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Crack propagation analysis of mechanically damaged compressor blades subjected to high cycle fatigue
This paper presents results of experimental crack propagation analysis of damaged compressor blades of the helicopter engine, subjected to high cycle fatigue. The blades used in investigations were preliminary defected to simulate the foreign object damage. The blades during experiment were entered into transverse vibration. The crack propagation process was conducted in resonance condition. During fatigue investigations the crack length
Lucjan Witek
Prediction of fatigue performance in gas turbine blades after foreign object damage
Foreign object damage is a significant cause of failure in gas turbine engines. This paper describes a series of experiments conducted on 'blade-like' fatigue specimens. The specimens were impacted with a cubical projectile at 250 m\\/s using a gas gun. They were subsequently fatigue loaded using the step method of testing to establish the fatigue strength in the damaged state.
D. Nowell; P. Duó; I. F. Stewart
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 of a generic blade and Miner's Rule, the accumulated theoretical damage (based on axial strains) resulting from a fatigue test with variable phase angles was compared to the damage resulting from a fatigue test with a constant phase angle. The nodal damage distribution at specific blade cross-sections are compared for the constant and variable phase angle cases. The sequence effects of various phase angle progressions were also considered. For this analysis, the finite element results were processed using the nonlinear Marco-Starkey damage accumulation model. Each phase angle sequence was constrained to have the same overall phase angle distribution and the same total number of cycles but the order in which the phase angles were applied was varied.
White, D. L.; Musial, W. D.
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
Research on fatigue damage detection for wind turbine blade based on high-spatial-resolution DPP-BOTDA
NASA Astrophysics Data System (ADS)
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
Damage tolerance based life prediction in gas turbine engine blades under vibratory high cycle fatigue
A novel fracture mechanics approach has been used to predict crack propagation lives in gas turbine engine blades subjected to vibratory high cycle fatigue (HCF). The vibratory loading included both a resonant mode and a nonresonant mode, with one blade subjected to only the nonresonant mode and another blade to both modes. A life prediction algorithm was utilized to predict
D. P. Walls; R. E. deLaneuville; S. E. Cunningham
Damage tolerance based life prediction in gas turbine engine blades under vibratory high cycle fatigue
A novel fracture mechanics approach has been used to predict crack propagation lives in gas turbine engine blades subjected to vibratory high cycle fatigue (HCF). The vibratory loading included both a resonant mode and a nonresonant mode, with one blade subjected to only the nonresonant mode and another blade to both modes. A life prediction algorithm was utilized to predict HCF propagation lives for each case. The life prediction system incorporates a boundary integral element (BIE) derived hybrid stress intensity solution, which accounts for the transition from a surface crack to corner crack to edge crack. It also includes a derivation of threshold crack length from threshold stress intensity factors to give crack size limits for no propagation. The stress intensity solution was calibrated for crack aspect ratios measured directly from the fracture surfaces. The model demonstrates the ability to correlate predicted missions to failure with values deduced from fractographic analysis. This analysis helps to validate the use of fracture mechanics approaches for assessing damage tolerance in gas turbine engine components subjected to combined steady and vibratory stresses.
Walls, D.P.; deLaneuville, R.E.; Cunningham, S.E. [United Technologies Pratt and Whitney, West Palm Beach, FL (United States)
An analysis of fatigue damage inflicted to the blades of gas turbine units during their long-term operation on gas mains
NASA Astrophysics Data System (ADS)
Results from studies of factors due to which fatigue damage is inflicted to the turbine and compressor blades of stationary gas turbine units operating at the compressor stations installed on gas mains of Russia are considered.
Dashunin, N. V.; Laskin, A. S.; Getsov, L. B.; Rybnikov, A. I.; Mozhaiskaya, N. V.
Fatigue Analysis of the Compressor Blades with V- Notches
\\u000a This paper presents results of experimental and numerical fatigue analysis of damaged compressor blades, subjected to vibration.\\u000a The blades used in experimental investigations were preliminary defected to simulate the foreign object damage. The crack\\u000a propagation process was conducted in resonance condition. During the fatigue investigations, the crack length and amplitude\\u000a of the blade tip displacement were monitored. The main result
Lucjan Witek
Fatigue life evaluation in composite rotor blade of multipurpose helicopter
The prediction of fatigue life and strength of the composite rotor blade for multipurpose helicopter was studied using a residual strength degradation concept. A flight-by-flight load spectrum was introduced on the basis of FELIX standard data. The composite structure analysis was performed to obtain the local stress near blade root in laminate skin and glass roving spar where fatigue damage
Jung-Ho Kwon; Kyung-Jung Hwang; Seok-Soo Kim; Pan-Jo Kim; Choon-Sam Kim
Fatigue life estimation procedure for a turbine blade under transient loads
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. 16 refs.
Vyas, N.S.; Rao, J.S. (Indian Inst. of Technology, Kanpur (India) Indian Inst. of Technology, New Delhi (India))
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.
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
Damage and fatigue Continuum damage mechanics modeling
Damage and fatigue Continuum damage mechanics modeling for fatigue of materials and structures Cachan Cedex, France firstname.lastname@example.com ABSTRACT. Application of damage mechanics to fatigue damage mechanics (CDM) is a powerful tool to model the degrada- tion of materials, the stress softening
Cumulative fatigue damage models
NASA Technical Reports Server (NTRS)
The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use, can yield grossly unconservative results under certain loading conditions. Research at the NASA Lewis Research Center has led to the development of a nonlinear cumulative damage model, named the double damage curve approach (DDCA), that has greatly improved predictive capability. This model, which considers the life (or loading) level dependence of damage evolution, was applied successfully to two polycrystalline materials, 316 stainless steel and Haynes 188. The cumulative fatigue behavior of the PWA 1480 single-crystal material is currently being measured to determine the applicability of the DDCA for this material.
Mcgaw, Michael A.
Ris-R-1168 (EN) Fatigue damage development
Risø-R-1168 (EN) Fatigue damage development and failure in unidirectional and angle-ply glass fibre are under consideration as the blades are getting larger than 30-40 metres. The tensile fatigue behaviour investigated. Dynamic measurements of mechanical properties were carried out during the fatigue process
Jumplike fatigue crack growth in compressor blades
NASA Astrophysics Data System (ADS)
It is shown that power relations between the two main fractographic characteristics of fracture surfaces forming during jumplike fatigue crack growth, namely, the crack depth and the corresponding crack front length, can be used to estimate the fracture stress during vibration tests of the compressor blades of an aviation gas turbine engine, which are made of VT3-1 titanium alloy.
Limar', L. V.; Demina, Yu. A.; Botvina, L. R.
Composite blade damaging under impact
NASA Astrophysics Data System (ADS)
Composites materials are now being used in primary aircraft structures, and other domains because of numerous advantages. A part of a continuous in-flight operating costs, gas turbine engine manufacturers are always looking for ways to decrease engine weight. This is the case of compressor blades which have to satisfy, for example, the standard bird strike or debris in order to measure the crashworthiness. Bird strike impacts are actually among the most challenging loads that composite blades must accommodate. Thus for the further development of composite structures, it becomes important to have available predictive tools for simulating the response of composite structures under crash or impact loads, which will allow to evaluate damage state in the structure in function of time. A composites damage model, without mesh dependency, is presented, and allows to obtain agreement with impact experiment. Examples of finite element simulations for the impact response of blade based on this materials model are developped. These numerical results correspond to a bird strike on an equivalent composites blade, and insists on damage evolution in structure.
Menouillard, T.; Réthoré, J.; Bung, H.; Suffis, A.
Modeling of cumulative fatigue damage
NASA Astrophysics Data System (ADS)
An investigation of cumulative fatigue damage under condition of block cyclic loading is presented. The general form of a damage function including the influence of loading history on cumulative damage is presented.
Golos, Krzysztof M.; Osinski, Zbigniew
Probabilistic Evaluation of Blade Impact Damage
NASA Technical Reports Server (NTRS)
The response to high velocity impact of a composite blade is probabilistically evaluated. The evaluation is focused on quantifying probabilistically the effects of uncertainties (scatter) in the variables that describe the impact, the blade make-up (geometry and material), the blade response (displacements, strains, stresses, frequencies), the blade residual strength after impact, and the blade damage tolerance. The results of probabilistic evaluations results are in terms of probability cumulative distribution functions and probabilistic sensitivities. Results show that the blade has relatively low damage tolerance at 0.999 probability of structural failure and substantial at 0.01 probability.
Chamis, C. C.; Abumeri, G. H.
Probabilistic Fatigue Damage Program (FATIG)
NASA Technical Reports Server (NTRS)
FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.
Michalopoulos, Constantine
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 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.
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 each wind speed. The Rayleigh probability density function allows the distribution of vibratory stresses to be described by the RMS of the stress vs. time signal. With the RMS stress level described for all wind speeds, the complete stress history of the turbine blades is known. Miner's linear cumulative damage rule is used as a basis for summing the fatigue damage over all operating conditions. An analytical expression is derived to predict blade fatigue life.
Veers, P.S.
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 each wind speed. The Rayleigh probability density function allows the distribution of vibratory stresses to be described by the RMS of the stress vs. time signal. With the RMS stress level described for all wind speeds, the complete stress history of the turbine blades is known. Miner's linear cumulative damage rule is used as a basis for summing the fatigue damage over all operating conditions. An analytical expression is derived to predict blade fatigue life.
Veers, P.S.
Fatigue of Wind Blade Laminates:Fatigue of Wind Blade Laminates: Effects of Resin and Fabric Structure
Fatigue of Wind Blade Laminates:Fatigue of Wind Blade Laminates: Effects of Resin and Fabric Materials · Recent Findings, Resin and Fabric Structure Interactions for InfusedStructure Interactions and potential fibers, fabrics, resins, fiber sizings, processes, processing aids, laminate lay-ups, fiber
A review of damage detection methods for wind turbine blades
NASA Astrophysics Data System (ADS)
Wind energy is one of the most important renewable energy sources and many countries are predicted to increase wind energy portion of their whole national energy supply to about twenty percent in the next decade. One potential obstacle in the use of wind turbines to harvest wind energy is the maintenance of the wind turbine blades. The blades are a crucial and costly part of a wind turbine and over their service life can suffer from factors such as material degradation and fatigue, which can limit their effectiveness and safety. Thus, the ability to detect damage in wind turbine blades is of great significance for planning maintenance and continued operation of the wind turbine. This paper presents a review of recent research and development in the field of damage detection for wind turbine blades. Specifically, this paper reviews frequently employed sensors including fiber optic and piezoelectric sensors, and four promising damage detection methods, namely, transmittance function, wave propagation, impedance and vibration based methods. As a note towards the future development trend for wind turbine sensing systems, the necessity for wireless sensing and energy harvesting is briefly presented. Finally, existing problems and promising research efforts for online damage detection of turbine blades are discussed.
Li, Dongsheng; Ho, Siu-Chun M.; Song, Gangbing; Ren, Liang; Li, Hongnan
High Sensitive Methods for Health Monitoring of Compressor Blades and Fatigue Detection
The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF) have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM), experimental modal analysis (EMA) and tip timing (TTM) methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy), have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed. PMID:24191135
Wito?, Miros?aw
High sensitive methods for health monitoring of compressor blades and fatigue detection.
The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF) have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM), experimental modal analysis (EMA) and tip timing (TTM) methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy), have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed. PMID:24191135
Wito?, Miros?aw
Loading Analysis of Composite Wind Turbine Blade for Fatigue Life Prediction of Adhesively Bonded Root Joint
NASA Astrophysics Data System (ADS)
Nowadays wind energy is widely used as a non-polluting cost-effective renewable energy resource. During the lifetime of a composite wind turbine which is about 20 years, the rotor blades are subjected to different cyclic loads such as aerodynamics, centrifugal and gravitational forces. These loading conditions, cause to fatigue failure of the blade at the adhesively bonded root joint, where the highest bending moments will occur and consequently, is the most critical zone of the blade. So it is important to estimate the fatigue life of the root joint. The cohesive zone model is one of the best methods for prediction of initiation and propagation of debonding at the root joint. The advantage of this method is the possibility of modeling the debonding without any requirement to the remeshing. However in order to use this approach, it is necessary to analyze the cyclic loading condition at the root joint. For this purpose after implementing a cohesive interface element in the Ansys finite element software, one blade of a horizontal axis wind turbine with 46 m rotor diameter was modelled in full scale. Then after applying loads on the blade under different condition of the blade in a full rotation, the critical condition of the blade is obtained based on the delamination index and also the load ratio on the root joint in fatigue cycles is calculated. These data are the inputs for fatigue damage growth analysis of the root joint by using CZM approach that will be investigated in future work.
Salimi-Majd, Davood; Azimzadeh, Vahid; Mohammadi, Bijan
Scale levels for fatigue fracture mechanisms of in-service crack growth in longerons of helicopter rotor blades
Cases of in-service fatigue crack growth in aluminium longerons of helicopter Mi-8 rotor blades were reviewed. Fatigue fracture\\u000a surface patterns for micro- and meso-scale levels of crack growth mechanisms for in-service fatigued longerons are discussed.\\u000a Meso-beach-marks were used to estimate the fatigue crack growth period in one of the damaged longerons with the least crack\\u000a size. Results of these estimations
A. A. Shaniavski
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 to obtain a Goodman Diagram that is suitable for analyzing wind turbine blades. The LIFE2 fatigue analysis code for wind turbines is then used for the fatigue analysis of a typical turbine blade with a known load spectrum. In the analysis, a linear damage model, Miner`s Rule, is used to demonstrate the prediction of the service lifetime for a typical wind turbine blade under assumed operating strain ranges and stress concentration factors. In contrast to typical European data, the asymmetry in this data base predicts failures under typical loads to be compressive.
Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States); Mandell, J.F. [Montana State Univ., Bozeman, MT (United States)
Damage identification by NSMS blade resonance tracking in mistuned rotors
Damage in rotor blades, including cracks, tend to shift the blades' resonant frequencies. Blade resonances have thus been envisioned as a damage indicator. This paper studies issues that arise in blade resonance identification using Non-contacting Stress Monitoring Systems (NSMS) when blade resonances have slight variation (mistuning) and are dynamically coupled. The study compares simulation results to experimental data obtained during
Mathieu Mercadal; Andy von Flotow; Peter Tappert
Analysis of aeroelastic loads and their contributions to fatigue damage
NASA Astrophysics Data System (ADS)
The paper presents an analysis of the aeroelastic loads on a wind turbine in normal operation. The characteristic of the loads causing the highest fatigue damage are identified, so to provide indications to the development of active load alleviation systems for smart- rotor applications. Fatigue analysis is performed using rain-flow counting and Palmgren-Miner linear damage assumption; the contribution to life-time fatigue damage from deterministic load variations is quantified, as well as the contributions from operation at different mean wind speeds. A method is proposed to retrieve an estimation of the load frequencies yielding the highest fatigue contributions from the bending moment spectra. The results are in good agreement with rain-flow counting analysis on filtered time series, and, for the blade loads, show dominant contributions from frequencies close to the rotational one; negligible fatigue contributions are reported for loads with frequencies above 2 Hz.
Bergami, L.; Gaunaa, M.
Assessment of fatigue life for small composite wind turbine blades
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
Cumulative fatigue damage dynamic interference statistical model
After studying in depth the statistical characteristics of cumulative fatigue damage D(t) and its critical value Dc, a new dynamic interference statistical model for fatigue reliability analysis is presented in this paper. Because the non-linearity of fatigue damage accumulation has been taken into account, this model is able to predict the fatigue reliability for random spectrum loading. To verify the
Liao Min; Xu Xiaofei; Yang Qing-Xiong
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 type of deformation occurred in two areas of the upper skin of the blade. One of these was near the blade root and the other was about the middle of the tested portion of the blade. The emission monitoring indicated that no damage was taking place in the area near the root, but in the deforming area near the middle of the blade, damage occurred from the first cycles at the higher load. The test was stopped after approximately one day and the blade was declared destroyed, although no gross damage had occurred. Several weeks later the test was resumed, to be continued until gross damage occurred. The upper skin tore approximately one half hour after the cycling was restarted.
Beattie, A.G.
Fatigue Failure of Space Shuttle Main Engine Turbine Blades
NASA Technical Reports Server (NTRS)
Experimental validation of finite element modeling of single crystal turbine blades is presented. Experimental results from uniaxial high cycle fatigue (HCF) test specimens and full scale Space Shuttle Main Engine test firings with the High Pressure Fuel Turbopump Alternate Turbopump (HPFTP/AT) provide the data used for the validation. The conclusions show the significant contribution of the crystal orientation within the blade on the resulting life of the component, that the analysis can predict this variation, and that experimental testing demonstrates it.
Swanson, Gregrory R.; Arakere, Nagaraj K.
Structural damage identification in wind turbine blades using piezoelectric active sensing with ultrasonic validation
This paper gives a brief overview of a new project at LANL in structural damage identification for wind turbines. This project makes use of modeling capabilities and sensing technology to understand realistic blade loading on large turbine blades, with the goal of developing the technology needed to automatically detect early damage. Several structural health monitoring (SHM) techniques using piezoelectric active materials are being investigated for the development of wireless, low power sensors that interrogate sections of the wind turbine blade using Lamb wave propagation data, frequency response functions (FRFs), and time-series analysis methods. The modeling and sensor research will be compared with extensive experimental testing, including wind tunnel experiments, load and fatigue tests, and ultrasonic scans - on small- to mid-scale turbine blades. Furthermore, this study will investigate the effect of local damage on the global response of the blade by monitoring low-frequency response changes.
Claytor, Thomas N [Los Alamos National Laboratory; Ammerman, Curtt N [Los Alamos National Laboratory; Park, Gyu Hae [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory; Atterbury, Marie K [Los Alamos National Laboratory
Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis
NASA Astrophysics Data System (ADS)
Canada has aggressive targets for introducing wind energy across the country, but also faces challenges in achieving these goals due to the harsh Canadian climate. One issue which has received little attention in other countries not experiencing these extremes is the behaviour of composite blades in winter conditions. The scope of the work presented is to analyze the static stresses and fatigue response in cold climates using finite element models of the blade. The work opens with a quantification of the extremes of cold experienced in candidate Canadian wind turbine deployment locations. The thesis then narrows its focus to a consideration of the stresses in the root of the composite blades, specifically two common blade-hub connection methods: embedded root carrots and T-bolts. Finite element models of the root are proposed to properly simulate boundary conditions, applied loading and thermal stresses for a 1.5 MW wind turbine. It is shown that the blade root is strongly affected by the thermal stresses caused by the mismatch and orthotrophy of the coefficients of thermal expansion of the blade root constituents. Fatigue analysis of a blade is then presented using temperature dependent material properties including estimated fatigue coefficients.It was found that the natural frequencies of a 1.5 MW wind turbine blade are not significantly altered at cold temperatures. Additionally, cold temperatures slightly increase stresses in the composite blade skin when the blade is loaded, due to an increase in stiffness. Cold temperatures also lead to higher cyclic flapwise bending moments acting on the blade. However, this increase was found not to affect the lifetime fatigue damage. Finally, it was found that the cold climate as seen in Canada improves the fatigue strength of the saturated composite materials used in the blade. The predicted fatigue damage of the triaxial fabric and the spar cap layers in cold climates was therefore predicted to be half that of the fatigue damage at room temperature. This is caused solely by the temperature dependence of the fatigue coefficient b which requires further experimental verification to validate the numerical results of the current study.
Lillo Gallardo, Patricio Andres
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 at 25% of its design load, and then with steadily increasing loads until it failed. Various data were collected between and during fatigue loading sessions. The data were measured over multiple frequency ranges using a variety of acquisition equipment, including off-the-shelf systems and specially designed hardware developed by the authors. Modal response, diffuse wave-field transfer functions, and ultrasonic guided wave methods were applied to assess the condition of the wind turbine blade. The piezoelectric sensors themselves were also monitored using a sensor diagnostics procedure. This paper summarizes experimental procedures and results, focusing particularly on fatigue crack detection, and concludes with considerations for implementing such damage identification systems, which will be used as a guideline for future SHM system development for operating wind turbine blades.
Taylor, Stuart G. [Los Alamos National Laboratory; Farinholt, Kevin M. [Los Alamos National Laboratory; Jeong, Hyomi [Chonbuk National University, Korea; Jang, JaeKyung [Chonbuk National University, Korea; Park, Gyu Hae [Los Alamos National Laboratory; Todd, Michael D. [Los Alamos National Laboratory; Farrar, Charles R. [Los Alamos National Laboratory; Ammerman, Curtt N. [Los Alamos National Laboratory
Microstructural evaluation of cumulative fatigue damage below the fatigue limit
The objective of this work is to evaluate the microstructural changes induced near and below the fatigue limit in a pressure vessel steel plate, SA508. Dislocation cell to cell misorientation differences, {theta}, which increase with fatigue damage accumulation, are measured by the Selected Area Diffraction (SAD) method. The misorientation difference, {theta}, of the sample failed just above the fatigue limit is about 4.0 degrees on the average, which is about the same as that for the failure conditions of low cycle fatigue at higher stresses. The {theta} value increases even below the fatigue limit, but it does not increase at stresses which are lower than 50% of the fatigue limit.
Fukuoka, C.; Nakagawa, Y.G. [IHI, Tokyo (Japan). Research Inst.] [IHI, Tokyo (Japan). Research Inst.
Mechanics and mechanisms of fatigue damage and crack growth in advanced materials
and gas-turbines blades. Whereas these materials oer vastly improved speci®c strength at high temperaturesMechanics and mechanisms of fatigue damage and crack growth in advanced materials R.O. Ritchie*, C 94720-1760, USA Abstract The mechanisms of fatigue-crack propagation in ceramics and intermetallics
Ritchie, Robert
Procedure for estimating the fatigue strength of gas turbine blades by method of acoustic emission
For the purpose of estimating the fatigue characteristics of blades of gas turbine engines in industrial laboratories, one subjects a control lot of such blades to fatigue tests until the first symptoms of fracture appear. As such a symptom one usually regards a decrease of the natural frequency of the blade fin by a certain amount. Experience in such testing
M. D. Banov; E. A. Konyaev; D. A. Troenkin
Nonlinear fatigue damage accumulation under random loading
The analytical expressions for the probability densities of the cumulative fatigue damage and fatigue life and for the reliability function are obtained for a mechanical or structural component subject to stationary random stress process on the basis of a stochastic theory of fatigue damage accumulation proposed by the first author and his co-worker and the Morrow`s nonlinear damage rule. The comparison between the results from Morrow`s and Palmgren-Miner`s damage rules for the case when the stress is a narrow-band stationary Gaussian process with zero mean is made and some important conclusions are drawn.
Zhu, W.Q.; Jiang, M.X. [Zhejiang Univ., Hangzhou (China). Dept. of Mechanics
The static and fatigue computation of the propeller blades retention system
NASA Astrophysics Data System (ADS)
The static and the fatigue computation of the propeller blades retention system to the monobloc hub with four blades is considered. The retention system contains a three-row ball bearing. The steel balls in parallel circumferential rows are placed around the blade root and are working along raceways of the blade retaining socket and those of the barrel.
Martin, Olga
Fatigue and damage tolerance scatter models
NASA Technical Reports Server (NTRS)
Effective Total Fatigue Life and Crack Growth Scatter Models are proposed. The first of them is based on the power form of the Wohler curve, fatigue scatter dependence on mean life value, cycle stress ratio influence on fatigue scatter, and validated description of the mean stress influence on the mean fatigue life. The second uses in addition are fracture mechanics approach, assumption of initial damage existence, and Paris equation. Simple formulas are derived for configurations of models. A preliminary identification of the parameters of the models is fulfilled on the basis of experimental data. Some new and important results for fatigue and crack growth scatter characteristics are obtained.
Raikher, Veniamin L.
Novelty detection applied to vibration data from a CX-100 wind turbine blade under fatigue loading
NASA Astrophysics Data System (ADS)
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 the entire wind turbine. In this study the SHM analysis will be based on experimental measurements of Frequency Response Functions (FRFs) extracted by using an input/output acquisition technique under a fatigue loading of a 9m CX-100 blade at the National Renewable Energy Laboratory (NREL) and National Wind Technology Center (NWTC) performed in the Los Alamos National Laboratory. The blade was harmonically excited at its first natural frequency using a Universal Resonant Excitation (UREX) system. For analysis, the Auto-Associative Neural Network (AANN) is a non-parametric method where a set of damage sensitive features gathered from the measured structure are used to train a network that acts as a novelty detector. This traditionally has a highly complex "bottleneck" structure with five layers in the AANN. In the current paper, a new attempt is also exploited based on an AANN with one hidden layer in order to reduce the theoretical and computational difficulties. Damage detection of composite bodies of blades is a "grand challenge" due to varying aerodynamic and gravitational loads and environmental conditions. A study of the noise tolerant capability of the AANN which is associated to its generalisation capacity is addressed. It will be shown that vibration response data combined with AANNs is a robust and powerful tool, offering novelty detection even when operational and environmental variations are present. The AANN is a method which has not yet been widely used in the structural health monitoring of composite blades.
Dervilis, N.; Choi, M.; Antoniadou, I.; Farinholt, K. M.; Taylor, S. G.; Barthorpe, R. J.; Park, G.; Worden, K.; Farrar, C. R.
Analysis of Fretting Fatigue Strength of Integral Shroud Blade for Steam Turbine
NASA Astrophysics Data System (ADS)
To improve the reliability and the thermal efficiency of LP (Low Pressure) end blades of steam turbine, new standard series of LP end blades have been developed. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. One of the probable failure modes of the ISB structure seems to be fretting fatigue, because the ISB utilizes friction damping between adjacent shrouds and stubs. Therefore, in order to design a blade with high reliability, the design procedure for evaluating the fretting fatigue strength was established by the model test and the nonlinear contact analysis. This paper presents the practical design method for predicting the fretting fatigue strength of the ISB structure, and the some applications are explained.
Kaneko, Yasutomo; Tomii, Masayuki; Ohyama, Hiroharu; Kurimura, Takayuki
Blade reliability collaborative : collection of defect, damage and repair data.
The Blade Reliability Collaborative (BRC) was started by the Wind Energy Technologies Department of Sandia National Laboratories and DOE in 2010 with the goal of gaining insight into planned and unplanned O&M issues associated with wind turbine blades. A significant part of BRC is the Blade Defect, Damage and Repair Survey task, which will gather data from blade manufacturers, service companies, operators and prior studies to determine details about the largest sources of blade unreliability. This report summarizes the initial findings from this work.
Ashwill, Thomas D.; Ogilvie, Alistair B.; Paquette, Joshua A.
77 FR 4890 - Damage Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures, and Damage Tolerance...
Federal Register 2010, 2011, 2012, 2013, 2014
...2120-AJ51 Damage Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures, and Damage Tolerance and Fatigue Evaluation for Metallic Structures...final rules, ``Damage Tolerance and Fatigue Evaluation for Composite...
Reliability assessment of high cycle fatigue design of gas turbine blades using the probabilistic Goodman Diagram
A probability-based procedure has been developed to predict the reliability of gas turbine engine blades subjected to high cycle fatigue. The procedure provides a systemic approach for predicting and designing turbomachinery blading reliability against various potential high cycle fatigue problems for all relevant vibratory modes, and taking into account variability in geometry (e.g. dimensional variation, surface smoothness, etc.). The variability
M.-H. Herman Shen
The relationship between observed fatigue damage and life estimation models
NASA Technical Reports Server (NTRS)
Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.
Kurath, Peter; Socie, Darrell F.
A model of continuum damage mechanics for fatigue failure
This paper describes the development of a generalized model of continuum damage mechanics for fatigue fracture. With the introduction of a new damage effect tensor, the necessary constitutive equations of elasticity and plasticity coupled with damage are for the first instance derived. This is followed by the formulations of fatigue damage dissipative potential function and a fatigue damage criterion which
C. L. Chow; Y. Wei
An investigation of fatigue failures of turbine blades in a gas turbine engine by mechanical analysis
Blade failures in gas turbine engines often lead to loss of all downstream stages and can have a dramatic effect on the availability of the turbine engines. Thorough failure investigation is essential for the effective management of engine airworthiness. In this paper blade fatigue failures are investigated by mechanical analyses and by examination of failed blades. A series of mechanical
Jianfu Hou; Bryon J Wicks; Ross A Antoniou
The objective of the program was to demonstrate and verify Certification-by-Analysis (CBA) capability for wind turbine blades made from advanced lightweight composite materials. The approach integrated durability and damage tolerance analysis with robust design and virtual testing capabilities to deliver superior, durable, low weight, low cost, long life, and reliable wind blade design. The GENOA durability and life prediction software suite was be used as the primary simulation tool. First, a micromechanics-based computational approach was used to assess the durability of composite laminates with ply drop features commonly used in wind turbine applications. Ply drops occur in composite joints and closures of wind turbine blades to reduce skin thicknesses along the blade span. They increase localized stress concentration, which may cause premature delamination failure in composite and reduced fatigue service life. Durability and damage tolerance (D&DT) were evaluated utilizing a multi-scale micro-macro progressive failure analysis (PFA) technique. PFA is finite element based and is capable of detecting all stages of material damage including initiation and propagation of delamination. It assesses multiple failure criteria and includes the effects of manufacturing anomalies (i.e., void, fiber waviness). Two different approaches have been used within PFA. The first approach is Virtual Crack Closure Technique (VCCT) PFA while the second one is strength-based. Constituent stiffness and strength properties for glass and carbon based material systems were reverse engineered for use in D&DT evaluation of coupons with ply drops under static loading. Lamina and laminate properties calculated using manufacturing and composite architecture details matched closely published test data. Similarly, resin properties were determined for fatigue life calculation. The simulation not only reproduced static strength and fatigue life as observed in the test, it also showed composite damage and fracture modes that resemble those reported in the tests. The results show that computational simulation can be relied on to enhance the design of tapered composite structures such as the ones used in turbine wind blades. A computational simulation for durability, damage tolerance (D&DT) and reliability of composite wind turbine blade structures in presence of uncertainties in material properties was performed. A composite turbine blade was first assessed with finite element based multi-scale progressive failure analysis to determine failure modes and locations as well as the fracture load. D&DT analyses were then validated with static test performed at Sandia National Laboratories. The work was followed by detailed weight analysis to identify contribution of various materials to the overall weight of the blade. The methodology ensured that certain types of failure modes, such as delamination progression, are contained to reduce risk to the structure. Probabilistic analysis indicated that composite shear strength has a great influence on the blade ultimate load under static loading. Weight was reduced by 12% with robust design without loss in reliability or D&DT. Structural benefits obtained with the use of enhanced matrix properties through nanoparticles infusion were also assessed. Thin unidirectional fiberglass layers enriched with silica nanoparticles were applied to the outer surfaces of a wind blade to improve its overall structural performance and durability. The wind blade was a 9-meter prototype structure manufactured and tested subject to three saddle static loading at Sandia National Laboratory (SNL). The blade manufacturing did not include the use of any nano-material. With silica nanoparticles in glass composite applied to the exterior surfaces of the blade, the durability and damage tolerance (D&DT) results from multi-scale PFA showed an increase in ultimate load of the blade by 9.2% as compared to baseline structural performance (without nano). The use of nanoparticles lead to a delay in the onset of delamination. Load-displacement relati
Galib Abumeri; Frank Abdi (PhD)
Stochastic fatigue damage accumulation under broadband loadings
Fatigue tests were conducted on 72 high-strength welded steel cruciform-shaped specimens subjected to stochastic loadings. Results of these tests are used to investigate experimentally the effects of loading non-normality and frequency bandwidth and truncation on the rate of fatigue damage accumulation. Test results are compared with predictions made using Rayleigh approximation and rainflow analysis in terms of cycles and time
D. P. Kihl; S. Sarkani; J. E. Beach
1 AIAA-2003-0692 NEW FATIGUE DATA FOR W IND TURBINE BLADE M ATERIALS John F. Mandell, Daniel D of the University of Montana Butte, Montana 59701 ABSTRACT This paper reports on recent fatigue data of interest) effects of fiber waviness; and (d) large tow carbon fibers. Tensile fatigue results from a specialized
Combined wind turbine fatigue and ultimate load reduction by individual blade control
NASA Astrophysics Data System (ADS)
If each blade of the wind turbine has individual pitch actuator, there is possibility of employing the pitch system to mitigate structural loads through advanced control methods. Previously, considerable reduction of blade lifetime equivalent fatigue loads has been achieved by Individual Blade Control (IBC) and in addition, it has also been shown the potential in blade ultimate loads reduction. However, both fatigue and ultimate loads impact on the design and life of wind turbine blades. In this paper, the design and application of IBC that concurrently reduce both blade fatigue and ultimate loads is investigated. The contributions of blade load spectral components, which are 1P, 2P and edgewise mode from blade in-plane and/or out-of-plane bending moments, are firstly explored. Four different control options for reducing various combinations of these load components are compared. In response to the different spectral peaks of both fatigue and ultimate loads, the controller has been designed so that it can act on different frequency components which vary with wind speed. The performance of the IBC controller on fatigue and ultimate load reduction is assessed by simulating a 5MW exemplar wind turbine. Simulation results show that with a proper selection of controlling inputs at different wind speed, the use of a single combined IBC can achieve satisfactory reduction on both fatigue and ultimate loads.
Han, Y.; Leithead, W. E.
Fatigue of Composite Materials and Substructures for Wind Turbine Blades
This report presents the major findings of the Montana State University Composite Materials Fatigue Program from 1997 to 2001, and is intended to be used in conjunction with the DOE/MSU Composite Materials Fatigue Database. Additions of greatest interest to the database in this time period include environmental and time under load effects for various resin systems; large tow carbon fiber laminates and glass/carbon hybrids; new reinforcement architectures varying from large strands to prepreg with well-dispersed fibers; spectrum loading and cumulative damage laws; giga-cycle testing of strands; tough resins for improved structural integrity; static and fatigue data for interply delamination; and design knockdown factors due to flaws and structural details as well as time under load and environmental conditions. The origins of a transition to increased tensile fatigue sensitivity with increasing fiber content are explored in detail for typical stranded reinforcing fabrics. The second focus of the report is on structural details which are prone to delamination failure, including ply terminations, skin-stiffener intersections, and sandwich panel terminations. Finite element based methodologies for predicting delamination initiation and growth in structural details are developed and validated, and simplified design recommendations are presented.
Cumulative Damage Models and Multi-Stress Fatigue Life Prediction
Cumulative damage during fatigue is studied analytically. Extensive reviews are per formed on the published damage models. Three different cumulative damage models are defined using several physical variables such as fatigue modulus and resultant strain. Proposed model I is defined using fatigue modulus, while models II and III are defined using resultant strains. Proposed models are derived as functions of
W. Hwang; K. S. Han
Procedure for estimating the fatigue strength of gas turbine blades by method of acoustic emission
For the purpose of estimating the fatigue characteristics of blades of gas turbine engines in industrial laboratories, one subjects a control lot of such blades to fatigue tests until the first symptoms of fracture appear. As such a symptom one usually regards a decrease of the natural frequency of the blade fin by a certain amount. Experience in such testing indicates that this criterion is applicable only when a fatigue crack has become sufficiently long. In many cases the natural frequency has been found to change nonmonotonically, moreover, owing to defectiveness buildup and changes in the forces constraining the test object in the course of testing. These circumstances call for new methods of objective determination of the fatigue strength when active blades of gas turbine engines are under test. In this study the method of acoustic emission is considered from such a standpoint.
Banov, M.D.; Konyaev, E.A.; Troenkin, D.A.
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 coupling to passively alleviate aerodynamic loads. In the fatigue tests, the CX-100 blade was loaded by a single hydraulic cylinder while the TX-100 blade was loaded via a hydraulically-actuated resonant loading system called the Universal Resonant Exciter. The blades were outfitted with approximately 30 strain gages as well as displacement and load sensors. Both blades survived to cycle counts sufficient to demonstrate a 20-year operational life. The CX-100 blade failed at approximately 1.6 million cycles because of a buckle and crack that formed and grew just outboard of max-chord. The TX-100 blade failed because of a crack that grew from the termination point of the spar cap at the midspan of the blade. This paper covers the results of the fatigue tests.
Paquette, J.; van Dam, J.; Hughes, S.; Johnson, J.
Evaluation of a threshold-based model of fatigue in gamma titanium aluminide following impact damage
NASA Astrophysics Data System (ADS)
Recent interest in gamma titanium aluminide (gamma-TiAl) for use in gas turbine engine applications has centered on the low density and good elevated temperature strength retention of gamma-TiAl compared to current materials. However, the relatively low ductility and fracture toughness of gamma-TiAl leads to serious concerns regarding its ability to resist impact damage. Furthermore, the limited fatigue crack growth resistance of gamma-TiAl means that the potential for fatigue failures resulting from impact damage is real if a damage tolerant design approach is used. A threshold-based design approach may be required if fatigue crack growth from potential impact sites is to be avoided. The objective of the present research is to examine the feasibility of a threshold-based approach for the design of a gamma-TiAl low-pressure turbine blade subjected to both assembly-related impact damage and foreign object damage. Specimens of three different gamma-TiAl alloys were damaged in such a way as to simulate anticipated impact damage for a turbine blade. Step-loading fatigue tests were conducted at both room temperature and 600°C. In terms of the assembly-related impact damage, the results indicate that there is reasonably good agreement between the threshold-based predictions of the fatigue strength of damaged specimens and the measured data. However, some discrepancies do exist. In the case of very lightly damaged specimens, prediction of the resulting fatigue strength requires that a very conservative small-crack fatigue threshold be used. Consequently, the allowable design conditions are significantly reduced. For severely damaged specimens, an analytical approach found that the potential effects of residual stresses may be related to the discrepancies observed between the threshold-based model and measured fatigue strength data. In the case of foreign object damage, a good correlation was observed between impacts resulting in large cracks and a long-crack threshold-based approximation of the fatigue strength. However, in the case of smaller impact sites, a lower small-crack threshold appears to be more appropriate. In some cases, a complete perforation of the material, or blowout, would result from the impact. Prediction of the reduction in fatigue strength resulting from this form of damage required the use of a stress concentration factor, rather than a threshold-based prediction.
