitre, L. J.
Mechanisms of fatigue failure in thermal spray coatings
The aim of this experimental study was to ascertain the fatigue failure modes of thermal spray coatings in rolling\\/sliding\\u000a contact. These failure modes outline the design requirements of thermal spray coatings for high-stress tribological applications\\u000a including impact and point or line contact loading. Recently, a number of scientific studies have addressed the fatigue performance\\u000a and durability of thermal spray coatings
R. Ahmed; M. Hadfield
Automated failure mode effects and criticality analyses for reliability prediction of multibody mechanical systems
NASA Astrophysics Data System (ADS)
Reliability is important to ensure both serviceability and safety of a mechanical system. A method for simulation-based Failure Mode Effects and Criticality Analysis (FMECA) for reliability prediction of mechanical systems is presented. This approach integrates recursive formulation for dynamic analysis, failure criteria for failure determination, graphics techniques for collision detection, and new techniques for modifying dynamics model during the simulation. The automated FMECA method developed consists of three libraries and a graphics collision detection technique. First, a library of mechanical failure modes is created using cause-effect relationships for mechanical failure modes. Second, a library of component failure criteria is constructed by collecting different material test data. Third, a library of simulation algorithms and supporting techniques is built by developing simulation technologies to perform FMECA for mechanical failure modes. In addition, the automated FMECA method uses the developed graphics software VDS for collision detection. Finally, this approach is used to investigate the consequences of four failure modes of a vehicle system. The difficulty in formulating mathematical expressions for a damaged mechanical system is resolved by manipulating the number of cut joint constraints and generalized coordinates to implicitly update the original system topology. Formulations for virtual joints are derived, as well as other new techniques to permit multiple failures during a dynamic simulation. A near-minimum set of generalized coordinates is thus retained throughout the dynamic simulation. Four general-purpose dynamics codes are implemented and effects of four mechanical failure modes of a mechanical system are investigated; suspension failure, joint degradation and breakage, joint stiction, and component yielding and breakage. Failure histories as well as Mean Time Between Failure (MTBF) and Mean Time To Failure (MTTF) are obtained. The automated FMECA method developed identifies critical components, critical failure modes, and operating limits of a mechanical system. This information can be used to redesign the critical components, thereby improving the reliability of a mechanical system. Automated FMECA also supports a failure reporting and corrective action system (FRACAS), and the test-analyze-and-fix (TAAF) methodology, and minimization of cost for both hard-prototype building and field tests.
Chiang, Alex Chih-Chien
In order to improve the hot corrosion resistance of conventional YSZ TBC system, a dense and continues overlay of Al{sub 2}O{sub 3} coating of about 25 {micro}m thick was deposited on the surface of TBC by EB-PVD and high velocity oxy-fuel (HVOF) spray techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5% V{sub 2}O5) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase of ZrO{sub 2} was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. During hot corrosion test, there were no significant interactions between overlay Al{sub 2}O{sub 3} coating and molten salts. After exposure, the alumina coating, especially produced by HVOF, was still very dense and cover the surface of YSZ, although they had been translated to {alpha}-Al{sub 2}O{sub 3} from original {gamma}-Al{sub 2}O{sub 3}. As a result, Al{sub 2}O{sub 3} overlay coating decreased the penetration of salts into the YSZ and prevented the YSZ from the attack by molten salts containing vanadium. Accordingly, only a few M-phase was formed in YSZ TBC, compared with TBC without overlay coating. The penetration of salts into alumina coating was thought to be through microcracks formed in overlay Al{sub 2}O{sub 3} coating and at the interface between alumina and zirconia due to the presence of tensile stress in the alumina coating. In the next year, we will study the mechanisms of cracking of the overlay Al{sub 2}O{sub 3} layer. The hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, the post-annealing will be carried out in vacuum (residual pressure 10{sup -3} Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay. The effect of thickness of Al{sub 2}O{sub 3} coating on hot corrosion resistance will also be investigated. We will prepare Al{sub 2}O{sub 3} coating by sol-gel method. The corrosion resistance of TBC with sol-gel Al{sub 2}O{sub 3} coating will be determined and discussed with the results of TBC with EB-PVD and HVOF Al{sub 2}O{sub 3} coating.
Scott X. Mao
Acute exercise and physiological insulin induce distinct phosphorylation signatures on TBC1D1 and TBC1D4 proteins in human skeletal muscle.
We investigated the phosphorylation signatures of two Rab-GTPase activating proteins TBC1D1 and TBC1D4 in human skeletal muscle in response to physical exercise and physiological insulin levels induced by a carbohydrate rich meal using a paired experimental design. Eight healthy male volunteers exercised in the fasted or fed state and muscle biopsies were taken before and immediately after exercise. We identified TBC1D1/4 phospho-sites that (1) did not respond to exercise or postprandial increase in insulin (TBC1D4: S666), (2) responded to insulin only (TBC1D4: S318), (3) responded to exercise only (TBC1D1: S237, S660, S700; TBC1D4: S588, S751), and (4) responded to both insulin and exercise (TBC1D1: T596; TBC1D4: S341, T642, S704). In the insulin-stimulated leg, Akt phosphorylation of both T308 and S473 correlated significantly with multiple sites on both TBC1D1 (T596) and TBC1D4 (S318, S341, S704). Interestingly, in the exercised leg in the fasted state TBC1D1 phosphorylation (S237, T596) correlated significantly with the activity of the ?2/?2/?3 AMPK trimer, whereas TBC1D4 phosphorylation (S341, S704) correlated with the activity of the ?2/?2/?1 AMPK trimer. Our data show differential phosphorylation of TBC1D1 and TBC1D4 in response to physiological stimuli in human skeletal muscle and support the idea that Akt and AMPK are upstream kinases. TBC1D1 phosphorylation signatures were comparable between in vitro contracted mouse skeletal muscle and exercised human muscle, and we show that AMPK regulated phosphorylation of these sites in mouse muscle. Contraction and exercise elicited a different phosphorylation pattern of TBC1D4 in mouse compared with human muscle, and although different circumstances in our experimental setup may contribute to this difference, the observation exemplifies that transferring findings between species is problematic. PMID:24247980
Treebak, Jonas T; Pehm�ller, Christian; Kristensen, Jonas M; Kj�bsted, Rasmus; Birk, Jesper B; Schjerling, Peter; Richter, Erik A; Goodyear, Laurie J; Wojtaszewski, J�rgen F P
Atmospheric Plasma Spraying of High Melting Temperature Complex Perovskites for TBC Application
NASA Astrophysics Data System (ADS)
High melting materials have always been very attractive candidates for materials development in thermal barrier coating (TBC) applications. Among these materials, complex perovskites with Ba(Mg1/3Ta2/3)O3 and La(Al1/4Mg1/2T1/4)O3 compositions have been developed and deposited in TBC systems by atmospheric plasma spraying. Spray parameters were optimized and in-flight particle temperatures were recorded using Accuraspray-g3 and DPV 2000. Plasma sprayed coatings were found to undergo non-stoichiometric decomposition of components which could have contributed to early failure of the coatings. Particle temperature diagnostics suggest that gun power of ~15 kW or lower where majority of the particles have already solidified upon impact to the substrate could probably prevent the decomposition of phases. Additionally, it has been found that the morphology of the powder feedstock plays a critical role during atmospheric plasma spraying of complex perovskites.
Jarligo, M. O.; Mack, D. E.; Mauer, G.; Va�en, R.; St�ver, D.
Member Failure Recovery Mechanism Using Context Ontology for Community Computing
Community computing is a new paradigm for building ubiquitous systems which can solve problems by collaborating between entities in ubiquitous environment. Community is a kind of collaborative group and members in the community interact with each other for achieving community goals - that is, seamless interaction is the key issue of the community computing. In this perspective, member failure is
Minsoo Kim; Minkoo Kim
Electrostatic discharge failure mechanism for cordless phone charge contacts
A comparison of the SEM EDX spectra for the metal charge contacts from the field-returned cordless phones and for the laboratory samples of fixed gap discharge (FGD) tests reveals similar chemical elements, suggesting that electrostatic discharge (ESD) is the possible source for cordless phone field failure.
Richard J Coyle; Min-Chung Jon
Failure mechanism of winding insulations in inverter-fed motors
The failure of magnet wires under repetitive pulses as seen in inverter-fed motors cannot be attributed to a single factor but is a result of the combined effects of partial discharge, dielectric heating, and space charge formation. Voltage overshoots produced by PWM drives may be above discharge inception voltage. Partial discharge may therefore be present in inverter-fed motors. In addition
Weijun Yin
76 FR 5494 - Pipeline Safety: Mechanical Fitting Failure Reporting Requirements
Federal Register 2010, 2011, 2012, 2013
...reporting of the revised Gas Distribution Annual...the revised 2011 Gas Distribution Annual...applicable to distribution pipelines. This final rule...Section-by-Section Analysis Section 191.12...Failure Report into the pipeline safety regulations...are detailed in the Gas Distribution...
Microstructure versus flaw: mechanisms of failure and strength in nanostructures.
Understanding failure in nanomaterials is critical for the design of reliable structural materials and small-scale devices with nanoscale components. No consensus exists on the effect of flaws on fracture at the nanoscale, but proposed theories include nanoscale flaw tolerance and maintaining macroscopic fracture relationships at the nanoscale with scarce experimental support. We explore fracture in nanomaterials using nanocrystalline Pt nanocylinders with prefabricated surface notches created using a "paused" electroplating method. In situ scanning electron microscopy (SEM) tension tests demonstrate that the majority of these samples failed at the notches, but that tensile failure strength is independent of whether failure occurred at or away from the flaw. Molecular dynamics simulations verify these findings and show that local plasticity is able to reduce stress concentration ahead of the notch to levels comparable with the strengths of microstructural features (e.g., grain boundaries). Thus, failure occurs at the stress concentration with the highest local stress whether this is at the notch or a microstructural feature. PMID:24168654
Gu, X Wendy; Wu, Zhaoxuan; Zhang, Yong-Wei; Srolovitz, David J; Greer, Julia R
Premature failure in Pt-GaAs IMPATT's�Recombination-assisted diffusion as a failure mechanism
We have recently observed an aging anomaly in platinum-- GaAs IMPATT diodes. The effect is observed during temperature stress aging of diodes operating in avalanche. At temperatures above about 300�C, the devices follow a log-normal failure distribution with an activation energy of 1.6 eV. At lower temperatures, however, a change in activation energy to the range of 0.2 to 0.4
W. C. Ballamy; LIONEL C. KIMERLING
A New Method of Proactive Recovery Mechanism for Large-Scale Network Failures
This paper proposes a novel recovery mechanism from large-scale network failures caused by earthquakes, ter- rorist attacks, large-scale power outages and software bugs. Our method, which takes advantage of overlay networking technologies, pre-calculates multiple routing configurations to prevent possible simultaneous network failures and selects one configuration immediately after detecting the failures. Through numerical calculation results using actual AS-level topology, we
Takuro Horie; Go Hasegawa; Satoshi Kamei; Masayuki Murata
Oxidation characteristics of a platinized MCrAlY bond coat for TBC systems during cyclic oxidation at 1000 �C
The scale growth mechanisms of a platinized NiCoCrAlY bond coat (BC) beneath a ceramic thermal barrier coating (TBC) were studied during cyclic oxidation in air at 1000 �C. The thermally grown oxide scales (TGO) after exposure times ranging from 100 to 9100 h were characterized by scanning electron microscopy and laser fluorescence spectroscopy. The TGO appeared to consist of alumina
W. J. Quadakkers; V. Shemet; D. Sebold; R. Anton; E. Wessel; L. Singheiser
Investigating compression failure mechanisms in composite laminates with a transient fiberglass-epoxy birefringent material
NASA Technical Reports Server (NTRS)
An experimental study is reported in which a nondestructive technique involving the use of a transparent fiberglass-epoxy composite birefringent material has been used to investigate compression failure mechanisms in graphite-epoxy laminates. It is shown that the birefringency and transparency of the fiberglass-epoxy material permits regions of high stress to be located and the mechanisms of local failure propagation to be identified within the laminate. The material may also be useful for studying stress fields and for identifying failure initiation and propagation mechanisms in a wide variety of composite-structure problems.
Shuart, M. J.; Williams, J. G.
Register of specialized sources for information on mechanics of structural failure
NASA Technical Reports Server (NTRS)
Specialized information sources that generate information relative to six problem areas in aerospace mechanics of structural failure are identified. Selection for inclusion was based upon information obtained from the individual knowledge and professional contacts of Martin Marietta Aerospace staff members and the information uncovered by the staff of technical reviewers. Activities listed perform basic or applied research related to the mechanics of structural failure and publish the results of such research. The purpose of the register is to present, in easy reference form, original sources for dependable information regarding failure modes and mechanisms of aerospace structures.
Carpenter, J. L., Jr.; Denny, F. J.
Failure modes and mechanisms in nickel alloys: Primarily austenitic stainless steel
Austenitic stainless steels and higher nickel alloys such as the Inconels are used extensively in the chemical and nuclear industries. This review will concentrate on their behavior in nuclear reactors because of the availability of information to the author. Emphasis is given to the failure modes and mechanisms occurring in the context of causal mechanisms and the implications of alloy composition. Major use is made of the austenitic steels both AISI 304 and 316 in United States nuclear plants. This is true for both boiling water reactors (BWRs) and pressurized water reactors (PWRs). Over the years there have been many failures in these materials where failure is defined as cracking, leaking, and, rarely, catastrophic breakage. This review will examine failure mechanisms such as stress corrosion cracking, both transgranular and intergranular, fatigue, including vibrational and thermal, and other corrosion-related failures. 16 refs., 12 figs.
Bush, S.H.
Mechanism-Based Therapeutic Approaches to Rhabdomyolysis-Induced Renal Failure
Rhabdomyolysis-induced renal failure represents up to 15% of all cases of acute renal failure. Many studies over the past four decades have demonstrated that accumulation of myoglobin in the kidney is central in the mechanism leading to kidney injury. However, some discussion exists regarding the mechanism mediating this oxidant injury. Although free iron-catalyzed fenton reaction has been proposed to explain the tissue injury, more recent evidence strongly suggests that the main cause of oxidant injury is myoglobin redox cycling and generation of oxidized lipids. These molecules can propagate tissue injury and cause renal vasoconstriction, two of the three main conditions associated with acute renal failure. This review presents the evidence supporting the two mechanisms of oxidative injury, describes the central role of myoglobin redox cycling in the pathology of renal failure associated with rhabdomyolysis, and discuss the value of therapeutic interventions aiming at inhibiting myoglobin redox cycling for the treatment of rhabdomyolysis-induced renal failure.
Boutaud, Olivier; Roberts, L. Jackson
This paper describes an application of data on cracking, leak and rupture events from nuclear power plant operating experience to estimate failure frequencies for piping components that had been previously evaluated using the PROLOCA and PRAISE probabilistic fracture mechanics (PFM) computer codes. The calculations had addressed the failure mechanisms of stress corrosion cracking, intergranular stress corrosion cracking and fatigue for materials and operating conditions that were known to have failed components. The first objective was to benchmark the calculations against field experience. A second objective was a review of uncertainties in the treatments of the data from observed failures and in the structural mechanics models. The database PIPExp-2006 was applied to estimate failure frequencies. Because the number of reported failure events was small, there were also statistical uncertainties in the estimates of frequencies. Comparisons of predicted and observed failure frequencies showed that PFM codes correctly predicted relatively high failure probabilities for components that had experienced field failures. However, the predicted frequencies tended to be significantly greater than those estimated from plant operating experience. A review of the PFM models and inputs to the models showed that uncertainties in the calculations were sufficiently large to explain the differences between the predicted and observed failure frequencies.
Simonen, Fredric A.; Gosselin, Stephen R.; Lydell, Bengt O.; Rudland, David L.; Wilkowski, Gery M.
Non-destructive microwave evaluation of TBC delamination induced by acute angle laser drilling
NASA Astrophysics Data System (ADS)
Laser drilling has been applied to the production of cooling holes of various size and angles in the modern aerospace gas turbine components such as turbine blades, nozzle guide vanes, combustion chambers and afterburner. These parts are usually made of heat resistant nickel superalloys. The superalloy substrate is coated with yttria-stabilized zirconia thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Drilling the parts at acute angles to the surface is complicated because (i) multiple layers are being drilled through, (ii) the melt ejection and heat flow patterns around the hole are non-symmetrical and (iii) the drilling distance is greater than when drilling normal to the surface. In a previous investigation by the authors, delamination of TBC was addressed as a main problem of angled drilling and mechanisms involved were discussed. Characterization of delamination cracks was normally performed via metallographic techniques. It involves sectioning the samples using an abrasive cutting machine, grinding with successively finer silicon carbide paper up to the centre of the hole and polishing to allow optical microscopic analysis of the cracks. However, clamping and sectioning process of thermal-spray-coated workpieces can introduce cracks in brittle coatings due to the drag of the cut-off wheels. Hence, it is not possible to decide if the delamination is caused as a result of post-process sectioning or laser drilling. In this paper, a microwave non-destructive testing (NDT) technique is employed to evaluate the integrity of TBC after acute angle laser drilling. An Agilent 8510 XF network analyser operating over the frequency range of 45 MHz to 110 GHz was used to measure the amplitude and phase variations of scattered waves. The results significantly indicated the existence of delamination of 1-1.5 mm long at the TBC/substrate interface on the leading edge part of an acute-angled hole laser drilled using a 400 W Nd:YAG laser.
Sezer, H. K.; Li, Lin; Wu, Z.; Anderson, B.; Williams, P.
Failure mechanisms and mechanisms-based life predictions for electron beam physical vapor deposition thermal barrier coatings
This research is designed to define failure mechanisms and to develop and experimentally validate non-destructive life prediction methodologies for electron beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs). It is shown that for the two TBCs of this study ((Ni,Pt)Al and NiCoCrAlY bond coated TBCs) different failure mechanisms are exhibited, and therefore, the selected life prediction methodologies are accordingly
Mei Wen
A study of the failure mechanism of chlorine anodes
Thin coating RuO{sub 2}{minus}TiO{sub 2} electrodes, which mimic the DSA anodes, have been prepared and tested for their activity toward the chlorine evolution reaction and subjected to life time testing. Rutherford Backscattering Spectrometry has been used concurrently with electrochemical measurements to analyze changes in the ruthenium content of the coating. The decrease in electrode activity is found to be closely related to a decrease in Ru content, and the measured profiles indicate that the loss takes place across the thin coating. Failure is observed for electrodes with a Ru content below a critical concentration, but there is no evidence for the build up of a pure TiO{sub 2} layer. AFM imaging of an anode after failure sustained the hypothesis of loss of material.
Vallet, C.E.; Zuhr, R.A. [Oak Ridge National Lab., TN (United States); Tilak, B.V.; Chen, C.P. [Occidental Chemical Corp., Grand Island, NY (United States)
Failure criteria used in a probabilistic fracture mechanics code
Two criteria are implemented in a piping reliability analysis code to assess the stability of crack growth in pipes. One is the critical net section stress criterion. It is simple and convenient but its application is limited to very ductile materials. The other is the tearing modulus stability criterion. This criterion has a solid technical base. However, calculating the J-integral, J, and the associated tearing modulus, T, usually requires a complicated finite element method (FEM). In this piping reliability code, existing J and T solutions in tabular or formula form instead of the FEM are used for computational efficiency. These two failure criteria are discussed and compared in terms of their effects on the estimation of pipe failure probability. 5 refs., 9 figs.
Lo, T.Y.
Endplate failure occurs frequently in osteoporotic vertebral fractures and may be related to the development of high tensile strain. To determine whether the highest tensile strains in the vertebra occur in the endplates, and whether such high tensile strains are associated with the material behavior of the intervertebral disc, we used micro-CT-based finite element analysis to assess tissue-level strains in twenty-two elderly human vertebrae (81.5 � 9.6 years) that were compressed through simulated intervertebral discs. In each vertebra, we compared the highest tensile and compressive strains across the different compartments: endplates, cortical shell, and trabecular bone. The influence of the Poisson-type expansion of the disc on the results was determined by compressing the vertebrae a second time in which we suppressed Poisson expansion. We found that the highest tensile strains occurred within the endplates whereas the highest compressive strains occurred within the trabecular bone. The ratio of strain to assumed tissue-level yield strain was highest for the endplates, indicating that the endplates had the greatest risk of initial failure. Suppressing the Poisson expansion of the disc decreased the amount of highly tensile-strained tissue in the endplates by 79.4 � 11.3%. These results indicate that the endplates are at the greatest risk of initial failure due to the development of high tensile strains, and that such high tensile strains are associated with the Poisson expansion of the disc. We conclude that initial failure of the vertebra is associated with high tensile strains in the endplates, which in turn are influenced by the material behavior of the disc.
Fields, Aaron J.; Lee, Gideon L.; Keaveny, Tony M.
Method of Testing and Predicting Failures of Electronic Mechanical Systems
NASA Technical Reports Server (NTRS)
A method employing a knowledge base of human expertise comprising a reliability model analysis implemented for diagnostic routines is disclosed. The reliability analysis comprises digraph models that determine target events created by hardware failures human actions, and other factors affecting the system operation. The reliability analysis contains a wealth of human expertise information that is used to build automatic diagnostic routines and which provides a knowledge base that can be used to solve other artificial intelligence problems.
Iverson, David L.; Patterson-Hine, Frances A.
Failure mechanisms in single-point incremental forming of metals
The last years saw the development of two different views on how failure develops in single-point incremental forming (SPIF).\\u000a Today, researchers are split between those claiming that fracture is always preceded by necking and those considering that\\u000a fracture occurs with suppression of necking. Each of these views is supported by convincing experimental and theoretical arguments\\u000a that are available in the
Maria B. Silva; Peter S. Nielsen; Niels Bay; P. A. F. Martins
Incidence and causes of non-invasive mechanical ventilation failure after initial success
BACKGROUNDThe rate of failure of non-invasive mechanical ventilation (NIMV) in patients with chronic obstructive pulmonary disease (COPD) with acute respiratory insufficiency ranges from 5% to 40%. Most of the studies report an incidence of �late failure� (after >48 hours of NIMV) of about 10�20%. The recognition of this subset of patients is critical because prolonged application of NIMV may unduly
Maurizio Moretti; Carmela Cilione; Auro Tampieri; Claudio Fracchia; Alessandro Marchioni; Stefano Nava
Failure mechanism of COF based Line Driver IC for Flat Panel Display by contamination
This study is about the field failure and mechanism of Chip on Film (COF) based Line Driver IC (LDI) for FPD. Due to LDI failure, there is vertical line defect on Flat Panel Display (FPD). Contamination is detected in bumps of LDI which is packaged by Resin. Chemical and physical method has applied for analyzing the elements and the isolation
Jae-Seong Jeong; Young Jeon Kim
Divalent ion metabolism in patients with acute renal failure: Studies on the mechanism of hypocalcemia
Divalent ion metabolism in patients with acute renal failure: Studies on the mechanism of hypocalcemia. Studies were carried out in ten patients with acute renal failure to characterize certain features of deranged divalent ion metabolism. During the oliguric period, the patients displayed hypocalcemia, hyperphosphatemia, hypermagnesemia and elevated levels of immunoreactive parathyroid hormone. Hypocalcemia and elevated levels of immunoreactive parathyroid hormone
Shaul G Massry; Allen I Arieff; Jack W Coburn; Genaro Palmieri; Charles R Kleeman
Investigation of thermally induced failure mechanisms in integrated spiral planar power passives
Research on the development of electromagnetically integrated passive structures have, in recent years, led to a number of technological improvements such as improved constructional technology. The reliability and physics of failure of these structures have in contrast received little attention. In this paper, the main thermally induced failure mechanisms are investigated experimentally for an integrated LC structure as representative of
J. T. Strydom; J. D. van Wyk
A study of the mechanism of flexural toppling failure of rock slopes
Summary The mechanism of flexural toppling failure of jointed rock slopes has been investigated through a series of centrifuge experiments conducted on models manufactured from two types of materials (brittle: a sand-gypsum mixture; and ductile: fibre-cement sheeting). The basal failure plane observed in the centrifuge models, has been found to emanate from the toe of the slope, and orient at
D. P. Adhikary; A. V. Dyskin; R. J. Jewell; D. P. Stewart
Mechanical properties and failure mechanisms of carbon fiber reinforced epoxy laminated composites
The mechanical behavior of quasi-isotropic and unidirectional epoxy-matrix carbon-fiber laminated composites subjected compressive loading at strain rates of 10{sup {minus}3} and 2000 s{sup {minus}1} are described. Failure in the studied composites was dominated by delamination which proceeded by brittle fracture of the epoxy-matrix. The matrix-fiber bonding in these composites is very strong and prevented the occurrence of significant fiber-pullout. The mode I delamination strain energy release rate of the unidirectional composites was determined using the double cantilever beam and hole in plate compression method. The DCB method indicated a significant R curve effect attributed to fiber bridging while the presently available hole in plate analytical methods show questionable validity for highly anisotropic materials.
Thissell, W.R.; Zurek, A.K.; Addessio, F.
Mechanical properties, microscopy, and failure mechanisms of carbon fiber reinforced epoxy laminated composites
The mechanical behavior of quasi-isotropic and unidirectional epoxy- matrix carbon-fiber laminated composites subjected to compressive loading at strain rates of 10{sup {minus}3} and 2000 s{sup {minus}1} are described. Failure in the studied composites was dominated by delamination which proceeded by brittle fracture of the epoxy matrix. The matrix-fiber bonding in these composites is very strong and prevented the occurrence of significant fiber-pullout. The mode I delamination strain energy release rate of the unidirectional composites was determined using the double cantilever beam and hole in plate compression methods. The DCB method indicated a significant R curve effect attributed to fiber bridging while the presently available hole in plate analytical methods show questionable validity for highly anisotropic materials.
Thissell, W.R.; Zurek, A.K.; Addessio, F.
Mechanics of dual-mode dilative failure in subaqueous sediment deposits
NASA Astrophysics Data System (ADS)
We introduce dual-mode dilative failure with flume experiments. Dual-mode dilative failure combines slow and steady release of sediments by breaching with periodic sliding, which rapidly releases an internally coherent wedge of sediments. It occurs in dilative sandy deposits. This periodic slope failure results from cyclic evolution of the excess pore pressure in the deposit. Sliding generates large, transient, negative excess pore pressure that strengthens the deposit and allows breaching to occur. During breaching, negative excess pore pressure dissipates, the deposit weakens, and ultimately sliding occurs once again. We show that the sliding frequency is proportional to the coefficient of consolidation. We find that thicker deposits are more susceptible to dual-mode dilative failure. Discovery of dual-mode dilative failure provides a new mechanism to consider when interpreting the sedimentary deposits linked to submarine slope failures.
You, Yao; Flemings, Peter; Mohrig, David
Rupture failure and mechanical strength of the electrode wire used in wire EDM
In the application of wire EDM, wire rupture is very troublesome and impedes further increase of cutting speed. Instead of the spark characteristics or the temperature distribution, the rupture mechanism and the mechanical strength of the wire are the focus of this investigation. Wire rupture is a mechanical failure in essence, although the process heat has significant influence on the
Y. F. Luo
Accelerated Thermal Cycling and Failure Mechanisms for BGA and CSP Assemblies
NASA Technical Reports Server (NTRS)
This paper reviews the accelerated thermal cycling test methods that are currently used by industry to characterize the interconnect reliability of commercial-off-the-shelf (COTS) ball grid array (BGA) and chip scale package (CSP) assemblies. Acceleration induced failure mechanisms varied from conventional surface mount (SM) failures for CSPs. Examples of unrealistic life projections for other CSPs are also presented. The cumulative cycles to failure for ceramic BGA assemblies performed under different conditions, including plots of their two Weibull parameters, are presented. The results are for cycles in the range of -30 C to 100 C, -55 C to 100 C, and -55 C to 125 C. Failure mechanisms as well as cycles to failure for thermal shock and thermal cycling conditions in the range of -55 C to 125 C were compared. Projection to other temperature cycling ranges using a modified Coffin-Manson relationship is also presented.
Ghaffarian, Reza
TBC: a clustering algorithm based on prokaryotic taxonomy.
High-throughput DNA sequencing technologies have revolutionized the study of microbial ecology. Massive sequencing of PCR amplicons of the 16S rRNA gene has been widely used to understand the microbial community structure of a variety of environmental samples. The resulting sequencing reads are clustered into operational taxonomic units that are then used to calculate various statistical indices that represent the degree of species diversity in a given sample. Several algorithms have been developed to perform this task, but they tend to produce different outcomes. Herein, we propose a novel sequence clustering algorithm, namely Taxonomy-Based Clustering (TBC). This algorithm incorporates the basic concept of prokaryotic taxonomy in which only comparisons to the type strain are made and used to form species while omitting full-scale multiple sequence alignment. The clustering quality of the proposed method was compared with those of MOTHUR, BLASTClust, ESPRIT-Tree, CD-HIT, and UCLUST. A comprehensive comparison using three different experimental datasets produced by pyrosequencing demonstrated that the clustering obtained using TBC is comparable to those obtained using MOTHUR and ESPRIT-Tree and is computationally efficient. The program was written in JAVA and is available from http://sw.ezbiocloud.net/tbc. PMID:22538644
Lee, Jae-Hak; Yi, Hana; Jeon, Yoon-Seong; Won, Sungho; Chun, Jongsik
Deformation and failure mechanisms of graphite/epoxy composites under static loading
NASA Technical Reports Server (NTRS)
The mechanisms of deformation and failure of graphite epoxy composites under static loading were clarified. The influence of moisture and temperature upon these mechanisms were also investigated. Because the longitudinal tensile properties are the most critical to the performance of the composite, these properties were investigated in detail. Both ultimate and elastic mechanical properties were investigated, but the study of mechanisms emphasized those leading to failure of the composite. The graphite epoxy composite selected for study was the system being used in several NASA sponsored flight test programs.
Clements, L. L.
Lubrication and failure mechanisms of graphite fluoride films
NASA Technical Reports Server (NTRS)
An optical microscope, equipped with a vertical illuminator and two polaroid filters (one rotatable), was used to visually study 440C HT steel surfaces lubricated with rubbed graphite fluoride films. Friction and wear results were compared to visual observations as a function of sliding distance for films applied to three surface finishes - polished, sanded, and sand-blasted. In general, the lubricating process was one of initial deformation or wear of metallic asperities into flat plateaus and then the formation of thin, layer-like, dynamic films which sheared between the flats and eventually flowed through the contact area. Failure was due to depletion of the graphite fluoride with the subsequent formation of excessive powdery metallic debris that formed a heavy, powdery film on both the rider and disk surfaces.
Fusaro, R. L.
Failure mechanisms associated with the thermally grown oxide in plasma-sprayed thermal barrier coatings
The microstructure and durability of a thermal barrier coating (TBC) produced by the thermal spray method have been characterized. Upon exposure, the bond coat chemistry and microstructure change by inter-diffusion with the substrate and upon thickening of the thermally grown oxide (TGO). A wedge impression test, in conjunction with observations by scanning electron microscopy, has been used to probe the
A Rabiei; A. G Evans
Annually, premature birth is a major public health problem accounting for over 13,000 deaths and 30,000 surviving infants with life-long morbidity. Preterm premature rupture of the membranes is the initiating event leading to preterm birth of 40% of these premature infants. Fetal membrane (FM) rupture is a catastrophic tissue failure, a unique event in normal physiology; other tissue failures (bone breaks, aneurism ruptures) are pathological processes. The mechanisms which cause FM failure and thereby rupture are not understood. A full understanding of FM failure process requires a complete characterization of structural and biomechanical behavior at near/full term under sub-failure (forces well below that which induce rupture) and failure conditions as well as elucidating the biological factors which modulate its failure. The relatively, highly loaded stated of the FM in vivo may also facilitate its susceptibility to enzymatic degradation, which was shown to be augmented with increased load in collagenous tissues. Indeed, this last observation may help to provide the link between biomechanical degradation and premature mechanical failure in the FM. This integrated approach will further the understanding of this unique physiological event and thereby provide insight into how to anticipate and when appropriate, intervene to prevent preterm FM rupture.
Joyce, Erinn M.; Moore, John J.; Sacks, Michael S.
Mechanical integrity of the IC device package-a key factor in achieving failure free product performance
A methodology has been developed to maximize product hardware integrity and practically eliminate service affecting field failures. This methodology starts with the analysis of the field failures reported over a period of 5 to 10 years. Failed parts are analyzed and similar failures are reproduced in laboratory conditions. This procedure allows researchers to identify the failure mechanisms and the factors
Sorin Witzman; Yves Giroux
A Mechanical Engine Simulator for Development of Aero Engine Failure Analysis Methods
\\u000a A mechanical engine simulator for method development is under construction at Berlin Institute of Technology. The new experimental\\u000a rig reflects nearly all mechanical characteristics of an aero engine. The mechanical engine simulator will enable the analysis\\u000a of diverse failure cases that need to be considered for an aero engine certification. Based on the experimental results using\\u000a the mechanical simulator, analytical
Robert Liebich
Investigation of failure mechanisms in integrated vacuum circuits
NASA Technical Reports Server (NTRS)
The fabrication techniques of integrated vacuum circuits are described in detail. Data obtained from a specially designed test circuit are presented. The data show that the emission observed in reverse biased devices is due to cross-talk between the devices and can be eliminated by electrostatic shielding. The lifetime of the cathodes has been improved by proper activation techniques. None of the cathodes on life test has shown any sign of failure after more than 3500 hours. Life tests of triodes show a decline of anode current by a factor of two to three after a few days. The current recovers when the large positive anode voltage (100 V) has been removed for a few hours. It is suggested that this is due to trapped charges in the sapphire substrate. Evidence of the presence of such charges is given, and a model of the charge distribution is presented consistent with the measurements. Solution of the problem associated with the decay of triode current may require proper treatment of the sapphire surface and/or changes in the deposition technique of the thin metal films.
Rosengreen, A.
Plant root reinforcement against local failure mechanism in protecting slope
NASA Astrophysics Data System (ADS)
Effectiveness of plant root reinforcement in protecting shallow landslides was investigated with a method of slope stability analysis. In the study, plant roots contributed effectively to increase the local safety factors of slope and subsequently increased the over-all safety factor to stabilize the slope. The natural plant roots increased the local safety factor by providing additional shear strength locally to the shear plane of the investigated slopes. Study showed that the strength of soil at certain location along the shear plane drastically reduced to a residual level and the local failure was imminent for slopes without root reinforcement. On the other hand, the roots significantly contributed additional strength to increase such local residual strength of slope soil and hence increased the safety factor for same slopes with root reinforcements. The shear strengths of roots were determined with root diameters, number of roots and tensile strength of roots. The root shear strengths were incorporated as reinforcements into the slope stability analysis method. The used method for slope stability analysis calculated the local as well as over-all factor of safety with root reinforcement. Existing published data regarding the roots were used in the analyses. A number of analyses for safety factor calculations were done with different root reinforcement situation in the slopes. Parametric studies among different root parameters with safety factor and shear strength were also studied.
Khan, Y. A.
Immunological mechanisms of pentoxifylline in chronic heart failure
The progressive syndrome of chronic heart failure (CHF) represents a common disease pathway that may be derived from a host of varying insults (including myocardial ischaemia and infarction, hypertension, viral infection, pregnancy, etc). Despite this multifarious aetiology, a common phenomena observed in CHF patients is elevated levels of tumour necrosis factor (TNF)-?. This has led to the widespread concept that TNF-? is directly involved in the pathophysiology of CHF and as such, attempts have been made to inhibit TNF-? production in this cohort. However, to date, there have been no clear beneficial effects from TNF-? inhibition and indeed trials of direct anti-TNF therapy have provoked worsening of clinical outcomes. Conversely, a possible exception is pentoxifylline (PTX), a putative TNF-? inhibitor with possible (but ill-defined) vasodilatory properties. Several small clinical trials assessing the use of PTX in CHF have suggested beneficial effects on multiple surrogate clinical markers. Interestingly, these trials failed to show a concordant effect on circulating TNF despite the clinical improvement, suggesting other key beneficial properties of this novel agent. This review article provides an insight into the potential beneficial mode of the action of PTX in CHF and calls for more investigation of this interesting agent.
Shaw, Steven M.; Shah, Mohammed K.H.; Williams, Simon G.; Fildes, James E.
