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Assessment of fatigue life for small composite wind turbine blades
Microsoft Academic Search
The present design and assessment of fatigue life for the small composite wind turbine blades (SCWTBs) can be certified by IEC 61400-2 "Wind Turbines - Part2: Design requirements of small wind turbines". The paper will establish an analytical method on the fatigue life analysis of SCWTBs. Using the Microsoft Office EXCEL to calculate the maximum stress, minimum stress and stress
Jia-Hroung Wu
Fatigue life estimation procedure for a turbine blade under transient loads
Fatigue analysis and consequent life prediction of turbomachine blading requires the stress load history of the blade. A blade designed for safe operation at particular constant rotor speeds may, however, incur damaging stresses during start-up and shut-down operations. During such operations the blade experiences momentary resonant stresses while passing through the criticals, which may lie in the speed range through
N. S. Vyas; J. S. Rao
Fatigue life prediction and strength degradation of wind turbine rotor blade composites
Wind turbine rotor blades are subjected to a large number of highly variable loads, but life predictions are typically based on constant amplitude fatigue behaviour. Therefore, it is important to determine how service life under variable amplitude fatigue can be estimated from constant amplitude fatigue behaviour.\\u000a\\u000aA life prediction contains different, partly independent, elements:\\u000a·\\u0009the counting method, used for
R. P. L. Nijssen
Blade fatigue life assessment with application to VAWTs
The possibility of satisfactory modeling of the vibratory stress level history of a vertical axis wind turbine (VAWT) is considered. Fatigue life prediction is expressed as a function of the vibratory stress level, the wind speed, and the wind speed distribution on-site. A statistical distribution of stress levels is asserted to more accurately simulate the stress level than determination of
P. S. Veers
Investigation of fatigue life for a medium scale composite wind turbine blade
In order to satisfy fatigue requirements in designing a cost effective wind turbine, the wind turbine blade, which is an expensive key component of the wind turbine system, must achieve very long operating life of 20–30 years. In this study, the fatigue life of a medium scale (750kW) horizontal axis wind turbine system (HAWIS), which has been developed by the
Changduk Kong; Taekhyun Kim; Dongju Han; Yoshihiko Sugiyama
This paper introduces a quantitative concept developed jointly by WR-ALC, the FAA, and the Technology for Energy Corporation to ensure the structural integrity of aluminum alloy propeller blades used on numerous military and civil aircraft. The propeller assembly of a turboprop engine is a highly energetic rotating assembly--that a catastrophic, single point failure in a propeller blade can cause catastrophic
T. Yentzer; B. Stillman; M. Fisher; B. Pardue; TN D. Krafsur; Knoxville TN T. Khaled
Comparison of Tensile Fatigue Resistance and Constant Life Diagrams for Several Potential Wind Turbine Blade Laminates
New fatigue test results are presented for four multidirectional laminates of current and potential interest for wind turbine blades, representing three types of fibers: E-glass, WindStrandTM glass, and carbon, all with epoxy resins. A broad range of loading conditions are included for two of the laminates, with the results represented as mean and 95\\/95 confidence level constant life diagrams. The
Daniel D. Samborsky; Timothy J. Wilson; John F. Mandell
A technique for fatigue damage assessment during variable speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes, and Miner's rule is employed to estimate the cumulation of fatigue.
Turbine blade thermal fatigue testing Pratt and Whitney aircraft hollow core blades
NASA Technical Reports Server (NTRS)
The results of low cycle fatigue testing on turbine blades for use in hydrogen/oxygen rocket engines is presented. Cored blade and cored blades with circulation were tested in the MSFC thermal fatigue tester. Both blade configurations showed significant low cycle fatigue life improvements when compared to baseline solid blades.
Ingram, J.; Gross, L.
Computation Method on Fatigue Life of a Full Composite Wind Turbine Blade
The generation of load spectrum for epoxy resin blade of large-scale wind turbine is researched in this paper, so are an engineering estimating method of the fatigue failure and accumulated fatigue damage. Meanwhile, Load cases are considered, calculated and evaluated. First, a 3 dimensional finite element modal for calculation of fatigue failure is proposed based on the composite laminated technology
Jing Wang; Zhihua Huang; Yinghui Li
Microcrack growth behavior and life in high temperature low cycle fatigue of blade root and disc joint for turbines
Low cycle fatigue tests were carried out at a temperature of 600°C using a component specimen of 12%-Cr steel, which simulates a blade root and disc joint for turbines. The growth behavior of micro-cracks in the joint region of the specimens was investigated to clarify the damage mechanism of blade-root joints used in high temperature environments and to improve life
Nobuhiro Isobe; Shuhei Nogami
Long-term fatigue life loss of turbine blades owing to noncharacteristic harmonic currents in asynchronous HVDC links
The long-term effect of noncharacteristic harmonic currents in asynchronous HVDC links on fatigue life expenditure in turbine–generator blades is studied in this paper. Because the frequencies of the two main harmonic current terms are subsynchronous and offer a probability distribution due to the asynchronous operation in a HVDC link, a systematic fatigue estimation approach was devised to investigate the long-term
Jong-Ian Tsai; Chi-Hshiung Lin; Ta-Peng Tsao
Fatigue life variability and reliability analysis of a wind turbine blade.
National Technical Information Service (NTIS)
Wind turbines must withstand harsh environments that induce many stress cycles into their components. A numerical analysis package is used to illustrate the sobering variability in predicted fatigue life with relatively small changes in inputs. The variab...
P. S. Veers H. J. Sutherland T. D. Ashwill
Estimation of spallation life of thermal barrier coating of gas turbine blade by thermal fatigue test
Plasma-sprayed thermal barrier coatings (TBCs) are applied to protect the blades of a gas turbine system from high-temperature gas and to lower the surface temperature of the blades. The failure of TBC is directly connected to the failure of the blades because the spallation of a ceramic layer leads to the acceleration of local corrosion and oxidation at the location
In-Hwan Shin; Jae-Mean Koo; Chang-Sung Seok; Sung-Ho Yang; Tack-Woon Lee; Bum-Soo Kim
Dynamic stress analysis and a fracture mechanics approach to life prediction of turbine blades
Emerging blade technologies are finding it increasingly essential to correlate blade vibrations to blade fatigue in order to assess the residual life of existing blading and for development of newer designs. In this paper an analytical code for dynamic stress analysis and fatigue life prediction of blades is presented. The life prediction algorithm is based on a combination method, which
J. S. Rao
Structural investigation of composite wind turbine blade considering various load cases and fatigue life
This study proposes a structural design for developing a medium scale composite wind turbine blade made of E-glass\\/epoxy for a 750kW class horizontal axis wind turbine system. The design loads were determined from various load cases specified at the IEC61400-1 international specification and GL regulations for the wind energy conversion system. A specific composite structure configuration, which can effectively endure
C. Kong; J. Bang; Y. Sugiyama
Study of fatigue damage in wind turbine blades
The inspection of damages detected in some blades of 300kW wind turbines revealed that the nature of these damages was probably due to a fatigue mechanism. The causes that had originated the failure (superficial cracks, geometric concentrator, abrupt change of thickness) have been studied, verifying, by means of the simplified evaluation procedure of fatigue life of the "Germanischer Lloyd" (GL)
J. C. Marín; A. Barroso; F. París; J. Cańas
Fatigue of fiberglass wind turbine blade materials
Fatigue behavior for a variety of generic materials used in wind turbine blades was explored. Coupon testing was carried out under constant amplitude tensile fatigue loading to beyond 10(exp 7) cycles for most materials. Unidirectional materials performed close to expectations despite fiber misalignment. Materials with triaxial (0\\/plus or minus 45) reinforcement showed greater fatigue sensitivity than expected, but lifetime trends
J. F. Mandell; R. M. Reed; D. D. Samborsky
Determination of Turbine Blade Life from Engine Field Data
It is probable that no two engine companies determine the life of their engines or their components in the same way or apply the same experience and safety factors to their designs. Knowing the failure mode that is most likely to occur minimizes the amount of uncertainty and simplifies failure and life analysis. Available data regarding failure mode for aircraft engine blades, while favoring low-cycle, thermal mechanical fatigue as the controlling mode of failure, are not definitive. Sixteen high-pressure turbine (HPT) T-1 blade sets were removed from commercial aircraft engines that had been commercially flown by a single airline and inspected for damage. Each set contained 82 blades. The damage was cataloged into three categories related to their mode of failure: (1) Thermal-mechanical fatigue, (2) Oxidation/Erosion, and (3) "Other." From these field data, the turbine blade life was determined as well as the lives related to individual blade failure modes using Johnson-Weibull analysis. A simplified formula for calculating turbine blade life and reliability was formulated. The L(sub 10) blade life was calculated to be 2427 cycles (11 077 hr). The resulting blade life attributed to oxidation/erosion equaled that attributed to thermal-mechanical fatigue. The category that contributed most to blade failure was Other. If there were there no blade failures attributed to oxidation/erosion and thermal-mechanical fatigue, the overall blade L(sub 10) life would increase approximately 11 to 17 percent.
Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.
Structural analysis: Fatigue life assessment
NASA Astrophysics Data System (ADS)
Lectures on the structural analysis of turbomachinery covering fatigue life assessment, stresses due to centrifugal, pressure, and thermal loads, and blade disc vibration and rotor dynamics, are presented. Concepts and techniques, modeling methods, and structural design evaluation and optimization are desribed.
Marscher, William D.
Structural-Response Analysis, Fatigue-Life Prediction, and Material Selection for 1 MW Horizontal-Axis Wind-Turbine Blades
The problem of mechanical design, performance prediction (e.g., flap-wise\\/edge-wise bending stiffness, fatigue-controlled life, the extent of bending-to-torsion coupling), and material selection for a prototypical\\u000a 1 MW horizontal-axis wind turbine (HAWT) blade is investigated using various computer-aided engineering tools. For example,\\u000a a computer program was developed which can automatically generate both a geometrical model and a full finite-element input\\u000a deck for a
M. Grujicic; G. Arakere; E. Subramanian; V. Sellappan; A. Vallejo; M. Ozen
Structural-Response Analysis, Fatigue-Life Prediction, and Material Selection for 1 MW Horizontal-Axis Wind-Turbine Blades
The problem of mechanical design, performance prediction (e.g., flap-wise/ edge-wise bending stiffness, fatigue-controlled life, the extent of bending-to-torsion coupling), and material selection for a prototypical 1 MW horizontal-axis wind turbine (HAWT) blade is investigated using various computer-aided engineering tools. For example, a computer program was developed which can automatically generate both a geometrical model and a full finite-element input deck for a given single HAWT-blade with a given airfoil shape, size, and the type and position of the interior load-bearing longitudinal beam/shear-webs. In addition, composite-material laminate lay-up can be specified and varied in order to obtain a best combination of the blade aerodynamic efficiency and longevity. A simple procedure for HAWT-blade material selection is also developed which attempts to identify the optimal material candidates for a given set of functional requirements, longevity and low weight.
Grujicic, M.; Arakere, G.; Subramanian, E.; Sellappan, V.; Vallejo, A.; Ozen, M.
General method for fatigue analysis of vertical-axis wind-turbine blades
The fatigue life of wind-turbine blades, which are exposed to the random loading environment of atmospheric winds, is described with random data analysis procedures. The incident windspeed and the stresses caused by these winds are expressed in terms of probability density functions while the fatigue life vs. stress level relationship is treated deterministically. This approach allows the fatigue damage to
Paul S. Veers
Fatigue behavior for a variety of generic materials used in wind turbine blades was explored. Coupon testing was carried out under constant amplitude tensile fatigue loading to beyond 10(exp 7) cycles for most materials. Unidirectional materials performed close to expectations despite fiber misalignment. Materials with triaxial (0/plus or minus 45) reinforcement showed greater fatigue sensitivity than expected, but lifetime trends flattened at high cycles. The uniaxial and triaxial materials could be normalized to a single S-N lifetime trend for each case. Results include the effects of differing matrix materials, manufacturing methods, reinforcement structure, and ply terminations.
Mandell, J. F.; Reed, R. M.; Samborsky, D. D.
LIFE Computer Code: Fatigue Life Prediction for Vertical Axis Wind Turbine Components.
The LIFE computer code was originally written by Veers to analyze the fatigue life of a vertical axis wind turbine (VAWT) blade. The basic assumptions built into this analysis tool are: the fatigue life of a blade component is independent of the mean stre...
H. J. Sutherland T. D. Ashwill N. Slack
It is probable that no two engine companies determine the life of their engines or their components in the same way or apply the same experience and safety factors to their designs. Knowing the failure mode that is most likely to occur minimizes the amount of uncertainty and simplifies failure and life analysis. Available data regarding failure mode for aircraft engine blades, while favoring low-cycle, thermal-mechanical fatigue (TMF) as the controlling mode of failure, are not definitive. Sixteen high-pressure turbine (HPT) T-1 blade sets were removed from commercial aircraft engines that had been commercially flown by a single airline and inspected for damage. Each set contained 82 blades. The damage was cataloged into three categories related to their mode of failure: (1) TMF, (2) Oxidation/erosion (O/E), and (3) Other. From these field data, the turbine blade life was determined as well as the lives related to individual blade failure modes using Johnson-Weibull analysis. A simplified formula for calculating turbine blade life and reliability was formulated. The L10 blade life was calculated to be 2427 cycles (11 077 hr). The resulting blade life attributed to O/E equaled that attributed to TMF. The category that contributed most to blade failure was Other. If there were no blade failures attributed to O/E and TMF, the overall blade L(sub 10) life would increase approximately 11 to 17 percent.
New Method for Dual-Axis Fatigue Testing of Large Wind Turbine Blades Using Resonance Excitation and Spectral Loading
SciTech Connect
The blades of a wind turbine are generally considered to be the most critical component of the wind turbine system. The fundamental purpose of performing fatigue tests on wind turbine blades is to demonstrate that a blade, when manufactured to a certain set of specifications, has the prescribed reliability and service life. The purpose of the research conducted for this project is the advancement of knowledge and capabilities in the area of wind turbine blade fatigue testing.
White, D.
A simulation model for wind turbine blade fatigue loads
The paper describes a horizontal axis wind turbine time domain simulation and fatigue estimation program written using the DelphiTM language. The program models the flapwise motion of a single rotor blade to determine the blade-root fatigue damage of a medium size wind turbine. The effects of turbulence intensity, mean wind speed, wind shear, vertical wind component, dynamic stall, stall hysteresis,
M. Noda; R. G. J. Flay
The blades of a wind turbine are generally considered to be the most critical component of the wind turbine system. The fundamental purpose of performing fatigue tests on wind turbine blades is to demonstrate that a blade, when manufactured to a certain set of specifications, has the prescribed reliability and service life. The purpose of the research conducted for this
A physical-base model for life prediction of single crystal turbine blades under creep-fatigue loading and thermal transient conditions
The damage estimation model developed herein can be used to predict service life under creep-fatigue loading in both isothermal (LCF) and variable temperature (TMF) conditions. This model is based upon a careful identification of basic physical mechanisms taking part in the damage process of a unit microstructural element. The damage is, in fact, considered to be the growth of micro
A. Koster; A. M. Alam; L. Rémy
This paper provides an overview of the results of recent studies of composite laminates of interest for wind turbine blade construction. In addition to the primary requirements of stiffness, strength, and ease of processing, wind blade materials must withstand severe fatigue loading under service environments. The large material volumes and cost constraints also lead to unusually thick plies and fabrics,
John F. Mandell; Daniel D. Samborsky
Fatigue Evaluation of WTS-3 Glassfibre Blade Material.
A first step in assessing the fatigue properties of the WTS-3 wind turbine blade material has been undertaken. Hereby flat test specimens of filament-wound material have been used for the fatigue tests. Woehler-diagrams (SN-curves) have been produced both...
A. F. Blom
Fatigue Evaluation of Wts-3 Glass Fiber Blade Material.
The fatigue properties of the WTS-3 wind turbine blade material were assessed. Flat test specimens of filament wound material were used for the fatigue tests. Wohler diagrams (SN curves) were produced both at purely tensile loading R = delta min/max = 0 a...
PZT Active Frequency Based Wind Blade Fatigue to Failure Testing Results for Various Blade Designs.
This paper summarizes NASA PZT Health Monitoring System results previously reported for 9 meter blade Fatigue loading to failure conducted at The National Renewable Energy Lab Wind blade testing facility results using the on the CX-100, TX-100 and BSDS de...
R. J. Werlink
Mitigation of FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel Compressor Blades with Surface Treatment
Compressor blades of a military aircraft turbine engine made of 17 -4 PH stainless steel have been reported to have blade edge foreign object damage (FOD), corrosion pitting, and erosion damage that reduce fatigue life. This paper reports the findings of a comprehensive investigation of the effect of residual compressive stresses, imparted by various surface treatments, to improve leading edge
Paul S. Prevéy; N. Jayaraman; Ravi Ravindranath
Erosion-fatigue of steam turbine blades
The premature failure of steam turbine rotor blades, manufactured in forged 12% Cr–NiMoV martensitic stainless steel, was investigated using visual inspection, non-destructive testing, macro and microfractography, microstructural characterization, EDS microanalysis, chemical analysis, micro hardness and tensile testing. The blades belonged to the last stage of a thermoelectric plant steam turbine generator (140MVA). The results indicated that the failure of the
C. R. F. Azevedo; A. Sinátora
Simulation of fatigue failure in composite axial compressor blades
Centrifugal forces are generated by a spinning impeller, of magnitudes that create large stresses. Aerodynamic forces are also imparted on an impeller blade, which varies with time and position. These two forces play different roles during compressor events. Damage accumulated from these events results in the fatigue failure of impeller material and structure. Therefore, it is important to design an
Qubo Li; Janusz Piechna; Norbert Müeller
Nonlinear Structural Analysis of Turbine Blade & Disk and its Application in Life Prediction
Nonlinear stress analysis of second stage turbine blade and disk of F100-PW-229 turbofan engine under centrifugal, aerodynamic and thermal load was performed. FEA results were reviewed and life-limiting locations were identified regarding each component's design criteria. Calculated stresses and strains in these critical locations of the blade were used in life predictions in terms of fatigue and creep, which are
Hong Chul Sohn; Jung Jun Suh
Turbine blade nonlinear structural and life analysis
The utility of advanced structural analysis and life prediction techniques was evaluated for the life assessment of a commercial air-cooled turbine blade with a history of tip cracking. Three dimensional, nonlinear finite element structural analyses were performed for the blade tip region. The computed strain-temperature history of the critical location was imposed on a uniaxial strain controlled test specimen to evaluate the validity of the structural analysis method. Experimental results indicated higher peak stresses and greater stress relaxation than the analytical predictions. Life predictions using the Strainrange Partitioning and Frequency Modified approaches predicted 1200 to 4420 cycles and 2700 cycles to crack initiation, respectively, compared to an observed life of 3000 cycles.
Mcknight, R. L.; Laflen, J. H.; Halford, G. R.; Kaufman, A.
Fatigue life prediction in composites
Because of the relatively large number of possible failure mechanisms in fibre reinforced composite materials, the prediction of fatigue life in a component is not a simple process. Several mathematical and statistical models have been proposed, but the experimental evidence to support them is limited so far. In this paper, an attempt has been made to fit experimental results to
R. J. Huston
Fatigue failure analysis of holding U-bolts of a cooling fan blade
Fatigue failure of holding U-bolt of a cooling fan blade is analyzed. Fractography of the fracture surface reveals the characteristics of a fatigue fracture. Finite element modeling is used for stress analyzing. Analysis of the loading conditions indicates that the bolts are under multiaxial fatigue. Effective alternating and mean stresses are obtained based on the multiaxial fatigue criteria. By using
M. Reihanian; K. Sherafatnia; M. Sajjadnejad
A probabilistic methodology for fatigue life prediction
This paper describes efforts in the probabilistic modelling of fatigue. The methodology proposed deals with crack nucleation from surface defects within a fracture mechanics framework. The methodology provides a quantitative understanding of the effects of bulk defects and their size distribution on the variation of fatigue life. It also considers the contributions of the variations of fatigue crack nucleation life
J. Luo; P. Bowen
Wind turbine blade fatigue tests: lessons learned and application to SHM system development
This paper presents experimental results of several structural health monitoring (SHM) methods applied to a 9-meter CX-100 wind turbine blade that underwent fatigue loading. The blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. It underwent harmonic excitation at its first natural frequency using a hydraulically actuated resonant excitation system. The blade was initially excited
Stuart G. Taylor; Kevin M. Farinholt; Hyomi Jeong; JaeKyung Jang; Gyu Hae Park; Michael D. Todd; Charles R. Farrar; Curtt N. Ammerman
A simple method of estimating wind turbine blade fatigue at potential wind turbine sites
This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade`s root flap bending moment. The model requires as input a simple set of wind measurements that may be obtained as part of a routine site characterization study. By using the model to simulate
J. C. Barnard; L. L. Wendell
Fatigue crack initiation life prediction of railroad
Study of multiaxial high-cycle fatigue initiation life prediction for railroad is done in this paper. Using ANSYS 11.0 software three dimensional elasto-plastic finite element model of rail/wheel contact is constructed and fine mesh technique in contact region is used to achieve both computational efficiency and accuracy. Stress analysis is performed and fatigue damage in railroad is evaluated numerically using multiaxial fatigue crack initiation model. Using the stress history during one loading cycle and fatigue damage model, the effects of vertical loading, material hardness material fatigue properties and wheel/rail contact situation on fatigue crack initiation life are investigated.
Tehrani, P. Hosseini; Saket, M.
This paper describes a method to predict fatigue lifetimes of fiber reinforced plastics in wind turbine blades. It is based on extensive testing within the EU-Joule program. The method takes the measured fatigue properties of a material into account so that credit can be given to materials with improved fatigue properties. The large number of test results should also give
A. T. Echtermeyer; C. Kensche; P. Bach; M. Poppen; H. Lllholt; S. I. Andersen; P. Brřndsted
The lead crack fatigue lifing framework
A fatigue lifing framework using a lead crack concept has been developed by the DSTO for metallic primary airframe components. The framework is based on years of detailed inspection and analysis of fatigue cracks in many specimens and airframe components, and is an important additional tool for determining aircraft component fatigue lives in the Royal Australian Air Force (RAAF) fleet.
L. Molent; S. A. Barter; R. J. H. Wanhill
Thermal Fatigue Life of Thermal Barrier Coatings
Two thermal barrier coatings (TBCs), the plasma sprayed (PS) and electron beam-physical vapor deposition (EB-PVD) coatings were selected to analyze the fatigue life. Firstly, the oxidation and thermal fatigue experiments were carried out, which were domestic spraying technology. The failure mechanisms of oxidation and thermal fatigue of TBCs were considered together. The weight of thermally grown oxide (TGO) was measured
Qi Hongyu; Li Rui; Yang Xiaoguang; Zhou Lizhu
Bayesian Network Combined Fuzzy C-means Methodology for Turbine Blades Fatigue Performance Evaluation
In this paper, a fatigue performance evaluation model for steam turbine blades based on Bayesian network combined fuzzy c-means algorithm was proposed. Bayesian network was viewed as a classification technique to evaluate fatigue performance. Fuzzy c-means algorithm was applied to perform cluster analysis of fatigue performance values and made them discrete. Low-cycle fatigue tests on certain kind of steam turbine
Jihong Yan; Xingman Xiong; Shifeng Zhu
High-Cycle Fatigue Testing of Turbine Blades Under Multiaxial Loading.
Gas turbine engine blades are subjected to a centrifugal force in the radial direction and high frequency transverse excitation under operating conditions. A multiaxial loading machine was proposed in the present SBIR program to perform high-cycle fatigue...
M. Balan B. Bornhorst S. R. Soni M. Xie
A real time neural net estimator of fatigue life
A neural net architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the Intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopump blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines. This neural net estimator of fatigue life is seen as the enabling technology to achieve component life prognosis, and therefore would be an important part of life extending control for reusable rocket engines.
Troudet, T.; Merrill, W.
Nitinol Fatigue Life for Variable Strain Amplitude Fatigue
Nitinol fatigue testing results are presented for variable strain amplitude cycling. The results indicate that cycles smaller than the constant amplitude fatigue limit may contribute to significant fatigue damage when they occur in a repeating sequence of large and small amplitude cycles. The testing utilized two specimen types: stent-like diamond specimens and Z-shaped wire specimens. The diamond specimens were made from nitinol tubing with stent-like manufacturing processes and the Z-shaped wire specimens were made from heat set nitinol wire. The study explored the hypothesis that duty cycling can have an effect on nitinol fatigue life. Stent-like structures were subjected to different in vivo loadings in order to create more complex strain amplitudes. The main focus in this study was to determine whether a combination of small and large amplitudes causes additional damage that alters the fatigue life of a component.
Lin, Z.; Pike, K.; Schlun, M.; Zipse, A.; Draper, J.
Fatigue life prediction in bending from axial fatigue information
Bending fatigue in the low cyclic life range differs from axial fatigue due to the plastic flow which alters the linear stress-strain relation normally used to determine the nominal stresses. An approach is presented to take into account the plastic flow in calculating nominal bending stress (S sub bending) based on true surface stress. These functions are derived in closed form for rectangular and circular cross sections. The nominal bending stress and the axial fatigue stress are plotted as a function of life (N sub S) and these curves are shown for several materials of engineering interest.
Manson, S. S.; Muralidharan, U.
The effect of combined cycle fatigue upon the fatigue performance of TI–6AL–4V fan blade material
Samples of Ti–6Al–4V (wt.%) were tested to failure under low cycle fatigue (LCF), high cycle fatigue (HCF), and combined cycle fatigue (CCF), respectively, in order to ascertain the effects of the combined cycle situation upon the total fatigue life. The results indicate that the effect of the combined loading is variable and dependent upon the conditions during testing. It has
C. Dungey; P. Bowen
Full-Scale Fatigue Test of 9-m CX-100 Wind Turbine Blades.
This paper presents the SHM result of a 9m CX-100 wind turbine blade under full-scale fatigue loads. The test was performed at the National Renewable Energy Laboratory. The 9-meter blade was instrumented with piezoelectric transducers, accelerometers, aco...
C. R. Farrar G. Park K. M. Farinholt S. G. Taylor
The development of a fatigue loading spectrum for small wind turbine blades
This paper details a formulation to create a fatigue loading procedure for the blade of a small wind turbine using a combination of detailed short-term aeroelastic and wind measurements and averaged long-term wind data from the Australian Bureau of Meteorology. Detailed aeroelastic measurements from the blade of an operating small wind turbine were acquired simultaneously with wind speed measurements and
Jayantha A. Epaarachchi; Philip D. Clausen
This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade's root flap bending moment. The model requires as input a simple set of wind measurements which may be obtained as part of a routine site characterization study. By using the model to simulate
Acoustic emission monitoring of a wind turbine blade during a fatigue test
A fatigue test of a wind turbine blade was conducted at the National Renewable Energy Laboratory in the fall of 1994. Acoustic emission monitoring of the test was performed, starting with the second loading level. The acoustic emission data indicated that this load exceeded the strength of the blade. From the first cycle at the new load, an oil can
A. G. Beattie
Fatigue Testing of 9 m Carbon Fiber Wind Turbine Research Blades
Fatigue testing was conducted on Carbon Experimental and Twist-Bend Experimental (CX-100 and TX-100) 9-m wind turbine research blades. The CX-100 blade was designed to investigate the use of a carbon spar cap to reduce weight and increase stiffness while being incorporated using conventional manufacturing techniques. The TX-100 blade used carbon in the outboard portion of the skin to produce twist-bend
J. Paquette; J. van Dam; S. Hughes; J. Johnson
Frequency domain analysis of the fatigue loads on typical wind turbine blades
The fatigue analysis of a wind turbine blade typically depends on converting time-series data to a series of load cycles using one of several cyclic counting algorithms. However, many structural analysis techniques yield frequency-domain stress spectra, and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the fatigue analysis of this class of
Herbert J. Sutherland
Simulation of fatigue failure in a full composite wind turbine blade
Lifetime prediction of a horizontal axis wind turbine composite blade is considered. Load cases are identified, calculated and evaluated. Static analysis is performed with a full 3-D finite element method and the critical zone where fatigue failure begins is extracted. Accumulated fatigue damage modeling is employed as a damage estimation rule based on generalized material property degradation. Since wind flow
Mahmood M. Shokrieh; Roham Rafiee
Life Time Prediction of Gas Turbine Components (Turbine Blades).
The problems of lifetime predictions for gas turbine blades made of cast alloys IN 738 LC and IN 939 were examined. The materials were tested under typical operating temperatures on their performance under fatigue and creep stress and with combined strain...
W. Hoffelner M. Nazmy C. Wuethrich
Strength and Fatigue Life of Wire Rope
A method is presented that predicts the fatigue life of a large diameter wire rope, from test data for small diameter rope. Dimensional analysis and the technique of interpolation and extrapolation are employed. The method is applied first to study size effects on the breaking strength of wire ropes and then to predict fatigue strength. Results are compared with experimental
Chi-Hui Chien; Raymond A. LeClair; George A. Costello
Constitutive and life modeling of single crystal blade alloys for root attachment analysis
Work to develop fatigue life prediction and constitutive models for uncoated attachment regions of single crystal gas turbine blades is described. At temperatures relevant to attachment regions, deformation is dominated by slip on crystallographic planes. However, fatigue crack initiation and early crack growth are not always observed to be crystallographic. The influence of natural occurring microporosity will be investigated by testing both hot isostatically pressed and conventionally cast PWA 1480 single crystal specimens. Several differnt specimen configurations and orientations relative to the natural crystal axes are being tested to investigate the influence of notch acuity and the material's anisotropy. Global and slip system stresses in the notched regions were determined from three dimensional stress analyses and will be used to develop fatigue life prediction models consistent with the observed lives and crack characteristics.
Meyer, T. G.; Mccarthy, G. J.; Favrow, L. H.; Anton, D. L.; Bak, Joe
Fatigue life prediction in titanium matrix composites
Methods used for life prediction of titanium matrix composites under isothermal and thermomechanical (TMF) fatigue are reviewed. Models containing a single parameter are shown to have applicability only under limited conditions. Two models, a dominant damage and a life fraction model, demonstrate predictive capabilities over a broad range of loads, frequencies, temperatures, and TMF parameters. Relationships between the underlying fatigue mechanisms and the individual terms in the models are illustrated.
Nicholas, T. [Wright Lab., Wright-Patterson AFB, OH (United States). Materials Directorate
Multiscale Fatigue Life Prediction for Composite Panels
Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.
Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.
Fatigue Life Characteristics of Waterworks Pipe Welds
The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many test results of standard specimens are very different from those of real structures or components because of geometrical effect, surface condition and so on. In this study, fatigue tests with specimens and pipes were carried out to evaluate the fatigue characteristic of a real waterworks pipe. Standard fatigue specimens and non-standard specimens were extracted from a steel pipe used in waterworks system. Also, fatigue tests of real pipes used in water service were carried out. This result was compared with that of standard specimens and non-standard specimens. To evaluate pipe's fatigue characteristics based on life distribution, the statistical analysis method was introduced. Probability density functions of the specimen based on the normal distribution function were obtained from fatigue tests at particular stress levels. These functions were then transformed to probability density functions based on a specific number of cycles to failure. This procedure was also adapted to the pipe's test results. From these results, the fatigue characteristic of waterworks pipe was evaluated.
Park, Jae Sil; Seok, Chang-Sung; Choi, Jung Hun
Fatigue crack growth simulation in a generator fan blade
The blades of Iran Montazer-Ghaem-Unit4 power plant failed just 10h after resuming operation following the last overhaul. The initial investigation showed that the design shortcoming was the main cause of the failure. A series of analytical, finite element and experimental analysis were utilized to determine the steady-state stresses and dynamic characteristic of the blade. It is concluded that the blade
E. Poursaeidi; M. Salavatian
This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade`s root flap bending moment. The model requires as input a simple set of wind measurements which may be obtained as part of a routine site characterization study. By using the model to simulate a time series of the root flap bending moment, fatigue damage rates may be estimated. The technique is evaluated by comparing these estimates with damage estimates derived from actual bending moment data; the agreement between the two is quite good. The simple connection between wind measurements and fatigue provided by the model now allows one to readily discriminate between damaging and more benign wind environments.
Barnard, J.C.; Wendell, L.L.
Application of the U.S. high cycle fatigue data base to wind turbine blade lifetime predictions
This paper demonstrates a methodology for predicting the service lifetime of wind turbine blades using the high-cycle fatigue data base for typical U.S. blade materials developed by Mandell, et al. (1995). The first step in the analysis is to normalize the data base (composed primarily of data obtained from specialized, relatively small coupons) with fatigue data from typical industrial laminates
Herbert J. Sutherland; John F. Mandell
Effect of Load Phase Angle on Wind Turbine Blade Fatigue Damage: Preprint
This paper examines the importance of phase angle variations with respect to fatigue damage. The operating loads on a generic conventional three-bladed upwind 1.5-MW wind turbine blade were analyzed over a range of operating conditions, and an aggregate probability distribution for the actual phase angles between the in-plane (lead-lag) and out-of-plane (flap) loads was determined. Using a finite element model
D. L. White; W. D. Musial
New Method for Dual-Axis Fatigue Testing of Large Wind Turbine Blades Using Resonance Exicitation and Spectral Loading.
The blades of a wind turbine are generally considered to be the most critical component of the wind turbine system. The fundamental purpose of performing fatigue tests on wind turbine blades is to demonstrate that a blade, when manufactured to a certain s...