Harding, Trevor Scott
Constitutive Modeling of Material Damage for Fatigue Failure Prediction
This paper presents a constitutive modeling of material damage capable of characterizing fatigue damage and plastic damage for rate-independent materials under multiaxial loading with the theory of damage mechanics. First, an internal state variable known as the damage variable is introduced with two scalars to characterize material degradation due to the change of material microstructures under fatigue. Then, depending upon
C. L. Chow; Y. Wei
Brittleness Effect on Rock Fatigue Damage Evolution
NASA Astrophysics Data System (ADS)
The damage evolution mechanism of rocks is one of the most important aspects in studying of rock fatigue behavior. Fatigue damage evolution of three rock types (onyx marble, sandstone and soft limestone) with different brittleness were considered in the present study. Intensive experimental tests were conducted on the chosen rock samples and acoustic emission (AE) sensors were used in some of them to monitor the fracturing process. Experimental tests indicated that brittleness strongly influences damage evolution of rocks in the course of static and dynamic loading. AE monitoring revealed that micro-crack density induced by the applied loads during different stages of the failure processes increases as rock brittleness increases. Also, results of fatigue tests on the three rock types indicated that the rock with the most induced micro-cracks during loading cycles has the least fatigue life. Furthermore, the condition of failure surfaces of the studied rocks samples, subjected to dynamic and static loading, were evaluated and it was concluded that the roughness of failure surfaces is influenced by loading types and rock brittleness. Dynamic failure surfaces were rougher than static ones and low brittle rock demonstrate a smoother failure surface compared to high brittle rock.
Nejati, Hamid Reza; Ghazvinian, Abdolhadi
Cumulative fatigue damage behavior of MAR M-247
The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF
Michael A. McGaw; Gary R. Halford; Sreeramesh Kalluri
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
Fatigue life variability and reliability analysis of a wind turbine blade
NASA Astrophysics Data System (ADS)
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 variability of the input parameters is modeled to obtain estimates of the fatigue reliability of the turbine blades.
Veers, P. S.; Sutherland, H. J.; Ashwill, T. D.
Effects of Glass Fabric and Laminate Construction on the Fatigue of Resin Infused Blade Materials
Effects of Glass Fabric and Laminate Construction on the Fatigue of Resin Infused Blade Materials fabrics with epoxy resins over a range of fiber contents. Significant improvements in tensile fatigue on fabric architecture and stitching details. All stitched fabric laminates show a transition to lower
Astudy on life prediction of low cycle fatigue in superalloy for gas turbine blades
A more accurate life prediction for gas turbine blade takes into account the material behaviour under the Low Cycle Fatigue cycles normally encountered in turbine operation. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are
Jae-Hoon Kim; Ho-Young Yang; Keun-Bong Yoo
Mixed Mode Static and Fatigue Crack Growth in Wind Blade Paste Adhesives
, then adhesively bonded together. The large size coupled with cost constraints result in bond lines at least1 Mixed Mode Static and Fatigue Crack Growth in Wind Blade Paste Adhesives Daniel D. Samborsky and fatigue crack growth in thick adhesive joints with fiberglass laminate adherends, for three adhesive
Use of the WEST-1 wind turbine simulator to predict blade fatigue load distribution
NASA Technical Reports Server (NTRS)
To test the ability of WEST-1 to predict blade fatigue load distribution, actual wind signals were fed into the simulator and the response data were recorded and processed in the same manner as actual wind turbine data. The WEST-1 simulator was operated in a stable, unattended mode for six hours. The probability distribution of the cyclic flatwise bending moment for the blade was comparable to that for an actual wind turbine in winds with low turbulence. The input from a stationary anemometer was found to be inadequate for use in the prediction of fatigue load distribution for blade design purposes and modifications are necessary.
Janetzke, D. C.
Cumulative fatigue damage modeling—crack nucleation and early growth
Prior research into linear and nonlinear fatigue damage accumulation in metals and alloys is briefly reviewed, and general trends are identified. Nonlinear damage rules offer substantially more accurate, and hence less unconservative, fatigue life predictions than the classical linear damage rule (LDR). Increased accuracy does not require excessive cost of analysis or additional databases. The nonlinear damage curve approach and
Gary R Halford
Laboratory testing of wind turbine blades is required to meet wind turbine design standards, reduce machine cost, and reduce the technical and fi nancial risks of deploying mass-produced wind turbine models. Fatigue testing at the National Wind Technology Center (NWTC) is currently conducted using Universal Resonance Excitation (UREX) technology. In a UREX test, the blade is mounted to a rigid stand and hydraulic exciters mounted to the blade are used to excite the blade to its resonant frequency. A drawback to UREX technology is that mounting hydraulic systems to the blade is diffi cult and requires a relatively long set-up period. An alternative testing technology called the Mobile Oscillatory Fatigue Operator (MOFO) has been analyzed. The MOFO uses an oscillating blade test-stand rather than a rigid stand, avoiding the need to place hydraulic systems on the blade. The MOFO will be demonstrated by converting an existing test-stand at the NWTC to an oscillating stand that can test blades up to 25 m in length. To obtain the loads necessary to design the MOFO, the system motion is modeled using rigid body and lumped mass dynamics models. Preliminary modeling indicates the existing stand can be converted to a MOFO relatively easily. However, the blade dynamic models suggest that blade bending moment distributions are signifi cantly different for UREX and MOFO testing; more sophisticated models are required to assess the implication of this difference on the accuracy of the test.
Donohoo, P.E.; Cotrell, J.
The—S\\/N—Fatigue-life gage: A direct means of measuring cumulative fatigue damage
This paper describes the present state of development of a new type of sensor, a fatigue-life gage which generates an irreversible resistance change that is a continuous function of the fatigue experience of the structure to which it is attached. The gage accumulates fatigue-damage information whether or not it is connected to excitation or readout devices. Measurements of cumulative fatigue
Darrell R. Harting
Blade fatigue life assessment with application to VAWTs
NASA Astrophysics Data System (ADS)
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 the stress levels at each wind speed. Miner's cumulative damage rule is examined as a tool to generate a vibratory stress level distribution in terms of peak vibrations in a narrow-band Gaussian process. Examples are given for 30-40 sec intervals on the 17 m VAWT at Sandia Laboratories. A threshold was set beneath which no vibrations were recorded, yielding a Rayleigh distribution at the 0.5 significance level. It is concluded that a Rayleigh distribution from test data produces a cycle to failure versus wind speed curve which is superior to constant amplitude fatigue life data such as appropriate to Miner's Rule.
Veers, P. S.
Effect of Impact Damage on the Fatigue Response of TiAl Alloy-ABB-2
NASA Technical Reports Server (NTRS)
The ability of gamma-TiAl to withstand potential foreign or domestic object damage is a technical risk to the implementation of gamma-TiAl in low pressure turbine (LPT) blade applications. In the present study, the impact resistance of TiAl alloy ABB-2 was determined and compared to the impact resistance of Ti(48)Al(2)Nb(2)Cr. Specimens were impacted with four different impact conditions with impact energies ranging from 0.22 to 6.09 J. After impacting, the impact damage was characterized by crack lengths on both the front and backside of the impact. Due to the flat nature of gamma-TiAl's S-N (stress vs. cycles to failure) curve, step fatigue tests were used to determine the fatigue strength after impacting. Impact damage increased with increasing impact energy and led to a reduction in the fatigue strength of the alloy. For similar crack lengths, the fatigue strength of impacted ABB-2 was similar to the fatigue strength of impacted Ti(48)Al(2)Nb(2)Cr, even though the tensile properties of the two alloys are significantly different. Similar to Ti(48)Al(2)Nb(2)Cr, ABB-2 showed a classical mean stress dependence on fatigue strength. The fatigue strength of impacted ABB-2 could be accurately predicted using a threshold analysis.
Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Nazmy, M. Y.; Staubli, M.; Clemens, D. R.
Fretting Fatigue of Single Crystal/Polycrystalline Nickel Subjected to Blade/Disk Contact Loading
NASA Astrophysics Data System (ADS)
Fretting fatigue describes the formation and growth of cracks at the edge-of-contact of nominally clamped components subjected to cyclic loading. Components that are known to be subject to fretting fatigue include riveted lap joints and blade/disk contacts in launch vehicle turbomachinery. Recent efforts have shown that conventional mechanics tools, both fatigue and fracture based, can be used to model fretting fatigue experiments leading to successful life predictions. In particular, experiments involving contact load configurations similar to those that occur in the blade/disk connection of gas turbine engines have been performed extensively. Predictions of fretting fatigue life have been compared favorably to experimental observations [1]. Recent efforts are aimed at performing experiments at higher temperatures as shown in the photograph below along with a sample fracture surface. The talk will describe the status of these experiments as will as model developments relevant to the single crystal material properties.
Matlik, J. F.; Murthy, H.; Farris, T. N.
Cumulative fatigue damage behavior of MAR M-247
NASA Astrophysics Data System (ADS)
The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.
McGaw, Michael A.; Halford, Gary R.; Kalluri, Sreeramesh
Cumulative fatigue damage behavior of MAR M-247
NASA Technical Reports Server (NTRS)
The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.
Mcgaw, Michael A.; Halford, Gary R.; Kalluri, Sreeramesh
Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys
NASA Technical Reports Server (NTRS)
High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.
Arakere, Nagaraj K.; Swanson, Gregory R.
Fatigue of Composite Materials: Damage Mechanisms and Fatigue-Life Diagrams
The basic fatigue damage mechanisms in composite laminates are reviewed. Based on these mechanisms a pattern in the fatigue-life diagrams is proposed. Several experimental data are shown to agree with this basic pattern. Fatigue ratio is defined in terms of strains, and fatigue limit is shown to exist for unidirectional, cross-plied and angle-plied laminates. The limitations to the fatigue performance
R. Talreja
Damage concept in creep-fatigue: current theories and applications
The physical features of creep-fatigue damage are reviewed and both assessed and open questions are outlined. Four linear and non-linear cumulative damage rules, based on quite different damage concepts, are briefly exposed and discussed. Finally, the above models are applied to fatigue and hold-time fatigue of types 304 and 316 stainless steels, in the temperature range between 550 and 650/sup 0/C.
Del Puglia, A.; Vitale, E.
Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys
NASA Technical Reports Server (NTRS)
High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component S resistance to fatigue crack growth with- out adding additional weight or cost. [DOI: 10.1115/1.1413767
Arakere, N. K.; Swanson, G.
Implementation of a Biaxial Resonant Fatigue Test Method on a Large Wind Turbine Blade
A biaxial resonant test method was utilized to simultaneously fatigue test a wind turbine blade in the flap and edge (lead-lag) direction. Biaxial resonant blade fatigue testing is an accelerated life test method utilizing oscillating masses on the blade; each mass is independently oscillated at the respective flap and edge blade resonant frequency. The flap and edge resonant frequency were not controlled, nor were they constant for this demonstrated test method. This biaxial resonant test method presented surmountable challenges in test setup simulation, control and data processing. Biaxial resonant testing has the potential to complete test projects faster than single-axis testing. The load modulation during a biaxial resonant test may necessitate periodic load application above targets or higher applied test cycles.
Snowberg, D.; Dana, S.; Hughes, S.; Berling, P.
Damage tolerance and structural monitoring for wind turbine blades.
The paper proposes a methodology for reliable design and maintenance of wind turbine rotor blades using a condition monitoring approach and a damage tolerance index coupling the material and structure. By improving the understanding of material properties that control damage propagation it will be possible to combine damage tolerant structural design, monitoring systems, inspection techniques and modelling to manage the life cycle of the structures. This will allow an efficient operation of the wind turbine in terms of load alleviation, limited maintenance and repair leading to a more effective exploitation of offshore wind. PMID:25583858
McGugan, M; Pereira, G; Sřrensen, B F; Toftegaard, H; Branner, K
Modeling Fatigue Damage in Long-Fiber Thermoplastics
This paper applies a fatigue damage model recently developed for injection-molded long-fiber thermoplastics (LFTs) to predict the modulus reduction and fatigue lifetime of glass/polyamide 6,6 (PA6,6) specimens. The fatigue model uses a multiscale mechanistic approach to describe fatigue damage accumulation in these materials subjected to cyclic loading. Micromechanical modeling using a modified Eshelby-Mori-Tanaka approach combined with averaging techniques for fiber length and orientation distributions is performed to establish the stiffness reduction relation for the composite as a function of the microcrack volume fraction. Next, continuum damage mechanics and a thermodynamic formulation are used to derive the constitutive relations and the damage evolution law. The fatigue damage model has been implemented in the ABAQUS finite element code and has been applied to analyze fatigue of the studied glass/PA6,6 specimens. The predictions agree well with the experimental results.
Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.
On damage diagnosis for a wind turbine blade using pattern recognition
NASA Astrophysics Data System (ADS)
With the increased interest in implementation of wind turbine power plants in remote areas, structural health monitoring (SHM) will be one of the key cards in the efficient establishment of wind turbines in the energy arena. Detection of blade damage at an early stage is a critical problem, as blade failure can lead to a catastrophic outcome for the entire wind turbine system. Experimental measurements from vibration analysis were extracted from a 9 m CX-100 blade by researchers at Los Alamos National Laboratory (LANL) throughout a full-scale fatigue test conducted at the National Renewable Energy Laboratory (NREL) and National Wind Technology Center (NWTC). The blade was harmonically excited at its first natural frequency using a Universal Resonant EXcitation (UREX) system. In the current study, machine learning algorithms based on Artificial Neural Networks (ANNs), including an Auto-Associative Neural Network (AANN) based on a standard ANN form and a novel approach to auto-association with Radial Basis Functions (RBFs) networks are used, which are optimised for fast and efficient runs. This paper introduces such pattern recognition methods into the wind energy field and attempts to address the effectiveness of such methods by combining vibration response data with novelty detection techniques.
Dervilis, N.; Choi, M.; Taylor, S. G.; Barthorpe, R. J.; Park, G.; Farrar, C. R.; Worden, K.
Extremely low cycle fatigue life prediction based on a new cumulative fatigue damage model
In order to predict an extremely low cycle fatigue (ELCF) life for annealed low carbon steel of S20C, a new cumulative fatigue damage model has been proposed. The model was based on the concept that the damage due to ductility exhaustion should be considered besides the damage generated by crack propagation in the ELCF regime where excessive strain was applied.
Masatoshi Kuroda
Fatigue Damage Evolution in Silicon Films for Micromechanical Applications
"! \\' Fatigue Damage Evolution in Silicon Films for Micromechanical Applications by P. Shrotriya, S microelectromechanical systems (MEMS) structures. The surface topography evolu- tion that occurs during cyclic fatigue and Si layers. Finally, the implications of the results are discussed for the prediction of fatigue
Suo, Zhigang
Cumulative creep fatigue damage in 316 stainless steel
NASA Technical Reports Server (NTRS)
The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.
Mcgaw, Michael A.
Modelling of fatigue damage in aluminum cylinder heads. R. Salapeteb
fatigue damage that may cause Diesel engine to fail after a few thousand cycles on the test bench generates fatigue cracks, initiating from the fire deck of the cast aluminum cylinder head, which can lead : we describe the constitutive equations and the results of fatigue crack growth rate measurements
Paris-Sud XI, Université de
Reexamination of Cumulative Fatigue Damage Laws
NASA Technical Reports Server (NTRS)
Treatment of accumulated fatigue damage in materials and structures subjected to a history of nonsimple repetitive loadings has received a large amount of attention in recent years. A method used for the treatment of complex loading is known as linear damage rule. It was recognized that, this method could result in unconservative predictions of material and structural behavior. An intense flurry of activity followed in the pursuit of alternative methods of analysis that would predict behavior more accurately. So many methods were introduced that it became necessary periodically to prepare review papers placing all the new methods into perspective. The current integrated view regarding the state of the art as it applies to this effort is discussed. The more recently proposed cumulative damage life prediction methods are reviewed. The double linear damage rule (DLDR), which has evolved over the past 20 years, is reexamined with the intent of improving its accuracy and applicability to engineering problems. Modifications are introduced to the analytical formulation to achieve greater compatibility between the DLDR and the so-called damage curve approach, which is an alternative continuous representation of the DLDR.
Halford, G. R.; Manson, S. S.
Fatigue strength of working blades of turbines and compressors repaired by welding
A method of determining the welding repair zones of working blades of gas turbine engines is proposed based on the principle of equal strength of the component using the fatigue strength criteria. The method takes into account the difference of the mechanical properties of the deposit and the parent metal. Investigations were carried out on new and repaired working blades of turbines and compressors of different gas-pumping systems. The experimental results are used to prepare recommendations for repairing the working blades subjected to pilot-plant service conditions.
Gryaznov, B.A.; Gorodetskii, S.S.; Nalimov, Y.S. [Institute of Problems of Strength, Kiev (Ukraine)] [and others
Aspect of cumulative fatigue damage under multiaxial strain cycling.
NASA Technical Reports Server (NTRS)
The concept of order of loading and its effect on cumulative fatigue damage under multiaxial strain cyclings was investigated. The effect is illustrated through nonlinear relationships between biaxial fatigue damage and cycle-ratio diagrams. Uniaxial theories such as Miner's method, the convergence method, and the double linear damage rule in its special and generalized form, were examined and extended to the biaxial case through the octahedral shear strain theory. The generalized double linear damage rule was found more applicable to biaxial cumulative fatigue damage.
Zamrik, S. Y.; Tang, P. Y.
A study of cumulative fatigue damage in AISI 4130 steel
NASA Technical Reports Server (NTRS)
Experimental data were obtained using AISI 4130 steel under stress ratios of -1 and 0. A study of cumulative fatigue damage using Miner's and Kramer's equations for stress ratios of -1 and 0 for low-high, low-high-mixed, high-low, and high-low-mixed stress sequences has revealed that there is a close agreement between the theoretical and experimental values of fatigue damage and fatigue life. Kramer's equation predicts less conservative and more realistic cumulative fatigue damage than the popularly used Miner's rule does.
Jeelani, S.; Musial, M.
77 FR 50576 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; OMB Approval of...
Federal Register 2010, 2011, 2012, 2013, 2014
...RIN 2120-AJ52 Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures...final rule, ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures...final rule, ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft...
Conditioning monitoring by microstructural evaluation of cumulative fatigue damage
NASA Astrophysics Data System (ADS)
The objective of this work is to evaluate the damage induced below and above the fatigue limit (? ? t =360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell misorientation differences were measured by the selected area diffraction (SAD) method. Surface cracking was also studied by the replication method. Small cracks were observed after precycling both below and above the fatigue limit. It was, however, found that fatigue test bars had a longer lifetime after precycling below the fatigue limit, while precycling above the fatigue limit caused other specimens to fail even when subsequently cycled below the fatigue limit. Cell-to-cell misorientation usually increases with accumulation of fatigue damage, but it was found that the misorientations measured after precycling below the fatigue limit decreased again at the beginning of the subsequent cycling above the fatigue limit. It should be noted that the misorientation at failure was always about 4 to 5 deg, regardless of loading histories. Misorientation showed good correlation with the fatigue lifetime of the samples.
Fukuoka, C.; Nakagawa, Y. G.; Lance, J. J.; Pangborn, R. N.
Conditioning monitoring by microstructural evaluation of cumulative fatigue damage
The objective of this work is to evaluate the damage induced below and above the fatigue limit ({Delta}{sigma}{sub t} = 360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell misorientation differences were measured by the selected area diffraction (SAD) method. Surface cracking was also studied by the replication method. Small cracks were observed after precycling both below and above the fatigue limit. It was, however, found that fatigue test bars had a longer lifetime after precycling below the fatigue limit, while precycling above the fatigue limit caused other specimens to fail even when subsequently cycled below the fatigue limit. Cell-to-cell misorientation usually increases with accumulation of fatigue damage, but it was found that the misorientations measured after precycling below the fatigue limit decreased again at the beginning of the subsequent cycling above the fatigue limit. It should be noted that the misorientation at failure was always about 4 to 5 deg, regardless of loading histories. Misorientation showed good correlation with the fatigue lifetime of the samples.
Fukuoka, C.; Nakagawa, Y.G. [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan). Research Labs.; Lance, J.J. [Electric Power Research Inst., Charlotte, NC (United States). O and M Cost Control Technology; Pangborn, R.N. [Pennsylvania State Univ., University Park, PA (United States). Coll. of Engineering
Analysis of SNL/MSU/DOE fatigue database trends for wind turbine blade materials.
This report presents an analysis of trends in fatigue results from the Montana State University program on the fatigue of composite materials for wind turbine blades for the period 2005-2009. Test data can be found in the SNL/MSU/DOE Fatigue of Composite Materials Database which is updated annually. This is the fifth report in this series, which summarizes progress of the overall program since its inception in 1989. The primary thrust of this program has been research and testing of a broad range of structural laminate materials of interest to blade structures. The report is focused on current types of infused and prepreg blade materials, either processed in-house or by industry partners. Trends in static and fatigue performance are analyzed for a range of materials, geometries and loading conditions. Materials include: sixteen resins of three general types, five epoxy based paste adhesives, fifteen reinforcing fabrics including three fiber types, three prepregs, many laminate lay-ups and process variations. Significant differences in static and fatigue performance and delamination resistance are quantified for particular materials and process conditions. When blades do fail, the likely cause is fatigue in the structural detail areas or at major flaws. The program is focused strongly on these issues in addition to standard laminates. Structural detail tests allow evaluation of various blade materials options in the context of more realistic representations of blade structure than do the standard test methods. Types of structural details addressed in this report include ply drops used in thickness tapering, and adhesive joints, each tested over a range of fatigue loading conditions. Ply drop studies were in two areas: (1) a combined experimental and finite element study of basic ply drop delamination parameters for glass and carbon prepreg laminates, and (2) the development of a complex structured resin-infused coupon including ply drops, for comparison studies of various resins, fabrics and pry drop thicknesses. Adhesive joint tests using typical blade adhesives included both generic testing of materials parameters using a notched-lap-shear test geometry developed in this study, and also a series of simulated blade web joint geometries fabricated by an industry partner.
Mandell, John F. (Montana State University, Bozeman, MT); Ashwill, Thomas D.; Wilson, Timothy J. (Montana State University, Bozeman, MT); Sears, Aaron T. (Montana State University, Bozeman, MT); Agastra, Pancasatya (Montana State University, Bozeman, MT); Laird, Daniel L.; Samborsky, Daniel D. (Montana State University, Bozeman, MT)
Cumulative fatigue damage analysis under conditions of competing mechanisms
Two special cumulative damage problems in which two competing mechanisms operate have been examined. One of the mechanisms, active in both problems and detrimental to fatigue life, is the nonlinear damage interaction between the different levels of the applied loading. The second mechanism, which is beneficial to fatigue life, arises due to the nature of the applied loading and material
Sissay Hailu
77 FR 55105 - Aging Airplane Program: Widespread Fatigue Damage; Correction
Federal Register 2010, 2011, 2012, 2013, 2014
...FAA-2006-24281; Amendment Nos. 121-360A, 129-51A] RIN 2120-AI05 Aging Airplane Program: Widespread Fatigue Damage; Correction AGENCY...amendment to a final rule. The technical amendment is entitled ``Aging Airplane Program: Widespread Fatigue Damage'' (77 FR...
Room temperature fatigue response of {gamma}-TiAl to impact damage
Gamma based titanium aluminides have received considerable attention recently as candidate materials in gas turbine applications, particularly low pressure turbine blades. Their low density and high specific stiffness, result in potentially significant weight savings in structures such as gas turbine engines if substituted for current materials. The objective of the present study is to characterize and quantify the damage resulting from low-speed impacts on {gamma}-TiAl and to relate this impact damage to reductions in fatigue failure stress by the use of a threshold-based model.
Harding, T.S.; Jones, J.W. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering] [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering; Steif, P.S.; Pollock, T.M. [Carnegie Mellon Univ., Pittsburgh, PA (United States)] [Carnegie Mellon Univ., Pittsburgh, PA (United States)
Fatigue testing of low-cost fiberglass composite wind turbine blade materials
NASA Technical Reports Server (NTRS)
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.
Thermomechanics of damage and fatigue by a phase field model
In the paper we present an isothermal model for describing damage and fatigue by the use of the Ginzburg-Landau (G-L) equation. Fatigue produces progressive damage, which is related with a variation of the internal structure of the material. The G-L equation studies the evolution of the order parameter, which describes the constitutive arrangement of the system and, in this framework, the evolution of damage. The thermodynamic coherence of the model is proved. In the last part of the work, we extend the results of the paper to a non-isothermal system, where fatigue contains thermal effects, which increase the damage of materials.
Giovambattista Amendola; Mauro Fabrizio
Computed speckle decorrelation (CSD) for the study of fatigue damage
NASA Astrophysics Data System (ADS)
A video-based laser speckle technique has been developed for noncontact analysis of fatigue in situ and at speeds approaching video frame rates. This technique, computed speckle decorrelation (CSD), makes use of the speckle decorrelation associated with surface deformation. It is a method of full field inspection which both locates fatigue damage sites and measures damage severity. In its current application, CSD has been used to study the fatigue deformation progression in reverse bending fatigue of a cylindrically notched aluminum specimen. However, film based studies have shown the usefulness of laser speckle decorrelation to analyze fatigue deformation of thick graphite/epoxy composite materials as well. With the development of the CSD method it will now be possible to examine in greater detail the progression of fatigue damage in these materials, allowing a much faster and more quantitative analysis than was previously available.
Steckenrider, J. Scott; Wagner, James W.
Fatigue damage accumulation in various metal matrix composites
NASA Technical Reports Server (NTRS)
The purpose of this paper is to review some of the latest understanding of the fatigue behavior of continuous fiber reinforced metal matrix composites. The emphasis is on the development of an understanding of different fatigue damage mechanisms and why and how they occur. The fatigue failure modes in continuous fiber reinforced metal matrix composites are controlled by the three constituents of the system: fiber, matrix, and fiber/matrix interface. The relative strains to fatigue failure of the fiber and matrix will determine the failure mode. Several examples of matrix, fiber, and self-similar damage growth dominated fatigue damage are given for several metal matrix composite systems. Composite analysis, failure modes, and damage modeling are discussed. Boron/aluminum, silicon-carbide/aluminum, FP/aluminum, and borsic/titanium metal matrix composites are discussed.
Johnson, W. S.
Active sensing of fatigue damage using embedded ultrasonics
NASA Astrophysics Data System (ADS)
Dynamic measurements are widely used for structural condition assessment and damage detection. A wide range of studies are available on vibration-based detection and identification of fatigue cracks in simple and complex structures. This research explores the application of the electromechanical impedance method and nonlinear resonance measurements to high frequency detection of incipient fatigue damage in aluminum alloy specimens. The electromechanical impedance method relies on the coupling between the mechanical properties of a structure and the electrical properties of attached piezoelectric wafer active sensors (PWAS). This coupling allows structural properties to be inferred from the electrical impedance signature of the sensor. In this study, the electromechanical impedance method is utilized for assessment of material deterioration under cyclic fatigue loads. Aluminum specimens were subjected to increasing fatigue cycles at stress amplitudes below the yield point, and electromechanical impedance signatures were taken at discrete levels of fatigue damage. Linear and nonlinear features of the impedance signatures were compared for different damage conditions. The results show a downward frequency shift of impedance peaks with increasing fatigue load. This frequency shift is observed before visible crack development and fracture. Nonlinear resonance tests were applied to fatigued aluminum samples. PWAS were utilized for transmission and reception of elastic waves at increasing amplitude levels. Variations in structural dynamic characteristics were considered for different excitation conditions and increasing damage severity. This paper discusses damage detection capabilities of each method and provides perspectives for utilizing information on incipient damage for predicting structural performance under known operational loads.
Kruse, Walter A.; Zagrai, Andrei; Gigineishvili, Vlasi
Behavior of gamma TiAl subjected to impact damage and elevated temperature fatigue
Gamma titanium aluminide has received significant attention in recent years as a candidate material for use in aerospace and industrial gas turbine engine applications. It is well known that fatigue crack growth rates in {gamma}-TiAl alloys are very sensitive to stress intensity range and that there is a small difference between threshold stress intensity range and apparent fracture toughness in these materials. The result is limited damage tolerance and dramatic reductions in fatigue lifetime in the presence of extrinsic damage, such as that produced from an impact event. To apply a damage tolerance approach to this situation would require improved crack detection techniques and would increase the life cycle cost of the engine by decreasing the inspection interval. Using a threshold-based approach, on the other hand, would ensure that pre-existing or service indices cracks would not grow and that failure by fatigue would not occur. The present study investigates the feasibility of using a threshold calculation to estimate the fatigue strength reduction caused by impact damage at elevated temperatures (600 C). The results are part of a larger investigation into the feasibility of using {gamma}-TiAl for low-pressure turbine blades.
Harding, T.S.; Jones, J.W.
A fatigue damage model for the cement-bone interface.
Loss of fixation at the cement-bone interface can contribute to clinical loosening of cemented total hip replacements. In this study, the fatigue damage response was determined for cement-bone constructs subjected to shear fatigue loading. A typical three-phase fatigue response was observed with substantial early damage, followed by a long constant damage rate region and a final abrupt increase in damage to fracture. All of the damage resulted from creep (permanent) deformation during fatigue loading and there was no loss in cyclic stiffness. Using a Von Mises equivalent stress/strain concept, a general damage model was developed to describe the fatigue creep response of the cement-bone interface under either shear or tensile fatigue loading. Time to failure was highly correlated (r2=0.971) with equivalent creep strain rate and moderately related (r2=0.428) with equivalent initial strain for the two loading regimes. The equivalent creep strain at failure (0.052+/-0.018) was found to be independent of the applied equivalent stress. A combination of the creep damage model (to describe the damage process) with a constant final equivalent strain (as a failure criteria) could be used to assess the cement-bone failure response of cemented implant systems. PMID:15336925
Kim, Do-Gyoon; Miller, Mark A; Mann, Kenneth A
The characterization of widespread fatigue damage in fuselage structure
NASA Technical Reports Server (NTRS)
The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology, and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.
Piascik, Robert S.; Willard, Scott A.; Miller, Matthew
The characterization of widespread fatigue damage in fuselage structure
NASA Technical Reports Server (NTRS)
The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this work were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.
Piascik, Robert S.; Willard, Scott A.; Miller, Matthew
75 FR 793 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures
Federal Register 2010, 2011, 2012, 2013, 2014
...RIN 2120-AJ52 Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures...amendment would require evaluation of fatigue and residual static strength of composite...using a damage tolerance evaluation, or a fatigue evaluation, if the applicant...
14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.
Code of Federal Regulations, 2010 CFR
... false Metallic damage tolerance and fatigue evaluation of commuter category airplanes...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category...
14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.
Code of Federal Regulations, 2010 CFR
...2010-01-01 false Damage tolerance and fatigue evaluation of structure. 23.573 Section...COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.573 Damage tolerance and fatigue evaluation of structure. (a)...
Cumulative fatigue damage analysis under conditions of competing mechanisms
NASA Astrophysics Data System (ADS)
Two special cumulative damage problems in which two competing mechanisms operate have been examined. One of the mechanisms, active in both problems and detrimental to fatigue life, is the nonlinear damage interaction between the different levels of the applied loading. The second mechanism, which is beneficial to fatigue life, arises due to the nature of the applied loading and material behavior. The first problem is encountered when dealing with an irreversibly hardening material. In such a material, initial cycles applied at high strainranges can alter the material such that subsequently applied cycles are essentially on a new material with improved fatigue properties. In this case, life relations determined from conventional constant amplitude fatigue data are inadequate for treatment of cumulative fatigue damage. A procedure, which uses two-level step test data in conjunction with a nonlinear cumulative damage model, is proposed for establishing effective life relations which can be used successfully under any loading history. Tests conducted at room temperature on 304 stainless steel, a material which irreversibly hardens, indicate that cumulative fatigue damage behavior can be accurately predicted using the proposed procedure. The second problem is found in applications involving creep-fatigue loading. Compressive and tensile creep strains imposed at different times during the life of a material can interact to produce a "healing" effect. Under variable amplitude loading, this benign interaction can compete with the unfavorable interactions occurring between the different loading levels. Life prediction analyses were carried out for two loading histories and three types of materials classified according to their creep-fatigue life relations. The results suggest that the beneficial effects of the creep strain interactions on creep-fatigue life are very substantial, and that the detrimental load interaction effects are usually insignificant. Experimental results obtained from creep-fatigue tests conducted on MAR-M-247, a nickel-base superalloy, at 1600sp°F showed good agreement with analytically determined creep-fatigue life behavior.
Hailu, Sissay
Resolution of tower shadow models for downwind mounted rotors and its effects on the blade fatigue
NASA Astrophysics Data System (ADS)
A simulation study on the wind field resolution in computer load simulations has been conducted, both in transversal/vertical and longitudinal direction, to determine the effect on blade fatigue loading. Increasing the transversal/vertical resolution decreased the loading significantly, while only small changes to the load, at very low frequencies were found for increased longitudinal resolution. Next the influence of the tower shadow for a downwind mounted rotor was investigated, with respect to blade fatigue loading. The influence of different components to the total tower shadow effect was studied, both for a monopile and a truss tower, latter at inclination 0 and 22.5 degrees with respect to the incoming wind direction. Four components were considered, both individually and in combinations: mean wind speed, mean velocity deficit, unsteady motions from vortex shedding, and turbulence. The mean velocity deficit and turbulence were the main contributors to blade fatigue loading, and the unsteady motions can be neglected for the truss tower. For the monopile, neglecting the unsteady motions resulted in an underestimation of fatigue loading in the order of 3 percent.
Reiso, M.; Muskulus, M.
Helicopter rotor blade frequency evolution with damage growth and signal processing
NASA Astrophysics Data System (ADS)
Structural damage in materials evolves over time due to growth of fatigue cracks in homogenous materials and a complicated process of matrix cracking, delamination, fiber breakage and fiber matrix debonding in composite materials. In this study, a finite element model of the helicopter rotor blade is used to analyze the effect of damage growth on the modal frequencies in a qualitative manner. Phenomenological models of material degradation for homogenous and composite materials are used. Results show that damage can be detected by monitoring changes in lower as well as higher mode flap (out-of-plane bending), lag (in-plane bending) and torsion rotating frequencies, especially for composite materials where the onset of the last stage of damage of fiber breakage is most critical. Curve fits are also proposed for mathematical modeling of the relationship between rotating frequencies and cycles. Finally, since operational data are noisy and also contaminated with outliers, denoising algorithms based on recursive median filters and radial basis function neural networks and wavelets are studied and compared with a moving average filter using simulated data for improved health-monitoring application. A novel recursive median filter is designed using integer programming through genetic algorithm and is found to have comparable performance to neural networks with much less complexity and is better than wavelet denoising for outlier removal. This filter is proposed as a tool for denoising time series of damage indicators.
Roy, Niranjan; Ganguli, Ranjan
Continuum damage mechanics analysis of fatigue crack initiation
The crack initiation period in an originally defect-free component can be a significant portion of its total fatigue life. The initiation phase is generally believed to constitute the nucleation and growth of short cracks, but the threshold crack length at which initiation occurs lacks a uniform definition. Moreover, available methods for predicting fatigue damage growth usually require an existing flaw
Baidurya Bhattacharya; Bruce Ellingwood
in the wind turbine blade. It was tried to apply a new source location method, which has a developed algorithm assessment, source location, wind turbine blade, hybrid composites INTRODUCTION Structural health managementQUANTITATIVE DAMAGE ASSESSMENT OF HYBRID COMPOSITE WIND TURBINE BLADES BY ENERGY BASED ACOUSTIC
Boyer, Edmond
Drag amplification and fatigue damage in vortex-induced vibrations
Fatigue damage and drag force amplification due to Vortex-Induced-Vibrations (VIV) continue to cause significant problems in the design of structures which operate in ocean current environments. These problems are magnified ...
Jhingran, Vikas Gopal
a Crack Growth Model Based on Fatigue Damage Accumulation
NASA Astrophysics Data System (ADS)
A novel model for predicting the fatigue crack growth had been developed based on the concept of the fatigue damage accumulation. Fatigue crack growth was considered as a process of continuous crack nucleation. The crack tip failed to form a fresh crack while the accumulative fatigue damage reached the critical damage. A simplified model of the general crack growth model was proposed with the assumption that the damage zone can be divided into many different zones and each zone had the same crack growth rate. The model was applied to predict the crack growth of the compact specimen made of 16MnR steel under the constant amplitude loading. The predicted crack growth rate was in excellent agreement with the experimental observations.
Qiu, Baoxiang; Wang, Xiaogui; Gao, Zengliang
Mean stress and the exhaustion of fatigue-damage resistance
NASA Technical Reports Server (NTRS)
Mean-stress effects on fatigue life are critical in isothermal and thermomechanically loaded materials and composites. Unfortunately, existing mean-stress life-prediction methods do not incorporate physical fatigue damage mechanisms. An objective is to examine the relation between mean-stress induced damage (as measured by acoustic emission) and existing life-prediction methods. Acoustic emission instrumentation has indicated that, as with static yielding, fatigue damage results from dislocation buildup and motion until dislocation saturation is reached, after which void formation and coalescence predominate. Correlation of damage processes with similar mechanisms under monotonic loading led to a reinterpretation of Goodman diagrams for 40 alloys and a modification of Morrow's formulation for life prediction under mean stresses. Further testing, using acoustic emission to monitor dislocation dynamics, can generate data for developing a more general model for fatigue under mean stress.