Application of damage mechanics to ice failure in compression
In this work some principles of viscoelastic theory as applicable to ice are reviewed. A multiaxial ice model, incorporating nonlinear damage, is presented based on the Burgers viscoelastic body with nonlinear dashpots in both the Kelvin and the Maxwell units. This mechanical ice model is found to be very efficient and accurate, especially for short loading periods. It includes the
J. Xiao; I. J. Jordaan
Outcome of mechanical ventilation for acute respiratory failure in patients with pulmonary fibrosis
Objective: During the course of idiopathic pulmonary fibrosis patients may need invasive mechanical ventilation because of acute respiratory failure. We reviewed the charts of all patients with idiopathic pulmonary fibrosis admitted to our ICU for mechanical ventilation to describe their ICU course and prognosis. Design and setting: Retrospective, observational case series, from December 1996 to March 2001, in an 18-bed
Thierry Fumeaux; Claudia Rothmeier; Philippe Jolliet
Analysis of failure mechanisms observed in axial collapse of thin-walled circular fibreglass composite tubes
Theoretical analysis of the failure mechanism of the stable mode of collapse of thin-walled fibreglass composite tubes under static axial compression, based on experimental observations and taking into account all possible energy absorbing mechanisms developed during the process, is reported. Crushing loads and the energy absorbed are theoretically predicted. The proposed theoretical model was experimentally verified for various composite materials
A. G. Mamalis; D. E. Manolakos; G. A. Demosthenous; M. B. Ioannidis
Triggering mechanisms of slope instability processes and sediment failures on continental margins: a geotechnical approach
The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of
N. Sultan; P. Cochonat; M. Canals; A. Cattaneo; B. Dennielou; H. Haflidason; J. S. Laberg; D. Long; J. Mienert; F. Trincardi; R. Urgeles; T. O. Vorren; C. Wilson
A Probabilistic-Micro-mechanical Methodology for Assessing Zirconium Alloy Cladding Failure
Cladding failure of fuel rods caused by hydride-induced embrittlement is a reliability concern for spent nuclear fuel after extended burnup. Uncertainties in the cladding temperature, cladding stress, oxide layer thickness, and the critical stress value for hydride reorientation preclude an assessment of the cladding failure risk. A set of micro-mechanical models for treating oxide cracking, blister cracking, delayed hydride cracking, and cladding fracture was developed and incorporated in a computer model. Results obtained from the preliminary model calculations indicate that at temperatures below a critical temperature of 318.5 deg. C [605.3 deg. F], the time to failure by delayed hydride cracking in Zr-2.5%Nb decreased with increasing cladding temperature. The overall goal of this project is to develop a probabilistic-micro-mechanical methodology for assessing the probability of hydride-induced failure in Zircaloy cladding and thereby establish performance criteria. (authors)
Pan, Y.M. [Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 78238 (United States); Chan, K.S.; Riha, D.S. [Southwest Research Institute, San Antonio, TX, 78238 (United States)
Failure of thick, low density air plasma sprayed thermal barrier coatings
NASA Astrophysics Data System (ADS)
This research was directed at developing fundamental understandings of the variables that influence the performance of air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBC). Focus was placed on understanding how and why each variable influenced the performance of the TBC system along with how the individual variables interacted with one another. It includes research on the effect of surface roughness of NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying, the interdiffusion behavior of bond coats coupled to commercial superalloys, and the microstructural and compositional control of APS topcoats to maximize the coating thicknesses that can be applied without spallation. The specimens used for this research were prepared by Praxair Surface Technologies and have been evaluated using cyclic oxidation and thermal shock tests. TBC performance was sensitive to bond coat roughness with the rougher bond coats having improved cyclic performance than the smoother bond coats. The explanation being the rough bond coat surface hindered the propagation of the delamination cracks. The failure mechanisms of the APS coatings were found to depend on a combination of the topcoat thickness, topcoat microstructure and the coefficient of thermal expansion (CTE) mismatch between the superalloy and topcoat. Thinner topcoats tended to fail at the topcoat/TGO interface due to bond coat oxidation whereas thicker topcoats failed within the topcoat due to the strain energy release rate of the thicker coating exceeding the fracture strength of the topcoat. Properties of free-standing high and conventional purity YSZ topcoats of both a lowdensity (LD) and dense-vertically fissure (DVF) microstructures were evaluated. The densification rate and phase evolution were sensitive to the YSZ purity and the starting microstructure. Increasing the impurity content resulted in enhanced sintering and phase decomposition rates, with the exception of the conventional-purity DVF which exhibited a density decrease during sintering. A combination of the DVF and LD topcoat microstructures (dual TBC) resulted in significant increase in cyclic durability. A 1275 mum thick dual TBC coating was found to have a comparable furnace cyclic life to that of a 100 im LD TBC.
Helminiak, Michael Aaron
Failure modes and fracture mechanisms in flexure of Kevlar-epoxy composites
The results of testing in three-point bending of aramid fibre-reinforced epoxy composites are described. This loading mode\\u000a has been chosen in order to increase the variety of failure modes and of fracture mechanisms. The main failure modes observed\\u000a are tensile and delamination, with a transition at a fibre volume fraction of about 46%. This mode transition is detectable\\u000a by monitoring
M. Davidovitz; A. Mittelman; I. Roman; G. Marom
Mechanism of enhanced transcellular potassium�secretion in man with chronic renal failure
Mechanism of enhanced transcellular potassium�secretion in man with chronic renal failure. Previous studies from our laboratory demonstrated that net K secretion in human rectum was 2.5-fold higher in patients with chronic renal failure than in controls. The present study was performed to determine whether K secretion in human large intestine involves an active process and whether an active transport process
Sergio Panese; Rodolfo S M�rtin; Mirta Virginillo; Maria Litardo; Esteban Siga; Elvira Arrizurieta; John P Hayslett
Pathogenic mechanisms in early norepinephrine-induced acute renal failure: Functional and histological correlates of protection
Pathologic mechanisms in early norepinephrine-induced acute renal failure: Functional and histological correlates of protection. The present study investigated the protective effect of acute volume expansion (25%) with isotonic saline, isotonic mannitol, and hypertonic mannitol in a model of unilateral norepinephrine-induced acute renal failure (ARF). Three hours following a 40-min intrarenal infusion of norepinephrine (NE) (0.75 �g\\/kg\\/min), inulin clearance had fallen
Robert E Cronin; Antoine de Torrente; Paul D Miller; Ruth Ellen Bulger; Thomas J Burke; Robert W Schrier
Role of Cytokines in the Mechanism of Action of Amlodipine: The PRAISE Heart Failure Trial
Objectives. We sought to determine whether the beneficial effects of amlodipine in heart failure may be mediated by a reduction in tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) levels. We postulated that TNF-alpha and IL-6 levels may also have predictive value in patients with congestive heart failure (CHF).Background. The molecular mechanism for progression of CHF may involve cytokine overexpression. The
Emile R Mohler; Leif C Sorensen; Jalal K Ghali; Douglas D Schocken; Park W Willis; John A Bowers; Anne B Cropp; Milton L Pressler
Electrochemical evaluation of a corrosion fatigue failure mechanism in a duplex stainless steel
Laboratory corrosion fatigue studies on smooth and precracked samples indicated that two duplex stainless steels would have\\u000a similar service lives in a paper-processing environment; but, in service, one of these alloys has exhibited premature failures.\\u000a Since corrosion fatigue experiments had proven unable to detect this failure mechanism, electrochemical measurements and slow\\u000a strain rate tensile tests were used to evaluate four
M. R. Stoudt; R. E. Ricker
Failure mechanisms of a zirconia-8 wt% yttria thermal barrier coating
Isothermal and cyclic heat treatments of a plasma-sprayed zirconia-8 wt% yttria thermal barrier coating on a nickel superalloy substrate highlighted coating failure mechanisms. A reaction layer formed at the bond coat\\/ceramic interface, and failure of the coating initiated in the reaction layer due to opening thermal expansion mismatch stresses associated with a nonplanar interface. Crack propagation occurred in the ceramic
Andrew H. Bartlett; Roberto Dal Maschio
Predictors of extubation failure and reintubation in newborn infants subjected to mechanical ventilation
Objective To identify risk factors for extubation failure and reintubation in newborn infants subjected to mechanical ventilation and to establish whether ventilation parameters and blood gas analysis behave as predictors of those outcomes. Methods Prospective study conducted at a neonatal intensive care unit from May to November 2011. A total of 176 infants of both genders subjected to mechanical ventilation were assessed after extubation. Extubation failure was defined as the need to resume mechanical ventilation within less than 72 hours. Reintubation was defined as the need to reintubate the infants any time after the first 72 hours. Results Based on the univariate analysis, the variables gestational age <28 weeks, birth weight <1,000g and low Apgar scores were associated with extubation failure and reintubation. Based on the multivariate analysis, the variables length of mechanical ventilation (days), potential of hydrogen (pH) and partial pressure of oxygen (pO2) remained associated with extubation failure, and the five-minute Apgar score and age at extubation were associated with reintubation. Conclusion Low five-minute Apgar scores, age at extubation, length of mechanical ventilation, acid-base disorders and hyperoxia exhibited associations with the investigated outcomes of extubation failure and reintubation.
Costa, Ana Cristina de Oliveira; Schettino, Renata de Carvalho; Ferreira, Sandra Clecencio
Influence of Martensite Mechanical Properties on Failure Mode and Ductility of Dual Phase Steels
In this paper, the effects of the mechanical properties of the martensite phase on the failure mode and ductility of dual phase (DP) steels are investigated using a micromechanics-based finite element method. Actual microstructures of DP sheet steels obtained from scanning electron microscopy are used as representative volume element (RVE) in two-dimensional plane-stress finite element calculations. Failure is predicted as plastic strain localization in the RVE during deformation. The mechanical properties of the ferrite and martensite phases in a commercial DP 980 steel are obtained based on the in-situ X-ray diffraction measurements of a uniaxial tensile test. Computations are then conducted on the RVE in order to investigate the influence of the martensite mechanical properties and volume fraction on the macroscopic behavior and failure mode of DP steels. The computations show that, as the strength and volume fraction of the martensite phase increase, the ultimate tensile strength (UTS) of DP steels increases but the UTS strain and failure strain decrease. These results agree well with the general experimental observations on DP steels. Additionally, shear dominant failure modes usually develop for DP steels with lower martensite strengths, whereas split failure modes typically develop for DP steels with higher martensite strengths.
Choi, Kyoo Sil; Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.
Mechanisms of the beneficial effects of beta-adrenoceptor antagonists in congestive heart failure
Many clinical studies have documented favourable effects (reduced morbidity and mortality) of beta-adrenoceptor (?-AR) antagonists, such as carvedilol, metoprolol, propranolol, atenolol and bisoprolol, in congestive heart failure. These agents attenuate the effects of sympathetic activation during the development of heart failure, prevent ventricular remodelling and improve cardiac function. Because ?-AR blockers are known to exert negative inotropic action, the mechanisms responsible for their beneficial effects in heart failure have been a subject of debate. While attenuation of changes in ?-AR cyclic AMP-mediated signal transduction in heart failure is considered to be responsible for the beneficial effects of ?-AR antagonists, other mechanisms such as the effects of these agents on subcellular remodelling, oxidative stress, apoptosis and defect in calcium handling, are equally important in preventing cardiac alterations in the failing heart. Moreover, ?-AR antagonists are not a homogeneous group of drugs because they differ in their pharmacokinetics and pharmacodynamics, in addition to the selective and nonselective nature of their actions on ?-AR. Various ?-AR blocking agents have been shown to possess different ancillary properties and produce effects that are independent of ?-AR. In fact, different ?-AR antagonists have been observed to lower the elevated levels of plasma catecholamines in heart failure. Thus, the beneficial effects of ?-AR antagonists are not only elicited through their interaction with mediated ?-AR signal transduction sites in the myocardium, but other mechanisms may also contribute to their favourable actions in heart failure.
Rehsia, Navneet S; Dhalla, Naranjan S
Original mechanism of failure initiation revealed through modelling of naturally occurring microstructures
NASA Astrophysics Data System (ADS)
Motivated to reveal original mechanisms of failure resistance, we developed a material model that encompasses most reoccurring microstructural features of natural composites. The interesting result of the work is a notion that material failure is governed by the quality of interactions between hierarchical levels in the material microstructure. With intelligent use of the structure, these interactions can be tuned to create a powerful synergetic effect on the material failure behaviour. For example, while exploring different mechanisms of failure initiation in composites with bimodal size reinforcements (an indirect way to model two levels of hierarchy simultaneously) we found that failure initiation could be shifted from stress concentration sites of the higher level to the lower level. One could say that the material behaviour became insensitive to the presence of reinforcements on the higher level�a phenomenon that is counterintuitive to what is commonly known. The new mechanism of failure initiation could only be activated in composites with a highly controlled structural organization�in the studied case, reinforcements of the lower level needed to establish lamellar pathways between reinforcements of the higher level. These pathways lead to formation of an intriguing network-like microstructure. Intelligent communication between reinforcements in such a network created the necessary synergy to change the failure initiation mechanism in a discontinuous fashion. Another finding was that by establishing such a network, tensile stresses near dangerous stress concentration sites were locally transformed into compressive stresses. Resemblance of the revealed mechanism to phenomena on the nano-scale was also discussed. In the course of this work a new method was developed to investigate interactions between reinforcements and their collective input into effective and local properties of a composite. The reinforcement phase was modelled with the use of rigid-line inhomogeneities.
Gorbatikh, Larissa; Lomov, Stepan V.; Verpoest, Ignaas
Solvent stress cracking and failure mechanisms in polyetherimide composites
Solvent stress cracking studies have been carried out in o-xylene and other solvents on polyetherimide-based materials including neat resin, woven fabric composites, and adhesively bonded systems. The results show crack growth in solvents at very low G(I) levels as compared with tests in air. The composite and adhesively bonded systems have sufficiently high residual thermal stresses to drive an array of intersecting matrix/adhesive cracks even without mechanical loading. The matrix/adhesive residual stress-driven crack patterns retard main delamination crack growth relative to that in the neat resin, and raise the applied threshold G(I) level for main crack growth by about a factor of 10. 30 refs.
Hsieh, A.J.; Schneider, N.S.; Mandell, J.F. (Army Materials Technology Laboratory, Watertown, MA (USA) Montana State Univ., Bozeman (USA))
Product Reliability Trends, Derating Considerations and Failure Mechanisms with Scaled CMOS
NASA Technical Reports Server (NTRS)
As microelectronics is scaled into the deep sub-micron regime, space and aerospace users of advanced technology CMOS are reassessing how scaling effects impact long-term product reliability. The effects of electromigration (EM), time-dependent-dielectric-breakdown (TDDB) and hot carrier degradation (HCI and NBTI) wearout mechanisms on scaled technologies and product reliability are investigated, accelerated stress testing across several technology nodes is performed, and FA is conducted to confirm the failure mechanism(s).
White, Mark; Vu, Duc; Nguyen, Duc; Ruiz, Ron; Chen, Yuan; Bernstein, Joseph B.
Characterization of Alumina Interfaces in TBC Systems
Interfacial segregants in thermally grown {alpha}-Al{sub 2}O{sub 3} scales formed during high temperature exposure of thermal barrier coating systems reflect the oxygen-active dopants present in the bond coating and substrate, such as Y and Hf. These dopants diffuse outward and segregate to the substrate-alumina interface and the alumina grain boundaries. Related studies suggest that these segregants affect the growth and mechanical properties of the alumina-scale; however, the characterization of segregation in alumina formed on coated superalloy systems has been limited. Segregation examples evaluated using analytical transmission electron microscopy are given from traditional Pt-modified aluminide coatings and newer Pt diffusion coatings. Model systems are used to illustrate that grain boundary segregants on the columnar alumina boundaries are not because of the reverse diffusion of cations from the Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} top coating, and that interstitial elements in the substrate likely affect the outward flux of cation dopants. The dynamic nature of this segregation and oxygen-potential gradient-driven diffusion is discussed in light of observations of substrate dopant and interstitial contents affecting coating performance.
Pint, Bruce A [ORNL; More, Karren Leslie [ORNL
Time-Dependent Failure Mechanisms in Silicon Carbide Composites for Fusion Energy Applications
Silicon carbide has many properties that are attractive for applications in fusion energy systems. The reliability of monolithic silicon carbide is insufficient for its use in large components, due to its brittle failure behavior and flaw sensitivity. Ceramic matrix composites, on the other hand, offer greater flaw tolerance and reliability, but their failure mechanisms are less well understood. This work has focussed on studying potential failure mechanisms in silicon carbide fiber-reinforced, silicon carbide matrix (SiCf/SiCm) composites. In the event of cracks caused by accidental overloads, excessive creep, thermal shock from plasma disruptions, handling during installation, or resulting from processing, subcritical crack growth will occur due to creep of fibers that bridge the crack faces. It is presumed that irradiation will enhance the creep rate of the fibers and, subsequently, the subcritical crack growth rate. At certain temperatures the presence of even small amounts of oxygen leads to oxidation of the interphase material to gaseous products. In this case, subcritical crack growth occurs by a separate mechanism. In addition, fiber shrinkage or weakening due to exposure to radiation can promote additional failure mechanisms, including embrittlement. These mechanisms, the conditions, under which they occur, and the current state of models of the crack growth mechanisms will be discussed.
Lewinsohn, Charles A.; Youngblood, Gerald E.; Henager, Charles H.; Simonen, Edward P.; Jones, Russell H.
Failure mechanism of Ta diffusion barrier between Cu and Si
NASA Astrophysics Data System (ADS)
The reaction mechanisms in the Si/Ta/Cu metallization system and their relation to the microstructure of thin films are discussed on the basis of experimental results and the assessment of the ternary Si-Ta-Cu phase diagram at 700 �C. With the help of sheet resistance measurements, Rutherford backscattering spectroscopy, x-ray diffraction, a scanning electron microscope, and a transmission electron microscope, the Ta barrier layer was observed to fail at temperatures above 650 �C due to the formation of TaSi2, the diffusion of Cu through the silicide layer, and the resulting formation of Cu3Si precipitates. However, in order for the TaSi2 phase to form first, the Ta diffusion barrier layer must be thick enough (e.g., 50-100 nm) to prevent Cu diffusion into the Si substrate up to the temperature of TaSi2 formation (~650 �C). Independent of the Ta layer thickness, Cu3Si was present as large nodules, whereas the TaSi2 existed as a uniform layer. The resulting reaction structure was found to be in local equilibrium on the basis of the assessed Si-Ta-Cu phase diagram at 700 �C, and therefore no further reactions were expected. The role of oxygen was also found to be important in the reactions and it seems to have a strong effect on the thermal stability of the barrier layer.
Laurila, Tomi; Zeng, Kejun; Kivilahti, Jorma K.; Molarius, Jyrki; Suni, Ilkka
Effect of interface roughness and coating thickness on interfacial shear mechanical properties of EB-PVD yttria-partially stabilized zirconia thermal barrier coating systems
The effect of interface roughness and thickness of thermal barrier coating (TBC) on the interfacial shear mechanical properties of electron beam-physical vapor deposited (EB-PVD)-TBC was examined using as-sprayed and polished bond coats (BC) 200?m and 500?m TBC thickness systems, by using a barb test method. The residual compressive stress in the TBC layer from the interface to the top surface
Shuqi Guo; Yoshihisa Tanaka; Yutaka Kagawa
Investigation of the failure mechanism of thermal barrier coatings prepared by electron beam physical vapor deposition
Two-layer structure thermal barrier coatings (TBCs) (NiCoCrAlY [bond coat]+[6�8 wt.%] Y2O3-stabilized ZrO2 [YSZ top coat]) were deposited by electron beam physical vapor deposition (EB-PVD) on a Ni-base superalloy. Pre-treatments were carried out in a vacuum to improve the oxidation resistance of the bond coat, and the thermal cyclic life of the TBC system was investigated through thermal cyclic tests. It
Xiaofang Bi; Huibin Xu; Shengkai Gong
Restoration mechanisms based on tunable lasers for handling channel and link failures in optical WDM networks
NASA Astrophysics Data System (ADS)
In this paper, we study restoration mechanisms to handle channel and link failures in an optical WDM wavelength-routed wide-area backbone network based on a mesh topology. The solution uses a small number of tunable lasers per link to provide restoration capability. In addition to link failures, we consider individual channel failures link-level mechanisms are presented: redirection algorithm (RDA) and disjoint path algorithm (DPA). These mechanisms use WDM-specific link information to compute the link restoration routes. We present results based on discrete-event simulations to understand the performance of the proposed mechanisms, in terms of restoration efficiency and restoration times. The results show that for networks of varying size and node degree with 32 wavelengths on each link, using as few as 8 tunable lasers per link provides good restoration efficiency under moderate traffic load. which might occur when one or more transceivers fail at the source of the lightpath or due to a failure in the switch fabric. Restoration is first attempted using the tunable lasers to transmit on the failed wavelengths. If all the failed lightpaths cannot be restored using the tunable lasers, unused wavelengths on the same link are used (this requires optical wavelength conversion at the nodes). For the remaining lightpaths requiring restoration, link-level restoration mechanisms are attempted. Two different
Krishnamurthy, Harini; Sivalingam, Krishna M.; Mishra, Manav
Analysis of interfacial cracks in a TBC\\/superalloy system under thermal loading
Thermal barrier coatings (TBCs) provide thermal insulation to high temperature superalloys. Residual stresses develop in TBCs during cool down from processing temperatures and subsequent thermal cyclic loading due to the thermal expansion mismatch between the different layers (substrate, bond coat, and TBC). These residual stresses can initiate microcracks at the bond coat\\/TBC interface and can lead to debonding at the
S. Nusier; G. Newaz
Design and modeling of multiple layered TBC system with high reflectance
Ceramic thermal barrier coatings (TBCs) are playing an increasingly critical role in advanced gas turbine engines due to their ability to sustain further increases in operating temperatures. However, these increases in temperature could raise considerable issues associated with increased radiative heat transfer into the TBC systems. This study was conducted to design a ceramic based multiple layered TBC system with
Dongmei Wang; Xiao Huang; Prakash Patnaik
Effect of Bond Coat Materials on Thermal Fatigue Failure of EB-PVD Thermal Barrier Coatings
NASA Astrophysics Data System (ADS)
Effect of MCrAlY bond coat alloy systems on thermal fatigue failure of thermal barrier coatings (TBCs) was investigated, where the TBC specimen consisted of Ni-based superalloy IN738LC substrate, bond coat, and 8 wt.% Y2O3-stabilized ZrO2 (YSZ) top coat. The top coat was fabricated by EB-PVD method with 250 ?m in thickness. Three kinds of MCrAlY alloys were studied as the bond coat material. Employing the originally developed test equipment, thermal fatigue tests were carried out, by applying thermal cycles between 400 and 950�C in air. Special attention was paid not only to the failure life of the TBC specimen, but also the underlying failure mechanisms. The experimental results clearly demonstrated that the effect of MCrAlY bond coat alloys on the thermal fatigue life was very significant. Some discussions were made on the experimental results based on the measurements of mechanical and metallurgical properties of the bond coat alloys: i.e., elastic stiffness, thermal expansion coefficient and high temperature oxidation resistance.
Yamagishi, Satoshi; Okazaki, Masakazu; Sakaguchi, Motoki; Matsubara, Hideaki
Dynamic Mechanical Behavior and Failure Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Whiskers
NASA Astrophysics Data System (ADS)
Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers (T-ZnOw) in two loading directions are investigated by a split Hopkinson pressure bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope. Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data. The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties. Finally, the strengthening and toughening mechanisms of T-ZnOw are analyzed. It is shown that T-ZnOw can improve mechanical properties of the composites, and can make the composites have some new features. The present results provide a reliable basis for advanced composite design and manufacture, and have broad applications in the field of aerospace.
Rong, Ji-Li; Wang, Dan; Wang, Xi; Li, Jian; Xu, Tian-Fu; Lu, Ming-Ming; Cao, Mao-Sheng
The microstructural mechanism of electromigration failure in narrow interconnects of Al alloys
This thesis reports a study of the mechanism of electromigration failure in Al-2Cu-1Si thin-film conducting lines on Si. Samples were patterned from 0.5 {mu}m thick vapor-deposited films with various mean grain sizes (G), and had lines widths (W) of 1.3, 2, 4 and 6 {mu}m. The lines were aged at various conditions to change the Cu-precipitate distribution and were tested to failure at T = 225{degrees}C and j = 2.5 {times} 10{sup 6} A/cm{sup 2}. Some samples were tested over a range of substrate temperatures, current densities and current reversal times. Aging produces an initially dense distribution of metastable {Theta}{prime} (Al{sub 2}Cu; coherent) in the grain interiors, with stable {Theta} (Al{sub 2}Cu; incoherent) at the grain boundaries. The intragranular {theta}{prime} is gradually absorbed into the grain boundary precipitates. In the wide lines the mean time to failure increases slowly and monotonically with pre-aging time and current reversal time. The failure mode is the formation and coalescence of voids that form on grain boundaries with an apparent activation energy of 0.65 eV. In the narrow lines, the lines failed by a transgranular-slit mechanism with an activation energy near 0.93 eV. The distribution of the polygranular segments and the kinetics of failure varies with the linewidths. Failure occurs after Cu has been swept from the grains that fail. Pre-aging the line to create a more stable distribution of Cu significantly increases the time to failure. When the density of intragranular {Theta}-phase precipitates is maximized, the transgranular-slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. The results from the current reversal test indicate that the time to sweep Cu in the polygranular segments is longer for longer polygranular segments. Thus the time to first failure in an array of lines is much longer than predicted by a log-normal fit to the distribution of failure times.
Kim, Choongun
Mechanics of rainfall-induced flow failure in unsaturated shallow slopes (Invited)
NASA Astrophysics Data System (ADS)
The increase in pore water pressure due to rain infiltration can be a dominant component in the activation of slope instabilities. This work shows an application of the theory of material stability to the triggering analysis of this important class of natural hazards. The goal is to identify the mechanisms through which the process of rain infiltration promotes instabilities of the flow-type in the soil covers. The interplay between increase in pore water pressure and failure mechanisms is investigated at material point level. To account for multiple failure mechanisms, the second-order energy input is linked to the controllability theory and used to define different types of stability indices, each associated with a specific mode of slope failure. It is shown that the theory can be used to assess both shear failure and static liquefaction in saturated and unsaturated soil covers. In particular, it is shown that these instability modes are regulated by the hydro-mechanical characteristics of the soil covers, as well as by their mutual coupling. This finding discloses the importance of the constitutive functions that simulate the interaction between the response of the solid skeleton and the fluid-retention characteristics of the soil. As a consequence, they suggest that even material properties that are not be to directly associated with the shearing resistance (e.g., the potential for wetting compaction) may play a role in the initiation of catastrophic slope failures. According to the proposed interpretation, the process of pore pressure increase can be seen as the trigger of uncontrolled strains, which can anticipate the onset of frictional failure and promote a solid-to-fluid transition.
Buscarnera, G.
Basic failure mechanisms in advanced composites. [composed of epoxy resins reinforced with carbon fibers
NASA Technical Reports Server (NTRS)
The fundamental failure mechanisms which result from the interaction of thermal cycling and mechanical loading of carbon-epoxy composites were studied. This work was confined to epoxy resin uniderictionally reinforced with HTS carbon fibers, and consists of first identifying local fiber, matrix and interface failure mechanisms using the model composite specimen containing a small number of fibers so that optical techniques can be used for characterization. After the local fracture process has been established for both mechanical loading and thermal cycling, engineering composite properties and gross fracture modes are then examined to determine how the local events contribute to real composite performance. Flexural strength in high fiber content specimens shows an increase in strength with increased thermal cycling. Similar behavior is noted for 25 v/o material up to 200 cycles; however, there is a drastic reduction after 200 cycles indicating a major loss of integrity probably through the accumulation of local cleavage cracks in the tensile region.
Mazzio, V. F.; Mehan, R. L.; Mullin, J. V.
Performance and failure mechanisms of TiN diffusion barrier layers in submicron devices
Defects in reactively sputtered titanium nitride diffusion barriers in submicron devices were investigated. Four different failure mechanisms could be extracted, two originating from the production of the layers, two related to foregoing process steps. The latter are contact hole overetch and topology inside the contact hole, i.e., edges, created by deviating isotropic etch ratios of different dielectric layers in a
A. Kohlhase; M. M�ndl; W. Pamler
Effect of Substrate Surface Finish on the Lubrication and Failure Mechanisms of Molybdenum Disulfide Films
NASA Technical Reports Server (NTRS)
An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrates were rough, flat plateaus were created during 'run in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X ray diffraction to consist primarily of alpha iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha iron and some residual MoS2. No molybdenum oxides were found.
Fusaro, R. L.
Lubrication and failure mechanisms of molybdenum disulfide films. 2: Effect of substrate roughness
NASA Technical Reports Server (NTRS)
An optical microscope was used to study the lubrication and failure mechanisms of rubbed MoS2 films applied to three substrate surface finishes; polished, sanded, and sandblasted as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrate was rough, flat plateaus were created during run-in and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and as deposit sites for wear debris. In moist air the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X-ray diffraction to be alpha iron, MoO3, and possibly FeMoO3. In dry argon the failure mechanism was the gradual depletion of MoS2 from the contact region by transverse flow, and the wear debris on the track at failure was alpha iron, residual MoS2, and possibly FeS.
Fusaro, R. L.
The influence of test method on failure mechanisms and durability of a thermal barrier system
Failure mechanisms that occur in commercial thermal barrier systems with a Pt�aluminide bond coat and an electron beam vapor deposited thermal barrier coating have been compared for two different test protocols. The two methods consist, respectively, of a furnace cycle test and a burner rig test that differ in their configuration (disk relative to cylinder) and in their cycle time\\/rate.
D. R. Mumm; M. Watanabe; A. G Evans; J. A Pfaendtner
Mechanisms and future directions for prevention of vein graft failure in coronary bypass surgery
Coronary artery bypass grafting has been utilized as a beneficial treatment for myocardial ischemic disease for over three decades. Failure of coronary artery venous grafts occurs at a substantial rate and has a large impact on two main endpoints, survival and quality of life. An exhaustive amount of basic research has been generated to delineate possible mechanisms responsible for graft
Jeffrey H Shuhaiber; Alexander N Evans; Malek G Massad; Alexander S Geha
Mechanisms and future directions for prevention of vein graft failure in coronary bypass surgery
Summary Coronary artery bypass grafting has been utilized as a beneficial treatment for myocardial ischemic disease for over three decades. Failure of coronary artery venous grafts occurs at a substantial rate and has a large impact on two main endpoints, survival and quality of life. An exhaustive amount of basic research has been generated to delineate possible mechanisms responsible for
Jeffrey H. Shuhaiber; Alexander N. Evans; Malek G. Massad; Alexander S. Geha
Some Aspects of the Failure Mechanisms in BaTiO3-Based Multilayer Ceramic Capacitors.
National Technical Information Service (NTIS)
The objective of this presentation is to gain insight into possible failure mechanisms in BaTiO3-based ceramic capacitors that may be associated with the reliability degradation that accompanies a reduction in dielectric thickness, as reported by Intel Co...
D. D. Liu M. J. Sampson
The Rab-GTPase-activating protein TBC1D1 regulates skeletal muscle glucose metabolism.
The Rab-GTPase-activating protein TBC1D1 has emerged as a novel candidate involved in metabolic regulation. Our aim was to determine whether TBC1D1 is involved in insulin as well as energy-sensing signals controlling skeletal muscle metabolism. TBC1D1-deficient congenic B6.SJL-Nob1.10 (Nob1.10(SJL)) and wild-type littermates were studied. Glucose and insulin tolerance, glucose utilization, hepatic glucose production, and tissue-specific insulin-mediated glucose uptake were determined. The effect of insulin, AICAR, or contraction on glucose transport was studied in isolated skeletal muscle. Glucose and insulin tolerance tests were normal in TBC1D1-deficient Nob1.10(SJL) mice, yet the 4-h-fasted insulin concentration was increased. Insulin-stimulated peripheral glucose utilization during a euglycemic hyperinsulinemic clamp was similar between genotypes, whereas the suppression of hepatic glucose production was increased in TBC1D1-deficient mice. In isolated extensor digitorum longus (EDL) but not soleus muscle, glucose transport in response to insulin, AICAR, or contraction was impaired by TBC1D1 deficiency. The reduction in glucose transport in EDL muscle from TBC1D1-deficient Nob1.10(SJL) mice may be explained partly by a 50% reduction in GLUT4 protein, since proximal signaling at the level of Akt, AMPK, and acetyl-CoA carboxylase (ACC) was unaltered. Paradoxically, in vivo insulin-stimulated 2-deoxyglucose uptake was increased in EDL and tibialis anterior muscle from TBC1D1-deficient mice. In conclusion, TBC1D1 plays a role in regulation of glucose metabolism in skeletal muscle. Moreover, functional TBC1D1 is required for AICAR- or contraction-induced metabolic responses, implicating a role in energy-sensing signals. PMID:22693207
Szekeres, Ferenc; Chadt, Alexandra; Tom, Robby Z; Deshmukh, Atul S; Chibalin, Alexander V; Bj�rnholm, Marie; Al-Hasani, Hadi; Zierath, Juleen R
Disruption of AMPKalpha1 signaling prevents AICAR-induced inhibition of AS160/TBC1D4 phosphorylation and glucose uptake in primary rat adipocytes.
The aim of this study was to investigate the molecular mechanisms by which AMP-kinase (AMPK) activation inhibits basal and insulin-stimulated glucose uptake in primary adipocytes. Rat epididymal adipocytes were exposed to 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) for 1 h. Subsequently, basal and insulin-stimulated glucose uptake and the phosphorylation of AMPK, acetyl-CoA carboxylase, Akt, and the Akt substrate of 160 kDa (AS160/TBC1D4) were determined. In order to investigate whether these effects of AICAR were mediated by AMPK activation, these parameters were also assessed in adipocytes either expressing LacZ (control) or a kinase-dead AMPKalpha1 mutant. AICAR increased AMPK activation without affecting basal and insulin-stimulated Akt1/2 phosphorylation on Thr(308) and Ser(473) residues. However, AMPK activation suppressed the phosphorylation of AS160/TBC1D4 and its interaction with the 14-3-3 signal transduction-regulatory protein, which was accompanied by significant reductions in plasma membrane glucose transporter 4 content and glucose uptake under basal and insulin-stimulated conditions. Phosphorylation of Akt substrates glycogen synthase kinase 3alpha and -beta were unaltered by AICAR, indicating that the AMPK-regulatory effects were specific to the AS160/TBC1D4 signaling pathway. Expression of the kinase-dead AMPKalpha1 mutant fully prevented the suppression of AS160/TBC1D4 phosphorylation, plasma membrane glucose transporter 4 content, and the inhibitory effect of AICAR-induced AMPK activation on basal and insulin-stimulated glucose uptake. This study is the first to provide evidence that disruption of AMPKalpha1 signaling prevents the suppressive effects of AMPK activation on AS160/TBC1D4 phosphorylation and glucose uptake, indicating that insulin-signaling steps that are common to white adipose tissue and skeletal muscle regulation of glucose uptake are distinctly affected by AMPK activation. PMID:20501641
Gaidhu, Mandeep P; Perry, Robert L S; Noor, Fawad; Ceddia, Rolando B
Failure cause identification of tribo-mechanical systems using fault tree�a digraph approach
A procedure for the failure cause identification of tribo-mechanical systems is presented based on fault-tree using a digraph approach. A variable-event system digraph for a tribo-mechanical system is suggested which takes into account structure of the system. A top event or undesirable event for the system is then defined and the fault-tree for this top event is deduced from the
Rakesh Sehgal; O. P. Gandhi; S. Angra
Failure Mechanisms During Isothermal Fatigue of SiC/Ti-24Al-11Nb Composites
NASA Technical Reports Server (NTRS)
Failure mechanisms during isothermal fatigue of unidirectional SiC/Ti-24Al-11Nb (at.%) composites have been determined by microstructural analysis of samples from tests interrupted prior to the end of life and from tests conducted to failure. Specimens from three regions of life were examined based on the maximum strain from a fatigue life diagram: Region 1 (high strain), Region 2 (mid-strain) and Region 3 (low strain). Crack lengths were also measured from interrupted samples and compared based on temperature (23-815 C), region of life and numbers of cycles. Region 1 was controlled by fiber-dominated failure. A transition zone was observed between Regions 1 and 2 due to competition between failure mechanisms. Failure in Region 2 was generally described as surface-initiated cracking with varying amounts of fiber bridging. However, the specific descriptions of crack propagation through the fibers and matrix varied with strain and temperature over this broad region. Region 3 exhibited endurance behaviour at 23 C with no cracking after lO(exp 6) cycles. However at 425 C, surface-initiated cracking was observed after 10(exp 6) cycles with fractured fibers in the crack wake. If endurance behaviour exists for conditions of isothermal fatigue in air at temperatures of greater than or equal to 425 C, it may only be found at very low strains and at greater than 10(exp 6) cycles.
Brindley, P. K.; Bartolotta, P. A.
Impermeable thin AI2O3 overlay for TBC protection from sulfate and vanadate attack in gas turbines
25 {micro}m and a 2 {micro}m thick Al{sub 2}O{sub 3} overlay were deposited by HVOF thermal spray and by sol-gel coating method, respectively, onto to the surface of YSZ coating. Indenter test was employed to investigate the spalling of YSZ with and without Al{sub 2}O{sub 3} overlay after hot corrosion. The results showed that Al{sub 2}O{sub 3} overlay acted as a barrier against the infiltration of the molten salt into the YSZ coating during exposure, thus significantly reduced the amount of M-phase of ZrO{sub 2} in YSZ coating. Thick Al{sub 2}O{sub 3} overlay will increase compressive stress and failure in TBC. During next reporting time, Al{sub 2}O{sub 3} overlay will be deposited on the YSZ surface by the composite-sol-gel route (CSG). Hot corrosion tests will be carried out on the TBC.
Scott X. Mao
Investigation of static and cyclic bearing failure mechanisms for GR/EP laminates
NASA Technical Reports Server (NTRS)
Static, cyclic load (fatigue), and residual strength testing of graphite-epoxy (GR/EP) and aluminum pin bearing joints was completed to study bearing failure mechanisms. Parameters investigated included static strength, failure mode, fatigue life, hole growth, joint stiffness, and residual strength. Comparative evaluation of these results show that the MIL-HDBK-5 convention for the definition of bearing strength can be used for GR/EP materials while maintaining the same, or improved, level of structural integrity shown for metal joints.
Walter, R. W.; Tuttle, M. M.