D. White
A new method for dual-axis fatigue testing of large wind turbine blades using resonance excitation and spectral loading
The demand for cost effective renewable energy sources has resulted in the continual refinement of modern wind turbine designs. These refinements generally result in larger wind turbines and wind turbine blades. In order to reduce maintenance expenses, and improve quality and reliability, each new blade design must be subjected to a high cycle fatigue test. With blades expected to soon
Darris L. White
Accelerated Full Scale Fatigue Testing Of A Small Composite Wind Turbine Blade Using A Mechanically Operated Test Rig
A 2.5m long glass fibre reinforced plastic composite wind turbine blade was fatigue tested by means of a mechanically operated test rig. The rig uses a crank eccentric mechanism to flex the blade by a constant displacement in the flapwise direction for each load cycle. A yearly fatigue-loading spectrum for the blades has been developed from using short-term detailed aeroelastic
Reliability-based fatigue design of wind-turbine rotor blades
A probabilistic model for analysis of the safety of a wind-turbine rotor blade against fatigue failure in flapwise bending is presented. The model is based on a Miner's rule approach to cumulative damage and capitalizes on a conventional S–N curve formulation for fatigue resistance in conjunction with a new `distorted Weibull' distribution for representation of wind-induced bending moment ranges. The
Knut O. Ronold; Jakob Wedel-Heinen; Carl J. Christensen
Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine
In-service Very-High-Cycle-Fatigue (VHCF) regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17 and superalloy GS6K, respectively, was considered. Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades. Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface. This material behavior reflected lifetime limit that was reached by the criterion VHCF. In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet. This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology. In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream. Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations. Recommendations to continue aircrafts airworthiness were made for in-service blades.
Shanyavskiy, A. A.
Fatigue Measurement for Remaining Life.
The objective of this work was to follow track pin surface residual stress as a function of fatigue test cycles. Twenty pins were selected from a group of 250 new T-142 track pins for this test. They were selected on the basis of being representative of p...
S. B. Catalano
A neural network architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopumps blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high-frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines.
Considerations concerning fatigue life of metal matrix composites
Since metal matrix composites (MMC) are composed from two very distinct materials each having their own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMC's were analyzed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fiber fracture and matrix were also quantitatively defined.
Radhakrishnan, V. M.; Bartolotta, Paul A.
Fatigue testing of low-cost fiberglass composite wind turbine blade materials
The static and fatigue behavior of transverse filament tape (TFT) fiberglass/epoxy and TFT/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.
Hofer, K. E.; Bennett, L. C.
The static and fatigue behavior of transverse filament tape (TFT) fiberglass\\/epoxy and TFT\\/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.
K. E. Hofer; L. C. Bennett
WISPER and WISPERX: Final definition of two standardised fatigue loading sequences for wind turbine blades
Relevant information used to develop WISPER (Wind turbine reference Spectrum) and WISPERX, standardized variable amplitude test loading histories for use in the fatigue design of horizontal axis wind turbine blades, is presented. WISPER and WISPERX are based on flap load service measurements on nine different horizontal axis wind turbines, covering a wide range of materials, rotor diameters and geographical locations.
A. A. Tenhave
This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade's root flap bending moment. The model requires as input a simple set of wind measurements which may be obtained as part of a routine site characterization study. By using the model to simulate a time series of the root flap bending moment, fatigue damage rates may be estimated. The technique is evaluated by comparing these estimates with damage estimates derived from actual bending moment data; the agreement between the two is quite good. The simple connection between wind measurements and fatigue provided by the model now allows one to readily discriminate between damaging and more benign wind environments.
Barnard, J. C.; Wendell, L. L.
Predicting fatigue life of metal bellows
Classical method of presenting fatigue data in plots of alternating stress vs number of deflection cycles is applied to bellows formed of various metals, including corrosion-resistant steel, nickel alloys, and aluminum alloys. The expected life of a new bellows design can then be determined before fabrication and testing.
Daniels, C. M.
Fatigue life prediction of bonded primary joints
The validation of a proposed fatigue life prediction methodology was sought through the use of aluminum butt and scarf joint and graphite/epoxy butt joint specimens in a constant amplitude fatigue environment. The structural properties of the HYSOL 9313 adhesive system were obtained by mechanical test of molded heat adhesive specimens. Aluminum contoured double cantilever beam specimens were used to generate crack velocity versus stress intensity factor data. The specific objectives were: (1) to ascertain the feasibility of predicting fatigue failure of an adhesive in a primary bonded composite structure by incorporating linear elastic crack growth behavior; and (2) to ascertain if acoustic emission and/or compliance measurement techniques can be used to detect flaws.
Knauss, J. F.
Implementation of a Two-Axis Servo-Hydraulic System for Full-Scale Fatigue Testing of Wind Turbine Blades.
Recently, the blade fatigue testing capabilities at NREL were upgraded from single-axis to two-axis loading. To implement this, several practical challenges were addressed, as hardware complexity increased dramatically with two actuators applying the load...
S. D. Hughes W. D. Musial T. Stensland
Evaluation of the New B-REX Fatigue Testing System for Multi-Megawatt Wind Turbine Blades. Preprint. Conference Paper.
The National Renewable Energy Laboratory (NREL) recently developed a new hybrid fatigue testing system called the Blade Resonance Excitation (B-REX) test system. The new system uses 65% less energy to test large wind turbine blades in half the time of NRE...
D. White W. Musial S. Engberg
Fatigue Life of Superalloy Haynes 188 in Hydrogen
The effects of hydrogen and surface finish on the mean low cycle fatigue life of Haynes 188 were studied. Specimens were prepared and fatigue tested with gage sections having low stress ground (LSG) and electro-discharge machined (EDM) surfaces. Fatigue tests were performed at temperatures of 25 to 650 °C with varied strain conditions, in hydrogen and helium environments. Fatigue life decreased with increasing strain range, strain ratio, temperature, and with hydrogen atmosphere. A Smith-Watson-Topper stress parameter could be used to account for variations in strain range and strain ratio, and most strongly influenced life. Hydrogen reduced fatigue life by about 5× (80%) at 25 °C, but was much less harmful at 650 °C. Standard EDM finish did not consistently reduce mean fatigue life from that of LSG finish specimens. Additional tests indicated fatigue life in hydrogen was maintained for varied EDM conditions, provided specimen roughness and maximum recast layer thickness were not excessive.
Gabb, T. P.; Webster, H.; Ribeiro, G.; Gorman, T.; Gayda, J.
Deformation and fatigue behavior of SSME turbopump blade materials
Directionally solidified and single crystal superalloys which are intended for use as turbopump blade materials are anisotropic both elastically and plastically. Therefore, isotropic constitutive models must be modified. Several models which are now being developed are based on metallurgical theories of deformation in these types of alloys. However, these theories have not been fully justified, and the temperature and strain regimes over which they may be valid are poorly defined. The objective of this work is to study the deformation behavior of the alloys, in order to determine the validity of these models and to thereby support the ongoing research efforts in solid mechanics.
Milligan, Walter W.; Antolovich, Stephen D.
Effects of cyclic stress distribution models on fatigue life predictions.
The fatigue analysis of a wind turbine component typically uses representative samples of cyclic loads to determine lifetime loads. In this paper, several techniques currently in use are compared to one another based on fatigue life analyses. The generali...
H. J. Sutherland P. S. Veers
Surface Fatigue Life of High Temperature Gear Materials.
Three high temperature gear materials were evaluated using spur gear surface fatigue tests. These materials were, VASCO max 350, VASCO matrix 2, and nitralloy N and were evaluated for possible use in high temperature gear applications. The fatigue life of...
D. P. Townsend
Prestraining and Its Influence on Subsequent Fatigue Life.
An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid...
G. R. Halford M. A. Mcgaw Kalluri
The effects of controls on fatigue loads in two-bladed teetered rotor wind turbines
This paper presents a quantitative analysis of the fatigue loads in a down wind, yaw-controlled, fixed pitch, two-bladed teetered-rotor wind turbine using proportional-integral, full-state optimal, and fuzzy logic controllers. Time-domain simulation data is generated using the EASY5x\\/WT software developed at the University of Texas at El Paso. The simulation data reveal that the choice of controller type, or the controller
K. C. Wu; R. De La Guardia
Prevention of fatigue failures in elastic coupling discs and in fan blades
It is proven by fatigue tests that the generalized SN curve is an invariant in relation to a load cycle asymmetry. It is shown by tests on a large batch of coupling elastic discs and fan blades that the SN curve, represented in relative stresses (relative to the endurance limit Sar), i.e. S\\/Sar-N, can be effectively applied to studies of
L. A. Pereyaslavets
Thermomechanical fatigue, oxidation, and Creep: Part II. Life prediction
A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation),\\u000a and creep damage. The model handles different strain-temperature phasings(i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings).\\u000a Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature\\u000a phasings. An
R. W. Neu; Huseyin Sehitoglu
Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations
A methodology is presented for determining the fatigue life of composite structures based on fatigue characterization data and geometric nonlinear finite element (FE) analyses. To demonstrate the approach, predicted results were compared to fatigue tests performed on specimens which represented a tapered composite flange bonded onto a composite skin. In a first step, tension tests were performed to evaluate the debonding mechanisms between the flange and the skin. In a second step, a 2D FE model was developed to analyze the tests. To predict matrix cracking onset, the relationship between the tension load and the maximum principal stresses transverse to the fiber direction was determined through FE analysis. Transverse tension fatigue life data were used to -enerate an onset fatigue life P-N curve for matrix cracking. The resulting prediction was in good agreement with data from the fatigue tests. In a third step, a fracture mechanics approach based on FE analysis was used to determine the relationship between the tension load and the critical energy release rate. Mixed mode energy release rate fatigue life data were used to create a fatigue life onset G-N curve for delamination. The resulting prediction was in good agreement with data from the fatigue tests. Further, the prediction curve for cumulative life to failure was generated from the previous onset fatigue life curves. The results showed that the methodology offers a significant potential to Predict cumulative fatigue life of composite structures.
Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin; Minguet, Pierre J.
A methodology is presented for determining the fatigue life of bonded composite skin/stringer structures based on delamination fatigue characterization data and geometric nonlinear finite element analyses. Results were compared to fatigue tests on stringer flange/skin specimens to verify the approach.
Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin
Prediction of residual fatigue life using nonlinear ultrasound
Prediction of fatigue life of components during service is an on-going and unsolved challenge for the NDT and structural health monitoring community. It has been demonstrated by a number of researchers that nonlinear guided waves or the acoustic nonlinear signature of fatigued cracked material provides clear signs of the progressive fatigue damage in the material, unlike linear guided waves. However,
Mikael Amura; Michele Meo
Fatigue life of automotive rubber jounce bumper
It is evident that most rubber components in the automotive industry are subjected to repetitive loading. Vigorous research is needed towards improving the safety and reliability of the components. The study was done on an automotive rubber jounce bumper with a rubber hardness of 60 IRHD. The test was conducted in displacement-controlled environment under compressive load. The existing models by Kim, Harbour, Woo and Li were adopted to predict the fatigue life. The experimental results show strong similarities with the predicted models.
Sidhu, R. S.; Ali, Aidy
Thermal fatigue life evaluation of CSP joints by mechanical fatigue testing
The interrelation between a thermal cycle test and a mechanical shear fatigue test has been studied for CSP joints from the view point of fatigue life and the microstructural damage of solder joints. The fatigue lives in both methods are almost equivalent even though loading method is different. From the viewpoint of microstructure, the fact is attributed to that the
Yoshihiko Kanda; Kunihiro Zama; Yoshiharu Kariya; Hironori Oota; Shunichi Kikuchi; Hideki Yamabe; Kazuhiko Nakamura
Estimation of fatigue damage and fatigue life of components under random loading
To examine the applicability of methods proposed in the estimation of fatigue damage and fatigue life of components under random loading, a batch of specimens made of 7075-T651 aluminium alloy has been studied and some of the results are reported in the present paper. The paper describes different methods and rules in the calculation of fatigue damage, especially when random
W. F. Wu; H. Y. Liou; H. C. Tse
High Cycle Fatigue Crack Initiation Study of Case Blade Alloy Rene 125
This study was conducted in order to investigate and document the high cycle fatigue crack initiation characteristics of blade alloy Rene 125 as cast by three commercially available processes. This alloy is typically used in turbine blade applications. It is currently being considered as a candidate alloy for high T3 compressor airfoil applications. This effort is part of NASA's Advanced Subsonic Technology (AST) program which aims to develop improved capabilities for the next generation subsonic gas turbine engine for commercial carriers. Wrought alloys, which are customarily used for airfoils in the compressor, cannot meet the property goals at the higher compressor exit temperatures that would be required for advanced ultra-high bypass engines. As a result cast alloys are currently being considered for such applications. Traditional blade materials such as Rene 125 have the high temperature capabilities required for such applications. However, the implementation of cast alloys in compressor airfoil applications where airfoils are typically much thinner does raise some issues of concern such as thin wall castability, casting cleaningness, and susceptibility to high-cycle fatigue (HCF) loading.
Kantzos, P.; Gayda, J.; Miner, R. V.; Telesman, J.; Dickerson, P.
Fatigue criterion to system design, life and reliability
A generalized methodology to structural life prediction, design, and reliability based upon a fatigue criterion is advanced. The life prediction methodology is based in part on work of W. Weibull and G. Lundberg and A. Palmgren. The approach incorporates the computed life of elemental stress volumes of a complex machine element to predict system life. The results of coupon fatigue testing can be incorporated into the analysis allowing for life prediction and component or structural renewal rates with reasonable statistical certainty.
Zaretsky, E. V.
Reinforced wind turbine blades--an environmental life cycle evaluation.
A fiberglass composite reinforced with carbon nanofibers (CNF) at the resin-fiber interface is being developed for potential use in wind turbine blades. An energy and midpoint impact assessment was performed to gauge impacts of scaling production to blades 40 m and longer. Higher loadings force trade-offs in energy return on investment and midpoint impacts relative to the base case while remaining superior to thermoelectric power generation in these indicators. Energy-intensive production of CNFs forces impacts disproportionate to mass contribution. The polymer nanocomposite increases a 2 MW plant's global warming potential nearly 100% per kWh electricity generated with 5% CNF by mass in the blades if no increase in electrical output is realized. The relative scale of impact must be compensated by systematic improvements whether by deployment in higher potential zones or by increased life span; the trade-offs are expected to be significantly lessened with CNF manufacturing maturity. Significant challenges are faced in evaluating emerging technologies including uncertainty in future scenarios and process scaling. Inventories available for raw materials and monte carlos analysis have been used to gain insight to impacts of this development. PMID:22857256
Merugula, Laura; Khanna, Vikas; Bakshi, Bhavik R
The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many test results of standard specimens are very different from those of real structures or components because of geometrical effect, surface condition and so on. In this study, fatigue tests with specimens and pipes were carried out to evaluate the fatigue characteristic
Jae Sil Park; Chang-Sung Seok; Jung Hun Choi
Effect of surface irregularities on bellows fatigue life
Report presents test data on the bending fatigue life of notched sheet specimens. The influence of a surface irregularity on the fatigue life of a metal bellows is evaluated, with emphasis on accidental defects in ducting bellows which are impossible to avoid short of completely eliminating human contact.
Schmidt, E. H.; Sheaffer, E. F.; Turner, J. D.; Zeimer, R. L.
Relevant information used to develop WISPER (Wind turbine reference Spectrum) and WISPERX, standardized variable amplitude test loading histories for use in the fatigue design of horizontal axis wind turbine blades, is presented. WISPER and WISPERX are based on flap load service measurements on nine different horizontal axis wind turbines, covering a wide range of materials, rotor diameters and geographical locations. Their backgrounds are reported, basic data and associated data handling procedures are described, and quantitative data analysis results and statistical information on both standards are presented. The information given will enable fatigue specialists to judge whether the standard will suit their test objectives and to check for correct application of the load sequences on their test equipment.
Tenhave, A. A.
Effect of the flap and edgewise bending moment phase relationships on the fatigue loads of a typical HAWT blade
The load spectrum unposed upon a horizontal-axis wind turbine blade is typically decomposed into two primary bending moments; flap and edgewise bending. The critical fatigue loads (stress cycles) imposed on the blade may not be on one of these axes, especially if die two bending loads are in-phase with one another. To quantify the correlation of these two bending moments and determine the impact of this correlation on off-axis fatigue loads, an extensive data set for a typical wind turbine blade is examined. The results are compared using their respective cycle count matrices. These results illustrate that the harmonic components of die principal bending stresses are correlated, and that the random components are not. The analysis techniques described in the paper provide the turbine designer with a spectral technique for combining primary bending spectra into off-axis fatigue loads.
Sutherland, H. J.
Research on fatigue damage detection for wind turbine blade based on high-spatial-resolution DPP-BOTDA
In this paper, a fatigue damage detection system used for wind turbine blade is successfully developed by using highspatial- resolution differential pulse-width pair Brillouin optical time-domain analysis (DPP-BOTDA) sensing system. A piece of polarization-maintaining optical fiber is bonded on the blade surface to form the distributed sensing network. A DPP-BOTDA system, with a spatial resolution of 20cm and sampling interval of 1cm, is adopted to measuring distributed strain and detecting fatigue damage of wind turbine blade during fatigue test using the differential pulse pair of 39.5ns/41.5ns. Strain and the Brillouin gain spectra changes from undamaged state to fatigue failure are experimentally presented. The experimental results reveal that fatigue damage changes the strain distribution especially around the high strain area, and the width, amplitude and central frequency of the Brillouin gain spectra are sensitive to fatigue damage as the stiffness degradation and accumulated cracks change local strain gradient. As the damage becomes larger, the width of the Brillouin gain spectra becomes broader. Consequently, location and size of fatigue damage could be estimated. The developed system shows its potentiality for developing highly reliable wind turbine monitoring system as the effectiveness of damage detection and distributed sensing.
Xu, Jinlong; Dong, Yongkang; Li, Hui
Effect of spectral shape on acoustic fatigue life estimates
Methods for estimating fatigue life due to random loading are briefly reviewed. These methods include a probabilistic approach in which the expected value of the rate of damage accumulation is computed by integrating over the probability density of damaging events and a method which consists of analyzing the response time history to count damaging events. It is noted that it is necessary to employ a time domain approach to perform Rainflow counting, while simple peak counting may be accomplished using the probabilistic method. Data obtained indicate that Rainflow counting produces significantly different fatigue life predictions than other methods that are commonly used in acoustic fatigue predictions. When low-frequency oscillations are present in a signal along with high-frequency components, peak counting will produce substantially shorter fatigue lives than Rainflow counting. It is concluded that Rainflow counting is capable of providing reliable fatigue life predictions for acoustic fatigue studies.
Miles, R. N.
Evaluation of the New B-REX Fatigue Testing System for Multi-Megawatt Wind Turbine Blades: Preprint
The National Renewable Energy Laboratory (NREL) recently developed a new hybrid fatigue testing system called the Blade Resonance Excitation (B-REX) test system. The new system uses 65% less energy to test large wind turbine blades in half the time of NREL's dual-axis forced-displacement test method with lower equipment and operating costs. The B-REX is a dual-axis test system that combines
D. White; W. Musial; S. Engberg
Fatigue life characterization for piezoelectric macrofiber composites
In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from - 15 to 145?°C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number.
Henslee, Isaac A.; Miller, David A.; Tempero, Tyler
Effects of Materials Parameters and Design Details on the Fatigue of Composite Materials for Wind Turbine Blades
This paper presents an analysis of the results of nine years of fatigue testing represented in the USDOE/Montana State University (DOE/MSU) Composite Materials Fatigue Database. The focus of the program has been to explore a broad range of glass-fiber-based materials parameters encompassing over 4500 data points for 130 materials systems. Significant trends and transitions in fatigue resistance are shown as the fiber content and fabric architecture are varied. The effects of structural details including ply drops, bonded stiffeners, and other geometries that produce local variations in fiber packing and geometry are also described. Fatigue tests on composite beam structures are then discussed; these show generally good correlation with coupon fatigue data in the database. Goodman diagrams for fatigue design are presented, and their application to predicting the service lifetime of blades is described.
Mandell, J.F.; Samborsky, D.D.; Sutherland, H.J.
Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications
Surface enhancement technologies such as shot peening, laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. For successful integration into turbine design, the process must be affordable and compatible with the manufacturing environment. LPB provides thermally stable compression of comparable magnitude and even greater depth than other methods, and can be performed in conventional machine shop environments on CNC machine tools. LPB provides a means to extend the fatigue lives of both new and legacy aircraft engines and ground-based turbines. Improving fatigue performance by introducing deep stable layers of compressive residual stress avoids the generally cost prohibitive alternative of modifying either material or design. The X-ray diffraction based background studies of thermal and mechanical stability of surface enhancement techniques are briefly reviewed, demonstrating the importance of minimizing cold work. The LPB process, tooling, and control systems are described. An overview of current research programs conducted for engine OEMs and the military to apply LPB to a variety of engine and aging aircraft components are presented. Fatigue performance and residual stress data developed to date for several case studies are presented including: * The effect of LPB on the fatigue performance of the nickel based super alloy IN718, showing fatigue benefit of thermal stability at engine temperatures. * An order of magnitude improvement in damage tolerance of LPB processed Ti-6-4 fan blade leading edges. * Elimination of the fretting fatigue debit for Ti-6-4 with prior LPB. * Corrosion fatigue mitigation with LPB in Carpenter 450 steel. *Damage tolerance improvement in 17-4PH steel. Where appropriate, the performance of LPB is compared to conventional shot peening after exposure to engine operating temperatures.
Prevey, Paul S.; Shepard, Michael; Ravindranath, Ravi A.; Gabb, Timothy
How surface damage removal affects fatigue life
The effect of the removal of work hardened surface layers from specimens of 2024-T4 aluminum alloy and AISI-4130 steel on their fatigue lives has been investigated. Specimens were fatigued at selected stress levels for a given number of cycles, and the surface layer was removed followed by subsequent fatigue cycling. Results confirm that when a material is subjected to fatigue loading, damage accumulates in the surface layers in the form of work hardening. Removal of the surface layer brings the specimen back to its pre-fatigued condition.
Jeelani, S.; Scott, M. A.
Development of an improved method of consolidating fatigue life data
A fatigue data consolidation model that incorporates recent advances in life prediction methodology was developed. A combined analytic and experimental study of fatigue of notched 2024-T3 aluminum alloy under constant amplitude loading was carried out. Because few systematic and complete data sets for 2024-T3 were available in the program generated data for fatigue crack initiation and separation failure for both zero and nonzero mean stresses. Consolidations of these data are presented.
Leis, B. N.; Sampath, S. G.
Tubomachinery blade vibration amplitude measurement through tip timing with capacitance tip clearance probes
Turbomachinery blade vibrations can cause high cycle fatigue (HCF), which reduces blade life. In order to observe this vibration a non-intrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. Much research and development has
Craig P. Lawson; Paul C. Ivey
Implementation of a TwoAxis Servo-Hydraulic System for Full-Scale Fatigue Testing of Wind Turbine Blades
Recently, the blade fatigue testing capabilities at NREL were upgraded from single-axis to two-axis loading. To implement this, several practical challenges were addressed, as hardware complexity increased dramatically with two actuators applying the loads at right angles to each other. A custom bellcrank was designed and implemented to minimize the load angle errors and to prevent actuator side loading. The
S. D. Hughes; W. D. Musial; T. Stensland
a Study on the Fretting Fatigue Life of Zircaloy Alloys
Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. The main component of zircaloy alloy is Zr, and it possesses good mechanical characteristics at high
Jae-Do Kwon; Dae-Kyu Park; Seung-Wan Woo; Young-Suck Chai
Development of a fatigue-life methodology for composite structures subjected to out-of-plane load components
The efforts to identify and implement a fatigue life methodology applicable to demonstrate delamination failures for use in certifying composite rotor blades are presented. The RSRA/X-Wing vehicle was a proof-of-concept stopped rotor aircraft configuration which used rotor blades primarily constructed of laminated carbon fiber. Delamination of the main spar during ground testing demonstrated that significant interlaminar stresses were produced. Analysis confirmed the presence of out-of-plane load components. The wear out (residual strength) methodology and the requirements for its implementation are discussed.
Sumich, M.; Kedward, K.T.
The demand for cost effective renewable energy sources has resulted in the continual refinement of modern wind turbine designs. These refinements generally result in larger wind turbines and wind turbine blades. In order to reduce maintenance expenses, and improve quality and reliability, each new blade design must be subjected to a high cycle fatigue test. With blades expected to soon reach 70 meters in length, traditional fatigue test systems and methods are becoming less practical. Additionally, the relationship between the flap and lead-lag bending moments has not been well understood. This work explores the accuracy of current test methods compared to service loads, presents a new method for fatigue testing larger blades and experimentally validates the analysis. A dynamic model of a generic wind turbine blade and test system has been developed to evaluate the strain profiles during testing, evaluate control strategies and optimize the test accuracy. The relationship between the flap and lead-lag strains resulting from service bending moments has been analyzed. A load spectrum based on the relationship between the flap and lead-lag loads has been developed and compared to traditional test conditions. The effect of using the load spectrum on the test system stability has been analyzed and a new state-space controller has been designed. A 3-D finite element model of a generic wind turbine blade has been used to evaluate the damage accumulation for current test load conditions and the proposed load spectrum. A nonlinear damage accumulation model has been derived to evaluate the effects of load sequencing. Additionally, a new method for applying the fatigue loads to the blades has been developed and implemented. A system that applies a harmonic force at the resonance frequency of the blade in the flap direction has been designed. The new system will reduce the costs and time associated with performing a fatigue test on wind turbine blades. The new system is also capable of matching a greater range of service load distribution than the current test system. An optimization routine has been used to make the test load distribution match the target: load distribution.
White, Darris L.
Predicting mooring system fatigue life by probabilistic methods
Failure of moored structures from accumulated fatigue damage in shackles, connecting links, chain and wire rope components is common. When systems will be deployed for long periods, it is especially important to determine at the design, inspection and maintenance stages the fatigue damage. Since slack moored structures behave in a highly nonlinear manner, commonly used fatigue analysis procedures are normally inadequate. This paper reviews present probablistic fatigue analysis methods, and provides a means for incorporating nonlinear mooring behavior into analysis and design to predict accumulated damage and remaining service life. The procedures presented are general, and they are also applicable to ship and buoy moorings, offshore terminals, and guyed and tension leg platforms.
Saders, D.R.; Dominguez, R.F.; Ho, K.C.; Lai, N.W.
Rotorcraft fatigue life-prediction: Past, present, and future
In this paper the methods used for calculating the fatigue life of metallic dynamic components in rotorcraft is reviewed. In the past, rotorcraft fatigue design has combined constant amplitude tests of full-scale parts with flight loads and usage data in a conservative manner to provide 'safe life' component replacement times. This is in contrast to other industries, such as the automobile industry, where spectrum loading in fatigue testing is a part of the design procedure. Traditionally, the linear cumulative damage rule has been used in a deterministic manner using a conservative value for fatigue strength based on a one in a thousand probability of failure. Conservatism on load and usage are also often employed. This procedure will be discussed along with the current U.S. Army fatigue life specification for new rotorcraft which is the so-called 'six nines' reliability requirement. In order to achieve the six nines reliability requirement the exploration and adoption of new approaches in design and fleet management may also be necessary if this requirement is to be met with a minimum impact on structural weight. To this end a fracture mechanics approach to fatigue life design may be required in order to provide a more accurate estimate of damage progression. Also reviewed in this paper is a fracture mechanics approach for calculating total fatigue life which is based on a crack-closure small crack considerations.
Everett, Richard A., Jr.; Elber, W.
Probabilistic fatigue life prediction of metallic and composite materials
Fatigue is one of the most common failure modes for engineering structures, such as aircrafts, rotorcrafts and aviation transports. Both metallic materials and composite materials are widely used and affected by fatigue damage. Huge uncertainties arise from material properties, measurement noise, imperfect models, future anticipated loads and environmental conditions. These uncertainties are critical issues for accurate remaining useful life (RUL) prediction for engineering structures in service. Probabilistic fatigue prognosis considering various uncertainties is of great importance for structural safety. The objective of this study is to develop probabilistic fatigue life prediction models for metallic materials and composite materials. A fatigue model based on crack growth analysis and equivalent initial flaw size concept is proposed for metallic materials. Following this, the developed model is extended to include structural geometry effects (notch effect), environmental effects (corroded specimens) and manufacturing effects (shot peening effects). Due to the inhomogeneity and anisotropy, the fatigue model suitable for metallic materials cannot be directly applied to composite materials. A composite fatigue model life prediction is proposed based on a mixed-mode delamination growth model and a stiffness degradation law. After the development of deterministic fatigue models of metallic and composite materials, a general probabilistic life prediction methodology is developed. The proposed methodology combines an efficient Inverse First-Order Reliability Method (IFORM) for the uncertainty propogation in fatigue life prediction. An equivalent stresstransformation has been developed to enhance the computational efficiency under realistic random amplitude loading. A systematical reliability-based maintenance optimization framework is proposed for fatigue risk management and mitigation of engineering structures.
Xiang, Yibing
Fatigue Life of Composite Structures in Extreme Environments.
Prediction of the dynamic response and the fatigue life of structures, i.e. panels, subjected to both high temperatures/ thermal gradients and high level acoustic excitations. The determination of reliable approximations of the statistics of the panel res...
P. C. Chen M. P. Mignolet
Fatigue Life Prediction Modeling for Turbine Hot Section Materials.
A major objective of the fatigue and fracture efforts under the NASA Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas...
G. R. Halford T. G. Meyer R. S. Nelson D. M. Nissley G. A. Swanson
Fatigue life of friction stir welded Al-Mg alloys
The following alloys EN- AW 5058 H321 and EN-AW 5059 H321 (Alustar) were welded by FSW (friction stir welding) method. The FSW welds showed better properties in comparison to the joints welded by the MIG method. The low-cycle fatigue life test was carried out in the symmetric cycle: in air and in 3.5% NaCl. Fatigue life of 5083 alloy welded
M. Czechowski
Laser machining of micro-notches for fatigue life
Evaluation of fatigue life for engineering components used in structurally demanding applications is very important. Micro-notches need to be fabricated on test specimens to replicate surface defects for experimental determination of fatigue life studies. A study for generating micro-notches on engineering materials like stainless steel and aluminum alloys using a nano-second pulsed fiber laser has been carried out and results
Aniruddha Kumar; Mool. C. Gupta
Temperature evolution and life prediction in fatigue of superalloys
Low-cycle fatigue behavior of two superalloys, ULTIMET® alloy, Co-26 pct Cr-9 pct Ni (wt pct), and HAYNES® HR-120® alloy, Ni-33 pct Fe-25 pct Cr, was studied at room temperature. An infrared thermography system was employed to monitor the temperature evolution of fatigue processes for both superalloys. Temperature changes during fatigue were related to the hysteresis effect, and were successfully predicted, based on the consideration of the hysteresis effect and heat conduction. The temperature increase of a specimen from the initial to the equilibrium stages was used as an index to predict the fatigue life of the two superalloys. It was found that the fatigue-life predictions using the present model were in good agreement with the experimental results.
Jiang, L.; Wang, H.; Liaw, P. K.; Brooks, C. R.; Chen, L.; Klarstrom, D. L.
Prestraining and its influence on subsequent fatigue life
An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.
Halford, Gary R.; Mcgaw, Michael A.; Kalluri, Sreeramesh
Halford, G.R.; Mcgaw, M.A.; Kalluri, S.
Tensile-mode fatigue tests and fatigue life predictions of single crystal silicon in humidity controlled environments
This paper reports on a tensile-mode fatigue test in a constant humidity, even in a very high humidity, to reveal the mechanism of fatigue fractures of MEMS materials. A newly developed tensile-mode fatigue tester using the electrostatic grip can control the humidity from 25% RH to 90% RH. Using this tester, the fatigue life and strength of single crystal silicon
Y. Yamaji; K. Sugano; O. Tabata; T. Tsuchiya
Life prediction of thermal-mechanical fatigue using strainrange partitioning
This paper describes the applicability of the method of Strainrange Partitioning to the life prediction of thermal-mechanical strain-cycling fatigue. An in-phase test on 316 stainless steel is analyzed as an illustrative example. The observed life is in excellent agreement with the life predicted by the method using the recently proposed Step-Stress Method of experimental partitioning, the Interaction Damage Rule, and the life relationships determined at an isothermal temperature of 705 C. Implications of the present study are discussed relative to the general thermal fatigue problem.
Halford, G. R.; Manson, S. S.
Non-destructive measurement and role of surface residual stress monitoring in residual life assessment of a steam turbine blading material
Steam turbine blades in power generation equipment are made from martensitic stainless steels having high strength, good toughness and corrosion resistance. However, these steels are susceptible to pitting which can promote early failures of blades in the turbines, particularly in the low pressure dry/wet areas by stress corrosion and corrosion fatigue. Presence of tensile residual stresses is known to accelerate failures whereas compressive stresses can help in delaying failures. Shot peening has been employed as an effective tool to induce compressive residual stresses which offset a part of local surface tensile stresses in the surface layers of components. Maintaining local stresses at stress raisers, such as pits formed during service, below a threshold level can help in preventing the initiation microcracks and failures. The thickness of the layer in compression will, however, depend of the shot peening parameters and should extend below the bottom of corrosion pits. The magnitude of surface compressive drops progressively during service exposure and over time the effectiveness of shot peening is lost making the material susceptible to micro-crack initiation once again. Measurement and monitoring of surface residual stress therefore becomes important for assessing residual life of components in service. This paper shows the applicability of surface stress monitoring to life assessment of steam turbine blade material based on data generated in laboratory on residual surface stress measurements in relation to fatigue exposure. An empirical model is proposed to calculate the remaining life of shot peened steam turbine blades in service.