Berkovits, Avraham
Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage
Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the Damage Curve concept or the Double Linear Damage Rule. A single equation is provided for use with the Damage Curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the Double
S. S. Manson; G. R. Halford
Study of the effect of technical factors on the fatigue limit of the working blades of gas turbine motors
Conclusions 1.The examined deviations in the production technology for working blades in a turbine of one of the gas turbine motors (patterns, burn-ons, additional glossing operation) do not have any essential effect on the magnitude of the maximum fatigue limit of the blade on the basis of 108 cycles at temperatures of 20 and 570°. The range of changes in
V. T. Troshchenko; B. A. Gryaznov; S. S. Gorodetskii; A. B. Roitman; Yu. S. Nalimov
On the concept of cumulative fatigue damage
A general notion of the cumulative damage is introduced which accounts for the previous damage history and loading order effect. The dimensionless damage is specified in terms of a damage function containing a controlling damage variable, ?, and material parameter, p. This nonlinear damage accumulation model is based on the phenomenological approach which relates the rate of increase of damage
D. Kujawski; F. Ellyin
A probabilistic fatigue analysis of multiple site damage
NASA Technical Reports Server (NTRS)
The variability in initial crack size and fatigue crack growth is incorporated in a probabilistic model that is used to predict the fatigue lives for unstiffened aluminum alloy panels containing multiple site damage (MSD). The uncertainty of the damage in the MSD panel is represented by a distribution of fatigue crack lengths that are analytically derived from equivalent initial flaw sizes. The variability in fatigue crack growth rate is characterized by stochastic descriptions of crack growth parameters for a modified Paris crack growth law. A Monte-Carlo simulation explicitly describes the MSD panel by randomly selecting values from the stochastic variables and then grows the MSD cracks with a deterministic fatigue model until the panel fails. Different simulations investigate the influences of the fatigue variability on the distributions of remaining fatigue lives. Six cases that consider fixed and variable conditions of initial crack size and fatigue crack growth rate are examined. The crack size distribution exhibited a dominant effect on the remaining fatigue life distribution, and the variable crack growth rate exhibited a lesser effect on the distribution. In addition, the probabilistic model predicted that only a small percentage of the life remains after a lead crack develops in the MSD panel.
Rohrbaugh, S. M.; Ruff, D.; Hillberry, B. M.; Mccabe, G.; Grandt, A. F., Jr.
Wind turbine blade damage detection using an active sensing approach
NASA Astrophysics Data System (ADS)
The wind energy sector is one of the fastest growing parts of the clean energy industry. As the wind energy sector grows, so does an increasing concern for the damage detection of wind turbine blades. This paper proposes an active sensing approach by utilizing piezoceramic transducers as actuators and sensors. The influence of the crack quantity, location, length and depth on the wave propagation was experimentally studied. Sweep sine signals ranging from 1 khz to 50 khz were used as input signals for active sensing. The change in the energy that propagated through the cracks was verified as feasible in detecting crack-related damage. An innovative polar plot analysis method based on Fast Fourier transform was developed to compare the minuscule difference between the damage signals and the baseline signal. The polar plot was able to make apparent differences in both the magnitude and the phase of the signals, which could be correlated to crack depth and plane geometry, respectively, based on the observation of the damage.
Ruan, Jiabiao; Ho, Siu Chun Michael; Patil, Devendra; Li, Mo; Song, Gangbing
Probabilistic prediction of the fatigue life of gas-turbine engine compressor blades under two-level programmed loading
The authors devise and substantiate a combined theoretical and experimental method of probalistic evaluation of the fatigue life of the compressor blades of gas turbine engines in programmed loading based on the Monte Carlo method. The possible variants of the result of events of fatigue crack propagation in a material in programmed two-level completely reversed loading are examined. It was
M. V. Baumshtein; V. N. Fzhov; A. V. Prokopenko
A new cumulative fatigue damage model for fibre-reinforced plastics
A cumulative fatigue damage model is presented for predicting the fatigue life of fibre-reinforced plastics (FRP) subjected to variable amplitude fatigue loading. It is assumed that the cumulative fatigue damage caused by the cyclic loading is proportional to the strength loss of FRP, and that the damage state in laminates can be described phenomenologically by residual strength. Some experimental results
W. X. Yao; N. Himmel
Damage evolution in adhesive joints subjected to impact fatigue
NASA Astrophysics Data System (ADS)
There is increasing interest in the effects of low-velocity impacts produced in components and structures by vibrating loads. This type of loading is known as impact-fatigue. The main aim of this paper is to investigate the behaviour of adhesive joints exposed to low-velocity impacting, to study the impact-fatigue life and to compare this loading regime with standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). To this effect, bonded aluminium single lap joints have been subjected to multiple impacting tensile loads and it has been shown that this is an extremely damaging load regime compared to standard fatigue. Two modifications of the accumulated time-stress model have been proposed to characterise the impact-fatigue results presented in this paper. The first model has been termed the modified load-time model and relates the total cumulative loading time of the primary tensile load wave to the mean maximum force. The second model attempts to characterise sample damage under impact-fatigue by relating the maximum force normalised with respect to initial maximum force to the accumulated loading time normalised with respect to the total accumulated loading time. This model has been termed the normalised load-time model. It is shown that both models provide a suitable characterisation of impact-fatigue in bonded joints.
Casas-Rodriguez, J. P.; Ashcroft, I. A.; Silberschmidt, V. V.
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
Effects of geometry and materials on low cycle fatigue life of turbine blades in LOX/hydrogen rocket engines
NASA Technical Reports Server (NTRS)
This paper presents the results of an advanced turbine blade test program aimed at improving turbine blade low cycle fatigue (LCF) life. A total of 21 blades were tested in a blade thermal tester. The blades were made of MAR-M-246(Hf)DS and PWA-1480SC in six different geometries. The test results show that the PWA-1480SC material improved life by a factor of 1.7 to 3.0 over the current MAR-M-246(Hf)DS. The geometry changes yielded life improvements as high as 20 times the baseline blade made of PWA-1480SC and 34 times the baseline MAR-M-246DS blade.
Ryan, R. M.; Gross, L. A.
An experiemental and computational study of the aerodynamics of turbine blades with damage
NASA Astrophysics Data System (ADS)
Investigations have been made of the aerodynamic effects of in-service damage on the performance of axial turbine blades. Two aspects of blade damage were considered: surface roughening and trailing edge damage. The work is related to gas turbine engine health monitoring. Correlations for the effects of surface roughness were developed based on a database obtained from Kind et al. (1998). The correlations account for the effects of the roughness height as well as the location and extent of the roughness patch on the blade surface. The effect of trailing edge damage at transonic flow conditions was investigated both experimentally and computationally. Computational investigation was conducted for only trailing-edge damage using a three- dimensional Navier-Stokes solver developed by Dawes (1988). The computations with trailing edge damage represent a novel application of the code and the wind tunnel measurements were therefore used to validate the computations. Results showed that surface roughening and trailing edge damage produced significantly different aerodynamic behavior of the flow. Surface roughening largely influences the profile losses and trailing edge damage has a considerable effect on the flow deviation. The effect of trailing edge damage on the loss characteristics of the blades was found to be fairly small over the full range of flow conditions. In fact, the overall measured profile losses were actually lower for 20% damage than for the undamaged blade. The measured flow deviation increased with the increase in damage size as well as cascade exit Mach number. Computational investigations were made to identify the parameters that influence flow deviation in turbines with both undamaged and damaged blades so that correlations could be developed. It was found that the deviation is primarily determined by the blade loading towards the trailing edge. The blade row parameters which influence this pressure difference were identified. The deviation correlation for undamaged blades is applicable for subsonic flow cases and that for damaged blades is applicable for the full range of Mach numbers studied. The new subsonic deviation correlation for undamaged blades appears to be significantly more successful than existing correlations. The three dimensional Navier-Stokes solver of Dawes predicted many of the measured results for damaged blades. Particularly, predictions of deviation for different undamaged and damaged blade geometries were found to be quite satisfactory and the code was extensively used to generate deviation data to supplement experimental measurements. (Abstract shortened by UMI.)
Islam, Alamgir M. T.
An empirical modified fatigue damage model for impacted GFRP laminates
NASA Astrophysics Data System (ADS)
The aim of the present paper is to evaluate the residual strength of GFRP laminates following a low-velocity impact event under cyclic loading. The residual strength is calculated using a linear fatigue damage model. According to an investigation into the effect of low-velocity impact on the fatigue behavior of laminates, it seems laminate fatigue life decreases after impact. By normalizing the fatigue stress against undamaged static strength, the Fatigue Damage parameter "FD" is presented with a linear relationship as its slope which is a linear function of the initial impact energy; meanwhile, the constants were attained from experimental data. FD is implemented into a plane-stress continuum damage mechanics based model for GFRP composite laminates, in order to predict damage threshold in composite structures. An S-N curve is implemented to indicate the fatigue behavior for 2 mm thickness encompassing both undamaged and impacted samples. A decline in lifespan is evident when the impact energy level increases. Finally, the FD is intended to capture the unique GFRP composite characteristics.
Naderi, S.; Hassan, M. A.; Bushroa, A. R.
Multiaxial and thermomechanical fatigue considerations in damage tolerant design
NASA Technical Reports Server (NTRS)
In considering damage tolerant design concepts for gas turbine hot section components, several challenging concerns arise: Complex multiaxial loading situations are encountered; Thermomechanical fatigue loading involving very wide temperature ranges is imposed on components; Some hot section materials are extremely anisotropic; and coatings and environmental interactions play an important role in crack propagation. The effects of multiaxiality and thermomechanical fatigue are considered from the standpoint of their impact on damage tolerant design concepts. Recently obtained research results as well as results from the open literature are examined and their implications for damage tolerant design are discussed. Three important needs required to advance analytical capabilities in support of damage tolerant design become readily apparent: (1) a theoretical basis to account for the effect of nonproportional loading (mechanical and mechanical/thermal); (2) the development of practical crack growth parameters that are applicable to thermomechanical fatigue situations; and (3) the development of crack growth models that address multiple crack failures.
Leese, G. E.; Bill, R. C.
Local fatigue damage accumulation around notch attending crack initiation
NASA Astrophysics Data System (ADS)
The subsequent recrystallization technique was used to study the process of local damage accumulation around a notch under conditions of low-cycle fatigue. A 0.8-in. compact tension specimen of 304 stainless steel with a notch radius of 1 mm was used. The accumulated plastic zone around notch increases with the number of cycles N. The accumulated plastic strain within the zone also increases with N, producing the strain gradient (damage gradient). A fatigue crack initiates when the accumulated plastic strain at the notch root reaches a critical value equal to the fracture strain of the material; that is, when the accumulated plastic work at the crack initiation site becomes critical. The fatigue crack emanating from a notch root grows through the pre-existing damaged zone. It is shown that this local damage accumulation approach can explain the fast growth of a short crack from a notch.
Iino, Y.
Monitoring Fatigue Damage Accumulation with Rayleigh Wave Harmonic Generation Measurements
NASA Astrophysics Data System (ADS)
The use of nonlinear acoustics, and in particular harmonic generation, continues to gain interest as a means to characterize microstructural changes in engineering materials as a result of processing and in-service conditions. Typical measurements involve the propagation of a monochromatic longitudinal wave toneburst through the bulk of a sample in a through-transmission arrangement. This arrangement is not well suited for field applications, where two sided access is limited and parallel surfaces are rare. Harmonic generation measurements to monitor fatigue damage in acro engine alloys subject to fatigue will be presented. The use of Rayleigh waves has allowed one sided access and accommodates a small amount of surface curvature while restricting the probing wave to the surface where fatigue damage is typically initiated. Early results using uncalibrated receiving transducers on Ni-based alloys demonstrate a sensitivity to damage accumulation in low cycle fatigue, where damage is spread over the sample surface. Damage accumulation in high cycle fatigue is concentrated in small regions on the sample surface and so has not yet been revealed by changes in the generation of harmonics using the uncalibrated probes.
Barnard, D. J.; Brasche, L. J. H.; Raulerson, D.; Degtyar, A. D.
Estimation of fatigue damage of airplane landing gear
Taking the main landing gears of fighter and transport airplanes as examples, the fatigue life was estimated by means of the\\u000a Miner's rule and from the spectrum of the real measurements. The computed results show that the landing damage to the fighter\\u000a and transport airplanes is 75% and 60% of the total damage, and the damage caused by the landing
Ke-ge Liu; Chu-liang Yan; Shu-ming Zhang
High Cycle Fatigue Crack Initiation Study of Case Blade Alloy Rene 125
NASA Technical Reports Server (NTRS)
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.
Reduction in fiber damage thresholds due to static fatigue
NASA Astrophysics Data System (ADS)
Damage mechanisms may occur during the transmission of Q-switched, Nd/YAG laser pulses through fused silica fibers. Fiber end-face characteristics, laser characteristics, and aspects of the laser-to-fiber injection typically determine dominant damage mechanisms. However, an additional damage process has been observed at internal sites where fibers were experiencing significant local stresses due to fixturing or bends in the fiber path. A transmission reduction prior to damage was typically not measurable at these sites. Damage would not always occur during initial testing, but sometimes occurred later in time at laser levels that previously had been transmitted without damage. In these cases the time at stress appeared to be more important than the number of transmitted shots prior to damage. A possible relation between internal damage thresholds at stressed sites and the total time under stress is suggested by the fact that silica fibers experience static fatigue processes. These processes involve the slow growth of local defects under tensile stress at rates that depend upon environmental conditions. Defects reaching sufficient size and having appropriate location could be sites for reduced laser-induced damage thresholds. The present work looks into the possibility that static fatigue processes can affect damage thresholds. The experiments used a laser injection and fiber routing configuration that produced significantly elevated fluences within fiber core regions under tensile stress. In order to establish initial strength and fatigue properties for these fibers, a number of samples were used to generate time-to-failure data at various stress levels. Other fiber samples were subjected to conditions that greatly accelerated fatigue processes. Internal damage thresholds were then measured in these fibers and compared to thresholds measured in fresh fibers. Conclusive comparisons were frustrated by sample-to-sample and lot-to-lot variations in fiber defects.
Setchell, R. E.
Damage and fatigue in cross-linked rubbers
NASA Astrophysics Data System (ADS)
Damage and fatigue of elastomers have not been fundamentally understood because of the complex nature of these materials. All currently existing models are completely phenomenological. Therefore two problems have been investigated in this research to address those fundamental issues. The first problem was creating an innovative concept with a mathematical modeling, which would be able to describe the damage using molecular characteristics of elastomers. The second problem is developing new approaches to study fatigue, and especially impact fatigue of elastomers. The following results have been obtained in this research. A theoretical model of damage has been developed which involves the basic molecular characteristics of cross-linked elastomers and takes into account the effects of viscoelasticity and stress-induced crystallization. This model was found very reliable and successful in description of numerous quasi-static simple extension experiments for monotonous and repeating loadings. It also roughly predicts in molecular terms the failure of elastomers with various degrees of cross-linking. Quasi-impact fatigue tests with different geometry of an indenter have also been performed. Some microscopic features of rubber damage have been investigated using optical microscopy and SEM. In particular, the accumulation of a completely de-vulcanized, liquid-like substance was observed under intense, multi-cycle impacts. All the findings discovered in quasi-impact experiments are consistent with the damage model predictions.
Melnikov, Alexei
Structural and Damage Assessment of Multi-Section Modular Hybrid Composite Wind Turbine Blade
to the absence of damage in the composite layers and the balsa core. Our study showed that the modular blade followed the single length blade response without any significant alterations to its structural response. It is concluded that the proposed computational...
Nanami, Norimichi
sound detection. We optimized and tested the algorithm with our airborne sound recordings of a full]. Fibre optic microphones can be used for recording sound inside a rotor blade. Their cords are electricalDETECTION OF IMPULSE-LIKE AIRBORNE SOUND FOR DAMAGE IDENTIFICATION IN ROTOR BLADES OF WIND TURBINES
Boyer, Edmond
The objective of the program was to demonstrate and verify Certification-by-Analysis (CBA) capability for wind turbine blades made from advanced lightweight composite materials. The approach integrated durability and damage tolerance analysis with robust design and virtual testing capabilities to deliver superior, durable, low weight, low cost, long life, and reliable wind blade design. The GENOA durability and life prediction software
Galib Abumeri; Frank Abdi
WISPER and WISPERX: Final definition of two standardised fatigue loading sequences for wind turbine blades
NASA Astrophysics Data System (ADS)
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.
75 FR 24502 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; Reopening of Comment...
Federal Register 2010, 2011, 2012, 2013, 2014
...Notice No. 10-09] RIN 2120-AJ52 Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; Reopening of...793) Notice No. 09-12, entitled ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures'' that...
Author's personal copy Statistical pattern analysis of ultrasonic signals for fatigue damage detection
Author's personal copy Statistical pattern analysis of ultrasonic signals for fatigue damage online 6 June 2008 Keywords: Fatigue damage monitoring Ultrasonic sensing nethodology Pattern identification a b s t r a c t This paper addresses online monitoring of fatigue damage in polycrystalline alloy
Ray, Asok
Symbolic time series analysis of ultrasonic signals for fatigue damage monitoring in polycrystalline alloys
The paper presents the concept and experimental validation of an analytical tool for fatigue damage monitoring in polycrystalline alloys. Ultrasonic signals are utilized for early detection of fatigue damage during the crack initiation period. Small microstructural changes occurring inside the material during the initial stages of fatigue damage cause attenuation and distortion of transmitted waves at the receiver end. The
Shalabh Gupta; Asok Ray; Eric Keller
Fatigue strength of model active gas turbine blades subjected to programmed temperature changes close to operating temperatures
Conclusions 1.The static tensile load leads to a sharp reduction of the amplitudes of the failure stress for the ZhS6K alloy at higher temperatures.2.Under steady temperature conditions and sign-constant tensile cyclic loading the difference in fatigue strength and life between testpieces and model blades is insignificant.3.With programmed temperature changes similar to those in operating gas turbine engines the fatigue strength
B. N. Sinaiskii
Sliding contact fatigue damage in layered ceramic structures.
Porcelain-veneered restorations often chip and fracture from repeated occlusal loading, making fatigue studies relevant. Most fatigue studies are limited to uni-axial loading without sliding motion. We hypothesized that bi-axial loading (contact-load-slide-liftoff, simulating a masticatory cycle), as compared with uni-axial loading, accelerates the fatigue of layered ceramics. Monolithic glass plates were epoxy-joined to polycarbonate substrates as a transparent model for an all-ceramic crown on dentin. Uni-and bi-axial cyclic contact was applied through a hard sphere in water, by means of a mouth-motion simulator apparatus. The uni-axial (contact-load-hold-liftoff) and traditional R-ratio fatigue (indenter never leaves the specimen surface) produced similar lifespans, while bi-axial fatigue was more severe. The accelerated crack growth rate in bi-axial fatigue is attributed to enhanced tensile stresses at the trailing edges of a moving indenter. Fracture mechanics descriptions for damage evolution in brittle materials loaded repeatedly with a sliding sphere are provided. Clinical relevance is addressed. PMID:17959894
Kim, J-W; Kim, J-H; Thompson, V P; Zhang, Y
Fatigue and creep-fatigue damage of austenitic stainless steels under multiaxial loading
The objectives of the present study are to observe and model physical damage induced by cyclic multiaxial (tension-torsion) loading of 316L stainless steel both at room temperature and at elevated temperature. Four types of experiments were carried out on thin tubular specimens: (a) continuous pure fatigue (PF) tests; (b) PF sequential tests with different sequences of push-pull and torsional loading; (c) creep-fatigue (CF) tests with superimposed hold time at maximum tensile strain; and (d) sequential tests involving sequences of PF and CF loadings. Optical microscopy and scanning electron microscopy (SEM) were used to study quantitatively the damage, in particular, to determine the orientation of cracks and to measure the kinetics of crack nucleation and crack growth. It is shown that in PF at 600 C, the classical crack initiation stage one is bypassed due to a strong interaction between cyclic plasticity, oxidation, and cracking. Intense slip bands act as diffusional short circuits, leading to the formation of external and internal oxide scales. The orientation of the microcracks during initiation and propagation stages, which is strongly affected by oxidation effects, explains qualitatively the significant deviations observed in the sequential tests from the Miner linear damage cumulative rule. It is also shown that CF damage, which involves intergranular damage, is a complex process rather than a simple superposition of fatigue and creep damage. A stochastic model based on a Monte-Carlo simulation is developed. This model includes damage equations based on quantitative metallographical observations. Damage is modeled as the continuous nucleation of a population of growing cracks which eventually coalesce to lead to final fracture. It is shown that this simulation is able to reproduce with a good accuracy the fatigue lives measured under multiaxial continuous and sequential tests.
Weiss, J. (Dartmouth Coll., Hanover, NH (United States). Ice Research Lab.); Pineau, A. (Ecole des Mines, Evry (France). Centre des Materiaux)
Continuum Fatigue Damage Modeling for Use in Life Extending Control
NASA Technical Reports Server (NTRS)
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.
Reduction in fiber damage thresholds due to static fatigue
NASA Astrophysics Data System (ADS)
For a number of years we have been investigating laser-induced damage mechanisms that can occur during the transmission of Q-switched, Nd/YAG laser pulses through fused silica fibers. We have found that fiber end-face characteristics, laser characteristics, and aspects of the laser-to-fiber injection typically determine dominant damage mechanisms. However, an additional damage process has been observed occasionally at internal sites where fibers were experiencing significant local stresses due to fixturing or to bends in the fiber path. A transmission reduction prior to damage was typically not measureable at these sites. Damage would not always occur during initial testing, but sometimes occurred later in time at laser levels that previously had been transmitted without damage. In these cases the time at stress appeared to be more important than the number of transmitted shots prior to damage. A possible relation between internal damage thresholds at stressed sites and the total time under stress is suggested by the fact that silica fibers experience static fatigue processes. These processes involve the slow growth of local defects under tensile stress at rates that depend upon environmental conditions. Defects reaching sufficient size and having appropriate location could be sites for reduced laser-induced damage thresholds. This possibility could have important implications for high-power fiber transmission systems that must satisfy extended lifetime requirements. The needs of the telecommunications industry have motivated extensive studies into initial fiber defect characteristics and their likely growth mechanisms. The present work used the understanding developed in these studies to guide a preliminary experimental investigation into the possibility that static fatigue processes can affect damage thresholds. The experiments used a laser injection and fiber routing configuration that produced significantly elevated fluences within fiber core regions under tensile stress. In one set of experiments, internal damage thresholds were determined in available fiber samples that had been assembled in stress-imposing fixtures for periods up to 24 months. A decline in mean thresholds with time was observed, although measured values showed significant scatter. In order to establish initial strength and fatigue properties for these fibers, a number of additional samples were used to generate time-to-failure data at various stress levels. Based on these results, other fiber samples were subjected to conditions that greatly accelerated fatigue processes. Internal damage thresholds were then measured in these fibers and compared to thresholds measured in fresh fibers. Conclusive comparisons were frustrated by sample-to-sample and lot-to-lot variations in fiber defects.
Setchell, Robert E.
Recovery of Fatigue Damage and Life Prediction by Laser Irradiation Healing Treatment for Copper Film
NASA Astrophysics Data System (ADS)
A fatigue life prediction method was investigated after healing fatigue damage by excimer laser irradiation treatment for the damaged copper film. First, the variations of residual fatigue life and strain range for the damaged specimens after laser irradiation healing treatment were analyzed. The results showed that the fatigue damage can be effectively healed by laser irradiation for copper film. The presented healing phenomenon during laser irradiation process showed that the recovery of fatigue damage can result in the improvement in fatigue life for the damaged copper film. Then, based on the fact that the strain concentration factor of copper film had not been changed before and after laser irradiation treatment, a residual fatigue life prediction method was proposed by the local stress transformation. The predicted residual fatigue lives by the proposed method agreed well with the experimental results for copper film after laser irradiation treatment.
Guo, Yu-Bo; Shang, De-Guang; Liu, Xiao-Dong; Ren, Chong-Gang; Liu, Feng-Zhu; Zhang, Li-Hong; Sun, Yu-Juan
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 fatigue--nozzles, combustors; environmental attack, such as oxidation, sulfidation, hot corrosion, and standby corrosion--hot-section blades and stators, transition pieces, and combustors; creep damage--hot-section nozzles and blades; erosion and wear; impact overload damage; thermal aging; combined failure mechanisms, such as creep/fatigue corrosion/fatigue, oxidation/erosion, and so on. Avoiding GT blade problems requires that two conditions be met: first, and most important, the basic design has to be sound, with adequate safety factors incorporates. Second, the proper operating regime must be maintained. Properly applied, condition monitoring can help maintain the operating regime and minimize blade distress. Should blade failures occur, data captured in a monitoring program may provide valuable clues to help identify the root causes. Reviewed here are the latest GT condition monitoring techniques, as well as several case histories that illustrate their importance.
Meher-Homji, C.B. [Boyce Engineering International Inc., Houston, TX (United States)
Influence of porosity on fatigue cumulative damage of sintered iron
Fatigue represents a common mechanical condition during service for materials used in structural components. This type of loading becomes particularly critical when alternating stress amplitude may be expected to vary, or change, in some way during the service life. Such variations and changes in load amplitude make the direct use of standard S-N curves inapplicable, because these curves are developed and presented for constant stress amplitude operation. In the present paper, results of cumulative damage under fatigue of porous materials are reported. The specimens used were produced by compacting and sintering iron powder. Their as-sintered porosity contents were P{sub 0} = 4.1 and 12.4%. Uniaxial fatigue tests (tensile-compression) were carried out at room temperature on a hydraulic testing machine.
Palma, E.S. [Federal Univ. of Minas Gerais, Belo Horizonte, MG (Brazil). Dept. of Mechanical Engineering
Influence of porosity on fatigue cumulative damage of sintered iron
NASA Astrophysics Data System (ADS)
Fatigue represents a common mechanical condition during service for materials used in structural components. This type of loading becomes particularly critical when alternating stress amplitude may be expected to vary, or change, in some way during the service life. Such variations and changes in load amplitude make the direct use of standard S-N curves inapplicable, because these curves are developed and presented for constant stress amplitude operation. In the present paper, results of cumulative damage under fatigue of porous materials are reported. The specimens used were produced by compacting and sintering iron powder. Their as-sintered porosity contents were P 0 = 4.1 and 12.4 %. Uniaxial fatigue tests (tensile-compression) were carried out at room temperature on a hydraulic testing machine.
Palma, E. S.
The treatment of fatigue and damage accumulation in composite design
NASA Astrophysics Data System (ADS)
Differences between the treatment of damage, damage accumulation, and fatigue for various types of advanced composite systems, for example, polymer matrix composites (PMCs), ceramic matrix composites (CMCs), and MMCs are discussed in general. The approach for PMCs from the aspect of damage mechanics is reviewed next and extended to a discussion of various aerospace certification approaches adopted for PMC structures. Following this an explanation of the theoretical foundations for the 'wearout philosophy' in conjunction with related damage and fracture mechanics relationships is provided. This concludes with a survey of flaw, or more precisely, damage growth rate exponents for various matrix and/or interface-dominated failure mechanisms for PMCs and adhesively bonded joints.
Kedward, K. T.; Beaumont, P. W. R.
Continuum damage mechanics (CDM) modelling demonstrates that ligament fatigue damage accumulates by different mechanisms than creep damage.
Ligaments can be subjected to creep and fatigue damage when loaded to higher than normal stresses due to injury of a complementary joint restraint. Continuum damage mechanics (CDM) assumes that diffuse damage accumulates in a material, thereby reducing the effective cross-sectional area and leading to eventual rupture. The objective of this study was to apply CDM modelling to ligament creep and fatigue to reveal mechanisms of damage. Fatigue was modelled by cyclically varying the stress in the creep model. A few novel approaches were used. First, area reduction was not assumed equal to modulus reduction; thus, allowing damaged fibres to potentially contribute to load-bearing through the extracellular matrix. Modulus ratio was related to area reduction using residual strength. Second, damage rate was not assumed constant but rather was determined directly from the modulus ratio change with respect to time. Third, modulus ratio was normalized to maximum modulus to avoid artificial calculation of negative damage. With this approach, the creep time-to-rupture was predicted with -4% error at 60% UTS and -13% error at 30% UTS. At 15% UTS, no test was undertaken experimentally for a duration as long as the 24 days predicted theoretically. Oscillating the time-dependent damage in the creep model could not completely explain the fatigue behaviour because the fatigue time-to-rupture was predicted with over 1300% error at all stresses. These results suggest that a cycle-dependent damage mechanism, in addition to a time-dependent one, was responsible for fatigue rupture. Cycle-dependent damage may be an important consideration for rehabilitation activities following injury of a complementary ligament restraint. PMID:17582420
Schwab, Timothy D; Johnston, Clifton R; Oxland, Thomas R; Thornton, Gail M
Lamb Wave Assessment of Fatigue and Thermal Damage in Composites
NASA Technical Reports Server (NTRS)
Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper describes two studies which monitor fatigue damage and two studies which monitor thermal damage in composites using Lamb waves. In the fatigue studies, the Lamb wave velocity is compared to modulus measurements obtained using strain gage measurements in the first experiment and the velocity is monitored along with the crack density in the second. In the thermal damage studies, one examines samples which were exposed to varying temperatures for a three minute duration and the second includes rapid thermal damage in composites by intense laser beams. In all studies, the Lamb wave velocity is demonstrated to be an excellent method to monitor damage in composites.
Seale, Michael D.; Smith, Barry T.; Prosser, W. H.
A new multiaxial fatigue damage model for various metallic materials under the combination of tension and torsion loadings
Based on the critical plane approach, a new damage parameter for multiaxial fatigue damage is presented. Both components of strain and stress are considered in this parameter. Thus, a new multiaxial fatigue damage model is given based on the critical plane approach. The capability of fatigue life prediction for the proposed fatigue damage model is checked against the experimental data
Jing Li; Zhong-ping Zhang; Qiang Sun; Chun-wang Li; Yan-jiang Qiao
Continuum Damage Mechanics for hysteresis and fatigue of quasi-brittle materials and structures
Continuum Damage Mechanics for hysteresis and fatigue of quasi-brittle materials and structures R in the present work that damage, from the Continuum Damage Mechanics point of view, may be seen as the firstname.lastname@example.com, tel: 33 1 47 40 74 60, fax: 33 1 47 40 74 65 #12;CONTINUUM DAMAGE MECHANICS FOR HYSTERESIS AND FATIGUE
Stochastic Measure of Fatigue Crack Damage for Health Monitoring of Ductile
245 Stochastic Measure of Fatigue Crack Damage for Health Monitoring of Ductile Alloy Structures 16802, USA This paper models a stochastic measure of fatigue crack damage in ductile alloys of fracture mechanics and are substantiated by Karhunen-Loe`ve decomposition of fatigue test data where
Ray, Asok
Two scale damage model and related numerical issues for thermo-mechanical High Cycle Fatigue
On the idea that fatigue damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), a three-dimensional two scale damage model has been proposed for High Cycle Fatigue applications. It is extended here to anisothermal cases and then to thermo-mechanical fatigue. The modeling consists in the micromechanics analysis of a
R. Desmorat; A. Kane; M. Seyedi; J. P. Sermage
A stress invariant based criterion to estimate fatigue damage under multiaxial loading
This paper summarises an attempt to propose a novel stress invariant based approach suitable for estimating fatigue damage in the presence of complex multiaxial fatigue loadings. In more detail, according to the devised method, fatigue damage is evaluated by studying the components of the deviator path projected along the axes of a convenient frame of reference, whose orientation univocally depends
A. Cristofori; L. Susmel; R. Tovo
77 FR 30877 - Aging Airplane Program: Widespread Fatigue Damage; Technical Amendment
Federal Register 2010, 2011, 2012, 2013, 2014
...121-360, 129-51] RIN 2120-AI05 Aging Airplane Program: Widespread Fatigue Damage...FAA published a final rule entitled, ``Aging Airplane Program: Widespread Fatigue Damage...the preamble of the rule entitled, ``Aging Airplane Program: Widespread Fatigue...
A continuum damage modelling of quasi-static fatigue strength of plain concrete
A continuum damage modelling of quasi-static fatigue strength of plain concrete S. H. Maia,b , F of concrete. The approach is based on the framework of continuum damage mechanics where the fatigue model fatigue tests have been performed on a concrete the formulation of which is close to the one used
Paris-Sud XI, Université de
On fatigue damage assessment in bimodal random processes
Rainflow fatigue damage in bimodal Gaussian processes is discussed. Some methods specifically developed for bimodal processes (e.g., single-moment, Jiao–Moan, Sakai–Okamura and Fu–Cebon method) are compared with the Tovo–Benasciutti method, a new approach valid for the broader class of wide-band processes. Further, an improvement of the Fu–Cebon method is also proposed. Numerically simulated bimodal random processes are used to compare the
D. Benasciutti; R. Tovo
Fatigue Crack Growth Database for Damage Tolerance Analysis
NASA Technical Reports Server (NTRS)
The objective of this project was to begin the process of developing a fatigue crack growth database (FCGD) of metallic materials for use in damage tolerance analysis of aircraft structure. For this initial effort, crack growth rate data in the NASGRO (Registered trademark) database, the United States Air Force Damage Tolerant Design Handbook, and other publicly available sources were examined and used to develop a database that characterizes crack growth behavior for specific applications (materials). The focus of this effort was on materials for general commercial aircraft applications, including large transport airplanes, small transport commuter airplanes, general aviation airplanes, and rotorcraft. The end products of this project are the FCGD software and this report. The specific goal of this effort was to present fatigue crack growth data in three usable formats: (1) NASGRO equation parameters, (2) Walker equation parameters, and (3) tabular data points. The development of this FCGD will begin the process of developing a consistent set of standard fatigue crack growth material properties. It is envisioned that the end product of the process will be a general repository for credible and well-documented fracture properties that may be used as a default standard in damage tolerance analyses.
Forman, R. G.; Shivakumar, V.; Cardinal, J. W.; Williams, L. C.; McKeighan, P. C.
Static and fatigue damage in high temperature composites. Final report
This final report presents the experimental and theoretical work performed in our research program on static and fatigue damage in high temperature composites. The theoretical part focused on development and implementation of a new Transformation Field Analysis (TFA) for inelastic laminates, which employs unit-call, periodic array models, as well as averaging micromechanical models together with any constitutive law for thermo-viscoplastic and other inelastic deformation. Moreover, we have initiated modeling of damage by debonding and frictional sliding at the fiber interface, using the TFA computational scheme and the finite element method.
Dvorak, G.J.; Bahei-El-Din, Y.A.
Blasim: A computational tool to assess ice impact damage on engine blades
NASA Astrophysics Data System (ADS)
A portable computer called BLASIM was developed at NASA LeRC to assess ice impact damage on aircraft engine blades. In addition to ice impact analyses, the code also contains static, dynamic, resonance margin, and supersonic flutter analysis capabilities. Solid, hollow, superhybrid, and composite blades are supported. An optional preprocessor (input generator) was also developed to interactively generate input for BLASIM. The blade geometry can be defined using a series of airfoils at discrete input stations or by a finite element grid. The code employs a coarse, fixed finite element mesh containing triangular plate finite elements to minimize program execution time. Ice piece is modeled using an equivalent spherical objective that has a high velocity opposite that of the aircraft and parallel to the engine axis. For local impact damage assessment, the impact load is considered as a distributed force acting over a region around the impact point. The average radial strain of the finite elements along the leading edge is used as a measure of the local damage. To estimate damage at the blade root, the impact is treated as an impulse and a combined stress failure criteria is employed. Parametric studies of local and root ice impact damage, and post-impact dynamics are discussed for solid and composite blades.
Reddy, E. S.; Abumeri, G. H.; Chamis, C. C.
Application of PVDF Film Sensor to Detect Early Damage in Wind Turbine Blade Components
Monitoring technique for detection of early damage in the wind turbine blade has been investigated using PVDF film sensor and strain gages. The trailing edge component with shear web was prepared by sectioning the full-scale blade with a box spa. Several PVDF film sensors with dimension of 10x10x0.054 mm3 and strain gages were installed on shear web and skin of
Y.-H. Huh; J. I. Kim; J. H. Lee; S. G. Hong; J. H. Park
Detection of Pre-Crack Fatigue Damage in a U.S. Army MH47E Chinook Aft Rotor Shaft
Accumulated fatigue damage in flight critical helicopter dynamic components prior to crack initiation and detection is currently estimated by fatigue analysis based upon fatigue test results. To more accurately assess the operational fatigue damage and remaining useful life of a critical component prior to the initiation of a detectable crack, a non-destructive evaluation (NDE) process that directly measures accumulated fatigue
D. Granger; C. A. Rideout; S. Yano; D. J. White
Estimation of fatigue damage parameters using guided wave technique
NASA Astrophysics Data System (ADS)
In the present work we have considered the problem of monitoring a fatigue crack growth in a thin plate specimen. The problem is first solved analytically by modeling the structure with a cyclic plastic zone around the crack. The damaged region is modeled as a visco-elastic zone and other regions are modeled as elastic zones. Using the one-dimensional guided wave model, the reflected and transmitted energies of the guided waves from the fatigue crack and plastic zone are studied. Experimental study of the reflected and transmitted energies is done using guided waves generated and received by piezoelectric wafers. The reflected and transmitted energies are derived at various cycles of fatigue loading till the failure of the structure. Validation of the results from the analytical model is done by comparing the results obtained from the experiments. The reflected and transmitted energy is related to the size of crack size or the magnitude of loading. Using crack size and the nature of loading, a method is proposed to estimate the fatigue life using fracture mechanics approach.