Failure mechanism analysis of electromigration dominated damage in TiSi2 nanowires
NASA Astrophysics Data System (ADS)
Electromigration-induced damage has been an important concern in very large scale integrated circuit design for a long time and will be a major road block in the pursuit of nanoelectronics devices and next generation power electronics. In this letter, the failure mechanism analysis on two-terminal TiSi2 nanowire devices was reported. Electromigration dominant mass migration is observed and verified by energy dispersive spectroscopy. The contribution of thermomigration is discussed based on temperature simulation. This work provides useful reference for future devices and the failure analysis on nanostructures.
Zou, Chen-Xia; Xu, Jun; Zhang, Xin-Zheng; Song, Xue-Feng; Yu, Da-Peng
Time-dependent failure mechanisms in silicon carbide composites for fusion energy applications
NASA Astrophysics Data System (ADS)
Silicon carbide has many properties that are attractive for applications in fusion energy systems. The reliability of monolithic silicon carbide, however, is insufficient for its use in large components. Ceramic matrix composites offer greater flaw tolerance and reliability, but their failure mechanisms are less well understood. This work has focussed on studying potential failure mechanisms in silicon carbide fiber-reinforced, silicon carbide matrix (SiC f/SiC m) composites. In the event of pre-existing cracks, subcritical crack-growth may occur due to creep of fibers that bridge the crack faces. Irradiation-enhanced creep will enhance the subcritical crack-growth rate. The presence of oxygen leads to oxidation of the interphase material and subcritical crack-growth controlled by the rate of interphase recession. In addition, fiber shrinkage or weakening due to exposure to radiation can promote additional failure mechanisms, including embrittlement. These mechanisms, the conditions, under which they occur, and the current state of models of the crack-growth mechanisms will be discussed.
Lewinsohn, C. A.; Youngblood, G. E.; Henager, C. H.; Simonen, E. P.; Jones, R. H.
Compression failure mechanisms of single-ply, unidirectional, carbon-fiber composites
NASA Technical Reports Server (NTRS)
A single-ply composite compression test was used to study compression failure mechanisms as a function of fiber type, matrix type, and interfacial strength. Composites made with low- and intermediate-modulus fibers (Hercules AS4 and IM7) in either an epoxy (Hercules 3501-6) or a thermoplastic (ULTEM and LARC-TPI) matrix failed by kink banding and out-of-plane slip. The failures proceeded by rapid and catastrophic damage propagation across the specimen width. Composites made with high-modulus fibers (Hercules HMS4/3501-6) had a much lower compression strength. Their failures were characterized by kink banding and longitudinal splitting. The damage propagated slowly across the specimen width. Composites made with fibers treated to give low interfacial strength had low compression strength. These composites typically failed near the specimen ends and had long kink bands.
Ha, Jong-Bae; Nairn, John A.
Charpy impact properties and failure mechanism of 3D MWK composites at room and cryogenic temperatures
NASA Astrophysics Data System (ADS)
The charpy impact experiments on the 3D MWK (Multi-axial warp knitted) composites with four different fiber architectures are performed at room (20 �C) and liquid nitrogen temperatures (as low as -196 �C). Macro-Fracture morphology and SEM micrographs are examined to understand the impact deformation and failure mechanism. The results show that the impact properties decrease significantly with the increase of the fiber ply angle at both room and liquid nitrogen temperatures. Meanwhile, the impact energy at liquid nitrogen temperature has been improved significantly than that at room temperature. Moreover, the fiber architecture has remarkable effect on the impact damage and failure patterns of composites at room and liquid nitrogen temperatures. At liquid nitrogen temperature, the matrix solidification and the interfacial adhesion capacity increase greatly, which effectively hinders the stress wave propagation. However, more micro-cracks appear and the brittle failure feature becomes more obvious.
Li, Dian-sen; Jiang, Nan; Zhao, Chuang-qi; Jiang, Lei; Tan, Yi
Root-soil mechanical interactions during pullout and failure of root bundles
NASA Astrophysics Data System (ADS)
Roots play a major role in reinforcing and stabilizing steep hillslopes. Most studies in slope stability implement root reinforcement as an apparent cohesion by upscaling the behavior of static individual roots. Recent studies, however, have shown that much better predictions of slope stability can be made if the progressive failure of bundles of roots are considered. The characteristics of progressive failure depend on interactions between soil deformation and root bundle geometric and mechanical properties. We present a detailed model for the quantitative description of the mechanical behavior of a bundle of roots under strain-controlled mechanical forcing. The Root Bundle Model explicitly considers typical values of root-size spatial distribution (number and dimension of roots), geometric factors (diameter-length proportion, tortuosity, and branching characteristics), and mechanical characteristics (tensile strength and Young's modulus) and interactions under various soil conditions (soil type, confining pressure, and soil moisture). We provide systematic analyses of the roles of these factors on the mechanical response of the bundle and explore the relative importance of various parameters to the macroscopic root-soil mechanical response. We distinguish between increased strength imparted by small roots at small deformations and the resilience imparted by larger roots to the growth of large tensile cracks, showing that the maximal reinforcement of fine roots is reached within the first 5 cm of displacement whereas a root of 20 mm diameter may reach its maximal pullout force after 10 cm displacement. The model reproduces the gradual straining and ultimate residual failure behavior of root systems often observed in hillslopes, with progressive growth of tension cracks improving estimations of root reinforcement when considering the effects of root distribution and the variation of the pullout force as a function of displacement. These results enhance understanding of root reinforcement mechanisms and enable more realistic implementation of root reinforcement modeling for stability calculations of vegetated slopes and for guiding ongoing experimental efforts to gather critical root-soil mechanical information.
Schwarz, M.; Cohen, D.; Or, D.
Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions
NASA Astrophysics Data System (ADS)
A critical assessment is carried out of the microstructural changes in respect of the associated reductions in material mechanical properties and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found in armor structures made of high-performance aluminum alloys (including solution-strengthened and age-hardenable aluminum alloy grades). It is argued that due to the large width of FSW joints found in thick aluminum-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld zones (e.g., heat-affected zone, the thermomechanically affected zone, the nugget, etc.). Thus, in order to assess the overall ballistic survivability of an armor weldment, one must predict/identify welding-induced changes in the material microstructure and properties, and the operative failure mechanisms in different regions of the weld. Toward this end, a procedure is proposed in the present study which combines the results of the FSW process modeling, basic physical-metallurgy principles concerning microstructure/property relations, and the fracture mechanics concepts related to the key blast/ballistic-impact failure modes. The utility of this procedure is demonstrated using the case of a solid-solution strengthened and cold-worked aluminum alloy armor FSW-weld test structure.
Grujicic, M.; Pandurangan, B.; Arakere, A.; Yen, C.-F.; Cheeseman, B. A.
Examination of cadmium safety rod thermal test specimens and failure mechanism evaluation
The reactor safety rods may be subjected to high temperatures due to gamma heating after the core coolant level has dropped during the ECS phase of a hypothetical LOCA event. Accordingly, an experimental cadmium safety rod testing subtask was established as part of a task to address the response of reactor core components to this accident. Companion reports describe the experiments and a structural evaluation (finite element analysis) of the safety rod. This report deals primarily with the examination of the test specimens, evaluation of possible failure mechanisms, and confirmatory separate effects experiments. It is concluded that the failures observed in the cadmium safety rod thermal tests which occurred at low temperature (T < 600{degrees}C) with slow thermal ramp rates (slow cladding strain rates) resulted from localized dissolution of the stainless steel cladding by the cadmium/aluminum solution and subsequent ductility exhaustion and rupture. The slow thermal ramp rate is believed to be the root cause for the failures; specifically, the slow ramp rate led to localized cladding shear deformation which ruptured the protective oxide film on the cladding inner surface and allowed dissolution to initiate. The test results and proposed failure mechanism support the conclusion that the rods would not fail below 500{degrees}C even at slow ramp rates. The safety rod thermal test specimen failures which occurred at high temperature (T > 800{degrees}C) with fast thermal ramp rates are concluded to be mechanical in nature without significant environmental degradation. Based on these tests, tasks were initiated to design and manufacture B{sub 4}C safety rods to replace the cadmium safety rods. The B{sub 4}C safety rods have been manufactured at this time and it is currently planned to charge them to the reactor in the near future. 60 refs.
Thomas, J.K.; Peacock, H.B.; Iyer, N.C.
Genesis of channel bank overhangs in the Niger Delta and analysis of mechanisms of failure
NASA Astrophysics Data System (ADS)
The instability of channel banks carries a significant economic implication because of its effect on navigation and channel commercial development. The impact of bank instability in the Niger Delta is accentuated by the dense network of rivers and creeks. The occurrence of overhangs in channel banks is not restricted to stratified banks in which clay overlies sand. Field observation and analysis indicate that factors such as stratigraphy, local climate, bio-technical and fluvio-tidal processes act singly or in combination to generate overhangs in channel banks. The failure of channel banks with overhangs involves one of four mechanism, namely; rotation, beam, shear, and tension failure. A mathematical basis for the discrimination of these failure mechanisms is described. The significance of identifying the critical location of tension cracks for the failure of the overhang is discussed. Although the study is based on experience in the Niger Delta, the principles applied and the conclusions reached undoubtedly apply to areas of similar geological and environmental conditions.
Abam, T. K. S.
Analysis of seismic disaster failure mechanism and dam-break simulation of high arch dam
NASA Astrophysics Data System (ADS)
Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code (3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, influence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far field energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.
Zhang, Jingkui; Zhang, Liaojun
Alterations in beta-adrenoceptor mechanisms in the aging heart. Relationship with heart failure.
In chronic heart failure substantial and characteristic changes occur in the function of the adrenergic nervous system. Studies in isolated left ventricular muscle and in single cardiomyocytes from experimental models of aging and, recently, from humans show an age-related reduced contractile response to beta-adrenoceptor stimulation. "beta-adrenoceptor desensitization" is thought to be a general and common mechanism to explain the age- and heart failure-related decrease in beta-adrenoceptor response. The aim of this review is to compare alterations in beta-adrenoceptor mechanisms in physiological cardiovascular aging and chronic heart failure. From an analysis of the overall data on the role of aging in beta-adrenoceptor regulation in human and animal hearts, it is possible to conclude that the reduced response to beta-agonists is common to all species and all cardiac tissues. Moreover, the age-related changes are limited to beta-adrenoceptor-G-protein (s)-adenylyl cyclase system abnormalities, while the type and level of abnormalities change with species and tissues. The modifications shown in the aging heart are not very different from some observed in heart failure. In particular, both in aged and failing hearts we may see that the decrease in beta-adrenoceptor responsiveness is related to changes in G-protein function. PMID:9553617
Ferrara, N; Davia, K; Abete, P; Rengo, F; Harding, S E
Fatigue of the Resin-Enamel Bonded Interface and the Mechanisms of Failure
The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under both static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p?0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominately by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding.
Yahyazadehfar, Mobin; Mutluay, Mustafa Murat; Majd, Hessam; Ryou, Heonjune; Arola, Dwayne
The Mechanics of Left Ventricular Contraction in Acute Experimental Cardiac Failure*
The effects of acute cardiac failure induced by pentobarbital or pronethalol on the basic mechanical properties of the intact left ventricle were examined in the dog, and the influence on auxotonic and isovolumic contractions of the increase in end-diastolic volume that usually accompanies cardiac failure was assessed. The right heart bypass preparation was employed, and isovolumic beats were induced by sudden balloon occlusion of the aortic root. The ventricular pressure-volume curve was determined directly, and the mechanical responses of the myocardial fibers and contractile elements were calculated. When end-diastolic pressure was held constant, failure reduced the extent of circumferential fiber shortening, and the tension-velocity relation calculated during isovolumic beats was always shifted, with reductions in both maximal velocity (average decrease 30%) and maximal developed tension (average 23%); in addition, during failure achievement of maximal contractile element velocity and maximal tension was delayed, whereas the total duration of contraction was always prolonged. Acetylstrophanthidin tended to reverse all of these changes. When end-diastolic volume was augmented during failure at a constant stroke volume, the extent of circumferential fiber shortening was reduced (3.82 cm to 2.02 cm), and during ejection the fiber and contractile element velocities were diminished at wall tensions comparable to control; maximal velocity and velocity at peak tension were also decreased. The tension-velocity relation during isovolumic beats was shifted by failure with consistent reductions in maximal shortening velocity, but changes in maximal tension were small. Maximal instantaneous power was always reduced by failure, and a striking alteration occurred in the relation between work expended in stretching the series elastic component and the external work; the former, �internal work,� increased by an average of 90%, the latter diminished by 11%, and the total contractile element work remained essentially unchanged. These findings are discussed within the framework of a three dimensional model that included fiber length, wall tension, and contractile element velocity. The experimental techniques employed appear to permit a more complete definition of the abnormalities of the ventricular myocardium in experimental failure. They are potentially applicable in the closed-chest animal and allow quantitative determinations of the contractile properties of the left ventricle. Images
Ross, John; Covell, James W.; Sonnenblick, Edmund H.
Failure modes of complex materials with spatially-correlated mechanical properties - the critical role of internal damage
NASA Astrophysics Data System (ADS)
The study reports a systematic evaluation of the role of spatially correlated mechanical elements on failure behavior of heterogeneous materials represented by fiber bundle models (FBM) with different load redistribution rules. Results indicate that FBM failure mode varies dramatically with increasing correlation length and localized load sharing rules. Systems with similar composition of mechanical elements exhibit a dramatic transition from ductile and diffuse damage for global load sharing to brittle single failure for correlated and local load sharing. These changes in mechanical responses also affect the statistical properties of fiber failure avalanches (micro-cracks) activity preceding rupture and sought after in various early warning scenarios. While diffuse damage behavior exhibits clear precursory signals (such as increased seismic activity prior to global failure), brittle failure occurs abruptly with only few precursors. Although increasing spatial correlations of mechanical properties promotes abrupt ruptures at lower external load, this study identified an "universal" global failure criterion based on macroscopic properties which is independent of the rupture mode, load redistribution rules, or the spatial organization of mechanical properties. This metric that considers the combined role of external load and cumulative damage provides a means for evaluating imminence of failure of heterogeneous materials without resolving details of the heterogeneity. This study also provides new insights that are potentially useful for understanding landslide (but also snow avalanche or rockfall) triggering and points out the importance of spatial organization of heterogeneities on the failure behavior of complex geomaterials.
Faillettaz, J�rome; Or, Dani
Mechanical characterization of damage and failure in polymeric foams and glass/epoxy composites
NASA Astrophysics Data System (ADS)
The mechanical characterization including evolution of damage and failure of foams and composites are becoming increasingly important, as they form the basic components of sandwich structures. Sandwich structures consist of two faceplates that surround a core material. In many modern applications, faceplates and cores are typically comprised of composite materials and polymeric foam, respectively. Knowledge of the failure behavior of these individual components is necessary for understanding the failure behavior and design of sandwich structures. A systematic investigation of the damage evolution and failure behavior of foams and composites was conducted using a variety of experimental techniques.In-situ ultrasonic measurements were used to track the damage behavior in PVC polymeric foams with densities ranging from 130 to 250 kg/m3. The wave speeds were measured by two quartz piezoelectric shear transducers with a resonant frequency of 5 MHz in the transmission mode. A fixture was developed and constructed to protect the transducers during compression, while allowing them to take sound speed measurements of the sample along the axis of the load train. This fixture was placed in a servo-hydraulic MTS (Materials Testing System) machine, where the load-displacement response of the foam was recorded. A digital image correlation (DIC) method was used to capture the progression of failure under compression. Two dominant failure modes, elastic buckling and plastic collapse, were identified - and their onsets corresponded to the change in elastic wave speeds in the material, measured by the in-situ ultrasonic technique.The transverse response of S-Glass/Epoxy unidirectional composites was investigated under varying degrees of confinement and strain rates. The experimental setup utilizes a fixture that allowed for independent measurement of the three principal stresses in a confined specimen. A servo-hydraulic materials testing system and a Kolsky (split Hopkinson) pressure bar generated strain rates between 10-3 to 104 s-1. Post-test scanning electron microscopy (SEM) observations suggest that under transverse loading at low-strain rates, confinement contributes to localized band formation. In addition, micrographs indicated that macroscopic transverse failure is dominated by shear stress, and occurs within these localized bands. These shear dominated failure bands were found inclined in a direction approximately 35 degrees to the direction of loading. Implications of this orientation deviation of failure bands from maximum shear trajectories at 45 degrees are discussed in reference to the state of confinement.
Kidd, Theresa Hiromi
Mechanical circulatory support for heart failure: past, present and a look at the future.
Heart transplantation remains the gold standard for long-term cardiac replacement, but a shortage of donor organs will always limit this option. For both transplant-eligible and noneligible patients, advances in mechanical circulatory support have revolutionized the options for the management of end-stage heart failure, and this technology continues to bring us closer to a true alternative to heart transplantation. This review provides a perspective on the past, present and future of mechanical circulatory support and addresses the changes in technology, patient selection and management strategies needed to have this therapy fully embraced by the heart failure community, and perhaps replace heart transplantation either as the therapy of choice or as a strategy by which to delay transplantation in younger patients. PMID:23278224
Moazami, Nader; Hoercher, Katherine J; Fukamachi, Kiyotaka; Kobayashi, Mariko; Smedira, Nicholas G; Massiello, Alex; Horvath, David J
Mechanical heart valves: Changes in patient survival and valve failure rates
The effect of patient related variables and mechanical heart valve substitutes on survival and valve failure rates was studied\\u000a in 2,778 patients operated between 1966 and 1986. Of these 48.2% were operated without cardioplegic protection (phase I) and\\u000a 51.8% thereafter (phase II). Mitral vlave replacement (MVR) was performed in 1,257 patients (phase I: 51.58%, phase II: 48.42%);\\u000a aortic valve replacement
T. K. Kaul; J. L. Mercer; D. R. Ramsdale
Acute heart failure: Multiple clinical profiles and mechanisms require tailored therapy
Acute heart failure (HF) is the most common diagnosis at discharge in patients aged >65years. It carries a dismal prognosis with a high in-hospital mortality and very high post-discharge mortality and re-hospitalization rates. It is a complex clinical syndrome that cannot be described as a single entity as it varies widely with respect to underlying pathophysiologic mechanisms, clinical presentations and,
Marco Metra; G. Michael Felker; Valerio Zac�; Silvia Bugatti; Carlo Lombardi; Luca Bettari; Adrian A. Voors; Mihai Gheorghiade; Livio Dei Cas
An Experimental Approach to Investigate Detailed Failure Mechanisms in Fibre Metal Laminates
This paper propose an experimental approach, based on digital image correlation, which enables detailed quantitative description\\u000a of the most important failure mechanisms occurring in Fibre Metal Laminates during fatigue and static load. Digital image\\u000a correlation provided measurement of the crack tip plasticity, fatigue delamination shape and fibre bridging in different FMLs.\\u000a Digital image correlation showed to be the most versatile
Riccardo Rodi; Ren� Alderliesten; Rinze Benedictus
Stress and failure analysis of mechanically fastened joints in composite laminates
The literature published on single mechanically fastened joints in fiber-reinforced plastics is reviewed. A finite-element model is developed to predict the response of pin-loaded composite plates. The model takes into account contact at the pin�hole interface, progressive damage, large deformation theory, and a non-linear shear stress�strain relationship. To predict the progressive ply failure, the analysis combines Hashin and the maximum
Marie-Laure Dano; Guy Gendron; Andr� Picard
Prevent boiler tube failures--Part 1: Fire-side mechanisms
A boiler tube fails when the structural integrity of the tube is compromised. For boilers that have been previously operating, some change must occur to effect tube failure. Usually this change is wrought through some combination of corrosion and erosion acting on the boiler tube to weaken it. Boiler tubes depend on a complex metal oxide layer for protection from the hot furnace environment. Fire-side corrosion and erosion remove or alter the oxide layer, rendering the tube vulnerable to attack. Corrosion and erosion are destructive mechanisms that ravage boiler tubes. They are distinguished by the cause of the destruction--corrosion is caused by chemical or electrochemical attack, whereas erosion is caused by abrasive action of a moving fluid or solid. Both mechanisms can and often do operate simultaneously. This article focuses on the fire side of the tube. It explains the major mechanisms responsible for fire-side boiler tube failures, how to recognize the underlying cause of the failure, and how to avoid such problems. Fuel oil, coal, and municipal solid waste boilers are discussed.
Colannino, J.
Characterization of Tbc2, a nucleus-encoded factor specifically required for translation of the chloroplast psbC mRNA in Chlamydomonas reinhardtii
enetic analysis has revealed that the three nucleus- encoded factors Tbc1, Tbc2, and Tbc3 are involved in the translation of the chloroplast psbC mRNA of the eukaryotic green alga Chlamydomonas reinhardtii . In this study we report the isolation and phenotypic characterization of two new tbc2 mutant alleles and their use for cloning and characterizing the Tbc2 gene by genomic
Andrea H. Auchincloss; William Zerges; Karl Perron; Jacqueline Girard-Bascou; Jean-David Rochaix
Failure mechanisms of polycrystalline diamond compact drill bits in geothermal environments
Over the past few years the interest in polycrystalline diamond compact (PDC) drill bits has grown proportionately with their successful use in drilling oil and gas wells in the North Sea and the United States. This keen interest led to a research program at Sandia to develop PDC drill bits suitable for the severe drilling conditions encountered in geothermal fields. Recently, three different PDC drill bits were tested using either air or mud drilling fluids: one in the laboratory with hot air, one in the Geysers field with air, and one in the Geysers field with mud. All three tests were unsuccessful due to failure of the braze joint used to attach the PDC drill blanks to the tungsten carbide studs. A post-mortem failure analysis of the defective cutters identified three major failure mechanisms: peripheral nonbonding caused by braze oxidation during the brazing step, nonbonding between PDC drill blanks and the braze due to contamination prior to brazing, and hot shortness. No evidence was found to suggest that the braze failures in the Geysers field tests were caused by frictional heating. In addition, inspection of the PDC/stud cutter assemblies using ultrasonic techniques was found to be ineffective for detecting the presence of hot shortness in the braze joint.
Hoover, E.R.; Pope, L.E.
Cardiac arrhythmia mechanisms in rats with heart failure induced by pulmonary hypertension
Pulmonary hypertension provokes right heart failure and arrhythmias. Better understanding of the mechanisms underlying these arrhythmias is needed to facilitate new therapeutic approaches for the hypertensive, failing right ventricle (RV). The aim of our study was to identify the mechanisms generating arrhythmias in a model of RV failure induced by pulmonary hypertension. Rats were injected with monocrotaline to induce either RV hypertrophy or failure or with saline (control). ECGs were measured in conscious, unrestrained animals by telemetry. In isolated hearts, electrical activity was measured by optical mapping and myofiber orientation by diffusion tensor-MRI. Sarcoplasmic reticular Ca2+ handling was studied in single myocytes. Compared with control animals, the T-wave of the ECG was prolonged and in three of seven heart failure animals, prominent T-wave alternans occurred. Discordant action potential (AP) alternans occurred in isolated failing hearts and Ca2+ transient alternans in failing myocytes. In failing hearts, AP duration and dispersion were increased; conduction velocity and AP restitution were steeper. The latter was intrinsic to failing single myocytes. Failing hearts had greater fiber angle disarray; this correlated with AP duration. Failing myocytes had reduced sarco(endo)plasmic reticular Ca2+-ATPase activity, increased sarcoplasmic reticular Ca2+-release fraction, and increased Ca2+ spark leak. In hypertrophied hearts and myocytes, dysfunctional adaptation had begun, but alternans did not develop. We conclude that increased electrical and structural heterogeneity and dysfunctional sarcoplasmic reticular Ca2+ handling increased the probability of alternans, a proarrhythmic predictor of sudden cardiac death. These mechanisms are potential therapeutic targets for the correction of arrhythmias in hypertensive, failing RVs.
Benoist, David; Stones, Rachel; Drinkhill, Mark J.; Benson, Alan P.; Yang, Zhaokang; Cassan, Cecile; Gilbert, Stephen H.; Saint, David A.; Cazorla, Olivier; Steele, Derek S.; Bernus, Olivier
Presence of Intervertebral Discs Alters Observed Stiffness and Failure Mechanisms in the Vertebra
Ex vivo mechanical testing is an essential tool for study of vertebral mechanics. However, the common method of testing vertebral bodies in the absence of adjacent intervertebral discs (IVDs) may limit the physiological relevance of the results. The goal of this study was to determine the influence of IVDs on vertebral mechanical properties and failure mechanisms. Rabbit thoracic vertebral bodies were tested with and without IVDs in a stepwise fashion that incorporated a micro-computed tomography scan at each loading step. The image sequences were analyzed using digital volume correlation to quantify deformations throughout the vertebral body. The observed deformation patterns differed substantially between the groups. Specimens tested with IVDs exhibited a slow increase in strain in the inferior and posterior regions, followed by a sudden increase in strain in the anterior cortex right at the yield point. In contrast, the highest strains in the isolated vertebral bodies were in the posterior regions throughout the test. Specimens tested with IVDs had lower stiffness (507.49 � 184.73 N/mm vs. 845.61 � 296.09 N/mm; p = 0.044), higher ultimate displacement (2.00 � 0.68 mm vs. 1.17 � 0.54 mm; p = 0.043), and higher maximum shear strains (e.g. top 25th percentile: 0.19 � 0.11 vs. 0.06 � 0.07mm/mm; p < 0.0458), and tended to have lower ultimate force (690.28 � 160.25 N vs. 873.81 � 131.48 N; p = 0.056). Similar work to failure (648.15 � 317.86 N-mm vs. 603.49 � 437.95 N-mm; p = 0.844) was observed between the two groups. These results indicate that testing vertebral bodies in the absence of IVDs can elicit artifactual failure mechanisms. These artifacts may be more prominent than the effects on vertebral strength and toughness.
Hussein, Amira I.; Mason, Zachary D.; Morgan, Elise F.
Influence of substrate material on oxidation behavior and cyclic lifetime of EB-PVD TBC systems
EB-PVD NiCoCrAlY\\/P-YSZ TBCs on several polycrystalline, directionally solidified, and single crystalline (SX) substrate alloys were thermally cycled at 1100�C. TBC spallation does not correlate solely to TGO thickness, but depends also very much on the substrate alloy. The longest lifetimes are achieved on Hf-containing alloys while SX alloys suffer from early TBC spallation. The formation of the thermally grown oxide
U Schulz; M Menzebach; C Leyens; Y. Q Yang
Parameters affecting TGO growth and adherence on MCrAlY-bond coats for TBC's
Electron Beam�Physical Vapor Desposited Thermal Barrier Coatings (EB�PVD TBC) on the Ni-base superalloy IN738LC were tested in respect to non-isothermal and cyclic oxidation resistance at 1100��C. Two types of MCrAlY's (M = Ni, Co), a Co-base and a Ni-base, were used as bond coats (BC) for the TBC's. Additionally, free standing MCrAlY specimens of 2�mm thickness were manufactured by vacuum
J. Toscano; R. Va?en; A. Gil; M. Subanovic; D. Naumenko; L. Singheiser; W. J. Quadakkers
Metal-glass based composites for application in TBC-systems
A new type of thermal barrier coating (TBC) based on metal-glass composite (MGC) consisting of an ordinary container glass and a NiCoCrAlY-alloy has been recently presented. This TBC material provides the possibility to easily adjust its thermal expansion coefficient to match the substrate by changing the metal to glass ratio of the composite. Vacuum plasma spraying (VPS) has been applied
D. E. Mack; R. Va�en; D. St�ver; S. M. Gross
Metal-glass based composites for application in TBC-systems
A new type of thermal barrier coating (TBC) based on metal-glass composite (MGC) consisting of an ordinary container glass\\u000a and a NiCoCrAlY-alloy has been recently presented. This TBC material provides the possibility to easily adjust its thermal\\u000a expansion coefficient to match the substrate by changing the metal to glass ratio of the composite. Vacuum plasma spraying\\u000a (VPS) has been applied
D. E. Mack; R. Va�en; D. St�ver; S. M. Gross
Insulin-stimulated phosphorylation of the Rab GTPase-activating protein TBC1D1 regulates GLUT4 translocation.
Insulin stimulates the translocation of the glucose transporter GLUT4 from intracellular locations to the plasma membrane in adipose and muscle cells. Prior studies have shown that Akt phosphorylation of the Rab GTPase-activating protein, AS160 (160-kDa Akt substrate; also known as TBC1D4), triggers GLUT4 translocation, most likely by suppressing its Rab GTPase-activating protein activity. However, the regulation of a very similar protein, TBC1D1 (TBC domain family, member 1), which is mainly found in muscle, in insulin-stimulated GLUT4 translocation has been unclear. In the present study, we have identified likely Akt sites of insulin-stimulated phosphorylation of TBC1D1 in C2C12 myotubes. We show that a mutant of TBC1D1, in which several Akt sites have been converted to alanine, is considerably more inhibitory to insulin-stimulated GLUT4 translocation than wild-type TBC1D1. This result thus indicates that similar to AS160, Akt phosphorylation of TBC1D1 enables GLUT4 translocation. We also show that in addition to Akt activation, activation of the AMP-dependent protein kinase partially relieves the inhibition of GLUT4 translocation by TBC1D1. Finally, we show that the R125W variant of TBC1D1, which has been genetically associated with obesity, is equally inhibitory to insulin-stimulated GLUT4 translocation, as is wild-type TBC1D1, and that healthy and type 2 diabetic individuals express approximately the same level of TBC1D1 in biopsies of vastus lateralis muscle. In conclusion, phosphorylation of TBC1D1 is required for GLUT4 translocation. Thus, the regulation of TBC1D1 resembles that of its paralog, AS160. PMID:19740738
Peck, Grantley R; Chavez, Jose A; Roach, William G; Budnik, Bogdan A; Lane, William S; Karlsson, H�kan K R; Zierath, Juleen R; Lienhard, Gustav E
Insulin-stimulated Phosphorylation of the Rab GTPase-activating Protein TBC1D1 Regulates GLUT4 Translocation*
Insulin stimulates the translocation of the glucose transporter GLUT4 from intracellular locations to the plasma membrane in adipose and muscle cells. Prior studies have shown that Akt phosphorylation of the Rab GTPase-activating protein, AS160 (160-kDa Akt substrate; also known as TBC1D4), triggers GLUT4 translocation, most likely by suppressing its Rab GTPase-activating protein activity. However, the regulation of a very similar protein, TBC1D1 (TBC domain family, member 1), which is mainly found in muscle, in insulin-stimulated GLUT4 translocation has been unclear. In the present study, we have identified likely Akt sites of insulin-stimulated phosphorylation of TBC1D1 in C2C12 myotubes. We show that a mutant of TBC1D1, in which several Akt sites have been converted to alanine, is considerably more inhibitory to insulin-stimulated GLUT4 translocation than wild-type TBC1D1. This result thus indicates that similar to AS160, Akt phosphorylation of TBC1D1 enables GLUT4 translocation. We also show that in addition to Akt activation, activation of the AMP-dependent protein kinase partially relieves the inhibition of GLUT4 translocation by TBC1D1. Finally, we show that the R125W variant of TBC1D1, which has been genetically associated with obesity, is equally inhibitory to insulin-stimulated GLUT4 translocation, as is wild-type TBC1D1, and that healthy and type 2 diabetic individuals express approximately the same level of TBC1D1 in biopsies of vastus lateralis muscle. In conclusion, phosphorylation of TBC1D1 is required for GLUT4 translocation. Thus, the regulation of TBC1D1 resembles that of its paralog, AS160.
Peck, Grantley R.; Chavez, Jose A.; Roach, William G.; Budnik, Bogdan A.; Lane, William S.; Karlsson, Hakan K. R.; Zierath, Juleen R.; Lienhard, Gustav E.
Finite Element Analyses of Failure Mechanisms and Structure-Property Relationships in Microtruss Materials
NASA Astrophysics Data System (ADS)
Microtruss materials are assemblies of struts or columns arranged periodically in space. The majority of past research efforts have focused on the key issue of microtruss architectural optimization. By contrast, this study focuses on the internal material structure at the level of the individual struts. Microstructural, geometrical, and material design techniques are used to improve their mechanical properties. The finite element method is used to verify and create predictive analytical models, explain the dependence of strut properties on geometry, material properties and failure mechanisms, and extend the strut design analysis into suggestions for the improvement of fabrication methods. Three strut design methods are considered. First, microstructural design is performed by considering the influence of strut geometry on the strain energy imparted during stretch bending. By using the perforation geometry to modify the location and magnitude of this strain energy, microtruss materials with lower density and higher strength can be fabricated. Second, structural sleeves of aluminum oxide and electrodeposited nanocrystalline nickel are used to reinforce architecturally optimized aluminum alloy microtruss assemblies, creating hybrid materials with high weight-specific strength. The mechanical properties are controlled by the interaction between material and mechanical failure; this interaction is studied through finite element analyses and a proposed analytical relationship to provide suggestions for further improvements. Finally, hollow cylindrical struts are fabricated from electrodeposited nanocrystalline nickel. The high strength to weight ratio achieved in these struts is due to the microstructural and cross-sectional efficiency of the material.
Bele, Eral
Investigation of moisture-induced delamination failure in a semiconductor package via multi-scale mechanics
NASA Astrophysics Data System (ADS)
In this work, moisture-induced interfacial delamination in a semiconductor package was investigated by experiment and multi-scale numerical analysis. The interfacial adhesion strength between a silicon wafer and an epoxy adhesive layer was characterized by a die-shear test with respect to moisture concentration and temperature. Molecular dynamics simulation was performed to study the effect of moisture and temperature on the interfacial adhesion energy and strength at the Si/epoxy adhesive interface. Based on the molecular dynamics predicted interfacial adhesion strength, a numerical stress analysis was performed considering hygro-swelling stress and the thermo-mechanical stress during a solder reflow process to predict the moisture-induced delamination failure of the semiconductor package. The multi-scale simulation result was compared with the actual reliability test result. From this study, it was concluded that the proposed multi-scale simulation technique can be used successfully for the prediction of moisture-induced package failure.
Kim, Hak-Sung; Huh, Jeehyang; Ryu, Jongeun
Investigation of failure mechanism of thermal barrier coatings (TBCs) deposited by EB-PVD technique
NASA Astrophysics Data System (ADS)
Failure mechanism of thermal barrier coatings (TBCs) prepared by electron beam physical vapor deposition (EB-PVD) technique owing to formation of micro cracks was investigated. The TBCs were deposited on the Ni-based super alloy IN-100 and the micro cracks were observed within the top ceramic coat of thermally cycled TBCs at 1050�C. It was observed that these cracks propagate in the ceramic coat in the direction normal to interface while no cracks were observed in the bond coat. SEM/EDS studies revealed that some non-uniform oxides were formed on the interface between ceramic top and metallic bond coat just below the cracks. Study proposed that the cracks were initiated due to stress owing to big difference in Pilling-Bed worth ratio of non-uniform oxides as well as thermal stress, which caused the formation of cracks in top ceramic coat leading to failure of TBCs
Shahid, M. R.; Abbas, Musharaf
Congestive heart failure with preserved ejection fraction is associated with severely impaired dynamic Starling mechanism
Sedentary aging leads to increased cardiovascular stiffening, which can be ameliorated by sufficient amounts of lifelong exercise training. An even more extreme form of cardiovascular stiffening can be seen in heart failure with preserved ejection fraction (HFpEF), which comprises ?40?50% of elderly patients diagnosed with congestive heart failure. There are two major interrelated hypotheses proposed to explain heart failure in these patients: 1) increased left ventricular (LV) diastolic stiffness and 2) increased arterial stiffening. The beat-to-beat dynamic Starling mechanism, which is impaired with healthy human aging, reflects the interaction between ventricular and arterial stiffness and thus may provide a link between these two mechanisms underlying HFpEF. Spectral transfer function analysis was applied between beat-to-beat changes in LV end-diastolic pressure (LVEDP; estimated from pulmonary artery diastolic pressure with a right heart catheter) and stroke volume (SV) index. The dynamic Starling mechanism (transfer function gain between LVEDP and the SV index) was impaired in HFpEF patients (n = 10) compared with healthy age-matched controls (n = 12) (HFpEF: 0.23 � 0.10 ml�m?2�mmHg?1 and control: 0.37 � 0.11 ml�m?2�mmHg?1, means � SD, P = 0.008). There was also a markedly increased (3-fold) fluctuation of LV filling pressures (power spectral density of LVEDP) in HFpEF patients, which may predispose to pulmonary edema due to intermittent exposure to higher pulmonary capillary pressure (HFpEF: 12.2 � 10.4 mmHg2 and control: 3.8 � 2.9 mmHg2, P = 0.014). An impaired dynamic Starling mechanism, even more extreme than that observed with healthy aging, is associated with marked breath-by-breath LVEDP variability and may reflect advanced ventricular and arterial stiffness in HFpEF, possibly contributing to reduced forward output and pulmonary congestion.