Prabhu-Gaunkar, Gajanana; Rawat, M. S.; Prasad, C. R.
A comparison of fatigue life prediction methodologies for rotorcraft
Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.
Everett, R. A., Jr.
Dramatic increase in fatigue life in hierarchical graphene composites.
We report the synthesis and fatigue characterization of fiberglass/epoxy composites with various weight fractions of graphene platelets infiltrated into the epoxy resin as well as directly spray-coated on to the glass microfibers. Remarkably only ?0.2% (with respect to the epoxy resin weight and ?0.02% with respect to the entire laminate weight) of graphene additives enhanced the fatigue life of the composite in the flexural bending mode by up to 1200-fold. By contrast, under uniaxial tensile fatigue conditions, the graphene fillers resulted in ?3-5-fold increase in fatigue life. The fatigue life increase (in the flexural bending mode) with graphene additives was ?1-2 orders of magnitude superior to those obtained using carbon nanotubes. In situ ultrasound analysis of the nanocomposite during the cyclic fatigue test suggests that the graphene network toughens the fiberglass/epoxy-matrix interface and prevents the delamination/buckling of the glass microfibers under compressive stress. Such fatigue-resistant hierarchical materials show potential to improve the safety, reliability, and cost effectiveness of fiber-reinforced composites that are increasingly the material of choice in the aerospace, automotive, marine, sports, biomedical, and wind energy industries. PMID:20863061
Yavari, F; Rafiee, M A; Rafiee, J; Yu, Z-Z; Koratkar, N
Surface Fatigue Life of High Temperature Gear Materials
Three high temperature gear materials were evaluated using spur gear surface fatigue tests. These materials were, VASCO max 350, VASCO matrix 2, and nitralloy N and were evaluated for possible use in high temperature gear applications. The fatigue life of the three high temperature gear materials were compared with the life of the standard AISI 9310 aircraft gear material. Surface fatigue tests were conducted at a lubricant inlet temperature of 321 K (120 F), a lubricant outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), a speed of 10,000 rpm, and with a synthetic paraffinic lubricant. The life of the nitralloy N was approximately the same as the AISI 9310, the life of the VASCO max 350 was much less than the AISI 9310 while the life of the VASCO matrix 2 was several times the life of the AISI 9310. The VASCO max 350 also showed very low fracture toughness with approximately half of the gears failed by tooth fracture through the fatigue spall. The VASCO matrix 2 had approximately 10-percent fracture failure through the fatigue spalls indicating moderate to good fracture toughness.
Townsend, Dennis P.
Surface fatigue life of high temperature gear materials
In land-based gas turbines, thermal barrier coatings are used for thermal insulation of hot components (combustor, turbine vanes and to some extent blades). The thermal barrier maintains the metal temperature of a coated component at moderate temperature levels during turbine operation. If the coating spalls off, the underlying metal will suffer from creep damage and oxidation with risk of severe
Johansson S
X-43A Rudder Spindle Fatigue Life Estimate and Testing
Fatigue life analyses were performed using a standard strain-life approach and a linear cumulative damage parameter to assess the effect of a single accidental overload on the fatigue life of the Haynes 230 nickel-base superalloy X-43A rudder spindle. Because of a limited amount of information available about the Haynes 230 material, a series of tests were conducted to replicate the overload and in-service conditions for the spindle and corroborate the analysis. Both the analytical and experimental results suggest that the spindle will survive the anticipated flight loads.
Glaessgen, Edward H.; Dawicke, David S.; Johnston, William M.; James, Mark A.; Simonsen, Micah; Mason, Brian H.
A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation), and creep damage. The model handles different strain-temperature phasings (i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings). Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature phasings. An oxide growth (oxide damage) model is based on the repeated microrupture process of oxide observed from microscopic measurements. A creep damage expression, which is stress-based, is coupled with a unified constitutive equation. A set of interrupted tests was performed to provide valuable damage progression information. Tests were performed in air and in helium atmospheres to isolate creep damage from oxidation damage.
Neu, R. W.; Sehitoglu, Huseyin
Fatigue life scatter in 7xxx series aluminum alloys
Specimens of Al 7175-T7452 and Al 7075-T6511 were fatigue tested under several spectra to obtain estimates of the standard deviation of the log of the fatigue life and to determine if there was bimodality as was found for Al 7050-T7451. The 7175 alloy showed no sign of being bimodal when tested under a spectrum which included large compressive loads. The
D. L. DuQuesnay; P. R. Underhill
Volume effects on fatigue life of equine cortical bone.
Materials, including bone, often fail due to loading in the presence of critical flaws. The relative amount, location, and interaction of these flaws within a stressed volume of material play a role in determining the failure properties of the structure. As materials are generally imperfect, larger volumes of material have higher probabilities of containing a flaw of critical size than do smaller volumes. Thus, larger volumes tend to fail at fewer cycles compared with smaller volumes when fatigue loaded to similar stress levels. A material is said to exhibit a volume effect if its failure properties are dependent on the specimen volume. Volume effects are well documented in brittle ceramics and composites and have been proposed for bone. We hypothesized that (1) smaller volumes of cortical bone have longer fatigue lives than similarly loaded larger volumes and (2) that compared with microstructural features, specimen volume was able to explain comparable amounts of variability in fatigue life. In this investigation, waisted rectangular specimens (n=18) with nominal cross-sections of 3x4 mm and gage lengths of 10.5, 21, or 42 mm, were isolated from the mid-diaphysis of the dorsal region of equine third metacarpal bones. These specimens were subjected to uniaxial load controlled fatigue tests, with an initial strain range of 4000 microstrain. The group having the smallest volume exhibited a trend of greater log fatigue life than the larger volume groups. Each volume group exhibited a significant positive correlation between the logarithm of fatigue life and the cumulative failure probability, indicating that the data follow the two-parameter Weibull distribution. Additionally, log fatigue life was negatively correlated with log volume, supporting the hypothesis that smaller stressed volumes of cortical bone possess longer fatigue lives than similarly tested larger stressed volumes. PMID:17632110
Bigley, R F; Gibeling, J C; Stover, S M; Hazelwood, S J; Fyhrie, D P; Martin, R B
Physical fitness, fatigue, and quality of life after liver transplantation
Fatigue is often experienced after liver transplantation. The aims of this cross-sectional study were to assess physical fitness\\u000a (cardiorespiratory fitness, neuromuscular fitness, body composition) in liver transplant recipients and to explore whether\\u000a physical fitness is related to severity of fatigue. In addition, we explored the relationship between physical fitness and\\u000a health-related quality of life. Included were 18 patients 1–5 years after
Berbke T. J. van Ginneken; Rita J. G. van den Berg-Emons; Geert Kazemier; Herold J. Metselaar; Hugo W. Tilanus; Henk J. Stam
Fatigue life prediction modeling for turbine hot section materials
A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.
Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.
A major objective of the fatigue and fracture efforts under the NASA Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.
NASA GRC Fatigue Crack Initiation Life Prediction Models
Metal fatigue has plagued structural components for centuries, and it remains a critical durability issue in today's aerospace hardware. This is true despite vastly improved and advanced materials, increased mechanistic understanding, and development of accurate structural analysis and advanced fatigue life prediction tools. Each advance is quickly taken advantage of to produce safer, more reliable, more cost effective, and better performing products. In other words, as the envelope is expanded, components are then designed to operate just as close to the newly expanded envelope as they were to the initial one. The problem is perennial. The economic importance of addressing structural durability issues early in the design process is emphasized. Tradeoffs with performance, cost, and legislated restrictions are pointed out. Several aspects of structural durability of advanced systems, advanced materials and advanced fatigue life prediction methods are presented. Specific items include the basic elements of durability analysis, conventional designs, barriers to be overcome for advanced systems, high-temperature life prediction for both creep-fatigue and thermomechanical fatigue, mean stress effects, multiaxial stress-strain states, and cumulative fatigue damage accumulation assessment.
Arya, Vinod K.; Halford, Gary R.
Creep fatigue life prediction for engine hot section materials (isotropic)
The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.
Moreno, Vito; Nissley, David; Lin, Li-Sen Jim
Fatigue life estimates for helicopter loading spectra
Helicopter loading histories applied to notch metal samples are used as examples, and their fatigue lives are calculated by using a simplified version of the local strain approach. This simplified method has the advantage that it requires knowing the loading history in only the reduced form of ranges and means and number of cycles from the rain-flow cycle counting method. The calculated lives compare favorably with test data.
Khosrovaneh, A. K.; Dowling, N. E.; Berens, A. P.; Gallagher, J. P.
Effect of Vacuum on the Fatigue Life of Aluminum.
The effect of vacuum on the fatigue life of aluminum under a constant stress cyclic bending deformation was studied. Specimens made of commercially pure polycrystalline aluminum, cycled at two frequencies, 49 and 76 c/s, were tested at 9700 psi and 11700 ...
H. Shen S. E. Podlaseck I. R. Kramer
Rapid Fatigue Life Projection for Thermal and Acoustic Loads.
Report developed under an SBIR Phase I contract for topic AF02-244. The focus of this investigation is on the prediction of the fatigue life of aircraft panels subjected to the combination of a strong random acoustic excitation and to steady thermal effec...
P. C. Chen, X. Gao, D. D. Liu, M. P. Mignolet
Surface Fatigue Life of Contour Induction Hardened AISI 1552 Gears.
Two groups of spur gears manufactured from two different materials and heat treatments were endurance tested for surface fatigue life. One group was manufactured from AISI 1552 and was finished ground to a 0.4 micron (16 micro-in.) rms surface finish and ...
D. P. Townsend A. Turza M. Chaplin
Fatigue life assessment under multiaxial variable amplitude loading.
A variable amplitude multiaxial fatigue life prediction method is presented in this paper. It is based on a stress as input data are the stress tensor histories which may be calculated by FEM analysis or measured directly on the structure during the servi...
P. Morilhat B. Kenmeugne E. Vidal-Salle J. L. Robert
Mean Strain Effects on the Strain Life Fatigue Curve.
Aluminum 7075-T6 was tested using a Fatigue Material Test System. After creating the monotonic and cyclic stress-strain curves to verify material properties, strain life test data were replicated twenty times each to obtain the statistical description of ...
B. L. Smith
A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of h...
Approach to the fatigue analysis of vertical-axis wind-turbine blades
A cursory analysis of the stress history of wind turbine blades indicates that a single stress level at each wind speed does not adequately describe the blade stress history. A statistical description is required. Blade stress data collected from the DOE\\/ALCOA Low Cost experimental turbines indicate that the Rayleigh probability density function adequately describes the distribution of vibratory stresses at
Fatigue life analysis of a turboprop reduction gearbox
A fatigue life analysis of the Allison T56/501 turboprop reduction gearbox was developed. The life and reliability of the gearbox was based on the lives and reliabilities of the main power train bearings and gears. The bearing and gear lives were determined using the Lundberg-Palmgren theory and a mission profile. The five planet bearing set had the shortest calculated life among the various gearbox components, which agreed with field experience where the planet bearing had the greatest incidences of failure. The analytical predictions of relative lives among the various bearings were in reasonable agreement with field experience. The predicted gearbox life was in excellent agreement with field data when the material life adjustment factors alone were used. The gearbox had a lower predicted life in comparison with field data when no life adjustment factors were used or when lubrication life adjustment factors were used either alone or in combination with the material factors.
Lewicki, D. G.; Black, J. D.; Savage, M.; Coy, J. J.
Estimation of fatigue life using electromechanical impedance technique
Fatigue induced damage is often progressive and gradual in nature. Structures subjected to large number of fatigue load cycles will encounter the process of progressive crack initiation, propagation and finally fracture. Monitoring of structural health, especially for the critical components, is therefore essential for early detection of potential harmful crack. Recent advent of smart materials such as piezo-impedance transducer adopting the electromechanical impedance (EMI) technique and wave propagation technique are well proven to be effective in incipient damage detection and characterization. Exceptional advantages such as autonomous, real-time and online, remote monitoring may provide a cost-effective alternative to the conventional structural health monitoring (SHM) techniques. In this study, the main focus is to investigate the feasibility of characterizing a propagating fatigue crack in a structure using the EMI technique as well as estimating its remaining fatigue life using the linear elastic fracture mechanics (LEFM) approach. Uniaxial cyclic tensile load is applied on a lab-sized aluminum beam up to failure. Progressive shift in admittance signatures measured by the piezo-impedance transducer (PZT patch) corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression. With the use of LEFM, prediction of the remaining life of the structure at different cycles of loading is possible.
Lim, Yee Yan; Soh, Chee Kiong
Characterisation of Zircaloy corrosion fatigue phenomena in an iodine environment. Part 2: Fatigue life
After some work performed on crack growth rates in corrosion fatigue, the present authors have studied the fatigue corrosion life of Zircaloy 4 in iodine environment on smooth tensile specimens. Two types of recrystallized Zry-4 have been tested at room temperature in a methyl alcohol solution of iodine. A corrosion fatigue phenomenon was observed resulting in a reduction of numbers of cycles to failure at intermediate stress levels. No reduction of the fatigue strength was noted. SEM fractography showed that the initiation step consists of only intergranular corrosion governed by the chemistry of the environment. A sharp transition to transgranular crack growth takes place when the stress intensity factor at the crack tip reaches a threshold value about 3.0 MPa ?m, close to KI- scc values found in literature. A static load tensile test performed under the same conditions confirms that the initiation step originates in SCC. Whether in SCC or corrosion fatigue, transgranular propagation takes place when pseudo-cleavage on the basal plane becomes possible. If stress loading is static, pseudo-cleavage is accompanied by fluting. If loading is cyclic, the grains ruptured by pseudo-cleavage will have juxtaposing grains where the crack has grown in pure fatigue, by plastic deformation by shear on prismatic planes.
Schuster, Isabelle; Lemaignan, Clément
Development and evaluation of life assessment and reconditioning methods for gas turbine blading
The blades and vanes of power generating gas turbines are critical components which can limit the turbine life. They normally subject to degradation as a result both of microstructural changes, resulting in embrittlement and creep life exhaustion and of environmental attack, leading to destruction of protective coatings (if present) and the base material itself. The aim of this program has
R. Buergel; W. Ebeling; J. Ellner; R. Fried; W. Hoffelner; N. Kasik; M. Nazmy; K. Schneider; A. Scholz; V. Sova; M. Staubli
Tension fatigue analysis and life prediction for composite laminates
A tension fatigue life prediction methodology for composite laminates is presented. Tension fatigue tests were conducted on quasi-isotropic and orthotropic glass epoxy, graphite epoxy, and glass/graphite epoxy hybrid laminates. Edge delamination onset data were used to generate plots of strain energy release rate as a function of cycles to delamination onset. These plots were then used along with strain energy release rate analyses of delaminations initiating at matrix cracks to predict local delamination onset. Stiffness loss was measured experimentally to account for the accumulation of matrix cracks and for delamination growth. Fatigue failure was predicted by comparing the increase in global strain resulting from stiffness loss to the decrease in laminate failure strain resulting from delaminations forming at matrix cracks through the laminate thickness. Good agreement between measured and predicted lives indicated that the through-thickness damage accumulation model can accurately describe fatigue failure for laminates where the delamination onset behavior in fatigue is well characterized, and stiffness loss can be monitored in real time to account for damage growth.
Obrien, T. K.; Rigamonti, M.; Zanotti, C.
Fatigue, Creep-Fatigue, and Thermomechanical Fatigue Life Testing of Alloys.
The fatigue crack initiation resistance of an alloy is determined by conducting a series of tests over a range of values of stress amplitude or strain range. The observed number of cycles to failure is plotted against the stress amplitude or strain range ...
G. R. Halford B. A. Lerch M. A. McGaw
Equivalent linearization for fatigue life estimates of a nonlinear structure
An analysis is presented of the suitability of the method of equivalent linearization for estimating the fatigue life of a nonlinear structure. Comparisons are made of the fatigue life of a nonlinear plate as predicted using conventional equivalent linearization and three other more accurate methods. The excitation of the plate is assumed to be Gaussian white noise and the plate response is modeled using a single resonant mode. The methods used for comparison consist of numerical simulation, a probabalistic formulation, and a modification of equivalent linearization which avoids the usual assumption that the response process is Gaussian. Remarkably close agreement is obtained between all four methods, even for cases where the response is significantly linear.
Use of Composite Materials for Helicopter Rotor Blades.
The availability of locally produced glass fiber and epoxy resin, the unlimited fatigue life, and the low cost of the composite blade in comparison with an equivalent imported all-metal blade are arguments favoring the developing of a South African helico...
M. S. Hunt
Modeling fatigue crack growth for life-extending control
This dissertation presents a nonlinear dynamic model of fatigue crack growth in the state-space setting under variable amplitude cyclic load. The model is especially suited to the needs of real-time decision-making for life-extending control. The state variables are crack length and crack opening stress. The model is capable of capturing the effects of a single-cycle overload, block loads, random loads,
Ravindra Prakash Patankar
Fatigue Life of Tapered Roller Bearings under Minimal Lubricant Films
A series of fatigue tests were run on a 3.25 inch O.D. tapered roller bearing to establish the effect on bearing life of lubricant film thicknesses in the 0.5–4.0 micro-inch range. Based on the ratio of calculated film thickness to composite surface roughness, results from eleven individual tests indicate the bearings operated normally under conditions which should have resulted in
Charles H. Danner
The Hot Section Technology (HOST) program, creep fatigue life prediction for engine hot section materials (isotropic), is reviewed. The program is aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components. Significant results include: (1) cast B1900 and wrought IN 718 selected as the base and alternative materials respectively; (2) fatigue test specimens indicated that measurable surface cracks appear early in the specimen lives, i.e., 15% of total life at 871 C and 50% of life at 538 c; (3) observed crack initiation sites are all surface initiated and are associated with either grain boundary carbides or local porosity, transgrannular cracking is observed at the initiation site for all conditions tested; and (4) an initial evaluation of two life prediction models, representative of macroscopic (Coffin-Mason) and more microscopic (damage rate) approaches, was conducted using limited data generated at 871 C and 538 C. It is found that the microscopic approach provides a more accurate regression of the data used to determine crack initiation model constants, but overpredicts the effect of strain rate on crack initiation life for the conditions tested.
Moreno, V.
Novelty detection applied to vibration data from a CX100 wind turbine blade under fatigue loading
The remarkable evolution of new generation wind turbines has led to a dramatic increase of wind turbine blade size. In turn, a reliable structural health monitoring (SHM) system will be a key factor for the successful implementation of such systems. Detection of damage at an early stage is a crucial issue as blade failure would be a catastrophic result for
N Dervilis; M Choi; I Antoniadou; K M Farinholt; S G Taylor; R J Barthorpe; K Worden; C R Farrar
Implementation of a Two-Axis Servo-Hydraulic System for Full-Scale Fatigue Testing of Wind Turbine Blades
Recently, the blade fatigue testing capabilities at NREL were upgraded from single-axis to two-axis loading. To implement this, several practical challenges were addressed, as hardware complexity increased dramatically with two actuators applying the loads at right angles to each other. A custom bellcrank was designed and implemented to minimize the load angle errors and to prevent actuator side loading. The control system was upgraded to accept load and displacement feedback from two actuators. The inherent long strokes uniquely associated with wind turbine blade-tests required substantial real-time corrections for both the control and data systems. A custom data acquisition and control system was developed using a National Instruments LabVIEW platform that interfaces with proprietary servo-hydraulic software developed by MTS Corporation. Before testing, the program is run under quasi-static (slow speed) conditions and iterates to determine the correct operational control parameters for the controller, taking into consideration geometry, test speed, and phase angle errors between the two actuators. Comparisons are made between single-axis and two-axis test loads using actual test load data and load uncertainties are qualitatively described. To date, two fatigue tests have been completed and another is currently ongoing using NREL's two-axis capability.
Hughes, S. D.; Musial, W. D. [National Renewable Energy Lab., Golden, CO (US); Stensland, T. [Stensland Technologies (US)
Test evaluation of a laminated wood wind turbine blade concept
A series of tests conducted on a root end section of a laminated wood wind turbine blade are reported. The blade to hub transition of the wood blade uses steel studs cast into the wood D spar with a filled epoxy. Both individual studs and a full scale, short length, root section were tested. Results indicate that the bonded stud concept is more than adequate for both the 30 year life fatigue loads and for the high wind or hurricane gust loads.
Faddoul, J. R.
Life design of high-temperature turbine blades with minimum cooling requirements
The problem of minimizing fuel requirements for the air cooling of gas turbine blades, while providing for a specified service life, is stated and solved for a dual-mode engine. It is shown that, for a multimode engine, the problem should be solved by using nonlinear programming methods. It is further shown that fuel consumption for blade cooling can be minimized only by controlling air flow rate with allowance for the operation mode. Recommendations concerning practical applications of the results of the study are given.
Nagoga, G. P.; Tseitlin, V. I.; Balter, V. P.
Estimation of fatigue life of railway bridges under traffic loads
Random modelling of railway bridge loading enables fatigue damage to be calculated on the basis of the cumulative damage theory of Palmgren-Miner and the classification of the stress-time history by means of the "rain-flow" counting method. The results of calculations are the mean value of the damage and the standard deviation of the stresses, and thus an estimation of the bridge fatigue life. Accordingly the bridge life is dependent on the number of stress cycles and their distribution, the standard deviation of stresses, and on the shape of the Wöhler curve. Bridge life increasing span and decreases with an increasing traffic load. Results are presented as obtained in a detailed study of the effects on the bridge life of different parameters (vehicle speed, damping of bridge vibrations, variability in length and time of the moving load and its magnitude, number of stress cycles and their distribution). The equivalent damage method (the ?T-method) in the integral form enables one to compare the effects of the traffic loads with those of the standard loading.
Frýba, L.
Lubricant and additive effects on spur gear fatigue life
Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided into four batches each of which had a different additive content. Lubricants tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulfur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt % sulfur and 0.1 wt % phosphorus EP additives in the lubricant had reactive films that were 200 to 400 (0.8 to 1.6 microns) thick.
Townsend, D. P.; Zaretsky, E. V.; Scibbe, H. W.
Fatigue-life behavior and matrix fatigue crack spacing in unnotched SCS-6/Timetal 21S metal matrix composites
Fatigue tests of the SCS-6/Timetal 21S composite system were performed to characterize the fatigue behavior for unnotched conditions. The stress-life behavior of the unnotched (9/90)2s laminates was investigated for stress ratios of R = 0.1 and R = 0.3. The occurrence of matrix cracking was also examined in these specimens. This revealed multiple matrix crack initiation sites throughout the composite, as well as evenly spaced surface cracks along the length of the specimens. No difference in fatigue lives were observed for stress ratios of R = 0.1 and R = 0.3 when compared on a stress range basis. The unnotched SCS-6/Timetal 21S composites had shorter fatigue lives than the SCS-6/Ti-15-3 composites, however the neat Timetal 21S matrix material had a longer fatigue life than the neat Ti-15-3.
Ward, G. T.; Herrmann, D. J.; Hillberry, B. M.
An experimental study on fatigue life of interference-fit composite joint
An experimental study on fatigue life of an interference-fit composite joint is presented. The experimental results show that suitable interference can increase fatigue life in comparison with the push-fit case. For the material and the laying studied, when the interference is 2 percent, the fatigue life is increased 2-3 times. An explanation for the result is given. In order to obtain the current result, some methods of processing and assembling are emphasized in the experiment. An explanation is given for the definition of fatigue life limitation and the choice of the best interference.
Liu, Ping; Zhang, Kaida
Monosemousness of Thermal Plastic Strain on Thermal Fatigue Life in Ferrite Ductile Cast Iron
In this study, the monosemous effect of thermal plastic strain on the thermal fatigue life is newly found on ferrite ductile cast iron around the alpha phase field. At first, the monosemousness is defined and its meaning described. Next, the monosemousness of thermal fatigue is demonstrated by its conditional equation and its existence is verified by the thermal fatigue test
Morihito Hayashi; Hayato Mouri
The experience of fatigue and quality of life in patients with advanced lung cancer
Fatigue is the most prevalent and distressing symptom experienced by patients with advanced lung cancer and especially among those patients undergoing therapy. Advanced lung cancer and its associated symptoms can significantly impact the quality of life (QOL) of those who have the disease. The primary purpose of this study was to measure fatigue levels, characterize the fatigue experience, and assess
Andrea Shaffer
Continuum Fatigue Damage Modeling for Use in Life Extending Control
This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.
Lorenzo, Carl F.
A New Three-Parameter Model for Predicting Fatigue Crack Initiation Life
Based on the idea that the fatigue damage is caused by the cyclic damage strain, a concept of the critical damage quantity is introduced and a new three-parameter model is developed. The model contains three material performance parameters, i.e., the fatigue ductility coefficient, the fatigue ductility exponent, and the theoretical strain endurance limit. The fatigue ductility coefficient reflects the existence of the critical damage quantity. The fatigue ductility exponent shows the damage resistance ability of the material. And the theoretical strain endurance limit represents the existence of the critical cyclic strain. By using the proposed model, the fatigue crack initiation life of metallic materials can be predicted.
Zhang, Zhongping; Sun, Qiang; Li, Chunwang; Qiao, Yanjiang; Zhang, Dongwei
A low-order model for analysing effects of blade fatigue load control
A new low-order mathematical model is introduced to analyse blade dynamics and blade load-reducing control strategies for wind turbines. The model consists of a typical wing section model combined with a rotor speed model, leading to four structural degrees of freedom (flapwise, edgewise and torsional blade oscillations and rotor speed). The aerodynamics is described by an unsteady aerodynamic model. The equations of motion are derived in non-linear and linear form. The linear equations of motion are used for stability analysis and control design. The non-linear equations of motion are used for time simulations to evaluate control performance. The stability analysis shows that the model is capable of predicting classical flutter and stall-induced vibrations. The results from the stability analysis are compared with known results, showing good agreement. The model is used to compare the performance of one proportional-integral-derivative controller and two full-state feedback controllers. Copyright
Kallesře, B. S.
Fatigue Life Methodology for Tapered Composite Flexbeam Laminates
The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to non-linear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse displacement. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.
Murri, Gretchen B.; OBrien, T. Kevin; Rousseau, Carl Q.
Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability
Two computational models to determine the fatigue life and reliability of a commercial turboprop gearbox are compared with each other and with field data. These models are (1) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising the system and (2) two-parameter Weibull distribution function for bearings and gears comprising the system using strict-series system reliability to combine the calculated individual component lives in the gearbox. The Monte Carlo simulation included the virtual testing of 744,450 gearboxes. Two sets of field data were obtained from 64 gearboxes that were first-run to removal for cause, were refurbished and placed back in service, and then were second-run until removal for cause. A series of equations were empirically developed from the Monte Carlo simulation to determine the statistical variation in predicted life and Weibull slope as a function of the number of gearboxes failed. The resultant L(sub 10) life from the field data was 5,627 hr. From strict-series system reliability, the predicted L(sub 10) life was 774 hr. From the Monte Carlo simulation, the median value for the L(sub 10) gearbox lives equaled 757 hr. Half of the gearbox L(sub 10) lives will be less than this value and the other half more. The resultant L(sub 10) life of the second-run (refurbished) gearboxes was 1,334 hr. The apparent load-life exponent p for the roller bearings is 5.2. Were the bearing lives to be recalculated with a load-life exponent p equal to 5.2, the predicted L(sub 10) life of the gearbox would be equal to the actual life obtained in the field. The component failure distribution of the gearbox from the Monte Carlo simulation was nearly identical to that using the strict-series system reliability analysis, proving the compatibility of these methods.
Zaretsky, Erwin V.; Lewicki, David G.; Savage, Michael; Vlcek, Brian L.
Fatigue load spectra for upwind and downwind rotors
Effect of both alternating and mean load on the fatigue life of an upwind and downwind MOD-2 wind turbine system is presented. It was shown that the fatigue damage varies as the product of the stress range cubed and the maximum stress. Hence, the alternating flapwise load caused by tower shadow and wind gradient is an important factor in determining rotor blade life.
Andrews, J. S.
Structural health monitoring of wind towers: residual fatigue life estimation
In a recent paper (Benedetti et al 2011 Smart Mater. Struct. 20 055009), the authors investigated the possibility of detecting cracks in critical sites of onshore wind towers using a radial arrangement of strain sensors around the tower periphery in the vicinity of the base welded joint. Specifically, the strain difference between adjacent strain sensors is used as a damage indicator. The number of sensors to be installed is determined by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule. In this companion paper, we address these issues by investigating possible strategies for residual fatigue life assessment and management of onshore wind towers once the crack has been detected. For this purpose, fracture mechanics tests are carried out using welded samples to quantify the resistance to fatigue crack growth as well as the elastic-plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality.
Benedetti, M.; Fontanari, V.; Battisti, L.
Finite element analysis with an improved failure criterion for composite wind turbine blades
Some interesting studies are made in this paper on the life management of a composite wind turbine\\u000a blade. It presents the details of finite element modeling and validation, blade response under service\\u000a loading conditions, power coefficient evaluation for the optimum design parameters of the blade configuration,\\u000a development of failure envelope and fatigue life estimations. Finite element analysis results are found\\u000a to
J. Selwin Rajadurai; T. Christopher; G. Thanigaiyarasu; B. Nageswara Rao
Corrosion and fatigue failure analysis of a forced draft fan blade
The present work was carried out to investigate the failure mechanism of a power plant forced draft fan (FDF) blade made of 2014-T6 Al alloy, using visual examination, microstructural characterizations, study of the fracture surface and hardness testing. Based on the obtained results, surface defects including corrosion pits due to the existence of Cl ion and also erosion pits due
H. Kazempour-Liacy; M. Mehdizadeh; M. Akbari-Garakani; S. Abouali
Improved drive-train and blade fatigue mitigation in flexible wind turbines using disturbance utilization control
Modern wind turbines are experiencing rapid growth in both physical size and rated capacity. As wind turbines grow larger with necessarily lighter construction materials, dampening flexible modes with active control becomes more critical. In this paper we apply the theory of ldquodisturbance utilization controlrdquo (DUC) to a 600 kW upwind machine to dampen drive-train torsion and blade flap while regulating
Glenn A. Parker; C. D. Johnson
On the sonic fatigue life estimation of skin structures at room and elevated temperatures
Fighter/trainer empennages and STOL (Short Take-Off and Landing) aircraft flap systems are subjected to severe acoustic pressure levels as high as 150-170 dB. As a result, acoustic fatigue has become one of the major factors in design. Empennages and flap systems are also subject to high temperatures and thus the influence of thermal buckling on fatigue life must be taken into consideration. To estimate the sonic fatigue life of skin structures, combined use is made of the Monte Carlo method of non-linear panel response analysis and local stress-strain simulations with rheological models. Calculations were conducted and comparison of the results with experimental data shows that the method estimates the sonic fatigue life accurately when adequate values of fatigue notch factors are chosen. Example calculations with thermal as well as static pressure effects were also carried out and the effect of thermal buckling on sonic fatigue life is clarified.
Maekawa, S.
Fatigue life prediction of multi-spot-welded panel structures using an equivalent stress intensity factor
Fatigue failure of spot-welded panel structures can be evaluated by means of a fracture parameter, since a weld-spot has an external crack type geometry. Recasting the load vs. fatigue life relations experimentally obtained from single-spot-welded specimens, we predict the fatigue life of spot-welded specimens with a parameter denoted the equivalent stress intensity factor (Ke). This crack driving parameter describes the
Hyungyil Lee; Namho Kim
Relations between sleep, fatigue and health-related quality of life in individuals with insomnia
PubMed Central
Objective This study explored the relations between sleep, fatigue and health-related quality of life in a sample of individuals with chronic insomnia. Methods A total of 160 adults meeting diagnostic criteria for chronic insomnia underwent three nights of polysomnography (PSG) and completed sleep diaries and questionnaires assessing daytime functioning including fatigue and health-related quality of life. Results A cluster analysis was conducted based on PSG-defined sleep disturbances and fatigue severity. A four-cluster solution (R2 = 0.68) was found, classifying individuals as having either (a) both severe sleep disturbance and severe fatigue (n = 15); (b) severe sleep disturbance but milder fatigue (n = 15); (c) milder sleep disturbance but severe fatigue (n = 68) or (d) both milder sleep disturbance and milder fatigue (n = 61). Health-related quality of life was lower in both clusters with severe fatigue compared to those with milder fatigue, and was further decreased when severe sleep disturbances were present. Relations between several indicators of fatigue and health-related quality of life were then examined using factor analysis in order to identify different domains of impairment. A three-factor structure was selected, suggesting that daytime symptoms can be classified as relating to fatigue, physical health, or mental health. These different subtypes of daytime impairment were predicted by distinct sets of variables. Conclusion More severe fatigue is not necessarily related to poorer PSG-defined sleep but appears associated with greater impairment in health-related quality of life. Fatigue and health-related quality of life appear to be distinct but interrelated constructs.
Fortier-Brochu, Emilie; Beaulieu-Bonneau, Simon; Ivers, Hans; Morin, Charles M.
Application of Design Data Derived from Fatigue Tests with Service Like Load Sequences to Life Prediction.
Reliable fatigue life curves were established for a load sequence and a cumulative frequency distribution which are typical at the wing structure for transport aircraft. The life estimation for details subjected to load spectra varying from that applied t...