Rathod, V. T.; Roy Mahapatra, D.
Cumulative fatigue damage and life prediction theories: a survey of the state of the art for homogeneous materials
Fatigue damage increases with applied load cycles in a cumulative manner. Cumulative fatigue damage analysis plays a key role in life prediction of components and structures subjected to field load histories. Since the introduction of damage accumulation concept by Palmgren about 70 years ago and 'linear damage rule' by Miner about 50 years ago, the treatment of cumulative fatigue damage
A. Fatemi; L. Yang
Periostin Deficiency Increases Bone Damage and Impairs Injury Response to Fatigue Loading in Adult Mice
Bone damage removal and callus formation in response to fatigue loading are essential to prevent fractures. Periostin (Postn) is a matricellular protein that mediates adaptive response of cortical bone to loading. Whether and how periostin influences damage and the injury response to fatigue remains unknown. We investigated the skeletal response of Postn-/- and Postn+/+ mice after fatigue stimulus by axial compression of their tibia. In Postn+/+ mice, cracks number and surface (CsNb, CsS) increased 1h after fatigue, with a decrease in strength compared to non-fatigued tibia. At 15 days, CsNb had started to decline, while CtTV and CtBV increased in fatigued vs non-fatigued tibia, reflecting a woven bone response that was present in 75% of the fatigued bones. Cortical porosity and remodelling also prominently increased in the fatigued tibia of Postn+/+ mice. At 30 days, paralleling a continuous removal of cortical damage, strength of the fatigued tibia was similar to the non-fatigue tibia. In Postn-/- mice, cracks were detectable even in the absence of fatigue, while the amount of collagen crosslinks and tissue hardness was decreased compared to Postn+/+. Fatigue significantly increased CsNb and CsS in Postn-/-, but was not associated with changes in CtTV and CtBV, as only 16% of the fatigued bones formed some woven bone. Cortical porosity and remodelling did not increase either after fatigue in Postn-/- , and the level of damage remained high even after 30 days. As a result, strength remained compromised in Postn-/- mice. Contrary to Postn+/+ , which osteocytic lacunae showed a change in the degree of anisotropy (DA) after fatigue, Postn-/- showed no DA change. Hence periostin appears to influence bone materials properties, damage accumulation and repair, including local modeling/remodeling processes in response to fatigue. These observations suggest that the level of periostin expression could influence the propensity to fatigue fractures. PMID:24167618
Bonnet, Nicolas; Gineyts, Evelyne; Ammann, Patrick; Conway, Simon J.; Garnero, Patrick; Ferrari, Serge
Near-terminal creep damage does not substantially influence fatigue life under physiological loading.
Cortical bone specimens were damaged using repeated blocks of tensile creep loading until a near-terminal amount of creep damage was generated (corresponding to a reduction in elastic modulus of 15%). One group of cortical bone specimens was submitted to the near-terminal damage protocol and subsequently underwent fatigue loading in tension with a maximum strain of 2000 ?? (Damage Fatigue, n=5). A second group was submitted to cyclic fatigue loading but was not pre-damaged (Control Fatigue, n=5). All but one specimen (a damaged specimen) reached run-out (10 million cycles, 7.7 days). No significant differences in microscopic cracks or other tissue damage were observed between the two groups or between either group and additional, completely unloaded specimens. Our results suggest that damage in cortical bone allograft that is not obvious or associated with a stress riser may not substantially affect its fatigue life under physiologic loading. PMID:21592481
Stern, Lorraine C; Brinkman, Jennifer G; Furmanski, Jevan; Rimnac, Clare M; Hernandez, Christopher J
The effect of yield strength and ductility to fatigue damage
NASA Technical Reports Server (NTRS)
The cumulative damage of aluminium alloys with different yield strength and various ductility due to seismic loads was studied. The responses of an idealized beam with a centered mass at one end and fixed at the other end to El Centro's and Taft's earthquakes are computed by assuming that the alloys are perfectly elastoplastic materials and by using numerical technique. Consequently, the corresponding residual plastic strain can be obtained from the stress-strain relationship. The revised Palmgren-Miner cumulative damage theorem is utilized to calculate the fatigue damage. The numerical results show that in certain cases, the high ductility materials are more resistant to seismic loads than the high yield strength materials. The results also show that if a structure collapse during the earthquake, the collapse always occurs in the very early stage.
Yeh, H. Y.
Fatigue damage model for injection-molded short glass fibre reinforced thermoplastics
The present paper is a contribution to the phenomenological modelling of fatigue non-linear cumulative diffuse damage in short glass fibre reinforced thermoplastic matrix composites. In such materials, fatigue damage kinetic exhibits three stages, namely: (i) material softening and damage initiation, (ii) coalescence and propagation of micro-cracks and (iii) macroscopic cracks propagation and material failure. The proposed model is built in
H. Nouri; F. Meraghni; P. Lory
Cycle distribution and fatigue damage under broad-band random loading
Fatigue damage under broad-band loading is analysed by summarizing and reviewing available analytical solutions. Relationships between fatigue damage assessment and counting methods are investigated by establishing when, in frequency domain analysis, analytical solutions of expected damage are connected with a counting procedure assumption and how this is related to the rainflow counting procedure. A new approach is also proposed for
Roberto Tovo
Online fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach
The paper presents an analytical tool for early detection and online monitoring of fatigue damage in polycrystalline alloys that are commonly used in mechanical structures of human-engineered complex systems. Real-time fatigue damage monitoring algorithms rely on time series analysis of ultrasonic signals that are sensitive to micro-structural changes occurring inside the material during the early stages of fatigue damage; the
Shalabh Gupta; Asok Ray; Eric Keller
Model-Trained Neural Networks and Electronic Holography Demonstrated to Detect Damage in Blades
NASA Technical Reports Server (NTRS)
Detect Damage in Blades Electronic holography can show damaged regions in fan blades at 30 frames/sec. The electronic holograms are transformed by finite-element-model-trained artificial neural networks to visualize the damage. The trained neural networks are linked with video and graphics to visualize the bending-induced strain distribution, which is very sensitive to damage. By contrast, it is very difficult to detect damage by viewing the raw, speckled, characteristic fringe patterns. For neural-network visualization of damage, 2 frames or 2 fields are used, rather than the 12 frames normally used to compute the displacement distribution from electronic holograms. At the NASA Lewis Research Center, finite element models are used to compute displacement and strain distributions for the vibration modes of undamaged and cracked blades. A model of electronic time-averaged holography is used to transform the displacement distributions into finite-element-resolution characteristic fringe patterns. Then, a feedforward neural network is trained with the fringe-pattern/strain-pattern pairs, and the neural network, electronic holography, and video are implemented on a workstation. Now that the neural networks have been tested successfully at 30 frames/sec on undamaged and cracked cantilevers, the electronic holography and neural-network processing are being adapted for onsite damage inspection of twisted fan blades and rotormounted blades. Our conclusion is that model-trained neural nets are effective when they are trained with good models whose application is well understood. This work supports the aeromechanical testing portion of the Advanced Subsonic Technology Project.
Decker, Arthur J.; Fite, E. Brian; Mehmed, Oral; Thorp, Scott A.
Damage evolution in metal matrix composites subjected to thermomechanical fatigue
A thermomechanical analysis of unidirectional continuous fiber metal matrix composites is presented. The analysis includes the effects of processing induced residual thermal stresses, interface cracking, and inelastic matrix behavior on damage evolution. Due to the complexity of the nonlinear effects, the analysis is performed computationally using the finite element method. The interface fracture is modeled by a nonlinear constitutive model. The problem formulation is summarized and results are presented for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue.
Allen, D.H. [Texas A and M Univ., College Station, TX (United States). Center for Mechanics of Composites; Hurtado, L.D.; Helms, K.L.E. [Sandia National Labs., Albuquerque, NM (United States)
Corrosion fatigue behavior of coated 4340 steel for blade retention bolts of the AH1G helicopter. Final report
The main rotor blade bolt for the 540 helicopter rotor system of the AH-1G, UH-1C, and UH-1M helicopters is proposed to be improved by substituting plasma-sprayed tungsten carbide coating on the outer shank of the 4340 steel bolt for the present cadmium or chromium plate. This study was undertaken to determine the effects of these coating systems on the fatigue
M. Levy; J. L. Morrossi
Determination of Turbine Blade Life from Engine Field Data
NASA Technical Reports Server (NTRS)
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.
Fatigue crack growth spectrum simplification: Facilitation of on-board damage prognosis systems
Better lifetime predictions of systems subjected to fatigue loading are needed in support of the optimization of the costs of life-cycle engineering. In particular, the climate is especially encouraging for the development of safer aircraft. One issue is that aircraft experience complex fatigue loading and current methods for the prediction of fatigue damage accumulation rely on intensive computational tools that
Matthew Adam Adler
High cycle fatigue damage mechanisms in cast aluminium subject to complex loads
High cycle fatigue damage mechanisms in cast aluminium subject to complex loads Imade Koutiria to the high cycle fatigue behaviour of cast hypo-eutectic AlÂSi alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue
Paris-Sud XI, Université de
Effective AE source location of damages in the wind turbine blade
NASA Astrophysics Data System (ADS)
Acoustic emission (AE) has emerged as a powerful nondestructive tool to detect preexisting defects or to characterize failure mechanisms. Recently, this technique or this kind of principle, that is an in-situ monitoring of inside damages of materials or structures, becomes increasingly popular for monitoring the integrity of large structures like a huge wind blade. Therefore, it is required to find a symptom of damage propagation before catastrophic failure through a continuous monitoring. In this study, we have tried to develop a source location algorithm for damage identification on the part of real wind turbine blade. First, it was focused to understand the activities of acoustic emission events generated from the glass fiber reinforced plastic (GFRP) structures such as a wind blade. Secondly, this study aims to identify and locate the damages from blade specimens. In this work, the activities of AE signals generated from external artificial sources was evaluated and located by new developed source location algorithm. The results show that new suggested source location algorithm was much higher performance than conventional source location method.
Yoon, D. J.; Han, B. H.
Modeling progressive damage accumulation in thin walled composite beams for rotor blade applications
In the present study, models of the key damage modes in composite materials such as matrix cracking, debonding\\/delamination and fiber breakage are included in a thin walled composite beam analysis for helicopter rotor blade applications. The effects of transverse shear, elastic couplings and restrained warping are also included while modeling the thin walled composite beams. Matrix cracking is modeled at
Prashant M. Pawar; Ranjan Ganguli
Study of crack initiation or damage in very high cycle fatigue using ultrasonic fatigue test and microstructure analysis.
Fatigue damage behaviors of four metal materials in the very high cycle fatigue (VHCF) regime have been studied using ultrasonic fatigue test and microstructure analysis. The results show that the fatigue crack initiation in VHCF regime could occur at subsurface non-defect fatigue crack origin (SNDFCO), where the accumulated cyclic strains or damage in the specimens were highly localized, especially in the materials with some softer phase, where the local maximum strain can be eight times higher than the average strain value in the specimen. This high strain localization can cause a local plasticity exhaustion that leads to a stress concentration and consequently fatigue crack initiation, and finally the formation of SNDFCO. For pure single phase austenitic material, strain localization can also occur due to dislocation accumulation at or near grain boundaries, which can become fatigue crack initiation origin in the VHCF regime. The results in this study show that fatigue damage and crack initiation mechanisms in the VHCF regime can be different in different metals due to the mechanisms for local plasticity exhaustion. PMID:23850182
Chai, Guocai; Zhou, Nian
Damage evolution during thermo-mechanical fatigue of a coated monocrystalline nickel-base superalloy
To prevent hot gas corrosion nickel-base turbine blades used in today's jet engines, they are protected with so called Pt-modified ?-NiAl coatings which are also subjected to thermo-mechanical loading during service. The effects of thermo-mechanical fatigue (TMF) loading on the coating as well as TMF life are the subjects of this paper. Microstructural investigations before, during and after thermo-mechanical fatigue
R. Nützel; E. Affeldt; M. Göken
A study of cumulative fatigue damage in titanium 6Al-4V alloy
NASA Technical Reports Server (NTRS)
Experimental data were obtained using titanium 6Al-4V alloy under stress ratios of -1, 0, and negative infinity. A study of cumulative fatigue damage using Miner's (1945) and Kramer's (1974) equations for stress ratios of -1 and 0 for low-high, low-high mixed, high-low, and high-low mixed stress sequences has revealed close agreement between the theoretical and experimental values of fatigue damage and fatigue life. Kramer's equation predicts less conservative and more realistic cumulative fatigue damage than does the popularly used Miner's rule.
Jeelani, S.; Ghebremedhin, S.; Musial, M.
A thermo-mechanical fatigue damage model for variable temperature and loading amplitude conditions
A fatigue life prediction method for thermo-mechanical fatigue damage under variable temperature and loading amplitudes was proposed. In this approach, a rainflow cycle counting technique was used to extract cycle counts from the mechanical loading history. For each loading cycle, an equivalent damage temperature was determined. Once the equivalent temperature was used, the loop would be guaranteed closed. This approach
Hong Tae Kang; Yung-Li Lee; Jim Chen; David Fan
Micro-Mechanics of Fatigue Damage in Pb-Sn Solder Due to Vibration
age and experience fatigue damage due to complex combinations of vibration loading and cyclic thermo-mechanical caused by thermo-mechanical cycling. This paper mechanistically explores fatigue damage accumulation to thermo-mechanical cycling. 1. INTRODUCTION EUTECTIC Pb-Sn SOLDER used in electronic packaging
Sharma, Pradeep
Cumulative damage with interaction effect due to fatigue under torsion loading
The cumulative-fatigue damage concept previously developed by means of the test results obtained under axial loading is adapted for the cyclic-torsion case. The development allows one to establish the fatigue diagram (shear strain versus cycles at failure) and to calculate the remaining life under several level straining. As the damage function is strain dependent, the predictions are different from those
Thang Bui-Quoc
Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions
NASA Astrophysics Data System (ADS)
Strain-controlled low-cycle fatigue (LCF) tests were conducted on ductile cast iron (DCI) at strain rates of 0.02, 0.002, and 0.0002/s in the temperature range from room temperature to 1073 K (800 °C). A constitutive-damage model was developed within the integrated creep-fatigue theory (ICFT) framework on the premise of strain decomposition into rate-independent plasticity and time-dependent creep. Four major damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation were considered in a nonlinear creep-fatigue interaction model which represents the overall damage accumulation process consisting of oxidation-assisted fatigue crack nucleation and propagation in coalescence with internally distributed damage ( e.g., IE and creep), leading to final fracture. The model was found to agree with the experimental observations of the complex DCI-LCF phenomena, for which the linear damage summation rule would fail.
Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Sloss, Clayton
Fiber-Optic Defect and Damage Locator System for Wind Turbine Blades
IFOS in collaboration with Auburn University demonstrated the feasibility of a Fiber Bragg Grating (FBG) integrated sensor system capable of providing real time in-situ defect detection, localization and quantification of damage. In addition, the system is capable of validating wind turbine blade structural models, using recent advances in non-contact, non-destructive dynamic testing of composite structures. This new generation method makes it possible to analyze wind turbine blades not only non-destructively, but also without physically contacting or implanting intrusive electrical elements and transducers into the structure. Phase I successfully demonstrated the feasibility of the technology with the construction of a 1.5 kHz sensor interrogator and preliminary instrumentation and testing of both composite material coupons and a wind turbine blade.
Dr. Vahid Sotoudeh; Dr. Richard J. Black; Dr. Behzad Moslehi; Mr. Aleks Plavsic
Fatigue damage evolution in uni-directional metal matrix composites using a micro-mechanical damage model
In recent years Metal Matrix Composites (MMC) have drawn wide attention as candidate materials for high temperature applications needed in aerospace and aeronautic industries. Especially the Titanium Matrix Composites (TMC) have been favored for such applications mainly due to their high strength to weight ratio and their ability to maintain their structural integrity even at elevated temperatures. Despite the increased use of these TMC`s for the last decade there is still a need for appropriate material models able to simulate the material behavior of such advanced MMC`s under severe loading conditions such as fatigue loading. Modeling fatigue behavior of MMC`s requires the prediction of material degradation during the material lifetime through the concept of damage and damage evolution. A micro-mechanical fatigue damage model is proposed here capable of modeling damage evolution at the constituent level. Damage criteria are defined for each individual constituent and appropriate damage evolution laws are derived. Furthermore damage evolution in the interface region is considered separately. The overall composite damage is obtained through the employment of a homogenization procedure such as the Mori-Tanaka averaging scheme. Numerical results are shown for high cycle fatigue with respect to a variation in various material and damage model parameters. Furthermore the damage evolution in the fiber, the matrix and the overall composite is presented for a complete fatigue simulation.
Echle, R.; Voyiadjis, G.Z. [Louisiana State Univ., Baton Rouge, LA (United States). Dept. of Civil and Environmental Engineering
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
Damage estimates for European and US sites using the US high-cycle fatigue data base
This paper uses two high-cycle fatigue data bases, US blade materials and one for European materials the service lifetime of a wind turbine blade sit WISPER load spectrum for northern European sit 19921 and the WISPER protocol load spectrum farm sites. The US data base, developed by Mandell, et al. (1995), contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. Further, the analyses demonstrate that the European and the US fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the US data base predicting significantly shorter service lifetimes than the European data base.
Sutherland, H.J.
Acoustic Emission Monitoring of Small Wind Turbine Blades
Wind turbine blade certification tests, comprising a static test, a fatigue test, and finally a residual strength test, often involve sudden audible cracking sounds from somewhere within the blade, without the operators being able to locate the noise source, or to determine whether damage (minor or major) has occurred. A current EC-funded research project is looking at the possibility of
P. A. Joosse; A. G. Dutton; D. A. Kouroussis; T. P. Philippidis; P. S. Vionis
Modelling of damage and failure of glass\\/epoxy composite plates subject to impact fatigue
An investigation has been carried out to study the impact fatigue damage of glass\\/epoxy laminated composites. Accumulation of damage, such as matrix cracking, delamination and fibre breakage, with repeated impact of the composite material may reduce the overall stiffness. These damage modes have been combined in a very complicated way to describe damage growth and fracture. A model is proposed
K Azouaoui; S Rechak; Z Azari; S Benmedakhene; A Laksimi; G Pluvinage
Fatigue analysis of cemented hip prosthesis: damage accumulation scenario and sensitivity analysis
This work is dedicated to the fatigue analysis of cemented total hip arthroplasty. In particular the damage evaluation scenario is simulated and a sensitivity analysis is performed. To this end, two different damage evaluation algorithms (the elasto-brittle and the continuous damage one) are proposed and implemented in the finite element code ABAQUS®. Some global damage criteria are introduced to quantify
P. Colombi
A Damage Mechanics-Based Fatigue Life Prediction Model for Solder Joints
A thermomechanical fatigue life prediction model based on the theory of damage mechan- ics is presented. The damage evolution, corresponding to the material degradation under cyclic thermomechanical loading, is quantified thermodynamic framework. The damage, as an internal state variable, is coupled with unified viscoplastic constitutive model to characterize the response of solder alloys. The damage-coupled viscoplastic model with kinematic and
Hong Tang
An anisotropic mechanical fatigue damage evolution model for Pb-free solder materials
Evaluating state of damage in a ductile material as it experiences mechanical fatigue and cyclic loading poses much complexity, and has been the subject of many researches. This study revisits the anisotropic damage model developed by Lemaitre [Lemaitre, J. 1992. A course on damage mechanics. Springer-Verlag Publishing, Berlin] and proposes to use his model combined with two damage models, a
Leila J. Ladani; Jafar Razmi
Numerical and experimental investigations into life assessment of blade–disc connections of gas turbines
The positively engaged connection between blade and disc of a gas turbine is highly stressed by fatigue and creep fatigue loadings. For this purpose, a new calculating method based on inelastic finite element analyses considering the main influences on damage was developed at MPA Stuttgart. Low cycle fatigue (LCF) tests with component-like specimens have been conducted for verification. Experimental data
Stephan Issler; Eberhard Roos
Characterization of fretting fatigue damage using nondestructive approaches
NASA Astrophysics Data System (ADS)
Ti-6Al-4V alloy specimens cut form a forged plate with a duplex microstructure, similar to the microstructure used in fan blades were tested under conditions of high-cycle fretting fatigue. The contact geometry, the normal stress, as well as the cyclic stress were selectee such that the mixed, slip-stick regime prevails during the experiments. Following testing, the specimens as well as the fretting pads were characterized by a variety of techniques including white light interference profilometry, scanning electron microscopy, ultrasonic force microscopy, microhardness testing, and electron dispersive spectroscopy (EDS). The results revealed that the surface roughness of the slip region increases compared to the roughness of the stick, and non-contact ones. In addition, at the higher spatial frequencies, the power spectral density (PSD) of the slip region increases compared to the PSD of the stick and non- contact regions, thus revealing that an increase of the population of the smaller size asperities occurs. The microstructure of the material below the slip zone was found to be transformed to a finer one; and the percentage of the transformed beta phase has been decreased substantially. The elastic property variation of this region was determined by ultrasonic force microscopy; the results revealed that in contrast to what found for the bulk of the material, there are significant local differences of the elastic properties inside the fretting-affected zone. In addition, the changes in the plastic behavior of the region below the slip zone, was determined using microhardness measurements. It was found that this transformed microstructure area, has also a higher hardness compared to the hardness of the bulk structure. Booth elastic and plastic property variations were attributed to the increased percent of alpha phase and the decreased amount of beta in the transformed zone, since the former phase exhibits higher elastic moduli as well as flow stresses.In addition, changes in the concentration of the oxygen at the specimen's surface as well as inside the transformed zone were examined by energy dispersive spectroscopy (EDS). The EDS analysis revealed a high concentration of oxygen on the specimen's surface only at the slip region of the two contacting materials. This finding indicates that elevated temperatures were developed during the fretting fatigue testing, which enable the diffusion of oxygen from the atmosphere to the alloy. However, within the transformed zone, no detectable differences in the oxygen concentration were revealed. This finding allowed us to assume that stress induced transformation is the most probable mechanism.
Matikas, Theodore E.; Shell, Eric B.; Nicolaou, Perikles D.
Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage
NASA Technical Reports Server (NTRS)
Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is provided for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are provided for determining the two phases of life. The procedure involves two steps, each similar to the conventional application of the commonly used linear damage rule. When the sum of cycle ratios based on phase 1 lives reaches unity, phase 1 is presumed complete, and further loadings are summed as cycle ratios on phase 2 lives. When the phase 2 sum reaches unity, failure is presumed to occur. No other physical properties or material constants than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons of both methods are discussed.
Manson, S. S.; Halford, G. R.
Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage
NASA Technical Reports Server (NTRS)
Simple procedures are given for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is given for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are given for determining the two phases of life. The procedure comprises two steps, each similar to the conventional application of the commonly used linear damage rule. Once the sum of cycle ratios based on Phase I lives reaches unity, Phase I is presumed complete, and further loadings are summed as cycle ratios based on Phase II lives. When the Phase II sum attains unity, failure is presumed to occur. It is noted that no physical properties or material constants other than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons are discussed for both methods.
Manson, S. S.; Halford, G. R.
Fatigue damage in cross-ply titanium metal matrix composites containing center holes
NASA Technical Reports Server (NTRS)
The development of fatigue damage in (0/90) sub SCS-6/TI-15-3 laminates containing center holes was studied. Stress levels required for crack initiation in the matrix were predicted using an effective strain parameter and compared to experimental results. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state of damage consisting of matrix cracks and fiber matrix debonding was obtained which reduced the composite modulus. Matrix cracks were bridged by the 0 deg fibers. The fatigue limit (stress causing catastrophic fracture of the laminates) was also determined. The static and post fatigue residual strengths were accurately predicted using a three dimensional elastic-plastic finite element analysis. The matrix damage that occurred during fatigue loading significantly reduced the notched strength.
Bakuckas, J. G., Jr.; Johnson, W. S.; Bigelow, C. A.
Determination of engineering strain distribution in a rotor blade with fibre Bragg grating array and a rotary optic coupler
Structural damage occurs in materials subjected to repeated or fluctuating stresses that must be minimized by design to increase fatigue life, and strains distributed in a blade need to be experimentally determined for evaluating stress levels. In order to measure local strains in a rotating blade, efficient signal transmission between a sensor installed on a blade and a stationary interrogator
Kyungmok Kim; Jong Min Lee; Yoha Hwang
Impact behavior of filament-wound graphite/epoxy fan blades. [foreign object damage to turbofan engines
NASA Technical Reports Server (NTRS)
The fabrication and impact tests of graphite/epoxy filament wound fan blades are discussed. Blades which were spin tested at tip speeds up to 305 m/sec retained their structural integrity. Two blades were each impacted with a 454-g slice of a 908-g simulated bird at a tip speed of 263 deg and impact angles of 22 deg and 32 deg. The impact tests were recorded with high-speed movie film. The blade which was impacted at 22 deg sustained some root delamination but remained intact. The 32 deg impact separated the blade from the root. No local damage other than leading-edge debonding was observed for either blade. The results of a failure mode analysis are also discussed.
Bowles, K. J.
Acousto-ultrasonics-based fatigue damage characterization: Linear versus nonlinear signal features
NASA Astrophysics Data System (ADS)
Engineering structures are prone to fatigue damage over service lifespan, entailing early detection and continuous monitoring of the fatigue damage from its initiation through growth. A hybrid approach for characterizing fatigue damage was developed, using two genres of damage indices constructed based on the linear and the nonlinear features of acousto-ultrasonic waves. The feasibility, precision and practicability of using linear and nonlinear signal features, for quantitatively evaluating multiple barely visible fatigue cracks in a metallic structure, was compared. Miniaturized piezoelectric elements were networked to actively generate and acquire acousto-ultrasonic waves. The active sensing, in conjunction with a diagnostic imaging algorithm, enabled quantitative evaluation of fatigue damage and facilitated embeddable health monitoring. Results unveiled that the nonlinear features of acousto-ultrasonic waves outperform their linear counterparts in terms of the detectability. Despite the deficiency in perceiving small-scale damage and the possibility of conveying false alarms, linear features show advantages in noise tolerance and therefore superior practicability. The comparison has consequently motivated an amalgamation of linear and nonlinear features of acousto-ultrasonic waves, targeting the prediction of multi-scale damage ranging from microscopic fatigue cracks to macroscopic gross damage.
Su, Zhongqing; Zhou, Chao; Hong, Ming; Cheng, Li; Wang, Qiang; Qing, Xinlin
Cumulative creep-fatigue damage evolution in an austenitic stainless steel
NASA Technical Reports Server (NTRS)
A model of cumulative creep-fatigue damage has been developed which is based on the use of damage curve equations to describe the evolution of creep-fatigue damage for four basic creep-fatigue cycle types. These cycle types correspond to the four fundamental cycles of the Strain Range Partitioning Life Prediction approach of Manson, Halford, and Hirschberg. A concept referred to as Damage Coupling is introduced to analytically account for the differences in the nature of the damage introduced by each cycle type. For application of this model, the cumulative creep-fatigue damage behavior of type 316 stainless steel at 816 C has been experimentally established for the two-level loading cases involving fatigue and creep-fatigue, in various permutations. The tests were conducted such that the lower life (high strain) cycling was applied first, for a controlled number of cycles, and the higher life (lower strain) cycling was conducted at the second level, to failure. The proposed model correlated the majority of the observed cumulative creep-fatigue data.
Mcgaw, Michael A.
Fatigue is more damaging than creep in ligament revealed by modulus reduction and residual strength.
Following injury of a complementary joint restraint, ligaments can be subjected to higher than normal stresses. Normal ligaments are exposed to static (creep) and cyclic (fatigue) loading from which damage can accumulate at these higher than normal stresses. This study tracked damage accumulation during creep and fatigue loading of normal rabbit medial collateral ligaments (MCLs) over a range of stresses, using modulus reduction as a marker of damage. Creep tests were interrupted occasionally with unloading/reloading cycles to measure modulus. Test stresses were normalized to ultimate tensile strength (UTS): 60%, 30%, and 15% UTS. Not all creep and fatigues tests progressed until rupture but were stopped and followed by an assessment of the residual strength of that partially damaged ligament using a monotonic failure test. Fatigue loading caused earlier modulus reduction than creep. Modulus reduction occurred at lower increases in strain (strain relative to initial strain) for fatigue than creep. In other words, at the same time or increase in strain, fatigue is more damaging than creep because the modulus ratio reduction is greater. These findings suggest that creep and fatigue have different strain and damage mechanisms. Ligaments exposed to creep or fatigue loading which produced a modulus reduction had decreased residual strength and increased toe-region strain in a subsequent monotonic failure test. This finding confirmed that modulus reduction during creep and fatigue is a suitable marker of partial damage in ligament. Cyclic loading caused damage earlier than static loading, likely an important consideration when ligaments are loaded to higher than normal magnitudes following injury of a complementary joint restraint. PMID:17629791
Thornton, Gail M; Schwab, Timothy D; Oxland, Thomas R
Analytical Methodology for Predicting the Onset of Widespread Fatigue Damage in Fuselage Structure
NASA Technical Reports Server (NTRS)
NASA has developed a comprehensive analytical methodology for predicting the onset of widespread fatigue damage in fuselage structure. The determination of the number of flights and operational hours of aircraft service life that are related to the onset of widespread fatigue damage includes analyses for crack initiation, fatigue crack growth, and residual strength. Therefore, the computational capability required to predict analytically the onset of widespread fatigue damage must be able to represent a wide range of crack sizes from the material (microscale) level to the global structural-scale level. NASA studies indicate that the fatigue crack behavior in aircraft structure can be represented conveniently by the following three analysis scales: small three-dimensional cracks at the microscale level, through-the-thickness two-dimensional cracks at the local structural level, and long cracks at the global structural level. The computational requirements for each of these three analysis scales are described in this paper.
Harris, Charles E.; Newman, James C., Jr.; Piascik, Robert S.; Starnes, James H., Jr.
A micro-mechanically based continuum damage model for fatigue life prediction of filled rubbers
during high cycle fatigue test is a very hard task because multi-physics and multi-scale effectsA micro-mechanically based continuum damage model for fatigue life prediction of filled rubbers J: decohesion between fillers and matrix at a micro-scale followed by a crack nucleation at a macro
Paris-Sud XI, Université de
SUBSPACE-BASED DETECTION OF FATIGUE DAMAGE ON JACKET SUPPORT STRUCTURES OF OFFSHORE WIND TURBINES turbine structures. Aim of the study was therefore to analyze the usability and effi- ciency structures of wind energy turbines. Based on results of an experimental fatigue test on a steel frame
Paris-Sud XI, Université de
Tensile fatigue damage and degradation of random short-fiber SMC composite
Fatigue damage and degradation in a random short-fiber SMC-R50 composite were investigated experimentally and theoretically. In the study of homogeneous damage, experiments were conducted to examined fundamental mechanisms and characteristics of fatigue damage and its evolution. The statistical nature of microcracks was evaluated by the introduction of damage distribution functions. Results showed that the cumulative distribution and density of microcrack length followed the form of a three-parameter Weibull function, whereas those of orientation followed a power form of the cos(theta) function. Constitutive equations for the damaged composite are derived based on the self-consistent mechanics scheme in conjunction with a three-dimensional elastic crack theory and probabilistic functions. Agreement between theoretical predictions and experimental data is excellent. The theory and analysis are able to evaluate the tensorial nature of fatigue damage and degradation of all material elastic constants. A damage tensor is introduced to describe quantitatively the degree of homogeneous fatigue damage. Stiffness degradation is related to the rate of change of microcrack evolution and accumulation, and a power-law relationship is found between the rate of damage development and fatigue loading cycles.
Chim, E.S.M.
Statistical fatigue properties in the large strain region of a stainless steel sheet for use as an abrasion strip on helicopter rotor blades
The objective of this study was to evaluate the statistical fatigue properties of a thin sheet of a stainless steel for use as an abrasion strip on helicopter rotor blades made of glass fiber\\/epoxy composite materials. The sheet was an AISI 301 1\\/4-hard stainless steel. Tensile fatigue tests were conducted up to 107 cycles on unnotched specimens under constant amplitude
Toshiyuki Shimokawa; Yasumasa Hamaguchi; Shigeru Machida; Takeshi Ogawa; Hiroaki Itabe
Effects of wave-current and fluid-structure interactions on fatigue damages of offshore structures
This paper investigates effects of wave-current and fluid-structure interactions on fatigue damages of offshore structures. Some basic formulations of the spectral analysis under a uniform current condition is presented prior to the calculation of the fatigue damages. In these formulations, a linearized Morison`s equation is used with a linearization constant which contains effects of wave-current and fluid-structure coupling. In the calculation of fatigue damages, a multi-linear S-N fatigue model is used with a non-narrow banded stress process. The probability distribution of stress ranges in a sea state is given in terms of some parameters which are determined on the basis of a rainflow cycle counting. The damage is then calculated probabilistically from contributions of the segments of the S-N model. Finally, a demonstration is presented by an example jacket structure.
Karadeniz, H. [Delft Univ. of Technology (Netherlands)
Microstructural evaluation of cumulative fatigue damage in a plant component sample
Fatigue damage accumulated in a real plant was evaluated in terms of microstructural conditioning. Microstructural damage induced in laboratory by cyclic deformation near and below the fatigue limit was also examined. A Transmission Electron Microscopy (TEM) technique called the Selected Area Diffraction (SAD) method was employed in this study. In earlier studies, it was found that the SAD value indicating a magnitude of crystallographic misorientation in the substructure (dislocation cells) was increasing with the increase of fatigue damage accumulation. Small samples removed from PWR feed water nozzle welds were examined by the SAD. It was found that the damage state measured by the SAD well agreed with the morphological evidence. Cyclic stresses near or below the fatigue limit were applied to samples taken from a SA508 steel plate at various stresses. The SAD value increased even below the fatigue limit, but there was no sign of microstructural conditioning below the stresses of 50% of the fatigue limit. These results suggested that at stresses below the current design curve (below half the fatigue limit) no microstructural conditioning proceeded. It was concluded that the microstructural method was effective to evaluate damage accumulation in real plant components, and also that the current design curve was adequate in terms of microstructural conditioning state.
Fukuoka, C.; Nakagawa, Y.G.; Yoshida, K. [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan); Lance, J.J. [Electric Power Research Inst., Charlotte, NC (United States). Nuclear Power Group
A new cumulative fatigue damage model for glass fibre reinforced plastic composites under step\\/discrete loading
This paper presents and discusses a new fatigue damage accumulation model for Glass Fibre Reinforced Plastics under step loading. This model was formulated from a single-step constant amplitude fatigue model previously developed by the authors. Fatigue damage is defined and quantified in this paper. The model was tested using independent experimental data and predictions were found to be in excellent
Jayantha A. Epaarachchi; Philip D. Clausen
Introduction of a fretting-fatigue mapping concept: Development of a dual crack nucleation – crack propagation approach to formalize fretting-fatigue damage
Fretting-fatigue induced by combined localized cyclic contact motion and external bulk fatigue loadings may result in premature and dramatic failure of the contacting components. Depending on fretting and fatigue loading conditions, crack nucleation and possibly crack propagation can be activated. This paper proposes a procedure for estimating these two damage thresholds. The crack nucleation boundary is formalized by applying the
S. Fouvry; K. J. Kubiak
Fatigue-induced damage in Zr-based bulk metallic glasses.
In the present work, we investigate the effect of "fatigue" on the fatigue behavior and atomic structure of Zr-based BMGs. Fatigue experiments on the failed-by-fatigue samples indicate that the remnants generally have similar or longer fatigue life than the as-cast samples. Meanwhile, the pair-distribution-function (PDF) analysis of the as-cast and post-fatigue samples showed very small changes of local atomic structures. These observations suggest that the fatigue life of the 6-mm in-diameter Zr-based BMG is dominated by the number of pre-existing crack-initiation sites in the sample. Once the crack initiates in the specimen, the fatigue-induced damage is accumulated locally on these initiated sites, while the rest of the region deforms elastically. The results suggest that the fatigue failure of BMGs under compression-compression fatigue experiments is a defect-controlled process. The present work indicates the significance of the improved fatigue resistance with decreasing the sample size. PMID:23999496
Chuang, Chih-Pin; Yuan, Tao; Dmowski, Wojciech; Wang, Gong-Yao; Freels, Matt; Liaw, Peter K; Li, Ran; Zhang, Tao
Fatigue-Induced Damage in Zr-Based Bulk Metallic Glasses
In the present work, we investigate the effect of "fatigue" on the fatigue behavior and atomic structure of Zr-based BMGs. Fatigue experiments on the failed-by-fatigue samples indicate that the remnants generally have similar or longer fatigue life than the as-cast samples. Meanwhile, the pair-distribution-function (PDF) analysis of the as-cast and post-fatigue samples showed very small changes of local atomic structures. These observations suggest that the fatigue life of the 6-mm in-diameter Zr-based BMG is dominated by the number of pre-existing crack-initiation sites in the sample. Once the crack initiates in the specimen, the fatigue-induced damage is accumulated locally on these initiated sites, while the rest of the region deforms elastically. The results suggest that the fatigue failure of BMGs under compression-compression fatigue experiments is a defect-controlled process. The present work indicates the significance of the improved fatigue resistance with decreasing the sample size. PMID:23999496
Chuang, Chih-Pin; Yuan, Tao; Dmowski, Wojciech; Wang, Gong-Yao; Freels, Matt; Liaw, Peter K.; Li, Ran; Zhang, Tao
Microstructure: Property correlation. [multiaxial fatigue damage evolution in waspaloy
NASA Technical Reports Server (NTRS)
Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional (when the axial and torsional strain cycles are in-phase) and non-proportional (when the axial and torsional strain cycles are 90 deg out-of-phase) cyclic conditions. The deformation behavior under these different cyclic conditions were evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions and it was shown that when the slip deformation is predominant, non-proportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under non-proportional cyclic conditions, deformation was through multiple slip as opposed single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.