Shibata, Shigeki; Hastings, Jeff L.; Prasad, Anand; Fu, Qi; Bhella, Paul S.; Pacini, Eric; Krainski, Felix; Palmer, M. Dean; Zhang, Rong
On the mechanism of wetting failure during fluid displacement along a moving substrate
NASA Astrophysics Data System (ADS)
This work investigates the onset of wetting failure for displacement of Newtonian fluids in parallel channels. A hydrodynamic model is developed for planar geometries where an advancing fluid displaces a receding fluid along a moving substrate. The model is evaluated with three distinct approaches: (i) the low-speed asymptotic theory of Cox [J. Fluid Mech. 168, 169-194 (1986)], (ii) a one-dimensional (1D) lubrication approach, and (iii) a two-dimensional (2D) flow model solved with the Galerkin finite element method (FEM). Approaches (ii) and (iii) predict the onset of wetting failure at a critical capillary number Cacrit, which coincides with a turning point in the steady-state solution family for a given set of system parameters. The 1D model fails to accurately describe interface shapes near the three-phase contact line when air is the receding fluid, producing large errors in estimates of Cacrit for these systems. Analysis of the 2D flow solution reveals that strong pressure gradients are needed to pump the receding fluid away from the contact line. A mechanism is proposed in which wetting failure results when capillary forces can no longer support the pressure gradients necessary to steadily displace the receding fluid. The effects of viscosity ratio, substrate wettability, and fluid inertia are then investigated through comparisons of Cacrit values and characteristics of the interface shape. Surprisingly, the low-speed asymptotic theory (i) matches trends computed from (iii) throughout the entire investigated parameter space. Furthermore, predictions of Cacrit from the 2D flow model compare favorably to values measured in experimental air-entrainment studies, supporting the proposed wetting-failure mechanism.
Vandre, E.; Carvalho, M. S.; Kumar, S.
Mechanical properties and failure mechanisms of closed-cell PVC foams
A comprehensive study of the mechanical behaviour of closed-cell polyvinyl chloride (PVC) foams with varying densities is conducted under tension, compression and impact loading. Experimental results on four classes of high-performance PVC foams show that the elastic modulus, strength and energy absorption of such foams are highly dependent on density. The compressive energy absorption is considerably higher than that under
Michele Colloca; Gleb Dorogokupets; Nikhil Gupta; Maurizio Porfiri
Methods And Systms For Analyzing The Degradation And Failure Of Mechanical Systems
Methods and systems for identifying, understanding, and predicting the degradation and failure of mechanical systems are disclosed. The methods include measuring and quantifying stressors that are responsible for the activation of degradation mechanisms in the machine component of interest. The intensity of the stressor may be correlated with the rate of physical degradation according to some determinable function such that a derivative relationship exists between the machine performance, degradation, and the underlying stressor. The derivative relationship may be used to make diagnostic and prognostic calculations concerning the performance and projected life of the machine. These calculations may be performed in real time to allow the machine operator to quickly adjust the operational parameters of the machinery in order to help minimize or eliminate the effects of the degradation mechanism, thereby prolonging the life of the machine. Various systems implementing the methods are also disclosed.
Jarrell, Donald B. (Kennewick, WA); Sisk, Daniel R. (Richland, WA); Hatley, Darrel D. (Kennewick, WA); Kirihara, Leslie J. (Richland, WA); Peters, Timothy J. (Richland, WA)
TBC1D5 and the AP2 complex regulate ATG9 trafficking and initiation of autophagy.
The RabGAP protein TBC1D5 controls cellular endomembrane trafficking processes and binds the retromer subunit VPS29 and the ubiquitin-like protein ATG8 (LC3). Here, we describe that TBC1D5 also associates with ATG9 and the active ULK1 complex during autophagy. Moreover, ATG9 and TBC1D5 interact with clathrin and the AP2 complex. Depletion of TBC1D5 leads to missorting of ATG9 to late endosomes upon activation of autophagy, whereas inhibition of clathrin-mediated endocytosis or AP2 depletion alters ATG9 trafficking and its association with TBC1D5. Taken together, our data show that TBC1D5 and the AP2 complex are important novel regulators of the rerouting of ATG9-containing vesicular carriers toward sites of autophagosome formation. PMID:24603492
Popovic, Doris; Dikic, Ivan
Failure analysis of radio frequency (rf) micro-electro-mechanical systems (MEMS)
NASA Astrophysics Data System (ADS)
MEMS are rapidly emerging as critical components in the telecommunications industry. This enabling technology is currently being implemented in a variety of product and engineering applications. MEMS are currently being used as optical switches to reroute light, tunable filters, and mechanical resonators. Radio frequency (RF) MEMS must be compatible with current Gallium Arsenide (GaAs) microwave integrated circuit (MMIC) processing technologies for maximum integration levels. The RF MEMS switch discussed in this paper was fabricated using various layers of polyimide, silicon oxynitride (SiON), gold, and aluminum monolithically fabricated on a GaAs substrate. Fig. 1 shows a metal contacting series switch. This switch consists of gold signal lines (transmission lines), and contact metallization. SiON was deposited to form the fixed-fixed beam, and aluminum was deposited to form the top actuation electrode. To ensure product performance and reliability, RF MEMS switches are tested at both the wafer and package levels. Various processing irregularities may pass the visual inspection but fail electrical testing. This paper will focus on the failure mechanisms found in the first generation of RF MEMS developed at Sandia National Laboratories. Various tools and techniques such as scanning electron microscopy (SEM), resistive contrast imaging (RCI), focused ion beam (FIB), and thermally-induced voltage alteration (TIVA) have been employed to diagnose the failure mechanisms. The analysis performed using these tools and techniques led to corrective actions implemented in the next generation of RF MEMS metal contacting series switches.
Walraven, Jeremy A.; Cole, Edward I.; Sloan, Lynn R.; Hietala, Susan L.; Tigges, Chris P.; Dyck, Christopher W.
Failure Predictions for VHTR Core Components using a Probabilistic Contiuum Damage Mechanics Model
The proposed work addresses the key research need for the development of constitutive models and overall failure models for graphite and high temperature structural materials, with the long-term goal being to maximize the design life of the Next Generation Nuclear Plant (NGNP). To this end, the capability of a Continuum Damage Mechanics (CDM) model, which has been used successfully for modeling fracture of virgin graphite, will be extended as a predictive and design tool for the core components of the very high- temperature reactor (VHTR). Specifically, irradiation and environmental effects pertinent to the VHTR will be incorporated into the model to allow fracture of graphite and ceramic components under in-reactor conditions to be modeled explicitly using the finite element method. The model uses a combined stress-based and fracture mechanics-based failure criterion, so it can simulate both the initiation and propagation of cracks. Modern imaging techniques, such as x-ray computed tomography and digital image correlation, will be used during material testing to help define the baseline material damage parameters. Monte Carlo analysis will be performed to address inherent variations in material properties, the aim being to reduce the arbitrariness and uncertainties associated with the current statistical approach. The results can potentially contribute to the current development of American Society of Mechanical Engineers (ASME) codes for the design and construction of VHTR core components.
Fok, Alex
User-defined Material Model for Thermo-mechanical Progressive Failure Analysis
NASA Technical Reports Server (NTRS)
Previously a user-defined material model for orthotropic bimodulus materials was developed for linear and nonlinear stress analysis of composite structures using either shell or solid finite elements within a nonlinear finite element analysis tool. Extensions of this user-defined material model to thermo-mechanical progressive failure analysis are described, and the required input data are documented. The extensions include providing for temperature-dependent material properties, archival of the elastic strains, and a thermal strain calculation for materials exhibiting a stress-free temperature.
Knight, Norman F., Jr.
Fracture and failure: Analyses, mechanisms and applications; Proceedings of the Symposium, Los Angeles, CA, March 17-20, 1980
NASA Technical Reports Server (NTRS)
Papers are presented on the application of fracture mechanics to spacecraft design, fracture control applications on the Space Shuttle reaction control thrusters, and an assessment of fatigue crack growth rate relationships for metallic airframe materials. Also considered are fracture mechanisms and microstructural relationships in Ni-base alloy systems, the use of surface deformation markings to determine crack propagation directions, case histories of metallurgical failures in the electronics industry, and a failure analysis of silica phenolic nozzle liners.
Tung, P. P. (editor); Agrawal, S. P.; Kumar, A.; Katcher, M.
Growth of interfacial cracks in a TBC\\/superalloy system due to oxide volume induced internal pressure and thermal loading
Residual stresses develop in thermal barrier coating during cool down from processing temperature due to the thermal expansion mismatch between the different layers e.g., substrate, bond coat, thermally grown oxide, and TBC. These residual stresses can initiate microcracks at the bond coat\\/TGO\\/TBC interfaces and can lead to debonding at the bond coat\\/TGO\\/TBC interfaces. Crack like flaws at the interface can
S. Q. Nusier; G. M. Newaz
Failure mode, effect and criticality analysis (FMECA) on mechanical subsystems of diesel generator at NPP.
National Technical Information Service (NTIS)
Largely, the RCM approach can be divided in three phases; (1) Functional failure analysis (FFA) on the selected system or subsystem, (2) Failure mode, effect and criticality analysis (FMECA) to identify the impact of failure to plant safety or economics, ...
T. W. Kim B. Singh T. Y. Sung J. H. Park Y. H. Lee
Manipulating failure mechanism of rapid prototyped scaffolds by changing nodal connectivity and geometry of the pores.
The performance of cellular solids in biomedical applications relies strongly on a detailed understanding of the effects of pore topology on mechanical properties. This study aims at characterizing the failure mechanism of scaffolds based on nodal connectivity (number of struts that meet in joints) and geometry of the pores. Plastic models of scaffolds having the same relative density but different cubic and trigonal unit cells were designed and then fabricated via three dimensional (3-D) printing. Unit cells were repeated in different arrangements in 3-D space. An in-situ imaging technique was utilized to study the progressive deformation of the scaffold models. Different nodal connectivities resulted in a wide range of compressive behaviors in scaffold models, from elastic-plastic to fully brittle. The Maxwell necessary criterion for rigidity was used to explain mechanical behavior of the scaffolds. Nodal connectivity of 4 satisfied Maxwell's criterion for rigidity in the examined structures. In a stress-strain curve of scaffolds with cubic unit cells and nodal connectivities of 3 and 4, pore deformation was observed after yielding. On the other hand, scaffolds with trigonal unit cells and nodal connectivities of 4 and 6, exhibited brittle behavior in the absence of pore deformation. These results highlight the role of nodal connectivity on failure mechanism and subsequently mechanical performance of scaffolds. This study reveals that appropriate pore geometry can provide sufficient condition for rigidity when Maxwell's necessary condition is satisfied. In addition, this study demonstrates that Maxwell's criterion can be used in pre-designing of pore geometries for scaffolds with distinct nodal connectivities. PMID:22985476
Amirkhani, Soodeh; Bagheri, Reza; Zehtab Yazdi, Alireza
Substrate specificity and effect on GLUT4 translocation of the Rab GTPase-activating protein Tbc1d1.
Insulin stimulation of the trafficking of the glucose transporter GLUT4 to the plasma membrane is controlled in part by the phosphorylation of the Rab GAP (GTPase-activating protein) AS160 (also known as Tbc1d4). Considerable evidence indicates that the phosphorylation of this protein by Akt (protein kinase B) leads to suppression of its GAP activity and results in the elevation of the GTP form of a critical Rab. The present study examines a similar Rab GAP, Tbc1d1, about which very little is known. We found that the Rab specificity of the Tbc1d1 GAP domain is identical with that of AS160. Ectopic expression of Tbc1d1 in 3T3-L1 adipocytes blocked insulin-stimulated GLUT4 translocation to the plasma membrane, whereas a point mutant with an inactive GAP domain had no effect. Insulin treatment led to the phosphorylation of Tbc1d1 on an Akt site that is conserved between Tbc1d1 and AS160. These results show that Tbc1d1 regulates GLUT4 translocation through its GAP activity, and is a likely Akt substrate. An allele of Tbc1d1 in which Arg(125) is replaced by tryptophan has very recently been implicated in susceptibility to obesity by genetic analysis. We found that this form of Tbc1d1 also inhibited GLUT4 translocation and that this effect also required a functional GAP domain. PMID:17274760
Roach, William G; Chavez, Jose A; M�inea, Cristinel P; Lienhard, Gustav E
Substrate specificity and effect on GLUT4 translocation of the Rab GTPase-activating protein Tbc1d1
Insulin stimulation of the trafficking of the glucose transporter GLUT4 to the plasma membrane is controlled in part by the phosphorylation of the Rab GAP (GTPase-activating protein) AS160 (also known as Tbc1d4). Considerable evidence indicates that the phosphorylation of this protein by Akt (protein kinase B) leads to suppression of its GAP activity and results in the elevation of the GTP form of a critical Rab. The present study examines a similar Rab GAP, Tbc1d1, about which very little is known. We found that the Rab specificity of the Tbc1d1 GAP domain is identical with that of AS160. Ectopic expression of Tbc1d1 in 3T3-L1 adipocytes blocked insulin-stimulated GLUT4 translocation to the plasma membrane, whereas a point mutant with an inactive GAP domain had no effect. Insulin treatment led to the phosphorylation of Tbc1d1 on an Akt site that is conserved between Tbc1d1 and AS160. These results show that Tbc1d1 regulates GLUT4 translocation through its GAP activity, and is a likely Akt substrate. An allele of Tbc1d1 in which Arg125 is replaced by tryptophan has very recently been implicated in susceptibility to obesity by genetic analysis. We found that this form of Tbc1d1 also inhibited GLUT4 translocation and that this effect also required a functional GAP domain.
Roach, William G.; Chavez, Jose A.; Miinea, Cristinel P.; Lienhard, Gustav E.
Accurate in vitro identification of fracture onset in bones: failure mechanism of the proximal human femur.
Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700 kHz. High-speed videos (12,000 frames/s, 0.1-0.2 mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50 ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200 ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling than high-speed cameras. The present findings elucidate some aspects of the failure mechanism of the proximal human femoral metaphysis. PMID:23218142
Juszczyk, Mateusz Maria; Cristofolini, Luca; Salv�, Marco; Zani, Lorenzo; Schileo, Enrico; Viceconti, Marco
Characterization of alumina scales formed during isothermal and cyclic oxidation of plasma-sprayed TBC systems at 1150 C
The isothermal- and cyclic-oxidation behavior of thermal barrier coating (TBC) systems consisting of vacuum plasma-sprayed (VPS) Ni-22Cr-10Al/Y (wt%) bond coatings and air plasma-sprayed (APS) Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} (YSZ) top coatings (on single-crystal superalloys) was investigated. The microstructures, flaw contents, and fracture behavior of the Al{sub 2}O{sub 3} scales formed during oxidation testing at 1150 C were characterized (by analysis of coating and scale fracture surfaces and metallographic cross sections). Significant localized fracture and buckling of the Al{sub 2}O{sub 3} scales that formed along the bond-coat--top-coat interfaces were observed after cyclic oxidation of TBCs. However, substantial amounts of localized scale damage did not induce rapid TBC failure. Decohesion of the columnar alumina scales on the rough bond-coat surfaces occurred by both internal Al{sub 2}O{sub 3} fracture (parallel to the metal surface) and oxide-metal delamination. There were microstructural indications of Al{sub 2}O{sub 3} scale crack healing by sintering into planar arrays of voids. Alumina scales that formed on convex NiCrAlY surfaces (with radii of 50 {micro}m or less) after cyclic oxidation, whereas scales formed by isothermal oxidation contained few visible voids. Accelerated void growth in Al{sub 2}O{sub 3} scales on the irregular NiCrAlY surfaces appeared to be creep-related and was attributed to the synergistic effects of geometric and thermal stresses.
Haynes, J.A.; Ferber, M.K.; Porter, W.D. [Oak Ridge National Lab., TN (United States). High Temperature Materials Lab.] [Oak Ridge National Lab., TN (United States). High Temperature Materials Lab.; Rigney, E.D. [Univ. of Alabama, Birmingham, AL (United States). Dept. of Materials and Mechanical Engineering] [Univ. of Alabama, Birmingham, AL (United States). Dept. of Materials and Mechanical Engineering
Mechanisms of exercise intolerance in heart failure with preserved ejection fraction.
Approximately half of patients with heart failure (HF) have a preserved ejection fraction (HFpEF), and with the changing age and comorbidity characteristics in the adult population, this number is growing rapidly. The defining symptom of HFpEF is exercise intolerance, but the specific mechanisms causing this common symptom remain debated and inadequately understood. Although diastolic dysfunction was previously considered to be the sole contributor to exercise limitation, recent studies have identified the importance of ventricular systolic, chronotropic, vascular, endothelial and peripheral factors that all contribute in a complex and highly integrated fashion to produce the signs and symptoms of HF. This review will explore the mechanisms underlying objective and subjective exercise intolerance in patients with HFpEF. PMID:24305634
Borlaug, Barry A
Mechanical Circulatory Support for End-Stage Heart Failure in Repaired and Palliated Congenital Heart Disease
Approximately one in one hundred children is born with congenital heart disease. Most can be managed with corrective or palliative surgery but a small group will develop severe heart failure, leaving cardiac transplantation as the ultimate treatment option. Unfortunately, due to the inadequate number of available donor organs, only a small number of patients can benefit from this therapy, and mortality remains high for pediatric patients awaiting heart transplantation, especially compared to adults. The purpose of this review is to describe the potential role of mechanical circulatory support in this context and to review current experience. For patients with congenital heart disease, ventricular assist devices are most commonly used as a bridge to cardiac transplantation, an application which has been shown to have several important advantages over medical therapy alone or support with extracorporeal membrane oxygenation, including improved survival to transplant, less exposure to blood products with less immune sensitization, and improved organ function. While these devices may improve wait list mortality, the chronic shortage of donor organs for children is likely to remain a problem into the foreseeable future. Therefore, there is great interest in the development of mechanical ventricular assist devices as potential destination therapy for congenital heart disease patients with end-stage heart failure. This review first discusses the experience with the currently available ventricular assist devices in children with congenital heart disease, and then follows to discuss what devices are under development and may reach the bedside soon.
Clark, Joseph B; Pauliks, Linda B; Myers, John L; Undar, Akif
Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers
NASA Technical Reports Server (NTRS)
Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents the results of testing that occurred from March through September of 2010 and builds on testing that occurred during the previous year.
Leimkuehler, Thomas O.; Stephan, Ryan A.; Hawkins-Reynolds, Ebony
Development, Testing, and Failure Mechanisms of a Replicative Ice Phase Change Material Heat Exchanger
NASA Technical Reports Server (NTRS)
Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. Wax PCM units have been baselined for the Orion thermal control system and also provide risk mitigation for the Altair Lander. However, the use of water as a PCM has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. An ice PCM heat exchanger that replicates the thermal energy storage capacity of an existing wax PCM unit was fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion are investigated. This paper presents the results to date of this investigation.
Leimkuehler, Thomas O.; Hansen, Scott; Stephan, Ryan A.
Development, Testing, and Failure Mechanisms of a Replicative Ice Phase Change Material Heat Exchanger
NASA Technical Reports Server (NTRS)
Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM's have over evaporators in this scenario is that they do not use a consumable. Wax PCM units have been baselined for the Orion thermal control system and also provide risk mitigation for the Altair Lander. However, the use of water as a PCM has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. An ice PCM heat exchanger that replicates the thermal energy storage capacity of an existing wax PCM unit was fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion are investigated. This paper presents the results to date of this investigation. Nomenclature
Leimkuehler, Thomas O.; Hansen, Scott; Stephan, Ryan A.
Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers
NASA Technical Reports Server (NTRS)
Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as specific spacecraft orientations in Low Earth Orbit (LEO) and low beta angle Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents the results of testing that occurred from March through September of 2010 and builds on testing that occurred during the previous year.
Leimkuehler, Thomas O.; Stephan, Ryan A.; Hawkins-Reynolds, Ebony
Mechanisms of Disease: detrimental adrenergic signaling in acute decompensated heart failure
SUMMARY Acute decompensated heart failure (ADHF) is responsible for more than 1 million hospital admissions each year in the US. Clinicians and scientists have developed therapeutic strategies that reduce mortality in patients with chronic heart failure (HF). Despite the widely appreciated magnitude of the ADHF problem, there is still a critical gap in our understanding of the cellular mechanisms involved and effective treatment strategies for hospitalized patients. Irrespective of the etiology, patients with ADHF present with similar symptoms (e.g. edema, altered hemodynamics and congestion) as multiple signaling pathways converge in a common phenotypic presentation. Investigations have shown that patients with ADHF have increased catecholamine levels, which cause chronic stimulation of ?-adrenergic receptors. This overstimulation leads to chronic G-protein activation and perturbations in myocyte signaling, as the patient�s heart attempts to adapt to progressive HF. Over time, these compensatory signaling mechanisms ultimately fail, and maladaptive signaling prevails with progressive worsening of symptoms. This Review summarizes some of the changes that occur during chronic adrenergic stimulation, and examines how downstream contractile dysfunction and myocyte death can alter the prognosis of patients with HF hospitalized for acute events.
Feldman, David S; Elton, Terry S; Sun, Benjamin; Martin, Mickey M; Ziolo, Mark T
Cortical and Spinal Mechanisms of Task Failure of Sustained Submaximal Fatiguing Contractions
In this and the subsequent companion paper, results are presented that collectively seek to delineate the contribution that supraspinal circuits have in determining the time to task failure (TTF) of sustained submaximal contractions. The purpose of this study was to compare adjustments in supraspinal and spinal excitability taken concurrently throughout the performance of two different fatigue tasks with identical mechanical demands but different TTF (i.e., force-matching and position-matching tasks). On separate visits, ten healthy volunteers performed the force-matching or position-matching task at 15% of maximum strength with the elbow flexors to task failure. Single-pulse transcranial magnetic stimulation (TMS), paired-pulse TMS, paired cortico-cervicomedullary stimulation, and brachial plexus electrical stimulation were delivered in a 6-stimuli sequence at baseline and every 2�3 minutes throughout fatigue-task performance. Contrary to expectations, the force-matching task TTF was 42% shorter (17.5�7.9 min) than the position-matching task (26.9�15.11 min; p<0.01); however, both tasks caused the same amount of muscle fatigue (p?=?0.59). There were no task-specific differences for the total amount or rate of change in the neurophysiologic outcome variables over time (p>0.05). Therefore, failure occurred after a similar mean decline in motorneuron excitability developed (p<0.02, ES?=?0.35�0.52) coupled with a similar mean increase in measures of corticospinal excitability (p<0.03, ES?=?0.30�0.41). Additionally, the amount of intracortical inhibition decreased (p<0.03, ES?=?0.32) and the amount of intracortical facilitation (p>0.10) and an index of upstream excitation of the motor cortex remained constant (p>0.40). Together, these results suggest that as fatigue develops prior to task failure, the increase in corticospinal excitability observed in relationship to the decrease in spinal excitability results from a combination of decreasing intracortical inhibition with constant levels of intracortical facilitation and upstream excitability that together eventually fail to provide the input to the motor cortex necessary for descending drive to overcome the spinal cord resistance, thereby contributing to task failure.
Williams, Petra S.; Hoffman, Richard L.; Clark, Brian C.
Effects of mechanical layering on magmatic reservoir failure and magma propagation within the Venusian lithosphere
NASA Astrophysics Data System (ADS)
Failure of magmatic reservoirs and propagation of magmas is controlled in part by the state of stress within the lithosphere. Such stresses are induced by a range of loadings (e.g., gravitational, magmatic and tectonic). In addition, the response of the lithosphere to these loadings depends on its physical properties. Magmatic reservoirs on planetary bodies have been studied using homogeneous lithosphere mainly composed of crustal material. However, planetary lithospheres may include substantial fractions of mantle material, with greater stiffness and density than those typical of crust. The mechanics of a heterogeneous lithosphere may influence the failure of a magmatic reservoir and the propagation of the magma. To explore this scenario, we created two-layered axisymmetric elastic models made of mantle and crustal components using the COMSOL Multiphysics finite element package, in which a stiffer and denser mantle is underlying a softer and lighter crust. A spherical reservoir was created at the contact between the two layers. In these models, we analyzed the magmatic reservoir stability, the amount of overpressure needed to reach failure and the type of resulting intrusions within the two-layered lithosphere for three distinct environments: 1- lithostatic; 2- upward flexure due to a rising mantle plume; and 3- downward flexure due to a basaltic shield volcano. The results show that in most cases, magmatic reservoirs fail below the mantle-crust contact. The resulting failure is driven by the in-plane stress tangential to the chamber, favoring lateral sill injections. In the flexure cases, magma chambers may become unstable (i.e., require no additional overpressure to fail) depending on the crust/mantle ratio. In some cases, we observed that the magma chambers failure can be driven by the (out-of-plane) hoop stress favoring radial dike intrusions. The stability of magmatic reservoirs and the type and orientation of magmatic intrusions on Venus are influenced by the state of stress and heterogeneities within the lithosphere. Using our result, we can infer the potential crust/mantle ratios of the Venusian lithosphere in a particular tectonic environment in order to sustain stable and viable magmatic reservoirs and generate radial dikes as observed on the surface of Venus.
Le Corvec, N.; McGovern, P. J.
How mechanical circulatory support helps not to need it--new strategies in pediatric heart failure.
During the past 3 years, seven potential candidates for mechanical circulatory support (MCS) were treated at our center. Ultimately, only one of them needed MCS (extracorporeal membrane oxygenation [ECMO] for 16 days), although 5 years earlier, all would have been considered for MCS at our center. Seven consecutive patients were seen in this period: four toddlers (three suffering from fulminant myocarditis and one with dilated cardiomyopathy associated with spongy myocardium) and three adolescents (two with postmyocarditis cardiomyopathy and one with hypertrophic cardiomyopathy and severe restrictive dysfunction after an ischemic event with cardiopulmonary resuscitation [stunned heart]). All patients presented in acute cardiocirculatory decompensation. All were admitted to the intensive care unit (ICU); all but one were sedated and intubated. A combination of levosimendan, milrinone, and nesiritide was administered to all patients. Use of catecholamines was kept short (<48 h in six individuals). MCS (ECMO, Berlin Heart Excor Pediatric, and Heartware) was always available. MCS initiation was indicated in only one patient, who was developing progressive multiorgan failure (MOF). The three toddlers with myocarditis recovered with complete normalization of myocardial function within 6 months. The fourth toddler is still at the ICU while waiting for transplantation. The three adolescents were listed with high urgency for heart transplantation, and all received a graft within 3 weeks. The adolescent with the stunned heart developed progressive MOF and was successfully supported with ECMO until transplantation. All six patients with completed course were discharged home in New York Heart Association Heart Failure Functional Classification System I condition without neurological deficits. Combined use of levosimendan, milrinone, and nesiritide, avoidance of catecholamines as much as possible, and MCS as backup are the new strategies at our center. This cardioprotective approach gives excellent outcome at lower risk and better cost-effectiveness in our pediatric patients with acute heart failure. Pediatric trials are recommended to evaluate combined use of newer cardioprotective drugs. PMID:21954874
Schweigmann, Ulrich; Velik-Salchner, Corinna; Kilo, Juliane; Schermer, Elisabeth
Finite element analysis of the failure mechanism of gentle slopes in weak disturbed clays
NASA Astrophysics Data System (ADS)
Italian south-eastern Apennines are affected by a large number of deep slow active landslide processes that interact with urban structures and infrastructures throughout the region, thus causing damages and economic losses. For most landslide processes in the region, the main predisposing factors for instability are represented by the piezometric regime and the extremely poor mechanical properties of the weak disturbed clays in the lower and central portions of the slopes that are overlaid in some cases by a stiffer cap layer, formed of rocky flysch, e.g. alternations of rock and soil strata. Based on phenomenological approaches, landslide processes are deemed to be triggered within the weaker clay layer and later on to develop upward to the stiffer cap, with the shear bands reaching also high depths. The paper presents the results of two-dimensional numerical analyses of the failure mechanisms developing in the unstable slopes of the region, carried out by means of the finite element method (Plaxis 2011) applied to slope conditions representative for the region. In particular, the effects of slope inclination, along with the thickness and the strength of the material forming the caprock at the top of the slope, on the depth of the sliding surface, the mobilised strengths, the evolution of the landslide process and the predisposing factors of landsliding have been explored by means of the finite element analysis of an ideal case study representative of the typical geomechanical context of the region. In particular, the increase of slope inclination is shown to raise the depth of the shear band as well as to extend landslide scarp upwards, in accordance with the field evidence. Moreover, the numerical results indicate how the increase of the caprock thickness tends to confine the development of the shear band to the underlying weaker clay layer, so that the depth of the shear band is also observed to reduce, and when the stiffer top stratum becomes involved in the retrogression of the failure process. The numerical results allow also for the investigation of the variation in seepage conditions that combine with the variations in litostratigraphy in determining the variations of the features of the failure mechanism.
Lollino, Piernicola; Mezzina, Giuseppe; Cotecchia, Federica
Failure of fluid-saturated granular materials: a unified approach to capture diffuse and localized instability mechanisms
NASA Astrophysics Data System (ADS)
Granular materials are susceptible to a wide variety of failure and deformation mechanisms, especially because of their interaction with the pore fluids and the surrounding environment. An adequate modeling of their mechanical response is therefore essential for understanding a number of geological processes, such as the onset of rapid landslides, hillslope denudation and sediment transport, or even the mechanics of fault gauges. Depending on the type of material, the groundwater conditions and the surrounding kinematic constraints, both diffuse and localized mechanisms are possible, and these may occur under either drained or undrained conditions. In the geomechanics literature, failure modes are usually explained and modeled with the tools of continuum mechanics, such as the mathematical theory of plasticity. Due to the complexity of granular material behavior, however, most classical models for frictional strength are unable to capture the variety of instability mechanisms observed for such class of geomaterials (e.g., liquefaction, shear banding, etc.). Sophisticated strain-hardening plasticity models are therefore required for numerical modeling purposes, thus making the evaluation of critical failure conditions less straightforward than in perfect plasticity theories. Here we propose a mathematical strategy that can be adapted to any elastoplastic model and allows the onset of failure in elastoplastic geomaterials to be expressed in a more general manner. More specifically, our theory expresses the failure conditions as a function of local kinematics and solid-fluid interactions. The stability criterion used in this study is based on the so-called stability modulus, a scalar index of failure that was formulated by linking the physical concept controllability to the mathematical notion of plastic admissibility upon an incremental loading path [Buscarnera et al, 2011]. In this contribution, different loading constraints are considered, accounting for the possible occurrence of diffuse and localized failure mechanisms. While the mathematical strategy to calculate the failure indices is discussed in a general manner, a particular application is presented, focused on the simulation of the mechanical response of loose, saturated sands. Failure mechanisms are simulated under axisymmetric, plane-strain and simple shear conditions. For each of these cases, the indices are used to infer whether a failure mode is more likely to occur in a localized or homogeneous manner. At this reference, the role of drainage conditions is specifically explored. The results of numerical analyses are compared to data from classical experiments available in the literature. Finally, the theory is used to explain the mechanisms of failure that may have provoked a series of underwater flow failures in the shallow sand veneers located along the banks of the Jamuna River, in Bangladesh [Hight et al, 1998] The analyses conducted in this work elucidate the remarkable dependence of geomaterial stability on both kinematic conditions and pore-fluid constraints. In particular, the links between generalized failure mechanisms and the onset of landslides has been elucidated through numerical simulations. The results obtained by our analyses therefore provide a simple and consistent strategy to unify the mathematical description of the material instabilities that are involved in a variety of failure mechanisms of geological settings. Buscarnera G., Dattola G., Di Prisco C. (2011) " Controllability, uniqueness and existence of the incremental response: A mathematical criterion for elastoplastic constitutive laws", International Journal of Solids and Structures, 48 (13), pp. 1867-1878. Hight, D. W., Georgiannou, V. N., Martin, P. L., and Mundegar, A. K. (1998) "Flow slides in micaceous sand." Problematic soils, Yanagisawa, E., Moroto, N., and Mitachi, T., eds., Baklema, Rotterdam, Sendai, Japan, pp. 945-958.
Mihalache, Constance; Buscarnera, Giuseppe
Failure mechanics in low-velocity impacts on thin composite plates
NASA Technical Reports Server (NTRS)
Eight-ply quasi-isotropic composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were tested to establish the degree of equivalence between low-velocity impact and static testing. Both the deformation and failure mechanics under impact were representable by static indentation tests. Under low-velocity impacts such as tool drops, the dominant deformation mode of the plates was the first, or static, mode. Higher modes are excited on contact, but they decay significantly by the time the first-mode load reaches a maximum. The delamination patterns were observed by X-ray analysis. The areas of maximum delamination patterns were observed by X-ray analysis. The areas of maximum delamination coincided with the areas of highest peel stresses. The extent of delamination was similar for static and impact tests. Fiber failure damage was established by tensile tests on small fiber bundles obtained by deplying test specimens. The onset of fiber damage was in internal plies near the lower surface of the plates. The distribution and amount of fiber damage was similar fo impact and static tests.
Elber, W.
ME3738 protects from concanavalin A-induced liver failure via an IL-6-dependent mechanism.
ME3738 is a new compound that attenuates liver disease in several models of acute and chronic liver inflammation. We used the concanavalin A (Con A) model to elucidate the molecular mechanisms of ME3738 to block liver cell damage. Pretreatment of BALB/c mice with ME3738 prior to Con A injection resulted in a significant reduction in liver injury. The protective effect of ME3738 prior to Con A injection was associated with a reduction in IL-6 serum levels and NF-kappaB DNA binding in liver nuclear extracts. However, STAT3 DNA binding was induced via ME3738 prior to Con A injection. Further analysis showed that ME3738 induces IL-6 serum levels and activates STAT3 DNA binding and target gene transcription. The relevance of this finding was assessed in IL-6(-/-) mice. In these animals, ME3738 induced no increase in IL-6 serum expression, and activation of IL-6-dependent pathways was not found. In addition, ME3738 did not protect IL-6(-/-) animals from Con A-induced liver failure, while IL-6 injection was still effective. Therefore, we demonstrate that ME3738 triggers IL-6 expression, which activates pathways that are relevant to protect from Con A-induced liver failure. PMID:12884300
Klein, Christian; W�stefeld, Torsten; Heinrich, Peter C; Streetz, Konrad L; Manns, Michael P; Trautwein, Christian
Levosimendan may improve survival in patients requiring mechanical assist devices for post-cardiotomy heart failure
Introduction Most case series suggest that less than half of the patients receiving a mechanical cardiac assist device as a bridge to recovery due to severe post-cardiotomy heart failure survive to hospital discharge. Levosimendan is the only inotropic substance known to improve medium term survival in patients suffering from severe heart failure. Methods This retrospective analysis covers our single centre experience. Between July 2000 and December 2004, 41 consecutive patients were treated for this complication. Of these, 38 patients are included in this retrospective analysis as 3 patients died in the operating room. Levosimendan was added to the treatment protocol for the last nine patients. Results Of 29 patients treated without levosimendan, 20 could be weaned off the device, 9 survived to intensive care unit discharge, 7 left hospital alive and 3 survived 180 days. All 9 patients treated with levosimendan could be weaned, 8 were discharged alive from ICU and hospital, and 7 lived 180 days after surgery (p < 0.002 for 180 day survival). Plasma lactate after explantation of the device was significantly lower (p = 0.002), as were epinephrine doses. Time spent on renal replacement therapy was significantly shorter (p = 0.023). Conclusion Levosimendan seems to improve medium term survival in patients failing to wean off cardiopulmonary bypass and requiring cardiac assist devices as a bridge to recovery. This retrospective analysis justifies prospective randomised investigations of levosimendan in this group of patients.
Braun, Jan-Peter; Jasulaitis, Dominik; Moshirzadeh, Maryam; Doepfmer, Ulrich R; Kastrup, Marc; von Heymann, Christian; Dohmen, Pascal M; Konertz, Wolfgang; Spies, Claudia
Mechanisms of force failure during repetitive maximal efforts in a human upper airway muscle.
The upper airway respiratory muscles play an important role in the regulation of airway resistance, but surprisingly little is known about their contractile properties and endurance performance. We developed a technique that allows measurement of force and the electromyogram (EMG) of human nasal dilator muscles (NDMs). Endurance performance was quantified by measuring NDM "flaring" force and EMG activity as healthy human subjects performed 10 s maximal voluntary contractions (MVCs), separated by 10 s rest, until the area under the force curve fell to 50% MVC (the time limit of the fatigue task, Tlim), which was reached in 34.2 +/- 3.1 contractions (685.0 +/- 62.3 s). EMG activity was unchanged except at Tlim, where it averaged 78.7 +/- 3.6% of pretest activity (P < 0.01). M-wave amplitude did not change, suggesting that neuromuscular propagation was not impaired. MVC force increased to 80% of the pretest level within 10 min of recovery but twitch force failed to recover, suggesting low-frequency fatigue. The data suggest that a failure of the nervous system to excite muscle could explain at most only a small fraction of the NDM force loss during an intermittent fatigue task, and then only at Tlim. Thus, the majority of the force failure during this task is due to impairment of mechanisms that reside within the muscle fibers. PMID:12115954
DelloRusso, Christiana; Khurana, Nilam; Rankin, Lucinda; Sullivan, Jenna; Fregosi, Ralph F
Bypass balloon pumping: a newly developed device for mechanical circulatory support in heart failure.
Various types of assist devices have been developed for severe heart failures. Among them, intra-aortic balloon pumping (IABP) has achieved popularity, mainly in the treatment of patients with either severe cardiac infarction or low cardiac output syndrome (LOS) after open-heart surgery. However, IABP has a limitation in that although it acts as a pressure support, it cannot directly support flow volume. In cases of severe pump failure, stronger pump support would be required. However, there is a limit in the clinical use of temporary mechanical support using a pump because of the costs of the expensive equipment. With this in mind, we came up with a new idea in which the motion of a balloon in IABP system is converted into a power source for creating a one-way stream. In order to realize our idea, we made a J-shaped sample model of pulsating chamber incorporating two ball valves. In the hydrodynamic experiment using our new device, flows over 2500 ml/min (Max. 3475 ml/min) were obtained. The percent changes in parameters such as TTI, DPTI and bypass flows obtained by the experiment of left ventricular bypass have demonstrated that our assist system is effective for reducing cardiac work. PMID:12587080
Hoshino, M; Asakura, T; Yasuura, K; Ogawa, Y; Okamoto, H; Matsuura, A
TBC1D24 Mutation Causes Autosomal-Dominant Nonsyndromic Hearing Loss.