D. Schuetz H. Lowak
Low power laser heat treatments to improve fatigue life of low carbon steel
An industrial laser cutting machine tool was used to harden 1117 and 1144 steel to examine effects on fatigue life. Transformation hardening leaves residual compressive stresses at the surface, which greatly enhance fatigue life in addition to increasing the hardness. The laser, which creates localized heating, allows faster cooling rates than conventional heat treatment methods. As a result, the application
D. E. Fly; J. T. Black; B. Singleton
Probabilistic fatigue life prediction model for alloys with defects: applied to A206
Presented here is a model for the prediction of fatigue life based on the statistical distribution of pores, intermetallic particles and grains. This has been applied to a cast Al alloy A206, before and after friction stir processing (FSP). The model computes the probability to initiate a small crack based on the probability of finding combinations of defects and grains on the surface. The crack initiation and propagation life of small cracks due to these defect and grain combinations are computed and summed to obtain the total fatigue life. The defect and grain combinations are ranked according to total fatigue life and the failure probability computed. Bending fatigue experiments were carried out on A206 before and after FSP. FSP eliminated the porosity, broke down the particles and refined the microstructure. The model predicted the fatigue life of A206 before and after FSP well. The cumulative probability distribution vs. fatigue life was fitted to a three parameter Weibull distribution function. The scatter reduced after FSP and the threshold of fatigue life increased. The potential improvement in the fatigue life of A206 for a microstructure consisting of a finer distribution of particle sizes after FSP was predicted using the model.
Kapoor, Rajeev; Sree Hari Rao, V.; Mishra, Rajiv S.; Baumann, John A.; Grant, Glenn J.
The Effect of Aircraft Gas Turbine Oils on Roller Bearing Fatigue Life
A series of fatigue life tests on aircraft gear box size (45 mm bore) roller bearings were conducted with various aircraft gas turbine lubricants and with specific reference to Mil-L-7808 and variations thereof. It is shown that the 7808 lubricants generally cause a marked reduction in fatigue life as compared to that obtained with a medium viscosity mineral oil. It
Mark E. Otterbein
Multiaxial fatigue life prediction of a high temperature steam turbine rotor using a critical plane approach
This paper deals with the problem of multiaxial fatigue life assessment of engineering components. A computer-based procedure for multiaxial fatigue life assessment incorporating critical plane multiaxial damage models, suitable for use in design evaluations of engineering components based on finite element analysis results, is presented and applied to correlate results from tests conducted on SAE 1045 steel notched shaft specimens.
Jayanta Das; Srinivasan M. Sivakumar
An evaluation of multiaxial fatigue life assessment methods for engineering components
This article deals with the problem of multiaxial fatigue life assessment of engineering components. General aspects of the critical plane damage models are discussed first. A computer-based procedure for multiaxial fatigue life assessment incorporating critical plane damage models, suitable for use in design evaluations of engineering components based on finite element analysis results, is presented and applied to correlate results
J Das; S. M Sivakumar
Estimation of fatigue strain-life curves for austenitic stainless steels in light water reactor environments.
The ASME Boiler and Pressure Vessel Code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels (SSs) in light water reactor (LWR) environments. Unlike those of carbon and low-alloy steels, environmental effects on fatigue lives of SSs are more pronounced in low-dissolved-oxygen (low-DO) water than in high-DO water, This paper summarizes available fatigue strain vs. life data on the effects of various material and loading variables such as steel type, DO level, strain range, and strain rate on the fatigue lives of wrought and cast austenitic SSs. Statistical models for estimating the fatigue lives of these steels in LWR environments have been updated with a larger data base. The significance of the effect of environment on the current Code design curve has been evaluated.
Chopra, O. K.; Smith, J. L.
Dynamic stall on wind turbine blades
Dynamic loads must be predicted accurately in order to estimate the fatigue life of wind turbines operating in turbulent environments. Dynamic stall contributes to increased dynamic loads during normal operation of all types of horizontal-axis wind turbine (HAWTs). This report illustrates how dynamic stall varies throughout the blade span of a 10 m HAWT during yawed and unyawed operating conditions.
C. P. Butterfield; D. Simms; G. Scott; A. C. Hansen
Corrosion fatigue of high strength fastener materials in seawater
Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength
D. G. Tipton
Overload effects on corrosion fatigue crack initiation life and life prediction of aluminum notched elements under variable amplitude loading
In this study, corrosion fatigue tests under both constant and variable amplitude loading are carried out to investigate the overload effect on the corrosion fatigue crack initiation (CFCI) life and life prediction model of the notched specimens of LY12CZ aluminum alloy sheets, which has the continuous strain hardening characteristics. Analysis of test results of CFCI life in 3.5% NaCl solution
Xiulin Zheng; Rong Wang
The fatigue life prediction of aluminium alloy using genetic algorithm and neural network
The behavior of the fatigue life of the industrial materials is very important. In many cases, the material with experiencing fatigue life cannot be avoided, however, there are many ways to control their behavior. Many investigations of the fatigue life phenomena of alloys have been done, but it is high cost and times consuming computation. This paper report the modeling and simulation approaches to predict the fatigue life behavior of Aluminum Alloys and resolves some problems of computation. First, the simulation using genetic algorithm was utilized to optimize the load to obtain the stress values. These results can be used to provide N-cycle fatigue life of the material. Furthermore, the experimental data was applied as input data in the neural network learning, while the samples data were applied for testing of the training data. Finally, the multilayer perceptron algorithm is applied to predict whether the given data sets in accordance with the fatigue life of the alloy. To achieve rapid convergence, the Levenberg-Marquardt algorithm was also employed. The simulations results shows that the fatigue behaviors of aluminum under pressure can be predicted. In addition, implementation of neural networks successfully identified a model for material fatigue life.
Susmikanti, Mike
Development of a Composite Delamination Fatigue Life Prediction Methodology
Delamination is one of the most significant and unique failure modes in composite structures. Because of a lack of understanding of the consequences of delamination and the inability to predict delamination onset and growth, many composite parts are unnecessarily rejected upon inspection, both immediately after manufacture and while in service. NASA Langley is leading the efforts in the U.S. to develop a fatigue life prediction methodology for composite delamination using fracture mechanics. Research being performed to this end will be reviewed. Emphasis will be placed on the development of test standards for delamination characterization, incorporation of approaches for modeling delamination in commercial finite element codes, and efforts to mature the technology for use in design handbooks and certification documents.
OBrien, Thomas K.
Experimental fatigue life investigation of cylindrical thrust chambers
The thrust chambers studied in the investigation have been designed for a possible use in the Space Shuttle main engine. An annular combustion chamber configuration was used, consisting of an annular injector, a liquid hydrogen cooled outer cylinder, which served as the test section, and a contoured water cooled centerbody which formed the throat. Twenty-two cylinders were fabricated by milling cooling channels into liners fabricated from the material to be evaluated. The three materials chosen for the liners include OFHC copper, Amzirc, and NARloy-Z. The cylinders were cyclically tested until failure occurred due to fatigue cracks in the hot-gas-side wall. It was found that cylinders with liners fabricated from NARloy-Z and aged Amzirc had the best cyclic life characteristics.
Quentmeyer, R. J.
The application of strain field intensity method in the steel bridge fatigue life evaluation
Asce's survey shows that 80%--90% bridge damage were associated with fatigue and fracture problems. With the operation of vehicle weight and traffic volume increases constantly, the fatigue of welded steel bridge is becoming more and more serious in recent years. A large number of studies show that most prone to fatigue damage of steel bridge is part of the welding position. Thus, it's important to find a more precise method to assess the fatigue life of steel bridge. Three kinds of fatigue analysis method is commonly used in engineering practice, such as nominal stress method, the local stress strain method and field intensity method. The first two methods frequently used for fatigue life assessment of steel bridge, but field intensity method uses less ,and it widely used in fatigue life assessment of aerospace and mechanical. Nominal stress method and the local stress strain method in engineering has been widely applied, but not considering stress gradient and multiaxial stress effects, the accuracy of calculation stability is relatively poor, so it's difficult to fully explain the fatigue damage mechanism. Therefore, it used strain field intensity method to evaluate the fatigue life of steel bridge. The fatigue life research of the steel bridge based on the strain field method and the fatigue life of the I-section plate girder was analyzed. Using Ansys on the elastoplastic finite element analysis determined the dangerous part of the structure and got the stress-strain history of the dangerous point. At the same time, in order to divide the unit more elaborate introduced the sub-structure technology. Finally, it applies K.N. Smith damage equation to calculate the fatigue life of the dangerous point. In order to better simulating the actual welding defects, it dug a small hole in the welding parts. It dug different holds from different view in the welding parts and plused the same load to calculate its fatigue life. Comparing the results found that the welding defect in different parts had different influence on the fatigue life. Simultaneously, it based on S-N curve the I-shaped beam and combined with Palmgren - Miner linear cumulative damage theory to calculate the fatigue life of the dangerous part. The corresponding calculation results proved the superiority of the strain field intensity method.
Zhao, Xuefeng; Wang, Yanhong; Cui, Yanjun; Cao, Kaisheng
Effect of lubricant extreme pressure additives on rolling element fatigue life
The effects of surface active additives on rolling-element fatigue life were investigated with the five-ball fatigue tester at conditions where classical subsurface initiated rolling-element fatigue is the sole mode of failure. Test balls of AISI 52100, AISI M-50, and AISI 1018 were run with an acid-treated white oil containing either 2.5 percent sulfurized terpene, 1 percent didodecyl phosphite, or 5 percent chlorinated wax. In general, it was found that the influence of surface active additives was detrimental to rolling-element fatigue life. The chlorinated-wax additive significantly reduced fatigue life by a factor of 7. The base oil with the 2.5 percent sulfurized-terpene additive can reduce fatigue life by as much as 50 percent. No statistical change in fatigue life occurred with the base oil having the 1 percent didodecyl-phosphite additive. The additives used with the base oil did not change the ranking of the bearing steels where rolling-element fatigue life was of subsurface origin.
Parker, R. J.; Zaretsky, E. V.
Evaluation of Creep-Fatigue Life by Fraction of Cavity Area
The components of power plant such as main steam pipe and gas turbines are operated under static and cyclic load conditions. As the period of static load increases, the service life of these components decreases. Generally, the increase of cyclic load results in fatigue damage and the increase of static load period results in the metallurgical degradation by the effect of creep. Under the creep-fatigue interaction, cavities cause rapid degradation of material and decreases the creep-fatigue life of high temperature components. In this paper, creep-fatigue tests were performed to investigate the relationship between the cavity and creep-fatigue life under various tensile hold times. Test materials were HAZ and base metal of P122 (12Cr-2W) alloy weldment. The effect of hold times on the cavity damage was examined and the fraction of cavity area was analyzed. From the linear relationship of Fca (fraction of cavity area) and experimental life, a new parameter for life evaluation, Fca, was introduced and the creep-fatigue life was predicted by Fca. Good agreement was found between experimental and predicted life. Under the same hold time condition, the Fca of HAZ was greater than that of base metal while the creep-fatigue life of HAZ was shorter than that of base metal.
Kim, Bumjoon; Lim, Byeongsoo
Transverse Tension Fatigue Life Characterization Through Flexure Testing of Composite Materials
The transverse tension fatigue life of S2/8552 glass-epoxy and IM7/8552 carbon-epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass-epoxy laminates. Results showed that 90-degree bend specimens with polished machined edges and polished tension-side surfaces, where bending failures where observed, had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law was examined using the carbon-epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice-versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S-N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S-N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives.
OBrien, T. Kevin; Chawan, Arun D.; Krueger, Ronald; Paris, Isabelle
Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life
Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.
Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.
Effects of stress concentrations on the fatigue life of a gamma-based titanium aluminide
S?N curves for a gamma-based titanium aluminide alloy of nominal chemistry Ti-48Al-2Mn-2Nb (at.%) + 2TiB2 (wt.%) have been used to define the fatigue life. The microstructure, residual stress and surface roughness have been observed to influence the fatigue life. Fully lamellar microstructures show an increased life when compared with near-lamellar microstructures. Residual tensile stresses and microcracking are introduced by electrodischarge
S. J. Trail; P. Bowen
Evaluation fo Pressurization Fatigue Life of 1441 Al-Li Fuselage Panel
A study was conducted to evaluate the pressurization fatigue life of fuselage panels with skins fabricated from 1441 Al-Li, an attractive new Russian alloy. The study indicated that 1441 Al-Li has several advantages over conventional aluminum fuselage skin alloy with respect to fatigue behavior. Smooth 1441 Al-Li sheet specimens exhibited a fatigue endurance limit similar to that for 1163 Al (Russian version of 2024 Al) sheet. Notched 1441 Al-Li sheet specimens exhibited greater fatigue strength and longer fatigue life than 1163 Al. In addition, Tu-204 fuselage panels fabricated by Tupolev Design Bureau using Al-Li skin and ring frames with riveted 7000-series aluminum stiffeners had longer pressurization fatigue lives than did panels constructed from conventional aluminum alloys. Taking into account the lower density of this alloy, the results suggest that 1441 Al-Li has the potential to improve fuselage performance while decreasing structural weight.
Bird, R. Keith; Dicus, Dennis I.; Fridlyander, Joseph; Davydov, Valentin
Evaluation of Pressurization Fatigue Life of 1441 Al-li Fuselage Panel
Evaluation of remaining fatigue life model for hot-mix asphalt airfield pavements
Several design criteria exist for predicting the fatigue life of hot-mix asphalt (HMA) pavements. Researchers previously developed an Aged Asphalt fatigue criterion from laboratory testing of aged field HMA airfield pavements. This criterion is unique because the majority of the existing fatigue criteria were developed from laboratory-prepared specimens. In this paper, a comparison of the Department of Defense (DoD), the
Haley P. Bell; Isaac L. Howard; Reed B. Freeman; E. Ray Brown
Effect of carbide distribution on rolling-element fatigue life of AMS 5749
Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.
Parker, R. J.; Bamberger, E. N.
Fatigue, depression and quality of life in cancer patients: how are they related?
In a study concerning a group of cancer patients undergoing radiotherapy three research questions were addressed. (1) Is\\u000a fatigue a valid criterion for depression in these somatically ill patients? (2) What is the 'cause-and-effect' relation between\\u000a fatigue and depression? (3) To what extent are fatigue and depression related to patients' quality of life. A heterogeneous\\u000a sample of cancer patients (n?=?250)
M. R. M. Visser; E. M. A. Smets
Fatigue in multiple sclerosis is related to disability, depression and quality of life
Fatigue in multiple sclerosis is a frequent and disabling symptom that can interfere in daily functioning. The aim of this study is to demonstrate the relationship between fatigue and disability, disease course, depression and quality of life.We administered French valid versions of the Fatigue Impact Scale (EMIF-SEP), the short form of the Beck depression inventory (13 items) and the SF-36
S. Pittion-Vouyovitch; M. Debouverie; F. Guillemin; N. Vandenberghe; R. Anxionnat; H. Vespignani
Fatigue Life of Titanium Alloys Fabricated by Additive Layer Manufacturing Techniques for Dental Implants
Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.
Chan, Kwai S.; Koike, Marie; Mason, Robert L.; Okabe, Toru
Fatigue analysis and life prediction of bridges with structural health monitoring data — Part I: methodology and strategy
This paper is aimed at developing a methodology and strategy for fatigue damage assessment and life prediction of bridge-deck sections of existing bridges with online structural health monitoring data. A fatigue damage model based on the continuum damage mechanics (CDM) is developed for evaluating accumulative fatigue damage of existing bridges. A structural model for the fatigue stress analysis of bridge-deck
Z. X. Li; T. H. T. Chan; J. M. Ko
Feasibility study of pultruded blades for wind turbine rotors
In work performed under subcontract to the National Renewable Energy Laboratory (NREL), a preliminary design study and proof-of-concept field test were conducted to evaluate the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study, and a scaled 80 kW rotor was fabricated and tested as a demonstration of the concept. To examine the feasibility of pultruded blades, several issues were addressed, including power performance, tower strikes, yaw stability, stall flutter, fatigue, and rotor cost. Results showed that with proper design, rotors using pultruded blades demonstrate acceptable fatigue life and stable yaw behavior without tower strikes. Furthermore, blades using this technology may be manufactured for approximately half the cost of conventional blades. Field tests of the scaled rotor provided experimental data on power performance and loads while verifying stable yaw operation.
Migliore, P.G.; Cheney, M.C.
Crack growth-based fatigue-life prediction using an equivalent initial flaw model. Part II: Multiaxial loading
A general methodology is proposed in this paper for fatigue-life prediction using crack growth analysis. This is the part II of the paper and focuses on the fatigue-life prediction under proportional and nonproportional multiaxial loading. The proposed multiaxial fatigue-life prediction is based on a critical plane-based multiaxial fatigue damage model and the Equivalent Initial Flaw Size (EIFS) concept. An equivalent
Zizi Lu; Yibing Xiang; Yongming Liu
Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness
Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400?kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.
Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati
Ultrasonic attenuation as an indicator of fatigue life of graphite/epoxy fiber composite
The narrow band ultrasonic longitudinal wave velocity and attenuation were measured as a function of the transfiber compression-compression fatigue of unidirectional graphite/epoxy composites. No change in velocity was detected at any point in fatigue life. For specimens fatigued at 80% of static strength, there was generally a 5% to 10% increase in attenuation, however, this increase does not appear to be a satisfactory indicator of fatigue life. On the other hand, there appears to be a correlation between initial attenuation (measured prior to cycling) and cycles to fracture. Initial attenuation as measured at 1.5 MHz and 2.0 MHz appears to be a good indicator of relative fatigue life.
Williams, J. H., Jr.; Doll, B.
Life Prediction Technologies for Aeronautical Propulsion Systems.
Fatigue and fracture problems continue to occur in aeronautical gas turbine engines. Components whose useful life is limited by these failure modes include turbine hot-section blades, vanes, and disks. Safety considerations dictate that catastrophic failu...
M. A. Mcgaw
Fatigue and fracture problems continue to occur in aeronautical gas turbine engines. Components whose useful life is limited by these failure modes include turbine hot-section blades, vanes and disks. Safety considerations dictate that catastrophic failur...
M. A. McGaw
Low-cycle fatigue life of steel P92 under gradual loading
The aim of the study was to determine low-cycle fatigue life characteristics of P92 steel used in the power unit components that work under the highest effort. Steel service life was determined in the tests for total fixed strain ??t ranges from 0.6 to 1.2 % and with application of two-stage sequence loading. Low-cycle fatigue tests were conducted at room temperature and at 550 °C on MTS-810 testing machine. The tests under sequence loading were carried out for two strain ranges: ??t = 0.6 and 1.2 %. Sinusoidal load cycles of a coefficient R = -1 were used. Low-cycle fatigue life characteristics were developed with consideration of loading sequence impact. It was found out the fatigue life of an element under sequence loading is strictly correlated with its history of strain, which determines the degree of material microstructure damage. Higher degree of steel damage was found in two-stage tests, in which the larger range of strain ??t = 1.2 % was used as the first one. Fractography analyses of scrap revealed the patterns of fatigue lines and bands typical for this process as well as numerous secondary cracks occurred to the boundaries of former austenite grains. Analytic method of predicting low-cycle fatigue life of an element under two-stage sequence loading is presented. For this purpose, an energy criterion for the material life developed for tests carried out in conditions of low-cycle fatigue was used.
Cie?la, M.; Junak, G.
Assessment of the fatigue life of aluminium spot-welded and weld-bonded joints
In modern machinery and automobile structures weight reduction and increased durability are the main issues in design. In these applications, lap welded and\\/or bonded joints are widely used; therefore, tools are needed to accurately predict their fatigue life. This paper is concerned with the fatigue strength of single lap joints formed with thin plates of 6082-T6 aluminium alloy using a
A. M. Pereira; J. A. M. Ferreira; F. V. Antunes; P. J. Bártolo
Modeling the effects of prior exfoliation corrosion on fatigue life of aircraft wing skins
This paper presents a preliminary analytical model, which was developed to evaluate the effects of prior exfoliation corrosion on the residual fatigue life of wing skins. A literature review was completed on the effects of exfoliation corrosion and fatigue interaction and the most significant conclusions are presented in this paper. A number of coupons with fasteners were cut from naturally
Min Liao; N. C Bellinger; J. P Komorowski
Cyclic plastic response and fatigue life in superduplex 2507 stainless steel
Superduplex 2507 type steel has been subjected to symmetric cyclic loading with constant strain rate and constant plastic strain amplitude or sinusoidal cyclic loading with constant stress amplitude at room temperature in a wide interval of stress and plastic strain amplitudes. Fatigue hardening\\/softening curves were recorded and compared for both types of loading. Cyclic stress–strain curves and fatigue life curves
Jaroslav Polák; Martin Petrenec; Tomáš Kruml
The effect of holes quality on fatigue life of open hole
In this paper, a series of study were conducted on the effect of hole quality on the fatigue life of open holes in 2A12-T4 aircraft quality aluminum alloy. Four metrics that can define holes quality are analyzed. They are roughness, verticality, cylindricity and roundness. Firstly, open holes with different roughness were fatigue tested under constant amplitude remote tensile load and
J. Liu; X. J. Shao; Y. J. Liu; Z. F. Yue
Surface enhancement technologies such as shot peening, laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. For successful integration into turbine design, the process must be affordable and compatible with the manufacturing environment. LPB provides thermally stable
Paul S. Prevéy; Ravi A. Ravindranath; Michael Shepard; Timothy Gabb
Methodology for on line fatigue life monitoring : rainflow cycle counting method.
Green's function technique is used in on line fatigue life monitoring to convert plant data to stress versus time data. This technique converts plant data most efficiently to stress versus time data. To compute the fatigue usage factor the actual number o...
N. K. Mukhopadhyay B. K. Dutta H. S. Kushwaha
A fracture mechanics approach to thermal fatigue life prediction of solder joints
A life prediction approach for solder joints under thermal fatigue, based on fracture mechanics and assuming that the thermal fatigue crack propagation in solder joints is primarily controlled by the C* and the J Integrals, is presented. The approach is applied to model experiments in which surface mounted electronic components were mounted on substrates with eutectic Pb\\/Sn solder joints and
Yi-Hsin Pao
Effects of hole machining defects on strength and fatigue life of composite laminates
The effects of hole machining defects on strength and fatigue life of carbon\\/epoxy laminates subjected to static and fatigue loading are presented. Dry specimens were subjected to pin loading and uniaxial compressive loading at room temperature. The KTH method, a new method which gives defect-free holes, was used to machine holes in the specimens. For comparison, holes were also machined
Erik Persson; Ingvar Eriksson; Leif Zackrisson
Effects of LWR environments on fatigue life of carbon and low-alloy steels
SME Boiler and Pressure Vessel Code provides construction of nuclear power plant components. Figure I-90 Appendix I to Section III of the Code specifies fatigue design curves for structural materials. While effects of environments are not explicitly addressed by the design curves, test data suggest that the Code fatigue curves may not always be adequate in coolant environments. This paper reports the results of recent fatigue tests that examine the effects of steel type, strain rate, dissolved oxygen level, strain range, loading waveform, and surface morphology on the fatigue life of A 106-Gr B carbon steel and A533-Gr B low-alloy steel in water.
Chopra, O.K.; Shack, W.J.
Predicted Effect of Dynamic Load on Pitting Fatigue Life for Low-Contact-Ratio Spur Gears.
How dynamic load affects the surface pitting fatigue life of external spur gears was predicted by using NASA computer program TELSGE. Parametric studies were performed over a range of various gear parameters modeling low-contact-ratio involute spur gears....
D. G. Lewicki
Rolling-element fatigue life with two synthetic cycloaliphatic traction fluids
The life potential of two synthetic cycloaliphatic hydrocarbon traction fluids in rolling element fatigue was evaluated in a five ball fatigue tester. Life comparisons with a MIL-L-23699 qualified tetraester oil showed that the traction test oils had good fatigue life performance, comparable to that of the tetraester oil. No statistically significant life differences between the traction fluids and the tetraester oil were exhibited under the accelerated fatigue test conditions. Erratic operating behavior was occasionally encountered during tests with the antiwear additive containing traction fluid for reasons thought to be related to excessive chemical activity under high contact pressure. This behavior occasionally resulted in premature test termination due to excessive surface distress and overheating.
Loewenthal, S. H.; Parker, R. J.
Effect of Different Axial Bearing Supports on the Fatigue Life of Ceramic Pressure Housings.
The fatigue life of underwater pressure housings composed of ceramic hull components assembled with epoxy-bonded metallic joint rings is dependent upon a number of parameters. The techniques used for bonding joint rings to the ceramic bearing surfaces is ...
R. P. Johnson R. R. Kurkchubasche J. D. Stachiw
Residual Stress Effects at a Notch Root in A723 Steel to Extend Fatigue Life.
Fatigue life tests were performed with notched bend specimens of ASTM A723 steel with three types of residual stress treatments and resulting residual stress: shot peening, bole swaging, and tensile overload. The three treatments produced widely different...
J. H. Underwood
Methodology for the Quantitative Evaluation of the Remaining Fatigue Life of Fracture Critical Bridges.
Two fracture critical bridges were instrumented using miniature, battery-powered data acquisition systems as part of this investigation. The measured rainflow response was then used to estimate the remaining fatigue life of each bridge. The primary advant...
P. K. Dean S. L. Wood
A Reliability Analysis Approach to Fatigue Life Dispersion of Laminated Glass Fiber Composite Materials.
The statistical nature of the fatigue life of laminated glass fiber composite materials (FRP) is studied. Four different FRP laminates (satin woven FRP, plain woven FRP, roving woven FRP, and SMC laminated FRP) were used in the experiments. Unidirectional...
T. Tanimoto S. Amijima H. Ishikawa K. J. Miller R. F. Smith
Review of the workshop on fatigue life methodologies for wind turbines.
From March 31--April 1, 1993, Sandia National Laboratories (SNL) and the National Renewable Energy Laboratory (NREL) hosted a workshop entitled ''Fatigue Life Methodologies.'' The purpose of this workshop was to bring together a representative panel of ex...
H. J. Sutherland C. P. Butterfield
Structural qualification testing and operational loading on a fiberglass rotor blade for the Mod-OA wind turbine
Fatigue tests were performed on full- and half-scale root end sections, first to qualify the root retention design, and second to induce failure. Test methodology and results are presented. Two operational blades were proof tested to design limit load to ascertain buckling resistance. Measurements of natural frequency, damping ratio, and deflection under load made on the operational blades are documented. The tests showed that all structural design requirements were met or exceeded. Blade loads measured during 3000 hr of field operation were close to those expected. The measured loads validated the loads used in the fatigue tests and gave high confidence in the ability of the blades to achieve design life.
Sullivan, T. L.
Fatigue Life Methodology for Tapered Hybrid Composite Flexbeams
Nonlinear-tapered flexbeam specimens from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. Two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) associated with simulated delamination growth in the flexbeams are presented from both codes. These results compare well with each other and suggest that the initial delamination growth from the tip of the ply-drop toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves for comparison with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared well with the test results.
urri, Gretchen B.; Schaff, Jeffery R.
Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams
Nonlinear-tapered flexbeam laminates from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. The two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) obtained from the above codes using the virtual crack closure technique (VCCT) at a resin crack location in the flexbeams are presented for both hybrid material types. These results compare well with each other and suggest that the initial delamination growth from the resin crack toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves and compared with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared reasonably well with the test results.
Murri, Gretchen B.; Schaff, Jeffery R.; Dobyns, Alan L.
Childhood Adversity and Cumulative Life Stress: Risk Factors for Cancer-Related Fatigue
Fatigue is a common symptom in healthy and clinical populations, including cancer survivors. However, risk factors for cancer-related fatigue have not been identified. On the basis of research linking stress with other fatigue-related disorders, we tested the hypothesis that stress exposure during childhood and throughout the life span would be associated with fatigue in breast cancer survivors. Stress exposure was assessed using the Stress and Adversity Inventory, a novel computer-based instrument that assesses for 96 types of acute and chronic stressors that may affect health. Results showed that breast cancer survivors with persistent fatigue reported significantly higher levels of cumulative lifetime stress exposure, including more stressful experiences in childhood and in adulthood, compared to a control group of nonfatigued survivors. These findings identify a novel risk factor for fatigue in the growing population of cancer survivors and suggest targets for treatment.
Bower, Julienne E.; Crosswell, Alexandra D.; Slavich, George M.
Residual stress evaluation and fatigue life prediction in the welded joint by x-ray diffraction
In the fossil power plant, the reliability of the components which consist of the many welded parts depends on the quality of welding. The residual stress is occurred by the heat flux of high temperature during weld process. This decreases the mechanical properties as the strength of fatigue and fracture. The residual stress of the welded part in the recently constructed power plants has been the cause of a variety of accidents. The objective of this study is measurement of the residual stress and the full width at half maximum intensity (FWHM) by X-ray diffraction method and to estimate the feasibility of this application for fatigue life assessment of the high-temperature pipeline. The materials used for the study is P92 steel for the use of high temperature pipe on super critical condition. The test results were analyzed by the distributed characteristics of residual stresses and FWHM in x-ray diffraction intensity curve. Also, X-ray diffraction tests using specimens simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the ratio of the FWHM due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.
Yoo, Keun Bong; Hwang, Kwon Tae; Chang, Jung Chel; Kim, Jae Hoon
An industrial laser cutting machine tool was used to harden 1117 and 1144 steel to examine effects on fatigue life. Transformation hardening leaves residual compressive stresses at the surface, which greatly enhance fatigue life in addition to increasing the hardness. The laser, which creates localized heating, allows faster cooling rates than conventional heat treatment methods. As a result, the application of the laser facilitates the hardening of low carbon steel which is not hardenable by conventional methods.
Fly, D.E. [Troxel Co., Moscow, TN (United States); Black, J.T. [Auburn Univ., AL (United States); Singleton, B. [Alabama Industrial Development and Training, Montgomery, AL (United States)
The aim of the study was to determine low-cycle fatigue life characteristics of P92 steel used in the power unit components that work under the highest effort. Steel service life was determined in the tests for total fixed strain ??t ranges from 0.6 to 1.2 % and with application of two-stage sequence loading. Low-cycle fatigue tests were conducted at room
M Cie?la; G Junak
Creep-fatigue damage and life prediction in P92 alloy by focused ultrasound measurements
In the present study, the characteristics of creep damage in P92 alloy were investigated via nondestructive evaluation. Generally,\\u000a as the hold time of a static load increases, the degradation of the material becomes more severe along with a reduction of\\u000a service life. Therefore, in power plants, the reduction of creep-fatigue strength and the creep-fatigue life of high pressure\\u000a vessels at
Bum-joon Kim; Hak-joon Kim; Byeong-soo Lim
Finite element prediction of high cycle fatigue life of aluminum alloys
A new method is described for calculating the long fatigue life (>105 cycles) portion of the stress-life (S-N) fatigue curve for precipitation-hardened aluminum alloys. It is based upon a finite element model of the deformation of\\u000a a persistent slipband (PSB), and the only material parameter required is the ultimate tensile strength (UTS) of the alloy.\\u000a The stress dependence of the
William J. Baxter; Pei-Chung Wang
Analysis of Hysteresis Damage Accumulation and the Effect on Fatigue Life
\\u000a In order to validate an existing energy-based fatigue life prediction understanding, the strain energy accumulation for interrupted\\u000a loading cycles was analyzed. The life prediction method being validated was developed based on the understanding that strain\\u000a energy density accumulated during monotonic fracture is a physical damage quantity that is equal to total cumulative hysteresis\\u000a strain energies in a fatigue process. If
Onome Scott-Emuakpor; Tommy George; Charles Cross; M.-H. Herman Shen
What roles do team climate, roster control, and work life conflict play in shiftworkers' fatigue longitudinally?
The study aimed to examine shiftworkers fatigue and the longitudinal relationships that impact on fatigue such as team climate, work life conflict, control of shifts and shift type in shift working nurses. We used a quantitative survey methodology and analysed data with a moderated hierarchical multiple regression. After matching across two time periods 18 months apart, the sample consisted of 166 nurses from one Australian hospital. Of these nurses, 61 worked two rotating day shifts (morning & afternoon/evening) and 105 were rotating shiftworkers who worked three shifts (morning afternoon/evening and nights). The findings suggest that control over shift scheduling can have significant effects on fatigue for both two-shift and three-shift workers. A significant negative relationship between positive team climate and fatigue was moderated by shift type. At both Time 1 and Time 2, work life conflict was the strongest predictor of concurrent fatigue, but over time it was not. PMID:24210672
Pisarski, Anne; Barbour, Jennifer P
Factors Influencing the Fatigue Life of an HY-80 Composition Steel Fully Quenched and Tempered to Various Strength Levels.
The report evaluates the effects of strength level, Charpy V-notch energy, prestraining, prestraining and stress relieving, and austenitizing temperature on the fatigue life of a fully quenched HY-80 steel composition. The fatigue data developed indicate ...
A. R. Willner M. L. Salive
Rolling-Element Fatigue Life of Silicon Nitride Balls.
The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of ...
R. J. Parker E. V. Zaretsky
A phenomenological model for predicting fatigue life in bovine trabecular bone.