Jayaraman, N.
USE OF COMPOSITE MATERIALS TO REPAIR STEEL STRUCTURES VULNERABLE TO FATIGUE DAMAGE By Fatih Alemdar Submitted to the graduate degree program in Civil Engineering and the Faculty of the Graduate School of the University of Kansas.../02/2010 ii ACCEPTANCE PAGE The Thesis Committee for Fatih Alemdar certifies that this is the approved version of the following thesis: USE OF COMPOSITE MATERIALS TO REPAIR STEEL STRUCTURES VULNERABLE TO FATIGUE DAMAGE...
Alemdar, Fatih
Investigation of closed-form solutions to estimate fatigue damage on a building
If a stress process is wide-band, it is not obvious what constitutes a cycle and how cycles should be counted so that the Miner's rule can be employed. If a stress process is non-Gaussian, the stress process may cause accelerated fatigue damage. In this study, high-cycle fatigue damage for fasteners of curtain walls on a side face of a square
Nag-Ho Ko; Young-Moon Kim
Fatigue damage accumulation and property degradation in flat versus cylindrical specimens
FATIGUE DAMAGE ACCUMULATION AND PROPERTY DEGRADATION IN FLAT VERSUS CYLINDRICAL SPECIMENS A Thesis by KRISTINE BACHTEL ANDREWS Submitted to the Office of Graduate Studies of Texas Adi:M University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE December 1992 Major Subject: Civil Engineering FATIGUE DAMAGE ACCUMULATION AND PROPERTY DEGRADATION IN FLAT VERSUS CYLINDRICAL SPECIMENS A Thesis by KRISTINE BACHTEL ANDREWS Approved as to style and content by; Ozden...
Andrews, Kristine Bachtel
Risk assessment of Cumberland unit 2 L-O blades
Concern about the reliability of the 1,300 mw Cumberland steam turbine units after an unexpected blade tip failure in the fall of 1995 caused TVA to conduct an investigation into the current reliability of the L-O blades. A probabilistic model based on the measured frequencies, damping and material fatigue data was generated. The influence of significant erosion damage on the blade natural frequencies and on the local stresses was estimated. A probabilistic model of the local fatigue limit was generated based on test data. Monte Carlo simulation was employed to estimate the probability of blade failure by comparing the dynamic stress with the fatigue limit. Risk assessment of the blade failure is presented.
Lam, T.C.T. [Stress Technology Inc., Rochester, NY (United States); Puri, A. [Tennessee Valley Authority, Chattanooga, TN (United States)
Creep dominates tensile fatigue damage of the cement-bone interface.
Fatigue damage from activities of daily living has been considered to be a major cause of aseptic loosening in cemented total hip arthroplasty. The cement-bone interface is one region where loosening could occur, but to date the fatigue response of the interface has not been examined. Cement-bone specimens were prepared from fresh frozen human cadaver tissue using simulated in vivo conditions. Tensile fatigue tests to failure were performed in an environmental chamber. Loss of specimen stiffness (stiffness damage) and permanent displacement after unloading (creep damage) were found in all specimens. At failure, creep damage accounted for the majority (79.9+/-10.6%) of the total strain damage accumulation at failure (apparent strain, epsilon=0.0114+/-0.00488). A power law relationship between strain-damage rate and time-to-failure showed that the strain-damage rate was an excellent predictor of the fatigue life of the cement-bone interface. The S-N response of the interface was obtained as a function of the applied stress ratio and the initial apparent strain. The total motion between cement and bone (72.2+/-29.8 microm) prior to incipient failure due to both stiffness and creep fatigue damage may be sufficient to result in fibrous tissue formation and contribute to eventual clinical loosening. PMID:15099645
Kim, Do-Gyoon; Miller, Mark A; Mann, Kenneth A
Fatigue damage evaluation of plain woven carbon fiber reinforced plastic (CFRP) modified with MFC (micro-fibrillated cellulose) by thermo-elastic damage analysis (TDA)
NASA Astrophysics Data System (ADS)
The aim of this study is to investigate characteristics of fatigue damage of CFRP modified with MFC by TDA under tensile cyclic loading. In this paper, fatigue life of CFRP modified with MFC was investigated under cyclic loading. Characteristics of fatigue damage of CFRP modified with MFC were evaluated by thermo-elastic damage analysis. Maximum improvement in fatigue life was also obtained under cyclic loading when epoxy matrix was enhanced with 0.3wt% of MFC as well as under static loading. Result of TDA showed same tendency as the result of fatigue test, and the result of TDA well expressed the fatigue damage behavior of plain woven CFRP plate. Eventually, TDA was effective for clear understanding the degree of fatigue damage progression of CFRP modified with MFC.
Aoyama, Ryohei; Okubo, Kazuya; Fujii, Toru
Finite Element Analysis on the Impact-Induced Damage of Composite Fan Blades Subjected to a Bird Strike
NASA Astrophysics Data System (ADS)
Carbon fiber-reinforced composites have been recently applied for engine fan blades, because of their high specific strength. In the design of the fan blade, the bird-strike impact is one of the greatest concerns, since impact-induced damage can lead to the engine stall. This study presented a numerical method to analyze the bird-strike impact as a soft-body impact on cantilevered composite panel. Especially, we coupled a stabilized dynamic contact analysis, which enables predicting impact force on the panel appropriately, with laminate damage analysis to predict the impact-induced progressive damage in the composite. This method was verified through the comparison with the experimental results. With the numerical method, we investigated the effect of impact condition, blade thickness and shape on the impact-induced damage in composite fan blade subjected to a bird strike. An intermediate blade thickness and a large blade curvature help improving the bird-striking impact resistance of the composite.
Nishikawa, Masaaki; Hemmi, Kei; Park, Sangchul; Nadabe, Takeaki; Takeda, Nobuo
Assessment of accumulated fatigue damage in solid plates using nonlinear Lamb wave approach
NASA Astrophysics Data System (ADS)
The feasibility of using the nonlinear effect of primary Lamb wave propagation for assessing accumulated fatigue damage in solid plates is theoretically analyzed. After the aluminum sheets are subjected to tension-tension fatigue loading for different numbers of loading cycles, they are subjected to ultrasonic tests near the driving frequency where Lamb waves have a strong nonlinearity. This is followed by the measurement of the amplitude-frequency curves for second harmonics of the considered Lamb waves. The experimental results show that the effect of second-harmonic generation by Lamb wave propagation is very sensitive to the accumulation of fatigue damage of solid plates.
Deng, Mingxi; Pei, Junfeng
Fatigue cracking in high-cycle- and very-high-cycle-fatigue areas of peened and unpeened Al-based alloys because of fretting damages
In-service fretting damage influenced the fatigue crack origination in materials under the damaged surface for the very-high-cycle fatigue. Specimens of BS L65 Al–Cu alloy with peened and unpeened surfaces tested under cyclic tension and static compression had the crack initiation on the surface because of fretting damage. The static compression was used to reproduce the fretting damage on the specimen
A. Shanyavskiy; M. Artamonov
Fatigue properties of MA 6000E, a gamma-prime strengthened ODS alloy. [Oxide Dispersion Strengthened Ni-base alloy for gas turbine blade applications
NASA Technical Reports Server (NTRS)
MA 6000E is a corrosion resistant, gamma-prime strengthened ODS alloy under development for advanced turbine blade applications. The high temperature, 1093 C, rupture strength is superior to conventional nickel-base alloys. This paper addresses the fatigue behavior of the alloy. Excellent properties are exhibited in low and high cycle fatigue and also thermal fatigue. This is attributed to a unique combination of microstructural features, i.e., a fine distribution of dispersed oxides and other nonmetallics, and the highly elongated grain structure which advantageously modify the deformation characteristics and crack initiation and propagation modes from that characteristic of conventional gamma-prime hardened superalloys.
Kim, Y. G.; Merrick, H. F.
A coupled/uncoupled deformation and fatigue damage algorithm utilizing the finite element method
NASA Technical Reports Server (NTRS)
A fatigue damage computational algorithm utilizing a multiaxial, isothermal, continuum based fatigue damage model for unidirectional metal matrix composites has been implemented into the commercial finite element code MARC using MARC user subroutines. Damage is introduced into the finite element solution through the concept of effective stress which fully couples the fatigue damage calculations with the finite element deformation solution. An axisymmetric stress analysis was performed on a circumferentially reinforced ring, wherein both the matrix cladding and the composite core were assumed to behave elastic-perfectly plastic. The composite core behavior was represented using Hill's anisotropic continuum based plasticity model, and similarly, the matrix cladding was represented by an isotropic plasticity model. Results are presented in the form of S-N curves and damage distribution plots.
Wilt, Thomas E.; Arnold, Steven M.
Dwell effects on high temperature fatigue damage mechanisms
The mechanisms controlling deformation and failure under high temperature creep-fatigue conditions of materials are examined in this paper. The materials studied were pure alloys, solder alloys, copper alloys, low alloy steels, stainless steels, titanium alloys, tantalum alloys, and Ni-based alloys. The deformation and failure mechanisms were different (fatigue, creep, oxidation and their interactions) depending on test and material parameters employed.
Tarun Goswami; Hannu Hanninen
Continuum damage mechanics modeling for fatigue life of elastomeric materials
Purpose – The purpose of this paper is to investigate the fatigue behavior of rubber using dumb-bell test specimens under uniaxial loading. Design\\/methodology\\/approach – The material used is a vulcanized natural rubber with a formulation typical for engine mounts and an international rubber hardness degree of 60. Fatigue tests are conducted under the displacement controlled condition with a sine waveform
Aidy Ali; Maryam Hosseini; Barkawi Sahari
Energy criteria and cumulative damage during fatigue crack growth
This paper considers the strain energy density generated ahead of a fatigue crack as predicted by elastic and non-linear plastic theory. In both cases this decays inversely with distance ahead of the tip. The process zone just ahead of the tip fails when the accumulated energy density reaches a critical value after a certain number of fatigue cycles. A simple
R. P. Skelton; T. Vilhelmsen; G. A. Webster
Fatigue damage mechanisms in (0, 90) s composite laminate
The high strength to weight ratio of CFRP composite materials is certainly an attractive structural characteristic. However, in many circumstances consideration must also be given to the fatigue properties. It is well established by now that the failure of multidirectional composite laminates during either monotonic load or fatigue initiates in the plies that are most desoriented with respect to the
E. Petitpas; M. Renault; D. Valentin
The octahedral shear strain theory and its relation to biaxial cumulative fatigue damage.
NASA Technical Reports Server (NTRS)
The octahedral shear strain range concept is used in analyzing multiaxial fatigue damage. Limited test data from a two-step loading sequence show that the loading effect is still pronounced in the multiaxial case and that the relation between damage and cycle ratio is nonlinear. Among uniaxial cumulative damage concepts, the modified multiaxial double linear damage rule seems to show the most favorable experimental results.
Zamrik, S. Y.
... 21, 2014 Select a Language: Fact Sheet 551 Fatigue WHAT IS FATIGUE? IS FATIGUE IMPORTANT? HOW DO ... It can be physical or psychological. With physical fatigue , your muscles cannot do things as easily as ...
Structural health monitoring and condition based fatigue damage prognosis of complex metallic structures
NASA Astrophysics Data System (ADS)
Current practice in fatigue life prediction is based on assumed initial structural flaws regardless of whether these assumed flaws actually occur in service. Furthermore, the model parameters are often estimated empirically based on previous coupon test results. Small deviations of the initial conditions and model parameters may generate large errors in the expected dynamical behavior of fatigue damage growth. Consequently, a large degree of conservatism is incorporated into structural designs due to these expected uncertainties. The current research in the area of Structural Health Monitoring (SHM) and probabilistic fatigue modeling can help in improved fatigue damage modeling and remaining useful life estimation (RULE) techniques. This thesis discusses an integrated approach of SHM and adaptive prognosis model that not only estimates the current health, but can also forecast the future health and calculate RULE of an aerospace structural component with high level of confidence. The approach does not assume any fixed initial condition and model parameters. This dissertation include the following novel contributions. 1) A Bayesian based off-line Gaussian Process (GP) model is developed, which is the core of the present condition based prognosis approach. 2) Different passive and active SHM approaches are used for on-line damage state estimation. Applications of passive sensing are shown to estimate the time-series fatigue damage states both under constant and random fatigue loading. It is found that there is a good correlation between estimated damage states and optically measured damage states. In addition, applications for both narrow and broadband active sensing approaches are presented to estimate smaller incipient damage. It is demonstrated that the active sensing techniques not only can identify smaller incipient damage but also can quantify fatigue damage during all the three stages (stages I, II, and III) of fatigue life. 3) An integrated on-line SHM and off-line GP predictive model is developed for real-time condition based damage state estimation of complex Aluminum structures under fatigue loading. It is found that the proposed technique can forecast the future damage states well before the final failure.
Mohanty, Subhasish
Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188
NASA Technical Reports Server (NTRS)
Post failure fractographic and metallographic studies were conducted on Haynes 188 specimens fatigued under bithermal and thermomechanical loading conditions between 316 and 760 C. Bithermal fatigue specimens examined included those tested under high strain rate in-phase and out-phase, tensile creep in-phase, and compressive creep out-of-phase loading conditions. Specimens tested under in-phase and out-of-phase thermomechanical fatigue were also examined. The nature of failure mode (transgrandular versus intergranular), the topography of the fracture surface, and the roles of oxidation and metallurgical changes were studied for each type of bithermal and thermomechanical test.
Kalluri, Sreeramesh; Halford, Gary R.
Foreign object damage and fatigue crack threshold: Cracking outside shallow indents
Foreign Object Damage (FOD) usually happens when objects are ingested into jet engines powering military or civil aircraft. Under extreme conditions, FOD can lead to severe structural damage. More commonly it produces local impacted sites of the fan and compressor airfoils, lowering fatigue life of these components. FOD is a prime cause for maintenance and repair in aircraft engines. In
Xi Chen; John W. Hutchinson
Linear and nonlinear acoustic control of accumulated fatigue damage in steel
NASA Astrophysics Data System (ADS)
We present results of linear and nonlinear acoustic testing of steel samples with different levels of fatigue damage. The steel specimens were tested under programed cyclic loading on a fatigue testing machine and accumulated different levels of fatigue damage. No visible surface-crack formations during fatigue cycling were observed. In other words, the emphasis was placed on the characterization of continued but physically invisible in service life conditions damage in different materials and structures. Both linear and nonlinear acoustic techniques were used to assess damage accumulation. (1) Impulse resonant acoustic spectroscopy (IRAS) is based on analysis of the free-sample vibration after impact excitation. It demonstrated the increasing of the resonance frequencies and Q factor with damage accumulation. (2) Nonlinear resonant acoustic spectroscopy (NRAS) is based on measurement of the resonance response for different levels of acoustic excitation. The amplitude-dependent frequency shift for damaged steel was observed to increased with damage accumulation. (3) Nonlinear wave modulation spectroscopy (NWMS) implies the modulation of ultrasound wave by lower frequency vibration. High level of the side-band components for damaged samples were observed. The comparison of different methods is given.
Sutin, Alexander; Kin, Yulian; Johnson, Paul
Damage rate is a predictor of fatigue life and creep strain rate in tensile fatigue of human cortical bone samples.
We present results on the growth of damage in 29 fatigue tests of human femoral cortical bone from four individuals, aged 53-79. In these tests we examine the interdependency of stress, cycles to failure, rate of creep strain, and rate of modulus loss. The behavior of creep rates has been reported recently for the same donors as an effect of stress and cycles. In the present paper we first examine how the evolution of damage (drop in modulus per cycle) is associated with the stress level or the "normalized stress" level (stress divided by specimen modulus), and results show the rate of modulus loss fits better as a function of normalized stress. However, we find here that even better correlations can be established between either the cycles to failure or creep rates versus rates of damage than any of these three measures versus normalized stress. The data indicate that damage rates can be excellent predictors of fatigue life and creep strain rates in tensile fatigue of human cortical bone for use in practical problems and computer simulations. PMID:15971698
Cotton, John R; Winwood, Keith; Zioupos, Peter; Taylor, Mark
Computed speckle decorrelation (CSD) and its application for fatigue damage monitoring
NASA Astrophysics Data System (ADS)
CSD is shown to be an effective monitoring method for both incremental and cumulative fatigue damage; it also discerns instantaneous damage accumulation, thereby indicating that previously deformed regions were comparatively unchanged in subsequent fatigue cycles. In the case of localized corrosion processes, CSD would be able to determine in situ regions of corrosion and thereby entail only visual access to the corroding surface. In the case of localized impact damage, CSD could localize the surface plastic zone around the impact. In addition, regions of wear could be localized.
Steckenrider, J. S.; Wagner, James W.
Evaluation of micro-damage accumulation in holed plain-woven CFRP composite under fatigue loading
NASA Astrophysics Data System (ADS)
Fluorescence method was used to detect the micro-damage caused by fatigue in a plain-woven carbon fiber reinforced polymer (CFRP). Fluorescence measurement is a method which estimates micro-damage by measuring fluorescent intensity change inside materials. The principle is, larger micro-damage means larger plastic strain, thus more space in that damaged spot which allows more fluorescent dyes coming in the material. By detecting fluorescent intensity in CFRP layer by layer using confocal laser microscopy, micro-damage can be estimated. Results show that there's a good relationship between micro-damage and fluorescent intensity gradient.
Ying, Jia; Nishikawa, Masaaki; Hojo, Masaki
Fatigue damage mechanisms in unidirectional carbon-fibre-reinforced plastics
The fatigue life behaviour and the underlying micromechanisms have been studied in two different Types of unidirectional carbon-fibre-reinforced plastics loaded in tension-tension along the fibre direction. The carbon fibres (AS4) were the same in the two composite systems. One thermoplastic matrix (polyetheretherketone, PEEK) and one thermosetting matrix (epoxy toughened with a thermoplastic additive) were used. The macroscopic fatigue behaviour was
E. K. Gamstedt; R. Talreja
Drilling induced fatigue damage in titanium aluminum vanadate
NASA Astrophysics Data System (ADS)
The objective of this work is to develop an understanding of the relationship between hole drilling processes and the fatigue performance of the resulting part in Ti-6Al-4V. This problem is significant, as on the order of one-hundred thousand to a million holes are created in a typical large aircraft, and the limiting performance criterion is usually the fatigue lifetime. The path between the drilling process parameters and the fatigue performance has two main steps: characterization of the thermo-mechanical drill process and assessment of the relationship between the hole integrity left by the drill process and the fatigue performance. Development has been limited by the robustness of previously available thermal characterization systems, poor correlation between drill processes and physical observations of metallic effects, and limited success identifying the key hole integrity characteristics. This work develops robust novel thermal methods which enable integration into current drill process development techniques. The key integrity drivers in the hole wall are identified, characterized, and a system to assess is presented. The thermal and hole integrity trends are presented as guidance for drill process development providing significant opportunities to optimize processes. Thus, this work advances knowledge of the process to fatigue lifetime relationship by correlating the thermo-mechanical drill process to fatigue life in Ti-6Al-4V.
Castle, James B.
Methodology for Predicting the Onset of Widespread Fatigue Damage in Lap-Splice Joints
NASA Technical Reports Server (NTRS)
NASA has conducted an Airframe Structural Integrity Program to develop the methodology to predict the onset of widespread fatigue damage to lap-splice joints of fuselage structures. Several stress analysis codes have been developed or enhanced to analyze the lap-splice-joint configuration. Fatigue lives in lap-splice-joint specimens and fatigue-crack growth in a structural fatigue test article agreed well with calculations from small-crack theory and fatigue-crack growth analyses with the FASTRAN code. Residual-strength analyses of laboratory specimens and wide stiffened panels were predicted quite well from the critical crack-tip-opening angle (CTOA) fracture criterion and elastic-plastic finite-element analyses (two- or three-dimensional codes and the STAGS shell code).
Newman, J. C., Jr.; Harris, C. E.; Piascik, R. S.; Dawicke, D. S.
Estimation of Fatigue Damage for an Austenitic Stainless Steel (SUS304) Using Magnetic Methods
There are some fatigue damage estimation methods of the austenitic stainless steel that uses the martensitic transformation. For instance, they are the remanent magnetization method, the excitation method, and so on. Those two methods are being researched also in our laboratory now. In the remanent magnetization method, it is well known that the relation between fatigue damage and the remanent magnetization is simple, clear, and reproducible. However, this method has the disadvantage to need a special magnetizer. This method cannot be easily used on the site such as the factory. On the other hand, because the special magnetizer is unnecessary, the excitation method can use easily on the site. The output signal of this method is small. In this paper, two fatigue evaluation methods such as the remanent magnetization method and the excitation method are introduced. In addition, we report on the result of comparing the fatigue evaluation performances of two methods.
Oka, M. [Department of Computer and Control Engineering, Oita National College of Technology, 1666 Maki, Oita, 870-0152 (Japan); Yakushiji, T. [Department of Mechanical Engineering, Oita National College of Technology, 1666 Maki, Oita, 870-0152 (Japan); Tsuchida, Y.; Enokizono, M. [Department of Electrical and Electronic Engineering, Faculty of Engineering, Oita University, 700 Dannoharu, Oita, 870-1192 (Japan)
Estimation of Fatigue Damage for an Austenitic Stainless Steel (SUS304) Using Magnetic Methods
NASA Astrophysics Data System (ADS)
There are some fatigue damage estimation methods of the austenitic stainless steel that uses the martensitic transformation. For instance, they are the remanent magnetization method, the excitation method, and so on. Those two methods are being researched also in our laboratory now. In the remanent magnetization method, it is well known that the relation between fatigue damage and the remanent magnetization is simple, clear, and reproducible. However, this method has the disadvantage to need a special magnetizer. This method cannot be easily used on the site such as the factory. On the other hand, because the special magnetizer is unnecessary, the excitation method can use easily on the site. The output signal of this method is small. In this paper, two fatigue evaluation methods such as the remanent magnetization method and the excitation method are introduced. In addition, we report on the result of comparing the fatigue evaluation performances of two methods.
Oka, M.; Yakushiji, T.; Tsuchida, Y.; Enokizono, M.
Simplification of Fatigue Test Requirements for Damage Tolerance of Composite Interstage Launch Vehicle Hardware
NASA Technical Reports Server (NTRS)
The issue of fatigue loading of structures composed of composite materials is considered in a requirements document that is currently in place for manned launch vehicles. By taking into account the short life of these parts, coupled with design considerations, it is demonstrated that the necessary coupon level fatigue data collapse to a static case. Data from a literature review of past studies that examined compressive fatigue loading after impact and data generated from this experimental study are presented to support this finding. Damage growth, in the form of infrared thermography, was difficult to detect due to rapid degradation of compressive properties once damage growth initiated. Unrealistically high fatigue amplitudes were needed to fail 5 of 15 specimens before 10,000 cycles were reached. Since a typical vehicle structure, such as the Ares I interstage, only experiences a few cycles near limit load, it is concluded that static compression after impact (CAI) strength data will suffice for most launch vehicle structures.
Nettles, A. T.; Hodge, A. J.; Jackson, J. R.
Swept Blade Aero-Elastic Model for a Small Wind Turbine (Presentation)
A preprocessor for analyzing preswept wind turbines using the in-house aero-elastic tool coupled with a multibody dynamic simulator was developed. A baseline 10-kW small wind turbine with straight blades and various configurations that featured bend-torsion coupling via blade-tip sweep were investigated to study their impact on ultimate loads and fatigue damage equivalent loads.
Damiani, R.; Lee, S.; Larwood, S.
An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components
NASA Astrophysics Data System (ADS)
A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth™ technology to a PC.
Fernandes, B.; Gaydecki, P.; Burdekin, F. Michael
An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components
A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth{sup TM} technology to a PC.
Fernandes, B.; Gaydecki, P. [Department of Instrumentation and Analytical Science, UMIST, PO Box 88, Manchester M60 1QD (United Kingdom); Burdekin, F. Michael [Fatigue Monitoring Bureau, Macclesfield, Sk10 5LX (United Kingdom)
Damage Assessment of CFRP [90\\/±45\\/0] Composite Laminates over Fatigue Cycles
The present paper develops a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon\\u000a fiber reinforced polymer (CFRP) [90\\/±45\\/0] composite laminates with various stacking sequences. The damage model is constructed\\u000a based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region\\u000a III) and (ii) corresponding stiffness reduction of unidirectional plies
G. R. Ahmadzadeh; A. Shirazi; A. Varvani-Farahani
Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime
The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A "mountain shape" correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The "mountain shape" correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.
Zhang, Jianfeng; Xuan, Fu-Zhen, E-mail: firstname.lastname@example.com [MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China)
Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth
NASA Technical Reports Server (NTRS)
A technique was developed to calculate the stress intensity factor for multiple interacting cracks. The analysis was verified through comparison with accepted methods of calculating stress intensity factors. The technique was incorporated into a fatigue crack growth prediction model and used to predict the fatigue crack growth life for multiple-site damage (MSD). The analysis was verified through comparison with experiments conducted on uniaxially loaded flat panels with multiple cracks. Configuration with nearly equal and unequal crack distribution were examined. The fatigue crack growth predictions agreed within 20 percent of the experimental lives for all crack configurations considered.
Dawicke, D. S.; Newman, J. C., Jr.
Characterization of Fatigue Strength and Damage Behavior in Glass-Particle-Reinforced Nylon 66 Composites
NASA Astrophysics Data System (ADS)
This paper deals with fatigue strength and damage behavior of glass-particle-reinforced Nylon 66 composites. Fatigue tests are carried out on seven kinds of glass-particle-reinforced Nylon 66 composites in which a volume fraction of glass particles and interface treatment between particles and matrix are changed. The fatigue strength is low in the interface-untreated composite and is high in the interface-treated composite as compared with that of the Nylon 66. Variation of stiffness during fatigue is determined from the equilibrium stress-strain relations obtained by multi-step relaxation tests after given stress cycles, which eliminate the influence of viscous deformation of the Nylon 66 matrix. The stiffness reduces significantly at the early stage of stress cycles and then becomes constant in the Nylon 66 and both composites. In the fatigue tests under the applied stress for the same fatigue life, the stiffness reduction is more remarkable in both composites than in Nylon 66 because of the debonding damage. From the variation of the equilibrium stress-strain relations during fatigue, it is found that the viscous component of deformation gradually disappears with increasing stress cycles.
Tohgo, Keiichiro; Itoh, Yasuo; Kim, Taewoo
Inuence of foreign-object damage on crack initiation and early crack growth during high-cycle fatigue of Ti6Al4V
; Ti±6Al±4V 1. Introduction The high-cycle fatigue (HCF) of aircraft gas-turbine engine components has of small surface fatigue cracks in a Ti±6Al±4V alloy, processed for typical turbine blade applications-cycle fatigue of Ti±6Al±4V J.O. Peters, R.O. Ritchie * Department of Materials Science and Mineral Engineering
Ritchie, Robert
Fatigue damage localization using time-domain features extracted from nonlinear Lamb waves
NASA Astrophysics Data System (ADS)
Nonlinear guided waves are sensitive to small-scale fatigue damage that may hardly be identified by traditional techniques. A characterization method for fatigue damage is established based on nonlinear Lamb waves in conjunction with the use of a piezoelectric sensor network. Theories on nonlinear Lamb waves for damage detection are first introduced briefly. Then, the ineffectiveness of using pure frequency-domain information of nonlinear wave signals for locating damage is discussed. With a revisit to traditional gross-damage localization techniques based on the time of flight, the idea of using temporal signal features of nonlinear Lamb waves to locate fatigue damage is introduced. This process involves a time-frequency analysis that enables the damage-induced nonlinear signal features, which are either undiscernible in the original time history or uninformative in the frequency spectrum, to be revealed. Subsequently, a finite element modeling technique is employed, accounting for various sources of nonlinearities in a fatigued medium. A piezoelectric sensor network is configured to actively generate and acquire probing Lamb waves that involve damageinduced nonlinear features. A probability-based diagnostic imaging algorithm is further proposed, presenting results in diagnostic images intuitively. The approach is experimentally verified on a fatigue-damaged aluminum plate, showing reasonably good accuracy. Compared to existing nonlinear ultrasonics-based inspection techniques, this approach uses a permanently attached sensor network that well accommodates automated online health monitoring; more significantly, it utilizes time-domain information of higher-order harmonics from time-frequency analysis, and demonstrates a great potential for quantitative characterization of small-scale damage with improved localization accuracy.
Hong, Ming; Su, Zhongqing; Lu, Ye; Cheng, Li
On the application of the KitagawaTakahashi diagram to foreign-object damage and high-cycle fatigue
-object damage (FOD) and its effect on high-cycle fatigue (HGF) failures in a turbine engine Ti 6Al4V alloy at the impact site, and can be readily described through the use of a fatigue-crack growth threshold concept by the stress-concentration corrected smooth-bar fatigue limit (at microstructurally small crack sizes
Hutchinson, John W.
Computer simulation of variable amplitude fatigue crack initiation behaviour using a new strain-based cumulative damage model
Computer software for the prediction of fatigue crack initiation has been developed. Based on a model derived from the closure behaviour of microcracks and the intrinsic resistance of metals and alloys to fatigue damage, this software allows predictions to be readily applied to quickly provide fatigue crack initiation life predictions for a wide range of alloys based on inputs of
A. K. Lynn; D. L. DuQuesnay
Improving Fatigue Damage Resistance of Alumina through Surface Grading
Porcelain-veneered alumina crown restorations often fail from bulk fracture resulting from radial cracks that initiate at the cementation surface with repeated flexure of the stiffer crown layers on the soft dentin support. We hypothesized that bulk fracture may be substantially mitigated by grading the elastic modulus at the crown surfaces. In this study, we fabricated graded structures by infiltrating glass into dense alumina plates, resulting in a diminished modulus at the surface layers. The plates were then bonded to polycarbonate substrates and subjected to fatigue loading in water. Tests were terminated when fracture occurred at the cementation tensile surface or at the fatigue endurance limit (1 million cycles). Infiltrated specimens showed a significant increase in fatigue fracture loads over non-infiltrated controls. Our results indicate that controlled elastic gradients at the surface could be highly beneficial in the design of fracture-resistant alumina crowns. PMID:21555776
Ren, L.; Liu, L.; Bhowmick, S.; Gerbig, Y.B.; Janal, M.N.; Thompson, V.P.; Zhang, Y.
Thermo-elastic nondestructive evaluation of fatigue damage in PMR-15 resin
NASA Astrophysics Data System (ADS)
Thermoset polyimide resins are used as the polymer matrix in high temperature composites for aerospace applications such as engine shrouds. At these locations the components have to withstand high temperatures and significant vibration. A number of studies have investigated the effects of thermal exposure on mechanical properties of polyimide resins, and the effects of fatigue on thermoplastics have been discussed at length. However, the effects of fatigue on thermosets, in particular polyimides, have largely been overlooked. In this paper we present studies of nondestructive evaluation of fatigue damage in a thermoset polyimide resin, PMR-15, performed by measuring the changes in the evolution of heat in the samples during cyclic loading. The temperature changes are measured using a high sensitivity IR camera as a function of number of fatigue cycles. Interrupted fatigue tests were performed on four samples. The temperature rise during an increment of fatigue cycling shows two linear regions each with a different slope (region 1 and region 2). Region 1 remains constant for every increment of fatigue, while region 2 increases. The onset of region 2 occurs at the same increase in temperature due to hysteretic heating for all samples. Experimental observations are explained using a phenomenological two phase model based on crosslinking density variations in observed in other thermoset resins at microscopic scales. The results of these experiments are discussed in reference to utilizing this technique for detection and evaluation of fatigue in PMR-15 resin and composites.
Welter, J. T.; Sathish, S.; Tandon, G. P.; Schehl, N.; Cherry, M.; Nalladega, V.; Lindgren, E. A.; Hall, R.
Nonlinear Resonant Ultrasound Spectroscopy (NRUS) applied to fatigue damage evaluation in a pure copper
NASA Astrophysics Data System (ADS)
We studied a monitoring technique of fatigue damage in 3N polycrystalline copper under a cyclic zero-to-tension loading by the nonlinear resonant ultrasound spectroscopy (NRUS). In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. We used an electromagnetic acoustic transducer (EMAT) to monitor NRUS of bulk-shear-wave propagating in the thickness direction of the plate sample. NRUS exhibits much larger sensitivity to the damage accumulation than the velocity. It rapidly increases from 70% of fatigue life to the fracture. The attenuation shows the peak at 80% of the life. This NRUS novel phenomenon is interpreted in terms of dislocation mobility. This technique has potential to assess the damage advance and to predict the fatigue life of metals.
Ohtani, Toshihiro; Ishii, Yutaka
Computational fluid dynamics analysis of blade tip clearances on hemodynamic performance and blood damage in a centrifugal ventricular assist device.
An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 microm. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 microm. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 microm compared to 50 microm and 200 microm. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized. PMID:19832736
Wu, Jingchun; Paden, Bradley E; Borovetz, Harvey S; Antaki, James F
Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC
NASA Technical Reports Server (NTRS)
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.
Isothermal fatigue behavior and damage modeling of a high temperature woven PMC[Polymer Matrix Composite
This study focuses on 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 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 greater 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 covering 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, A.L.
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Development of a new fatigue damage growth model for polymer matrix composites
NASA Astrophysics Data System (ADS)
The objective of this research is to develop a new fatigue crack growth model for fiber reinforced polymer composites. This new model takes into account the progressive damage that occurs at each load increment in fatigue cycling through a weighted average stress intensity factor. The fatigue crack growth rate is modeled using a power law equation; however, the fatigue damage controlling parameters used in this equation are the stress intensity range as well as the weighted stress intensity factor. The model was developed and verified using three different polymer matrix composites, namely, a randomly oriented short carbon fiber reinforced thermoplastic (PEEK), a polyester sheet molding compound composite containing randomly oriented short glass fibers and a plain weave glass fabric reinforced epoxy. Fatigue crack growth experiments were conducted using either a compact tension specimen or a double cantilever beam specimen. The stress intensity approach is used for the first two composites. The strain energy release rate approach is used for the woven fabric reinforced epoxy matrix composite since delamination growth was the primary mode of fatigue failure in these laminates and delamination growth can be better modeled using the strain energy release rate. In all cases, it was observed that the proposed model given by the following equation can represent the fatigue crack growth rate at different load ratio in a unified equation${da/ dN}=B(Ksbsp{average}{gamma}.Delta Ksp{1-gamma})sp {p}where, B, gamma$ and p are the model constants determined from the fatigue crack growth rate data. The fatigue crack growth rate predicted with this single power law equation for each load ratio gives a close agreement with the experimental data for all three composites under study.
Atodaria, Devrajsinh R.
Fatigue damage analysis of aluminized glass fiber composites
Aluminized glass fiber composite with epoxy and polyester matrix were used in this work in order to study fatigue properties and its comparison to conventional glass fiber composites. Until now aluminized glass fiber materials have been only used as decoy flares in military applications. The innovative advantages of these composites, using modified fibers, are potentially the improvement of thermal and
J. M. Ferreira; J. T. B. Pires; J. D. Costa; Z. Y. Zhang; O. A. Errajhi; M. Richardson
PZT active health monitoring for fatigue accumulative damage of concrete beam containing nano-particles for pavement
NASA Astrophysics Data System (ADS)
Based on the actuation and sense function of piezoceramic materials, PZT active health monitoring for fatigue accumulative damage of concrete beam containing nano-particles (TiO II) for pavement is experimentally studied. The test results indicate that the vibration signals received by PZT patches have three development stages obviously: the damage-formation stage, the damage-steady-growth stage and the damage-sharp-growth stage, which shows that PZT patch can monitor the whole course of the formation and growth of cracks in concrete and the failure of concrete beam. The fatigue damage index of concrete based on wavelet packet decomposition is established, and its change trend is similar to that of fatigue damage of concrete. In the range of 0%-10% of fatigue life, the damage index is approximately zero, which means that the concrete beam is basically in a healthy state and internal cracks are germinating. In the range of 10%-90% of fatigue life, the damage index increases from zero to a smaller value slowly, which means that the cracks in concrete propagate slowly. After the 90% of fatigue life, the damage index increases rapidly, which means that the cracks in concrete extend sharply and run through up to the fracture failure of concrete beam. The magnitude of damage index can show the serious extent of fatigue damage in concrete and the healthy status of concrete. The fatigue damage in concrete can be located by comparing the amplitude character of break signals or the change regularity of damage indices of PZT patches attached on concrete beam in different position. Moreover, the smaller the distance of PZT patch from the damage is, the more obvious the signal break and the change of damage index of PZT patch are, and the more sensitive the identification of PZT patch to the damage is.
Zhang, Mao-hua; Li, Hui; Ou, Jin-ping
Damage detection in carbon composite material typical of wind turbine blades using auto-associative neural networks
NASA Astrophysics Data System (ADS)
The structure of a wind turbine blade plays a vital role in the mechanical and structural operation of the turbine. As new generations of offshore wind turbines are trying to achieve a leading role in the energy market, key challenges such as a reliable Structural Health Monitoring (SHM) of the blades is significant for the economic and structural efficiency of the wind energy. Fault diagnosis of wind turbine blades is a "grand challenge" due to their composite nature, weight and length. The damage detection procedure involves additional difficulties focused on aerodynamic loads, environmental conditions and gravitational loads. It will be shown that vibration dynamic response data combined with AANNs is a robust and powerful tool, offering on-line and real time damage prediction. In this study the features used for SHM are Frequency Response Functions (FRFs) acquired via experimental methods based on an LMS system by which identification of mode shapes and natural frequencies is accomplished. The methods used are statistical outlier analysis which allows a diagnosis of deviation from normality and an Auto-Associative Neural Network (AANN). Both of these techniques are trained by adopting the FRF data for normal and damage condition. The AANN is a method which has not yet been widely used in the condition monitoring of composite materials of blades. This paper is trying to introduce a new scheme for damage detection, localisation and severity assessment by adopting simple measurements such as FRFs and exploiting multilayer neural networks and outlier novelty detection.