Hereditary hearing loss is extremely heterogeneous. Over 70 genes have been identified to date, and with the advent of massively parallel sequencing, the pace of novel gene discovery has accelerated. In a family segregating progressive autosomal-dominant nonsyndromic hearing loss (NSHL), we used OtoSCOPE� to exclude mutations in known deafness genes and then performed segregation mapping and whole-exome sequencing to identify a unique variant, p.Ser178Leu, in TBC1D24 that segregates with the hearing loss phenotype. TBC1D24 encodes a GTPase-activating protein expressed in the cochlea. Ser178 is highly conserved across vertebrates and its change is predicted to be damaging. Other variants in TBC1D24 have been associated with a panoply of clinical symptoms including autosomal recessive NSHL, syndromic hearing impairment associated with onychodystrophy, osteodystrophy, mental retardation, and seizures (DOORS syndrome), and a wide range of epileptic disorders. PMID:24729539
Azaiez, Hela; Booth, Kevin T; Bu, Fengxiao; Huygen, Patrick; Shibata, Seiji B; Shearer, A Eliot; Kolbe, Diana; Meyer, Nicole; Black-Ziegelbein, E Ann; Smith, Richard J H
Characterization of the fatigue failure mechanisms in austenitic and high nitrogen austenitic stainless steels
NASA Astrophysics Data System (ADS)
The aim of this study was to compare the properties of an implant grade 21Cr-23Mn-1N nitrogen-stabilized stainless (HNS) steel, to 316L and 22Cr-13Ni-5Mn stainless steels with a long history of implant use. The HNS steel showed excellent tensile, corrosion, and corrosion fatigue properties. However, the fracture surfaces of the notched tensile, notched stress corrosion cracking (SCC), smooth corrosion fatigue, and notched corrosion fatigue samples in the HNS steel showed a mixed-mode fracture consisting of areas of brittle facets intermingled with typical ductile features. Mixed-mode fractures were not exhibited in the other two nickel-stabilized stainless steel alloys. Since a substantial number of implant failures occur due to fatigue, the differences shown in fatigue fracture morphology for the HNS steel were of particular interest. It was hypothesized that the fatigue crack initiation and/or propagation mechanisms may be different for the HNS steel, and lead to the unusual fracture morphologies shown for the austenitic material. The current research set out to test this hypothesis, and compare the fatigue crack initiation and propagation mechanisms of 21Cr-23Mn-1N and 316L cold-worked implant grade steels. Electron backscattered diffraction (EBSD) techniques were used to analyze representative areas of the microstructure on the free surface of fatigue samples. Both low-cycle and high-cycle fatigue loading conditions were evaluated over a series of fatigue intervals for each alloy. Atomic Force Microscopy (AFM) was also employed in order to determine the surface topography on the nanometer scale associated with representative surface deformation features. In addition the fracture surfaces of selected fatigue samples were examined using scanning electron microscopy (SEM) failure analysis techniques. The EBSD crack initiation and propagation data were associated with fracture morphology features shown in the SEM analysis. Results from the EBSD analysis revealed former annealing twin boundaries to be a strongly preferred location for fatigue crack initiation in the 21Cr-23Mn-1N HNS alloy. Crack propagation was shown to typically follow a transcrystalline direction. Analysis of selected extended fatigue cracks suggested a mechanism involving preferential initiation along former annealing twin and grain boundaries followed by transcrystalline crack propagation to interconnect the previously initiated cracks. SEM failure analysis of the HNS alloy showed a large number of facets in the crack initiation regions of the fatigue fractures. The large number of brittle facets in the initiation region of the fatigue fracture surface agrees well with the preferential former annealing twin boundary crack initiation location shown in the EBSD analysis. In Contrast, EBSD analysis of the 316L alloy showed transgranular slip markings along {111} planes to be the strongly preferred location for fatigue crack initiation. Crack propagation was also shown to typically follow a transcrystalline direction in this alloy. Analysis of selected extended fatigue cracks suggested a mechanism of preferential initiation along slip markings followed by transcrystalline crack propagation to interconnect the previously initiated cracks. SEM failure analysis of the 316L alloy showed relatively few facets, which also supported the EBSD results showing a preference for transgranular slip marking crack initiation. AFM analysis revealed small extrusions due to dislocation pile-up along slip markings shown on the fatigue sample free surfaces of both alloys. The reduced heights of the extrusions compared to those shown previous studies on annealed alloys, was attributed to the degree of cold-working already present in the material prior to fatigue testing. In conclusion, EBSD analysis revealed the preferential location of fatigue crack initiation for the two alloys to be very different. These differences in fatigue crack initiation locations explain the differences shown in fracture morphologies in the two alloy systems. Also the addition of EBSD and AFM analys
Roach, Michael David
Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients
NASA Technical Reports Server (NTRS)
Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.
Zju, Dongming; Ghosn, Louis J.; Miller, Robert A.
Durable mechanical circulatory support in advanced heart failure: a critical care cardiology perspective.
Though cardiac transplantation for advanced heart disease patients remains definitive therapy for patients with advanced heart failure, it is challenged by inadequate donor supply, causing durable mechanical circulatory support (MCS) to slowly become a new primary standard. Selecting appropriate patients for MCS involves meeting a number of prespecifications as is required in evaluation for cardiac transplant candidacy. As technology evolves to bring forth more durable smaller devices, selection criteria for appropriate MCS recipients will likely expand to encompass a broader, less sick population. The "Holy Grail" for MCS will be a focus on clinical recovery and explantation of devices rather than the currently more narrowly defined indications of bridge to transplantation or lifetime device therapy. PMID:24188222
Lala, Anuradha; Mehra, Mandeep R
Finite Element Modeling of the Different Failure Mechanisms of a Plasma Sprayed Thermal Barrier Coatings System
NASA Astrophysics Data System (ADS)
A new finite element model is used to investigate catastrophic failures of a thermal barrier coatings system due to crack propagation along the interfaces between the ceramic top-coat, thermally grown oxide, and bond-coat layers, as well as between the lamellas structure of the ceramic layer. The thermo-mechanical model is designed to take into account a non-homogenous temperature distribution and the effects of the residual stresses generated during the coating process. Crack propagation is simulated using the contact tool "Debond" present in the ABAQUS finite element code. Simulations are performed with a geometry corresponding to similar or dissimilar amplitudes of asperity, and for different thicknesses of the oxide layer. The numerical results have shown that crack evolution depends crucially on the ratio of the loading rate caused by growth and swelling of the oxide layer and also on the interface roughness obtained during the spraying of coatings.
Ranjbar-Far, M.; Absi, J.; Mariaux, G.
A mechanics framework for a progressive failure methodology for laminated composites
NASA Technical Reports Server (NTRS)
A laminate strength and life prediction methodology has been postulated for laminated composites which accounts for the progressive development of microstructural damage to structural failure. A damage dependent constitutive model predicts the stress redistribution in an average sense that accompanies damage development in laminates. Each mode of microstructural damage is represented by a second-order tensor valued internal state variable which is a strain like quantity. The mechanics framework together with the global-local strategy for predicting laminate strength and life is presented in the paper. The kinematic effects of damage are represented by effective engineering moduli in the global analysis and the results of the global analysis provide the boundary conditions for the local ply level stress analysis. Damage evolution laws are based on experimental results.
Harris, Charles E.; Allen, David H.; Lo, David C.
Nontraumatic Fracture of the Femoral Condylar Prosthesis in a Total Knee Arthroplasty Leading to Mechanical Failure
This paper reports a case of fatigue fracture of the femoral component in a cruciate-retaining cemented total knee arthroplasty (TKA). A 64-year-old man had undergone a primary TKA for osteoarthritis 10 years previously at another institution using the PFC-Sigma prosthesis. The patient recovered fully and was back to his regular activities. He presented with a history of sudden onset pain and locking of the left knee since the preceding three months. There was no history of trauma, and the patient was mobilizing with difficulty using crutches. Radiographs revealed fracture of the posterior condyle of the femoral prosthesis. Revision surgery was performed as an elective procedure revealing the broken prosthesis. The TC3RP-PFC revision prosthesis was used with a medial parapatellar approach. The patient recovered fully without any squeal. Mechanical failure of the knee arthroplasty prosthesis is rare, and nontraumatic fracture of the femoral metallic component has not been reported before.
Swamy, Girish N.; Quah, Conal; Bagouri, Elmunzar; Badhe, Nitin P.
Effect of beam angle on HAZ, recast and oxide layer characteristics in laser drilling of TBC nickel superalloys
Industrial applications of laser drilling include the production of cooling holes at acute angles in certain parts of the aero-engine components. These parts are often covered with ceramic thermal barrier coatings (TBC) to protect them from reaching excessive temperatures in hot engine environments. Acute angle TBC drilling brings three major simultaneous complications to the process. These are: (i) multi-layer drilling,
H. K. Sezer; L. Li; M. Schmidt; A. J. Pinkerton; B. Anderson; P. Williams
Thiotepa, busulfan, cyclophosphamide (TBC) and autologous hematopoietic transplantation: an intensive regimen for the treatment of multiple myeloma
The study was designed to evaluate the efficacy and safety of an intensive, tri-alkylator conditioning regimen, consisting of thiotepa, busulfan and cyclophosphamide (TBC), prior to autologous hematopoietic cell transplantation in patients with multiple myeloma (MM) and to analyze factors associated with outcome. One hundred and twenty patients with MM received high-dose chemotherapy with TBC followed by autologous bone marrow (n
A Shimoni; TL Smith; A Aleman; D Weber; M Dimopoulos; P Anderlini; B Andersson; D Claxton; NT Ueno; I Khouri; M Donato; M Korbling; R Alexanian; R Champlin; S Giralt
Impermeable Thin Al(2)O(3) Overlay for TBC Protection from Sulfate and Vanadate Attack in Gas Turbines.
National Technical Information Service (NTIS)
In order to improve the hot corrosion resistance of conventional YSZ TBC system, a dense and continues overlay of Al(2)O(3) coating of about 25 micrometers thick was deposited on the surface of TBC by EB-PVD and high velocity oxy-fuel (HVOF) spray techniq...
Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections�Part 2: Failure Mechanisms
NASA Astrophysics Data System (ADS)
Part 1 of this study focused on identifying the effects of (i) temperature difference (? T), (ii) lower dwell temperature and shorter dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate on the lifetime of ball grid array (with 144 solder balls) component boards. Based on the characteristic lifetime, the studied thermal cycling profiles were categorized into three groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. In this work, the observed differences in component board lifetime are explained by studying the failure mechanisms and microstructural changes that take place in the three groups of loading conditions. It was observed that, under the standardized thermal cycling conditions (highly accelerated conditions), the networks of grain boundaries formed by recrystallization provided favorable paths for cracks to propagate intergranularly. It is noteworthy that the coarsening of intermetallic particles was strong in the recrystallized regions (the cellular structure had disappeared completely in the crack region). However, under real-use conditions (mildly/nonaccelerated conditions), recrystallization was not observed in the solder interconnections and cracks had propagated transgranularly in the bulk solder or between the intermetallic compound (IMC) layer and the bulk solder. The real-use conditions showed slight coarsening of the microstructure close to the crack region, but the solder bulk still included finer IMC particles and ?-Sn cells characteristic of the as-solidified microstructures. These findings suggest that standardized thermal cycling tests used to assess the solder interconnection reliability of BGA144 component boards create failure mechanisms that differ from those seen in conditions representing real-use operation.
Hokka, Jussi; Mattila, Toni T.; Xu, Hongbo; Paulasto-Kr�ckel, Mervi
Mechanisms of improvement of respiratory failure in patients with COPD treated with NIV
Background Noninvasive ventilation (NIV) improves gas-exchange and symptoms in selected chronic obstructive pulmonary disease (COPD) patients with hypercapnic respiratory failure. We hypothesized NIV reverses respiratory failure by one or all of increased ventilatory response to carbon-dioxide, reduced respiratory muscle fatigue, or improved pulmonary mechanics. Methods Nineteen stable COPD patients (forced expiratory volume in one second 35% predicted) were studied at baseline (D0), 5�8 days (D5) and 3 months (3M) after starting NIV. Results Ventilator use was 6.2 (3.7) hours per night at D5 and 3.4 (1.6) at 3M (p = 0.12). Mean (SD) daytime arterial carbon-dioxide tension (PaCO2) was reduced from 7.4 (1.2) kPa to 7.0 (1.1) kPa at D5 and 6.5 (1.1) kPa at 3M (p = 0.001). Total lung capacity decreased from 107 (28) % predicted to 103 (28) at D5 and 103 (27) % predicted at 3M (p = 0.035). At D5 there was an increase in the hypercapnic ventilatory response and some volitional measures of inspiratory and expiratory muscle strength, but not isolated diaphragmatic strength whether assessed by volitional or nonvolitional methods. Conclusion These findings suggest decreased gas trapping and increased ventilatory sensitivity to CO2 are the principal mechanism underlying improvements in gas-exchange in patients with COPD following NIV. Changes in some volitional but not nonvolitional muscle strength measures may reflect improved patient effort.
Nickol, Annabel H; Hart, Nicholas; Hopkinson, Nicholas S; Hamnegard, Carl-Hugo; Moxham, John; Simonds, Anita; Polkey, Michael I
Mechanisms of Recurrent Ventricular Fibrillation in a Rabbit Model of Pacing-Induced Heart Failure
Objectives To determine the mechanisms of spontaneous ventricular fibrillation (SVF) after initial successful defibrillation in a rabbit model of heart failure (HF). Background Successful defibrillation may be followed by recurrent SVF. The mechanisms of postshock SVF are unclear. Methods We performed simultaneous optical mapping of intracellular calcium (Cai) and membrane potential (Vm) in 12 rabbit hearts with chronic pacing-induced heart failure, in 4 sham operated hearts and in 5 normal hearts during fibrillation-defibrillation episodes. Results We recorded 28 SVF episodes after initial successful defibrillation in 4 failing hearts (SVF Group) but not in the remaining 8 failing hearts (no-SVF Group) or in the normal or sham operated hearts. The action potential duration (APD80) before pacing-induced VF was 209�9 ms (SVF-Group) and 212�14 ms (no-SVF Group, P=NS). After successful defibrillation, the APD80 in SVF Group shortened to 147�26 ms while in no-SVF Group shortened to 176�14 ms (P=0.04). However, the duration of Cai after defibrillation was not different between these two groups (246�21 ms vs. 241�17 ms, p=NS), resulting in elevated Cai during late phase 3 or phase 4 of the action potential. Standard glass microelectrode recording in an additional 5 failing hearts confirmed postshock APD shortening and afterdepolarizations. The APD80 of normal and sham operated hearts was not shortened after defibrillation. Conclusions HF promotes acute shortening of the APD immediately after termination of VF in failing hearts. Persistent Cai elevation during the late phase 3 and phase 4 of the shortened action potential result in afterdepolarizations, triggered activity and SVF.
Ogawa, Masahiro; Morita, Norishige; Tang, Liang; Karagueuzian, Hrayr S.; Weiss, James N.; Lin, Shien-Fong; Chen, Peng-Sheng
Study the mechanical pulmonary changes in patients with congestive heart failure (CHF) by impulse oscillometry
Background Heart failure is one of the most leading cause of death worldwide, but the mechanical characteristics of the pulmonary system in these patients have not been studied enough. The aim of this study was to measure mechanical pulmonary changes in patients with congestive heart failure (CHF) by using impulse oscillometry (IOS), which can obtain data by simpler means and independently from respiratory muscle strength. Materials and methods We assessed 24 CHF patients and 24 controls by spirometry and IOS using the Jaeger IOS system. IOS measures central and peripheral airway resistances (R20, R5) and central and peripheral reactances (X20, X5) using sound waves with different frequencies, which superimposed on the patients respiratory tidal volume and then records reflects. P value�<�0.05 was taken to be significant. Results The mean age of patients and controls was 61���10 and 57���7 years, respectively. The mean ejection fraction (EF) was 37���17% for patients and 55���7% for controls. Patients had a lower X5 (?0.20���0.13 vs�?0.13���0.07; P�<�0.05), forced expiratory volume in 1�second (FEV1; 2.26���0.68 vs 3.09���0.82: P�<�0.01�L/min), and forced vital capacity (FVC; 2.55���0.86 vs 3.32���0.87; P�<�0.05) compared to the controls. They also had elevated R5: 0.37���0.21 vs 0.27���0.09; P�<�0.06). X5 was correlated with spirometric abnormalities (P�<�0.05) and was lower in patients than in controls. Conclusion X5 was lower and R5 was higher in patients than in controls. CHF patients can be assessed by IOS more comfortable than by spirometry. IOS can reliably measure peripheral airway resistance in this group of patients.
Nourizadeh, Mohammad; Ghelich, Yunose; Amin, Ahmad; Eidani, Esmaeel; Gholampoor, Yousef; Asadmoghadam, Mahsa; Asadinia, Najme
Microstructure-property relationships of SiC fiber-reinforced magnesium aluminosilicates. 2: Mechanical properties and failure characteristics
Interfacial frictional shear stresses, flexural properties and failure mechanisms are reported for two magnesium aluminosilicates unidirectionally reinforced with Nicalon SiC fibers. Composites A and B were hot-pressed at 1,500 and 920 C, respectively. High values of interfacial frictional shear stresses inferred from Marshall`s analysis of the micro-indentation technique could be attributed in part to the presence of compressive radial stresses at the fiber-matrix interfaces. Although both composites failed non-catastrophically in symmetrical four point bend testing at room temperature, the failure modes were different. Extensive matrix microcracking, fiber failure and then fiber pull-put were commonly observed in composite A. Failure modes in composite B included the formation of a limited number of matrix cracks, the failure of fibers in the matrix crack front and progressive delamination. The observations demonstrate that the mechanical properties, the interfacial frictional shear stresses and the failure mechanisms of both composites are governed by their microstructural features, in particular the chemistry and structure of the matrix-fiber interfacial region.
Kumar, A.; Knowles, K.M. [Univ. of Cambridge (United Kingdom). Dept. of Materials Science and Metallurgy] [Univ. of Cambridge (United Kingdom). Dept. of Materials Science and Metallurgy
The unsteady nature of sea cliff retreat due to mechanical abrasion, failure and comminution feedbacks
NASA Astrophysics Data System (ADS)
Sea cliff retreat is often linked to large waves, heavy precipitation and seismic events, but the specific operative mechanics have not been well constrained. In particular, what is the role of mechanical abrasion by beach sediments in cliff/platform evolution and how does it relate to the episodic nature of cliff retreat observed at certain locations? Here we present a simple, numerical model of sea cliff retreat that incorporates mechanical abrasion of a basal notch, threshold-controlled failure of the cantilevered block, and a feedback mechanism wherein retreat is dependent on the rate of sediment comminution within the surf zone. Using shore platform and cliff characteristics found in two coastal settings (the central California coast and the English North Sea coast), the model produces retreat rates comparable to those observed via field measurements. The highest retreat rates coincide with the steepest shore platforms and increasing wave height. Steeper platforms promote wave access to the cliff toe and, correspondingly, the receding cliff face produces additional accommodation space for the platform beach, preserving the erosive efficacy of the beach sediments. When exposed to energetic wave forcing, the slope of the inner platform segment controls retreat rates for concave platforms, whereas the slope of the outer platform segment exerts greater control for convex platforms. Platform beaches approached a long-term dynamic equilibrium on the concave profiles, leading to more consistent and steady retreat. Platform beaches were ephemeral on convex profiles, mirroring observed sand wave (Ord) migration on the Holderness coast, UK. These findings agree with previous field observations and support mechanical abrasion as a viable cause of temporal heterogeneity in cliff retreat rate for both coastlines.
Kline, Shaun W.; Adams, Peter N.; Limber, Patrick W.
Comparison of the Failures during Cyclic Oxidation of Yttria-Stabilized (7 to 8 Weight Percent) Zirconia Thermal Barrier Coatings Fabricated via Electron Beam Physical Vapor Deposition and Air Plasma Spray
The failures during oxidation of electron beam physical vapor deposition (EBPVD) and air plasma spray (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) on different bond coats, namely, platinum-modified aluminide and NiCoCrAlY, are described. It is shown that oxidation of the bond coats, along with defects existing near the TBC\\/bond coat interface, plays a very important role in TBC failures.
N. M. Yanar; M. Helminiak; G. H. Meier; F. S. Pettit
Comparison of the Failures during Cyclic Oxidation of Yttria-Stabilized (7 to 8 Weight Percent) Zirconia Thermal Barrier Coatings Fabricated via Electron Beam Physical Vapor Deposition and Air Plasma Spray
The failures during oxidation of electron beam physical vapor deposition (EBPVD) and air plasma spray (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) on different bond coats, namely, platinum-modified aluminide and NiCoCrAlY, are described. It is shown that oxidation of the bond coats, along with defects existing near the TBC\\/bond coat interface, plays a very important role in TBC failures.
N. M. Yanar; M. Helminiak; G. H. Meier; F. S. Pettit
Comparison of the Failures during Cyclic Oxidation of Yttria-Stabilized (7 to 8 Weight Percent) Zirconia Thermal Barrier Coatings Fabricated via Electron Beam Physical Vapor Deposition and Air Plasma Spray
The failures during oxidation of electron beam physical vapor deposition (EBPVD) and air plasma spray (APS) yttria-stabilized\\u000a zirconia (YSZ) thermal barrier coatings (TBCs) on different bond coats, namely, platinum-modified aluminide and NiCoCrAlY,\\u000a are described. It is shown that oxidation of the bond coats, along with defects existing near the TBC\\/bond coat interface,\\u000a plays a very important role in TBC failures.
N. M. Yanar; M. Helminiak; G. H. Meier; F. S. Pettit
Identification of Regions Critical for the Integrity of the TSC1-TSC2-TBC1D7 Complex
The TSC1-TSC2-TBC1D7 complex is an important negative regulator of the mechanistic target of rapamycin complex 1 that controls cell growth in response to environmental cues. Inactivating TSC1 and TSC2 mutations cause tuberous sclerosis complex (TSC), an autosomal dominant disorder characterised by the occurrence of benign tumours in various organs and tissues, notably the brain, skin and kidneys. TBC1D7 mutations have not been reported in TSC patients but homozygous inactivation of TBC1D7 causes megaencephaly and intellectual disability. Here, using an exon-specific deletion strategy, we demonstrate that some regions of TSC1 are not necessary for the core function of the TSC1-TSC2 complex. Furthermore, we show that the TBC1D7 binding site is encoded by TSC1 exon 22 and identify amino acid residues involved in the TSC1-TBC1D7 interaction.
Santiago Lima, Arthur Jorge; Hoogeveen-Westerveld, Marianne; Nakashima, Akio; Maat-Kievit, Anneke; van den Ouweland, Ans; Halley, Dicky; Kikkawa, Ushio; Nellist, Mark
Mechanical support for isolated right ventricular failure in patients after cardiotomy
BackgroundPatients with acute right ventricular (RV) failure after cardiotomy have a poor prognosis. We evaluated the surgical and long-term outcomes of patients with isolated RV failure that required right ventricular assist device (RVAD) support.
Nader Moazami; Michael K. Pasque; Marc R. Moon; Rachel L. Herren; Marci S. Bailey; Jennifer S. Lawton; Ralph J. Damiano
The Mechanisms and Countermeasures of Failure in Low-Voltage Electronic Watt-Hour-Meters Caused by Lightning
NASA Astrophysics Data System (ADS)
Experimental study was carried out for classified a mechanism of failure of low-voltage electronic Watt-Hour Meters. As the results, the mechanism of failure of electronic meters is clarified into two patterns. One is due to the magnetic field generated by lightning current passing through the inside of an electronic meter. The other is due to the blow out of electric wire caused by lightning current flowing into the power supply circuit for processing unit. For these failure mechanisms, following counter measures were clarified. One is that a magnetic shielding measure using a metallic plate covering the processing unit was effective for reducing the magnetic field. The other measure is that a relocation of the ZnO device in the electronic meter was effective for reducing the lightning current flowing into the power supply circuit.
Asakawa, Akira; Hurukawa, Seiji; Takahashi, Akihisa; Ishimoto, Kazuyuki
Discovery of TBC1D1 as an Insulin-, AICAR-, and Contraction-stimulated Signaling Nexus in Mouse Skeletal Muscle*
The Akt substrate of 160 kDa (AS160) is phosphorylated on Akt substrate (PAS) motifs in response to insulin and contraction in skeletal muscle, regulating glucose uptake. Here we discovered a dissociation between AS160 protein expression and apparent AS160 PAS phosphorylation among soleus, tibialis anterior, and extensor digitorum longus muscles. Immunodepletion of AS160 in tibialis anterior muscle lysates resulted in minimal depletion of the PAS band at 160 kDa, suggesting the presence of an additional PAS immunoreactive protein. By immunoprecipitation and mass spectrometry, we identified this protein as the AS160 paralog TBC1D1, an obesity candidate gene regulating GLUT4 translocation in adipocytes. TBC1D1 expression was severalfold higher in skeletal muscles compared with all other tissues and was the dominant protein detected by the anti-PAS antibody at 160 kDa in tibialis anterior and extensor digitorum longus but not soleus muscles. In vivo stimulation by insulin, contraction, and the AMP-activated protein kinase (AMPK) activator AICAR increased TBC1D1 PAS phosphorylation. Using mass spectrometry on TBC1D1 from mouse skeletal muscle, we identified several novel phosphorylation sites on TBC1D1 and found the majority were consensus or near consensus sites for AMPK. Semiquantitative analysis of spectra suggested that AICAR caused greater overall phosphorylation of TBC1D1 sites compared with insulin. Purified Akt and AMPK phosphorylated TBC1D1 in vitro, and AMPK, but not Akt, reduced TBC1D1 electrophoretic mobility. TBC1D1 is a major PAS immunoreactive protein in skeletal muscle that is phosphorylated in vivo by insulin, AICAR, and contraction. Both Akt and AMPK phosphorylate TBC1D1, but AMPK may be the more robust regulator.
Taylor, Eric B.; An, Ding; Kramer, Henning F.; Yu, Haiyan; Fujii, Nobuharu L.; Roeckl, Katja S. C.; Bowles, Nicole; Hirshman, Michael F.; Xie, Jianxin; Feener, Edward P.; Goodyear, Laurie J.
Reliability characterizations and failure mechanism of ultra-thin oxides for MOS devices
NASA Astrophysics Data System (ADS)
The aggressive scaling of smaller/faster logic and memory devices demands accurate reliability characterization and knowledge of the failure mechanisms of ultra-thin (<30 A) silicon dioxide (SiO 2) layers in the gates of metal-oxide semiconductor (MOS) structures. The increased occurrence of soft breakdown in ultra-thin oxide films necessitates the development of more sophisticated techniques to detect breakdown. One such technique is by interrupting stress and monitoring stress-induced leakage current (SILC) or interface state density (Dit). The effect of interrupting stress was carefully studied and determined not to affect device lifetime. A comprehensive time-dependent dielectric breakdown (TDDB) study was conducted on ultra-thin oxide over a temperature ranging from 220�C to 350�C to study temperature acceleration. The results of the study showed that both hard and soft breakdown modes exhibit the same temperature dependence. The choice of a failure model for time/charge to breakdown (tBD /QBD) is critical for accurate reliability extrapolation. In this work, two more experiments were carried out to clarify the current physical mechanisms responsible to dielectric wear-out. The first experiment investigated the effects of pulsed biased stress on device lifetime. A lifetime enhancement under bipolar pulse stress was observed. The results suggest that previously proposed mechanism of hole de-trapping in thick oxide may not be responsible for the lifetime increase observed here for ultra-thin oxides. The second experiment studied the effects of heavy ion on the reliability of ultra-thin SiO2. Annealing and electron injection experiments on irradiated devices with heavy ion implied that holes were significantly created and trapped inside SiO2 without causing the SiO2 to breakdown. The results from these two studies suggest that breakdown of ultra-thin oxides is not caused by holes and that the anode hole injection (AHI) model for constant voltage stress (CVS) is unwarranted in the ultra-thin regime.
Wang, Bin
Interferometry of AlN-based microcantilevers to determine the material properties and failure mechanisms
NASA Astrophysics Data System (ADS)
Micro-electro-mechanical systems are exposed to a variety of environmental stimuli, making a prediction of operational reliability difficult. Here, we investigate environmental effects on properties of piezoelectrically actuated microcantilevers, where AlN is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under normal conditions. Investigated properties are defined for the static and dynamic behavior of microcantilevers. A Twyman-Green interferometer, operating in both stroboscopic regime and time-average interferometry mode, is used as a metrology tool. The initial deflection and frequency changes of the first resonance mode of the microcantilevers are monitored during accelerated thermal aging tests, humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests accelerated by application of a high voltage are accomplished to evaluate a lifetime of microcantilevers. Monitoring the micromechanical behaviors of devices driven by AlN during the lifetime tests assists monitoring of their long-term stability. FEM calculation is used to identify critical areas of stress concentration in the cantilever structure and to further explain various failure mechanisms.
Gorecki, Christophe; Krupa, Katarzyna; J�zwik, Micha?
Numerical modeling of the failure mechanisms in silicon thin film anode for lithium-ion batteries
NASA Astrophysics Data System (ADS)
In recent times, the demand for the storage of electrical energy has grown rapidly for both static applications and the portable electronics enforcing the substantial improvement in battery systems, and Li-ion batteries have been proven to have maximum energy storage density in all rechargeable batteries. However, major breakthroughs are required to consummate the requirement of higher energy density with lower cost to penetrate new markets. Graphite anode having limited capacity has become a bottle neck in the process of developing next generation batteries and can be replaced by higher capacity metals such as Silicon. In the present study we are focusing on the mechanical behavior of the Si-thin film anode under various operating conditions. A numerical model is developed to simulate the intercalation induced stress and the failure mechanism of the complex anode structure. Effect of the various physical phenomena such as diffusion induced stress, plasticity and the crack propagation are investigated to predict better performance parameters for improved design.
Patel, Siddharth H.
Mechanical Failure Begins Preferentially Near Resorption Cavities in Human Vertebral Cancellous Bone Under Compression
Summary The amount of bone turnover in the body has been implicated as a factor that can influence fracture risk and bone strength. Here we test the idea that remodeling cavities promote local tissue failure by determining if microscopic tissue damage (microdamage) caused by controlled loading in vitro is more likely to form near resorption cavities. Specimens of human vertebral cancellous bone (L4, 7 male and 2 female, age 70 � 10, mean � SD) were loaded in compression to the yield point, stained for microscopic tissue damage and submitted to three-dimensional fluorescent imaging using serial milling (image voxel size 0.7 � 0.7 � 5.0 �m). We found the resulting damage volume per bone volume (DV/BV) was correlated with percent eroded surface (p < 0.01, r2 = 0.65), demonstrating that whole specimen measures of resorption cavities and microdamage are related. Locations of microdamage were more than two times as likely to have a neighboring resorption cavity than randomly selected sites without microdamage (relative risk 2.39, 95% confidence interval of relative risk: 2.09 � 2.73), indicating a spatial association between resorption cavities and microdamage at the local level. Individual microdamage sites were 48,700 (40,100; 62,700) �m3 in size (median, 25th and 75th percentiles). That microdamage was associated with resorption cavities when measured at the whole specimen level as well as at the local level provides strong evidence that resorption cavities play a role in mechanical failure processes of cancellous bone and therefore have the potential to influence resistance to clinical fracture.
Slyfield, C.R.; Tkachenko, E.V.; Fischer, S.E.; Ehlert, K.M.; Yi, I. H.; Jekir, M. G.; O'Brien, R. G.; Keaveny, T.M.; Hernandez, C.J.
Three Potential Mechanisms for Failure of HIFU Ablation in Cardiac Tissue
Background High Intensity Focused Ultrasound (HIFU) has been introduced for treatment of cardiac arrhythmias, because it offers the ability to create rapid tissue modification in confined volumes without directly contacting the myocardium. In spite of the benefits of HIFU, a number of limitations have been reported, which hindered its clinical adoption. Methods and Results In this study, we used a multimodal approach to evaluate thermal and non-thermal effects of HIFU in cardiac ablation. We designed a computer-controlled system capable of simultaneous fluorescence mapping and HIFU ablation. Using this system, linear lesions were created in isolated rabbit atria (n = 6) and point lesions were created in the ventricles of whole-heart (n = 6) preparations by applying HIFU at clinical doses (4�16W). Additionally, we evaluate the gap size in ablation lines necessary for conduction in atrial preparations (n = 4). The voltage sensitive dye di-4-ANEPPS was used to assess functional damage produced by HIFU. Optical coherence tomography and general histology were used to evaluate lesion extent. Conduction block was achieved in 1 (17%) of 6 atrial preparations with a single ablation line. Following 10 minutes of rest, 0 (0%) of 6 atrial preparations demonstrated sustained conduction block from a single ablation line. Tissue displacement of 1�3mm was observed during HIFU application due to acoustic radiation force along the lesion line. Additionally, excessive acoustic pressure and high temperature from HIFU generated cavitation causing macroscopic tissue damage. A minimum gap size of 1.5mm was found to conduct electrical activity. Conclusions This study identified three potential mechanisms responsible for the failure of HIFU ablation in cardiac tissues. Both acoustic radiation force and acoustic cavitation in conjunction with inconsistent thermal deposition can increase the risk of lesion discontinuity and result in gap sizes that promote ablation failure.
Laughner, Jacob I.; Sulkin, Matthew S.; Wu, Ziqi; Deng, Cheri X.; Efimov, Igor R.
Damage and failure mechanisms of a 3-directional carbon/carbon composite under uniaxial tensile and shear loads
The mechanical behavior of a three-directional carbon/carbon (C/C) composite under tensile and shear loads is investigated in relation with the failure mechanisms and, the fiber architecture. This three-directional C/C composite was produced by Chemical Vapor Infiltration of a needled fiber preform of multiple layers of satin woven tows. The C/C composite exhibited several interesting features including an essentially non-linear stress-strain behavior and permanent deformations. Three families of matrix cracks were identified under tensile and shear loads, including microcracks in the tows, intertow delamination and cracks across the longitudinal tows. It was found that the delamination cracks affect preponderantly the stress-strain behavior and the mechanical properties. Similar features in the mechanical behavior and the failure mechanisms were highlighted under tension and under shear loading.
Siron, O.; Lamon, J. [CNRS-SEP-UB1, Pessac (France). Lab. des Composites Thermostructuraux] [CNRS-SEP-UB1, Pessac (France). Lab. des Composites Thermostructuraux
Impermeable Thin Al2O3 Overlay for TBC Protection from Sulfate and Vanadate Attack in Gas Turbines
Current advanced turbine system (ATS) requires thermal barrier coatings (TBCs) on turbine blades and vanes. The TBCs being specified, based on yttria stabilized zirconia (YSZ), have the limited durability for advanced industrial gas turbine applications that have longer durability requirements (30,000 hours versus <10,000 hours), particularly when dirty fuels are burned. Surface deposits (including molten sulfate and vanadate salts) can penetrate into porous TBCs and result in hot corrosion, leading to premature spalling. In the present project, it is planed to deposit a dense overlay Al2O3 on the surface of the YSZ coating to prevent YSZ coating from hot corrosion of deposits derived from combustion of low-grade fuel and air impurities. The dense overlay Al2O3 acts as a barrier to protect TBC and bond coat. The overlay Al2O3 will be deposited on the surface of the thermal barrier coating using physical vapor deposition (PVD) technique and solgel method, respectively. The hot corrosion resistance of the composite Al2O3/YSZ coating will be evaluated. The hot corrosion behavior of the Al2O3/YSZ/NiCrAlY/superalloy system will be compared with the YSZ/NiCrAlY/superalloy system. The corrosion behavior of the sol-gel-modified Al2O3/YSZ system will also be compared with that of the PVD-treated system. The mechanism of hot corrosion will be investigated. The processing-structure-properties relationship of the overlays will be determined. The implementation of the TBC technology is to improve the durability of turbine components and allow the service of turbines in fuels with impurity, which will contribute to the missions and goals of the DOE ''Vision 21'' R&D program in advanced materials, energy efficiency, environment stewardship and energy production.
Mao, Scott X.
TBC-8, a Putative RAB-2 GAP, Regulates Dense Core Vesicle Maturation in Caenorhabditis elegans
Dense core vesicles (DCVs) are thought to be generated at the late Golgi apparatus as immature DCVs, which subsequently undergo a maturation process through clathrin-mediated membrane remodeling events. This maturation process is required for efficient processing of neuropeptides within DCVs and for removal of factors that would otherwise interfere with DCV release. Previously, we have shown that the GTPase, RAB-2, and its effector, RIC-19, are involved in DCV maturation in Caenorhabditis elegans motoneurons. In rab-2 mutants, specific cargo is lost from maturing DCVs and missorted into the endosomal/lysosomal degradation route. Cargo loss could be prevented by blocking endosomal delivery. This suggests that RAB-2 is involved in retention of DCV components during the sorting process at the Golgi-endosomal interface. To understand how RAB-2 activity is regulated at the Golgi, we screened for RAB-2�specific GTPase activating proteins (GAPs). We identified a potential RAB-2 GAP, TBC-8, which is exclusively expressed in neurons and which, when depleted, shows similar DCV maturation defects as rab-2 mutants. We could demonstrate that RAB-2 binds to its putative GAP, TBC-8. Interestingly, TBC-8 also binds to the RAB-2 effector, RIC-19. This interaction appears to be conserved as TBC-8 also interacted with the human ortholog of RIC-19, ICA69. Therefore, we propose that a dynamic ON/OFF cycling of RAB-2 at the Golgi induced by the GAP/effector complex is required for proper DCV maturation.