Cyclic loading of bone during daily activities can lead to fatigue degradation and increased risk of fracture in both the young and elderly population. Damage processes under cyclic loading in trabecular bone result in the reduction of the elastic modulus and accumulation of residual strain. These effects increase with increasing stress levels, leading to a progressive reduction in fatigue life. The present work analyzes the effect of stress and strain variation on the above damage processes in bovine trabecular bone, and develops a phenomenological model relating fatigue life to the imposed stress level. The elastic modulus reduction of the bone specimens was observed to depend on the maximum compressive strain, while the rate of residual strain accumulation was a function of the stress level. A model was developed for the upper and lower bounds of bone elastic modulus reduction with increasing number of cycles, at each stress range. The experimental observations were described well by the model. The model predicted the bounds of the fatigue life with change in fatigue stress. The decrease in the fatigue life with increasing stress was related to corresponding increases in the residual strain accumulation rates at the elevated stress levels. The model shows the validity of fatigue predictions from relatively few cyclic experiments, by combining trends observed in the monotonic and the cyclic tests. The model also presents a relatively simple procedure for predicting the endurance limit for bovine trabecular bone specimens. PMID:15341169
Ganguly, P; Moore, T L A; Gibson, L J
Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model
The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. As part of a NAVAIR High Strength Steel Corrosion–Fatigue Assessment Program, methods were studied to predict the impact that corrosion-induced surface roughness has on the fatigue life of high-strength steel aircraft components. In order to adequately capture the corrosion damage features that cause fatigue
D. T. Rusk; W. Hoppe
Life prediction of thermal-mechanical fatigue using strain-range partitioning
The applicability is described of the method of Strainrange Partitioning to the life prediction of thermal-mechanical strain-cycling fatigue. An in-phase test on 316 stainless steel is analyzed as an illustrative example. The observed life is in excellent agreement with the life predicted by the method using the recently proposed Step-Stress Method of experimental partitioning, the Interation Damage Rule, and the life relationships determined at an isothermal temperature of 705 C. Implications of the study are discussed relative to the general thermal fatigue problem.
The Effect of Hole Quality on the Fatigue Life of 2024-T3 Aluminum Alloy Sheet
This paper presents the results of a study whose main objective was to determine which type of fabrication process would least affect the fatigue life of an open-hole structural detail. Since the open-hole detail is often the fundamental building block for determining the stress concentration of built-up structural parts, it is important to understand any factor that can affect the fatigue life of an open hole. A test program of constant-amplitude fatigue tests was conducted on five different sets of test specimens each made using a different hole fabrication process. Three of the sets used different mechanical drilling procedures while a fourth and fifth set were mechanically drilled and then chemically polished. Two sets of specimens were also tested under spectrum loading to aid in understanding the effects of residual compressive stresses on fatigue life. Three conclusions were made from this study. One, the residual compressive stresses caused by the hole-drilling process increased the fatigue life by two to three times over specimens that were chemically polished after the holes were drilled. Second, the chemical polishing process does not appear to adversely affect the fatigue life. Third, the chemical polishing process will produce a stress-state adjacent to the hole that has insignificant machining residual stresses.
Everett, Richard A., Jr.
Low cycle and thermomechanical fatigue of nickel base superalloys for gas turbine application
Isothermal low cycle (LCF) fatigue and thermomechanical (TMF) fatigue of some nickel base superalloys have been analysed comparing their fatigue life for different temperatures and strain history.Fatigue behaviour of CMSX4+Y single crystal alloy for turbine blades can be described either with TMF or with isothermal LCF testing. TMF results on MA6000 and MA760 ODS alloys are strongly different from those
M. Marchionni
Predicting the Fatigue Life of Adhesively-Bonded Joints
The fatigue behaviour of adhesively-bonded joints, which consisted of an epoxy-film adhesive bonding fibre-composite substrates, has been studied. Using a double-cantilever beam specimen, the rate of crack growth per cycle has been measured as a function of the maximum strain-energy release rate, Gmax. These data have then been modelled, and used to predict the fatigue lifetime of bonded single-lap joints.
A. J. Kinloch; S. O. Osiyemi
Reliability and fatigue life evaluation of railway axles
The axle is one of the most important components of a rail vehicle which transmits the weight of the vehicle to the wheels,\\u000a meets the vertical and horizontal loads formed during static and dynamic moving, and carries the driving moment and braking\\u000a moment. The prediction of fatigue failure of axles plays an important role in preventing fatigue fractures. Varying loads
Meral Bayraktar; Necati Tahrali; Rahmi Guclu
Smart structure for small wind turbine blade
Wind energy is seen as a viable alternative energy option for future energy demand. The blades of wind turbines are generally regarded as the most critical component of the wind turbine system. Ultimately, the blades act as the prime mover of the whole system which interacts with the wind flow during the production of energy. During wind turbine operation the wind loading cause the deflection of the wind turbine blade which can be significant and affect the turbine efficiency. Such a deflection in wind blade not only will result in lower performance in electrical power generation but also increase of material degradation due high fatigue life and can significantly shorten the longevity for the wind turbine material. In harnessing stiffness of the blade will contribute massive weight factor and consequently excessive bending moment. To overcome this excessive deflection due to wind loading on the blade, it is feasible to use shape memory alloy (SMA) wires which has ability take the blade back to its optimal operational shape. This paper details analytical and experimental work being carried out to minimize blade flapping deflection using SMA.
Supeni, E. E.; Epaarachchi, J. A.; Islam, M. M.; Lau, K. T.
Application of an energy-based life prediction model to bithermal and thermomechanical fatigue
The inelastic hysteresis energy applied to the material in a cycle is used as the basis for predicting nonisothermal fatigue life of a wrought cobalt-base superalloy, Haynes 188, from isothermal fatigue data. Damage functions that account for hold-time effects and time-dependent environmental phenomena such as oxidation and hot corrosion are proposed in terms of the inelastic hysteresis energy per cycle. The proposed damage functions are used to predict the bithermal and thermomechanical fatigue lives of Haynes 188 between 316 and 760 C from isothermal fatigue data. Predicted fatigue lives of all but two of the nonisothermal tests are within a factor of 1.5 of the experimentally observed lives.
Radhakrishnan, V. M.; Kalluri, Sreeramesh; Halford, Gary R.
Empirical modeling of environment-enhanced fatigue crack propagation in structural alloys for component life prediction
This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The approach couples empirical modeling of environmental FCP with corrosion fatigue experiments. Three different computer models have been developed and incorporated in the DOS executable program. UVAFAS. A multiple power law model is available, and can fit a set of fatigue data to a multiple power law equation. A model has also been developed which implements the Wei and Landes linear superposition model, as well as an interpolative model which can be utilized to interpolate trends in fatigue behavior based on changes in loading characteristics (stress ratio, frequency, and hold times).
Richey, Edward, III
Fatigue life prediction of an intermetallic matrix composite at elevated temperatures
A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the 'Universal Slopes' method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio (Vf), number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.
Bartolotta, P. A.
A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the Universal Slopes method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio, number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.
Bartolotta, Paul A.
Development of a low-cycle fatigue life curve for 80In15Pb5Ag
The purpose of this study is to develop a methodology to predict the low-cycle (large strain—from 0.1 to 0.35 strain) fatigue life of solders subject to thermal cycling. Solders are commonly used in electronic assemblies. Using thermal fatigue data measured for 80In15Pb5Ag, a low-cycle fatigue curve for 80In15Pb5Ag solder subject to thermal cycling was developed. Specifically a Coffin-Manson relationship was derived for the solder, with a high degree of correlation (see Table I), for four different failure criteria, defined in the body of the paper. This relationship, together with calculated strains in the solder joint, allows the low-cycle fatigue life of the solder joint to be predicted.
Edwards, L. K.; Nixon, W. A.; Lakes, R. S.
The Effect of Three Mineral Base Oils on Roller Bearing Fatigue Life
The effect of three mineral base oils on roller bearing fatigue life has been studied. Life performance tests were conducted, using a specially controlled group of 45-mm bore cylindrical roller bearings. The results indicate that base oil stock affects bearing performance. Of the highly naphthenic, naphthenic, and paraffinic mineral oils studied, bearings lubricated with the latter achieved superior lives. The
Irwin Koved
A generalized frequency modified damage function model for high temperature low cycle fatigue life prediction
The models for predicting high temperature low cycle fatigue (HTLCF) life are significant in the design of engineering components and structures working under high temperature and cyclic loading. In this paper, a review of the earlier models is given first, and then a new model for the HTLCF life prediction, a generalized frequency modified damage function (GFMDF) model, is set
Wang Yonglian
Fatigue and Quality of Life in Breast Cancer Patients Undergoing Autologous Stem Cell Transplantation
As more individuals are being treated for cancer with high-dose therapy and autologous stem cell rescue (ASCR), there is growing interest in treatment side effects and their impact on quality of life. The primary aim of this study was to determine if the severity of fatigue and its impact on quality of life is significantly greater in women undergoing ASCR
Danette M Hann; Natara Garovoy; Brigette Finkelstein; Paul B Jacobsen; Lora M Azzarello; Karen K Fields
Influence of Melatonin on Quality of Life in Patients with Chronic Fatigue and Late Melatonin Onset
, ABSTRACT. Medical Outcome Study Short Fonn-36 (MOS SF-36) qualities of life scores were studied in 38 chronic fatigue patients with late melatonin onset before and after treatment with melatonin. Before start of the treatment, quality of life was assessed twice. Pre-treatment scores were compared with each other and with the scores of 43 patients with Delayed Sleep Phase Syndrome
M. G. Smits; R. van Rooy; J. E. Nagtegaal
Mean vs. Life-Limiting Fatigue Behavior of a Nickel-Based Superalloy (Postprint).
The mean and the life-limiting behavior under fatigue of the nickel- based superalloy, IN100, separated (or converged) as a function of stress level and dwell loading. This behavior was related to the control of the life- limiting behavior by the small-cr...
J. M. Larsen M. J. Caton S. K. Jha
Horizontal Axis Wind Turbine Blade Aerodynamics in Experiments and Modeling
Turbine aerodynamics remains a challenging and crucial research area for wind energy. Blade aerodynamic forces responsible for power production must be augmented to maximize energy capture. At the same time, adverse aerodynamic loads that fatigue turbine components need to be mitigated to extend machine service life. Successful resolution of these conflicting demands and continued cost of energy reduction require accurate
Scott J. Schreck; Michael C. Robinson
Evaluation of the EHL film thickness and extreme pressure additives on gear surface fatigue life
Surface pitting fatigue life tests were conducted with seven lubricants, using AISI 9310 spur gears. The test lubricants can be classified as synthetic polyol-esters with various viscosities and additive packages. The lubricant with a viscosity that provided a specific film thickness greater than one and with an additive package produced gear surface fatigue lives that were 8.6 times that for lubricants with a viscosity that provided specific film thickness less than one. Lubricants with the same viscosity and similar additive packages gave equivalent gear surface fatigue lives.
Townsend, Dennis P.; Shimski, John
Effect of surface treatments on the fatigue life of titanium for biomedical applications.
Many surface treatments that are used in cementless and endosseous implants modify the topography and the roughness to increase the implant-bone contact area and thus favor bio-mechanical anchorage, shortening the period of osseointegration. Nevertheless, the effects that the surface treatments can have on the fatigue life of the material are not generally considered. In this sense, the superficial condition of the component is one of the features that affect the fatigue strength, specially the fatigue crack nucleation. The fatigue behaviour of annealed commercially pure titanium grade 4 was studied. The surface treatments used were acid etching, shot blasting and a dual treatment of blasting + acid etching. An as-machined surface condition was used as a reference. Topography, roughness, surface defects, microstructural changes and residual stresses were characterized in each case. Rotating-bending fatigue tests of each surface condition were conducted at room temperature with a frequency of 33 Hz. S-N curves and Basquin equations were obtained based on the results of these tests. Tested samples were also characterized to evaluate fatigue damage. The acid etching decreases the fatigue endurance, while the blasting and blasting + acid etching treatments showed a similar behaviour with respect to the reference condition. For acid etching, the modifications introduced (stress raisers) contributed to accelerate the nucleation of cracks. On the other hand, the treatments with a blasting stage besides generating stress raisers, introduced compressive residual stresses and superficial plastic deformation that tend to improve the fatigue endurance of the material. PMID:20621024
Pazos, L; Corengia, P; Svoboda, H
Objective: To assess the impact of post-polio-related fatigue on quality of life. Design: Cross-sectional case control study. Subjects: Patients without additional health problems that may induce fatigue were selected from among 82 polio survivors. Twenty-six patients with post-polio syndrome and 10 without post-polio syndrome were included. Control group consisted of 30 healthy volunteers. Methods: We assessed presence and severity of
Arzu Yagiz On; Julide Oncu; Funda Atamaz; Berrin Durmaz
Fatigue life estimation of steel girder of Yangpu cable-stayed Bridge due to buffeting
As the main span of modern cable-stayed bridges becomes longer and longer, the buffeting-induced fatigue damage problem of steel girders located in strong wind regions may have to be taken into consideration in the design of the bridge. This paper presents a method in the mixed frequency–time domain for estimating the fatigue life of steel girders of the Yangpu cable-stayed
M. Gu; Y. L. Xu; L. Z. Chen; H. F. Xiang
Fatigue life and mechanical behaviors of bearing steel by nitrogen plasma immersion ion implantation
Rolling contact fatigue (RCF) performance and mechanical characteristics of nitrogen plasma immersion ion implantation (PIII) on AISI52100 bearing steel surface has been investigated using a conventional three ball-on-rod rig. Testing investigations include optical microscopy (OM), friction and wear behavior, rolling contact fatigue life, and nano-indentation measurements. Results indicate that the rolling elements failed at the surface or near-surface layer. Moreover,
Hongxi Liu; Baoyin Tang; Langping Wang; Xiaofeng Wang; Bo Jiang
Effect of grinding conditions on the fatigue life of titanium 5Al-2.5Sn alloy
An investigation into the effect of grinding conditions on the fatigue life of titanium 5Al-2.5Sn is presented. Damage to surface integrity and changes in the residual stresses distribution are studied to assess changes in fatigue life. A surface grinding machine, operating at speeds ranging from 2000 to 6000 fpm and using SiC wheels of grit sizes 60 and 120, was used to grind flat subsize specimens of 0.1-in. thickness. After grinding, the specimens were fatigued at a chosen stress and compared with the unadulterated material. A standard profilometer, a microhardness tester, and a scanning electron microscope were utilized to examine surface characteristics and measure roughness and hardness. Increased grinding speed in both wet and dry applications tended to decrease the fatigue life of the specimens. Fatigue life increased markedly at 2000 fpm under wet conditions, but then decreased at higher speeds. Grit size had no effect on the fatigue life.
Rangaswamy, P.; Terutung, H.; Jeelani, S.
Detection and Influence of Shrinkage Pores and Nonmetallic Inclusions on Fatigue Life of Cast Aluminum Alloys
In the current study, test bars of cast aluminum alloys EN AC-AlSi8Cu3 and EN AC-AlSi7Mg0.3 were produced with a defined amounts of shrinkage pores and oxides. For this purpose, a permanent mold with heating and cooling devices for the generation of pores was constructed. The oxides were produced by contaminating the melt. The specimens and their corresponding defect distributions were examined and quantified by X-ray computer tomography (CT) and quantitative metallography, respectively. A special test algorithm for the simultaneous image analyses of pores and oxides was developed. Fatigue tests were conducted on the defective samples. It was found that the presence of shrinkage pores lowers the fatigue strength, and only few oxide inclusions were found to initiate fatigue cracks when shrinkage pores are present. The results show that the pore volume is not sufficient to characterize the influence of shrinkage pores on fatigue life. A parametric model for the calculation of fatigue life based on the pore parameters obtained from CT scans was implemented. The model accounts for the combined impact of pore location, size, and shape on fatigue life reduction.
Tijani, Yakub; Heinrietz, André; Stets, Wolfram; Voigt, Patrick
Effect of helium on fatigue crack growth and life of reduced activation ferritic/martensitic steel
The effects of helium on the fatigue life, micro-crack growth behavior up to final fatigue failure, and fracture mode under fatigue in the reduced activation ferritic/martensitic steel, F82H IEA-heat, were investigated by low cycle fatigue tests at room temperature in air at a total strain range of 0.6-1.5%. Significant reduction of the fatigue life due to helium implantation was observed for a total strain range of 1.0-1.5%, which might be attributable to an increase in the micro-crack propagation rate. However, the reduction of fatigue life due to helium implantation was not significant for a total strain range of 0.6-0.8%. A brittle fracture surface (an original point of micro-crack initiation) and a cleavage fracture surface were observed in the helium-implanted region of fracture surface. A striation pattern was observed in the non-implanted region. These fracture modes of the helium-implanted specimen were independent of the strain range.
Nogami, Shuhei; Takahashi, Manabu; Hasegawa, Akira; Yamazaki, Masanori
A Fatigue Life Prediction Model of Welded Joints under Combined Cyclic Loading
A practical and robust methodology is developed to evaluate the fatigue life in seam welded joints when subjected to combined cyclic loading. The fatigue analysis was conducted in virtual environment. The FE stress results from each loading were imported to fatigue code FE-Fatigue and combined to perform the fatigue life prediction using the S x N (stress x life) method. The measurement or modelling of the residual stresses resulting from the welded process is not part of this work. However, the thermal and metallurgical effects, such as distortions and residual stresses, were considered indirectly through fatigue curves corrections in the samples investigated. A tube-plate specimen was submitted to combined cyclic loading (bending and torsion) with constant amplitude. The virtual durability analysis result was calibrated based on these laboratory tests and design codes such as BS7608 and Eurocode 3. The feasibility and application of the proposed numerical-experimental methodology and contributions for the technical development are discussed. Major challenges associated with this modelling and improvement proposals are finally presented.
Goes, Keurrie C.; Camarao, Arnaldo F.; Pereira, Marcos Venicius S.; Ferreira Batalha, Gilmar
Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop
Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment.
Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo
The effect of coating residual stress on the fatigue life of thermal spray-coated steel and aluminum
The acceptance of thermal spray coatings in many applications depends on the effect of the coating on the fatigue performance of the coated part. One of the factors that influences the fatigue life of thermal spray-coated components is the residual stress in the coating. This study investigates the fatigue performance of tungsten carbide–cobalt (WC–Co) thermal spray coating systems. Bending fatigue
R. T. R McGrann; D. J Greving; J. R Shadley; E. F Rybicki; T. L Kruecke; B. E Bodger
Fatigue reliability of wind turbine components
Fatigue life estimates for wind turbine components can be extremely variable due to both inherently random and uncertain parameters. A structural reliability analysis is used to qualify the probability that the fatigue life will fall short of a selected target. Reliability analysis also produces measures of the relative importance of the various sources of uncertainty and the sensitivity of the reliability to each input parameter. The process of obtaining reliability estimates is briefly outlined. An example fatigue reliability calculation for a blade joint is formulated; reliability estimates, importance factors, and sensitivities are produced. Guidance in selecting distribution functions for the random variables used to model the random and uncertain parameters is also provided.
Veers, P. S.
Effect Of Solidification Speed On Fatigue Properties
Fast solidification increases fatigue life, but failure distribution becomes less predictable. Report describes effects of rate of solidification on nickel-based super-alloy MAR-M246(Hf) used in turbine blades. Based on experiments in which specimens directionally solidified at 5 cm/h and 30 cm/h, then tested for high cycle fatigue. Specimens also inspected by energy-dispersive x-ray (EDX) analysis and optical and electron microscopy.
Mccay, M. H.; Schmidt, D. D.; Hamilton, W. D.; Alter, W. S.; Parr, R. A.
Monitoring fatigue life in concrete bridge deck slabs
Concrete bridge deck slabs are the most common form of bridge deck construction in short and medium span bridge structures in North America. Understanding and monitoring the condition of these bridge decks is an important component of a bridge management strategy. Progressive deterioration due to fatigue occurs in concrete decks due to the large number of cycles of heavy wheels
J. Newhook; V. Limaye
Probabilistic Fatigue Life Analysis of High Density Electronics Packaging
The fatigue of thin film metal interconnections in high density electronics packaging subjected to thermal cycling has been evaluated using a probabilistic fracture mechanics methodology. This probabilistic methodology includes characterization of thin film stress using an experimentally calibrated finite element model and simulation of flaw growth in the thin films using a stochastic crack growth model.
Moore, N. R.; Kolawa, E. A.; Sutharshana, S.; Newlin, L. E.; Creager, M.
A study of stiffness, residual strength and fatigue life relationships for composite laminates
Qualitative and quantitative exploration of the relationship between stiffness, strength, fatigue life, residual strength, and damage of unnotched, graphite/epoxy laminates subjected to tension loading. Clarification of the mechanics of the tension loading is intended to explain previous contradictory observations and hypotheses; to develop a simple procedure to anticipate strength, fatigue life, and stiffness changes; and to provide reasons for the study of more complex cases of compression, notches, and spectrum fatigue loading. Mathematical models are developed based upon analysis of the damage states. Mathematical models were based on laminate analysis, free body type modeling or a strain energy release rate. Enough understanding of the tension loaded case is developed to allow development of a proposed, simple procedure for calculating strain to failure, stiffness, strength, data scatter, and shape of the stress-life curve for unnotched laminates subjected to tension load.
Ryder, J. T.; Crossman, F. W.
Effects of High Temperature Exposures on Fatigue Life of Disk Superalloys
The effects on fatigue life of high temperature exposures simulating service conditions were considered for two disk superalloys. Powder metallurgy processed, supersolvus heat treated Udimet (trademark) 720 and ME3 fatigue specimens were exposed in air at temperatures of 650 to 704 C, for times of 100 h to over 1000 h. They were then tested using conventional fatigue tests at 650 and 704 C, to determine the effects of exposure on fatigue resistance. Cyclic dwell verification tests were also performed to contrast the effects of intermixed exposures and fatigue cycles. The prior exposures reduced life by up to 70% and increased the scatter in life, compared to unexposed levels. Cyclic dwell tests reduced lives even more. Fractographic evaluations indicated the failure mode was shifted by the exposures and cyclic dwells from predominantly internal to often surface crack initiations. The increased scatter in life was related to the competition between internal crack initiations at inclusions or large grains producing longer lives, and surface crack initiations at an environmentally affected surface layer producing shorter lives.
Gabb, Tim P.; Telesman, Jack; Kantzos, Pete T.; Smith, James W.; Browning, Paul F.
A simplified method for creep-fatigue life prediction for structures subjected to thermal loadings
A simplified creep-fatigue failure prevention-life prediction method (TTSDS) for pressure vessels and pipings subjected to thermal expansion-thermal transient loadings is presented. The method was constructed based on numerous SUS304 material-structure test data, and incorporates a linear cumulative damage rule with an instrinsic life reduction factor. When the TTSDS method was applied using no safety factors, good life predictions for piping
Katsumi Watashi
An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.
Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.
Hudson, C. M.
Thermomechanical fatigue life prediction in gas turbine superalloys: A fracture mechanics approach
A model is presented that was developed to predict thermomechanical fatigue crack initiation and estimate mode I crack growth of gas turbine hot section gas path superalloys. The model is based on a strain energy density fracture mechanics approach modified to account for thermal exposure and single crystal anisotropy. Thermomechanical fatigue crack initiation and small crack growth is modeled by employing an initial material defect size. Model capability was quantified by applying the model to two hot section gas path superalloys: uncoated MAR-M509 and MCrAlY overlay coated PWA 1480. Thermomechanical fatigue model stresses were obtained from nonlinear finite element analysis of thermomechanical fatigue specimen strain-temperature history. Nonlinear stress-strain behavior was predicted using unified viscoplastic constitutive models. Model thermomechanical fatigue life predictions were in good agreement with observed uniaxial thermomechanical fatigue specimen lives. Thermomechanical fatigue cracking effects captured by the model included coating thickness, single crystal anisotropy, cycle waveshape, dwell, and thermal exposure. 45 refs.
Nissley, D.M. [United Technologies Corp., East Hartford, CT (United States)
Effect of electric discharge machining on the fatigue life of Inconel 718
The effect of electric discharge machining on the fatigue life of Inconel 718 alloy at room temperature was investigated. Data were generated in the uniaxial tension fatigue mode at ambient temperature using flat 3.175 mm thick specimens. The specimens were machined on a wire-cut electric discharge machine at cutting speeds ranging from 0.5 to 2 mm per minute. The specimens were fatigued at a selected stress, and the resulting fatigue lives compared with that of the virgin material. The surfaces of the fatigued specimens were examined under optical and scanning electron microscopes, and the roughness of the surfaces was measured using a standard profilometer. From the results of the investigation, it was concluded that the fatigue life of the specimens machined using EDM decreased slightly as compared with that of the virgin material, but remained unchanged as the cutting speed was changed. The results are explained using data produced employing microhardness measurements, profilometry, and optical and scanning microscopy.
Jeelani, S.; Collins, M. R.
Panel resonant behavior of wind turbine blades
The principal design drivers in the certification of wind turbine blades are ultimate strength, fatigue resistance, adequate tip-tower clearance, and buckling resistance. Buckling resistance is typically strongly correlated to both ultimate strength and fatigue resistance. A composite shell with spar caps forms the airfoil shape of a blade and reinforcing shear webs are placed inside the blade to stiffen the
Joshua A. Paquette; Daniel Todd Griffith
Fatigue life prediction analysis of surface cracked straight pipes
In piping components, for the stability assessment it is important to calculate the point of initiation of the crack and to\\u000a monitor the subsequent crack propagation behaviour. The objective of this paper is to use the finite element method backed\\u000a up with experimental results to determine the crack initiation stage and to subsequently predict the crack propagation behaviour\\u000a under fatigue
Sanjeev Saxena; N. Ramakrishnan; J. S. Chouhan
Effect of modafinil on fatigue, mood, and health-related quality of life in patients with narcolepsy
Introduction In addition to excessive sleepiness, patients with narcolepsy often have significant fatigue, depressed mood, and decreased quality of life. Objective To determine whether treatment with modafinil for excessive sleepiness improves fatigue, mood, and health-related quality of life (HRQOL) in patients with narcolepsy. Materials and methods Outpatients with narcolepsy underwent a 14-day washout of psychostimulants and then were enrolled in
Philip M. Becker; Jonathan R. L. Schwartz; Neil T. Feldman; Rod J. Hughes
An analytical method to predict fatigue life of thermoplastics in uniaxial loading: sensitivity to wave type, frequency and stress amplitude
A method is presented that allows fatigue life predictions on the basis of creep life data. The approach is based on the assumption that the time-dependent failure of polymers is determined by the intrinsic strain softening that is initiated when a critical threshold value of the plastic strain is surpassed. To facilitate fatigue predictions, an acceleration factor is defined that
Roel P. M. Janssen; Leon E. Govaert; Han E. H. Meijer
The effect of cryogenic treatment on the fatigue life of chrome silicon steel compression springs
The purpose of this dissertation is to explore the effect of cryogenic treatment on the fatigue life of compression springs. Product manufacturers are constantly searching for ways to make their products last longer. This dissertation addresses three questions: (1) What is the effect of cryogenic treatment on the fatigue life of chrome silicon steel compression springs? Does the life increase, decrease, or remain the same? (2) What is the effect of cryogenic treatment on the Percent Load Loss (Stress Relaxation) of chrome silicon steel compression springs? (3) What are the possible changes in the material that cause these effects? The following tests were carried out; wire tensile test, hardness test, chemical analysis, residual stress, retained austenite, lattice parameter, force vs. deflection, percent load loss (stress relaxation), fatigue, microstructures, and eta carbides. This research produced a number of key findings: (1) The cryogenically treated springs had a longer cycle life and a higher endurance limit than the untreated springs. (2) The percent load loss (stress relaxation) of the cryogenically treated springs was similar to the untreated springs. (3) The cryogenically treated springs had a higher compressive residual stress at the surface than the untreated springs. The conclusions of this research are that the cryogenic treatment of chrome silicon steel compression springs led to an increase in compressive residual stress on the wire surface, which in turn led to an increase in fatigue life and a higher endurance limit. A recommended future study would be to compare cryogenically treated springs to shot peened springs.
Smith, Debra Lynn
A Three-Parameter Model for Predicting Fatigue Life of Ductile Metals Under Constant Amplitude Multiaxial Loading
In this article, a fatigue damage parameter is proposed to assess the multiaxial fatigue lives of ductile metals based on the critical plane concept: Fatigue crack initiation is controlled by the maximum shear strain, and the other important effect in the fatigue damage process is the normal strain and stress. This fatigue damage parameter introduces a stress-correlated factor, which describes the degree of the non-proportional cyclic hardening. Besides, a three-parameter multiaxial fatigue criterion is used to correlate the fatigue lifetime of metallic materials with the proposed damage parameter. Under the uniaxial loading, this three-parameter model reduces to the recently developed Zhang's model for predicting the uniaxial fatigue crack initiation life. The accuracy and reliability of this three-parameter model are checked against the experimental data found in literature through testing six different ductile metals under various strain paths with zero/non-zero mean stress.
Liu, Jia; Li, Jing; Zhang, Zhong-ping
Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements
The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al2O3-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (? = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (? = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy ( p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.
Koike, Mari; Chan, Kwai S.; Hummel, Susan K.; Mason, Robert L.; Okabe, Toru
Characterization of the strain-life fatigue properties of thin sheet metal using an optical extensometer
Characterizing the strain-life fatigue behavior of thin sheet metals is often challenging since the required specimens have short gauge lengths to avoid buckling, thereby preventing the use of conventional mechanical extensometers. To overcome this obstacle a microscopic optical imaging system has been developed to measure the strain amplitude during fatigue testing using Digital Image Correlation (DIC). A strategy for rapidly recording images is utilized to enable sequential image sampling rates of at least 10 frames per second (fps) using a general digital camera. An example of a complete strain-life fatigue test for thin sheet steel under constant displacement control is presented in which the corresponding strain within the gage section of the specimen is measured using the proposed imaging system. The precision in strain measurement is assessed and methods for improving the image sampling rates in dynamic testing are discussed.
Zhang, Shuiqiang; Mao, Shuangshuang; Arola, Dwayne; Zhang, Dongsheng
A Statistical Simulation Approach to Safe Life Fatigue Analysis of Redundant Metallic Components
This paper introduces a dual active load path fail-safe fatigue design concept analyzed by Monte Carlo simulation. The concept utilizes the inherent fatigue life differences between selected pairs of components for an active dual path system, enhanced by a stress level bias in one component. The design is applied to a baseline design; a safe life fatigue problem studied in an American Helicopter Society (AHS) round robin. The dual active path design is compared with a two-element standby fail-safe system and the baseline design for life at specified reliability levels and weight. The sensitivity of life estimates for both the baseline and fail-safe designs was examined by considering normal and Weibull distribution laws and coefficient of variation levels. Results showed that the biased dual path system lifetimes, for both the first element failure and residual life, were much greater than for standby systems. The sensitivity of the residual life-weight relationship was not excessive at reliability levels up to R = 0.9999 and the weight penalty was small. The sensitivity of life estimates increases dramatically at higher reliability levels.
Matthews, William T.; Neal, Donald M.
Analysis and Tests of Pultruded Blades for Wind Turbine Rotors
PS Enterprises, Inc. investigated a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades. A rotor was designed, manufactured and tested in the field. A preliminary design study and proof of concept test were conducted to assess the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study and a scaled 80 kW rotor was fabricated and field tested as a demonstration of the concept. The design studies continued to support the premise that pultruded blades offer the potential for significant reductions in rotor weight and cost. The field test provided experimental performance and loads data that compared well with predictions using the FLEXDYNE aeroelastic analysis. The field test also demonstrated stable yaw behavior and the absence of stall flutter over the wind conditions tested. During the final year of the contract, several studies were conducted by a number of independent consultants to address specific technical issues related to pultruded blades that could impact the commercial viability of turbines using this technology. The issues included performance, tower strikes, yaw stability, stall flutter, fatigue, and costs. While the performance of straight pultruded blades was projected to suffer a penalty of about 13% over fully twisted and tapered blades, the study showed that an aerodynamic fairing over the inner 40% could recover 85% of that loss while still keeping the blade cost well below that of conventional blades. Other results of the study showed that with proper design, rotors using pultruded blades could operate without aeroelastic problems, have acceptable fatigue life, and cost less than half that of rotors employing conventionally manufactured blades.
Cheney, M. C. (PS Enterprises, Glastonbury, Connecticut); Olsen, T.; Quandt, G.; Archidiacono, P.
... 20-40% in the short term. Trials using modafinil in MS fatigue have involved small numbers and ... studies are recommended to ascertain the effect of modafinil in the longer term and the appropriate dose. ...
Effect of surface treatments on the fatigue life of titanium for biomedical applications
Many surface treatments that are used in cementless and endosseous implants modify the topography and the roughness to increase the implant-bone contact area and thus favor bio-mechanical anchorage, shortening the period of osseointegration. Nevertheless, the effects that the surface treatments can have on the fatigue life of the material are not generally considered. In this sense, the superficial condition of
L. Pazos; P. Corengia; H. Svoboda
Quality of Life in Patients with Multiple Sclerosis: The Impact of Depression, Fatigue, and Disability
ERIC Educational Resources Information Center
Aim: The aim of this study was to assess the quality of life (QoL) in patients with multiple sclerosis (MS), and to evaluate its association with disability and psychosocial factors especially depression and fatigue. Methods: Demographic characteristics, education level, disease severity, and disease duration were documented for each patient. QoL,…
Goksel Karatepe, Altlnay; Kaya, Taciser; Gunaydn, Rezzan; Demirhan, Aylin; Ce, Plnar; Gedizlioglu, Muhtesem
Modeling cyclic ratcheting based fatigue life of HSLA steels using crystal plasticity FEM simulations and experiments
This paper develops a plastic ratcheting based fatigue failure model for HSLA steels from a combination of results from experiments and finite element simulations using crystal plasticity constitutive relations. It predicts the nucleation of major cracks in the microstructure in ratcheting. Subsequently, the total life is limited by the growth of ductile fracture in the microstructure, which is factored in
Shashwat Sinha; Somnath Ghosh
Long-Life Fatigue Test Results for Two Nickel-Base Structural Alloys.
The results are reported of fatigue tests on two nickel--base alloys, hot-cold-worked and stress-relieved nickel--chrome--iron Alloy 600 and mill-annealed nickel--chrome--moly--iron Alloy 625 in which S-N data were obtained in the life range of 10 exp 6 t...