Dervilis, N.; Barthorpe, R. J.; Antoniadou, I.; Staszewski, W. J.; Worden, K.
Fatigue analysis of multiple site damage at a row of holes in a wide panel
NASA Astrophysics Data System (ADS)
This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.
Buhler, Kimberley; Grandt, Alten F., Jr.; Moukawsher, E. J.
Cumulative damage and the response of human bone in two-step loading fatigue.
It has already been shown that in fatigue tests in vitro human cortical bone accumulates damage in the form of microcracks and that the total number of microcracks generated prior to the creation of the fatal macrocrack, and their effect (softening) on the material properties, depends on the level of applied stress. At each stress level the amount of accumulated damage has also been shown to be a non-linear function of the cycle number (Zioupos et al., 1996a, b; Pattin et al., 1996). The theoretical implications of the previous findings and two possible models for cumulative damage were put to the test here by performing tensile fatigue tests in two-step level (high/low or low/high) loading on human cortical bone specimens. The results indicate that the accumulation of damage in-vitro is highly dependent on the level of stress and the stress history. Usual linear expressions for fatigue lifetime predictions, like the Palmgren-Miner rule, substantially over or underestimate the outcome depending on whether the stress was applied in a high/low or a low/high sequence, respectively. In view of these discrepancies we conclude that predicting the fatigue lifetime of any bone in vivo under variable loading and complex history regimes is an extremely difficult task to which the study of accumulation of damage can offer a significant but, perhaps, still limited contribution. PMID:9802783
Zioupos, P; Casinos, A
Fatigue analysis of multiple site damage at a row of holes in a wide panel
NASA Technical Reports Server (NTRS)
This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.
Buhler, Kimberley; Grandt, Alten F., Jr.; Moukawsher, E. J.
Development of NDE technology to evaluate fatigue damage of steam generator tube
There have been two accidental tube failures relating to fatigue in the steam generators of PWR nuclear plants. Though the primary failure mechanism and the major causal factors leading to these events were adequately demonstrated and identified and corrective measures to prevent the occurrence of similar fatigue failure have been implemented, it still seems necessary to develop a method to non-destructively detect early fatigue damage in order to improve the integrity of steam generator tubes. JAPEIC (Japan Power Engineering and Inspection Corporation) has initiated a research project for the development of such a method. It began by making a literature survey to investigate fatigue phenomena that possibly occur in steam generator tubes, and by selecting the techniques which have potential to detect early fatigue damage in tubes that are in operation. In order to determine which technique has the most potential, it then conducted a comparative study on the techniques that were selected using interrupted fatigue test tubes. In the future, a method using the optimal technique will be developed for application to in-service inspection of steam generator tubes. This paper introduces the outline of the project and the main results that have been obtained.
Goto, T.; Enami, K. [Mitsubishi Heavy Industries, Ltd., Takasago (Japan); Fukui, S. [Mitsubishi Heavy Industries, Ltd., Kobe (Japan); Uesugi, N. [Japan Power Engineering and Inspection Corp., Yokohama (Japan)
Observations of fatigue crack initiation and damage growth in notched titanium matrix composites
NASA Technical Reports Server (NTRS)
The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.
Naik, R. A.; Johnson, W. S.
Modeling nonlinearities of ultrasonic waves for fatigue damage characterization: theory, simulation, and experimental validation.
A dedicated modeling technique for comprehending nonlinear characteristics of ultrasonic waves traversing in a fatigued medium was developed, based on a retrofitted constitutive relation of the medium by considering the nonlinearities originated from material, fatigue damage, as well as the "breathing" motion of fatigue cracks. Piezoelectric wafers, for exciting and acquiring ultrasonic waves, were integrated in the model. The extracted nonlinearities were calibrated by virtue of an acoustic nonlinearity parameter. The modeling technique was validated experimentally, and the results showed satisfactory consistency in between, both revealing: the developed modeling approach is able to faithfully simulate fatigue crack-incurred nonlinearities manifested in ultrasonic waves; a cumulative growth of the acoustic nonlinearity parameter with increasing wave propagation distance exists; such a parameter acquired via a sensing path is nonlinearly related to the offset distance from the fatigue crack to that sensing path; and neither the incidence angle of the probing wave nor the length of the sensing path impacts on the parameter significantly. This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously. PMID:24156928
Hong, Ming; Su, Zhongqing; Wang, Qiang; Cheng, Li; Qing, Xinlin
Three technical issues in fatigue damage assessment of nuclear power plant components
This paper addresses three technical issues that affect the fatigue damage assessment of nuclear power plant components: the effect of the environment on the fatigue life, the importance of the loading sequence in calculating the fatigue crack-initiation damage, and the adequacy of current inservice inspection requirements and methods to characterize fatigue cracks. The environmental parameters that affect the fatigue life of carbon and low alloy steel components are the sulphur content in the steel, the temperature, the amount of dissolved oxygen in the coolant, and the presence of oxidizing agents such as copper oxide. The occurrence of large-amplitude stress cycles early in a component's life followed by low-amplitude stress cycles may cause crack initiation at a cumulative usage factor less than 1.0. The current inservice inspection requirements include volumetric inspections of welds but not of some susceptible sites in the base metal. In addition, the conventional ultrasonic testing techniques need to be improved for reliable detection and accurate sizing of fatigue cracks. 28 refs., 4 figs., 1 tab.
Ware, A.G.; Shah, V.N.
Fatigue life prediction of rotor blade composites: Validation of constant amplitude formulations with variable amplitude experiments
NASA Astrophysics Data System (ADS)
The effect of Constant Life Diagram (CLD) formulation on the fatigue life prediction under variable amplitude (VA) loading was investigated based on variable amplitude tests using three different load spectra representative for wind turbine loading. Next to the Wisper and WisperX spectra, the recently developed NewWisper2 spectrum was used. Based on these variable amplitude fatigue results the prediction accuracy of 4 CLD formulations is investigated. In the study a piecewise linear CLD based on the S-N curves for 9 load ratios compares favourably in terms of prediction accuracy and conservativeness. For the specific laminate used in this study Boerstra's Multislope model provides a good alternative at reduced test effort.
Westphal, T.; Nijssen, R. P. L.
Cumulative damage fatigue tests on nuclear reactor Zircaloy-2 fuel tubes at room temperature and 300°C
NASA Astrophysics Data System (ADS)
Cumulative damage fatigue tests were conducted on the Zircaloy-2 fuel tubes at room temperature and 300°C on the modified Moore type, four-point-loaded, deflection-controlled, rotating bending fatigue testing machine. The cumulative cycle ratio at fracture for the Zircaloy-2 fuel tubes was found to depend on the sequence of loading, stress history, number of cycles of application of the pre-stress and the test temperature. A Hi-Lo type fatigue loading was found to be very much damaging at room temperature and this feature was not observed in the tests at 300°C. Results indicate significant differences in damage interaction and damage propagation under cumulative damage tests at room temperature and at 300°C. Block-loading fatigue tests are suggested as the best method to determine the life-time of Zircaloy-2 fuel tubes under random fatigue loading during their service in the reactor.
Pandarinathan, P. R.; Vasudevan, P.
Assessment of fatigue damage in solid plates through the ultrasonic Lamb wave approach
NASA Astrophysics Data System (ADS)
Changes (degradations) in the mechanical properties of solid plates induced by cyclic fatigue loading will influence the features of ultrasonic Lamb wave propagation, such as dispersion and attenuation. This paper has qualitatively analyzed the feasibility of using the amplitude-frequency characteristics and the stress wave factors (SWFs) of ultrasonic Lamb wave propagation to assess fatigue damage in solid plates. Liquid wedge transducers located on the surface of solid plates tested are used to generate and detect the Lamb wave signals. Based on the Ritec-SNAP ultrasonic measurement system, the experimental setup for assessing the degree of fatigue damage in solid plates using ultrasonic Lamb wave approach has been established. For several rolled aluminum sheets subjected to tension-tension cyclic loading, the experimental examinations have been performed for the relationships between the amplitude-frequency characteristics of ultrasonic Lamb wave propagation and the numbers of loading cycles (denoted by N), as well as the correlations between the Lamb wave SWFs and N. The experimental results show that the Lamb wave SWFs decrease monotonously and sensitively with the increment of cycles of fatigue loading. Based on the correlations between the Lamb wave SWFs and N, it is further verified that ultrasonic Lamb wave propagation combined with the Lamb wave SWFs can be used to effectively assess early fatigue damage in solid plates.
Deng, Mingxi; Pei, Junfeng
Dependence of Microelastic-plastic Nonlinearity of Martensitic Stainless Steel on Fatigue Damage Accumulation
NASA Technical Reports Server (NTRS)
Self-organized substructural arrangements of dislocations formed in wavy slip metals during cyclic stress-induced fatigue produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter Beta extracted from acoustic harmonic generation measurements. The contributions to Beta from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model as a function of percent full fatigue life to fracture. A wave interaction factor f(sub WI) is introduced into the model to account experimentally for the relative volume of material fatigue damage included in the volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and f(sub WI) = 0.013 the model predicts a monotonic increase in Beta from dislocation substructures of almost 100 percent from the virgin state to roughly 95 percent full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, over the last five percent of fatigue life the model predicts a rapid monotonic increase of Beta by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551 MPa from zero to full tensile load with a measured f(sub WI) of 0.013.
Cantrell, John H.
Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation
NASA Astrophysics Data System (ADS)
Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter ? extracted from acoustic harmonic generation measurements. The contributions to ? from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model [Proc. R. Soc. London, Ser. A 460, 757 (2004)] as a function of percent full fatigue life to fracture. A wave interaction factor fWI is introduced into the model to account experimentally for the relative volume of fatigue damage included in the total volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551MPa and fWI=0.013 the model predicts a monotonic increase in ? from dislocation substructures of almost 100% from the virgin state to roughly 95% full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, during the last 5% of fatigue life the model predicts a rapid monotonic increase of ? by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551MPa from zero to full tensile load with a measured fWI of 0.013.
Cantrell, John H.
Thermography Inspection for Early Detection of Composite Damage in Structures During Fatigue Loading
NASA Technical Reports Server (NTRS)
Advanced composite structures are commonly tested under controlled loading. Understanding the initiation and progression of composite damage under load is critical for validating design concepts and structural analysis tools. Thermal nondestructive evaluation (NDE) is used to detect and characterize damage in composite structures during fatigue loading. A difference image processing algorithm is demonstrated to enhance damage detection and characterization by removing thermal variations not associated with defects. In addition, a one-dimensional multilayered thermal model is used to characterize damage. Lastly, the thermography results are compared to other inspections such as non-immersion ultrasonic inspections and computed tomography X-ray.
Zalameda, Joseph N.; Burke, Eric R.; Parker, F. Raymond; Seebo, Jeffrey P.; Wright, Christopher W.; Bly, James B.
Under-filled BGA solder joint vibration fatigue damage
The paper (1) experimentally determines the survivability\\/durability of the solder joints of ball grid array (BGA) with\\/without under-filled materials when subjected to military vibration environment and (2) develops a vibration fatigue life prediction model, which is qualitatively calibrated by test. A test vehicle (TV), on which various sizes of BGA daisy-chained packages with\\/without under-filled materials, e.g., Hysol (non-reworkable) and Hacthane
T. E. Wong; F. W. Palmieri; H. S. Fenger
Tensile and bending thermo-mechanical fatigue testing on cylindrical and flat specimens of CMSX-4 for design of turbine blades
This paper briefly describes thermo-mechanical fatigue tests performed on cylindrical and flat specimens of the single crystal material CMSX-4 in ?001?, ?011? and ?111?-orientation. The test matrix was defined based on the thermo-mechanical loading identified at different positions of actual turbine rotor blades. It included tensile strain-controlled TMF-test conditions on the cylindrical plain specimens and tensile load-controlled TMF-test conditions on
J. Xu; S. Reuter; W. Rothkegel
Procedure and results of the investigation of full-scale lock joints of blades of compressors of gas-turbine engines for fretting fatigue
We analyze the experimental procedures aimed at testing specimens which simulate contact pairs and full-scale lock joints\\u000a of blades of compressors of gas-turbine engines with grooved disks for fretting fatigue. The experimental results corroborate\\u000a the efficiency of these procedures and enable one to choose coatings and procedures of treatment of contacting surfaces which\\u000a guarantee the attainment of higher values of
G. V. Tsybanev; Yu. S. Nalimov; O. N. Gerasimchuk
Fatigue damage rule of LY12CZ aluminium alloy under sequential biaxial loading
NASA Astrophysics Data System (ADS)
A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ aluminium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter ? which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental data for two-level loading, multi-level loading of LY12CZ aluminium alloy, and multi-level loading of 45 steel. Fatigue lives predicted are within a factor of 2 scatter band.
Wang, YingYu; Zhang, DaChuan; Yao, WeiXing
Fatigue Damage Evaluation through Stiffness Measurements in Boron-Epoxy Laminates
Stiffness reductions, resulting from fatigue damage, were measured for unnotched [±45]s, [0\\/90] s, and [0\\/90\\/ ±45 ] s boron\\/epoxy laminates. Deg radation in the various in-plane stiffnesses (Exx, Byy, Gxy) were measured using a combination of uniaxial tension, rail shear, and flexure tests. An attempt was made to predict stiffness loss at failure from a secant modulus criterion. Damage growth
T. Kevin OBrien; Kenneth L. Reifsnider
Fatigue damage accumulation in steel 45 under loading regimes involving low-cycle overloads
NASA Astrophysics Data System (ADS)
The paper presents the results of experimental investigations into the regularities of fatigue damage accumulation in steel 45 under block loading involving elastoplastic (low-cycle) overloads. The experiments were carried out using the methods of the factorial design theory. Mathematical models are developed for damage accumulation depending on the variation of the parameters (factors) investigated: the level of the main (elastic) strain, the relative level of overloads, and their relative number.
Shlyushenkov, A. P.; Tatarintsev, V. A.
A simple and efficient multiaxial fatigue damage model for engineering applications of macro-crack initiation
This paper is devoted to the presentation of a multiaxial fatigue damage model, derived from Chaboche's uniaxial formulation. Fit for use in the entire range of crack initiation life, it takes a number of different effects into account, including mean-stress influence and cumulative damage under nonperiodic proportional and nonproportional loadings. Its identification and integration is described, and it is shown as a simple but efficient engineering tool. Several examples, taken from different authors allows one to validate this kind of model.
Chaudonneret, M. (Office National d'Etudes et de Recherches, Chatillon (France))
The Characteristics of Fatigue Damage in the Fuselage Riveted Lap Splice Joint
NASA Technical Reports Server (NTRS)
An extensive data base has been developed to form the physical basis for new analytical methodology to predict the onset of widespread fatigue damage in the fuselage lap splice joint. The results of detailed destructive examinations have been cataloged to describe the physical nature of MSD in the lap splice joint. ne catalog includes a detailed description, e.g., crack initiation, growth rates, size, location, and fracture morphology, of fatigue damage in the fuselage lap splice joint structure. Detailed examinations were conducted on a lap splice joint panel removed from a full scale fuselage test article after completing a 60,000 cycle pressure test. The panel contained a four bay region that exhibited visible outer skin cracks and regions of crack link-up along the upper rivet row. Destructive examinations revealed undetected fatigue damage in the outer skin, inner skin, and tear strap regions. Outer skin fatigue cracks were found to initiate by fretting damage along the faying surface. The cracks grew along the faying surface to a length equivalent to two to three skin thicknesses before penetrating the outboard surface of the outer skin. Analysis of fracture surface marker bands produced during full scale testing revealed that all upper rivet row fatigue cracks contained in a dim bay region grow at similar rates; this important result suggests that fracture mechanics based methods can be used to predict the growth of outer skin fatigue cracks in lap splice structure. Results are presented showing the affects of MSD and out-of-plane pressure loads on outer skin crack link-up.
Piascik, Robert S.; Willard, Scott A.
Role of brain macrophages on IL1? and fatigue following eccentric exercise-induced muscle damage
Fatigue associated with recovery from muscle damage has recently been linked to increases in brain and muscle proinflammatory cytokines. However, little is known regarding the origin of these cytokines. Since macrophage-like cells in the brain are a primary source of cytokines, we used a brain specific macrophage depletion technique involving liposome encapsulated clodronate (CLD) to examine the role of macrophages
Martin D. Carmichael; J. Mark Davis; E. Angela Murphy; James A. Carson; N. Van Rooijen; Eugene Mayer; Abdul Ghaffar
Symbolic time series analysis of ultrasonic data for early detection of fatigue damage
This paper presents a novel analytical tool for early detection of fatigue damage in polycrystalline alloys that are commonly used in mechanical structures. Time series data of ultrasonic sensors have been used for anomaly detection in the statistical behaviour of structural materials, where the analysis is based on the principles of symbolic dynamics and automata theory. The performance of the
Shalabh Gupta; Asok Ray; Eric Keller
Mechanisms of microstructural damage during rolling contact fatigue of bearing steels
Mechanisms of Microstructural Damage during Rolling Contact Fatigue of Bearing Steels JeeHyun Kang Darwin College University of Cambridge A dissertation submitted for the degree of Doctor of Philosophy at the University of Cambridge, October 2013... tempering . . . . . . . . . . . . . . . . . . . 75 4.1.1 Carbon transport . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.1.2 Dislocation assisted diffusion . . . . . . . . . . . . . . . . . . . . . 82 4.1.3 Hardness evolution...
Kang, JeeHyun
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. PMID:24574866
Huang, Hong-Zhong; Yuan, Rong
A fatigue damage estimator using RBF, backpropagation, and CID4 neural algorithms
NASA Technical Reports Server (NTRS)
Fatigue damage estimation using neural networks is described in the paper. Attention is focused on the method of data generation for both the training and test data used by radial basis function (RBF), backpropagation, and CID4 algorithms used in this study. The performance results of the three neural algorithms are analyzed in terms of their strengths and weaknesses in training.
Cios, Krzysztof J.; Tjia, Robert E.; Liu, Ning
Cumulative damage and the response of human bone in two-step loading fatigue
It has already been shown that in fatigue tests in vitro human cortical bone accumulates damage in the form of microcracks and that the total number of microcracks generated prior to the creation of the fatal macrocrack, and their effect (softening) on the material properties, depends on the level of applied stress. At each stress level the amount of accumulated
Peter Zioupos; Adriŕ Casinos
Determination of Turbine Blade Life from Engine Field Data
NASA Technical Reports Server (NTRS)
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.
Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.
Deformation history and load sequence effects on cumulative fatigue damage and life predictions
NASA Astrophysics Data System (ADS)
Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless steel is a material with strong deformation history effects and phase transformation resulting from plastic straining, such load sequence and variable amplitude loading effects are significant to its fatigue behavior and life predictions. The goal of this study was to investigate the effects of cyclic deformation on fatigue behavior of stainless steel 304L as a deformation history sensitive material and determine how to quantify and accumulate fatigue damage to enable life predictions under variable amplitude loading conditions for such materials. A comprehensive experimental program including testing under fully-reversed, as well as mean stress and/or mean strain conditions, with initial or periodic overloads, along with step testing and random loading histories was conducted on two grades of stainless steel 304L, under both strain-controlled and load-controlled conditions. To facilitate comparisons with a material without deformation history effects, similar tests were also carried out on aluminum 7075-T6. Experimental results are discussed, including peculiarities observed with stainless steel behavior, such as a phenomenon, referred to as secondary hardening characterized by a continuous increase in the stress response in a strain-controlled test and often leading to runout fatigue life. Possible mechanisms for secondary hardening observed in some tests are also discussed. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in strain control and ratcheting in load control and their influence on fatigue life are discussed. Some unusual mean strain test results are presented for stainless steel 304L, where in spite of mean stress relaxation fatigue lives were significantly longer than fully-reversed tests. Prestraining indicated no effect on either deformation or fatigue behavior of aluminum, while it induced considerable hardening in stainless steel 304L and led to different results on fatigue life, depending on the test control mode. In step tests for stainless steel 304L, strong hardening induced by the first step of a high-low sequence significantly affects the fatigue behavior, depending on the test control mode used. For periodic overload tests of stainless steel 340L, hardening due to the overloads was progressive throughout life and more significant than in high-low step tests. For aluminum, no effect on deformation behavior was observed due to periodic overloads. However, the direction of the overloads was found to affect fatigue life, as tensile overloads led to longer lives, while compressive overloads led to shorter lives. Deformation and fatigue behaviors under random loading conditions are also presented and discussed for the two materials. The applicability of a common cumulative damage rule, the linear damage rule, is assessed for the two types of material, and for various loading conditions. While the linear damage rule associated with a strain-life or stress-life curve is shown to be fairly accurate for life predictions for aluminum, it is shown to poorly represent the behavior of stainless steel, especially in prestrained and high-low step tests, in load control. In order to account for prior deformation effects and achieve accurate fatigue life predictions for stainless steel, parameters including both stress and strain terms are required. The Smith-Watson-Topper and Fatemi-Socie approaches, as such parameters, are shown to correlate most test data fairly accurately. For damage accumulation under variable amplitude loading, the linear damage rule associated with strain
Colin, Julie
A Coupled/Uncoupled Computational Scheme for Deformation and Fatigue Damage Analysis of Unidirectional Metal-Matrix Composites
NASA Technical Reports Server (NTRS)
A fatigue damage computational algorithm utilizing a multiaxial, isothermal, continuum-based fatigue damage model for unidirectional metal-matrix composites has been implemented into the commercial finite element code MARC using MARC user subroutines. Damage is introduced into the finite element solution through the concept of effective stress that fully couples the fatigue damage calculations with the finite element deformation solution. Two applications using the fatigue damage algorithm are presented. First, an axisymmetric stress analysis of a circumferentially reinforced ring, wherein both the matrix cladding and the composite core were assumed to behave elastic-perfectly plastic. Second, a micromechanics analysis of a fiber/matrix unit cell using both the finite element method and the generalized method of cells (GMC). Results are presented in the form of S-N curves and damage distribution plots.
Wilt, Thomas E.; Arnold, Steven M.; Saleeb, Atef F.
Fatigue damage in superalloys determined using Doppler broadening positron annihilation
NASA Technical Reports Server (NTRS)
Axial fatigue specimens of three superalloys, Inconel 718, Incoloy 903 and Haynes 188, were machined from solution-heat-treated material and artificially aged. They were subjected to cyclic loading for a selected number of cycles after which the S parameter was determined using Doppler broadening positron annihilation. Initially, the S parameter decreased, followed by a large increase and a subsequent decline leading to fracture. This has been interpreted as the removal of residual vacancies, the introduction of new defects by cyclic loading, and, finally, a clustering of the defects as microcracks which grow to cause failure.
Hoeckelman, Donald; Leighly, H. P., Jr.
Dependence of the Perpendicular Residual Leakage Magnetic Flux Density on Fatigue Damage in an Austenitic Stainless Steel
NASA Astrophysics Data System (ADS)
In order to estimate the amount of plane bending fatigue damage in an austenitic stainless steel (SUS304), we were investigating the relationship between plane bending fatigue damage and the perpendicular residual leakage magnetic flux density caused by martensitic structure induced by plane bending fatigue. A specimen such as SUS304 had been excited in a constant external magnetic field perpendicularly to measure dependence of the perpendicular residual leakage magnetic flux density on plane bending fatigue damage accurately. The Z component of the magnetic flux density at 1 mm above a specimen is measured by using a thin-film flux-gate (FG) magnetic sensor. Residual magnetization is caused by partial martensitic structure in an austenitic stainless steel induced by cyclic bending stress. From our experiments, we can evaluate dependence of the perpendicular residual leakage magnetic flux density on plane bending fatigue damage and know the relationship between growth of a crack and the perpendicular residual leakage magnetic flux density.
Oka, M.; Yakushiji, T.; Tsuchida, Y.; Enokizono, M.
Numerical fatigue life assessment of cardiovascular stents: A two-scale plasticity-damage model
NASA Astrophysics Data System (ADS)
Cardiovascular disease has become a major global health care problem in the last decades. 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, numerical approaches for fatigue life assessment of stents have gained special interest in the engineering community. Numerical fatigue life predictions can be used to modify the design and prevent failure without making and testing numerous physical devices, thus preventing from undesired fatigue failures. We present a numerical fatigue life model for the analysis of cardiovascular balloon-expandable stainless steel stents that can hopefully provide useful information either to be used for product improvement or for clinicians to make life-saving decisions. This model incorporates a two-scale continuum damage mechanics model and the so-called Soderberg fatigue failure criterion. We provide numerical results for both Palmaz-Schatz and Cypher stent designs and demonstrate that a good agreement is found between the numerical and the available experimental results.
Santos, H. A. F. A.; Auricchio, F.; Conti, M.
Experimental Evaluation of Fatigue Damage Progression in Postbuckled Single Stringer Composite Specimens
NASA Technical Reports Server (NTRS)
The durability and damage tolerance of postbuckled composite structures are not yet completely understood, and remain difficult to predict due to the nonlinearity of the geometric response and its interaction with local damage modes. A research effort was conducted to investigate experimentally the quasi-static and fatigue damage progression in a single-stringer compression (SSC) specimen. Three specimens were manufactured with a hat-stiffener, and an initial defect was introduced with a Teflon film embedded between one flange of the stringer and the skin. One of the specimens was tested under quasi-static compressive loading, while the remaining two specimens were tested by cycling in postbuckling. The tests were performed at the NASA Langley Research Center under controlled conditions and with instrumentation that allows a precise evaluation of the postbuckling response and of the damage modes. Three-dimensional digital image correlation VIC-3D systems were used to provide full field displacements and strains on the skin and the stringer. Passive thermal monitoring was conducted during the fatigue tests using an infrared camera that showed the location of the delamination front while the specimen was being cycled. The live information from the thermography was used to stop the fatigue tests at critical stages of the damage evolution to allow detailed ultrasonic scans.
Bisagni, Chiara; Davila, Carlos G.; Rose, Cheryl A.; Zalameda, Joseph N.
A fracture mechanics based model for cumulative damage assessment as part of fatigue life prediction
NASA Astrophysics Data System (ADS)
Cumulative damage related phenomena are considered, and a model for fatigue life prediction in the crack initiation stage is presented. The model interprets damage accumulation as a process of crack growth and takes into account load sequence dependent crack opening and closing levels which are controlled by the elastoplastic strain history and damage sum dependent decrease of the fatigue limit. A crack-driving parameter based on elastoplastic fracture mechanics is derived. Experiments based on two steels, an aluminum alloy, and several types of loading spectra revealed the improved accuracy of the model in comparison with previous approaches. It is concluded that the model can successfully predict load interaction effects which control the effective material straining and the phenomenon of a transient endurance limit for variable amplitude loading sequences.
Vormwald, M.; Heuler, P.; Seeger, T.
The effect of cement creep and cement fatigue damage on the micromechanics of the cement-bone interface.
The cement-bone interface provides fixation for the cement mantle within the bone. The cement-bone interface is affected by fatigue loading in terms of fatigue damage or microcracks and creep, both mostly in the cement. This study investigates how fatigue damage and cement creep separately affect the mechanical response of the cement-bone interface at various load levels in terms of plastic displacement and crack formation. Two FEA models were created, which were based on micro-computed tomography data of two physical cement-bone interface specimens. These models were subjected to tensile fatigue loads with four different magnitudes. Three deformation modes of the cement were considered: 'only creep', 'only damage' or 'creep and damage'. The interfacial plastic deformation, the crack reduction as a result of creep and the interfacial stresses in the bone were monitored. The results demonstrate that, although some models failed early, the majority of plastic displacement was caused by fatigue damage, rather than cement creep. However, cement creep does decrease the crack formation in the cement up to 20%. Finally, while cement creep hardly influences the stress levels in the bone, fatigue damage of the cement considerably increases the stress levels in the bone. We conclude that at low load levels the plastic displacement is mainly caused by creep. At moderate to high load levels, however, the plastic displacement is dominated by fatigue damage and is hardly affected by creep, although creep reduced the number of cracks in moderate to high load region. PMID:20692663
Waanders, Daan; Janssen, Dennis; Mann, Kenneth A; Verdonschot, Nico
The effect of cement creep and cement fatigue damage on the micromechanics of the cement-bone interface
The cement-bone interface provides fixation for the cement mantle within the bone. The cement-bone interface is affected by fatigue loading in terms of fatigue damage, or micro cracks, and creep, both mostly in the cement. This study investigates how fatigue damage and cement creep separately affect the mechanical response of the cement-bone interface at various load levels in terms of plastic displacement and crack formation. Two FEA models were created, which were based on micro-computed tomography data of two physical cement-bone interface specimens. These models were subjected to tensile fatigue loads with four different magnitudes. Three deformation modes of the cement were considered; 'only creep', 'only damage' or 'creep and damage'. The interfacial plastic deformation, the crack reduction as a result of creep and the interfacial stresses in the bone were monitored. The results demonstrate that, although some models failed early, the majority of plastic displacement was caused by fatigue damage, rather than cement creep. However, cement creep does decrease the crack formation in the cement up to 20%. Finally, while cement creep hardly influences the stress levels in the bone, fatigue damage of the cement considerably increases the stress levels in the bone. We conclude that at low load levels the plastic displacement is mainly caused by creep. At moderate to high load levels, however, the plastic displacement is dominated by fatigue damage and is hardly affected by creep, although creep reduced the number of cracks in moderate to high load region. PMID:20692663
Waanders, Daan; Janssen, Dennis; Mann, Kenneth A.; Verdonschot, Nico
A model for predicting damage induced fatigue life of laminated composite structural components
NASA Technical Reports Server (NTRS)
This paper presents a model for predicting the life of laminated composite structural components subjected to fatigue induced microstructural damage. The model uses the concept of continuum damage mechanics, wherein the effects of microcracks are incorporated into a damage dependent lamination theory instead of treating each crack as an internal boundary. Internal variables are formulated to account for the effects of both matrix cracks and internal delaminations. Evolution laws for determining the damage variables as functions of ply stresses are proposed, and comparisons of predicted damage evolution are made to experiment. In addition, predicted stiffness losses, as well as ply stresses are shown as functions of damage state for a variety of stacking sequences.
Allen, David H.; Lo, David C.; Georgiou, Ioannis T.; Harris, Charles E.
Post-Impact Fatigue Damage Monitoring Using Fiber Bragg Grating Sensors
It has been shown that impact damage to composite materials can be revealed by embedded Fiber Bragg Gratings (FBG) as a broadening and splitting of the latter's characteristic narrow peak reflected spectrum. The current work further subjected the impact damaged composite to cyclic loading and found that the FBG spectrum gradually submerged into a rise of background intensity as internal damages progressed. By skipping the impact, directing the impact to positions away from the FBG and examining the extracted fibers, we concluded that the above change is not a result of deterioration/damage of the sensor. It is caused solely by the damages initiated in the composite by the impact and aggravated by fatigue loading. Evolution of the grating spectrum may therefore be used to monitor qualitatively the development of the incurred damages. PMID:24594609
Shin, Chow-Shing; Liaw, Shien-Kuei; Yang, Shi-Wei
Estimation of Fatigue Damage for AN Austenitic Stainless Steel (SUS304) Using a Pancake Type Coil
NASA Astrophysics Data System (ADS)
There are some fatigue damage estimation methods of an austenitic stainless steel that uses martensitic transformation. For instance, those are the remanent magnetization method, the excitation method, and so on. Those two methods are researched also in our laboratory now. In the remanent magnetization method, it is well known that the relationship between fatigue damage and the remanent magnetization is simple, clear, and reproducible. However, this method has the disadvantage to need a special magnetizer. Then, this method cannot be easily used at the job site such as the factory. On the other hand, as the special magnetizer is unnecessary, the excitation method can be easily used at the job site. But, this method has some disadvantages shown as follows. For instance, the output signal of this method is small. And the surface state of the specimen strongly influences the noise component of the output signal. It is well known that the inductance of a pancake type coil put on the metallic specimen changes according to the electromagnetic properties of the metallic specimen. In this paper, the method of evaluation of fatigue damage of an austenitic stainless steel (SUS304) by using a change of an inductance of a pancake type coil is shown. In addition, the fatigue evaluation performance of this method is described.
Oka, M.; Tsuchida, Y.; Nagato, S.; Yakushiji, T.; Enokizono, M.
The Growth of Multi-Site Fatigue Damage in Fuselage Lap Joints
NASA Technical Reports Server (NTRS)
Destructive examinations were performed to document the progression of multi-site damage (MSD) in three lap joint panels that were removed from a full scale fuselage test article that was tested to 60,000 full pressurization cycles. Similar fatigue crack growth characteristics were observed for small cracks (50 microns to 10 mm) emanating from counter bore rivets, straight shank rivets, and 100 deg counter sink rivets. Good correlation of the fatigue crack growth data base obtained in this study and FASTRAN Code predictions show that the growth of MSD in the fuselage lap joint structure can be predicted by fracture mechanics based methods.
Piascik, Robert S.; Willard, Scott A.
Nondestructive indication of fatigue damage and residual lifetime in ferromagnetic construction materials
NASA Astrophysics Data System (ADS)
A new revolutionary attitude toward investigation of fatigue damage in cyclically loaded steel samples is reported. The measurement is based on the method of magnetic adaptive testing, which--in contrast to traditional magnetic hysteresis investigations--picks up the relevant information from systematic measurement and evaluation of whole minor magnetic hysteresis loops and their derivatives. Satisfactory correlations between nondestructively measured magnetic descriptors and actual lifetime of the fatigued material were found. The presented method is able to serve as a powerful tool for indication of changes, which occur in the structure of the inspected objects during their industrial service lifetime, as long as they are manufactured from ferromagnetic materials.
Tomáš, Ivan; Ková?ík, Ond?ej; Vértesy, Gábor; Kadlecová, Jana
Some useful concepts for the designer in treating cumulative fatigue damage at elevated temperatures
NASA Technical Reports Server (NTRS)
The paper concentrates on three subjects: (1) further development of the double-linear damage rule for cumulative fatigue damage summation in the sub-creep temperature range; (2) a new consideration of the effect of strain reversals in the creep range of materials, whereby reversals that occur later in the histogram can influence the degree of damage caused by earlier loading events; and (3) the application of the minimum-commitment time-temperature parameter to the treatment of creep rupture of multiheats wherein considerable differences in properties of individual heats may occur. Numerical examples and plots are given.
Manson, S. S.
Damage accumulation, fatigue and creep behaviour of vacuum mixed bone cement.
The behaviour of bone cement under fatigue loading is of interest to assess the long-term in vivo performance. In this study, uniaxial tensile fatigue tests were performed on CMW-1 bone cement. Acoustic emission sensors and an extensometer were attached to monitor damage accumulation and creep deformation respectively. The S-N data exhibited the scatter synonymous with bone cement fatigue, with large pores generally responsible for premature failure; at 20 MPa specimens failed between 2 x 10(3) and 2 x 10(4) load cycles, while at 7 MPa specimens failed from 3 x 10(5) load cycles but others were still intact after 3 x 10(6) load cycles. Acoustic emission data revealed a non-linear accumulation of damage with respect to time, with increasing non-linearity at higher stress levels. The damage accumulation process was not continuous, but occurred in bursts separated by periods of inactivity. Damage in the specimen was located by acoustic emissions, and allowed the failure site to be predicted. Acoustic emission data were also used to predict when failure was not imminent. When this was the case at 3 million load cycles, the tests were terminated. Creep strain was plotted against the number of load cycles and a linear relationship was found when a double logarithmic scale was employed. This is the first time a brand of cement has been characterised in such detail, i.e. fatigue life, creep and damage accumulation. Results are presented in a manner that allows direct comparison with published data for other cements. The data can also be used to characterise CMW-1 in computational simulations of the damage accumulation process. Further evidence is provided for the condition-monitoring capabilities of the acoustic emission technique in orthopaedic applications. PMID:15860209
Jeffers, Jonathan R T; Browne, Martin; Taylor, Mark
Ultrasonic detection of fatigue damage in glass-epoxy composites
Energy storage flywheels fabricated of S2 glass-epoxy composite were studied to determine the behavior of the ultrasonic properties as a function of strain history and to identify possible predictors of incipient failure. Tensile specimens of the flywheel material were loaded uniaxially, and the ultrasonic properties (i.e., the shear and longitudinal wave velocities and the attenuation) were measured as a function of strain. Finished flywheels were similarly tested at various stages during cyclic spin testing; in addition, the polar backscattering intensity as a function of fatigue cycle was recorded. The velocities are excellent indicators of the maximum strain incurred at each point of the flywheel, and the attenuation delineates the region in which the stress is high enough to initiate microcracking in the matrix.
Simpson, W.A. Jr.; McClung, R.W.
Temporal Effect of In Vivo Tendon Fatigue Loading on the Apoptotic Response Explained in the Context of Number of Fatigue Loading Cycles and Initial Damage Parameters
Accumulation of damage is a leading factor in the development of tendinopathy. Apoptosis has been implicated in tendinopathy, but the biological mechanisms responsible for initiation and progression of these injuries are poorly understood. We assessed the relationship between initial induced damage and apoptotic activity 3 and 7 days after fatigue loading. We hypothesized that greater apoptotic activity (i) will be associated with greater induced damage and higher number of fatigue loading cycles, and (ii) will be higher at 7 than at 3 days after loading. Left patellar tendons were fatigue loaded for either 100 or 7,200 cycles. Diagnostic tests were applied before and after fatigue loading to determine the effect of fatigue loading on hysteresis, elongation, and loading and unloading stiffness (damage parameters). Cleaved Caspase-3 staining was used to identify and calculate the percent apoptosis in the patellar tendon. While no difference in apoptotic activity occurred between the 100 and 7,200 cycle groups, greater apoptotic activity was associated with greater induced damage. Apoptotic activity was higher at 7 than 3 days after loading. We expect that the decreasing number of healthy cells that can repair the induced damage in the tendon predispose it to further injury. PMID:24838769
Andarawis-Puri, Nelly; Philip, Anaya; Laudier, Damien; Schaffler, Mitchell B.; Flatow, Evan L.