Hannemann, Mandy; Sasidharan, Nikhil; Hegermann, Jan; Kutscher, Lena M.; Koenig, Sabine; Eimer, Stefan
TBC-8, a putative RAB-2 GAP, regulates dense core vesicle maturation in Caenorhabditis elegans.
Dense core vesicles (DCVs) are thought to be generated at the late Golgi apparatus as immature DCVs, which subsequently undergo a maturation process through clathrin-mediated membrane remodeling events. This maturation process is required for efficient processing of neuropeptides within DCVs and for removal of factors that would otherwise interfere with DCV release. Previously, we have shown that the GTPase, RAB-2, and its effector, RIC-19, are involved in DCV maturation in Caenorhabditis elegans motoneurons. In rab-2 mutants, specific cargo is lost from maturing DCVs and missorted into the endosomal/lysosomal degradation route. Cargo loss could be prevented by blocking endosomal delivery. This suggests that RAB-2 is involved in retention of DCV components during the sorting process at the Golgi-endosomal interface. To understand how RAB-2 activity is regulated at the Golgi, we screened for RAB-2-specific GTPase activating proteins (GAPs). We identified a potential RAB-2 GAP, TBC-8, which is exclusively expressed in neurons and which, when depleted, shows similar DCV maturation defects as rab-2 mutants. We could demonstrate that RAB-2 binds to its putative GAP, TBC-8. Interestingly, TBC-8 also binds to the RAB-2 effector, RIC-19. This interaction appears to be conserved as TBC-8 also interacted with the human ortholog of RIC-19, ICA69. Therefore, we propose that a dynamic ON/OFF cycling of RAB-2 at the Golgi induced by the GAP/effector complex is required for proper DCV maturation. PMID:22654674
Hannemann, Mandy; Sasidharan, Nikhil; Hegermann, Jan; Kutscher, Lena M; Koenig, Sabine; Eimer, Stefan
TBC1D24, an ARF6-interacting protein, is mutated in familial infantile myoclonic epilepsy.
Idiopathic epilepsies (IEs) are a group of disorders characterized by recurrent seizures in the absence of detectable brain lesions or metabolic abnormalities. IEs include common disorders with a complex mode of inheritance and rare Mendelian traits suggesting the occurrence of several alleles with variable penetrance. We previously described a large family with a recessive form of idiopathic epilepsy, named familial infantile myoclonic epilepsy (FIME), and mapped the disease locus on chromosome 16p13.3 by linkage analysis. In the present study, we found that two compound heterozygous missense mutations (D147H and A509V) in TBC1D24, a gene of unknown function, are responsible for FIME. In situ hybridization analysis revealed that Tbc1d24 is mainly expressed at the level of the cerebral cortex and the hippocampus. By coimmunoprecipitation assay we found that TBC1D24 binds ARF6, a Ras-related family of small GTPases regulating exo-endocytosis dynamics. The main recognized function of ARF6 in the nervous system is the regulation of dendritic branching, spine formation, and axonal extension. TBC1D24 overexpression resulted in a significant increase in neurite length and arborization and the FIME mutations significantly reverted this phenotype. In this study we identified a gene mutation involved in autosomal-recessive idiopathic epilepsy, unveiled the involvement of ARF6-dependent molecular pathway in brain hyperexcitability and seizures, and confirmed the emerging role of subtle cytoarchitectural alterations in the etiology of this group of common epileptic disorders. PMID:20727515
Falace, Antonio; Filipello, Fabia; La Padula, Veronica; Vanni, Nicola; Madia, Francesca; De Pietri Tonelli, Davide; de Falco, Fabrizio A; Striano, Pasquale; Dagna Bricarelli, Franca; Minetti, Carlo; Benfenati, Fabio; Fassio, Anna; Zara, Federico
TBC and PML conditions for 2D and 3D BPM: a comparison
Any implementation of the beam propagation method, when used to analyse open problems, requires a procedure allowing radiation to leave the computational window. In this paper we present the results of a case study on the effectiveness of the classical Hadley's Transparent Boundary Conditions (TBC) and the Perfectly Matched Layer (PML) to handle strong radiation at the boundaries. A polished
F. Fogli; G. Bellanca; P. Bassi
Study of thin biocovers (TBC) for oxidizing uncaptured methane emissions in bioreactor landfills
Bioreactor landfills are designed to accelerate municipal solid waste biodegradation and stabilization; however, the uncaptured methane gas escapes to the atmosphere during their filling. This research investigates the implementation of a novel methane emission control technique that involves thin biocovers (TBC) placed as intermediate waste covers to oxidize methane without affecting the operation of bioreactor landfills. Batch incubation experiments were
Konstantina Perdikea; Anil K. Mehrotra; J. Patrick A. Hettiaratchi
Special Education Management System Project Document. 3. Santa Cruz TBC Procedures.
ERIC Educational Resources Information Center
Presented in chart form with accompanying booklet is the Task Base Composite (TBC), part of the Santa Cruz Special Education Management System Project, which lists 700 staff tasks to aid in the administrative determination of personnel needs, deployment, and program costs. Listed tasks are either "Learner Line" (tasks directly involving or�
Santa Cruz County Superintendent of Schools, CA.
Two-source jumping beam evaporation for advanced EB-PVD TBC systems
The continuous increase of the turbine inlet temperature in gas turbines necessitates new TBCs with a temperature capability beyond the current partially yttria stabilized material coatings. The present paper focuses on two-source jumping EB-PVD processed novel candidate layers for future TBC applications. It is shown that mixtures of oxides with widely different vapor pressures can be manufactured by this technique.
U. Schulz; K. Fritscher; C. Leyens
Insulin stimulation regulates AS160 and TBC1D1 phosphorylation sites in human skeletal muscle
INTRODUCTION: Individuals with obesity and type 2 diabetes (T2D) are typically insulin resistant, exhibiting impaired skeletal muscle glucose uptake. Animal and cell culture experiments have shown that site-specific phosphorylation of the Rab-GTPase-activating proteins AS160 and TBC1D1 is critical for GLUT4 translocation facilitating glucose uptake, but their regulation in human skeletal muscle is not well understood. METHODS: Here, lean, obese and T2D subjects underwent a euglycemic-hyperinsulinemic clamp, and vastus lateralis muscle biopsies were obtained before, and at 30 and 180?min post insulin infusion. RESULTS: Obese and T2D subjects had higher body mass indexes and fasting insulin concentrations, and T2D subjects showed insulin resistance. Consistent with the clamp findings, T2D subjects had impaired insulin-stimulated phosphorylation of AS160 Thr642, a site previously shown to be important in glucose uptake in rodents. Interestingly, insulin-stimulated phosphorylation of TBC1D1 Thr590, a site shown to be regulated by insulin in rodents, was only increased in T2D subjects, although the functional significance of this difference is unknown. CONCLUSION: These data show that insulin differentially regulates AS160 and TBC1D1 phosphorylation in human skeletal muscle. Impaired insulin-stimulated glucose uptake in T2D subjects is accompanied by dysregulation of AS160 and TBC1D1 phosphorylation in skeletal muscle, suggesting that these proteins may regulate glucose uptake in humans.
Middelbeek, R J W; Chambers, M A; Tantiwong, P; Treebak, J T; An, D; Hirshman, M F; Musi, N; Goodyear, L J
Crystal Structures of Human TBC1D1 and TBC1D4 (AS160) RabGTPase-activating Protein (RabGAP) Domains Reveal Critical Elements for GLUT4 Translocation*
We have solved the x-ray crystal structures of the RabGAP domains of human TBC1D1 and human TBC1D4 (AS160), at 2.2 and 3.5 � resolution, respectively. Like the yeast Gyp1p RabGAP domain, whose structure was solved previously in complex with mouse Rab33B, the human TBC1D1 and TBC1D4 domains both have 16 ?-helices and no ?-sheet elements. We expected the yeast Gyp1p RabGAP/mouse Rab33B structure to predict the corresponding interfaces between cognate mammalian RabGAPs and Rabs, but found that residues were poorly conserved. We further tested the relevance of this model by Ala-scanning mutagenesis, but only one of five substitutions within the inferred binding site of the TBC1D1 RabGAP significantly perturbed catalytic efficiency. In addition, substitution of TBC1D1 residues with corresponding residues from Gyp1p did not enhance catalytic efficiency. We hypothesized that biologically relevant RabGAP/Rab partners utilize additional contacts not described in the yeast Gyp1p/mouse Rab33B structure, which we predicted using our two new human TBC1D1 and TBC1D4 structures. Ala substitution of TBC1D1 Met930, corresponding to a residue outside of the Gyp1p/Rab33B contact, substantially reduced catalytic activity. GLUT4 translocation assays confirmed the biological relevance of our findings. Substitutions with lowest RabGAP activity, including catalytically dead RK and Met930 and Leu1019 predicted to perturb Rab binding, confirmed that biological activity requires contacts between cognate RabGAPs and Rabs beyond those in the yeast Gyp1p RabGAP/mouse Rab33B structure.
Park, Sang-Youn; Jin, Wanzhu; Woo, Ju Rang; Shoelson, Steven E.
High levels of B-type natriuretic peptide predict weaning failure from mechanical ventilation in adult patients after cardiac surgery
OBJECTIVE: The failure to wean from mechanical ventilation is related to worse outcomes after cardiac surgery. The aim of this study was to evaluate whether the serum level of B-type natriuretic peptide is a predictor of weaning failure from mechanical ventilation after cardiac surgery. METHODS: We conducted a prospective, observational cohort study of 101 patients who underwent on-pump coronary artery bypass grafting. B-type natriuretic peptide was measured postoperatively after intensive care unit admission and at the end of a 60-min spontaneous breathing test. The demographic data, hemodynamic and respiratory parameters, fluid balance, need for vasopressor or inotropic support, and length of the intensive care unit and hospital stays were recorded. Weaning failure was considered as either the inability to sustain spontaneous breathing after 60 min or the need for reintubation within 48 h. RESULTS: Of the 101 patients studied, 12 patients failed the weaning trial. There were no differences between the groups in the baseline or intraoperative characteristics, including left ventricular function, EuroSCORE and lengths of the cardiac procedure and cardiopulmonary bypass. The B-type natriuretic peptide levels were significantly higher at intensive care unit admission and at the end of the breathing test in the patients with weaning failure compared with the patients who were successfully weaned. In a multivariate model, a high B-type natriuretic peptide level at the end of a spontaneous breathing trial was the only independent predictor of weaning failure from mechanical ventilation. CONCLUSIONS: A high B-type natriuretic peptide level is a predictive factor for the failure to wean from mechanical ventilation after cardiac surgery. These findings suggest that optimizing ventricular function should be a goal during the perioperative period.
Lara, Thiago Martins; Hajjar, Ludhmila Abrahao; de Almeida, Juliano Pinheiro; Fukushima, Julia Tizue; Barbas, Carmem Silvia Valente; Rodrigues, Adriano Rogerio Baldacin; Nozawa, Emilia; Feltrim, Maria Ignes Zanetti; Almeida, Elisangela; Coimbra, Vera; Osawa, Eduardo; de Moraes Ianotti, Rafael; Leme, Alcino Costa; Jatene, Fabio Biscegli; Auler-Jr., Jose Otavio Costa; Galas, Filomena Regina Barbosa Gomes
Impaired insulin-induced site-specific phosphorylation of TBC1 domain family, member 4 (TBC1D4) in skeletal muscle of type 2 diabetes patients is restored by endurance exercise-training
Aims\\/hypothesis��Insulin-mediated glucose disposal rates (R\\u000a d) are reduced in type 2 diabetic patients, a process in which intrinsic signalling defects are thought to be involved. Phosphorylation\\u000a of TBC1 domain family, member 4 (TBC1D4) is at present the most distal insulin receptor signalling event linked to glucose\\u000a transport. In this study, we examined insulin action on site-specific phosphorylation of TBC1D4 and
B. F. Vind; C. Pehm�ller; J. T. Treebak; J. B. Birk; M. Hey-Mogensen; H. Beck-Nielsen; J. R. Zierath; J. F. P. Wojtaszewski; K. H�jlund
Tbc1d1 mutation in lean mouse strain confers leanness and protects from diet-induced obesity.
We previously identified Nob1 as a quantitative trait locus for high-fat diet-induced obesity and diabetes in genome-wide scans of outcross populations of obese and lean mouse strains. Additional crossbreeding experiments indicated that Nob1 represents an obesity suppressor from the lean Swiss Jim Lambert (SJL) strain. Here we identify a SJL-specific mutation in the Tbc1d1 gene that results in a truncated protein lacking the TBC Rab-GTPase-activating protein domain. TBC1D1, which has been recently linked to human obesity, is related to the insulin signaling protein AS160 and is predominantly expressed in skeletal muscle. Knockdown of TBC1D1 in skeletal muscle cells increased fatty acid uptake and oxidation, whereas overexpression of TBC1D1 had the opposite effect. Recombinant congenic mice lacking TBC1D1 showed reduced body weight, decreased respiratory quotient, increased fatty acid oxidation and reduced glucose uptake in isolated skeletal muscle. Our data strongly suggest that mutation of Tbc1d1 suppresses high-fat diet-induced obesity by increasing lipid use in skeletal muscle. PMID:18931681
Chadt, Alexandra; Leicht, Katja; Deshmukh, Atul; Jiang, Lake Q; Scherneck, Stephan; Bernhardt, Ulrike; Dreja, Tanja; Vogel, Heike; Schmolz, Katja; Kluge, Reinhart; Zierath, Juleen R; Hultschig, Claus; Hoeben, Rob C; Sch�rmann, Annette; Joost, Hans-Georg; Al-Hasani, Hadi
Conventional knockout of Tbc1d1 in mice impairs insulin- and AICAR-stimulated glucose uptake in skeletal muscle.
In the obesity-resistant SJL mouse strain, we previously identified a naturally occurring loss-of-function mutation in the gene for Tbc1d1. Characterization of recombinant inbred mice that carried the Tbc1d1(SJL) allele on a C57BL/6J background indicated that loss of TBC1D1 protects from obesity, presumably by increasing the use of fat as energy source. To provide direct functional evidence for an involvement of TBC1D1 in energy substrate metabolism, we generated and characterized conventional Tbc1d1 knockout mice. TBC1D1-deficient mice showed moderately reduced body weight, decreased respiratory quotient, and an elevated resting metabolic rate. Ex vivo analysis of intact isolated skeletal muscle revealed a severe impairment in insulin- and AICAR-stimulated glucose uptake in glycolytic extensor digitorum longus muscle and a substantially increased rate of fatty acid oxidation in oxidative soleus muscle. Our results provide direct evidence that TBC1D1 plays a major role in glucose and lipid utilization, and energy substrate preference in skeletal muscle. PMID:23892475
Dokas, Janine; Chadt, Alexandra; Nolden, Tobias; Himmelbauer, Heinz; Zierath, Juleen R; Joost, Hans-Georg; Al-Hasani, Hadi
Arteriovenous fistula-associated high-output cardiac failure: a review of mechanisms
High-output cardiac failure can be a rare complication of high-output arterioveous fistula. The authors present a case in which a hemodialysis patient with a high-flow arteriovenous fistula has cardiac failure that improves with fistula closure. The hemodynamic effects of a fistula are reviewed, and the hemodialysis literature regarding high-output cardiac failure is summarized. To gain insight into the problem of
Jennifer M MacRae; Sanjay Pandeya; Dennis P Humen; Nikolai Krivitski; Robert M Lindsay
Investigating compression failure mechanisms in composite laminates with a transparent fiberglass-epoxy birefringent materials
NASA Technical Reports Server (NTRS)
The response and failure of a + or - 45s class laminate was studied by transparent fiberglass epoxy composite birefringent material. The birefringency property allows the laminate stress distribution to be observed during the test and also after the test if permanent residual stresses occur. The location of initial laminate failure and of the subsequent failure propagation are observed through its transparency characteristics. Experimental results are presented.
Shuart, M. J.; Williams, J. G.
Advanced composites: Design and application. Proceedings of the meeting of the Mechanical Failures Prevention Group
NASA Technical Reports Server (NTRS)
The design and application of advanced composites is discussed with emphasis on aerospace, aircraft, automotive, marine, and industrial applications. Failure modes in advanced composites are also discussed.
Shives, T. R.; Willard, W. A.
A Probe on the Failure Mechanism in Rubber-Modified Epoxy Blends: Morphological and Acoustic Emission Analysis
In this work, diglycidyl ether of bisphenol A based epoxy resin (DGEBA) was modified with varying amounts of two liquid rubbers: carboxyl terminated copolymer of butadiene and acrylonitrile (CTBN); and a hydroxyl terminated polybutadiene (HTPB), using an anhydride hardener. The ultimate aim of this study was to investigate the failure mechanism operating in the rubber-modified epoxies and to evaluate this
Raju Thomas; F. Ronkay; T. Czigany; Uro� Cvelbac; Miran Mozetic; Sabu Thomas
Direct evidence for central proinflammatory mechanisms in rats with experimental acute liver failure: protective effect of hypothermia
It has been proposed that proinflammatory mechanisms are involved in the pathogenesis of brain edema in acute liver failure (ALF). The aim of this study was to assess the contribution of cerebral inflammation to the neurologic complications of ALF and to assess the antiinflammatory effect of mild hypothermia. Upregulation of CD11b\\/c immunoreactivity, consistent with microglial activation, was observed in the
Wenlei Jiang; Paul Desjardins; Roger F Butterworth
Microstructures and Failure Mechanisms of Spot Friction Welds in Lap-Shear Specimens of Aluminum 5754 Sheets
Microstructures and failure mechanisms of spot friction welds (SFW) in aluminum 5754 lap-shear specimens were investigated. In order to study the effect of tool geometry on the joint strength of spot friction welds, a concave tool and a flat tool were used. In order to understand the effect of tool penetration depth on the joint strength, spot friction welds were
S. G. Arul; T. Pan; Z. Feng; M. L. Santella
The Role of the Concentration Mechanism in the Development of Acute Renal Failure: Micropuncture Studies Using Diabetes Insipidus Rats
Summary The role of the concentrating mechanism in the potentiation of acute renal failure by dehydration has been studied using rats with complete diabetes insipidus. These rats were shown to be continually dehydrated even when allowed free access to water. Despite massive volumes of highly dilute urine at the time that hemoglobinuria was induced by glycerol injection, these animals developed
D. R. Wilson; G. Thiel; M. L. Arce; D. E. Oken
Oxidation-induced failure of thermal barrier coatings. Annual report, 1 October 1997--31 October 1998
On prolonged high-temperature exposure in air, thermal barrier coatings (TBCs) on bond-coated superalloys fail by spalling. The author has focused on identifying the underlying mechanisms of failure and sought to establish whether it is a direct consequence of the failure of the underlying thermally grown oxide. He has discovered a new TBC failure mode, one in which failure is associated with moisture-enhanced sub-critical crack-growth along the bond-coat/thermally grown oxide interface. New insights into the mechanism underlying failure of the thermally grown oxide have come from direct optical microscopy. These indicate that failure is associated with surface roughness of the bond-coat and specifically that the thermally-grown oxide separates from the bond-coat on cooling at the concave (`crests`) surface features. These locally separated regions grow with oxidation time and are seen to link-up. These events are believed to be the precursor events that grow to provide the critical-sized flaws from which buckling and spalling of thermal barrier coatings occur.
Clarke, D.R.
Embryo malposition as a potential mechanism for mercury-induced hatching failure in bird eggs.
We examined the prevalence of embryo malpositions and deformities in relation to total mercury (THg) and selenium (Se) concentrations in American avocet (Recurvirostra americana), black-necked stilt (Himantopus mexicanus), and Forster's tern (Sterna forsteri) eggs in San Francisco Bay (CA, USA) during 2005 to 2007. Overall, 11% of embryos were malpositioned in eggs > or =18 d of age (n = 282) and 2% of embryos were deformed in eggs > or =13 d of age (n = 470). Considering only those eggs that failed to hatch (n = 62), malpositions occurred in 24% of eggs > or =18 d of age and deformities occurred in 7% of eggs > or =13 d of age. The probability of an embryo being malpositioned increased with egg THg concentrations in Forster's terns, but not in avocets or stilts. The probability of embryo deformity was not related to egg THg concentrations in any species. Using a reduced dataset with both Se and THg concentrations measured in eggs (n = 87), we found no interaction between Se and THg on the probability of an embryo being malpositioned or deformed. Results of the present study indicate that embryo malpositions were prevalent in waterbird eggs that failed to hatch and the likelihood of an embryo being malpositioned increased with egg THg concentrations in Forster's terns. We hypothesize that malpositioning of avian embryos may be one reason for mercury-related hatching failure that occurs late in incubation, but further research is needed to elucidate this potential mechanism. PMID:20821633
Herring, Garth; Ackerman, Joshua T; Eagles-Smith, Collin A
Mechanical failure of unsupported Huckstep intramedullary nail in malignant bone tumor reconstruction.
Seventeen segmental resections of diaphyseal tumors and five knee resection arthrodeses were reconstructed using the Huckstep nail with intercalary bone grafts (fibula), cementation, and ceramic and titanium spacers. Although the bone defects were 0 to 25.5 cm in length (mean, 13.1 cm), all patients had relief of pain and were able to move alone with a wheelchair or a cane. Nail breakage occurred in four patients who had reconstruction surgery using a ceramic spacer (four patients without intercalary fibula graft and one patient with intercalary fibula graft). The nail survival rate was significantly better in the patients with reinforcement by vascularized fibular graft (100% at 5 years and 75% at 10 years; n = 8) than in the patients without reinforcement by vascularized fibular graft (87.5% at 3 years and 0% at 5 years; n = 14). Huckstep nailing is a useful option for reconstruction of large bone defects in diaphyseal tumors and knee resection arthrodesis. It should be used in combination with a vascularized fibula graft to prevent mechanical failure and to achieve durability of limbs with defects from primary bone tumors. Huckstep nailing with nonbiologic augmentation is good for palliative surgery for bone metastases in patients with a shorter expected survival rate. PMID:11764359
Abe, S; Tateishi, A; Tokizaki, T; Takeyama, S; Nakano, H; Matsushita, T
Embryo malposition as a potential mechanism for mercury-induced hatching failure in bird eggs
We examined the prevalence of embryo malpositions and deformities in relation to total mercury (THg) and selenium (Se) concentrations in American avocet (Recurvirostra americana), black-necked stilt (Himantopus mexicanus), and Forster's tern (Sterna forsteri) eggs in San Francisco Bay (CA, USA) during 2005 to 2007. Overall, 11% of embryos were malpositioned in eggs ???18 d of age (n=282) and 2% of embryos were deformed in eggs ???13 d of age (n=470). Considering only those eggs that failed to hatch (n=62), malpositions occurred in 24% of eggs ???18 d of age and deformities occurred in 7% of eggs ???13 d of age. The probability of an embryo being malpositioned increased with egg THg concentrations in Forster's terns, but not in avocets or stilts. The probability of embryo deformity was not related to egg THg concentrations in any species. Using a reduced dataset with both Se and THg concentrations measured in eggs (n=87), we found no interaction between Se and THg on the probability of an embryo being malpositioned or deformed. Results of the present study indicate that embryo malpositions were prevalent in waterbird eggs that failed to hatch and the likelihood of an embryo being malpositioned increased with egg THg concentrations in Forster's terns. We hypothesize that malpositioning of avian embryos may be one reason for mercury-related hatching failure that occurs late in incubation, but further research is needed to elucidate this potential mechanism. ?? 2010 SETAC.
Herring, G.; Ackerman, J. T.; Eagles-Smith, C. A.
A neural mechanism underlying failure of optimal choice with multiple alternatives.
Despite widespread interest in neural mechanisms of decision-making, most investigations focus on decisions between just two options. Here we adapt a biophysically plausible model of decision-making to predict how a key decision variable, the value difference signal-encoding how much better one choice is than another-changes with the value of a third, but unavailable, alternative. The model predicts a surprising failure of optimal decision-making: greater difficulty choosing between two options in the presence of a third very poor, as opposed to very good, alternative. Both investigation of human decision-making and functional magnetic resonance imaging-based measurements of value difference signals in ventromedial prefrontal cortex (vmPFC) bore out this prediction. The vmPFC signal decreased in the presence of low-value third alternatives, and vmPFC effect sizes predicted individual variation in suboptimal decision-making in the presence of multiple alternatives. The effect contrasts with that of divisive normalization in parietal cortex. PMID:24509428
Chau, Bolton K H; Kolling, Nils; Hunt, Laurence T; Walton, Mark E; Rushworth, Matthew F S
Beneficial effects of yttrium on the mechanical failure and chemical stability of the passive film of 304 stainless steel
Recent studies demonstrated that yttrium improved the resistance of stainless steel to corrosive wear. However, the mechanism responsible for the beneficial effect of yttrium was not well understood. In this work, the breakdown of passive films of Y-free and Y-containing 304 stainless steel specimens during indentation and scratch testing was studied using a micro-mechanical probe. The failure of the passive
X. Y. Wang; D. Y. Li
Impact of left ventricular diastolic function on left atrial mechanics in systolic heart failure.
The relation between left atrial (LA) mechanics and left ventricular (LV) diastolic function and adverse cardiovascular events are not well established in chronic systolic heart failure (HF). In 108 patients, we performed comprehensive echocardiography with an assessment of LA global longitudinal strain (LA?) by Velocity Vector Imaging. We also performed complete diastolic examinations including mitral inflow, pulmonary vein flow, and tissue Doppler. Death, cardiac transplantation, and HF hospitalization were tracked for 5 years. In our study cohort (age 57 � 15 years, LV ejection fraction 25 � 6%), mean global LA negative (?negative), positive (?positive), and total ? (?total) were -6.8 � 4.4%, 7.7 � 5.7%, and 14.5 � 8.2%, respectively. All LA? indexes correlated with individual indexes of LV diastolic dysfunction, including mitral flow early (E) to late diastolic velocity ratio (p <0.05 for all), mitral deceleration time (p <0.01 for all), E to early diastolic velocity of the septal mitral annulus (e') ratio (p <0.05 for all), pulmonary vein flow systolic to diastolic velocity ratio (p <0.001 for all), and maximal LA volume index (p <0.01 for all). All LA? indexes increased across diastolic stage (p <0.001 for all). In multivariate logistic regression analysis, LA?negative and LA?total were associated with the presence of LV diastolic dysfunction grade III even after adjustment for E/e' septal and LA volume index. In Cox proportional hazards analysis, lower magnitude LA?negative predicted long-term adverse clinical events. In conclusion, more impaired LA mechanics are associated with more severe diastolic dysfunction and predict long-term adverse events in patients with chronic systolic HF. PMID:23764244
Motoki, Hirohiko; Borowski, Allen G; Shrestha, Kevin; Troughton, Richard W; Martin, Maureen G; Tang, W H Wilson; Klein, Allan L
Thermal cycling behavior and failure mechanism of LaTi 2Al 9O 19\\/YSZ thermal barrier coatings exposed to gas flame
As a potential thermal barrier coating (TBC) material, lanthanum titanium aluminum oxide (LaTi2Al9O19, LTA) possesses excellent phase stability between room temperature and 1600�C and desirable thermo-physical properties, but its thermal cycling performance is rather poor partially due to the low fracture toughness. In this work, LTA\\/yttria stabilized zirconia (YSZ) double ceramic layer TBC was prepared and its thermal cycling lifetime
Xiaoyun Xie; Hongbo Guo; Shengkai Gong; Huibin Xu
Modelling river bank erosion processes and mass failure mechanisms using 2-D depth averaged numerical model
NASA Astrophysics Data System (ADS)
Bank erosion is a key process that may cause a large number of economic and environmental problems (e.g. land loss, damage to structures and aquatic habitat). Stream bank erosion (toe erosion and mass failure) represents an important form of channel morphology changes and a significant source of sediment. With the advances made in computational techniques, two-dimensional (2-D) numerical models have become valuable tools for investigating flow and sediment transport in open channels at large temporal and spatial scales. However, the implementation of mass failure process in 2D numerical models is still a challenging task. In this paper, a simple, innovative algorithm is implemented in the Telemac-Mascaret modeling platform to handle bank failure: failure occurs whether the actual slope of one given bed element is higher than the internal friction angle. The unstable bed elements are rotated around an appropriate axis, ensuring mass conservation. Mass failure of a bank due to slope instability is applied at the end of each sediment transport evolution iteration, once the bed evolution due to bed load (and/or suspended load) has been computed, but before the global sediment mass balance is verified. This bank failure algorithm is successfully tested using two laboratory experimental cases. Then, bank failure in a 1:40 scale physical model of the Rhine River composed of non-uniform material is simulated. The main features of the bank erosion and failure are correctly reproduced in the numerical simulations, namely the mass wasting at the bank toe, followed by failure at the bank head, and subsequent transport of the mobilised material in an aggradation front. Volumes of eroded material obtained are of the same order of magnitude as the volumes measured during the laboratory tests.
Die Moran, Andres; El kadi Abderrezzak, Kamal; Tassi, Pablo; Herouvet, Jean-Michel
Protective effect and mechanism of stronger neo-minophagen C against fulminant hepatic failure
AIM: To investigate the protective effect of stronger neo-minophafen C (SNMC) on fulminant hepatic failure (FHF) and its underlying mechanism. METHODS: A mouse model of FHF was established by intraperitoneal injection of galactosamine (D-Gal N) and lipopolysaccharide (LPS). The survival rate, liver function, inflammatory factor and liver pathological change were obtained with and without SNMC treatment. Hepatocyte survival was estimated by observing the stained mitochondria structure with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate fluorescence nick end labeling (TUNEL) method and antibodies against cytochrome C (Cyt-C) and caspase-3. RESULTS: The levels of plasma tumor necrosis factor alpha (TNF-?), nitric oxide (NO), ET-1, interleukin-6 (IL-6), and the degree of hepatic tissue injury were decreased in the SNMC-treated groups compared with those in the model group (P < 0.01). However, there were no differences after different dosages administered at different time points. There was a significant difference in survival rates between the SNMC-treated groups and the model group (P < 0.01). The apoptosis index was 32.3% at 6 h after a low dose of SNMC, which was considerably decreased from 32.3% � 4.7% vs 5% � 2.83% (P < 0.05) to 5% on d 7. The expression of Cyt-C and caspase-3 decreased with the prolongation of therapeutic time. Typical hepatocyte apoptosis was obviously ameliorated under electron microscope with the prolongation of therapeutic time. CONCLUSION: SNMC can effectively protect liver against FHF induced by LPS/D-Gal N. SNMC can prevent hepatocyte apoptosis by inhibiting inflammatory reaction and stabilizing mitochondria membrane to suppress the release of Cyt-C and sequent activation of caspase-3.
Yang, Bao-Shan; Ma, Ying-Ji; Wang, Yan; Chen, Li-Yan; Bi, Man-Ru; Yan, Bing-Zhu; Bai, Lu; Zhou, Hui; Wang, Fu-Xiang
Platelet aggregation measurement for assessment of hemostasis failure mechanisms in patients with gastroduodenal ulcer bleeding
Background The purpose of this study was to identify factors associated with the risk of unsustainable hemostasis in patients with gastric and duodenal ulcer bleeding by in vitro assessment of platelet reactivity using artificial neural networks. Methods Patients with gastroduodenal ulcers complicated by bleeding were studied. Platelet aggregation was measured using aggregometry with adenosine diphosphate 5 ?M, epinephrine 2.5 ?M, 5-hydroxytryptophan 10 ?M, collagen 1 ?M, and thrombin 0.06 NIH Unit/mL as agonists. Multiple logistic regression was used to evaluate the independent relationship between demographic, clinical, endoscopic, and laboratory data and in vitro assessment of platelet reactivity and local parameters of hemostasis in patients with ulcer bleeding. Results Analysis of platelet aggregation in patients with gastroduodenal ulcer bleeding allowed the variability of platelet response to different agonists used in effective concentration which induces 50% platelet aggregation (EC50) to be established. The relationship between platelet aggregation and the spatial-temporal characteristics of ulcers complicated by bleeding was demonstrated. Adrenoreactivity of platelets was associated with time elapsed since the start of ulcer bleeding and degree of hemorrhage. The lowest platelet response to collagen and thrombin was detected in patients with active bleeding (P < 0.001) and unsustainable recent bleeding (P < 0.01). Decreased adenosine diphosphate-induced platelet aggregation in patients with ulcer bleeding was correlated with the platelet response to thrombin (r = 0.714, P < 0.001) and collagen (r = 0.584, P < 0.01). Conclusion Estimation of platelet reactivity in vitro indicates the key mechanisms of failure of hemostasis in patients with ulcer bleeding. In addition to gender, an important determinant of unsustainable hemostasis was a decreased platelet response to thrombin and adenosine diphosphate.
Barinov, Edward; Sulaieva, Oksana; Lyakch, Yuriy; Guryanov, Vitaliy; Kondratenko, Petr; Radenko, Yevgeniy
Hill Slope Failure as a Mechanism to Resurface Asteroids During Planetary Flybys
NASA Astrophysics Data System (ADS)
Laboratory measurements of meteorite reflectance spectra rarely match telescopic observations of asteroid reflectance spectra. This difference is likely due to the process(es) of space weathering, which rapidly redden asteroid surfaces on million year timescales (e.g. Chapman 2004, Annu. Rev. Earth Planet. Sci. 32, 539). While nearly all Main Belt asteroids are �weathered,� many asteroids on terrestrial planet crossing orbits appear �unweathered� (Marchi et al., 2006, MNRAS 368, L39). Numerical integration of the orbits of these unweathered asteroids suggest that close approaches within 16 Earth radii may reset the surfaces of asteroids, and erase the signatures of space weathering (Binzel et al. 2010, Nature 463, 331; Nesvorny et al. 2010, Icarus 209, 510). Despite the evidence that close approaches may play a role in resurfacing asteroids, the specific resurfacing mechanism is unknown. I hypothesize that tidal perturbations during planetary close approaches trigger debris flows, which resurface portions of the asteroid. I have developed an original numerical model for evaluating the stability of hill slopes on rigid asteroids of arbitrary shape, density, and spin during planetary flybys. I present preliminary results for a limited range of asteroid and flyby parameters, which suggest that significant fractions of the asteroid surface (a few percent) can become unstable to hill slope failure during flybys with close approach distances out to ~10 Earth radii. In future work, I will explore a range of asteroid and flyby parameters, in order to better constrain the critical distance required for resetting asteroid surfaces. By characterizing this critical distance, it may be possible to better constrain the space weathering rate on asteroids.
Keane, James; Matsuyama, I.
Regulatory mode shift of Tbc1d1 is required for acquisition of insulin-responsive GLUT4-trafficking activity
Tbc1d1 is key to skeletal muscle GLUT4 regulation. By using GLUT4 nanometry combined with a cell-based reconstitution model, we uncover a shift in the regulatory mode of Tbc1d1 by showing that Tbc1d1 temporally acquires insulin responsiveness, which triggers GLUT4 trafficking only after an exercise-mimetic stimulus such as aminoimidazole carboxamide ribonucleotide (AICAR) pretreatment. The functional acquisition of insulin responsiveness requires Ser-237 phosphorylation and an intact phosphotyrosine-binding (PTB) 1 domain. Mutations in PTB1, including R125W (a natural mutant), thus result in complete loss of insulin-responsiveness acquisition, whereas AICAR-responsive GLUT4-liberation activity remains intact. Thus our data provide novel insights into temporal acquisition/memorization of Tbc1d1 insulin responsiveness, relying on the PTB1 domain, possibly a key factor in the beneficial effects of exercise on muscle insulin potency.
Hatakeyama, Hiroyasu; Kanzaki, Makoto
Wheel Failure Mechanisms of Railroad Cars. Final Report. Volume 2 (Technical Task Summaries).
National Technical Information Service (NTIS)
The report presents the results of an extensive study into the causes of thermally induced wheel failure. Major issues addressed include the effects of wheel plate design, heat-treatment, ability to resist thermal damage, the relationship between discolor...