D. F. Mowbray E. V. Giaquinto F. J. Mehringer
Compassion Fatigue, Compassion Satisfaction, and Burnout: Factors Impacting a Professional's Quality of Life
This study examined the relationship between three variables, compassion fatigue (CF), compassion satisfaction (CS), and burnout, and provider and setting characteristics in a sample of 1,121 mental health providers in a rural southern state. Respondents completed the Professional Quality of Life Scale as part of a larger survey of provider…
Sprang, Ginny; Whitt-Woosley, Adrienne; Clark, James J.
The goal of this study is to correlate fatigue life with corrosion damage in AA2024-T3 with special emphasis on specimen orientation. Corrosion pits ranging from 100 to 400 microns in depth were electrochemically created on the surface of dogbone specimens aligned in five different orientations. A detailed topography of the corrosion pit surface was conducted using white light interference microscopy
Mohammad Khobaib; Chris Kacmar
Evaluation of Pressurization Fatigue Life of 1441 Al-Li Fuselage Panel.
A study was conducted to evaluate the pressurization fatigue life of fuselage panels with skins fabricated from 1441 Al-Li, an attractive new Russian alloy. The study indicated that 1441 Al-Li has several advantages over conventional aluminum fuselage ski...
D. I. Dicus J. Fridlyander R. K. Bird V. Davydov
Conductor fatigue life research: Eolian vibration of transmission lines: Final report
Wind-induced vibration can cause premature failure of transmission lines through conductor fatigue. This research identifies design considerations to reduce this effect. It also suggests methods to treat minimally damaged conductors so that the transmission line can achieve its full design life without the need for expensive splicing or reconductoring.
Ramey, G.E.
A Fatigue Life Comparison of Two-Row Tapered Roller Bearings and Spherical Roller Bearings
Tests were run to compare the fatigue life of two-row tapered roller bearings to that of spherical roller bearings. Both bearing types had an outer diameter of 110 mm with the spherical roller bearing having a 22 percent larger dynamic radial load rating than the tapered roller bearings. All tests were run at 165 percent of the respective two-row dynamic
Harry Zantopulos; Joel Z. Russell
Structural integrity and fatigue crack propagation life assessment of welded and weld-repaired structures
Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is
Mohammad Shah Alam
The State of the Art in the Fatigue Life Evaluation of Components.
The parameters of the chosen design data which do not fit the evaluated component were in most cases taken into consideration by very global factors. These factors and the inaccuracies of Miner's Rule provide only a rough estimate of the fatigue life of a...
D. Schuetz
An Analytical Solution of Equivalent Stress for Structure Fatigue Life Prediction under Broad Band Random Loading
An analytical solution of an equivalent stress-range calculation, based on the power-spectral density of stress in critical points of structures, and a statistical theory for the peak distribution of a stationary Gaussian random process are presented in this paper for fatigue life assessment under broad-band random loading. This model has more advantages than similar existing models.
Xiaoyun Liu; Pengmin Lü
Surface pitting fatigue life of noninvolute, low-contact-ratio gears
Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of noninvolute gears with low numbers of teeth and low contact ratios for use in advanced applications. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 8.89 cm (3.50 in.) with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.49 GPa (216 ksi), and a speed of 10 000 rpm. The following results were obtained: the noninvolute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design; and the surface pitting fatigue life of the 3.43-pitch AISI 8620 noninvolute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load but at a considerably higher maximum Hertz stress.
Random Vibration Tests for Prediction of Fatigue Life of Diffuser Structure for Gas Dynamic Laser
Static and dynamic strain measurements which were taken during test stand operations of the gas dynamic laser (GDL) for the AF Airborne Laser Laboratory indicated that higher than expected vibrational stress levels may possibly limit the fatigue life of the laser structure. Particularly the diffuser sidewall structure exhibited large amplitude random vibrations which were excited by the internal gas flow.
O. F. Maurer; D. L. Banaszak
Prediction of long-term fatigue life of quasi-isotropic CFRP laminates for aircraft use
We have proposed the accelerated testing method to predict the fatigue life of FRP under an arbitrary combination of frequency, temperature, and stress ratio based on the time–temperature superposition principle and discussed experimentally about the validity and applicability of our proposed method. It has been clarified from these studies that our proposed method is applicable to predict the tensile and
Yasushi Miyano; Masayuki Nakada; Kazuyoshi Nishigaki
Effect of vibration loading on the fatigue life of part-through notched pipe
A systematic experimental and analytical study has been carried out to investigate the effect of vibration loading on the fatigue life of the piping components. Three Point bend (TPB) specimens machined from the actual pipe have been used for the evaluation of Paris constants by carrying out the experiments under vibration + cyclic and cyclic loading as per the ASTM Standard E647.
Rahul Mittal; P. K. Singh; D. M. Pukazhendi; V. Bhasin; K. K. Vaze; A. K. Ghosh
The components of power plant such as main steam pipe and gas turbines are operated under static and cyclic load conditions. As the period of static load increases, the service life of these components decreases. Generally, the increase of cyclic load results in fatigue damage and the increase of static load period results in the metallurgical degradation by the effect
Bumjoon Kim; Byeongsoo Lim
Effect of lubricant extreme-pressure additives on surface fatigue life of AISI 9310 spur gears
Surface fatigue tests were conducted with AISI 9310 spur gears using a formulated synthetic tetraester oil (conforming to MIL-L-23699 specifications) as the lubricant containing either sulfur or phosphorus as the EP additive. Four groups of gears were tested. One group of gears tested without an additive in the lubricant acted as the reference oil. In the other three groups either a 0.1 wt % sulfur or phosphorus additive was added to the tetraester oil to enhance gear surface fatigue life. Test conditions included a gear temperature of 334 K (160 F), a maximum Hertz stress of 1.71 GPa (248 000 psi), and a speed of 10,000 rpm. The gears tested with a 0.1 wt % phosphorus additive showed pitting fatigue life 2.6 times the life of gears tested with the reference tetraester based oil. Although fatigue lives of two groups of gears tested with the sulfur additive in the oil showed improvement over the control group gear life, the results, unlike those obtained with the phosphorus oil, were not considered to be statistically significant.
Scibbe, H. W.; Townsend, D. P.; Aron, P. R.
Effects of various parameters on the fatigue life of Alloy 718.
A data bank from over 700 tests on several heats of Alloy 718 with various test parameters is used to show the effects of temperature, strain rate, hold time, grain size, mean stress, surface roughness, and thermal aging on fatigue life. Both strain contr...
G. E. Korth
Fatigue Life of Haynes 188 Superalloy in Direct Connect Combustor Durability Rig
The Direct Connect Combustor Durability Rig (DCR) will provide NASA a flexible and efficient test bed to demonstrate the durability of actively cooled scramjet engine structure, static and dynamic sealing technologies, and thermal management techniques. The DCR shall be hydrogen fueled and cooled, and test hydrogen coolded structural panels at Mach 5 and 7. Actively cooled Haynes 188 superalloy DCR structural panels exposed to the combustion environment shall have electrodischarge machined (EDM) internal cooling holes with flowing liquid hydrogen. Hydrogen combustion could therefore produce severe thermal conditions that could challenge low cycle fatigue durability of this material. The objective of this study was to assess low cycle fatigue capability of Haynes 188 for DCR application. Tests were performed at 25 and 650 C, in hydrogen and helium environments, using specimens with low stress ground (LSG) and electro-discharge machined (EDM) surface finish. Initial fatigue tests in helium and hydrogen indicate the low cycle fatigue life capability of Haynes 188 in hydrogen appears quite satisfactory for the DCR application. Fatigue capability did not decrease with increasing test temperature. Fatigue capability also did not decrease with EDM surface finish. Failure evaluations indicate retention of ductility in all conditions. Additional tests are planned to reconfirm these positive trends.
Gabb, TIm; Gayda, John; Webster, Henry; Ribeiro, Greg
Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength of AISI 41L4O in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials was studied. The AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35N were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data are fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.
Tipton, D. G.
A Multiaxial Low Cycle Fatigue Life Prediction Model for Both Proportional and Non-proportional Loading Conditions
This paper has presented a life prediction model in the field of multiaxial low-cycle fatigue. The proposed model is generally applied for constant amplitude multiaxial proportional and non-proportional loading. Depending upon applied strain path the equivalent strain varies within a cycle. Equivalent average strain amplitude is considered as fatigue damage parameter in the proposed model. The model has requirement of only two material constants and no other tuning parameters. The model is examined by the proportional and non-proportional low-cycle fatigue life experimental data for eight different types of materials. The model is successfully correlated with multiaxial fatigue lives of eight different materials.
Paul, Surajit Kumar
The effects of sheet spacing on the fatigue life of spotwelded joints
While investigating the fatigue strength of spot-welded joints, the effects of sheet spacing or gap amounts between sheet joints may be considered as one of the most important parameters on the fatigue life duration of the joints. The main goal of the present work is to study the influence of sheet spacing on the fatigue life of 5083-O aluminium alloy spot welded tensile-shear joints. The amounts of sheet spacing are the average values over three measurements of photograph observation of the cut-off surfaces from the nugget centre of the spot-welded joints. The amounts of gap distances between spot weld sheet joints for three different electrode clamping force levels were 0.09mm, 0.11mm and 0.13mm, respectively. The values of notch strength reduction factors have been obtained at all levels of applied loads based on volumetric approach. The fatigue lives of spot welded joints have been obtained according to the volumetric method using the notch strength reduction factors and the available smooth S-N curve of 5083-O aluminium alloy sheets. The results based on the volumetric approach have been compared with the experimental fatigue test data and there is good agreement between numerical predictions and experimental results.
Hassanifard, S.; Zehsaz, M.; Esmaeili, F.
Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction
Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.
Jones, David J.; Kurath, Peter
Effects of High-Temperature Exposures on the Fatigue Life of Disk Superalloys Examined
Tests used to characterize the low-cycle-fatigue resistance of disk superalloys are usually performed at cyclic frequencies of 0.33 Hz or faster. However, service conditions for disks in some aerospace and land-based gas turbine engines can produce major cycle periods extending from minutes to hours and days. Over a service life, this can produce total service times near the maximum temperature that exceed 100 hr for aerospace applications and 100,000 hr for land-based applications. Such time-dependent effects of realistic mission cycles on fatigue resistance can be significant in superalloy disks, and need to be considered for accurate disk life prediction. The purpose of this study at the NASA Glenn Research Center was to examine the effects of extended exposures and extended cycle periods on the fatigue resistance of two disk superalloys. Current alloy Udimet 720 (Special Metals Corporation, Huntington, WV) disk material was provided by Solar Turbines/Caterpillar Co., and advanced alloy ME3 was provided by the NASA Ultra-Efficient Engine Technologies (UEET) Project, in powder-metallurgy-processed, supersolvus heat-treated form. Fatigue specimens were fully machined and exposed in air at temperatures of 650 to 704 C for extended times. Then, they were tested using conventional fatigue tests with a total strain range of 0.70 percent and a minimum-to-maximum strain ratio of zero to determine the effects of prior exposure on fatigue resistance. Subsequent tests with extended dwells at minimum strain in each fatigue cycle were performed to determine cyclic exposure effects.
Gabb, Timothy P.; Telesman, Jack; Kantzos, Pete T.; Smith, James W.
Profiled Roller Stress/Fatigue Life Analysis Methodology and Establishment of an Appropriate Stress/Life Exponent
The objective of this work was to determine the three dimensional volumetric stress field, surface pressure distribution and actual contact area between a 0.50" square roller with different crown profiles and a flat raceway surface using Finite Element Analysis. The 3-dimensional stress field data was used in conjunction with several bearing fatigue life theories to extract appropriate values for stress-life exponents. Also, results of the FEA runs were used to evaluate the laminated roller model presently used for stress and life prediction.
Smoother Turbine Blades Resist Thermal Shock Better
Surface treatment increases resistance of turbine blades to low-cycle fatigue. Smoothing removes small flaws where cracks start. Intended for blades in turbines subject to thermal shock of rapid starting. No recrystallization occurs at rocket-turbine operating temperatures.
Czerniak, Paul; Longenecker, Kent; Paulus, Don; Ullman, Zane
Improved fatigue life of acrylic bone cements reinforced with zirconia fibers.
Poly(methyl methacrylate) (PMMA) bone cements have a long and successful history of use for implant fixation, but suffer from a relatively low fracture and fatigue resistance which can result in failure of the cement and the implant. Fiber or particulate reinforcement has been used to improve mechanical properties, but typically at the expense of the pre-cured cement viscosity, which is critical for successful integration with peri-implant bone tissue. Therefore, the objective of this study was to investigate the effects of zirconia fiber reinforcement on the fatigue life of acrylic bone cements while maintaining a relatively low pre-cured cement viscosity. Sintered straight or variable diameter fibers (VDFs) were added to a PMMA cement and tested in fully reversed uniaxial fatigue until failure. The mean fatigue life of cements reinforced with 15 and 20 vol% straight zirconia fibers was significantly increased by approximately 40-fold, on average, compared to a commercial benchmark (Osteobond) and cements reinforced with 0-10 vol% straight zirconia fibers. The mean fatigue life of a cement reinforced with 10 vol% VDFs was an order of magnitude greater than the same cement reinforced with 10 vol% straight fibers. The time-dependent viscosity of cements reinforced with 10 and 15 vol% straight fibers was comparable to the commercial benchmark during curing. Therefore, the addition of relatively small amounts of straight and variable diameter zirconia fibers was able to substantially improve the fatigue resistance of acrylic bone cement while exhibiting similar handling characteristics compared to current commercial products. PMID:20696415
Kane, Robert J; Yue, Weimin; Mason, James J; Roeder, Ryan K
Scatter in fatigue life due to effects of porosity in cast A356-T6 aluminum-silicon alloys
Porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed scatter in fatigue life of a cast A356-T6 aluminum-silicon alloy due to the presence of porosity. Specimens containing a controlled amount of porosity were prepared by employing a wedge-shaped casting mold and adjusting the degassing process during casting. High-cycle fatigue tests were conducted under fixed stress conditions on a series of specimens with controlled microstructures (especially, the secondary dendrite-arm spacing), and the degree of scatter in the results was assessed. Stochastically, such scatter was found to be adequately characterized by a three-parameter Weibull distribution function. Large pores at or close to the specimen surface were found to be responsible for crack initiation in all fatigue-test specimens, and the resultant fatigue life was related to the initiating pore size through a relationship based on the rate of small-fatigue-crack propagation. With respect to the probabilities for the pores of various sizes and locations to initiate a fatigue crack, a statistical model was developed to establish the relationship between the porosity population and the resultant scatter in fatigue life. The modeling predictions are in agreement with the experimental results. Moreover, Monte-Carlo simulation based on this model demonstrated that the average pore size, pore density, and standard deviation of the pore sizes, together with the specimen size and geometry, are all of consequence regarding scatter in fatigue life.
Yi, J. Z.; Gao, Y. X.; Lee, P. D.; Flower, H. M.; Lindley, T. C.
Fatigue Life Prediction of Served Aircraft Aluminum Alloy Structure
In this paper, the life prediction method of corroded aircraft aluminum alloy structure was proposed. The stress multiplication of aluminum alloy structure subjected to pitting corrosion damage was simulated by ANSYS software. Based upon the simulation results, the AFGROW software was used to carry out the crack growth analyses, the life cycles of corroded structure were estimated, and a very
Youhong Zhang; Shengli Zhou; Jupeng Liu; Enyi Chu; Rui Zhang
Split mandrel versus split sleeve coldworking: Dual methods for extending the fatigue life of metal structures
It is common practice to use split sleeve coldworking of fastener holes as a means of extending the fatigue life of metal structures. In search of lower manufacturing costs, the aerospace industry is examining the split mandrel (sleeveless) coldworking process as an alternative method of coldworking fastener holes in metal structures. The split mandrel process (SpM) significantly extends the fatigue life of metal structures through the introduction of a residual compressive stress in a manner that is very similar to the split sleeve system (SpSl). Since the split mandrel process is significantly less expensive than the split sleeve process and more adaptable to robotic automation, it will have a notable influence upon other new manufacture of metal structures which require coldworking a significant number of holes, provided the aerospace community recognizes that the resulting residual stress distributions and fatigue life improvement are the same for both processes. Considerable testing has validated the correctness of that conclusion. The findings presented in this paper represent the results of an extensive research and development program, comprising data collected from over 400 specimens fabricated from 2024-T3 and 7075-T651 aluminum alloys in varied configurations, which quantify the benefits (fatigue enhancement and cost savings) of automating a sleeveless coldworking system.
Rodman, Geoffrey A.; Creager, Matthew
Microstructure-based fatigue life prediction for cast A356-T6 aluminum-silicon alloys
Fatigue life prediction and optimization is becoming a critical issue affecting the structural applications of cast aluminum-silicon alloys in the aerospace and automobile industries. In this study, a range of microstructure and porosity populations in A356 alloy was created by controlling the casting conditions and by applying a subsequent hot isostatic pressing ("hipping") treatment. The microstructure and defects introduced during the processing were then quantitatively characterized, and their effects on the fatigue performance were examined through both experiment and modeling. The results indicated that whenever a pore is present at or near the surface, it initiates fatigue failure. In the absence of large pores, a microcell consisting of ?-Al dendrites and associated Si particles was found to be responsible for crack initiation. Crack initiation life was quantitatively assessed using a local plastic strain accumulation model. Moreover, the subsequent crack growth from either a pore or a microcell was found to follow a small-crack propagation law. Based on experimental observation and finite-element analysis, a unified model incorporating both the initiation and small crack growth stages was developed to quantitatively predict the dependency of fatigue life on the microstructure and porosity. Good agreement was obtained between the model and experiment.
Yi, J. Z.; Gao, Y. X.; Lee, P. D.; Lindley, T. C.
Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC
This dissertation focuses on the characterization of the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin, woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The residual elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed noticeable reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment composing the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.
Gyekenyesi, Andrew L.
Friction grip enclosure: a means for increasing the fatigue life of fuel rod end welds. LWBR Development Program
A friction grip enclosure was developed to increase the fatigue life of end welds in the LWBR fuel rods. This report describes the friction grip enclosure design concept and provides a sample analysis to illustrate the design application procedure. A cyclic proof test, performed to verify the fatigue performance of the friction grip enclosure, is also described. Adequate fatigue performance was demonstrated for the LWBR end welds when subjected to the maximum expected cyclic loads during LWBR operation.
Galtz, C.S.
Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps
Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.
Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.
Rolling-element fatigue life of AISI M-50 and 18-4-1 balls
Rolling element fatigue studies were conducted with AISI M-50, EFR 18-4-1, and VAR 18-4-1. Groups of 12.7 mm (1/2-in) diameter balls of each material were tested in the five ball fatigue tester. Test conditions included a load of 1540 N (347 lbf) giving a maximum Hertz stress of 5520 MPa (800 000 psi), a shaft speed of 10,700 rpm, and a contact angle of 30 deg. Tests were run at a race temperature of 339 K (150 F) with a type 2 ester lubricant. The rolling element fatigue life of AISI M-50 was not significantly different from that of EFR 18-4-1 or VAR 18-4-1 based on a statistical comparison of the test results.
Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers
During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The zirconium in this alloy was not evenly distributed in the chamber materials. The life that was achieved was nominally the same as would have been predicted from OFHC copper isothermal test data.
Hannum, N. P.; Kasper, H. J.; Pavli, A. J.
Corrosion fatigue of high strength fastener materials in seawater. Final report
Environmental effects can significantly reduce the fatigue life of metals. As such, corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L40 high strength steel blade-to-hub attachment bolt at the MOD-0A 200 kW wind turbine generator in Oahu, Hawaii prompted the current test program. Tests
Fatigue and health-related quality of life (HRQL) in chronic hepatitis C virus infection.
In addition to chronic hepatitis, many individuals infected with hepatitis C virus (HCV) suffer from fatigue, which may compromise their health-related quality of life (HRQL). To assess systematically health-related quality of life (HRQL) in patients with chronic hepatitis C and to determine if any clinical, biochemical, virologic, demographic, and histologic features are associated with HRQL status. In this cross-sectional observational study, one hundred thirty patients with chronic HCV infection (HCV RNA positive by PCR) and 61 healthy controls were enrolled from a tertiary care teaching medical center. All patients and controls completed one generic HRQL questionnaire (MOS SF-36) and one liver-disease specific instrument (Chronic Liver Disease Questionnaire, CLDQ). Ninety-five HCV patients and all the controls also completed a fatigue questionnaire (Chronic Fatigue Screener, CFS) and had immunologic markers determined (Cryoglobulin, Soluble IL-2 receptors, Rheumatoid Factor). We compared the HRQL of HCV-infected patients to the controls and, using data from other studies, to the general population, patients with diabetes, and patients with chronic low back pain. Patients with chronic HCV had greater HRQL impairment than healthy controls and those with type II diabetes. Fatigue was the most important symptom with negative impact on HRQL. Sixty-one percent of HCV-infected patients reported fatigue-related loss of activity. Additionally, other factors associated with HRQL were gender and histologic cirrhosis. Chronic HCV infection has a profound negative impact on patients' HRQL. Disabling fatigue is the most important factor that contributes to loss of well-being in this relatively young group of patients. PMID:17406828
Kallman, Jillian; O'Neil, Mary Margaret; Larive, Brett; Boparai, Navdeep; Calabrese, Leonard; Younossi, Zobair M
The effect of minimum stress and stress amplitude on the fatigue life of non strain crystallising elastomers
Fatigue tests on ethylene propylene (EPDM) and styrene-butadiene (SBR) rubber revealed physical behaviour that is not seen in conventional linear elastic solids. Uniaxial cyclical tests, using cylindrical dumbbell specimens, having a minimum stress of zero (?min=0) and varying stress amplitude (?a), predictably gave decreased fatigue life with increased stress amplitude and hence maximum stress (?max). However, tensile uniaxial cyclic tests
F. Abraham; T. Alshuth; S. Jerrams
Natalizumab Treatment Reduces Fatigue in Multiple Sclerosis. Results from the TYNERGY Trial; A Study in the Real Life Setting
Fatigue is a significant symptom in multiple sclerosis (MS) patients. First-generation disease modifying therapies (DMTs) are at best moderately effective to improve fatigue. Observations from small cohorts have indicated that natalizumab, an antibody targeting VLA-4, may reduce MS-related fatigue. The TYNERGY study aimed to further evaluate the effects of natalizumab treatment on MS-related fatigue. In this one-armed clinical trial including 195 MS patients, natalizumab was prescribed in a real-life setting, and a validated questionnaire, the Fatigue Scale for Motor and Cognitive functions (FSMC), was used both before and after 12 months of treatment to evaluate a possible change in the fatigue experienced by the patients. In the treated cohort all measured variables, that is, fatigue score, quality of life, sleepiness, depression, cognition, and disability progression were improved from baseline (all p values<0.0001). Walking speed as measured by the six-minute walk-test also increased at month 12 (p?=?0.0016). All patients were aware of the nature of the treatment agent, and of the study outcomes. Conclusion Natalizumab, as used in a real-life setting, might improve MS-related fatigue based on the results from this one-armed un-controlled stud. Also other parameters related to patients' quality of life seemed to improve with natalizumab treatment. Trial Registration ClinicalTrials.gov NCT00884481
Svenningsson, Anders; Falk, Eva; Celius, Elisabeth G.; Fuchs, Siegrid; Schreiber, Karen; Berko, Sara; Sun, Jennifer; Penner, Iris-Katharina; for the TYNERGY trial investigators
A Modified Nonlinear Damage Accumulation Model for Fatigue Life Prediction Considering Load Interaction Effects
Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation. A nonlinear fatigue damage accumulation model to consider the effects of load sequences was proposed in earlier literature, but the model cannot consider the load interaction effects, and sometimes it makes a major error. A modified nonlinear damage accumulation model is proposed in this paper to account for the load interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between the model prediction and experimental data is observed, and the predictions by proposed model are more possibly in accordance with experimental data than that by primary model and Miner's rule. Comparison between the predicted cumulative damage by the proposed model and an existing model shows that the proposed model predictions can meet the accuracy requirement of the engineering project and it can be used to predict the fatigue life of welded aluminum alloy joint of Electric Multiple Units (EMU); meanwhile, the accuracy of approximation can be obtained from the proposed model though more simple computing process and less material parameters calling for extensive testing than the existing model.
Huang, Hong-Zhong; Yuan, Rong
Effects of material and loading variables on fatigue life of carbon and low-alloy steels in LWR environments
The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Section III of the Code specifies fatigue design curves for structural materials. While effects of reactor coolant environments are not explicitly addressed by the design curves, test data suggest that the Code fatigue curves may not always be adequate in coolant environments. This paper reports the results of recent fatigue tests that examine the effects of steel type, strain rate, dissolved oxygen level, strain range, loading waveform, and surface morphology on the fatigue life of A106-Gr B carbon steel and A533-Gr B low-alloy steel in water.
Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results
The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that
D. T. Rusk; W. Hoppe; W. Braisted; N. Powar
The Effect of Drive Signal Limiting on High Cycle Fatigue Life Analysis
It is common practice to assume a Gaussian distribution of both the input acceleration and the response when modeling random vibration tests. In the laboratory, however, shaker controllers often limit the drive signal to prevent high amplitude peaks. The high amplitudes may either be truncated at a given level (socalled brick wall limiting or abrupt clipping), or compressed (soft limiting), resulting in drive signals which are no longer Gaussian. The paper first introduces several methods for limiting a drive signal, including brick wall limiting and compression. The limited signal is then passed through a linear time-invariant system representing a device under test. High cycle fatigue life predictions are subsequently made using spectral fatigue and rainflow cycle counting schemes. The life predictions are compared with those obtained from unclipped input signals. Some guidelines are provided to help the test engineer decide how clipping should be applied under different test scenarios.
Kihm, Frederic; Rizzi, Stephen A.
Comparison of Fatigue Life Estimation Using Equivalent Linearization and Time Domain Simulation Methods
The Monte Carlo simulation method in conjunction with the finite element large deflection modal formulation are used to estimate fatigue life of aircraft panels subjected to stationary Gaussian band-limited white-noise excitations. Ten loading cases varying from 106 dB to 160 dB OASPL with bandwidth 1024 Hz are considered. For each load case, response statistics are obtained from an ensemble of 10 response time histories. The finite element nonlinear modal procedure yields time histories, probability density functions (PDF), power spectral densities and higher statistical moments of the maximum deflection and stress/strain. The method of moments of PSD with Dirlik's approach is employed to estimate the panel fatigue life.
Mei, Chuh; Dhainaut, Jean-Michel
On the fatigue life of M50 NiL rolling bearings
The fatigue life of rolling bearings made of M50 NiL (a nickel-low carbon variant of M50 tool steel) was investigated using data from a battery of 15 R2 endurance test rigs specially modified to accommodate the aircraft application test conditions. Results indicate that bearings manufactured from case-hardened M50 NiL steel can provide significantly greater rolling contact fatigue life than bearings made from through-hardened M50 steel. In addition, it was found that M50 NiL bearings endurance-tested under conditions of heavy tensile hoop stresses showed no tendency toward raceway spalling or cracking through, unlike M50 bearings, which exhibited both tendencies.
Harris, T. A.; Skiller, John; Spitzer, Ronald F.
Weld tool travel speed effects on fatigue life of friction stir welds in 5083 aluminium
This paper reports the results of a study into the influence of weld tool travel speed (in the range 80–200 mm\\/min) on the occurrence of 'onion-skin' forging-type defects (similar to the root defects known as 'kissing bonds') in single pass friction stir (SP FS) welds, and on the effect of these defects on fatigue crack initiation and overall life. Results
M. N James; D. G Hattingh; G. R Bradley
Topology optimization of structures subject to random excitations with fatigue life constraints
In this paper a topology optimization strategy for randomly excited linear elastic structures with fatigue life constraints\\u000a is presented. In random vibration it is often convenient to describe the excitation and response in term of function in the\\u000a frequency domain. The random vibration theory was developed to deal with random excitations and is based on the assumption\\u000a of excitations fully
S. Lambert; E. Pagnacco; L. Khalij; A. Hami
High-cycle fatigue life extension of glass fiber\\/polymer composites with carbon nanotubes
The present work shows that the addition of small volume fractions of multi-walled carbon nanotubes (CNTs) to the matrix results\\u000a in a significant increase in the high-cycle fatigue life. It is proposed that carbon nanotubes tend to inhibit the formation\\u000a of large cracks by nucleating nano-scale damage zones. In addition, the contribution to energy absorption from the fracture\\u000a of nanotubes
Christopher S. Grimmer; C. K. H. Dharan
Flip-chip solder bump fatigue life enhanced by polymer encapsulation
Encapsulation of controlled collapse chip connection (C4) joints, using a filled epoxy resin having a matched coefficient of thermal expansion (CTE), has provided a substantial increase in the life of C4 joints in accelerated thermal cycle (ATC) fatigue testing on both low-CTE organic and ceramic chip carriers. The C4 joints are encapsulated by dispensing a bead of resin along an
D. Suryanarayana; R. Hsiao; T. P. Gall; J. M. McCreary
Reduction factors for creep strength and fatigue life of modified 9 Cr1 Mo steel weldments
The provisions of ASME B PV Code Case N-47 currently include reduction factors for creep strength and fatigue life of weldments. To provide experimental confirmation of such factors for modified 9 Cr-1 Mo steel, tests of tubular specimens were conducted at 538°C (1000°F). Three creep-rupture specimens with longitudinal welds were tested in tension; and, of three with circumferential welds, two
J. J. Blass; R. L. Battiste; D. G. OConnor
A micro-damage healing model that improves prediction of fatigue life in asphalt mixes
The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative
Rashid K. Abu Al-Rub; Masoud K. Darabi; Dallas N. Little; Eyad A. Masad
Prediction of thermal fatigue life of a turbine nozzle guide vane
Thermal fatigue (TF) is one of the most important factors that influence turbine's life. This paper establishes a 3D solid-fluid\\u000a coupling model for a steady temperature analysis of a high-pressure turbine nozzle at different turbine inlet gas total temperatures\\u000a (TIGTTs). The temperature analysis supplies the temperature load for subsequent 3D finite element analysis to obtain the strain\\u000a values. Following this,
Xin-qian Zheng; Tao Du; Yang-jun Zhang
Strainrange partitioning life predictions of the long time metal properties council creep-fatigue tests
The method of strainrange partitioning is used to predict the cyclic lives of the Metal Properties Council's long time creep-fatigue interspersion tests of several steel alloys. Comparisons are made with predictions based upon the time- and cycle-fraction approach. The method of strainrange partitioning is shown to give consistently more accurate predictions of cyclic life than is given by the time- and cycle-fraction approach.
Saltsman, J. F.; Halford, G. R.
Fatigue life analysis for traction drives with application to a toroidal type geometry
A contact fatigue life analysis for traction drives was developed which was based on a modified Lundberg-Palmgren theory. The analysis was used to predict life for a cone-roller toroidal traction drive. A 90-percent probability of survival was assumed for the calculated life. Parametric results were presented for life and Hertz contact stress as a function of load, drive ratio, and size. A design study was also performed. The results were compared to previously published work for the dual cavity toroidal drive as applied to a typical compact passenger vehicle drive train. For a representative duty cycle condition wherein the engine delivers 29 horsepower at 2000 rpm with the vehicle moving at 48.3 km/hr (30 mph) the drive life was calculated to be 19,200 km (11 900 miles).
Coy, J. J.; Loewenthal, S. H.; Zaretsky, E. V.
Blade Manufacturing Improvement: Remote Blade Manufacturing Demonstration
The objective of this program was to investigate manufacturing improvements for wind turbine blades. The program included a series of test activities to evaluate the strength, deflection, performance, and loading characteristics of the prototype blades. The original contract was extended in order to continue development of several key blade technologies identified in the project. The objective of the remote build task was to demonstrate the concept of manufacturing wind turbine blades at a temporary manufacturing facility in a rural environment. TPI Composites successfully completed a remote manufacturing demonstration in which four blades were fabricated. The remote demonstration used a manufacturing approach which relied upon material ''kits'' that were organized in the factory and shipped to the site. Manufacturing blades at the wind plant site presents serious logistics difficulties and does not appear to be the best approach. A better method appears to be regional manufacturing facilities, which will eliminate most of the transportation cost, without incurring the logistical problems associated with fabrication directly onsite. With this approach the remote facilities would use commonly available industrial infrastructure such as enclosed workbays, overhead cranes, and paved staging areas. Additional fatigue testing of the M20 root stud design was completed with good results. This design provides adhesive bond strength under fatigue loading that exceeds that of the fastener. A new thru-stud bonding concept was developed for the M30 stud design. This approach offers several manufacturing advantages; however, the test results were inconclusive.
Effect of shot peening on surface fatigue life of carburized and hardened AISI 9310 spur gears
Surface fatigue tests were conducted on two groups of AISI 9310 spur gears. Both groups were manufactured with standard ground tooth surfaces, with the second group subjected to an additional shot peening process on the gear tooth flanks. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a gear temperature of 350 K (170 F), a maximum Hertz stress of 1.71 billion N/sq m (248,000 psi), and a speed of 10,000 rpm. The shot peened gears exhibited pitting fatigue lives 1.6 times the life of standard gears without shot peening. Residual stress measurements and analysis indicate that the longer fatigue life is the result of the higher compressive stress produced by the shot peening. The life for the shot peened gear was calculated to be 1.5 times that for the plain gear by using the measured residual stress difference for the standard and shot peened gears. The measured residual stress for the shot peened gears was much higher than that for the standard gears.