Bone formation after damaging in vivo fatigue loading results in recovery of whole-bone monotonic strength and increased fatigue life.
Bone has a remarkable capacity for self-repair. We previously reported a woven bone response after damaging in vivo fatigue loading of the rat ulna that led to a rapid recovery of whole-bone strength. In the current study we asked: does the bone response in the 12 days after damaging fatigue loading result in a bone that has normal fatigue properties? The right forelimbs of 52 adult rats were subjected to a single bout of in vivo fatigue loading. Nonloaded left forelimbs were used as controls. Ulnar geometric properties were assessed by peripheral quantitative computed tomography (pQCT) and ex vivo mechanical properties were assessed by three-point bending. On day 0, ulnae from loaded forelimbs had a 15-20% reduction in stiffness and ultimate force versus controls (p < 0.10), indicative of structural damage. On day 12, bone area at the midshaft was increased by 27% (p < 0.001) and microCT scans revealed periosteal woven bone at this site. This bone response led to a recovery of the monotonic properties of loaded ulnae at day 12 versus control (stiffness, p = 0.73; ultimate force, p = 0.96). Importantly, fatigue testing ex vivo at day 12 demonstrated significantly greater fatigue life in in vivo loaded ulnae versus controls (p < 0.001). Additionally, the slope of the fatigue-life curve was significantly less in loaded versus control ulnae (p < 0.002). We conclude that woven bone "repair" of a bone damaged by fatigue loading restores whole-bone strength and enhances resistance to further damage by repetitive loading. PMID:17106875
Silva, Matthew J; Touhey, Daniel C
The influence of tensile fatigue damage on residual compressive strength of woven composites
The long term mechanical fatigue of a Celion G30-500/PMR-15 woven composite system is investigated to study the interrelationship between thermo-mechanical properties, namely the thermal expansion coefficient (TEC) and the compressive strength. Residual compressive strength measurements (IITRI fixture) conducted on specimens subjected to tension-tension fatigue cycling indicate that this material property is sensitive to cracks and delaminations which form during mechanical cycling. Measured compressive strength degradation are as large as 49% for this material undergoing mechanical fatigue cycling with TEC degradation as large as 61%. Experimental results show that a correlation exists between TEC measurements and compressive strength. This correlation suggests that TEC measurements may be used as a damage evaluation technique.
Mitrovic, M.; Carman, G.P. [Univ. of California, Los Angeles, CA (United States). Mechanical, Aerospace and Nuclear Engineering Dept.
Application of positron annihilation lineshape analysis to fatigue damage and thermal embrittlement for nuclear plant materials
Positron annihilation (PA) lineshape analysis is sensitive to detect microstructural defects such as vacancies and dislocations. The authors are developing a portable system and applying this technique to nuclear power plant material evaluations; fatigue damage in type 316 stainless steel and SA508 low alloy steel, and thermal embrittlement in duplex stainless steel. The PA technique was found to be sensitive in the early fatigue life (up to 10%), but showed a little sensitivity for later stages of the fatigue life in both type 316 stainless steel and SA508 ferritic steel. Type 316 steel showed a higher PA sensitivity than SA508 since the initial SA508 microstructure already contained a high dislocation density in the as-received state. The PA parameter increased as a fraction of aging time in CF8M samples aged at 350 C and 400 C, but didn`t change much in CF8 samples.
Uchida, M.; Ohta, Y.; Nakamura, N. [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan); Yoshida, K. [Ishikawajima-Harima Heavy Industries Co., Ltd., Kanagawa (Japan)
The effect of pseudo-accumulation in the measurement of fatigue laser-induced damage threshold
NASA Astrophysics Data System (ADS)
Laser-induced damage threshold determination as a function of the number of incident pulses on a specific optic is a classic problem in laser damage studies. There are several models of the fundamental mechanisms explaining the fatigue laser damage behavior including temperature accumulation and changes of electronic or chemical material structure. Herewith we discuss the effects of unstable laser radiation on S-on-1 laser-induced damage probability. Numerical simulations of S-on-1 measurements for specific cases of defect densities, spot sizes and beam jitters are performed. It is demonstrated that the statistical effects of "pseudo-accumulation" reasoned by unstable laser radiation in transparent dielectrics containing nanometer sized defects leads to accumulation-like behavior. The magnitudes of the random beam walking and the energy fluctuations are directly related to the damage probability. Experimental results are also introduced to illustrate the theoretical results.
Melninkaitis, A.; Mirauskas, J.; Jupé, M.; Ristau, D.; Arenberg, J. W.; Sirutkaitis, V.
Variable amplitude load models for fatigue damage and crack growth
Load models for fatigue analysis and testing are tailored to the level of complexity required for the application. Random variable models are developed and applied to analyses in which load sequence effects can be neglected. Conventional narrow-band load peak and range distributions are applied to crack initiation and growth. Distributions of significant peaks and ranges for wide band loadings are developed empirically through simulations with racetrack filtering. An efficient ''sequential'' simulation technique is introduced for continuous generation of both narrow- and wide-band random loads. Based on a simplified crack closure model, simulations of crack growth suggest that sequence effects are most influential when any or a combination of the following are present: larger ratios of crack opening stress to maximum applied stress, lower values of applied tensile mean stress, small values of yield stress and crack growth coefficient. When sequence effects are present, the regularity of the spacing between tensile overloads can be important. In particular, assumption of regularly spaced overloads can be nonconservative.
Veers, P.S.; Winterstein, S.R.; Nelson, D.V.; Cornell, C.A.
Acoustic emission and fatigue damage induced in plasma-sprayed hydroxyapatite coating layers.
In order to improve the adhesive strength of hydroxyapatite (HAp) coatings, grit blasting with Al(2)O(3) powder and then wet blasting with HAp/Ti mixed powders was carried out on a commercially pure Ti (cp-Ti) substrate. Subsequently, an HAp/Ti bond coat layer and HAp top coat layer were deposited by plasma spraying. Fatigue tests of the HAp-coated specimens were carried out under four-point bending. Acoustic emission (AE) signals during the entire fatigue test were monitored to investigate the fatigue cracking behavior of the HAp-coated specimens. The HAp-coated specimens could survive up to 10(7) cycles without spallation of the HAp coating layers at the stress amplitude of 120 MPa. The HAp-coated specimens without HAp/Ti bond coat layer showed shorter fatigue life and easy crack nucleation compared to the HAp-coated specimens with HAp/Ti bond coat layer. The delamination and spallation of the HAp top coat with HAp/Ti bond coat on cp-Ti was not observed until the crack propagated into the cp-Ti during the final fracture stage of the fatigue cycle. Therefore, the HAp/Ti bond coat layer was found to greatly improve the fatigue damage resistance of the HAp coating layer. Three stages of the fatigue failure behavior of the HAp top coat with HAp/Ti bond coat on a cp-Ti substrate can be clearly estimated by the AE monitoring technique. These stages are cracks nucleating and propagating in the coating layer, cracks propagating in the substrate, and cracks propagating unstably to final fracture. PMID:22402159
Laonapakul, Teerawat; Otsuka, Yuichi; Nimkerdphol, Achariya Rakngarm; Mutoh, Yoshiharu
The molecular response of the patellar tendon to fatigue loading explained in the context of the initial induced damage and number of fatigue loading cycles
Accumulation of sub-rupture fatigue damage has been implicated in the development of tendinopathy. We previously developed an in vivo model of damage accumulation using the rat patellar tendon. Our model allows us to control the input loading parameters to induce fatigue damage in the tendon. Despite this precise control, the resulting induced damage could vary among animals because of differences in size or strength among their patellar tendons. In this study, we used number of applied cycles and initial (day-0) parameters that are indicative of induced damage to assess the molecular response 7 days after fatigue loading. We hypothesized that day-0 hysteresis, elongation, and stiffness of the loading and unloading load-displacement curves would be predictive of the 7-day molecular response. Results showed correlations between the 7-day molecular response and both day-0 elongation and unloading stiffness. Additionally, loading resulted in upregulation of several extracellular matrix genes that suggest adaptation; however, several of these genes (Col-I, -XII, MMP 2, and TIMP 3) shut down after a high level of damage was induced. We showed that evaluating the 7-day molecular profile in light of day-0 elongation provides important insight that is lost from comparing number of fatigue loading cycles only. Our data showed that loading generally results in an adaptive response. However, the tendon's ability to effectively respond deteriorates as greater damage is induced. PMID:22227881
Andarawis-Puri, Nelly; Sereysky, Jedd B.; Sun, Hui B.; Jepsen, Karl J.; Flatow, Evan L.
Characterization of accumulated fatigue damage in titanium-(6)aluminum-(4)vanadium plate material using transmission electron microscopy and nonlinear acoustics
NASA Astrophysics Data System (ADS)
Internal damage accumulation of Ti-6Al-4V specimens subjected to controlled levels of low cycle fatigue (LCF) and high cycle fatigue (HCF) was studied for this dissertation. The objective of this work was to characterize controlled damage in the crack precursor stage in Ti-6Al-4V forged plate material for two microstructural conditions using transmission electron microscopy (TEM) and nonlinear acoustics (NLA). The purpose of the controlled-damage samples is to create calibration standards for damage characterization and quantification for the nondestructive technique of nonlinear acoustics. In addition, TEM identified the amount and types of accumulated damage present in the samples as a result of fatigue at various stages of partial life. The online, in-situ nonlinear acoustic curve generated during LCF experiments of the duplex microstructure showed sensitivity of the nonlinearity parameter to the early stages of fatigue damage. The localized measurements of the nonlinearity parameter on fractured LCF and HCF specimens with a duplex microstructure correlated with dislocation density measurements of samples with similar fatigue history, indicating that the NLA technique can detect accumulated damage at individual locations. The dislocation density was shown to increase steadily throughout the fatigue life with a drastic increase past 90% of life. Dislocations in LCF samples were found to accumulate in dense networks, while in HCF samples well-defined slip in slip bands was prevalent. Pyramidal slip was found to be the most common slip active in both microstructures of this alloy.
Maurer, Julia Lynn Stojak
A recursive Bayesian approach for fatigue damage prognosis: An experimental validation at the reliability component level
NASA Astrophysics Data System (ADS)
Fatigue-induced damage is one of the most uncertain and highly unpredictable failure mechanisms for a large variety of mechanical and structural systems subjected to cyclic and random loads during their service life. A health monitoring system capable of (i) monitoring the critical components of these systems through non-destructive evaluation (NDE) techniques, (ii) assessing their structural integrity, (iii) recursively predicting their remaining fatigue life (RFL), and (iv) providing a cost-efficient reliability-based inspection and maintenance plan (RBIM) is therefore ultimately needed. In contribution to these objectives, the first part of the paper provides an overview and extension of a comprehensive reliability-based fatigue damage prognosis methodology — previously developed by the authors — for recursively predicting and updating the RFL of critical structural components and/or sub-components in aerospace structures. In the second part of the paper, a set of experimental fatigue test data, available in the literature, is used to provide a numerical verification and an experimental validation of the proposed framework at the reliability component level (i.e., single damage mechanism evolving at a single damage location). The results obtained from this study demonstrate (i) the importance and the benefits of a nearly continuous NDE monitoring system, (ii) the efficiency of the recursive Bayesian updating scheme, and (iii) the robustness of the proposed framework in recursively updating and improving the RFL estimations. This study also demonstrates that the proposed methodology can lead to either an extent of the RFL (with a consequent economical gain without compromising the minimum safety requirements) or an increase of safety by detecting a premature fault and therefore avoiding a very costly catastrophic failure.
Gobbato, Maurizio; Kosmatka, John B.; Conte, Joel P.
Estimation of Fatigue life of Cortical Bone Considering Viscoelastic Properties and Damage Mechanics
\\u000a Recently, the Osteoporosis victims increase in the senior citizen. Therefore, the danger of the stress fracture due to the\\u000a decrease in bone strength is pointed out. Especially, the damage accumulation behavior of the bone in the cyclic load becomes\\u000a a problem for the fatigue of the bone. Moreover, it is necessary to consider the viscoelastic property for the prediction\\u000a of
Takenobu Sakai; Keita Yasui; Shuichi Wakayama
Structural-Response Analysis, Fatigue-Life Prediction, and Material Selection for 1 MW Horizontal-Axis Wind-Turbine Blades
NASA Astrophysics Data System (ADS)
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.
Simulated Fatigue Damage Index on Mooring Lines of a Gulf of Mexico Truss Spar Determined from Recorded Field Data
iii SIMULATED FATIGUE DAMAGE INDEX ON MOORING LINES OF A GULF OF MEXICO TRUSS SPAR DETERMINED FROM RECORDED FIELD DATA A Thesis by ADAM FULLER KIECKE Submitted to the Office of Graduate Studies of Texas A&M University... of Mexico Truss Spar Determined From Recorded Field Data Copyright 2012 Adam Fuller Kiecke v SIMULATED FATIGUE DAMAGE INDEX ON MOORING LINES OF A GULF OF MEXICO TRUSS SPAR DETERMINED FROM RECORDED FIELD DATA A Thesis by ADAM FULLER...
Kiecke, Adam Fuller
Binary tree SVM based framework for mining fatigue induced damage attributes in complex lug joints
NASA Astrophysics Data System (ADS)
Research is being conducted in damage diagnosis and prognosis to develop state awareness models and residual useful life estimates of aerospace structures. This work describes a methodology using Support Vector Machines (SVMs), organized in a binary tree structure to classify the extent of a growing crack in lug joints. A lug joint is a common aerospace 'hotspot' where fatigue damage is highly probable. The test specimen was instrumented with surface mounted piezoelectric transducers and then subjected to fatigue load until failure. A Matching Pursuit Decomposition (MPD) algorithm was used to preprocess the sensor data and extract the input vectors used in classification. The results of this classification scheme show that this type of architecture works well for categorizing fatigue induced damage (crack) in a computationally efficient manner. However, due to the nature of the overlap of the collected data patterns, a classifier at each node in the binary tree is limited by the performance of the classifier that is higher up in the tree.
Coelho, Clyde K.; Das, Santanu; Chattopadhyay, Aditi
The strainrange conversion principle for treating cumulative fatigue damage in the creep range
NASA Technical Reports Server (NTRS)
A formula is derived for combining effects of successive hysteresis loops in the creep range of materials when one loop has excess tensile creep, while the other contains excess compressive creep. The resultant effect resembles single loops involving balanced tensile and compressive creep. The attempt to use the Interaction Damage Rule as a tool in combining loops of non-equal size and complex strainrange content has led to important new concepts useful in future studies of creep-fatigue. It turns out that the Interaction Damage Rule is basically an expression of how a set of hysteresis loops involving only single generic strains can combine to produce the same micromechanistic damage as the loop containing the combined strainranges which it analyzes. Making use of the underlying concept of Strainrange Partitioning that only the strainrange content of a hysteresis loop governs fatigue life, not order of introducing strainranges, a rational derivation of the Interaction Damage Rule is provided, showing also how it can effectively be used to synthesize independent loops and determine both damaging and healing effects.
Manson, S. S.
On the Use of Infrared Thermography for Analysis of Fatigue Damage in Ti6Al4V-Welded Joints
NASA Astrophysics Data System (ADS)
The present work is aimed at comparatively studying fatigue damage evolution of a pulsed Nd:YAG laser beam-welded (LBW) joint and the base metal (BM) of Ti6Al4V alloy subjected to cyclic loading. To reveal crack nucleation and propagation during the fatigue process, in situ fatigue was generated using infrared measurement methods. The results indicate that the rate of damage accumulated in the LBW joint was higher than in the BM specimens during a fatigue test, which decreased the fatigue life of the LBW joint. This observation is attributable to the LBW joint fusion zone microstructure, which has a higher void nucleation and growth rate compared with the BM microstructure.
Liu, Jing; Gao, Xiao-Long; Zhang, Lin-Jie; Zhang, Jian-Xun
A continuum damage model of fatigue-induced damage in laminated composites
NASA Technical Reports Server (NTRS)
A model is presented which predicts the stress-strain behavior of continuous fiber reinforced laminated composites in the presence of microstructural damage. The model is based on the concept of continuum damage mechanics and uses internal state variables to characterize the various damage modes. The associated internal state variable growth laws are mathematical models of the loading history induced development of microstructural damage. The model is demonstrated by using it to predict the response of damaged AS-4/3502 graphite/epoxy laminate panels.
Harris, Charles E.; Allen, David H.
Systematic error in mechanical measures of damage during four-point bending fatigue of cortical bone.
Accumulation of fatigue microdamage in cortical bone specimens is commonly measured by a modulus or stiffness degradation after normalizing tissue heterogeneity by the initial modulus or stiffness of each specimen measured during a preloading step. In the first experiment, the initial specimen modulus defined using linear elastic beam theory (LEBT) was shown to be nonlinearly dependent on the preload level, which subsequently caused systematic error in the amount and rate of damage accumulation measured by the LEBT modulus degradation. Therefore, the secant modulus is recommended for measurements of the initial specimen modulus during preloading. In the second experiment, different measures of mechanical degradation were directly compared and shown to result in widely varying estimates of damage accumulation during fatigue. After loading to 400,000 cycles, the normalized LEBT modulus decreased by 26% and the creep strain ratio decreased by 58%, but the normalized secant modulus experienced no degradation and histology revealed no significant differences in microcrack density. The LEBT modulus was shown to include the combined effect of both elastic (recovered) and creep (accumulated) strain. Therefore, at minimum, both the secant modulus and creep should be measured throughout a test to most accurately indicate damage accumulation and account for different damage mechanisms. Histology revealed indentation of tissue adjacent to roller supports, with significant sub-surface damage beneath large indentations, accounting for 22% of the creep strain on average. The indentation of roller supports resulted in inflated measures of the LEBT modulus degradation and creep. The results of this study suggest that investigations of fatigue microdamage in cortical bone should avoid the use of four-point bending unless no other option is possible. PMID:19394019
Landrigan, Matthew D; Roeder, Ryan K
Modeling of long-term fatigue damage of soft tissue with stress softening and permanent set effects
One of the major failure modes of bioprosthetic heart valves is non-calcific structural deterioration due to fatigue of the tissue leaflets. Experimental methods to characterize tissue fatigue properties are complex and time-consuming. A constitutive fatigue model that could be calibrated by isolated material tests would be ideal for investigating the effects of more complex loading conditions. However, there is a lack of tissue fatigue damage models in the literature. To address these limitations, in this study, a phenomenological constitutive model was developed to describe the stress softening and permanent set effects of tissue subjected to long-term cyclic loading. The model was used to capture characteristic uniaxial fatigue data for glutaraldehyde-treated bovine pericardium and was then implemented into finite element software. The simulated fatigue response agreed well with the experimental data and thus demonstrates feasibility of this approach. PMID:22945802
Martin, Caitlin; Sun, Wei
Three-dimensional constitutive model considering transformation-induced damage and resulting fatigue failure in shape memory alloys
NASA Astrophysics Data System (ADS)
In this work, a constitutive model is developed that describe the behavior of shape memory alloys undergoing a large number of cycles, developing internal damage, and eventually failing. Physical mechanisms associated with martensitic phase transformation occurring during cyclic loadings such as transformation strain generation and recovery, transformation-induced plasticity, and fatigue damage are all taken into account within a thermo-dynamically consistent framework. Fatigue damage is described utilizing a continuum theory of damage. The damage growth rate has been formulated as a function of both the stress state and also the magnitude of the transformation strain, while the complete or partial nature of the transformation cycles is also considered as per experimental observations. Simulation results from the model developed are compared to uniaxial actuation fatigue tests at different stress levels. It is shown that both lifetime and the evolution irrecoverable strain can be accurately simulated.
Hartl, Darren J.; Chemisky, Yves; Meraghni, Fodil
PZT active health monitoring for fatigue accumulative damage of concrete beam containing nano-particles for pavement
Based on the actuation and sense function of piezoceramic materials, PZT active health monitoring for fatigue accumulative damage of concrete beam containing nano-particles (TiO2) for pavement is experimentally studied. The test results indicate that the vibration signals received by PZT patches have three development stages obviously: the damage-formation stage, the damage-steady-growth stage and the damage-sharp-growth stage, which shows that PZT
Mao-hua Zhang; Hui Li; Jin-ping Ou
Transition from dislocation glide to creep controlled damage in fatigued thin Cu films
NASA Astrophysics Data System (ADS)
The ultra-high cycle fatigue behavior of supported Cu films with thicknesses between 40 and 360 nm has been investigated using a novel atomic force microscope (AFM)-based resonance method. The damage created under strain controlled fatigue loading is investigated as a function of applied strain, film thickness, and cycle numbers up to 5 × 1010. For films thicker than 100 nm, extrusions and boundary cracks limit the fatigue performance but only appear above a threshold in the applied strain amplitude which scales inversely with the square root of the film thickness. The extrusion formation is attributed to dislocation activation. The grain boundary cracks are replaced by grain boundary grooves in films of 100 nm and thinner. The grooves are believed to form by diffusion mediated creep processes, similar to observations at higher temperatures but here driven by cyclic stresses and capillarity, and become detectable once the accumulated plastic strain exceeds a critical value. These results indicate that due to creep processes, thinner films can be less resistant to fatigue than thicker films, particularly for large cycle numbers.
Trinks, C.; Volkert, C. A.
Probabilistic Fatigue Damage Localization at Unknown Temperatures Using Guided Wave Methods
NASA Astrophysics Data System (ADS)
This research examines the current challenges of using Lamb wave interrogation methods to localize fatigue crack damage in a complex metallic structural component subjected to unknown temperatures. The goal of this work is to improve damage localization results for a structural component interrogated at an unknown temperature, by developing a probabilistic and reference-free framework for estimating Lamb wave velocities and the damage location. The methodology for damage localization at unknown temperatures includes the following key elements: i) a model that can describe the change in Lamb wave velocities with temperature; ii) the extension of an advanced time-frequency based signal processing technique for enhanced time-of-flight feature extraction from a dispersive signal; iii) the development of a Bayesian damage localization framework incorporating data association and sensor fusion. The technique requires no additional transducers to be installed on a structure, and allows for the estimation of both the temperature and the wave velocity in the component. Additionally, the framework of the algorithm allows it to function completely in an unsupervised manner by probabilistically accounting for all measurement origin uncertainty. The novel algorithm was experimentally validated using an aluminum lug joint with a growing fatigue crack. The lug joint was interrogated using piezoelectric transducers at multiple fatigue crack lengths, and at temperatures between 20°C and 80°C. The results showed that the algorithm could accurately predict the temperature and wave speed of the lug joint. The localization results for the fatigue damage were found to correlate well with the true locations at long crack lengths, but loss of accuracy was observed in localizing small cracks due to time-of-flight measurement errors. To validate the algorithm across a wider range of temperatures the electromechanically coupled LISA/SIM model was used to simulate the effects of temperatures. The numerical results showed that this approach would be capable of experimentally estimating the temperature and velocity in the lug joint for temperatures from -60°C to 150°C. The velocity estimation algorithm was found to significantly increase the accuracy of localization at temperatures above 120°C when error due to incorrect velocity selection begins to outweigh the error due to time-of-flight measurements.
Hensberry, Kevin
Damage repair in CMSX-4 alloy without fatigue life reduction penalty
NASA Astrophysics Data System (ADS)
The microstructural changes in a single-crystal Ni-base superalloy, CMSX-4, that might occur during the processes of repair and recoating of hot section components for advanced gas turbines were studied. It is shown that the cellular ?/?? microstructure is formed when the material is subjected to local plastic straining, followed by the reheat treatments during the course of damage recovery. The formation of cellular microstructure in the material led to the remarkably reduced fatigue strength. In order to reduce or prevent the preceding undesirable effect resulting from cellular microstructure, a new method based on applying overlay coating technique was developed. The method is based on an idea that the alloying elements that are depleted in base alloys could be supplemented via the overlay coating. An X alloy, which contains grain boundary strengthening elements, was selected and coated on the CMSX-4 with the cellular microstructure by low-pressure plasma spraying. The fatigue tests on the coated CMSX-4 specimens demonstrated the effectiveness of the method. The observations of the crack initiation site, the fatigue fracture mode, the crack density in the cellular transformed area, and the crack propagation morphologies near the prior interface strongly supported the validity of this approach. The method is expected to build a road to a so-called damage cure (or recovery) coating.
Okazaki, Masakazu; Ohtera, Issei; Harada, Yoshio
Fatigue damage estimate comparisons for northern European and U.S. wind farm loading environments
Typical loading histories associated with wind turbine service environments in northern Europe and within a large wind farm in the continental US were recently compared by Kelley (1995) using the WISPER [Ten Have, 1992] loading standard and its development protocol. In this study, an equivalent load spectrum for a US wind farm was developed by applying the WISPER development protocol to representative service load histories collected from two adjacent turbines operating within a large wind farm in San Gorgonio Pass, California. The results of this study showed that turbines operating in the California wind farm experience many more loading cycles with larger peak-to-peak values for the same mean wind speed classification than their European counterparts. In this paper, the impact of the two WISPER-protocol fatigue-load spectra on service lifetime predictions are used to compare and contrast the impact of the two loading environments with one another. The service lifetime predictions are made using the LIFE2 Fatigue Analysis Code [Sutherland and Schluter, 1989] with the fatigue properties of typical fiber glass composite blade materials. Additional analyses, based on rainflow counted time histories from the San Gorgonio turbines, are also used in the comparisons. In general, these results indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. The authors conclude that there are fundamental differences in the two service environments.
Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States). Wind Energy Technology Dept.; Kelley, N.D. [National Renewable Energy Lab., Golden, CO (United States). Wind Technology Div.
Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis
Element Analysis by Patricio Andres Lillo Gallardo B.Sc., Catholic University of Chile, 1999 M Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis by Patricio Andres Lillo using finite element models of the blade. The work opens with a quantification of the extremes of cold
Victoria, University of
Performance optimization of a diagnostic system based upon a simulated strain field for fatigue damage characterization
NASA Astrophysics Data System (ADS)
The work presented hereafter is about the development of a diagnostic system for crack damage detection, localization and quantification on a typical metallic aeronautical structure (skin stiffened through riveted stringers). Crack detection and characterization are based upon strain field sensitivity to damage. The structural diagnosis is carried out by a dedicated smart algorithm (Artificial Neural Network) which is trained on a database of Finite Element simulations relative to damaged and undamaged conditions, providing the system with an accurate predictor at low overall cost. The algorithm, trained on numerical damage experience, is used in a simulated environment to provide reliable preliminary information concerning the algorithm performances for damage diagnosis, thus further reducing the experimental costs and efforts associated with the development and optimization of such systems. The same algorithm has been tested on real experimental strain patterns acquired during real fatigue crack propagation, thus verifying the capability of the numerically trained algorithm for anomaly detection, damage assessment and localization on a real complex structure. The load variability, the discrepancy between the Finite Element Model and the real structure, and the uncertainty in the algorithm training process have been addressed in order to enhance the robustness of the system inference process. Some further algorithm training strategies are discussed, aimed at minimizing the risk for false alarms while maintaining a high probability of damage detection.
Sbarufatti, C.; Manes, A.; Giglio, M.
A study of fatigue damage mechanisms in Waspaloy from 25 to 800 C
NASA Technical Reports Server (NTRS)
The objective of the study was to examine the effect of various microstructures on the fatigue and damage accumulation behavior of Waspaloy, a nickel-base alloy commonly used in aircraft engines. Shearing was the dominant deformation mode in specimens with coarse grains and small (50-80 A) gamma prime particles, whereas Orowan looping was dominant in fine-grained specimens with large (about 900 A) gamma prime particles. At temperatures up to 500 C, cracks initiated transgranularly, while at 800 C the failure process was intergranular for both coarse-grained and fine-grained specimens. At temperatures above 500 C, a significant decrease in the fatigue life was observed for both coarse-grained and fine-grained material.
Lerch, B. A.; Jayaraman, N.; Antolovich, S. D.
Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage
NASA Technical Reports Server (NTRS)
A study was performed to evaluate fault detection effectiveness as applied to gear tooth pitting fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets of spur pinion and face gears run during a previous endurance evaluation study. Three common condition indicators (RMS, FM4, and NA4) were deduced from the time-averaged vibration data and used with the ODM to evaluate their performance for gear fault detection. The NA4 parameter showed to be a very good condition indicator for the detection of gear tooth surface pitting failures. The FM4 and RMS parameters performed average to below average in detection of gear tooth surface pitting failures. The ODM sensor was successful in detecting a significant amount of debris from all the gear tooth pitting fatigue failures. Excluding outliers, the average cumulative mass at the end of a test was 40 mg.
Lewicki, David G.; Dempsey, Paula J.; Heath, Gregory F.; Shanthakumaran, Perumal
Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring
NASA Technical Reports Server (NTRS)
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.
Continuum Fatigue Damage Modeling for Critical Design, Control, and Fault Prognosis
NASA Technical Reports Server (NTRS)
This paper develops a simplified continuum (continuous with respect to time, stress, etc.) fatigue damage model for use in critical design, Life Extending Control and fault prognosis. The work is based on the local strain cyclic damage modeling method. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modelling. Stress based continuum models are derived. Extension to plastic strain-strain rate models is also presented. Progress toward a non-zero mean stress based is presented. Also new nonlinear explicit equation forms in terms of stress amplitude are derived for this case. Application of the various models to design, control, and fault prognosis is considered.
Lorenzo, Carl F.
Acousto-ultrasonic measurements to monitor damage during fatigue of composites
NASA Technical Reports Server (NTRS)
An acousto-ultrasonic nondestructive testing method used to monitor damage during static and fatigue loading of thin graphite epoxy laminates is described. The experimental procedure, the signal analysis by the Fast Fourier Transform (FFT) algorithm, and the results of this analysis are discussed. Quasi-static tension tests showed a sharp decrease in the quantitative parameters when transverse cracks developed in the 90 degrees plies of a (0, 90/2/)s laminate. When internal micro-delaminations unite to form macro-delaminations, a sharp decrease in the parameters is also observed. The parameters are found to correlate well with other indications of damage development such as stiffness and degradation. The root mean square value of the moment is found to be more sensitive to damage than stiffness. Various signals and spectrums of graphite epoxy systems are presented.
Govada, A.; Henneke, E. G.; Talreja, R.
A comparative study of fatigue damage sensing in aluminum alloys using electrical impedance and laser ultrasonic methods
NASA Astrophysics Data System (ADS)
Fatigue damage sensing and measurement in aluminum alloys is critical to estimating the residual useful lifetime of a range of aircraft structural components. In this work, we present electrical impedance and ultrasonic measurements in aluminum alloy 2024 that has been fatigued under high cycle conditions. While ultrasonic measurements can indicate fatigue-induced damage through changes in stiffness, the primary indicator is ultrasonic attenuation. We have used laser ultrasonic methods to investigate changes in ultrasonic attenuation since simultaneous measurement of longitudinal and shear properties provides opportunities to develop classification algorithms that can estimate the degree of damage. Electrical impedance measurements are sensitive to changes in the conductivity and permittivity of materials - both are affected by the microstructural damage processes related to fatigue. By employing spectral analysis of impedance over a range of frequencies, resonance peaks can be identified that directly reflect the damage state in the material. In order to compare the impedance and ultrasonic measurements for samples subjected to tension testing, we use processing and classification tools that are matched to the time-varying spectral nature of the measurements. Specifically, we process the measurements to extract time-frequency features and estimate stochastic variation properties to be used in robust classification algorithms. Results are presented for fatigue damage identification in aluminum lug joint specimens.
Channels, Lindsey; Chakraborty, Debejyo; Butrym, Brad; Kovvali, Narayan; Spicer, James; Papandreou-Suppappola, Antonia; Afshari, Mana; Inman, Daniel; Chattopadhyay, Aditi
An investigation of rolling-sliding contact fatigue damage of carburized gear steels
NASA Astrophysics Data System (ADS)
The goal of this study was to evaluate the differences in RSCF performance between vacuum and gas carburized steels as well as to investigate the evolution of damage (wear and microstructure changes) leading to pitting. Vacuum and gas carburizing was performed on two gear steels (4120 and 4320) at 1010°C. The carburized specimens were tested in the as-carburized condition using a RSCF machine designed and built at the Colorado School of Mines. The tests were conducted at 3.2 GPa nominal Hertzian contact stress, based on pure rolling, 100°C, and using a negative twenty percent slide ratio. Tests were conducted to pitting failure for each condition for a comparison of the average fatigue lives. Pure rolling tests were also conducted, and were suspended at the same number of cycles as the average RSCF life for a comparison of fatigue damage developed by RCF and RSCF. Incremental tests were suspended at 1,000, 10,000, 100,000, and 200,000 cycles for the vacuum carburized steels to evaluate the wear and damage developed during the initial cycles of RSCF testing and to relate the wear and damage to pitting resistance. Incremental damage was not investigated for gas carburizing due to the limited number of available specimens. The vacuum carburized samples showed a decreased pitting fatigue resistance over the gas carburized samples, possibly due to the presence of bainite in the vacuum carburized cases. Pitting was observed to initiate from surface micropitting and microcracking. A microstructural change induced by contact fatigue, butterflies, was shown to contribute to micropitting and microcracking. Incremental testing revealed that the formation of a microcrack preceded and was necessary for the formation of the butterfly features, and that the butterfly features developed between 10,000 and 100,000 cycles. The orientation and depth of butterfly formation was shown to be dependent upon the application of traction stresses from sliding. RSCF butterflies formed nearly parallel to the rolling direction at a large range of depths. RCF butterflies formed at about 45° to the rolling direction in a more narrow range of depths. The surface roughness and surface profile were observed to change quickly in the first several thousand cycles of RSCF testing leading to a reduction in contact stress and increase in lambda ratio (ratio of lubricant fluid film thickness to composite surface roughness). The ability of a carburized sample wear track to reach and maintain a steady state morphology (run-in condition) during testing is postulated to translate to increased RSCF resistance.
Kramer, Patrick C.
Mitigation of fatigue damage in self-healing vascular materials A.R. Hamilton a,b,1
Mitigation of fatigue damage in self-healing vascular materials A.R. Hamilton a,b,1 , N.R. Sottos b is to provide a mechanism for recovery of mechanical integrity after damage. Self-healing materials accom- plish bonds within the matrix material [2]. Although several approaches to self-healing have successfully
Sottos, Nancy R.
Recent developments of continuous damage approaches for the analysis of material behavior under fatigue-creep loading
A review is presented with an analysis of some recent methods proposed in the literature for predicting failure of materials under a cumulative damage effect due either to fatigue, to creep, or to fatigue-creep combinations. This review is focused on the continuous damage concepts because of their possibilities of application for a wide range of testing conditions. A discussion of the potential of each damage concept is made by examining the correlation between the resulting expressions and available experimental data. The paper also points out particularities encountered in the interpretation of some of the concepts reviewed.
Bui-Quoc, T.
Characterization of Fatigue Damage for Bonded Composite Skin/Stringer Configurations
NASA Technical Reports Server (NTRS)
The fatigue damage was characterized in specimens which consisted of a tapered composite flange bonded onto a composite skin. Quasi-static tension tests were performed first to determine the failure load. Subsequently, tension fatigue tests were performed at 40%, 50%, 60% and 70% of the failure load to evaluate the debonding mechanisms. For four specimens, the cycling loading was stopped at intervals. Photographs of the polished specimen edges were taken under a light microscope to document the damage. At two diagonally opposite corners of the flange, a delamination appeared to initiate at the flange tip from a matrix crack in the top 45deg skin ply and propagated at the top 45deg/-45deg skin ply interface. At the other two diagonally opposite corners, a delamination running in the bondline initiated from a matrix crack in the adhesive pocket. In addition, two specimens were cut longitudinally into several sections. Micrographs revealed a more complex pattern inside the specimen where the two delamination patterns observed at the edges are present simultaneously across most of the width of the specimen. The observations suggest that a more sophisticated nondestructive evaluation technique is required to capture the complex damage pattern of matrix cracking and multi-level delaminations.
Paris, Isabelle; Cvitkovich, Michael; Krueger, Ronald
Noncontact acousto-thermal evaluation of evolving fatigue damage in polycrystalline Ti-6Al-4V
NASA Astrophysics Data System (ADS)
Non-Contact Acousto-Thermal Signature (NCATS) analysis uses conversion of acoustic energy to heat to characterize evolving damage in materials. In the past, the observed temperature changes were interpreted using phenomenological approaches. This paper presents details of the mechanisms and the theoretical models to predict the temperature change due to conversion of acoustic energy to heat. NCATS experimental measurements performed using 20 kHz high amplitude acoustic waves on as received and fatigued polycrystalline Ti-6Al-4V are compared with theoretical calculations based on the mechanisms of transverse thermal currents, inter-crystalline thermal currents, and dislocation density changes. In the as received samples, the transverse thermal currents contribution has been found to be negligible compared with inter-crystalline thermal currents contribution. The experimentally measured maximum temperature change in the as received sample has been found to be 0.5 °C, and the theoretical prediction based on inter-crystalline thermal currents is 0.08 °C. In the fatigue damaged samples, the maximum temperature change increases with increasing damage that can be attributed to the increasing dislocation density. The theoretical prediction of the maximum temperature attained by a sample that is near failure based on dislocation contribution is 2.0 °C, while the experimental measurements have been found to be 0.95 °C. The differences between the theoretical and the experimental measurements are discussed in the context of the uncertainties in several physical parameters used in the theoretical calculations.