B. R. Rajkumar D. H. Stone
Failure characteristics during cyclic oxidation of yttria stabilized zirconia thermal barrier coatings deposited via electron beam physical vapor deposition on platinum aluminide and on NiCoCrAlY bond coats with processing modifications for improved performances
In this study, the cyclic oxidation lives of the current state-of-the-art thermal barrier coating (TBC) systems (heavy grit-blasted\\u000a Pt aluminide and NiCoCrAlY bond coats with EBPVD TBCs) were investigated first, followed by TBC systems that were modified\\u000a based on the results obtained on the failure of the state-of-the-art TBC systems. The specimens were subjected to cyclic oxidation\\u000a testing, mostly at
N. M. Yanar; F. S. Pettit; G. H. Meier
Mechanics of progressive failures leading to rapid shallow landslides using the fiber bundle model
NASA Astrophysics Data System (ADS)
Shallow landslides are often sudden events caused by the rapid failure of a slip surface. Yet, such global failure is the culmination of a series of steps that begin with the initiation and growth of local cracks and failure planes that, with increased load eventually coalesce to form a continuous surface. The dynamics of such failure events is controlled, in part, by the rate of soil weakening during water infiltration and by distribution of tree roots that span across these failure zones. Conventional approaches rely on static limit-equilibrium analysis to compute the ratio of soil resistive strength to gravitational driving forces (factor of safety) to determine slope stability, often ignoring dynamics leading to failure as well as heterogeneities associated with land cover, subsurface material properties, hydrologic pathways, and presence of biological elements such as roots. Casting the problem in terms of stable or unstable slope does not describe the progressive formation of cracks in heterogeneous soils or the failure of roots that stretch across tension cracks or basal shear planes. Here we use the fiber bundle model (FBM) to describe soil and root failure focusing on landslide initiation. The FBM consists of a bundle of parallel, elastic-brittle fibers of identical length and stiffness stretched quasi-statically between two plates. Heterogeneity is introduced by fibers having finite threshold strength drawn randomly from a probability density function. Step-loading of the bundle causes weak fibers to break and load redistribution (either global or local) among surviving fibers can trigger secondary, tertiary, and so on, failures, a process known as an avalanche. We illustrate the potential utility of the FBM for two cases: (1) modeling of lateral root reinforcement where fibers represent roots of different sizes and strengths, and (2) modeling of progressive weakening of soils by water infiltration where fibers are analogs of bonds between soil aggregates whose strength distribution evolves with changes in water content. The main advantages of the fiber bundle model is its ability to account for progressive failure and heterogeneities of soils on slopes, to describe the complex rheological behavior of soils and soil elements such as roots using simple basic blocks (the fibers) whose properties can be directly related to the properties of the materials, and to represent physical processes of failure in soils and roots.
Cohen, Denis; Schwarz, Massimiliano; Or, Dani
Mechanics, energetics, and crossbridge kinetics of rabbit diaphragm during congestive heart failure
Crossbridge (CB) properties were in- vestigated in isolated diaphragm of rabbits during congestive heart failure (CHF, n�9) induced by chronic volume and pressure overload. This model induced cardiac hypertrophy and heart failure. Con- trols (C) were prepared (n�14). Compared to C, peak tension in CHF fell by 57% in twitch and by 40% in tetanus; Vmax declined by 47% in
A truncation mutation in TBC1D4 in a family with acanthosis nigricans and postprandial hyperinsulinemia.
Tre-2, BUB2, CDC16, 1 domain family member 4 (TBC1D4) (AS160) is a Rab-GTPase activating protein implicated in insulin-stimulated glucose transporter 4 (GLUT4) translocation in adipocytes and myotubes. To determine whether loss-of-function mutations in TBC1D4 might impair GLUT4 translocation and cause insulin resistance in humans, we screened the coding regions of this gene in 156 severely insulin-resistant patients. A female presenting at age 11 years with acanthosis nigricans and extreme postprandial hyperinsulinemia was heterozygous for a premature stop mutation (R363X) in TBC1D4. After demonstrating reduced expression of wild-type TBC1D4 protein and expression of the truncated protein in lymphocytes from the proband, we further characterized the biological effects of the truncated protein in 3T3L1 adipocytes. Prematurely truncated TBC1D4 protein tended to increase basal cell membrane GLUT4 levels (P = 0.053) and significantly reduced insulin-stimulated GLUT4 cell membrane translocation (P < 0.05). When coexpressed with wild-type TBC1D4, the truncated protein dimerized with full-length TBC1D4, suggesting that the heterozygous truncated variant might interfere with its wild-type counterpart in a dominant negative fashion. Two overweight family members with the mutation also manifested normal fasting glucose and insulin levels but disproportionately elevated insulin levels following an oral glucose challenge. This family provides unique genetic evidence of TBC1D4 involvement in human insulin action. PMID:19470471
Dash, Satya; Sano, Hiroyuki; Rochford, Justin J; Semple, Robert K; Yeo, Giles; Hyden, Caroline S S; Soos, Maria A; Clark, James; Rodin, Andrew; Langenberg, Claudia; Druet, Celine; Fawcett, Katherine A; Tung, Y C Loraine; Wareham, Nicolas J; Barroso, In�s; Lienhard, Gustav E; O'Rahilly, Stephen; Savage, David B
A truncation mutation in TBC1D4 in a family with acanthosis nigricans and postprandial hyperinsulinemia
Tre-2, BUB2, CDC16, 1 domain family member 4 (TBC1D4) (AS160) is a Rab-GTPase activating protein implicated in insulin-stimulated glucose transporter 4 (GLUT4) translocation in adipocytes and myotubes. To determine whether loss-of-function mutations in TBC1D4 might impair GLUT4 translocation and cause insulin resistance in humans, we screened the coding regions of this gene in 156 severely insulin-resistant patients. A female presenting at age 11 years with acanthosis nigricans and extreme postprandial hyperinsulinemia was heterozygous for a premature stop mutation (R363X) in TBC1D4. After demonstrating reduced expression of wild-type TBC1D4 protein and expression of the truncated protein in lymphocytes from the proband, we further characterized the biological effects of the truncated protein in 3T3L1 adipocytes. Prematurely truncated TBC1D4 protein tended to increase basal cell membrane GLUT4 levels (P = 0.053) and significantly reduced insulin-stimulated GLUT4 cell membrane translocation (P < 0.05). When coexpressed with wild-type TBC1D4, the truncated protein dimerized with full-length TBC1D4, suggesting that the heterozygous truncated variant might interfere with its wild-type counterpart in a dominant negative fashion. Two overweight family members with the mutation also manifested normal fasting glucose and insulin levels but disproportionately elevated insulin levels following an oral glucose challenge. This family provides unique genetic evidence of TBC1D4 involvement in human insulin action.
Dash, Satya; Sano, Hiroyuki; Rochford, Justin J.; Semple, Robert K.; Yeo, Giles; Hyden, Caroline S. S.; Soos, Maria A.; Clark, James; Rodin, Andrew; Langenberg, Claudia; Druet, Celine; Fawcett, Katherine A.; Tung, Y. C. Loraine; Wareham, Nicolas J.; Barroso, Ines; Lienhard, Gustav E.; O'Rahilly, Stephen; Savage, David B.
The Possibility of TBC1D21 as a Candidate Gene for Teat Numbers in Pigs
Based on a quantitative traits locus (QTL) study using a F2 intercross between Landrace and Korean native pigs, a significant QTL affecting teat numbers in SSC7 was identified. The strong positional candidate gene, TBC1D21, was selected due to its biological function for epithelial mesenchymal cell development. Sequence analysis revealed six single nucleotide polymorphisms (SNPs) in the TBC1D21 gene. Among these, two SNP markers, one silent mutation (SNP01) for g.13,050A>G and one missense mutation (SNP04) for c.829A>T (S277C), were genotyped and they showed significant associations with teat number traits (p value = 6.38E-05 for SNP01 and p value = 1.06E-07 for SNP04 with total teat numbers). Further functional validation of these SNPs could give valuable information for understanding the teat number variation in pigs.
Jin, S.; Lee, J. B.; Kang, K.; Yoo, C. K.; Kim, B. M.; Park, H. B.; Lim, H. T.; Cho, I. C.; Maharani, D.; Lee, J. H.
Comparison of the Failures during Cyclic Oxidation of Yttria-Stabilized (7 to 8 Weight Percent) Zirconia Thermal Barrier Coatings Fabricated via Electron Beam Physical Vapor Deposition and Air Plasma Spray
NASA Astrophysics Data System (ADS)
The failures during oxidation of electron beam physical vapor deposition (EBPVD) and air plasma spray (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) on different bond coats, namely, platinum-modified aluminide and NiCoCrAlY, are described. It is shown that oxidation of the bond coats, along with defects existing near the TBC/bond coat interface, plays a very important role in TBC failures. Procedures to improve TBC performance via modifying the oxidation characteristics of the bond coats and removing the as-processed defects are discussed. The influence of exposure conditions on TBC lives is described and factors such as cycle frequency and thermal gradients are discussed.
Yanar, N. M.; Helminiak, M.; Meier, G. H.; Pettit, F. S.
Characterization of rupture and fatigue resistance of TBC superalloy for combustion liners
High-temperature, high-cycle fatigue and accelerated creep properties of thermal barrier coated (TBC) Superni C263 alloy used as a candidate material in combustor liners of aero engines are highlighted in this paper. An acoustic emission technique has been utilised to detect the ductile�brittle transition temperature of the bond coat. Results revealed that the ductile-to-brittle transition temperature (DBTT) of this bond coat
A. K. Ray; D. K. Das; B. Venkataraman; P. K. Roy; B. Goswami; N. Roy; S. K. Das; N. Parida; S. Tarafder; S. Chaudhuri; S. K. Sahay; R. N. Ghosh
Effect of thermal exposure on stress distribution in TGO layer of EB-PVD TBC
The stress distributions in thermally grown oxide (TGO) layer of electron beam enhanced physical vapor deposited thermal barrier coating (EB-PVD TBC) before and after thermal exposure are measured by photo-stimulated luminescence spectrum. It is found that the stress in the TGO layer in original state is an order of ~3 GPa. It increases from 3.0�3.9 GPa with the increase of
T Tomimatsu; S Zhu; Y Kagawa
Optical performance of the TBC-2 solar collector before and after the 1993 mirror lustering
In 1993, the mirror facets of one of Sandia`s point-focusing solar collectors, the Test Bed Concentrator {number_sign}2 (TBC-2), were reconditioned. The concentrator`s optical performance was evaluated before and after this operation. This report summarizes and compares the results of these tests. The tests demonstrated that the concentrator`s total power and peak flux were increased while the overall flux distribution in the focal plane remained qualitatively the same.
Houser, R.; Strachan, J. [Sandia National Labs., Albuquerque, NM (United States). Solar Thermal Test Dept.
Synthesis of free-standing, curved Si nanowires through mechanical failure of a catalyst during metal assisted chemical etching.
The fabrication of orderly arrays of free-standing, curved Si nanowires over large areas (1 cm � 1 cm) was demonstrated by means of interference lithography and intentional mechanical failure of a perforated Au catalyst during metal assisted chemical etching. Photoresist microgrooves were deposited on the perforated Au film to cause uneven etching which resulted in the build-up of bending stresses in the Au film to the point of catastrophic failure. By considering the initial positions of the holes in the perforated Au film relative to the photoresist constraints, the precise location of the fracture can be predicted using simple beam mechanics. Therefore, the type of curved nanowires obtained can be designed with a high degree of reliability and control. Four distinct types of nanowire arrangements were demonstrated for this study. PMID:24879451
Lai, Chang Quan; Choi, W K
Effect of Hf Additions to Pt Aluminide Bond Coats on EB-PVD TBC Life
NASA Technical Reports Server (NTRS)
Small Hf additions were incorporated into a Pt aluminide coating during chemical vapor deposition (CVD) on single crystal RENE N5 substrates. Standard yttria-stabilized zirconia top coats were subsequently deposited onto the coated substrates by electron beam-physical vapor deposition (EB-PVD). The coated substrates underwent accelerated thermal cycle testing in a furnace at a temperature in excess of 1121 C (2050 F) (45 minute hot exposure, 15 minute cool to approximately 121 C (250 F)) until the thermal barrier coating (TBC) failed by spallation. Incorporating Hf in the bond coat increased the TBC life by slightly more than three times that of a baseline coating without added Hf. Scanning electron microscopy of the spalled surfaces indicated that the presence of the Hf increased the adherence of the thermally grown alumina to the Pt aluminide bond coat. The presence of oxide pegs growing into the coating from the thermally grown alumina may also partially account for the improved TBC life by creating a near-surface layer with a graded coefficient of thermal expansion.
Nesbitt, James; Nagaraj, Ben; Williams, Jeffrey
Negative pressure ventilation versus conventional mechanical ventilation in the treatment of acute respiratory failure in COPD patients
This case-control study was aimed to evaluate the effectiveness of nega- tive pressure ventilation (NPV) versus conventional mechanical ventilation (CMV) for the treatment of acute respiratory failure (ARF) in patients with chronic obstructive pulmonary disease (COPD) admitted to a respiratory intermediate intensive care unit (RIICU) and four general intensive care units (ICU). Twenty-six COPD patients in ARF admitted in 1994-95
A. Corrado; M. Gorini; R. Ginanni; C. Pelagatti; G. Villella; U. Buoncristiano; F. Guidi; E. Pagni; A. Peris; E. De Paola
Investigation of the Failure Mechanism for an S-Band Pillbox Output Window Applied in High-Average-Power Klystrons
On the basis of the results of X-ray photoelectron spectroscopy, theoretical analyses, and numerical simulations, the failure mechanism of an S-band pillbox output window applied in a high-average-power klystron is discussed. The influence of the high-order cylindrical-guide modes on the microwave power loss, the direction of the power flow and the window disk cracking are investigated. The high-order cylindrical-guide TM11
Fang Zhu; Zhao-Chuan Zhang; Ji-Run Luo; Yu-Wen Zhang
The behavior of the micro-mechanical cement-bone interface affects the cement failure in total hip replacement
In the current study, the effects of different ways to implement the complex micro-mechanical behavior of the cement-bone interface on the fatigue failure of the cement mantle was investigated. In an FEA-model of a cemented hip reconstruction the cement-bone interface was modeled and numerically implemented in four different ways: (I) as infinitely stiff, (II) as infinitely strong with a constant stiffness, (III) a mixed-mode failure response with failure in tension and shear, and (IV) realistic mixed mode behavior obtained from micro FEA-models. Case II, III and IV were analyzed using data from a stiff and a compliant micro-FEA model and their effects on cement failure were analyzed. The data used for Case IV was derived from experimental specimens that were tested previously. Although the total number of cement cracks was low for all cases, the compliant Case II resulted in twice as many cracks as Case I. All cases caused similar stress distributions at the interface. In all cases, the interface did not display interfacial softening; all stayed the elastic zone. Fatigue failure of the cement mantle resulted in a more favorable stress distribution at the cement-bone interface in terms of less tension and lower shear tractions. We conclude that immediate cement-bone interface failure is not likely to occur, but its local compliancy does affect the formation of cement cracks. This means that at a macro-level the cement-bone interface should be modeled as a compliant layer. However, implementation of interfacial post-yield softening does seem to be necessary.
Waanders, Daan; Janssen, Dennis; Mann, Kenneth A.; Verdonschot, Nico
Ventricular coupling of electrical and mechanical dyssynchronization in heart failure patients.
We studied the relationships of electrical and mechanical synchronization in patients with heart failure (CHF) and various degree of ventricular conduction delays. Ninety-two CHF patients (60 +/- 13 years old, LVEF < 45%), NYHA II-III-IV, and 35 age-matched control subjects were studied with angioscintigraphic phase analysis. We measured ejection fractions (LVEF, RVEF) and calculated the total activation time for the left (TtLV) and right ventricle (TtRV), and the synchronization time between right and left ventricle (TRVLV), and between LV apex and base (Tab). Patients were divided into three groups according to QRS duration: group 1 < 120 ms (n = 28), group 2 < 150 ms (n = 23), group 3 > or = 150 ms (n = 41). In group 1: LVEF = 31.1 +/- 10.9%, RVEF = 30.1 +/- 12.6%, TtLV = 204 +/- 70 ms, TtRV = 183 +/- 61 ms, TRVLV = 7 +/- 33 ms, Tab = 29 +/- 23 ms. In group 2, these were: 27.8 +/- 9.1%, 27.8 +/- 8.8%, 227 +/- 95 ms, 248 +/- 137 ms, 35 +/- 42 ms*, and 39 +/- 53 ms respectively. In group 3: LVEF = 20.5 +/- 9.5%t, RVEF = 28.4 +/- 16.1%, TtLV = 304 +/- 155 mst, TtRV = 234 +/- 106 mst, TRVLV = 64 +/- 42 mst, and Tab = 67 +/- 48 ms*, all P < 0.001 versus controls *P < 0.05 versus G1, tP < or = 0.01 versus G1. A significant relation links QRS to both inter- and intraventricular asynchrony (TRVLV: r = 0.65; TtLL: r = 0.70, Tab: r = 0.60), and to LV function (r = 0.72); while LVEF relates more closely to intraventricular asynchrony: TtLV (r = 0.52), TtLL (r = 0.67), than to interventricular asynchrony: TRVLV (r = 0.48); P < 0.01, P < or = 0.001. In CHF patients, electromechanical and contractile alterations are coupled; regional activation may be an early parameter allowing the detection of ventricular dyssynchronization. PMID:11915984
Toussaint, Jean-Fran�ois; Lavergne, Thomas; Kerrou, Khaldoun; de Dieuleveult, Barbara; Ponce, Felizardo; Froissart, Marc; Le Heuzey, Jean-Yves; Guize, Louis; Paillard, Michel
Thermal failure mechanism and voltammetry metrology for copper/barrier/low k integration
NASA Astrophysics Data System (ADS)
The present study investigates the thermal stability of Cu/barrier/porous low kappa (PLK) integration first, and then a new characterization method based on voltammetry is developed to characterize quality of diffusion barrier and pore structure in low kappa materials and its thermal stability. The study of thermal stability reveals that Cu/barrier/PLK interconnect fails by Cu out-diffusion through the defects of diffusion barrier into the PLK structure, which is driven by oxidation and stress gradient within the interconnect structure. The failure appears to be triggered by defects in diffusion barrier, however, such defects are not effectively detected by TEM observation due to their small and localized nature. This motivates the development of a new method to characterize defects of diffusion barrier and pore structure of low kappa materials in as processed Cu/barrier/PLK interconnect. Firstly, a cyclic voltammetry-based method is developed to detect the quality of diffusion barrier by monitoring the current resulting from an applied voltage on the established cell. It utilizes a fact that electrolyte solution is able to infiltrate into the low k layer between two interconnects and creates a situation essentially the same as two-electrode electrolytic cell. When the barrier is intact (defectfree), the I-V shows simple hysteresis without the presence of current peaks. On the other hand, when the barrier is defective, Cu is exposed to electrolyte and current peak is present in the I-V curve due to Cu redox reactions. The application of the developed method on an extensive number of real interconnects provides sufficient evidence that the method is simple, fast, and accurate in detecting the defective barrier. Furthermore, it has a potential to quantify defect density based on the intensity of the current peak and the integration areas within the I-V curves. Secondly, a step voltammetry-based method is developed to characterize pore structure by measuring the effective ions diffusivity. The study produces the identical activation energy and diffusivity results for bulk solution which are in good agreement with references, and reveals that electrolyte ions migrate in dense low kappa (DLK) and PLK with different mechanism. The application of the method reveals that pores in low kappa materials are not thermally stable but can either collapse or coalesce depending on the stress conditions.
Meng, Dongmei
[Failure mechanisms in the transfusion process. Importance of anticipatory operational safety analysis].
The methods used for the safety previsional analysis of operations represent an interesting set of tools to follow the so-called transfusion process, defined as all the steps from donors sensitization to recipients follow-up. FMECA (Failure Mode Effects and Criticality Analysis) can be used as a prevention tool, independently of any dysfunction in the process. Of course, it can also be used following a failure, in order to analyse its causes and to apply specific corrections. Operation safety, quality insurance, epidemiologic surveillance and safety monitoring act in synergy. These three aspects of transfusion safety constitute a dynamic system. PMID:7812465
Hergon, E; Crespeau, H; Rouger, P
Market failure in the pharmaceutical industry and how it can be overcome: the CureShare mechanism.
Allowing patients to take part in the initial investment for the development of cures for their illnesses can, under certain conditions, lead to the development of drugs that would have otherwise not been developed and to a dramatic welfare increase. We theoretically analyze these conditions. The suggested patient investment mechanism, which we call CureShare, does not involve any philanthropy or government subsidies. It is simply a way to overcome market failure. Based on empirical data, we estimate that applying this mechanism may save thousands of lives annually and may dramatically improve the quality of many others. PMID:23417217
Levy, Moshe; Rizansky, Adi
Mechanisms and causes of embankment slope failure at Talaimari location of the Rajshahi City Protection Embankment, Bangladesh
NASA Astrophysics Data System (ADS)
Two shallow slides were occurred at Talaimai location of the Rajshahi City Protection Embankment (RCPE) recenly. The Ganges river side slope of this part of the embankment was protected with concrete-block lining just before the flood season of 2008. The failures were took place during the first drawdown of the river water within the two months of the construction of concrete-block lining. Several slope stability analysis methods including Finite Element (FE) and Limit Equilibrium (LE) were used for these two failed slopes. Stability analyses of these failed slopes revealed the primary failure mechanisms and causes. The pore water pressure during the rapid drawdown of river water suddenly reduced the shear strength of the embankment soil and the weight of the concrete block resulted additional shear stresses. Study showed that the seepage related erosion of the embankment soil caused major contribution for slope failure. Due to the loosening of the embankment soil particles, the newly settled concrete-blocks were readjusted and the overall stress-strength equilibrium was lost and hence caused failures. The present paper suggests further study in detail for the greater safety of this embankment as well as the Rajshahi City.
Khan, Y. A.
Active wear and failure mechanisms of TiN-Coated high speed steel and tin-coated cemented carbide tools when machining powder metallurgically made stainless steels
In this study, active wear and failure mechanisms of both TiN-coated high speed steel and TiN-coated cemented carbide tools\\u000a when machining stainless steels made by powder metallurgy in low and high cutting speed ranges, respectively, have been investigated.\\u000a Abrasive wear mechanisms, fatigue-induced failure, and adhesive and diffusion wear mechanisms mainly affected the tool life\\u000a of TiN-coated high speed steel tools
Laizhu Jiang; Hannu H�nninen; Jukka Paro; Veijo Kauppinen
Mechanisms of Disease: apoptosis in heart failure�seeing hope in death
Apoptosis or programmed cell death is an evolutionarily conserved process of cell death, wherein cells die without provoking significant inflammatory response. There is convincing evidence that apoptosis contributes to the progression of heart failure. Apoptosis occurs through a cascade of subcellular events including cytochrome c release into the cytoplasm and activation of proteolytic caspases. Activated caspases lead to fragmentation of
Nezam Haider; Eloisa Arbustini; Y Chandrashekhar; Jagat Narula
A Distributed Load-Based Failure Recovery Mechanism for Advance ReservationEnvironments
Resource reservations in advance are a mature concept for theallocation of various resources, particularly in Grid environments.Common Grid tool kits support advance reservations and assign jobs toresources at admission time. In such a distributed environment, it isnecessary to develop carefully tailored failure recovery mechanismsthat provide seamless transparent migration of jobs from one resourceto another. As the migration of running jobs
Lars-olof Burchard; Barry Linnert; Joerg Schneider
Electrostatic discharge (ESD) mechanism for battery charge contact failure in cordless phones
A comparison of the SEM EDX spectra for the metal charge contacts from field-returned cordless phones and for laboratory samples of fixed gap discharge (FGD) tests reveals similar chemical elements, suggesting that electrostatic discharge (ESD) is the possible source for cordless phone field failure
Richard J. Coyle; Min-Chung Jon
Anemia and iron deficiency in heart failure: mechanisms and therapeutic approaches
Anemia and iron deficiency are common in patients with heart failure (HF), and are associated with worse symptoms and adverse outcomes in this population. Although the two can occur together, anemia in HF is often not caused by iron deficiency, and iron deficiency can be present without causing anemia. Erythropoiesis-stimulating agents have been investigated extensively in the past few years
Stefan D. Anker; Piotr Ponikowski; Iain C. Macdougall; Dirk J. van Veldhuisen
Myocyte Recovery After Mechanical Circulatory Support in Humans With End-Stage Heart Failure
Background�The failing myocardium is characterized by decreased force production, slowed relaxation, and depressed responses to b-adrenergic stimulation. In some heart failure patients, heart function is so poor that a left ventricular assist device (LVAD) is inserted as a bridge to transplantation. In the present research, we investigated whether circulatory support with an LVAD influenced the functional properties of myocytes from
Konstantina Dipla; Julian A. Mattiello; Valluvan Jeevanandam; Steven R. Houser; Kenneth B. Margulies
Root-soil mechanical interactions during pullout and failure of root bundles
Roots play a major role in reinforcing and stabilizing steep hillslopes. Most studies in slope stability implement root reinforcement as an apparent cohesion by upscaling the behavior of static individual roots. Recent studies, however, have shown that much better predictions of slope stability can be made if the progressive failure of bundles of roots are considered. The characteristics of progressive
M. Schwarz; D. Cohen; D. Or
Reduced Erythrocyte Defense Mechanisms against Free Radical Toxicity in Patients with Chronic Renal Failure
In this study, activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) enzymes were determined in the erythrocytes from patients with chronic renal failure (CRF) and from healthy subjects. In the conservative drug management group and intermittent ambulatory peritoneal dialysis group, CAT activity was lower than in the control group. However, SOD and GSH-Px activities of these groups
I. Durak; �. Akyol; O. Canbolat; M. Kavut�u
Prevent boiler tube failures--Part 1: Fire-side mechanisms
A boiler tube fails when the structural integrity of the tube is compromised. For boilers that have been previously operating, some change must occur to effect tube failure. Usually this change is wrought through some combination of corrosion and erosion acting on the boiler tube to weaken it. Boiler tubes depend on a complex metal oxide layer for protection from
Mechanisms of Disease: ?-adrenergic receptors�alterations in signal transduction and pharmacogenomics in heart failure
?-adrenergic signaling is an important regulator of myocardial function. During the progression of heart failure (HF), a reproducible series of biochemical events occurs that affects ?-adrenergic receptor (?-AR) signaling and cardiac function. Furthermore, there are pathophysiologic alterations in the expression and regulation of proteins that are regulated by ?-ARs during HF. Analyses of these complex signaling pathways have led to
Cynthia A Carnes; William T Abraham; Michael R Bristow; David S Feldman
Parametric studies of failure mechanisms in elastic EB-PVD thermal barrier coatings using FEM
Catastrophic failure of thermal barrier coatings (TBCs), usually occurs due to large scale buckling and spallation, primarily originating at the bond coat and TGO interface. Spallation in TBCs is preceded by a competition between buckling and interface delamination that is stimulated by the waviness of the interface. In the presence of thermal loading, the waviness is responsible for growth of
Himanshu Bhatnagar; Somnath Ghosh; Mark E. Walter
Influence of cyclic strain on life of a PVD TBC
A thermal mechanical fatigue (TMF) test has been developed to determine the effect of strain on the life of a thermal barrier coating. TMF tests were performed with different temperature�strain phasing and different applied strain levels to vary the imposed strain range on the coating and thus separate strain dependence of life from oxidation effects. Results for a single crystal
P Kennard Wright
A Study on Wire Ball\\/Pad Open Failure Mechanism of a Multi-Stack Package (MSP) under High Temperature Storage (HTS) Condition
The mechanism of a wire ball\\/pad open failure at a gold wire and bonding pad interface of a multi-stack package (MSP) under high temperature storage (HTS) condition, 150 degC, is studied. Failure analysis using FE-SEM (field emission) and FIB-SEM (focused ion beam) was conducted. The analysis revealed that the main factors that contribute to a ball\\/pad failure were the tensile
Se Young Yang; Hyeong-Jik Byun; Sang-Wook Park; Wang-Joo Lee
A method for intermediate strain rate compression testing and study of compressive failure mechanism of Mg-Al-Zn alloy
NASA Astrophysics Data System (ADS)
Obtaining meaningful information from the test results is a challenge in the split-Hopkinson pressure bar (SHPB) test method if the specimen does not fail during the test. Although SHPB method is now widely used for high strain rate testing, this limitation has made it difficult to use it for characterization of materials in the intermediate strain rate range (typically 10-1000 s-1). In the present work, a method is developed to characterize materials in the intermediate strain rate range using SHPB setup. In this method, the specimen is repeatedly tested under compression at a given strain rate until failure is achieved. The stress-strain graphs obtained from each test cycle are used to plot the master stress-strain graph for that strain rate. This method is used to study the strain rate dependence of compressive response of a Mg-Al-Zn alloy in the intermediate strain rate range. A remarkable difference is observed in the failure mechanism of the alloy under quasi-static and intermediate strain rate compression. Matrix cracking is the main failure mechanism under quasi-static compression, whereas shattering of intermetallic precipitates, along with plastic deformation of the matrix, is discovered to become prominent as the strain rate is increased.
Gupta, Nikhil; Luong, Dung D.; Rohatgi, Pradeep K.
Mutations in TBC1D24, a Gene Associated With Epilepsy, Also Cause Nonsyndromic Deafness DFNB86
Inherited deafness is clinically and genetically heterogeneous. We recently mapped DFNB86, a locus associated with nonsyndromic deafness, to chromosome 16p. In this study, whole-exome sequencing was performed with genomic DNA from affected individuals from three large consanguineous families in which markers linked to DFNB86 segregate with profound deafness. Analyses of these data revealed homozygous mutation c.208G>T (p.Asp70Tyr) or c.878G>C (p.Arg293Pro) in TBC1D24 as the underlying cause of deafness in the three families. Sanger sequence analysis of TBC1D24 in an additional large family in which deafness segregates with DFNB86 identified the c.208G>T (p.Asp70Tyr) substitution. These mutations affect TBC1D24 amino acid residues that are conserved in orthologs ranging from fruit fly to human. Neither variant was observed in databases of single-nucleotide variants or in 634 chromosomes from ethnically matched control subjects. TBC1D24 in the mouse inner ear was immunolocalized predominantly to spiral ganglion neurons, indicating that DFNB86 deafness might be an auditory neuropathy spectrum disorder. Previously, six recessive mutations in TBC1D24 were reported to cause seizures (hearing loss was not reported) ranging in severity from epilepsy with otherwise normal development to epileptic encephalopathy resulting in childhood death. Two of our four families in which deafness segregates with mutant alleles of TBC1D24 were available for neurological examination. Cosegregation of epilepsy and deafness was not observed in these two families. Although the causal relationship between genotype and phenotype is not presently understood, our findings, combined with published data, indicate that recessive alleles of TBC1D24 can cause either epilepsy or nonsyndromic deafness.
Rehman, Atteeq U.; Santos-Cortez, Regie Lyn P.; Morell, Robert J.; Drummond, Meghan C.; Ito, Taku; Lee, Kwanghyuk; Khan, Asma A.; Basra, Muhammad Asim R.; Wasif, Naveed; Ayub, Muhammad; Ali, Rana A.; Raza, Syed I.; Nickerson, Deborah A.; Shendure, Jay; Bamshad, Michael; Riazuddin, Saima; Billington, Neil; Khan, Shaheen N.; Friedman, Penelope L.; Griffith, Andrew J.; Ahmad, Wasim; Riazuddin, Sheikh; Leal, Suzanne M.; Friedman, Thomas B.
Mechanical torque measurement in the proximal femur correlates to failure load and bone mineral density ex vivo
Knowledge of local bone quality is essential for surgeons to determine operation techniques. A device for intraoperative measurement of local bone quality has been developed by the AO-Research Foundation (Densi - Probe�). We used this device to experimentally measure peak breakaway torque of trabecular bone in the proximal femur and correlated this with local bone mineral density (BMD) and failure load. Bone mineral density of 160 cadaver femurs was measured by ex situ dualenergy X-ray absorptiometry. The failure load of all femurs was analyzed by side-impact analysis. Femur fractures were fixed and mechanical peak torque was measured with the DensiProbe� device. Correlation was calculated whereas correlation coefficient and significance was calculated by Fisher�s Ztransformation. Moreover, linear regression analysis was carried out. The unpaired Student�s t-test was used to assess the significance of differences. The Ward triangle region had the lowest BMD with 0.511 g/cm2 (�0.17 g/cm2), followed by the upper neck region with 0.546 g/cm2 (�0.16 g/cm2), trochanteric region with 0.685 g/cm2 (�0.19 g/cm2) and the femoral neck with 0.813 g/cm2 (�0.2 g/cm2). Peak torque of DensiProbe� in the femoral head was 3.48 Nm (�2.34 Nm). Load to failure was 4050.2 N (�1586.7 N). The highest correlation of peak torque measured by Densi Probe� and load to failure was found in the femoral neck (r=0.64, P<0.001). The overall correlation of mechanical peak torque with T-score was r=0.60 (P<0.001). A correlation was found between mechanical peak torque, load to failure of bone and BMD in vitro. Trabecular strength of bone and bone mineral density are different aspects of bone strength, but a correlation was found between them. Mechanical peak torque as measured may contribute additional information about bone strength, especially in the perioperative testing.
Grote, Stefan; Noeldeke, Tatjana; Blauth, Michael; Mutschler, Wolf; Burklein, Dominik
Possible mechanisms causing failure of Thellier palaeointensity experiments in some basalts
NASA Astrophysics Data System (ADS)
The normally magnetized zone of the Jurassic Lesotho basalts, although providing apparently quite reliable palaeofield directions Kosterov & Perrin 1996), shows anomalous behaviour when studied in vacuum using the Thellier palaeointensity method: typically the slope of the natural remanent magnetization-thermoremanent magnetization (NRM-TRM) curves is very steep at intermediate temperatures (200 to 400-460�C). In order to elucidate the reasons for such an anomalous behaviour, six representative samples (from a total of 74 studied using this method) were subjected to a variety of analyses. These experiments indicate that the magnetic properties are dominated by pseudo-single-domain (PSD) magnetite grains some 1 ?m in size, resulting from high-temperature oxidation of titanomagnetite. Laboratory heatings in vacuum up to the Curie point do not change significantly the room-temperature hysteresis characteristics or the initial susceptibility k. Similarly, the k(T ) curves in vacuum are (with a single exception) rather reproducible. Since the laboratory TRMs yield almost ideal NRM-TRM plots, the anomalous NRM-TRM plot is presumably due to some peculiarity of the natural TRM. The partial TRM (pTRM) acquisition capacity in the moderate temperature range (cooling from 200 to 20�C) is generally very strongly reduced after heating to 270�C, which indicates that some magnetic alteration has already occurred at these temperatures. Hysteresis measurements between room temperature and the Curie temperature Tc show that some small (less than 10 per cent) but significant irreversible changes in hysteresis characteristics also occur during heating. In particular, the coercive force Hc0 at room temperature is typically reduced after heating at a moderate temperature (175�C) but increases after treatments at 475�C and, more pronouncedly, at 580�C. The saturation magnetization Js0 remains unchanged, except for a very small decrease (less than 5 per cent) occurring in some samples after the two latter treatments. These changes are most clearly seen on Hc(T )-Js(T ) bilogarithmic plots, which show that the moderate-temperature change in coercivity can extend up to 200-250�C. Thus hysteresis measurements as a function of temperature offer a promising tool for sample pre-selection for Thellier experiments. Alternating-field demagnetization and cycling of pTRMs at liquid-nitrogen temperature suggest that the blocking mechanism is largely multidomain-like near room temperature but becomes less so as the Curie point is approached. The main reason for the failure of the Thellier experiments is the loss of a fraction of the NRM (natural TRM) at temperatures apparently lower than the blocking temperatures in nature. It is suggested that this anomalous behaviour results from the reorganization of the domain structure of the PSD grains during heating. This transformation, which seems to be triggered by the coercivity decrease observed at very moderate temperatures, can reduce the NRM intensity without requiring any correlated pTRM acquisition.
Kosterov, Andrei A.; Pr�vot, Michel
Exercise intolerance in chronic heart failure: mechanisms and therapies. Part II.
Muscular fatigue and dyspnoea on exertion are among the most common symptoms in chronic heart failure; however their origin is still poorly understood. Several studies have shown that cardiac dysfunction alone cannot fully explain their origin, but the contribution of the multiorgan failure present in this syndrome must be highlighted. We aimed to summarize the existing evidence and the most controversial aspects of the complex interplay of different factors involved in the symptom generation. In the first part of the review, six key factors were revised (the heart, the lung, the skeletal muscle, the hormonal changes, the O2 delivery to the periphery, the endothelium). In this second part, the role of the excitatory reflexes and the cardiac cachexia are presented. Finally, potential therapeutic implications are discussed here. We believe that a better knowledge of the pathophysiology of this syndrome may contribute to the management of the patients and to the improvement in their stress tolerance and quality of life. PMID:21217245
Piepoli, Massimo F; Guazzi, Marco; Boriani, Giuseppe; Cicoira, Mariantonietta; Corr�, Ugo; Dalla Libera, Luciano; Emdin, Michele; Mele, Donato; Passino, Claudio; Vescovo, Giorgio; Vigorito, Carlo; Villani, Giovanni; Agostoni, Piergiuseppe
Mechanism of failure eleven years following a Buechel Pappas hip resurfacing.
Hip resurfacing is gaining popularity as an acceptable treatment option for young active patients with hip osteoarthritis. The Buechel-Pappas hip resurfacing system has a titanium alloy femoral and acetabular component with a polyethylene liner. The titanium nitride coating of the femoral component has been shown to have a very low wear rate during in vivo laboratory studies. Although it has been on the marketplace since 1989, we could find no followup results in the literature. We report a rare case of Buechel-Pappas hip resurfacing which presented with catastrophic failure at 11 years follow-up. The polyethylene liner was worn through, and there was severe metallosis with extensive titanium debris. The head of the femur was however viable, suggesting that the failure of the procedure was due to the bearing surface. PMID:18260496
Malviya, Ajay; Lobaz, Steven; Holland, James
Mechanism of electromigration failure in Al thin film interconnects containing Sc
In order to understand the role of Sc on electromigration (EM) failure, Al interconnects with 0.1 and 0.3 wt.% Sc sere tested as a function of post-pattern annealing time. In response to the evolution of the line structure, the statistics of lifetime evolved. While the addition of Sc greatly reduces the rate of evolution of the failure statistics because the grain growth rate decreases, the MTF variation was found to be very similar to that of pure Al. These observations seem to show that Sc has little influence on the kinetics of Al EM; however, it has some influence on the EM resistance of the line since it is an efficient grain refiner. Unlike Cu in Al, Sc does not seem to migrate, which may explain its lack of influence on the kinetics of Al EM.