Townsend, D. P.; Zaretsky, E. V.
Fatigue life models for SnAgCu and SnPb solder joints evaluated by experiments and simulation
In recent years, many solder fatigue models have been developed to predict the fatigue life of solder joints under thermal cycle conditions. While a variety of life prediction models have been proposed for near eutectic SnPb(Ag)-solder joints in the literature, not enough work has been reported in extending these models to lead-free soldered assemblies. The development of lie prediction models
A. Schubertt; R. Dudek; E. Auerswald; A. Gollbardt; B. Michel; H. Reichl
A low-cycle fatigue life model of nickel-based single crystal superalloys under multiaxial stress state
The low-cycle fatigue (LCF) behavior of smooth and notched specimens of nickel-based single-crystal superalloys DD3 was studied at 620°C. Based on experimental results and finite element analysis results, a low-cycle fatigue life model has been proposed for the nickel-based single-crystal superalloys under multiaxial stress states. In the model the mean stress effect has been considered. The LCF life model is
J. S. Wan; Z. F. Yue
Effect of small cycles and load spectrum truncation on the fatigue life scatter in 7050 Al alloy
This work examines the effect of dynamic buffet loads (small cycles) on the scatter in the fatigue life of aircraft aluminum. Current life cycle management of fighter airframes assumes, without engineering evidence, that buffet loads cause an increase in the scatter factor used in safe-life calculations. Hence, the role of small cycles in spectra representative of the CF-188 aileron inboard
P. R. Underhill; D. L. DuQuesnay
Laser Peening and Shot Peening Effects on Fatigue Life and Surface Roughness of Friction Stir Welded 7075-T7351 Aluminum
The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening conditions with different intensities, durations, and peening order were tested to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using laser peening compared to shot peened versus their native welded specimens.
Hatamleh, Omar; Lyons, Jed; Forman, Royce
Structural health monitoring of composite wind blades by fiber bragg grating
The wind turbine industry is the fastest growing market area for the use of composite materials. Fiber Bragg grating sensor can be used to monitor the mechanical behavior of composite wind blade. The internal strain of composite wind blade during a constant stress amplitude fatigue testing process was monitored with fiber Bragg gratings sensors. FBG sensors can not only be embedded in composite structures to detect fatigue damage, but also have excellent durability compared with other sensors such as electric strain gauges. After 1 million cycles, the FBG sensors can still keep good sensibility. FBGs as a fatigue indicator are a novel sensor to monitor, evaluate and give crash alert for the health state of composite wind blades during their whole service life.
Guo, Zhan-Sheng; Zhang, Junqian; Hu, Hongjiu; Guo, Xingming
A comparison of predicted wind turbine blade loads to test measurements
The accurate prediction of wind turbine blade loads and response is important in predicting the fatigue life of wind machines. At the SERI Wind Energy Research Center, a rotor code called FLAP (Force and Loads Analysis Program) is currently being validated by comparing predicted results to machine measurements. The FLAP code has been modified to allow the teetering degree of
A. D. Wright; R. W. Thresher
The accurate prediction of wind turbine blade loads and response is important in predicting the fatigue life of wind machines. At the SERI Wind Energy Research Center, a rotor code called FLAP (Force and Loads Analysis Program) is currently being validated by comparing predicted results to machine measurements. The FLAP code has been modified to allow the teetering degrees of
Fatigue criterion to system design, life and reliability: A primer
A method for estimating a component's design survivability by incorporating finite element analysis and probabilistic material properties was developed. The method evaluates design parameters through direct comparisons of component survivability expressed in terms of Weibull parameters. The analysis was applied to a rotating disk with mounting bolt holes. The highest probability of failure occurred at, or near, the maximum shear stress region of the bolt holes. Distribution of material failure as a function of Weibull slope affects the probability of survival. Where Weibull parameters are unknown for a rotating disk, it may be permissible to assume Weibull parameters, as well as the stress-life exponent, in order to determine the qualitative effect of disk speed on the probability of survival.
Zaretsky, Erwin V.
Effect of double vacuum melting and retained austenite on rolling-element fatigue life of AMS 5749 bearing steel
AMS 5749 steel combines the tempering, hot hardness, and hardness retention characteristics of AISI M-50 steel with the corrosion and oxidation resistance of AISI 440C stainless steel. The five-ball fatigue tester was used to evaluate the rolling-element fatigue life of AMS 5749. Double vacuum melting (vacuum induction melting plus vacuum arc remelting, VIM-VAR) produced AMS 5749 material with a rolling-element fatigue life at least 14 times that of vacuum induction melting alone. The VIM-VAR AMS 5749 steel balls gave lives from 6 to 12 times greater than VIM-VAR AISI M-50 steel balls. The highest level of retained austenite, 14.6 percent, was significantly detrimental to rolling-element fatigue life relative to the intermediate level of 11.1 percent.
Parker, R. J.; Hodder, R. S.
Influence of the Inclusion Shape on the Rolling Contact Fatigue Life of Carburized Steels
It has been well known that the flaking failure in rolling contact fatigue (RCF) originates from nonmetallic inclusions in steels, and their apparent size is one of the important factors affecting RCF life. However, the influence of inclusion shape on the RCF life has not been fully clarified. In this study, attention was paid to the influence of the inclusion shape on the RCF life. This was evaluated by using carburized JIS-SCM420 (SAE4320) steels that contained two different shapes of MnS—stringer type and spheroidized type—as inclusions. Sectional observations were made to investigate the relation between the occurrence of shear crack in the subsurface and the shape of MnS. It was found that the RCF life was well correlated with the length of MnS projected to the load axis, and the initiation of shear crack in subsurface was accelerated as the length of MnS increased.
Neishi, Yutaka; Makino, Taizo; Matsui, Naoki; Matsumoto, Hitoshi; Higashida, Masashi; Ambai, Hidetaka
High cycle fatigue life of 70 series engine cast aluminum rotor housing. Final report on task 2. 1. 6 extended life studies
Fatigue studies conducted to project the expected life and safety factors of the rotor housing of cast aluminum 2013R natural gas fueled rotary engines (NGREs) are documented. The rotor housing was selected because previous studies showed this major engine component to be the critical item in determining fatigue life. The report describes the sequential steps required for fatigue life calculations, including the heat transfer, thermal stress, pressure stress, fatigue life, and safety factor analyses. The fatigue analysis requires the determination of thermal and presure stresses. The former is viewed as providing the steady-state component, while the latter contributes both to the steady-state and the alternating components of the stresses in the fatigue analysis. Both of these stresses are a function of the engine peak combustion pressure at the rated condition, but are somewhat independent of speed. The rated speed enters only in the calculation of heat transfer coefficients, and when translating the projected cycles-to-failure into hours of operating life.
Bazaz, R.J.
The surface fatigue life of contour induction hardened AISI 1552 gears
Two groups of spur gears manufactured from two different materials and heat treatments were endurance tested for surface fatigue life. One group was manufactured from AISI 1552 and was finished ground to a 0.4 micron (16 micro-in.) rms surface finish and then dual frequency contour induction hardened. The second group was manufactured from CEVM AISI 9310 and was carburized, hardened, and ground to a 0.4 micron (16 micro-in.) rms surface finish. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a maximum Hertz stress of 1.71 GPa (248 ksi), a bulk gear temperature of approximately 350 K (170 F) and a speed of 10,000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The test results showed that the 10 percent surface fatigue (pitting) life of the contour hardened AISI 1552 test gears was 1.7 times that of the carburized and hardened AISI 9310 test gears. Also there were two early failures of the AISI 1552 gears by bending fatigue.
Townsend, Dennis P.; Turza, Alan; Chaplin, Mike
A generalized fitting technique for the LIFE2 fatigue analysis code
The analysis of component fatigue lifetime for a wind energy conversion system (WECS) requires that the component load spectrum be formulated in terms of stress cycles. Typically, these stress cycles are obtained from time series data using a cycle identification scheme. As discussed by many authors, the matrix or matrices of cycle counts that describe the stresses on a turbine are constructed from relatively short, representative samples of time series data. The ability to correctly represent the long-term behavior of the distribution of stress cycles from these representative samples is critical to the analysis of service lifetimes. Several techniques are currently used to convert representative samples to the lifetime cyclic loads on the turbine. There has been recently developed a set of fitting algorithms that is particularly useful for matching the body of the distribution of fatigue stress cycles on a turbine component. Fitting techniques are now incorporated into the LIFE2 fatigue/fracture analysis code for wind turbines. In this paper, the authors provide an overview of the fitting algorithms and describe the pre- and post-count algorithms developed to permit their use in the LIFE2 code. Typical case studies are used to illustrate the use of the technique.
Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States). Wind Energy Research Dept.; Wilson, T. [Univ. of New Mexico, Albuquerque, NM (United States). New Mexico Engineering Research Inst.
Fatigue-Life Computational Analysis for the Self-Expanding Endovascular Nitinol Stents
Self-expanding endovascular stents made of Nitinol (a Ni-Ti intermetallic compound possessing superelastic and shape-memory properties) are being widely used to treat a common circulatory problem in which narrowed arteries, primarily due to fatty deposits, hamper blood flow to the extremities (the problem commonly referred to as "peripheral artery disease"). The stents of this type unfortunately occasionally fail structurally (and, in turn, functionally) rendering the stenting procedure ineffective. The failure is most often attributed to the fatigue-induced damage since over its expected ten-year life span, the stent will normally experience 370-400 million pulsating-blood flow-induced loading cycles. Redesign/redevelopment of the stents using the conventional make-and-test approaches is quite expensive and time consuming and therefore is being increasingly complemented by computational engineering methods and tools. In the present study, advanced structural and fluid-structure interaction finite element computational methods are combined with the advanced fatigue-based durability analysis techniques to further enhance the use of the computational engineering analysis tools in the development of vascular stents with improved high-cycle fatigue life.
Grujicic, M.; Pandurangan, B.; Arakere, A.; Snipes, J. S.
Factors affecting quality of life and fatigue in patients with leukemia under chemotherapy
Background: The goal of treating chronic diseases, including hematologic malignancies, is to increase patients' life span and to improve their capabilities as much as possible; so that patients could maintain an appropriate level of quality of life (QoL) and continue their lives. Most studies performed to evaluate the treatment of various diseases were mostly focused on the increase of life expectancy regardless of the QoL and treatment issues. Furthermore, fatigue is one of the most common and distressing side effects of cancer and treatments related to it, which can affect a patient's QoL, and be followed by many problems. This study was designed and implemented with the aim to determine the factors affecting the QoL and fatigue in patients with leukemia undergoing chemotherapy. Materials and Methods: This was a cross-sectional correlation descriptive-analytical study. One hundred and fifteen patients with leukemia referred to Sayyed-Al-Shohada Hospital were enrolled in the study through convenient sampling method. To collect data, a three-part questionnaire was used: The first part was related to demographic characteristics and disease-related data and the second part was the fatigue check list and the third part was the Short-Form 36 Health Survey (SF-36) related to QoL. The data were analyzed after collection and coding through Software SPSS version 18 and descriptive and analytical statistics (analysis of variance test, independent t test, Pearson's and Spearman's correlation coefficient) with 95% confidence interval. Results: The results showed that there was a significant correlation between QoL in Physical Component Summary with gender (P = 0.03), educational level (P = 0.09), and marital status (P = 0.004), Also there was a significant correlation between QoL in Mental Component Summary with educational level (P = 0.01) and economic status (P = 0.02). Findings showed that there was a significant correlation between fatigue and marital status (P = 0.005). But statistically there was no significant correlation between demographic variables such as age, educational level, and employment status with patients' fatigue. Spearman correlation coefficient showed that there was a significant correlation between fatigues with pain (P = 0.005). Also findings revealed the statistically significant correlation between fatigues with economic status (P = 0.003). Conclusion: According to the present results, it seems that some demographic factors affect QoL and significant relationship exists between them. Fatigue in patients with leukemia dramatically affects their QoL. Therefore, it is important for medical staff to pay attention to demographics and fatigue in leukemic patients in order to improve their QoL and help them to organize their activities to promote health and QoL.
Musarezaie, Amir; Khaledi, Firuz; Esfahani, Homayoon Naji; Ghaleghasemi, Tahere Momeni
Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method
In this work, the parameters stress intensity factor (SIF), initial and final crack lengths ( a i and a f), crack growth parameters ( C and m), and fatigue strength (FAT) are investigated. The determination of initial crack length seems to be the most serious factor in fatigue life and strength calculations for welded joints. A fracture mechanics approach was used in these calculations based on SIF which was calculated with the finite element method (FEM). The weld toe crack was determined to be equal to 0.1 mm, whereas the weld root crack's length was varied depending on the degree of the weld penetration. These initial crack length values are applicable for all types of joints which have the same crack phenomenon. As based on the above calculated parameters, the new limits of FAT for new geometries which are not listed yet in recommendations can be calculated according to the current approach.
Al-Mukhtar, A. M.; Biermann, H.; Hübner, P.; Henkel, S.
Influence of different wind profiles due to varying atmospheric stability on the fatigue life of wind turbines
Offshore wind energy is being developed on a very large scale in the European seas. The objective of developing wind energy offshore is to capture greater wind speeds than are encountered onshore and as a result more energy. With this also come more challenges in the design of wind turbines due to the hostile offshore environment. Currently the standards for offshore wind turbines prescribe a site specific design for the support structures and the design for the rotor nacelle assembly according to onshore standards. Wind turbines are designed to withstand fatigue and ultimate loads. For the fatigue loading several input conditions have been prescribed, amongst which wind profile is one of them. Wind profile is represented by power law or logarithmic law as given in the standards. A neutral stability of the atmosphere is considered while obtaining the wind profile using the logarithmic law. In this paper the atmospheric stability is varied in order to estimate different wind profiles and simulations are run in Bladed to check its influence on the fatigue damage at the blade root. The variations in the atmospheric stability has been taken into account by using some typical values of Obukhov length. From steady state simulations it has been found that atmospheric stability is important for fatigue damage. The analysis showed that variation in the distribution of atmospheric stability causes large variations in the fatigue damage for different sites. Thus, it is worthwhile to carry out a full scale study using the turbulent winds and real data for wind turbine and environmental conditions.
Sathe, Ameya; Bierbooms, Wim
Slow Crack Growth and Fatigue Life Prediction of Ceramic Components Subjected to Variable Load History
Present capabilities of the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in slow crack growth (SCG) type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, while for cyclic fatigue applications various types of repetitive constant amplitude loads can be accounted for. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as, for example, engine start up, shut down, and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that takes into account the change in material response with time. In this paper, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code, which has also been modified to have the ability of interfacing with commercially available FEA codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.
Jadaan, Osama
Thermal-Transient Testing Of Turbine Blades
Testing apparatus applies pulses of heat to turbine blade to determine resistance to thermal fatigue. Uses nonintrusive inductive heating and records distribution of temperature on blade with infrared video camera. Allows precise control of heating and cooling. Designed for testing blades used in advanced high-pressure, high-temperature turbines.
Wagner, William R.; Pidcoke, Louis H.
Detect, troubleshoot gas-turbine blade failures
Approximately 40% of all gas-turbine failures stem from blading problems. This article describes state-of-the-art condition monitoring technologies that can help avoid or minimize the damage, and troubleshoot failures when they occur. In today`s gas-turbine (GT) fleet, predominant blade-failure mechanism and commonly affected components include: low-cycle fatigue--compressor and turbine disks; high-cycle fatigue--compressor and turbine blades and disks, compressor stator vanes; thermal
A model for life predictions of nickel-base superalloys in high-temperature low cycle fatigue
Extensive characterization of low-cycle fatigue damage mechanisms was performed on polycrystalline Rene 80 and IN100 tested in the temperature range from 871 to 1000 C. Low-cycle fatigue life was found to be dominated by propagation of microcracks to a critical size governed by the maximum tensile stress. A model was developed which incorporates a threshold stress for crack extension, a stress-based crack growth expression, and a failure criterion. The mathematical equivalence between this mechanistically based model and the strain-life low-cycle fatigue law was demonstrated using cyclic stress-strain relationships. The model was shown to correlate the high-temperature low-cycle fatigue data of the different nickel-base superalloys considered in this study.
Romanoski, Glenn R.; Pelloux, Regis M.; Antolovich, Stephen D.
Deterioration of rolling contact fatigue life of pearlitic rail steel due to dry-wet rolling-sliding line contact
This study is aimed at the deterioration of rolling contact fatigue (RCF) life of pearlitic rail steel, under rolling-sliding conditions, where the wet phase of the test is preceded by different numbers of dry cycles. It is shown that initial dry cycles above a critical number causes sudden and significant deterioration in RCF life. This effect has been explained using
W. R. Tyfour; J. H. Beynon; A. Kapoor
CARES/Life Ceramics Durability Evaluation Software Enhanced for Cyclic Fatigue
The CARES/Life computer program predicts the probability of a monolithic ceramic component's failure as a function of time in service. The program has many features and options for materials evaluation and component design. It couples commercial finite element programs--which resolve a component's temperature and stress distribution--to reliability evaluation and fracture mechanics routines for modeling strength-limiting defects. The capability, flexibility, and uniqueness of CARES/Life have attracted many users representing a broad range of interests and has resulted in numerous awards for technological achievements and technology transfer. Recent work with CARES/Life was directed at enhancing the program s capabilities with regards to cyclic fatigue. Only in the last few years have ceramics been recognized to be susceptible to enhanced degradation from cyclic loading. To account for cyclic loads, researchers at the NASA Lewis Research Center developed a crack growth model that combines the Power Law (time-dependent) and the Walker Law (cycle-dependent) crack growth models. This combined model has the characteristics of Power Law behavior (decreased damage) at high R ratios (minimum load/maximum load) and of Walker law behavior (increased damage) at low R ratios. In addition, a parameter estimation methodology for constant-amplitude, steady-state cyclic fatigue experiments was developed using nonlinear least squares and a modified Levenberg-Marquardt algorithm. This methodology is used to give best estimates of parameter values from cyclic fatigue specimen rupture data (usually tensile or flexure bar specimens) for a relatively small number of specimens. Methodology to account for runout data (unfailed specimens over the duration of the experiment) was also included.
Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.
Strength and fatigue life evaluation of composite laminate with embedded sensors
Prognosis regarding durability of composite structures using various Structural Health Monitoring (SHM) techniques is an important and challenging topic of research. Ultrasonic SHM systems with embedded transducers have potential application here due to their instant monitoring capability, compact packaging potential toward unobtrusiveness and noninvasiveness as compared to non-contact ultrasonic and eddy current techniques which require disassembly of the structure. However, embedded sensors pose a risk to the structure by acting as a flaw thereby reducing life. The present paper focuses on the determination of strength and fatigue life of the composite laminate with embedded film sensors like CNT nanocomposite, PVDF thin films and piezoceramic films. First, the techniques of embedding these sensors in composite laminates is described followed by the determination of static strength and fatigue life at coupon level testing in Universal Testing Machine (UTM). Failure mechanisms of the composite laminate with embedded sensors are studied for static and dynamic loading cases. The coupons are monitored for loading and failure using the embedded sensors. A comparison of the performance of these three types of embedded sensors is made to study their suitability in various applications. These three types of embedded sensors cover a wide variety of applications, and prove to be viable in embedded sensor based SHM of composite structures.
Rathod, Vivek T.; Hiremath, S. R.; Roy Mahapatra, D.
Fatigue Properties of an A356 (AlSi7Mg) Aluminium Alloy for Automotive Applications: Fatigue Life Prediction.
In the present paper a thorough study of the fatigue crack initiation mechanisms of a defect-free and a commercially cast A356 aluminum alloy are presented. Further, fatigue crack growth has been investigated in these materials. Finally an attempt to desc...
J. A. Oedegard, K. Pedersen
Fatigue life of fibre reinforced plastics at 295 K after thermal cycling between 295 K and 77 K
Results of low cycle three-point end fatigue tests at 295 K are reported. These were obtained from fibre reinforced plastics (FRP) flat specimens made of epoxy matrix reinforced with glass rovings only or glass rovings and Kevlar cloth. It is shown that previous thermal cycles between 295 K and 77 K exert an influence on the fatigue life as well on the acoustic emission results.
Belisario, G.; Caproni, F.; Marchetti, E.
Improvement of fatigue life of electrical discharge machined AISI D2 tool steel by TiN coating
This work presents the effects of titanium nitride (TiN) coating by physical vapor deposition (PVD) on the fatigue life of AISI D2 tool steel, which was electrical discharge machined (EDM) at various machining parameters, such as pulse current and pulse-on duration. Surface hardness, surface roughness, residual stress and fatigue strength were measured. Experimental results indicate that EDM treatment has a
Y. H. Guu; H. Hocheng
Fatigue life assessment of cardiovascular balloon-expandable stents: a two-scale plasticity-damage model approach.
Cardiovascular disease has become a major global health care problem in the present decade. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, as a result of the high number of cyclic loads these devices are subjected to in vivo, numerical approaches for fatigue life assessment of stents has gained special interest in the engineering community. Numerical fatigue predictions can be used to modify the design and prevent failure, without making and testing numerous physical devices, thus preventing from undesired fatigue failures. This work presents a fatigue life numerical method for the analysis of cardiovascular balloon-expandable stainless steel stents. The method is based on a two-scale continuum damage mechanics model in which both plasticity and damage mechanisms are assumed to take place at a scale smaller than the scale of the representative volume element. The fatigue failure criterion is based on the Soderberg relation. The method is applied to the fatigue life assessment of both PalmazShatz and Cypher stent designs. Validation of the method is performed through comparison of the obtained numerical results with some experimental results available for the PalmazShatz stent design. The present study gives also possible directions for future research developments in the framework of the numerical fatigue life assessment of real balloon-expandable stents. PMID:23032428
Argente dos Santos, H A F; Auricchio, F; Conti, M
Porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed scatter in fatigue life of a cast A356-T6 aluminum-silicon alloy due to the presence of porosity. Specimens containing a controlled amount of porosity were prepared by employing a wedge-shaped casting mold and adjusting the degassing process during casting. High-cycle
J. Z. Yi; Y. X. Gao; P. D. Lee; H. M. Flower; T. C. Lindley
Porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed\\u000a scatter in fatigue life of a cast A356-T6 aluminum-silicon alloy due to the presence of porosity. Specimens containing a controlled\\u000a amount of porosity were prepared by employing a wedge-shaped casting mold and adjusting the degassing process during casting.\\u000a High-cycle
The relationship between extrusion die line roughness and high cycle fatigue life of an AA6082 alloy
The effect of surface finish on the fatigue life of hollow extruded AA6082 was studied by comparing results from specimens with as-extruded surfaces to results from specimens with polished surfaces. Extrusion die lines are the main contributor to surface roughening, and since die lines are parallel to the extrusion direction, distinct variations exist between fatigue lives of as-extruded specimens taken
N. Nanninga; C. White
Advanced Failure Determination Measurement Techniques Used in Thermal Fatigue Life Testing of Electronic Packaging
Thermal fatigue life testing of various electronic packaging technologies is being performed by the Reliability Technology Group at the Jet Propulsion Laboratory. These testing efforts are in progress to improve uderstanding of the reliability issues associated with low volume packaging technologies for space applications and to develop qualification and acceptance approaches for these technologies. The work described here outlines the electrical failure detection techniques used during testing by documenting the circuits and components used to make these measurements, the sensitivity of the measurements, and the applicability of each specific measurement.
Wallace, A. P.; Cornford, S. L.; Gross, M. A.
Machine for use in monitoring fatigue life for a plurality of elastomeric specimens
An improved machine is described for use in determining the fatigue life for elastomeric specimens. The machine is characterized by a plurality of juxtaposed test stations, specimen support means located at each of the test stations for supporting a plurality of specimens of elastomeric material, and means for subjecting the specimens at each of said stations to sinusoidal strain at a strain rate unique with respect to the strain rate at which the specimens at each of the other stations is subjected to sinusoidal strain.
Fitzer, G. E. (inventor)
Effect of Environmental Exposures on Fatigue Life of P/M Disk Superalloys
As the temperature capability of Ni-base superalloy powder metallurgy disks is steadily increased, environmental resistance and protection of advanced nickel-based turbine disk components are becoming increasingly important. Localized surface hot corrosion attack and damage from oxidation have been shown to impair disk fatigue life and may eventually limit disk operating temperatures. NASA Research Announcement (NRA) contracts have been awarded to GE Aviation and Honeywell Aerospace to separately develop fatigue resistant metallic and ceramic coatings for corrosion resistance and the corrosion/fatigue results of selected coatings will be presented. The microstructural response of a bare ME3 disk superalloy has been evaluated for moderate (704 C) and aggressive (760-816 C) oxidizing exposures up to 2,020 hours. Cross section analysis reveals sub-surface damage (significant for aggressive exposures) that consists of Al2O3 "fingers", interfacial voids, a recrystallized precipitate-free layer and GB carbide dissolution. The effects of a Nichrome corrosion coating on this microstructural response will also be presented.
Draper, Susan
APPLICATION OF LOW PLASTICITY BURNISHING TO IMPROVE DAMAGE TOLERANCE OF A Ti6Al4V FIRST STAGE FAN BLADE
This paper describes the application of Low Plasticity Burnishing (LPB) to increase the damage tolerance and fatigue strength of a Ti-6Al-4V fan blade that is fatigue life limited by the occurrence of leading edge foreign object damage (FOD) as small as 0.1mm (0.005 in.). The size and location distributions of service generated FOD were documented; no FOD exceeded a depth
Ravi Ravindranath
Surface fatigue life and failure characteristics of EX-53, CBS 1000M, and AISI 9310 gear materials
Spur gear endurance tests and rolling-element surface fatigue tests are conducted to investigate EX-53 and CBS 1000M steels for use as advanced application gear materials, to determine their endurance characteristics, and to compare the results with the standard AISI 9310 gear material. The gear pitch diameter is 8.89 cm (3.50 in). Gear test conditions are an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. Bench-type rolling-element fatigue tests are conducted at ambient temperature with a bar specimen speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa (700 ksi). The EX-53 test gears have a surface fatigue life of twice that of the AISI 9310 spur gears. The CBS 1000M test gears have a surface fatigue life of more than twice that of the AISI 9310 spur gears. However, the CBS 1000M gears experience a 30-percent tooth fracture failure which limits its use as a gear material. The rolling-contact fatigue lines of RC bar specimens of EX-53 and ASISI 9310 are approximately equal. However, the CBS 1000M RC specimens have a surface fatigue life of about 50 percent that of the AISI 9310.
Townsend, D. P.
Fatigue life estimation of a 1D aluminum beam under mode-I loading using the electromechanical impedance technique
Structures in service are often subjected to fatigue loads. Cracks would develop and lead to failure if left unnoticed after a large number of cyclic loadings. Monitoring the process of fatigue crack propagation as well as estimating the remaining useful life of a structure is thus essential to prevent catastrophe while minimizing earlier-than-required replacement. The advent of smart materials such as piezo-impedance transducers (lead zirconate titanate, PZT) has ushered in a new era of structural health monitoring (SHM) based on non-destructive evaluation (NDE). This paper presents a series of investigative studies to evaluate the feasibility of fatigue crack monitoring and estimation of remaining useful life using the electromechanical impedance (EMI) technique employing a PZT transducer. Experimental tests were conducted to study the ability of the EMI technique in monitoring fatigue crack in 1D lab-sized aluminum beams. The experimental results prove that the EMI technique is very sensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model for fatigue life estimation has been developed by incorporating the linear elastic fracture mechanics (LEFM) theory into the finite element (FE) model. The prediction of the model matches closely with the experiment, suggesting the possibility of replacing costly experiments in future.
Lim, Yee Yan; Kiong Soh, Chee
Dynamic loads must be predicted accurately in order to estimate the fatigue life of wind turbines operating in turbulent environments. Dynamic stall contributes to increased dynamic loads during normal operation of all types of horizontal-axis wind turbine (HAWTs). This report illustrates how dynamic stall varies throughout the blade span of a 10 m HAWT during yawed and unyawed operating conditions. Lift, drag, and pitching moment coefficients during dynamics stall are discussed. Resulting dynamic loads are presented, and the effects of dynamic stall on yaw loads are demonstrated using a yaw loads dynamic analysis (YAWDYN). 12 refs., 22 figs., 1 tab.
Butterfield, C.P.; Simms, D.; Scott, G. (National Renewable Energy Lab., Golden, CO (United States)); Hansen, A.C. (Utah Univ., Salt Lake City, UT (United States))
Evaluation of flawed composite structural components under static and cyclic loading. [fatigue life of graphite-epoxy composite materials
The effects of initial defects on the fatigue and fracture response of graphite-epoxy composite laminates are presented. The structural laminates investigated were a typical angle ply laminate, a polar/hoop wound pressure vessel laminate, and a typical engine fan blade laminate. Defects investigated were full and half penetration circular holes, full and half penetration slits, and countersink holes. The effects of the defect size and type on the static fracture strength, fatigue performance, and residual static strength are shown as well as the results of loadings on damage propagation in composite laminates. The data obtained were used to define proof test levels as a qualification procedure in composite structure subjected to cyclic loading.
Porter, T. R.
Life prediction of thermomechanical fatigue using total strain version of strainrange partitioning (SRP): A proposal
A method is proposed (without experimental verification) for extending the total strain version of Strainrange Partitioning (TS-SRP) to predict the lives of thermomechanical fatigue (TMF) cycles. The principal feature of TS SRP is the determination of the time-temperature-waveshape dependent elastic strainrange versus life lines that are added subsequently to the classical inelastic strainrange versus life lines to form the total strainrange versus life relations. The procedure is based on a derived relation between failure and flow behavior. Failure behavior is represented by conventional SRP inelastic strainrange versus cyclic life relations, while flow behavior is captured in terms of the cyclic stress-strain response characteristics. Stress-strain response is calculated from simple equations developed from approximations to more complex cyclic constitutive models. For applications to TMF life prediction, a new testing technique, bithermal cycling, is proposed as a means for generating the inelastic strainrange versus life relations. Flow relations for use in predicting TMF lives would normally be obtained from approximations to complex thermomechanical constitutive models. Bithermal flow testing is also proposed as an alternative to thermomechanical flow testing at low strainranges where the hysteresis loop is difficult to analyze.
Saltsman, James F.; Halford, Gary R.
Oxidation and the Effects of High Temperature Exposures on Notched Fatigue Life of an Advanced Powder Metallurgy Disk Superalloy
Oxidation and the effects of high temperature exposures on notched fatigue life were considered for a powder metallurgy processed supersolvus heat-treated ME3 disk superalloy. The isothermal static oxidation response at 704 C, 760 C, and 815 C was consistent with other chromia forming nickel-based superalloys: a TiO2-Cr2O3 external oxide formed with a branched Al2O3 internal subscale that extended into a recrystallized - dissolution layer. These surface changes can potentially impact disk durability, making layer growth rates important. Growth of the external scales and dissolution layers followed a cubic rate law, while Al2O3 subscales followed a parabolic rate law. Cr- rich M23C6 carbides at the grain boundaries dissolved to help sustain Cr2O3 growth to depths about 12 times thicker than the scale. The effect of prior exposures was examined through notched low cycle fatigue tests performed to failure in air at 704 C. Prior exposures led to pronounced debits of up to 99 % in fatigue life, where fatigue life decreased inversely with exposure time. Exposures that produced roughly equivalent 1 m thick external scales at the various isotherms showed statistically equivalent fatigue lives, establishing that surface damage drives fatigue debit, not exposure temperature. Fractographic evaluation indicated the failure mode for the pre-exposed specimens involved surface crack initiations that shifted with exposure from predominately single intergranular initiations with transgranular propagation to multi-initiations from the cracked external oxide with intergranular propagation. Weakened grain boundaries at the surface resulting from the M23C6 carbide dissolution are partially responsible for the intergranular cracking. Removing the scale and subscale while leaving a layer where M23C6 carbides were dissolved did not lead to a significant fatigue life improvement, however, also removing the M23C6 carbide dissolution layer led to nearly full recovery of life, with a transgranular initiation typical to that observed in unexposed specimens.
Sudbrack, Chantal K.; Draper, Susan L.; Gorman, Timothy T.; Telesman, Jack; Gab, Timothy P.; Hull, David R.
Fatigue failure of a centrifugal compressor
A single stage centrifugal type compressor failed during operation and a blade detached. Failure analysis was carried out to delineate the cause of the failure.Investigation shows that multiple fatigue cracks were generated during service from forging defects in the root area of the blade. When they grew to a critical size under (high cycle fatigue) HCF, the blade detached from
N. Ejaz; I. Salam; A. Tauqir
Fatigue mechanics - An assessment of a unified approach to life prediction
Consideration is given to the development of a total-life prediction methodology for aerospace structures based solely on crack propagation from a microstructural defect at stress concentrations. Crack-growth lives were calculated for a given loading condition by integrating the crack-growth-rate-against-delta K relationships for crack growth from a microstructural defect size to failure. Both small- and large-crack growth rate data were used. The assessment was based on data on 2024-T3 aluminum alloy, 2090-T8E41 aluminum-lithium alloy, annealed Ti-6Al-4V titanium alloy, and high-strength 4340 steel under either constant-amplitude or spectrum loading. Good agreement was found between fatigue lives measured on notched specimens with those computed from the total-life analysis.
Newman, J. C., Jr.; Phillips, E. P.; Swain, M. H.; Everett, R. A., Jr.
Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring
Research was performed to determine if a diagnostic tool for detecting fatigue damage of helicopter tapered roller bearings can be used to determine remaining useful life (RUL). The taper roller bearings under study were installed on the tail gearbox (TGB) output shaft of UH- 60M helicopters, removed from the helicopters and subsequently installed in a bearing spall propagation test rig. The diagnostic tool was developed and evaluated experimentally by collecting oil debris data during spall progression tests on four bearings. During each test, data from an on-line, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results from the four bearings tested indicate that measuring the debris generated when a bearing outer race begins to spall can be used to indicate bearing damage progression and remaining bearing life.
Dempsey, Paula J.; Bolander, Nathan; Haynes, Chris; Toms, Allison M.
Thermal Fatigue Life of Glidcop Al-15 High-Heat-Load Components
Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation of synchrotron radiation light source and is presently under construction as a large scale national scientific project in China. Depending on the outstanding thermal and mechanical performance, Glidcop Al-15, a dispersion strengthened copper alloy, is chosen to serve for the high-heat-load components at beam line front end in SSRF. Present study is to investigate the thermal fatigue lives of critical SSRF components. A nonlinear finite element method (FEM) is used to simulate the nonlinear three dimensional stress-strain fields of the critical component-Mask2 at SSRF beam line. The method consists of transient temperature analyses followed by elastic-plastic stress analyses. Then, a critical plane approach is used to predict the thermal fatigue life of mask2. The critical plane approach is appropriate for estimating service life of critical SSRF components since the results are in good consistent with the experimental ones taken at the Advanced Photon Source (APS).
Jin, J. F.; Xiao, W. L.; Chen, H. B.
The application of probabilistic design theory to high temperature low cycle fatigue
Metal fatigue under stress and thermal cycling is a principal mode of failure in gas turbine engine hot section components such as turbine blades and disks and combustor liners. Designing for fatigue is subject to considerable uncertainty, e.g., scatter in cycles to failure, available fatigue test data and operating environment data, uncertainties in the models used to predict stresses, etc. Methods of analyzing fatigue test data for probabilistic design purposes are summarized. The general strain life as well as homo- and hetero-scedastic models are considered. Modern probabilistic design theory is reviewed and examples are presented which illustrate application to reliability analysis of gas turbine engine components.
Wirsching, P. H.
Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components
Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels.
Ko, W. L.; Carter, A. L.; Totton, W. W.; Ficke, J. M.
Microstructures and fatigue life of SnAgCu solder joints bearing Nano-Al particles in QFP devices
Microstructures and fatigue life of SnAgCu and SnAgCu bearing nano-Al particles in QFP (Quad flat package) devices were investigated, respectively. Results show that the addition of nano-Al particles into SnAgCu solder can refine the microstructures of matrix microstructure. Moreover, the nano-Al particles present in the solder matrix, act as obstacles which can create a back stress, resisting the motion of dislocations. In QFP device, it is found that the addition of nano-Al particles can increase the fatigue life by 32% compared with the SnAgCu solder joints during thermal cycling loading.
Zhang, Liang; Fan, Xi-ying; Guo, Yong-huan; He, Cheng-wen
A high temperature fatigue life prediction computer code based on the total strain version of StrainRange Partitioning (SRP)
A recently developed high-temperature fatigue life prediction computer code is presented and an example of its usage given. The code discussed is based on the Total Strain version of Strainrange Partitioning (TS-SRP). Included in this code are procedures for characterizing the creep-fatigue durability behavior of an alloy according to TS-SRP guidelines and predicting cyclic life for complex cycle types for both isothermal and thermomechanical conditions. A reasonably extensive materials properties database is included with the code.
Mcgaw, Michael A.; Saltsman, James F.
A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys
Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.
Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.
On the Fatigue Analysis of Wind Turbines
Modern wind turbines are fatigue critical machines that are typically used to produce electricalpower from the wind. Operational experiences with these large rotating machines indicated thattheir components (primarily blades and blade joints) were failing at unexpectedly high rates, whichled the wind turbine community to develop fatigue analysis capabilities for wind turbines. Ourability to analyze the fatigue behavior of wind turbine
Evaluation of effects of LWR coolant environments on fatigue life of carbon and low-alloy steels
The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figure I-90 of Appendix I to Section III of the Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Recent test data indicate a significant decrease in fatigue life of carbon and low-alloy steels in LWR environments when five conditions are satisfied simultaneously, viz., applied strain range, temperature, dissolved oxygen in the water, and sulfur content of the steel are above a minimum threshold level, and the loading strain rate is below a threshold value. Only a moderate decrease in fatigue life is observed when any one of these conditions is not satisfied. This paper summarizes available data on the effects of various material and loading variables such as steel type, dissolved oxygen level, strain range, strain rate, and sulfur content on the fatigue life of carbon and low-alloy steels. The data have been analyzed to define the threshold values of the five critical parameters. Methods for estimating fatigue lives under actual loading histories are discussed.
A Study on Fatigue Fracture Mechanism of Cr-Mo Steel SCM435 in Super Long Life Range
For high strength steels, a characteristic fatigue behavior, which S-N curve comes down again in the long life region of N > 107 cycles, was reported by many researchers. Specifically, for high strength steel, the fatigue limit is temporal value because of the fish-eye fracture in the long life region over about N = 107 cycles. However, fish eye fracture does not appear for medium strength steel in super long life range. In this paper, cantilever-type rotational bending fatigue tests were carried out for quenched and tempered Cr-Mo steel (JIS: SCM435) up to 109 cycles at room temperature in air. The S-N curve showed a horizontal part in long life region over 107 cycles. In addition, fish- eye fracture was not observed and for all specimens, the crack initiation occurred from the specimen surface. The fatigue fracture behavior of SCM435 in super long life was discussed based on optical microscopy observation and scanning electron microscopy observation.
Murakami, Ri Ichi; Yonekura, Daisuke; Murayama, Taishi
The Effect of Weld Profile and Geometries of Butt Weld Joints on Fatigue Life Under Cyclic Tensile Loading
The fatigue life of welded joint was calculated based on numerical integration of simple Paris' law and a reliable solution of the stress intensity factor (SIF). The initial crack length ( a i) was assumed to be equal to 0.1 mm in case of weld toe. This length was satisfactory for different butt joints geometries. The comparisons with the available data from standards and literature were demonstrated. It was shown numerically that the machining of weld reinforcements will increase the fatigue life. The increase of plate thickness decreases the fatigue strength (FAT) and the number of cycles to failure when using the proportional scaling of crack length. The validation processes of the current calculations have been shown. Therefore, it can be concluded that it will prevent the unnecessary waste of time consumed to carry out the experiments.
Fatigue life calculation of desuperheater for solving pipe cracking issue using finite element method (FEM) software
Desuperheater assembly experiences thermal cycling in operation by design. During power plant's start up, load change and shut down, thermal gradient is highest. Desuperheater should be able to handle rapid ramp up or ramp down of temperature in these operations. With "hump style" two nozzle desuperheater, cracks were appearing in the pipe after only few cycles of operation. From the field data, it was clear that desuperheater is not able to handle disproportionate thermal expansion happening in the assembly during temperature ramp up and ramp down in operation and leading to cracks appearing in the piping. Growth of thermal fatigue crack is influenced by several factors including geometry, severity of thermal stress and applied mechanical load. This paper seeks to determine cause of failure of two nozzle "hump style" desuperheater using Finite Element Method (FEM) simulation technique. Thermal stress simulation and fatigue life calculation were performed using commercial FEA software "ANSYS" [from Ansys Inc, USA]. Simulation result showed that very high thermal stress is developing in the region where cracks are seen in the field. From simulation results, it is also clear that variable thermal expansion of two nozzle studs is creating high stress at the water manifold junction. A simple and viable solution is suggested by increasing the length of the manifold which solved the cracking issues in the pipe.
Kumar, Aravinda; Singh, Jeetendra Kumar; Mohan, K.
Improvement in surface fatigue life of hardened gears by high-intensity shot peening
Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.
Initial Assessment of the Effects of Nonmetallic Inclusions on Fatigue Life of Powder-Metallurgy-Processed Udimet(TM) 720
The fatigue lives of modern powder metallurgy (PM) disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary due to the different steps of materials/component processing and machining. One of these variables, the presence of nonmetallic inclusions, has been shown to significantly degrade low-cycle fatigue (LCF) life. Nonmetallic inclusions are inherent defects in powder alloys that are a by-product of powder-processing techniques. Contamination of the powder can occur in the melt, during powder atomization, or during any of the various handling processes through consolidation. In modern nickel disk powder processing facilities, the levels of inclusion contamination have been reduced to less than 1 part per million by weight. Despite the efforts of manufacturers to ensure the cleanliness of their powder production processes, the presence of inclusions remains a source of great concern for the designer. the objective of this study was to investigate the effects on fatigue life of these inclusions. Since natural inclusions occur so infrequently, elevated levels of inclusions were carefully introduced in a nickel-based disk superalloy, Udimet 720 (registered trademark of Special Metals Corporation), produced using PM processing. Multiple strain-controlled fatigue tests were then performed on this material at 650 C. Analyses were performed to compare the LCF lives and failure initiation sites as functions of inclusion content and fatigue conditions. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface. The inclusions could reduce fatigue life by up to 100 times. These effects were found to be dependent on strain range and strain ratio. Tests at lower strain ranges and higher strain ratios produced larger effects of inclusions on life.
Gabb, T. P.; Telesman, J.; Kantzos, P. T.; Bonacuse, P. J.; Barrie, R. L.
The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel
Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.
Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.
Simulated Bladed MMC Disk LCF Validation
The goal of this program was to evaluate the low cycle fatigue behavior of an SCS-6/Ti-6Al-4V sub-component under bi-axial loading conditions at 316 C(600 F). A simulated bladed TMC disk was designed having thirty four blades representing the number that would be used in Allied Signal's JTAGG II impeller. The outer diameter of the bladed ring was 254 mm (10.0 inch) and the inner diameter 114.3 mm (4.50 inch). The outer and inner diameter of the composite zone was 177.8 mm (7.00 inch) and 127.O mm(5.00 inch) respectively. Stress analysis showed that the fatigue life of the bladed composite ring would be about 12000 cycles for the test conditions applied. A modal analysis was conducted which showed that the blades would have sufficient life margin from dynamic excitation. The arbor design was the same as that employed in the spin-to burst test of NAS3-27027. A systematic stress analysis of each part making up the arbor was undertaken to assure the design would meet the low cycle fatigue requirements of the program. The Textron Systems grooved foil-fiber process was chosen to make the SCS-6/Ti-6Al-4V core ring based on the success they had in contract NAS3-27027. Fiber buckling, however, was observed at several locations in the first ring made which rendered it unsuitable for spin testing. The fiber buckling was attributed to cracking of the graphite tooling during the consolidation process. On this basis a second ring was made but it too contained fiber buckling defects. Analysis by Textron indicated that the fiber buckling was most likely due to poor placement of the SCS-6 fiber in the etched grooves of the Ti-6Al-4V foil. This was also a contributor to the defects in the first ring. Since there was little indication of control in the process to manufacture a quality ring a third attempt at making a ring was not undertaken.
Merrick, H. F.; Costen, M.
The effect of porosity and gamma-gamma' eutectic content on the low cycle fatigue behavior of hydrogen-charged PWA-1480
Single crystal superalloys such as PWA 1480 are considered for turbopump blades in the main engines of the space shuttle. As fatigue resistance in a hydrogen environment is a key issue in this application, a study of the effect of porosity and gamma-gamma' eutectic content on the fatigue life of a hydrogen-charged PWA 1480 was performed. Porosity and eutectic were linked to fatigue initiation, and therefore reduction of either of both may be one means to improve fatigue life of PWA 1480 when hydrogen is present.
Gayda, John; Dreshfield, Robert L.; Gabb, Timothy P.
Quality of Life in Brain Tumor Patients: The Relative Contributions of Depression, Fatigue, Emotional Distress, and Existential Issues
Neuropsychiatric problems, and how they interact to impact on quality of life (QOL) in brain tumor patients, are generally poorly understood. The objectives of this study were: (1) to document the prevalence of depression, fatigue, emotional distress, and existential issues in a sample of brain tumor patients (2) to examine the interconnectedness of these problems, and (3) to explore their
Guy Pelletier; Marja J. Verhoef; Nasreen Khatri; Neil Hagen
Experiment study and fatigue life prediction of torsion shaft of self-propelled gun based on stochastic response surface method
The randomness of low cycle fatigue life of torsion shaft of self-propelled gun is the key factor affecting the reliability of the running system. A self-propelled gun experiment was carried through the field test to achieve the load spectrums of torsion shaft. The conclusion that the maximum tensile stress is the failure stress of torsion shaft was drawn. In order
Li Yadong; Zheng Jian; Jia Changzhi
Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminium alloy
This paper presents a systematic approach to optimising FSW process parameters (tool rotational speed and feed rate) through consideration of frictional power input. Frictional power governs the tensile strength and the fatigue life in this 5083-H321 alloy through its effect on plastic flow processes in the thermo-mechanically affected zone (TMAZ) of the weld. Although, a close relationship therefore exists between
H. Lombard; D. G. Hattingh; A. Steuwer; M. N. James
A Comparison of Flight Loads Counting Methods and Their Effects on Fatigue Life Estimates Using Data from Concorde.
Four load-time histories of turbulence encountered by Concorde are analyzed by six different peak-counting and level-crossing counting procedures. The frequency distributions obtained are then used to find fatigue life ratios using the Miner-Palmgren hypo...
A. G. Goodwillie
Variability in Room Temperature Fatigue Life of Alpha+Beta Processed Ti- 6Al-4V (Preprint).
In this program, smooth bar fatigue tests were conducted by several laboratories on the same lot of Ti-6Al-4V forged plate material. Multiple stress ratios and stress levels were tested to generate a fully populated stress-life curve. The tests, however, ...
J. Porter P. J. Golden R. John
Sensitivity study on material properties for the fatigue life prediction of solder joints under cyclic thermal loading
A computational study is presented in this paper to investigate the effect of variation in material properties on the fatigue life prediction of solder joints subjected to cyclic thermal loading. The package under investigation was a plastic quad flat pack (PQFP) with gull-wing leads. A commercial finite element code, ABAQUS, was employed to perform a two-dimensional plane stress analysis. While
Shi-Wei Ricky Lee; Xiaowu Zhang
Development of a device to study fatigue life of fixed partial dentures
Fixed partial dentures can be fabricated by means of different materials and with different manufacturing processes. In order to establish possible differences among them, their behaviour, as fatigue life or cement shear bond strength, have to be evaluated. This article presents a modular, economic and robust device to evaluate fixed partial dentures and dental crowns. A base to support the fixed partial dentures and a device to simulate masticatory loads have been developed. The device has got a simple design. It is based on a pneumatic piston, with a pressure regulator to control masticatory loads. On a first stage, only vertical forces have been taking into account. However, the device will allow simulating tangential masticatory loads on the other axis, studying the behaviour of the fixed partial dentures submerged in a solution similar to saliva, changing masticatory load application, etc. with little modifications.
Gutierrez, S. C.; Meseguer, M. D.; Estal, R.; Folguera, F.; Vidal, V.
Reliability approach to rotating-component design. [fatigue life and stress concentration
A probabilistic methodology for designing rotating mechanical components using reliability to relate stress to strength is explained. The experimental test machines and data obtained for steel to verify this methodology are described. A sample mechanical rotating component design problem is solved by comparing a deterministic design method with the new design-by reliability approach. The new method shows that a smaller size and weight can be obtained for specified rotating shaft life and reliability, and uses the statistical distortion-energy theory with statistical fatigue diagrams for optimum shaft design. Statistical methods are presented for (1) determining strength distributions for steel experimentally, (2) determining a failure theory for stress variations in a rotating shaft subjected to reversed bending and steady torque, and (3) relating strength to stress by reliability.
Kececioglu, D. B.; Lalli, V. R.
User's guide for the frequency domain algorithms in the LIFE2 fatigue analysis code
The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.
Sutherland, H. J.; Linker, R. L.
Static and dynamic strain measurements which were taken during test stand operations of the gas dynamic laser (GDL) for the AF Airborne Laser Laboratory indicated that higher than expected vibrational stress levels may possibly limit the fatigue life of the laser structure. Particularly the diffuser sidewall structure exhibited large amplitude random vibrations which were excited by the internal gas flow. The diffuser structure consists of two layers of brazed stainless steel, AISI-347, panels. Cooling ducts were milled into the outer face sheet. These in turn are backed by the inner face sheet. So called T-rail stiffeners silver-brazed to the outer face sheets add the required stiffness and divide the sidewall into smaller rectangular plate sections.
Maurer, O. F.; Banaszak, D. L.
Surface fatigue life of CBN and vitreous ground carburized and hardened AISI 9310 spur gears
Spur gear surface endurance tests were conducted to investigate CBN ground AISI 9310 spur gears for use in aircraft applications, to determine their endurance characteristics and to compare the results with the endurance of standard vitreous ground AISI 9310 spur gears. Tests were conducted with VIM-VAR AISI 9310 carburized and hardened gears that were finish ground with either CBN or vitreous grinding methods. Test conditions were an inlet oil temeprature of 320 K (116 F), an outlet oil temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. The CBN ground gears exhibited a surface fatigue life that was slightly better than the vitreous ground gears. The subsurface residual stress of the CBN ground gears was approximately the same as that for the standard vitreous ground gears for the CBN grinding method used.
Townsend, Dennis P.; Patel, P. R.
Current Developments in Aircraft Fatigue Evaluation Procedures.
Current developments in the field of aircraft fatigue evaluation are reviewed including the description of loads for fatigue evaluation, the damage tolerance concept, concepts for the prediction of fatigue life, fatigue life improvement during production,...
O. Buxaum D. Schutz
Fatigue life prediction for wind turbines: A case study on loading spectra and parameter sensitivity.
Wind turbines are fatigue-critical machines used to produce electrical energy from the wind. These rotating machines are subjected to environmental loadings that are highly irregular in nature. Historical examples of fatigue problems in both research and ...
H. J. Sutherland P. S. Veers T. D. Ashwill
Influence of Solid-State Diffusion during Equilibration on Microstructure and Fatigue Life of Superalloy Wide-Gap Brazements
The influence of solid-state diffusion-controlled solute-loss into additive powder particles (APPs), as determined by particles size, during the equilibration stage of wide-gap brazing, on microstructure and fatigue behavior of a brazed aerospace superalloy was studied. The results, which experimentally confirm previously reported numerical model simulation results, show that, in order to avoid degradation of fatigue life of wide-gap brazement, adequate solute-loss into the APPs, which is necessary to prevent their complete melting, but has not been generally considered, is imperative.
Osoba, L. O.; Ojo, O. A.
Grain boundary oxidation and an analysis of the effects of pre-oxidation on subsequent fatigue life
The effects of preoxidation on subsequent fatigue life were studied. Surface oxidation and grain boundary oxidation of a nickel-base superalloy (TAZ-8A) were studied at 600 to 1000 C for 10 to 1000 hours in air. Surface oxides were identified and the kinetics of surface oxidation was discussed. Grain boundary oxide penetration and morphology were studied. Pancake type grain boundary oxide penetrates deeper and its size is larger, therefore, it is more detrimental to fatigue life than cone-type grain boundary oxide. Oxide penetration depth, a (sub m), is related to oxidation temperature, T, and exposure time, t, by an empirical relation of the Arrhenius type. Effects of T and t on statistical variation of a (sub m) were analyzed according to the Weibull distribution function. Once the oxide is cracked, it serves as a fatigue crack nucleus. Statistical variation of the remaining fatigue life, after the formation of an oxide crack of a critical length, is related directly to the statistical variation of grain boundary oxide penetration depth.
Oshida, Y.; Liu, H. W.
Investigation of waviness in wind turbine blades: Structural health monitoring
Waviness in composite wind turbine blades was detected and characterized with the help of air coupled ultrasonics. Based on the aspect ratio, the detected marcels are either accepted or rejected. A passive structural health monitoring approach has been presented here to monitor the accepted marcels above a threshold. The fatigue life of specimen is most affected in the presence of a marcel. Hence this study focused on the damage evaluation after fatigue testing. Wavy laminate was subjected to fatigue load to investigate the fracture mechanisms near the marcel. Different types of defects were identified from this study and were used to develop appropriate instrumentation for health monitoring of a wavy laminate using PVDF patches.
Chakrapani, Sunil Kishore; Dayal, Vinay; Barnard, Daniel J.
A study of rolling-contact fatigue of bearing steel coated with physical vapor deposition TiN films: Coating response to cyclic contact stress and physical mechanisms underlying coating effect on the fatigue life
The effect of physical vapor deposition (PVD) TiN coatings of different thicknesses on the rolling-contact fatigue (RCF) life of coated specimens is studied experimentally. Based on the results of conventional three-ball-on-rod testing, the optimum film thickness is found to be about 0.75 ?m. Thinner coatings do not significantly affect the fatigue life, while much thicker ones have a negative effect
I. A. Polonsky; T. P. Chang; L. M. Keer; W. D. Sproul
Life prediction methodology for thermal-mechanical fatigue and elevated temperature creep design
Nickel-based superalloys are used for hot section components of gas turbine engines. Life prediction techniques are necessary to assess service damage in superalloy components resulting from thermal-mechanical fatigue (TMF) and elevated temperature creep. A new TMF life model based on continuum damage mechanics has been developed and applied to IN 738 LC substrate material with and without coating. The model also characterizes TMF failure in bulk NiCoCrAlY overlay and NiAl aluminide coatings. The inputs to the TMF life model are mechanical strain range, hold time, peak cycle temperatures and maximum stress measured from the stabilized or mid-life hysteresis loops. A viscoplastic model is used to predict the stress-strain hysteresis loops. A flow rule used in the viscoplastic model characterizes the inelastic strain rate as a function of the applied stress and a set of three internal stress variables known as back stress, drag stress and limit stress. Test results show that the viscoplastic model can reasonably predict time-dependent stress-strain response of the coated material and stress relaxation during hold times. In addition to the TMF life prediction methodology, a model has been developed to characterize the uniaxial and multiaxial creep behavior. An effective stress defined as the applied stress minus the back stress is used to characterize the creep recovery and primary creep behavior. The back stress has terms representing strain hardening, dynamic recovery and thermal recovery. Whenever the back stress is greater than the applied stress, the model predicts a negative creep rate observed during multiple stress and multiple temperature cyclic tests. The model also predicted the rupture time and the remaining life that are important for life assessment. The model has been applied to IN 738 LC, Mar-M247, bulk NiCoCrAlY overlay coating and 316 austenitic stainless steel. The proposed model predicts creep response with a reasonable accuracy for wide range of loading cases such as uniaxial tension, tension-torsion and tension-internal pressure loading.
Annigeri, Ravindra
Modeling of Damage Interaction in Fatigue Relaxation for Long-Term Life Prediction. Case of Alloy 800 Grade 2 Study at 550°C
Prediction of fatigue life in creep-fatigue at a temperature of 550°C has been made for an Inconel alloy with the help of 3 models of damage evolution: the Chaboche model, the Levaillant model, and a new model of creep-fatigue relaxation. The main advantages of the new model are that it requires only a few constants and provides high accuracy of
A. El Gharad; G. Pluvinage; Z. Azari; A. Elamraoui; A. Kifani
Displacement measurement on specimens subjected to non-Gaussian random vibrations in fatigue life tests
High-cycle fatigue life tests conducted using controlled random vibrations are commonly used to evaluate failure in components and structures. In most cases, a Gaussian distribution of both the input vibration and the stress response is assumed, while real-life loads may be non-Gaussian causing the response to be non-Gaussian as well. Generating non-Gaussian drive signals with high kurtosis and a given power spectral density, however, does not always guarantee that the stress response will actually be non-Gaussian, because this depends on the adherence of the tested system to the Central Limit Theorem. On the other side, suitable measurement methods need to be developed in order to estimate the stress amplitude response at critical failure locations, and therefore to evaluate and select input loads. In this paper, a simple test rig with a notched cantilevered specimen was developed to measure the response and examine the kurtosis values in the case of stationary Gaussian, stationary non-Gaussian, and non-stationary non-Gaussian excitation signals. The Laser Doppler Vibrometry (LDV) technique was used for the first time in this type of test, to estimate the specimen stress amplitude response in terms of differential displacement at the notch section ends. A method based on the use of accelerometers to correct for the occasional signal drops occurring during the experiment is described and the results are discussed with respect to the ability of the test procedure to evaluate the output signal.
Troncossi, M.; Di Sante, R.; Rivola, A.
Rolling-element fatigue life of silicon nitride balls. [as compared to that of steel, ceramic, and cermet materials
The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of bearing quality steel running against steel at stress levels typical rolling-element bearing application. The fatigue life of hot-pressed silicon nitride is considerably greater than that of any ceramic or cermet tested. Computer analysis indicates that there is no improvement in the lives of 120-mm-bore angular--contact ball bearings of the same geometry operating at DN values from 2 to 4 million where hot-pressed silicon nitride balls are used in place of steel balls.
Fatigue modeling for small wind systems: basic theory
This report discusses the theory of fatigue as applied to horizontal-axis wind systems and reviews current techniques for predicting fatigue loads and fatigue life. Wind systems are subjected to a complex and diverse variety of loads, ranging from simple gravity and centrifugal loads to complex and random wind loads. The categories of loads described here include transient, periodic, and control-induced loads, as well as loads induced by severe aeroelastic instabilities. Within these categories, load types include centrifugal, aerodynamic thrust and torque, parked rotor survival loads, gravity loads, gyroscopic loads, and aerodynamic loads induced by crossflow or yaw motion. Control systems can impose loads whenever they are activated. Catastrophic failure can result from severe aeroelastically-induced loads caused by flutter. Techniques available for predicting fatigue loads include various aerodynamic performance codes (such as PROP) and simplified methods for calculating the convection of the vortex wake. MOSTAB, an aeroelasticity computer code, treats all major load sources. Results using this code are shown to be fairly comparable to experimental data in the case of a rigid-bladed wind system. Fatigue life of a machine component can be predicted during design by several techniques, including the strength-of-materials method, the fatigue curve method, and the fatigue event method. The theories of Miner, Manson, and Corten-Dolan can be used to predict fatigue life based on test data and operational experience. A fatigue research project to be performed at Rocky Flats will attempt to resolve whether any of these theories or a combination of theories can be used with an acceptable degree of accuracy in predicting fatigue loads and life for wind systems. An appendix to the report provides sample calculations of fatigue load magnitudes made using available methods.
Waldon, C.A.; Hansen, A.C.
Neural network fatigue life prediction in steel i-beams using mathematically modeled acoustic emission data
The purpose of this research is to predict fatigue cracking in metal beams using mathematically modeled acoustic emission (AE) data. The AE data was collected from nine samples of steel Ibeam that were subjected to three-point bending caused by cyclic loading. The data gathered during these tests were filtered in order to remove long duration hits, multiple hit data, and obvious outliers. Based on the duration, energy, amplitude, and average frequency of the AE hits, the filtered data were classified into the various failure mechanisms of metals using NeuralWorksRTM Professional II/Plus software based self-organizing map (SOM) neural network. The parameters from mathematically modeled AE failure mechanism data were used to predict plastic deformation data. Amplitude data from classified plastic deformation data is mathematically modeled herein using bounded Johnson distributions and Weibull distribution. A backpropagation neural network (BPNN) is generated using MATLABRTM. This BPNN is able to predict the number of cycles that ultimately cause the steel I-beams to fail via five different models of plastic deformation data. These five models are data without any mathematical modeling and four which are mathematically modeled using three methods of bounded Johnson distribution (Slifker and Shapiro, Mage and Linearization) and Weibull distribution. Currently, the best method is the Linearization method that has prediction error not more than 17%. Multiple linear regression (MLR) analysis is also performed on the four sets of mathematically modeled plastic deformation data as named above using the bounded Johnson and Weibull shape parameters. The MLR gives the best prediction for the Linearized method which has a prediction error not more than 2%. The final conclusion made is that both BPNN and MLR are excellent tools for accurate fatigue life cycle prediction.
Selvadorai, Prathikshen N.
Fatigue sensitivity determination procedure
US Patent & Trademark Office Database
A method for determining the sensitivity of the fatigue life of a structural component with respect to specific design parameters includes obtaining the stress profile for a structural component under random process establishing a relationship between the stress profile and the fatigue life of the structural component, developing the sensitivity of the fatigue life with respect to design parameters, optimizing the design of the structural component based upon the design parameters to which the fatigue life is most sensitive.
Axial-thrust responses due to a gas turbine's rotor blade distortions
The axial thrust imposed on the shaft of a gas turbine depends upon its rotor blade inlet inclination to the turbine's axial direction: this inclination can change due to the distortions resulting from fouling, aging, tip rubbing, erosion, thermal-fatigue cracks, and corrosion. Relevant influential parameters for an operational gas turbine were measured. Theoretical predictions for the behavior of the same turbine were obtained from computer simulations. The results of both measurements and theoretical predictions were compared and showed qualitative correspondence. The rotor blade profile distortions result in significant increases in the axial thrust on the compressor, which adversely affects the gas turbine's thermodynamic performance, reliability, and operational life.
Lebele-Alawa, B. T.
Rolling-Element Fatigue Life with Traction Fluids and Automatic Transmission Fluid in a High-Speed Rolling-Contact Rig.
Rolling-element fatigue tests were run in standard and high-speed rolling-contact rigs at bar speeds from 5000 to 50,000 rpm to determine the effects of speed and lubricant film parameter on rolling-element fatigue life. AISI 52100 test bars were tested a...
R. J. Parker A. H. Nahm S. H. Loewenthal
Windmill blade
A windmill rotor of the vertical axis type is described, comprising: a rotatably mounted, upstanding shaft member; elongate upstanding blade members of airfoil design arranged in a helical configuration in surrounding relation to the shaft member; blade members being three in number and being spaced one hundred twenty degrees from one another and each blade member extending about twenty degrees of arc about an imaginary circle that is swept when the blade members rotate about the shaft member; horizontally disposed, radially extending upper strut members, each upper strut member connecting its associated blade member to the shaft member near the upper end of the shaft member, there being as many upper strut members as there are blade members; horizontally disposed, radially extending lower strut members; constant speed means for maintaining constant speed rotation of the blade members during conjoint rotation of the blade members, their associated strut members, and the shaft member.
Clancy, B.D.
Failure analysis of generator rotor fan blades
The failure analysis of a generator rotor fan blade was investigated by mechanical analysis and metallurgical examination of fracture surface. Fracture took place at the airfoil root, surface examination showed that the blade had cracked by a high cycle fatigue mechanism. However, there was no evidence of material defect. A series of analytical, finite element and experimental analysis was utilized
Simplified methods of creep-fatigue damage evaluations and the application to life extension
A simplified method for creep-fatigue damage evaluations is presented. The material requirements include the standard tensile, creep-rupture and fatigue data over temperature ranges and special creep-fatigue test data. From the average data of these tests the average cyclic constitutive relationships are determined without any reduction factors. These constitutive equations are used in the analyses of the design loadings to obtain
The effect of composite damage on fatigue life of the high pressure vessel for natural gas vehicles
In order to examine how the damages such as scratches, cuts and gouges on the composite materials have effects on the fatigue life of NGV vessels, several experiments on real vessels were conducted and finite element analyses were applied. The flaw depths of COPV used in the experiments were 1.5mm, 2.0mm, 3.0mm, and 4.0mm, while the flaw lengths were 50mm,
Young-Seob Kim; Lae-Hyun Kim; Ji-Sang Park
Effect of stress ratio on long life fatigue behavior of high carbon chromium bearing steel under axial loading
Effect of the stress ratio on fatigue properties of a bearing steel (JIS:SUJ2) in the long life regime was experimentally examined under axial loading. As a result, the duplex S–N characteristics given by superposition of S–N curves for surface-induced fracture and interior inclusion-induced fracture were obtained similar to the corresponding results in rotating bending. Fish-eye marks were necessarily observed on
Tatsuo Sakai; Yosuke Sato; Yoshiyuki Nagano; Mitsuhiro Takeda; Noriyasu Oguma
Effect of cyclic frequency on the fatigue life of ASME SA106B piping steel in PWR environments
Fatigue life tests in pressurized water reactor (PWR) environments were performed on smooth and sharply notched specimens\\u000a of ASME SA-106-B piping steel at cyclic frequencies of 1.0 Hz, 0.1 Hz, and 0.017 Hz. On the basis of these tests, it was concluded\\u000a that no effect of cyclic frequency existed for smooth specimens whereas a frequency of 0.017 Hz proved to
J. B. Terrell
Effects of pre-rolling and metal removal on the fatigue life of lubricated rolling\\/sliding contact
In this experiment, after the test specimens are preloaded at different first-step rolling cycles, the surface layer of the lower speed roller is ground to different depths by a grinder along the radial direction. With a new higher speed roller, the effects of the ground depth and first-step rolling cycle on the fatigue life of lubricated rolling\\/sliding contact are investigated
Rong-Tsong Lee; Yuang-Cherng Chiou; J. H. Chang
Dynamic analysis tool development for advanced geometry wind turbine blades
This dissertation describes work to develop a dynamic analysis code for swept wind turbine blades. Because of their aeroelastic behavior, swept blades offer the potential to increase energy capture and lower fatigue loads. This work was an outgrowth of United States Department of Energy contract on swept blades, where the author used the Adams(TM)dynamic software. The author based the new
Scott Michael Larwood
Prediction of Delamination in Wind Turbine Blade Structural Details
Delamination between plies is the root cause of many failures of composite materials structures such as wind turbine blades. Design methodologies to prevent such failures have not been widely available for the materials and processes used in blades. This paper presents simplified methodologies for the prediction of delamination under both static and fatigue loading at typical structural details in blades.
John F. Mandell; Douglas S. Cairns; Daniel D. Samborsky; Robert B. Morehead; Darrin J. Haugen