Kim, Choong-un; Kang, S.H.; Morris, J.W. Jr. [Lawrence Berkeley Lab., CA (United States); Genin, F.Y. [Lawrence Livermore National Lab., CA (United States)
Influence of residual stresses on the resistance of steel to corrosion-mechanical failure
The authors investigate the influence of first type residual stresses occurring during surface plastic deformation, pulsed hardening, and combined working on the resistance of steel to corrosion cracking and fatigue failure in hydrogen sulfide-containing media. Investigations showed that all of the forms of surface working increase the corrosion cracking resistance of steel but the degree of protection of the steel depends upon the form of working and the aggressiveness of the hydrogen sulfide-containing medium.
Berezhnitskaya, M.F.
Mechanisms of material failure for fast heating up at the center of ultra high temperature ceramic
ZrB2�20%SiC (ZS) and ZrB2�20%SiC�10%graphite (ZS10C) were fabricated by hot-press sintering method. A novel method was proposed to characterize material failure for heating up at the center of ultra high temperature ceramic. Thermal stress field was calculated under different center temperatures for ZS. It showed that the material would be failed when the center temperature was higher than 2300�C. It was
Songhe Meng; Chuping Liu; Guoqian Liu; Guanghui Bai; Chenghai Xu; Weihua Xie
Proportional and scale change models to project failures of mechanical components with applications to space station
NASA Technical Reports Server (NTRS)
In this paper we develop the mathematical theory of proportional and scale change models to perform reliability analysis. The results obtained will be applied for the Reaction Control System (RCS) thruster valves on an orbiter. With the advent of extended EVA's associated with PROX OPS (ISSA & MIR), and docking, the loss of a thruster valve now takes on an expanded safety significance. Previous studies assume a homogeneous population of components with each component having the same failure rate. However, as various components experience different stresses and are exposed to different environments, their failure rates change with time. In this paper we model the reliability of a thruster valves by treating these valves as a censored repairable system. The model for each valve will take the form of a nonhomogeneous process with the intensity function that is either treated as a proportional hazard model, or a scale change random effects hazard model. Each component has an associated z, an independent realization of the random variable Z from a distribution G(z). This unobserved quantity z can be used to describe heterogeneity systematically. For various models methods for estimating the model parameters using censored data will be developed. Available field data (from previously flown flights) is from non-renewable systems. The estimated failure rate using such data will need to be modified for renewable systems such as thruster valve.
Taneja, Vidya S.
Stochastic and systematic patterning failure mechanisms for contact-holes in EUV lithography: Part 2
NASA Astrophysics Data System (ADS)
Patterning uncertainty in EUV lithography arises from each lithographic component: the source, the photomask, the optical system, and the photoresist. All contribute to line roughness and contact disuniformity. In extreme cases, feature variability can result in patterning failures such as line microbridging or random missing contact holes. Historically, redundant contact holes (or vias) were placed to overcome the effects of a missing contact. Due to the aggressive CD shrink of feature size, the use of redundant contacts has been progressively decreased. For some types of devices, almost every contact of the billions found on the chip must be electrically active in order for the device to function. In such scenario, lithographic printing failures may cause catastrophic loss of yield, considering that closed contacts can hardly be corrected by smoothing techniques or etching. In this paper, the minimum contact CD which prints without failure - the contact hole printability limit - is studied for 54nm and 44nm pitch dense arrays. We find that the same resist may show dramatically different printability limits depending upon sizing dose and illumination conditions. This analysis will be implemented to estimate, through simulation-assisted experiments, the required exposure dose and aerial image to safely print sub-30nm contact holes.
Vaglio Pret, Alessandro; De Bisschop, Peter; Smith, Mark D.; Biafore, John J.
Short-crack mechanical properties and failure mechanisms of Si[sub 3]N[sub 4]-matrix/SiC-fiber composites
SiC-fiber-reinforced Si[sub 3]N[sub 4] composites were fabricated by hot pressing. The indentation-strength technique was applied to study the mechanical properties of these composites. This enabled the investigation of short-crack behavior of continuous-fiber ceramic composites (CFCCs). The flaw tolerance of composite ultimate strength, matrix-cracking stress, and work-of-fracture were investigated. Scanning electron microscopy was used to examine crack-fiber interactions. The ultimate strength was found to be independent of indentation load at a fiber volume fraction f = 0.29, while at f = 0.14 it exhibited a transition from flaw-sensitive to flaw-independent. The work-of-fracture was found to be independent of indentation load at both fiber volume fractions. The matrix-cracking stress was found to correspond to the first load-drop on the load-displacement curve. It decreased with increasing flaw size and therefore is not the steady-state matrix-cracking stress. A failure mechanism transition from catastrophic failure to non-catastrophic failure, coupled with the transition from flaw-sensitive to flaw-tolerant behavior, was observed by varying the preexisting flaw size and the fiber volume fraction. These transitions were explained by analyzing the relations between ultimate strength, matrix-cracking stress, fiber volume fraction, and preexisting flaw size of the composite materials. Experimental results were compared with predictions from available models.
Xu, H.H.K.; Ostertag, C.P.; Braun, L.M. (National Inst. of Standards and Technology, Gaithersburg, MD (United States)); Lloyd, I.K. (Univ. of Maryland, College Park, MD (United States). Dept. of Materials and Nuclear Engineering)
Failure Morphologies of Cyclically Oxidized ZrO2-Based Thermal Barrier Coatings
NASA Technical Reports Server (NTRS)
Advanced and baseline thermal barrier coatings (TBCs) were thermal cycle tested in air at 1163 C until delamination or spallation of the ceramic top coat. The top coat of the advanced TBC s consisted of ZrO2 with various amounts of Y2O3, Yb2O3, Gd2O3, or Nd2O3 dopants. The composition of the top coat of the baseline TBC was ZrO2-8wt.%Y2O3. All top coats were deposited by air plasma spraying. A NiCrAlY or NiCoCrAlY bond coat was deposited by low pressure plasma spraying onto a single-crystal, Ni-base superalloy. The TBC lifetime for the baseline coatings was approximately 190 cycles (45 minutes at 1163 C per cycle) while the lifetime for the advanced coatings was as high as 425 cycles. The fracture surfaces and sample cross sections were examined after TBC failure by SEM and optical microscopy, and the top coats were further examined by X-ray diffraction. These post-test studies revealed that the fracture path largely followed splat boundaries with some trans-splat fracture. However, there were no obvious distinguishing features which explained the difference in TBC lifetimes between some of the advanced and baseline coatings.
Nesbitt, James A.; Zhu, Dongming; Miller, Robert A.; Barrett, Charles A.
In order to improve the hot corrosion resistance of conventional YSZ TBC system, the overlay of Al{sub 2}O{sub 3} coating was deposited on the TBC by EB-PVD techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for different time up to 100h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. The amount of M-phase, which was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ, was increased with corrosion time. Al{sub 2}O{sub 3} overlay coating deposited by EB-PVD was dense, continues and adherent to the TBC. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and decrease the penetration of salts into the YSZ along porous and cracks in the YSZ TBC. The amount of M-phase formed in YSZ covered with an overlay Al{sub 2}O{sub 3} is substantially lower than that formed in conventional YSZ TBC, even after 100h exposure to the molten salts. In the next reporting period, the hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, the post-annealing will be carried out in vacuum (residual pressure 10 -3 Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay. In addition, the effect of the thickness of overlay Al{sub 2}O{sub 3} on corrosion resistance will also be investigated.
Scott X. Mao
Effects of Creep and Cyclic Loading on the Mechanical Properties and Failure of Human Achilles Tendons
The Achilles tendon is one of the most frequently injured tendons in humans, and yet the mechanisms underlying its injury are not well understood. This study examines the ex vivo mechanical behavior of excised human Achilles tendons to elucidate the relationships between mechanical loading and Achilles tendon injury. Eighteen tendons underwent creep testing at constant stresses from 35 to 75
Tishya A. L. Wren; Derek P. Lindsey; Gary S. Beaupr�; Dennis R. Carter
Structurally distinct bacterial TBC-like GAPs link Arf GTPase to Rab1 inactivation to counteract host defenses.
Rab GTPases are frequent targets of vacuole-living bacterial pathogens for appropriate trafficking of the vacuole. Here we discover that bacterial effectors including VirA from nonvacuole Shigella flexneri and EspG from extracellular Enteropathogenic Escherichia coli (EPEC) harbor TBC-like dual-finger motifs and exhibits potent RabGAP activities. Specific inactivation of Rab1 by VirA/EspG disrupts ER-to-Golgi trafficking. S. flexneri intracellular persistence requires VirA TBC-like GAP activity that mediates bacterial escape from autophagy-mediated host defense. Rab1 inactivation by EspG severely blocks host secretory pathway, resulting in inhibited interleukin-8 secretion from infected cells. Crystal structures of VirA/EspG-Rab1-GDP-aluminum fluoride complexes highlight TBC-like catalytic role for the arginine and glutamine finger residues and reveal a 3D architecture distinct from that of the TBC domain. Structure of Arf6-EspG-Rab1 ternary complex illustrates a pathogenic signaling complex that rewires host Arf signaling to Rab1 inactivation. Structural distinctions of VirA/EspG further predict a possible extensive presence of TBC-like RabGAP effectors in counteracting various host defenses. PMID:22939626
Dong, Na; Zhu, Yongqun; Lu, Qiuhe; Hu, Liyan; Zheng, Yuqing; Shao, Feng
Investigation of meso-failure behavior of rock under thermal-mechanical coupled effects based on high temperature SEM
NASA Astrophysics Data System (ADS)
It is extremely important to study and understand the deformation behavior and strength characteristics of rocks under thermal-mechanical (TM) coupling effects. Failure behavior and strength characteristics of Pingdingshan sandstone were investigated at room temperatures up to 300�C in an internally heated apparatus and tensile load through meso-scale laboratory experiments in this work. 33 experiments have successfully been conducted for Pingdingshan sandstone. Experimental results indicated that the tensile strength increased slowly with temperatures from 25�C to 100�C, and then sharply jumped from 100�C to 150�C, and finally decreased slightly with temperatures from 150�C to 300�C. And about 150�C is the threshold temperature of strength and thermal cracking. At low temperatures (25�C-150�C), sandstone strength is determined by relatively weak clay cement. However, at higher temperatures (150�C-300�C), because of the strength enhancement of clay cement, sandstone strength is controlled by both mineral particles and clay cement. The effects of cement clay, micro-cracks closing, and thermal cracking were the possible reasons for our detailed analysis. In addition, the typical fracture position maps and nominal stress-strain curves indicated that the temperature had strong effects on the failure mechanism of sandstone. The fractograph implied that the dominant fracture mechanism tended to transform from brittle at low temperatures to ductile at high temperatures.
Zuo, JianPing; Xie, HePing; Zhou, HongWei
Transition in Failure Mechanism Under Cyclic Creep in 316LN Austenitic Stainless Steel
NASA Astrophysics Data System (ADS)
Cyclic creep behavior of a type 316LN austenitic stainless steel was investigated in the temperature range from 823 K to 923 K (550 �C to 650 �C). A transition from fatigue-dominated to creep-dominated failure mode was observed with an increase in the mean stress. The threshold value of mean stress for the transition was seen to be a strong function of the test temperature. Occurrence of dynamic strain aging proved beneficial owing to a substantial reduction in the strain accumulation during cyclic loading.
Sarkar, Aritra; Nagesha, A.; Parameswaran, P.; Sandhya, R.; Mathew, M. D.
Mechanics of brittle deformation and slope failure at the North Menan Butte tuff cone, Eastern Snake River Plain, Idaho
NASA Astrophysics Data System (ADS)
The Menan Volcanic Complex consists of phreatomagmatic tuff cones that were emplaced as part of the regional volcanic activity in the Snake River Plain during the late Pleistocene. These tuff cones, the ';Menan Buttes', resulted from the eruption of basaltic magma through water-saturated alluvium and older basalts along the Snake River. The tuffs are composed primarily of basaltic glass with occasional plagioclase and olivine phenocrysts. The tuff is hydrothermally altered to a massive palagonitic tuff at depth but is otherwise poorly welded. Mass movements along the flanks of the cones were contemporaneous with tuff deposition. These slope failures are manifest as cm- to meter-scale pure folds, faults and fault-related folds, as well as larger slumps that are tens to a few hundred meters wide. Previous investigations classified the structural discontinuities at North Menan Butte based on orientation and sense of displacement, and all were recognized as opening-mode or shear fractures (Russell and Brisbin, 1990). This earlier work also used a generalized model of static (i.e., aseismic) gravity-driven shear failure within cohesionless soils to infer a possible origin for these fractures through slope failure. Recent work at North Menan Butte has provided novel insight into the styles of brittle deformation present, the effect of this deformation on the circulation of subsurface fluids within the tuff cone, as well as the mechanisms of the observed slope failures. Field observations reveal that the brittle deformation, previously classified as fractures, is manifest as deformation bands within the non-altered, poorly welded portions of the tuff. Both dilational and compactional bands, with shear, are observed. Slumps are bounded by normal faults, which are found to have developed within clusters of deformation bands. Deformation bands along the down-slope ends of these failure surfaces are predominantly compactional in nature. These bands have a ~3800 millidarcy permeability, a decrease from the ~9400 millidarcy permeability typical of the non-deformed, poorly-welded tuff. As such, these bands would have acted to slow to the circulation of local fluids through the tuff cone, possibly reducing the slopes' stability further. Future work will employ slope stability models to investigate the tendency for slumping of these tuffs shortly after their emplacement, accounting for water-saturated conditions and the effects of eruption-related seismicity. These results will improve current understanding of the mechanics of fault growth within basaltic tuff and enable more rigorous assessments of the hazards posed by slope instability on active phreatomagmatic tuff cones.
Okubo, C. H.
Oxidation Behaviour of TBC Systems on ?-TiAl Based Alloy Ti�45Al�8Nb
The lifetime of thermal barrier coating (TBC) systems on gamma titanium aluminides was determined in the temperature range\\u000a between 850��C and 950��C under cyclic oxidation conditions in air. Coupons of the alloy Ti�45Al�8Nb (at.%) were coated by\\u000a pack aluminizing. A subset of samples was subsequently annealed at 910��C for 312�h in argon. During this heat treatment,\\u000a the two-phase (Nb,Ti)Al3 plus
R. Braun; M. Fr�hlich; C. Leyens; D. Renusch
Exercise intolerance in chronic heart failure: mechanisms and therapies. Part I.
Muscular fatigue and dyspnoea on exertion are among the most common symptoms in chronic heart failure; however their origin is still poorly understood. Several studies have shown that cardiac dysfunction alone cannot fully explain their origin, but the contribution of the multiorgan failure present in this syndrome must be highlighted. In this study, divided in two parts (see part II: pp. 643�648), we aimed to summarize the existing evidence and the most controversial aspects of the complex interplay of different factors involved in symptom generation. In this first part of the review, six key factors are revised: the heart, the lung, the skeletal muscle, the hormonal changes, the O2 delivery to the periphery, the endothelium. In the second part, the role of the excitatory reflexes and the cardiac cachexia will be presented, and finally, the potential therapeutic implications are discussed. We believe that a better knowledge of the pathophysiology of this syndrome may contribute to the management of the patients and to the improvement in their stress tolerance and quality of life. PMID:21268774
Piepoli, Massimo F; Guazzi, Marco; Boriani, Giuseppe; Cicoira, Mariantonietta; Corr�, Ugo; Dalla Libera, Luciano; Emdin, Michele; Mele, Donato; Passino, Claudio; Vescovo, Giorgio; Vigorito, Carlo; Villani, Giovanni Q; Agostoni, Piergiuseppe
Distribution of coastal cliffs in Kerala, India: their mechanisms of failure and related human engineering response
NASA Astrophysics Data System (ADS)
The 560-km-long Kerala coast is characterised by long barriers with narrow beaches and steep cliffs. Distribution of cliffs from nine sections measuring a cumulative length of 63.5 km is evaluated in ArcGIS Software using topomaps and field survey data. The cliff sections in the southern coast comprise both permeable and impermeable rocks, whereas those along northern coast are comprised of either Precambrian crystalline and/or Tertiary formations. Notches, caves and even small arches are developed in Cannanore, Dharmadam and Kadalundi cliffs, where only primary laterites are exposed to wave attack. Stacks composed of laterite and Precambrian crystallines found in nearshore of cliffed coast indicate recession of shoreline. Mass wasting, mudslide and mudflow type of cliff failures are common in permeable to semi-permeable rocks, whereas rotational sliding, rockfall and toppling failure are found in hard rock cliffs. Retreat of cliff sections are induced by natural or anthropogenic activities or both. Rate of recession vary from a few centimetres to one metre/year depending upon the nature of lithology, structures and recession agents acting upon the cliffs. Various methods of cliff protection for e.g. hard structures�revetments, groins, seawalls, breakwater and jetties�and soft measures�artificial reefs/marsh creation, floating breakwaters, beach nourishment, beach scraping and vegetation planting�are suggested.
Kumar, Avinash; Seralathan, P.; Jayappa, K. S.
Acoustic emission and acousto-ultrasonic signature analysis of failure mechanisms in carbon fiber reinforced polymer materials
NASA Astrophysics Data System (ADS)
Fiber reinforced polymer composite materials, particularly carbon (CFRPs), are being used for primary structural applications, particularly in the aerospace and naval industries. Advantages of CFRP materials, compared to traditional materials such as steel and aluminum, include: light weight, high strength to weight ratio, corrosion resistance, and long life expectancy. A concern with CFRPs is that despite quality control during fabrication, the material can contain many hidden internal flaws. These flaws in combination with unseen damage due to fatigue and low velocity impact have led to catastrophic failure of structures and components. Therefore a large amount of research has been conducted regarding nondestructive testing (NDT) and structural health monitoring (SHM) of CFRP materials. The principal objective of this research program was to develop methods to characterize failure mechanisms in CFRP materials used by the U.S. Army using acoustic emission (AE) and/or acousto-ultrasonic (AU) data. Failure mechanisms addressed include fiber breakage, matrix cracking, and delamination due to shear between layers. CFRP specimens were fabricated and tested in uniaxial tension to obtain AE and AU data. The specimens were designed with carbon fibers in different orientations to produce the different failure mechanisms. Some specimens were impacted with a blunt indenter prior to testing to simulate low-velocity impact. A signature analysis program was developed to characterize the AE data based on data examination using visual pattern recognition techniques. It was determined that it was important to characterize the AE event , using the location of the event as a parameter, rather than just the AE hit (signal recorded by an AE sensor). A back propagation neural network was also trained based on the results of the signature analysis program. Damage observed on the specimens visually with the aid of a scanning electron microscope agreed with the damage type assigned by the signature analysis program. The load level at which significant damage occurred in the specimens was evaluated using ASME Boiler and Pressure Vessel criteria. AU testing proved inconclusive for characterization of the damage due to common problems associated with AU testing such as: reproducibility difficulties due to degradation of the attachment of the sensors, damage not detected unless in the line of sight between sensors, and large intrinsic variation of the data.
Carey, Shawn Allen
Barrier properties and failure mechanism of Ta-Si-N thin films for Cu interconnection
NASA Astrophysics Data System (ADS)
Cosputtered Ta-Si-N amorphous films of ten different compositions were investigated as a barrier material for Cu interconnection. The films of relatively low nitrogen content (<47 at. %) undergo an abrupt failure with the formation of tantalum silicides and copper silicide between Si and Cu during annealing. Ta43Si4N53 thin film is readily crystallized into TaNx in spite of a remarkable chemical stability with Cu. The films containing nitrogen more than 51 at. % are sacrificial barriers which show the formation of Cu3Si phase at Ta-Si-N/Cu interface even before the films crystallize to form tantalum silicide. According to electrical tests, the barriers which show the sacrificial characteristics are most effective and show no electrical degradation even after annealing at 500 �C for an hour in Si/Cu and 525 �C for an hour in SiO2/Cu metallization.
Lee, Yoon-Jik; Suh, Bong-Seok; Kwon, Myoung Seok; Park, Chong-Ook
Investigation of accelerated stress factors and failure/degradation mechanisms in terrestrial solar cells
NASA Technical Reports Server (NTRS)
Research on the reliability of terrestrial solar cells was performed to identify failure/degradation modes affecting solar cells and to relate these to basic physical, chemical, and metallurgical phenomena. Particular concerns addressed were the reliability attributes of individual single crystalline, polycrystalline, and amorphous thin film silicon cells. Results of subjecting different types of crystalline cells to the Clemson accelerated test schedule are given. Preliminary step stress results on one type of thin film amorphous silicon (a:Si) cell indicated that extraneous degradation modes were introduced above 140 C. Also described is development of measurement procedures which are applicable to the reliability testing of a:Si solar cells as well as an approach to achieving the necessary repeatability of fabricating a simulated a:Si reference cell from crystalline silicon photodiodes.
Lathrop, J. W.
Dynamic Fracture Toughness and Failure Mechanisms of ZnO Whiskers Secondary Reinforced Composites
NASA Astrophysics Data System (ADS)
Quasi-static and dynamic fracture properties and damage mechanism of glass fiber polymer composites embedded with different mass percentages of ZnO whiskers are investigated by using an Instron Testing machine and a Split-Hopkinson pressure bar. According to the experimental results and linear fracture mechanics, the quasi-static fracture toughness KIc and the dynamic fracture toughness KId under various impact velocities of specimens are obtained. Fracture mechanism is investigated by fractography analysis with a scanning electron microscope. The experimental results show that the mass percentage of ZnOw has little influence on the quasi-static fracture toughness, but a little influence on the dynamic fracture toughness and time of initial fracture point of specimens by the reason of various fracture mechanisms.
Rong, Ji-Li; Wang, Xi; Cao, Mao-Sheng; Xu, Tian-Fu
Failure mechanisms and optimum design for electroplated copper Through-Silicon Vias (TSV)
Through-silicon vias (TSVs) have garnered a lot of interest in recent years because TSV is a key enabling technology for three dimensional (3D) integrated circuit (IC) stacking, silicon interposer technology, and advanced wafer level packaging (WLP). There has been significant effort in TSV fabrication and electrical design. However, considerably less work has been done on thermo-mechanical analysis and mechanical design
Xi Liu; Qiao Chen; Pradeep Dixit; Ritwik Chatterjee; Rao R. Tummala; Suresh K. Sitaraman
Mechanical properties of coagulated albumin and failure mechanisms of liver repaired with the use of an argon-beam coagulator with albumin.
Hemostasis in the traumatized liver has been achieved by thermally denaturing topically applied albumin. In this article, the mechanical properties of liver and denatured albumin (solder) were measured, and the failure methods of liver repaired with albumin were identified. The ultimate tensile strength and Young's modulus were measured for healthy liver (N = 20) and thermally damaged liver (N = 20). The ultimate tensile strength and Young's modulus were measured for three concentrations of coagulated albumin (25, 38, and 53%) in a single layer and for two layers of denatured 38% albumin. Failure under tension of argon-beam coagulator soldered liver on the parenchymal surface (N = 30) with 38% albumin in two layers had a 70% occurrence for tearing at a mean stress of 39 kPa and a 23% occurrence for shearing at a mean stress of 7 kPa. Liver repaired on the interior surface (N = 11) failed in tension by tearing (64%) at a mean stress of 34 kPa and by shearing (36%) at a mean stress of 6 kPa. Argon-beam coagulator soldering with 38% albumin took 6 s/cm(2) for two layers of solder and gave the best balance of usability, strength, and matching of mechanical properties with those of the liver. PMID:12418016
Moffitt, T P; Baker, D A; Kirkpatrick, S J; Prahl, S A
Left Ventricular Twist Mechanics in a Canine Model of Reversible Congestive Heart Failure: A Pilot Study
Summary Left Ventricular (LV) twist dynamics play important roles in LV systolic and diastolic function. This preliminary study investigated LV twist dynamics in a canine model of reversible congestive heart failure (CHF). Pacing systems were implanted in adult dogs, and continuous chronic right ventricular pacing (230�250 bpm) was applied until CHF induction. Pacing was then stopped to allow the heart to recover. Echocardiography and LV catheterization were performed at baseline, during CHF while pacing was temporarily switched off, and during recovery. Left ventricular twist was computed as the difference between apical and basal rotations measured by two-dimensional speckle tracking. Torsion was further calculated as the LV twist divided by LV long axis. Untwisting rate was computed as the peak diastolic time derivative of twist. In 6 dogs that completed the study, we found that CHF developed after 2�4 weeks of pacing with LV end-diastolic volume, end-systolic volume, end-diastolic pressure, and time constant of relaxation during isovolumic relaxation period (tau) all increasing significantly compared to baseline, and recovering to normal levels 2�4 weeks after pacing was stopped. Left ventricular twist, torsion, and untwisting rate decreased significantly with CHF compared to baseline, and improved during recovery from CHF. In conclusion, LV twist dynamics reflect pacing-induced CHF and its reversal as assessed by echocardiographic speckle tracking.
Wang, Jianwen; Nagueh, Sherif F.; Mathuria, Nilesh S.; Shih, Hue-Teh; Panescu, Dorin; Khoury, Dirar S.
Hygrothermal effects on mechanical behavior of graphite/epoxy laminates beyond initial failure
NASA Technical Reports Server (NTRS)
An investigation was conducted to determine the critical load levels and associated cracking beyond which a multidirectional laminate can be considered as structurally failed. Graphite/epoxy laminates were loaded to different strain levels up to ultimate failure. Transverse matrix cracking was monitored by acoustic and optical methods. Residual stiffness and strength that were parallel and perpendicular to the cracks were determined and related to the environmental/loading history. Results indicate that cracking density in the transverse layers has no major effect on laminate residual properties as long as the angle ply layers retain their structural integrity. Exposure to hot water revealed that cracking had only a small effect on absorption and reduced swelling when these specimens were compared with uncracked specimens. Cracked, moist specimens showed a moderate reduction in strength when compared with their uncracked counterparts. Within the range of environmental/loading conditions of the present study, it is concluded that the transverse cracking process is not crucial in its effect on the structural performance of multidirectional composite laminates.
Ishai, O.; Garg, A.; Nelson, H. G.
Two-layer thermal barrier coating. I - Effects of composition and temperature on oxidation behavior and failure
NASA Technical Reports Server (NTRS)
The effects of 21 bond and 2 ceramic coating compositions on the specific mass gain, internal crack location at failure, and life of a two-layer thermal barrier coating (TBC) were studied by cyclic testing in a furnace. MAR-M 200 + Hf alloy specimens were completely coated with bond and thermal barrier (ceramic) coatings. Both coatings were applied by air plasma spray deposition. Cyclic test data were obtained at 1110, 1160, and 1220 deg C. The data show that the specific mass gain and the TBC life are significantly affected by the composition of the bond coating and the temperature and only slightly affected by the composition of the ceramic coating.
Stecura, Stephan
Involvement of Rho kinase pathway in the mechanism of renal vasoconstriction and cardiac hypertrophy in rats with experimental heart failure.
Rho-dependent kinases serve as downstream effectors of several vasoconstrictor systems, the activities of which are upregulated in congestive heart failure (CHF). We evaluated renal and cardiac effects of Y-27632, a highly selective Rho kinase inhibitor, in an experimental model of volume-overload CHF. Effects of acute administration of Y-27632 (0.3 mg/kg) on renal hemodynamic and clearance parameters and effects of chronic treatment (10.0 mg.kg(-1).day(-1) for 7 days via osmotic minipumps) on cardiac hypertrophy and cumulative Na+ excretion were studied in male Wistar rats with aortocaval fistula and control rats. The Y-27632-induced decrease in renal vascular resistance (from 40.4 +/- 4.6 to 26.0 +/- 3.1 resistance units, P < 0.01) in CHF rats was associated with a significant increase in total renal blood flow (+34%) and cortical and medullary blood flow (approx +37 and +27%, respectively). These values were significantly higher than those in control rats and occurred despite a decrease in mean arterial pressure (-15 mmHg). Despite the marked renal vasodilatory effect, Y-27632 did not alter glomerular filtration rate and renal Na+ excretion. Chronic administration of Y-27632 did not alter daily or cumulative renal Na+ excretion in CHF rats but was associated with a significant decrease in heart-to-body weight ratio, an index of cardiac hypertrophy: 0.32 +/- 0.007, 0.46 +/- 0.017, and 0.37 +/- 0.006% in control, CHF, and CHF + Y-27632 rats, respectively. The findings suggest that Rho kinase-dependent pathways are involved in the mechanisms of renal vasoconstriction and cardiac hypertrophy in rats with volume-overload heart failure. Selective blockade of these signaling pathways may be considered an additional tool to improve renal perfusion and attenuate cardiac hypertrophy in heart failure. PMID:16361369
Winaver, Joseph; Ovcharenko, Elena; Rubinstein, Irit; Gurbanov, Konstantin; Pollesello, Piero; Bishara, Bishara; Hoffman, Aaron; Abassi, Zaid
Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms
A new model considering both deformation and damage evolution under multiple viscoplastic mechanisms is used to represent high temperature creep deformation and damage of a martensitic stainless steel in a wide range of load levels. First, an experimental database is built to characterise both creep flow and damage behaviour using tests on various kinds of specimens. The parameters of the
V. Gaffard; J. Besson; A. F. Gourgues-Lorenzon
Failure probability assessment of wall-thinned nuclear pipes using probabilistic fracture mechanics
The integrity of nuclear piping system has to be maintained during operation. In order to maintain the integrity, reliable assessment procedures including fracture mechanics analysis, etc., are required. Up to now, this has been performed using conventional deterministic approaches even though there are many uncertainties to hinder a rational evaluation. In this respect, probabilistic approaches are considered as an appropriate
Sang-Min Lee; Yoon-Suk Chang; Jae-Boong Choi; Young-Jin Kim
A Randomized Trial of Initial Trophic versus Full-Energy Enteral Nutrition in Mechanically Ventilated Patients with Acute Respiratory Failure
Objective Enteral nutrition is provided to mechanically ventilated patients who cannot eat normally, yet the amount of support needed is unknown. We conducted this randomized, open-label study to test the hypothesis that initial low-volume (i.e. trophic) enteral nutrition would decrease episodes of gastrointestinal intolerance/complications and improve outcomes as compared to initial full-energy enteral nutrition in patients with acute respiratory failure. Design Randomized, open-label study Patients 200 Patients with acute respiratory failure expected to require mechanical ventilation for at least 72 hours Interventions Patients were randomized to receive either initial trophic (10 ml/hr) or full-energy enteral nutrition for the initial 6 days of ventilation. Measurements and Main Results The primary outcome measure was ventilator-free days to day 28. Baseline characteristics were similar between the 98 patients randomized to trophic and the 102 patients randomized to full-energy nutrition. At enrollment, patients had a mean APACHE II score of 26.9, PaO2/FiO2 of 182 and 38% were in shock. Both groups received similar duration of enteral nutrition (5.5 vs. 5.1 days; P=0.51). The trophic group received an average of 15 � 11% of goal calories daily through day 6 compared to 74.8 � 38.5% (P<0.001) for the full-energy group. Both groups had a median of 23.0 ventilator-free (P=0.90) and 21.0 ICU-free days (P=0.64). Mortality to hospital discharge was 22.4% for trophic vs. 19.6% for full-energy (P=0.62). In the first 6 days, the trophic group had trends for less diarrhea (19 vs. 24% of feeding days; P=0.08) and significantly fewer episodes of elevated gastric residual volumes (2 vs. 8% of feeding days; P<0.001). Conclusions Initial trophic enteral nutrition resulted in similar clinical outcomes in mechanically ventilated patients with acute respiratory failure as early full-energy enteral nutrition but with fewer episodes of gastrointestinal intolerance.
Rice, Todd W.; Mogan, Susan; Hays, Margaret A.; Bernard, Gordon R.; Jensen, Gordon L.; Wheeler, Arthur P.
Failure Analysis of Minuteman Integrated Circuit Failures.
National Technical Information Service (NTIS)
This program was devoted to the determination of the failure modes and to a study of the failure mechanisms in integrated circuits used in the Minuteman II control and guidance system. In-depth failure analyses were performed on 114 rejects from system eq...
P. J. Besser A. B. Menefee P. H. Eisenberg
Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion
NASA Technical Reports Server (NTRS)
Alumina scale adhesion to high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However, adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for thermal barrier coatings (TBCs), culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylation of aluminum from the alloy interface appears to be the relevant basic reaction.
Smialek, James L.
Ultrastructural and cellular basis for the development of abnormal myocardial mechanics during the transition from hypertension to heart failure.
Although the development of abnormal myocardial mechanics represents a key step during the transition from hypertension to overt heart failure (HF), the underlying ultrastructural and cellular basis of abnormal myocardial mechanics remains unclear. We therefore investigated how changes in transverse (T)-tubule organization and the resulting altered intracellular Ca(2+) cycling in large cell populations underlie the development of abnormal myocardial mechanics in a model of chronic hypertension. Hearts from spontaneously hypertensive rats (SHRs; n = 72) were studied at different ages and stages of hypertensive heart disease and early HF and were compared with age-matched control (Wistar-Kyoto) rats (n = 34). Echocardiography, including tissue Doppler and speckle-tracking analysis, was performed just before euthanization, after which T-tubule organization and Ca(2+) transients were studied using confocal microscopy. In SHRs, abnormalities in myocardial mechanics occurred early in response to hypertension, before the development of overt systolic dysfunction and HF. Reduced longitudinal, circumferential, and radial strain as well as reduced tissue Doppler early diastolic tissue velocities occurred in concert with T-tubule disorganization and impaired Ca(2+) cycling, all of which preceded the development of cardiac fibrosis. The time to peak of intracellular Ca(2+) transients was slowed due to T-tubule disruption, providing a link between declining cell ultrastructure and abnormal myocardial mechanics. In conclusion, subclinical abnormalities in myocardial mechanics occur early in response to hypertension and coincide with the development of T-tubule disorganization and impaired intracellular Ca(2+) cycling. These changes occur before the development of significant cardiac fibrosis and precede the development of overt cardiac dysfunction and HF. PMID:24186100
Shah, Sanjiv J; Aistrup, Gary L; Gupta, Deepak K; O'Toole, Matthew J; Nahhas, Amanda F; Schuster, Daniel; Chirayil, Nimi; Bassi, Nikhil; Ramakrishna, Satvik; Beussink, Lauren; Misener, Sol; Kane, Bonnie; Wang, David; Randolph, Blake; Ito, Aiko; Wu, Megan; Akintilo, Lisa; Mongkolrattanothai, Thitipong; Reddy, Mahendra; Kumar, Manvinder; Arora, Rishi; Ng, Jason; Wasserstrom, J Andrew
Downstream anastomotic hyperplasia. A mechanism of failure in Dacron arterial grafts.
The precise location and progression of anastomotic hyperplasia and its possible relationship to flow disturbances was investigated in femoro-femoral Dacron grafts in 28 dogs. In 13 grafts, the outflow from the end-to-side downstream anastomosis was bidirectional (BDO), and in 15 it was unidirectional (UDO) (distally). Grafts were electively removed at intervals of two to 196 days or at the time of thrombosis. Each anastomosis and adjacent artery was perfusion-fixed and sectioned sagittally. The mean sagittal section was projected onto a digitized pad, and the total area of hyperplasia internal to the arterial internal elastic lamina and within the adjacent graft was integrated by computer. The location of the hyperplasia was compared with previously established sites of flow separation and stagnation. The observation was made that hyperplasia is significantly greater at the downstream, as compared with the upstream, anastomosis in both groups (BDO = p less than 0.001 and UDO = p less than 0.001) (analysis of variance for independent groups). Furthermore, this downstream hyperplasia was progressive with time (BDO p less than 0.01) (UDO p less than 0.01); Spearman Rank Correlation. There was no significant increase in the extent of downstream hyperplasia where flow separation was known to be greater (BDO). Five grafts failed (three BDO, two UDO), as a result of complete occlusion of the downstream anastomosis by fibrous hyperplasia. Transmission electron microscopy showed the hyperplasia to consist of collagen-producing smooth muscle cells. Anastomotic hyperplasia is significantly greater at the downstream anastomosis, is progressive with time, and is the primary cause of failure of Dacron arterial grafts in this model. Quantitative analysis of downstream anastomotic hyperplasia may be a valuable measure of the biocompatibility of Dacron grafts. Images Fig. 2. Fig. 3. Fig. 5. Fig. 6. Fig. 7. Fig. 8.
LoGerfo, F W; Quist, W C; Nowak, M D; Crawshaw, H M; Haudenschild, C C
On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization
Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Power Generation, Inc proposed a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Power Generation, Inc. has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.
Dennis H. LeMieux
Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability, availability, and maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can, therefore, accelerate the degradation of substrate component materials and eventually lead to a premature failure of critical components and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.
Dennis H. LeMieux
Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability, availability, and maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can, therefore, accelerate the degradation of substrate component materials and eventually lead to a premature failure of critical components and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.
Dennis H. LeMieux
Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.