Sathish, S.; Welter, J. T.; Schehl, N.; Jata, K. V.
Integrated approach for stress based lifing of aero gas turbine blades
NASA Astrophysics Data System (ADS)
In order to analyse the turbine blade life, the damage due to the combined thermal and mechanical loads should be adequately accounted for. This is more challenging when detailed component geometry is limited. Therefore, a compromise between the level of geometric detail and the complexity of the lifing method to be implemented would be necessary. This research focuses on how the life assessment of aero engine turbine blades can be done, considering the balance between available design inputs and adequate level of fidelity. Accordingly, the thesis contributes to developing a generic turbine blade lifing method that is based on the engine thermodynamic cycle; as well as integrating critical design/technological factors and operational parameters that influence the aero engine blade life. To this end, thermo-mechanical fatigue was identified as the critical damage phenomenon driving the life of the turbine blade.. The developed approach integrates software tools and numerical models created using the minimum design information typically available at the early design stages. Using finite element analysis of an idealised blade geometry, the approach captures relevant impacts of thermal gradients and thermal stresses that contribute to the thermo-mechanical fatigue damage on the gas turbine blade. The blade life is evaluated using the Neu/Sehitoglu thermo-mechanical fatigue model that considers damage accumulation due to fatigue, oxidation, and creep. The leading edge is examined as a critical part of the blade to estimate the damage severity for different design factors and operational parameters. The outputs of the research can be used to better understand how the environment and the operating conditions of the aircraft affect the blade life consumption and therefore what is the impact on the maintenance cost and the availability of the propulsion system. This research also finds that the environmental (oxidation) effect drives the blade life and the blade coolant side was the critical location. Furthermore, a parametric and sensitivity study of the Neu/Sehitoglu model parameters suggests that in addition to four previously reported parameters, the sensitivity of the phasing to oxidation damage would be critical to overall blade life..
Abu, Abdullahi Obonyegba
The generation of deformation damage during fatigue loading in Al-Cu alloy studied by the Doppler Broadening technique
NASA Astrophysics Data System (ADS)
We have investigated the evolution of damage during fatigue loading in Al-Cu 2024-T3 alloys using the positron annihilation Doppler Broadening (DB) technique. This technique enables us to monitor in a non destructive way, at the atomic and vacancy level, the formation of deformation defects and their interaction with solute atoms at selected stages of fatigue testing. The changes in the S and W Doppler Broadening parameters are linked to the changes in fatigue behavior at lower stress levels. The material was tested under constant amplitude fatigue loading at four different stress levels and DB tests were conducted at selected stages of fatigue lifetime. The results are compared to those obtained during static tensile tests.
Ruiz-Ripoll, M. L.; Schut, H.; Van Dijk, N. H.; Alderliesten, R. C.; Van Der Zwaag, S.; Benedictus, R.
High-temperature, high-frequency fretting fatigue of a single crystal nickel alloy
Fretting is a structural damage mechanism arising from a combination of wear, corrosion, and fatigue between two nominally clamped surfaces subjected to an oscillatory loading. A critical location for fretting induced damage has been identified at the blade\\/disk and blade\\/damper interfaces of gas turbine engine turbomachinery and space propulsion components. The high-temperature, high-frequency loading environment seen by these components lead
John Frederick Matlik
Nondestructive evaluation of fatigue damage in aluminum 2024 by x-ray diffraction
NASA Technical Reports Server (NTRS)
Aluminum alloys are widely used in the automobile and aerospace industries. This is due to their attractive low density-high modulus and low density-high strength characteristics. Unfortunately, cyclic stress-strain deformations alter the microstructure of aluminum alloys when they are placed into service. These structural changes can lead to fatigue damage and ultimately service failure. Since x-ray diffraction analysis is known to be a sensitive nondestructive indicator of structural changes due to deformations, this technique is being used to evaluate changes in the microstructure of cycled aluminum 2024 commercial alloys. Line shapes, widths, and positions in an x-ray diffraction pattern depend on microstructural properties such as grain size, grain orientation, residual stress, microstrain, etc. Changes in the microstructure due to fatigue will appear as changes in the diffraction pattern. One parameter used to characterize a reflection in a diffraction pattern is the full width at half maximum (FWHM). Preliminary x-ray diffraction results on cycled Al 2024 indicate that the (111) and (222) reflections of the matrix phase do not show any variations in the FWHM due to an increase in the fatigue cycles. However, the FWHM of the (200) and (400) reflections of the same phase unexpectedly showed a dramatic decrease. These results can be interpreted as due to the relaxation of some initial nonuniform residual stresses in the matrix phase lattice. Further work is in progress to evaluate the FWHM of the second phase of the cycled alloys.
Ferguson, Milton W.
An overview of elevated temperature damage mechanisms and fatigue behavior of a unidirectional SCS-6/Ti-15-3 composite
NASA Technical Reports Server (NTRS)
The fatigue behavior of a unidirectionally reinforced titanium matrix composite (TMC), SiC/Ti-15-3, was thoroughly characterized to support life prediction modeling of advanced TMC disks designed for gas turbine engine applications. The results of this coupon-level experimental investigation are reviewed. On a stress basis, the isothermal fatigue behavior of the (0 deg) TMC revealed significant improvements over the unreinforced matrix. In contrast, the (90 deg) TMC exhibited degraded properties and lives for similar comparisons. This was attributed to the weak fiber/matrix interfacial bond. Encasing the (0 deg) TMC with a Ti-15-3 case did not affect isothermal fatigue lives at higher strain levels. However, at lower strain levels, rapid initiation and propagation of large fatigue cracks in the case degraded the fatigue lives. Thermomechanical fatigue (TMF) lives were significantly reduced for the (0 deg) TMC when compared to isothermal lives. At high strains, in-phase TMF produced extremely short lives. This degradation was attributed to fiber overload failures brought about by stress relaxation in the matrix. At low strains, out-of-phase TMF conditions became life limiting. Environment-assisted surface cracking was found to accelerate fatigue failure. This produced extensive matrix damage with minimal fiber damage. For the (90 deg) TMC, TMF conditions did not promote an additional degradation in cyclic life beyond that observed under isothermal conditions.
Castelli, Michael G.; Gayda, John
Micro/meso scale fatigue damage accumulation monitoring using nonlinear acoustic vibro-modulation measurements
NASA Astrophysics Data System (ADS)
Monitoring the incipient damage at the earliest possible stage is essential for predicting structural performance and remaining life of structural components. Existing prognostic methodologies incorporate conventional SHM and NDE techniques responsive to cracks and delaminations resulted from the irreversible material fracture and disintegration at the macro-scale. There is an increasing need for technologies that could allow for monitoring material degradation at the micro/meso scale before the onset of the macro-scale fracture. In this contribution, we report results of the real-time monitoring of the material micro/meso scale degradation using the nonlinear acoustic vibro-modulation technique. The technique explores nonlinear acoustic interaction of high frequency ultrasound and low frequency structural vibration at the site of the incipient damage. The indicator of the damage severity, nonlinear acoustic damage index (DI), was measured in real time during the strain-controlled three-point bending fatigue test of aluminum and steel specimens. Nondestructively, degradation of the specimen was revealed through the increase in the DI, which correlated well with the respective decrease in the specimen's stiffness. Destructive SEM examination confirmed sensitivity of the DI to the incipient micro/meso scale damage and advocated for utilizing the vibro-modulation approach for assessment of material degradation before fracture.
Zagrai, Andrei; Donskoy, Dimitri; Chudnovsky, Alexander; Golovin, Edward; Agarwala, Vinod S.
Experimental Investigations on Fatigue Damage and Residual Properties of Interacting Notched Woven E-Glass/Epoxy Composite
NASA Astrophysics Data System (ADS)
The interacting notched laminates of plain weave E-glass fiber reinforced with epoxy were fatigued at predetermined frequency in tension-tension to investigate the fatigue damage and residual properties. The results from stress-life curves summarize that damage growing around the notches due to stress concentration is the underlying cause for the variation in fatigue strengths among the geometrically different specimens considered. The residual strength and modulus decay with respect to cycle number at 50 % of the ultimate tensile strength were investigated. It is evident from the experimental data that the residual strength decreases with cycle number and increases due to redistribution of stress around the notches. The detailed study of the damage development under cyclic loads also explains the causes of modulus reduction for all the laminate geometries.
Bhaskara Rao, Pathakokila; Rama Krishna, Avasarala; Ramji, Koona; Satya Devi, Ambadipudi
Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites
NASA Technical Reports Server (NTRS)
A micromechanics analysis modeling method was developed to analyze the damage progression and fatigue failure of fabric reinforced composite structures, especially for the brittle ceramic matrix material composites. A repeating unit cell concept of fabric reinforced composites was used to represent the global composite structure. The thermal and mechanical properties of the repeating unit cell were considered as the same as those of the global composite structure. The three-phase micromechanics, the shear-lag, and the continuum fracture mechanics models were integrated with a statistical model in the repeating unit cell to predict the progressive damages and fatigue life of the composite structures. The global structure failure was defined as the loss of loading capability of the repeating unit cell, which depends on the stiffness reduction due to material slice failures and nonlinear material properties in the repeating unit cell. The present methodology is demonstrated with the analysis results evaluated through the experimental test performed with carbon fiber reinforced silicon carbide matrix plain weave composite specimens.
Min, J. B.; Xue, D.; Shi, Y.
Neural Network Modelling of Oscillatory Loads and Fatigue Damage Estimation of Helicopter Components
NASA Astrophysics Data System (ADS)
A neural network for the prediction of oscillatory loads used for on-line health monitoring of flight critical components in an AH-64A helicopter is described. The neural network is used to demonstrate the potential for estimating loads in the rotor system from fixed-system information. Estimates of the range of the pitch link load are determined by the neural network from roll, pitch, and yaw rates, airspeed, and other fixed-system information measured by the flight control computer on the helicopter. The predicted load range is then used to estimate fatigue damage to the pitch link. Actual flight loads data from an AH-64A helicopter are used to demonstrate the process. The predicted load ranges agree well with measured values for both training and test data. A linear model is also used to predict the load ranges, and its accuracy is noticeably worse than that of the neural network, especially at higher load values that cause fatigue damage. This demonstrates the necessity of the non-linear modelling capabilities of the neural network for this problem.
Cabell, R. H.; Fuller, C. R.; O'Brien, W. F.
Acoustic fatigue characterization of carbon/carbon panels
NASA Technical Reports Server (NTRS)
Data from a sonic fatigue test of a blade-stiffened carbon/carbon panel is analyzed to determine the progression of damage to failure. The reduction in stiffness, as observed from acceleration measurements taken during the test, is correlated with the physical damage. Damage was measured through visual inspection, thermographic measurements, and through the novel use of vibration data collected using a scanning laser vibrometer.
Rizzi, S. A.; Clevenson, S. A.; Daniels, E. F.
Experiments on a wind turbine blade testing an indication for damage using the causal and anti-causal Green's function reconstructed from a diffuse field
NASA Astrophysics Data System (ADS)
The increasing demand for renewable and clean power generation has resulted in increasing sizes of rotor blades in wind turbine systems. The demanding and variable operational environments have introduced the need for structural health monitoring systems in the blades in order to prevent unexpected downtime events in the operation of the power plant. Many non-destructive evaluation methods used for structural health monitoring purposes need external excitation sources. However, several systems already accepted in the wind turbine industry are passive. Here we present a new approach to health monitoring of a wind turbine blade using only passive sensors and the existing noise created on the blade during operation. This is achieved using a known method to reconstruct the causal and anticausal time-domain Green's function between any two points in an array of passive sensors placed in a diffuse field. Damage is indicated when the similarity between the causal and anticausal signals decrease due to nonlinearities introduced from structural damage. This method was studied experimentally using a CX-100 wind turbine test blade located at the UCSD's Powell Structural Laboratories where a diffuse field was approximated by exciting the skin of the blade with a random signal at several locations.
Tippmann, Jeffery D.; Lanza di Scalea, Francesco
An advanced test technique to quantify thermomechanical fatigue damage accumulation in composite materials
NASA Technical Reports Server (NTRS)
A mechanical test technique was developed to assist in quantifying the accumulation of damage in composite materials during thermomechanical fatigue (TMF) cycling. This was accomplished by incorporating definitive elastic mechanical property measurements into an ongoing load-controlled TMF test without disturbing the test specimen or significantly altering the test conditions. The technique allows two fundamental composite properties consisting of the isothermal elastic static moduli and the macroscopic coefficient of thermal expansion (CTE) to be measured and collected as functions of the TMF cycles. The specific implementation was incorporated into the commonly employed idealized in-phase and out-of-phase TMF cycles. However, the techniques discussed could be easily implemented into any form of load-controlled TMF mission cycle. By quantifying the degradations of these properties, tremendous insights are gained concerning the progression of macroscopic composite damage and often times the progression of damage within a given constituent. This information should also be useful for the characterization and essential for the verification of analytical damage modeling methodologies. Several examples utilizing this test technique are given for three different fiber lay-ups of titanium metal matrix composites.
Castelli, Michael G.
Experimental Verification of a Progressive Damage Model for IM7/5260 Laminates Subjected to Tension-Tension Fatigue
NASA Technical Reports Server (NTRS)
The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve structurally efficient and economical designs. The purpose of this research is to experimentally verify the application of a continuum damage model to predict progressive damage development in a toughened material system. Damage due to monotonic and tension-tension fatigue was documented for IM7/5260 graphite/bismaleimide laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables to predict stiffness loss in unnotched laminates. A damage dependent finite element code predicted the stiffness loss for notched laminates with good agreement to experimental data. It was concluded that the continuum damage model can adequately predict matrix damage progression in notched and unnotched laminates as a function of loading history and laminate stacking sequence.
Coats, Timothy W.; Harris, Charles E.
High-fidelity Modeling of Local Effects of Damage for Derated Offshore Wind Turbines
NASA Astrophysics Data System (ADS)
Offshore wind power production is an attractive clean energy option, but the difficulty of access can lead to expensive and rare opportunities for maintenance. As part of the Structural Health and Prognostics Management (SHPM) project at Sandia National Laboratories, smart loads management (controls) are investigated for their potential to increase the fatigue life of offshore wind turbine rotor blades. Derating refers to altering the rotor angular speed and blade pitch to limit power production and loads on the rotor blades. High- fidelity analysis techniques like 3D finite element modeling (FEM) should be used alongside beam models of wind turbine blades to characterize these control strategies in terms of their effect to mitigate fatigue damage and extend life of turbine blades. This study will consider a commonly encountered damage type for wind turbine blades, the trailing edge disbond, and show how FEM can be used to quantify the effect of operations and control strategies designed to extend the fatigue life of damaged blades. The Virtual Crack Closure Technique (VCCT) will be used to post-process the displacement and stress results to provide estimates of damage severity/criticality and provide a means to estimate the fatigue life under a given operations and control strategy.
Richards, Phillip W.; Griffith, D. Todd; Hodges, Dewey H.
On fatigue damage accumulation from in-line and cross-flow vortex-induced vibrations on risers
NASA Astrophysics Data System (ADS)
Large-scale model tests of a tensioned steel riser were performed at Hanřytangen outside Bergen, Norway in 1997. The length of the model was 90 m and the diameter was 3 cm. The information from these tests consists of measured bending strains, tension, flow speed and all relevant riser data. In this work, this information is reexamined in an attempt to improve our understanding of vortex-induced vibrations (VIV) for cases with very high order of responding modes. The aim is in particular to study the relative importance of in-line (IL) and cross-flow (CF) vibrations for fatigue damage accumulation. It is shown that fatigue damage is proportional to U (U is the flow velocity) when the modes are dominated by tension. When bending controls the modes, the fatigue damage is proportional to U. A linear SN-curve with slope parameter m=3 is used. The Hanřytangen riser fatigue damage goes as U7 for the lowest velocities and U4 for the highest current velocities. Based on the Hanřytangen data, it seems that the transition velocity between the tension and the bending-stiffness-dominated regions is at the current velocity that gives response at a mode number where a tensioned string and an untensioned beam have equal eigenfrequencies. IL response has a significant contribution to fatigue for cases dominated by the lowest modes. The reason is that IL oscillations will take place at double the frequency of those in CF. For a tension-controlled case, this corresponds to a mode with half the wavelength, while a bending-controlled case will tend to have a wavelength ratio of 2. Since the curvature for a given amplitude increases with the inverse modal wavelength squared, fatigue from IL tends to dominate for cases with tension-controlled modes (low current speed), while CF will dominate for bending-controlled modes (high current speed). This tendency is clearly seen in the experimental data for both CF and IL responses. Fatigue damage is calculated directly from the measured data and compared to results found by using a computer program based on a semi-empirical method. The program is able to calculate response frequencies, response amplitudes and fatigue damage. The method is limited to account for CF vibrations only. Computed results are compared to measurements. The agreement is in general good, but some discrepancy is seen for cases with high current velocity. In these cases, the real response contains high mode orders (above 25) and tends to have a stochastic nature, while the VIV-analysis model assumes that the response takes place at a limited number of discrete frequencies. Further development of the empirical model is therefore needed.
Baarholm, G. S.; Larsen, C. M.; Lie, H.
Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage
NASA Technical Reports Server (NTRS)
A study was performed to evaluate fault detection effectiveness as applied to gear-tooth-pitting-fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets of spur pinion and face gears run during a previous endurance evaluation study. Three common condition indicators (RMS, FM4, and NA4 [Ed. 's note: See Appendix A-Definitions D were deduced from the time-averaged vibration data and used with the ODM to evaluate their performance for gear fault detection. The NA4 parameter showed to be a very good condition indicator for the detection of gear tooth surface pitting failures. The FM4 and RMS parameters perfomu:d average to below average in detection of gear tooth surface pitting failures. The ODM sensor was successful in detecting a significant 8lDOunt of debris from all the gear tooth pitting fatigue failures. Excluding outliers, the average cumulative mass at the end of a test was 40 mg.
Lewicki, David G.; Dempsey, Paula J.; Heath, Gregory F.; Shanthakumaran, Perumal
Magnetic non-destructive evaluation of accumulated fatigue damage in ferromagnetic steels for nuclear plant component
NASA Astrophysics Data System (ADS)
We performed the measurement of magnetic properties of ferromagnetic steels that were degraded by tensile plastic deformation and cyclic loading, where lattice imperfections were produced in the steels. Magnetic hysteresis curves were changed depending on the load conditions. The changes in coercive force, residual magnetic flux density and permeability were obtained as functions of the magnitude of residual strain for the tensile tests and the number of loading cycles for the fatigue test. In the case of the tensile deformation, the coercive force increased and the residual magnetic flux density decreased with increasing the residual strains. In the case of fatigue damage accumulated by the cyclic loading, the residual magnetic flux density decreased with increasing the number of cyclic loading, while the coercive force remained constant. The changes in hysteresis curves were well consistent with the transmission electron microscopy (TEM) observation results of microstructural changes in the steels. We concluded that the magnetic property was enough sensitive to microstructural changes caused by mechanical deformation.
Morishita, K.; Gilanyi, A.; Sukegawa, T.; Uesaka, T.; Miya, K.
Fatigue Life of Damaged Bridge Deck Panels Strengthened With Carbon Fiber Hongseob Oh, Jongsung Sim, and Christian Meyer
, Jongsung Sim, and Christian Meyer ABSTRACT To simulate fatigue damage to bridge deck slabs, cyclic loading of the response of metal structures to repeated loads. Microscopic flaws, inclusions, and other stress raisers is well-established for metals, and modern metal structures subjected to multiple load applications
Meyer, Christian
A time-dependent damage operator approach to thermo-mechanical fatigue of Niresist D-5S
The damage operator approach is extended to time dependent viscoplasticity and creep. The oxidation is taken into account indirectly. Time efficient viscoplastic approximation based on the nonlinear Maxwell model and the corresponding lifetime prediction is presented. Both thermo-mechanical fatigue tests on the specimens and the thermal shock tests on turbine housings of a turbocharger subject to a complex change of
Marko Nagode; Frank Längler; Michael Hack
Constitutive model of micromechanical damage to predict reduction in stiffness of a fatigued SMC composite
NASA Astrophysics Data System (ADS)
Elastic behavior of sheet molding compound (SMC) composites with a given orientational distribution of fibers under cyclic loading is investigated herein. Fatigue tests were carried out over various strain ranges. During each test, evolution of Young's modulus was measured and the composite was analyzed using scanning electron microscopy. Observations revealed the principal form of degradation to be matrix fiber debonding. A constitutive model that takes into account the reduction of overall elastic properties, i.e., Young's modulus, was developed. This model uses a Mori-Tanaka mean field approach coupled with a micromechanical damage law. The energetic failure criterion and the failure probability are functions of local shear and normal stresses calculated at each point of the interface of each fiber family. A procedure for identifying the most appropriate material parameters is described in detail. The proposed model agrees well with the experimental results.
Ben Cheikh Larbi, A.; Sidhom, H.; Sai, K.; Baptiste, D.
Optical Sensing of the Fatigue Damage State of CFRP under Realistic Aeronautical Load Sequences.
We present an optical sensing methodology to estimate the fatigue damage state of structures made of carbon fiber reinforced polymer (CFRP), by measuring variations on the surface roughness. Variable amplitude loads (VAL), which represent realistic loads during aeronautical missions of fighter aircraft (FALSTAFF) have been applied to coupons until failure. Stiffness degradation and surface roughness variations have been measured during the life of the coupons obtaining a Pearson correlation of 0.75 between both variables. The data were compared with a previous study for Constant Amplitude Load (CAL) obtaining similar results. Conclusions suggest that the surface roughness measured in strategic zones is a useful technique for structural health monitoring of CFRP structures, and that it is independent of the type of load applied. Surface roughness can be measured in the field by optical techniques such as speckle, confocal perfilometers and interferometry, among others. PMID:25760056
Zuluaga-Ramírez, Pablo; Arconada, Álvaro; Frövel, Malte; Belenguer, Tomás; Salazar, Félix
Predicting sequence effects and cumulative damage in fatigue using a unified model for crack initiation and growth
A new unified fatigue model which covers both crack initiation and crack growth has been used to predict load sequence effects in fatigue failure of 7075-T6 aluminum subjected to two-level loading histories. Dubbed ''FATIGMOD,'' the model simulates fatigue as the successive failure of elements within, and on the surface of, a material; failure of each element occurs when the local variables at that element reach any one of the three failure criteria, which are formulated in terms of local accumulated plastic work density, local tensile stress, and local tensile strain. For ''smooth'' (i.e., unnotched and non-precracked) specimens, FATIGMOD predictions indicate that a ''high-low'' load sequence results in a cycle fraction sum at failure which is smaller than unity, while a ''low-high'' load history produces the reverse behavior. In contrast, the cycle fraction sum at failure for a precracked specimen is predicted to exceed unity in a stress reduction test but is less than one in a test with stress increases. These predictions are in good agreement with experimental results. The effects of load sequence on fatigue damage are explained in terms of the curves of crack length vs. number of cycles generated by the unified model. The predicted curves for fatigue and the resulting cumulative damage behavior are compared with those observed in stress corrosion cracking and creep rupture.
Miller, A.K.
Simulation of long-term fatigue damage in bioprosthetic heart valves: effects of leaflet and stent elastic properties.
One of the major failure modes of bioprosthetic heart valves (BHVs) is noncalcific structural deterioration due to fatigue of the tissue leaflets; yet, the mechanisms of fatigue are not well understood. BHV durability is primarily assessed based on visual inspection of the leaflets following accelerated wear testing. In this study, we developed a computational framework to simulate BHV leaflet fatigue, which is both efficient and quantitative, making it an attractive alternative to traditional accelerated wear testing. We utilize a phenomenological soft tissue fatigue damage model developed previously to describe the stress softening and permanent set of the glutaraldehyde-treated bovine pericardium leaflets in BHVs subjected to cyclic loading. A parametric study was conducted to determine the effects of altered leaflet and stent elastic properties on the fatigue of the leaflets. The simulation results show that heterogeneity of the leaflet elastic properties, poor leaflet coaptation, and little stent-tip deflection may accelerate leaflet fatigue, which agrees with clinical findings. Therefore, the developed framework may be an invaluable tool for evaluating leaflet durability in new tissue valve designs, including traditional BHVs as well as new transcatheter valves. PMID:24092257
Martin, Caitlin; Sun, Wei
Nondestructive evaluation of the fatigue damage accumulation process around a notch using a digital image measurement system
NASA Astrophysics Data System (ADS)
The fatigue damage accumulation process around a notch is studied using a noncontact digital image measurement system. This system incorporates a contrast correlation method to evaluate the level of plastic damage at each point of the studied area of the specimen from two images acquired before and after the introduction of fatigue deformation. A compact tension specimen of 304 stainless steel with a notch radius of 1 mm is analyzed during the first 1000 cycles of the crack growth stage. During this period, the externally given work not only impels the crack growth and its local plastic zone but also generates plastic damage around the notch. The obtained results are used to explain the behavior of cracks emanating from notches.
Díaz, F. V.; Armas, A. F.; Kaufmann, G. H.; Galizzi, G. E.
Cross-flow VIV-induced fatigue damage of deepwater steel catenary riser at touch-down point
NASA Astrophysics Data System (ADS)
A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point (TDP). The model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation model. In the present model, the hysteretic riser-soil interaction model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic riser-soil interaction. In order to validate the model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation riser model and the present full riser model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary riser at TDP.
Wang, Kun-peng; Tang, Wen-yong; Xue, Hong-xiang
Thermal shock and fatigue resistance evaluation of functionally graded coating for gas turbine blades by laser heating method
This paper presents results of thermal shock and fatigue tests conducted on ZrO2-based thermal barrier coating systems under the temperature environments for advanced gas turbines. A CO2 laser heating method was employed to heat two types of cylindrical specimens with conventional two-layer coating and functionally graded coating. Acoustic emission (AE) signals and temperatures were monitored to detect the fracture process
Masahiro Saito; T HASHIDA; H TAKAHASHI; M SAITO
Fretting Stresses in Single Crystal Superalloy Turbine Blade Attachments
NASA Technical Reports Server (NTRS)
Single crystal nickel base superalloy turbine blades are being utilized in rocket engine turbopumps and turbine engines because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal nickel base turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. High Cycle Fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Blade attachment regions are prone to fretting fatigue failures. Single crystal nickel base superalloy turbine blades are especially prone to fretting damage because the subsurface shear stresses induced by fretting action at the attachment regions can result in crystallographic initiation and crack growth along octahedral planes. Furthermore, crystallographic crack growth on octahedral planes under fretting induced mixed mode loading can be an order of magnitude faster than under pure mode I loading. This paper presents contact stress evaluation in the attachment region for single crystal turbine blades used in the NASA alternate Advanced High Pressure Fuel Turbo Pump (HPFTP/AT) for the Space Shuttle Main Engine (SSME). Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Blades and the attachment region are modeled using a large-scale 3D finite element (FE) model capable of accounting for contact friction, material orthotrophy, and variation in primary and secondary crystal orientation. Contact stress analysis in the blade attachment regions is presented as a function of coefficient of friction and primary and secondary crystal orientation, Stress results are used to discuss fretting fatigue failure analysis of SSME blades. Attachment stresses are seen to reach peak values at locations where fretting cracks have been observed. Fretting stresses at the attachment region are seen to vary significantly as a function of crystal orientation. Attempts to adapt techniques used for estimating fatigue life in the airfoil region, for life calculations in the attachment region, are presented. An effective model for predicting crystallographic crack initiation under mixed mode loading is required for life prediction under fretting action.
Arakere, Nagaraj K.; Swanson, Gregory
Helicopter rotor blade design for minimum vibration
NASA Technical Reports Server (NTRS)
The importance of blade design parameters in rotor vibratory response and the design of a minimum vibration blade based upon this understanding are examined. Various design approaches are examined for a 4 bladed articulated rotor operating at a high speed flight condition. Blade modal shaping, frequency placement, structural and aerodynamic coupling, and intermodal cancellation are investigated to systematically identify and evaluate blade design parameters that influence blade airloads, blade modal response, hub loads, and fuselage vibration. The relative contributions of the various components of blade force excitation and response to the vibratory hub loads transmitted to the fuselage are determined in order to isolate primary candidates for vibration alleviation. A blade design is achieved which reduces the predicted fuselage vibration from the baseline blade by approximately one half. Blade designs are developed that offer significant reductions in vibration (and fatigue stresses) without resorting to special vibration alleviation devices, radical blade geometries, or weight penalties.
Taylor, R. B.
Fatigue creep damage at the cement-bone interface: an experimental and a micro-mechanical finite element study.
The goal of this study was to quantify the micromechanics of the cement-bone interface under tensile fatigue loading using finite element analysis (FEA) and to understand the underlying mechanisms that play a role in the fatigue behavior of this interface. Laboratory cement-bone specimens were subjected to a tensile fatigue load, while local displacements and crack growth on the specimen's surface were monitored. FEA models were created from these specimens based upon micro-computed tomography data. To accurately model interfacial gaps at the interface between the bone and cement, a custom-written erosion algorithm was applied to the bone model. A fatigue load was simulated in the FEA models while monitoring the local displacements and crack propagation. The results showed the FEA models were able to capture the general experimental creep damage behavior and creep stages of the interface. Consistent with the experiments, the majority of the deformation took place at the contact interface. Additionally, the FEA models predicted fatigue crack patterns similar to experimental findings. Experimental surface cracks correlated moderately with FEA surface cracks (r(2)=0.43), but did not correlate with the simulated crack volume fraction (r(2)=0.06). Although there was no relationship between experimental surface cracks and experimental creep damage displacement (r(2)=0.07), there was a strong relationship between the FEA crack volume fraction and the FEA creep damage displacement (r(2)=0.76). This study shows the additional value of FEA of the cement-bone interface relative to experimental studies and can therefore be used to optimize its mechanical properties. PMID:19682690
Waanders, Daan; Janssen, Dennis; Miller, Mark A; Mann, Kenneth A; Verdonschot, Nico
Materials Science and Engineering A319321 (2001) 597601 Foreign-object damage and high-cycle fatigue of Ti6Al4V
Materials Science and Engineering A319Â321 (2001) 597Â601 Foreign-object damage and high-cycle fatigue of TiÂ6AlÂ4V J.O. Peters, R.O. Ritchie * Department of Materials Science and Engineering, Uni6ersity of California, Berkeley, CA 94720-1760, USA Abstract Recent high-cycle fatigue (HCF) related
Ritchie, Robert
Space Shuttle main engine powerhead structural modeling, stress and fatigue life analysis. Volume 3: Stress summay of blades and nozzles at FPL and 115 percent RPL loads. SSME HPFTP and HPOTP blades and nozzles
NASA Technical Reports Server (NTRS)
Gasdynamic environments applied to the turbine blades and nozzles of the HPFTP and HPOTP were analyzed. Centrifugal loads were applied to blades to account for the pump rotation of FPL and 115 percent RPL. The computer models used in the blade analysis with results presented in the form of temperature and stress contour plots are described. Similar information is given for the nozzles.
Hammett, J. C.; Hayes, C. H.; Price, J. M.; Robinson, J. K.; Teal, G. A.; Thomson, J. M.; Tilley, D. M.; Welch, C. T.
On the application of the Kitagawa–Takahashi diagram to foreign-object damage and high-cycle fatigue
The role of foreign-object damage (FOD) and its effect on high-cycle fatigue (HGF) failures in a turbine engine Ti–6Al–4V alloy is examined in the context of the use of the Kitagawa–Takahashi diagram to describe the limiting conditions for such failures. Experimentally, FOD is simulated by firing 1 and 3.2 mm diameter steel spheres onto the flat specimen surface of tensile
J. O. Peters; B. L. Boyce; X. Chen; J. M. McNaney; J. W. Hutchinson; R. O. Ritchie
Piezoelectric in situ transmission electron microscopy technique for direct observations of fatigue damage accumulation in constrained metallic thin films
NASA Astrophysics Data System (ADS)
A piezoelectric in situ transmission electron microscopy (TEM) technique has been developed to observe the damage mechanism in constrained metallic thin films under cyclic loading. The technique was based on the piezoelectric actuation of a multilayered structure in which a metallic thin film was sandwiched between a piezoelectric actuator and a silicon substrate. An alternating electric field with a static offset was applied on the piezoelectric actuator to drive the crack growth in the thin metallic layer while the sample was imaged in TEM. The technique was demonstrated on solder thin films where cavitation was found to be the dominant fatigue damage mechanism.
Tan, X.; Du, T.; Shang, J. K.
Competing damage mechanisms in the thermo-mechanical fatigue of AISI 304L stainless steel
Thermo-mechanical fatigue (TMF) in AISI 304L stainless steel is investigated in two temperature ranges using four phase differences between the mechanical loading and the temperature. In the temperature range from 450°C to 700°C, the fatigue life was lowest in the in-phase condition. However, in the temperature range from 400°C to 650°C, the minimum fatigue life occurs in the counter-clockwise-diamond condition.
Keun-Ho Bae; Hyun-Ho Kim; Soon-Bok Lee
The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)
NASA Technical Reports Server (NTRS)
The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (<0.74J) whereas Hertzian crack length (impact side damage) was the best predictor for higher energy impacts. The impacted gamma - TiAl samples displayed a classical mean stress dependence on the fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.
Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.
Utilizing Fiber-Reinforced Polymers to Retrofit Steel Bridge Girders Damaged by Fatigue Loading.
................................................................................................................................................................4 Experimental Program ............................................................................................................................................7 Removal of the composite block.... UNRETROFITTED SPECIMEN .................................................................................................................................................. 7 FIGURE 6: EXPERIMENTAL SETUP IN FRACTURE AND FATIGUE LAB AT M2SEC...
Bonet, Eric
Atomistic modeling of nanowires, small-scale fatigue damage in cast magnesium, and materials for MEMS.
Lightweight and miniaturized weapon systems are driving the use of new materials in design such as microscale materials and ultra low-density metallic materials. Reliable design of future weapon components and systems demands a thorough understanding of the deformation modes in these materials that comprise the components and a robust methodology to predict their performance during service or storage. Traditional continuum models of material deformation and failure are not easily extended to these new materials unless microstructural characteristics are included in the formulation. For example, in LIGA Ni and Al-Si thin films, the physical size is on the order of microns, a scale approaching key microstructural features. For a new potential structural material, cast Mg offers a high stiffness-to-weight ratio, but the microstructural heterogeneity at various scales requires a structure-property continuum model. Processes occurring at the nanoscale and microscale develop certain structures that drive material behavior. The objective of the work presented in this report was to understand material characteristics in relation to mechanical properties at the nanoscale and microscale in these promising new material systems. Research was conducted primarily at the University of Colorado at Boulder to employ tightly coupled experimentation and simulation to study damage at various material size scales under monotonic and cyclic loading conditions. Experimental characterization of nano/micro damage will be accomplished by novel techniques such as in-situ environmental scanning electron microscopy (ESEM), 1 MeV transmission electron microscopy (TEM), and atomic force microscopy (AFM). New simulations to support experimental efforts will include modified embedded atom method (MEAM) atomistic simulations at the nanoscale and single crystal micromechanical finite element simulations. This report summarizes the major research and development accomplishments for the LDRD project titled 'Atomistic Modeling of Nanowires, Small-scale Fatigue Damage in Cast Magnesium, and Materials for MEMS'. This project supported a strategic partnership between Sandia National Laboratories and the University of Colorado at Boulder by providing funding for the lead author, Ken Gall, and his students, while he was a member of the University of Colorado faculty.
Dunn, Martin L. (University of Colorado, Boulder, CO); Talmage, Mellisa J. (University of Colorado, Boulder, CO); McDowell, David L., 1956- (,-Georgia Institute of Technology, Atlanta, GA); West, Neil (University of Colorado, Boulder, CO); Gullett, Philip Michael (Mississippi State University , MS); Miller, David C. (University of Colorado, Boulder, CO); Spark, Kevin (University of Colorado, Boulder, CO); Diao, Jiankuai (University of Colorado, Boulder, CO); Horstemeyer, Mark F. (Mississippi State University , MS); Zimmerman, Jonathan A.; Gall, K (Georgia Institute of Technology, Atlanta, GA)
Load Mitigation with Bending/Twist-coupled Blades on Rotors using Modern Control Strategies
NASA Astrophysics Data System (ADS)
The prospect of installing blades that twist as they bend and/or extend on horizontal axis wind turbines provides opportunities for enhanced energy capture and/or load mitigation. Although this coupling could be achieved in either an active or a passive manner, the passive approach is much more attractive owing to its simplicity and economy. As an example, a blade design might employ coupling between bending and twisting, so that as the blade bends owing to the action of the aerodynamic loads, it also twists, modifying the aerodynamic performance in some way. For reducing loads the blades are designed to twist towards feather as they bend. For variable-speed pitch-controlled rotors, dynamic computer simulations with turbulent inflow show that twist coupling substantially decreases fatigue damage over all wind speeds, without reducing average power. Maximum loads also decrease modestly. For constant-speed stall-controlled and variable-speed stall-controlled rotors, significant decreases in fatigue damage are observed at the lower wind speeds and smaller decreases at the higher wind speeds. Maximum loads also decrease slightly. As a general observation, whenever a rotor is operating in the linear aerodynamic range (lower wind speeds for stall control and all wind speeds for pitch control), substantial reductions in fatigue damage are realized.
Lobitz, Don W.; Veers, Paul S.
Space Shuttle main engine powerhead structural modeling, stress and fatigue life analysis. Volume 2: Dynamics of blades and nozzles SSME HPFTP and HPOTP
NASA Technical Reports Server (NTRS)
Normal modes of the blades and nozzles of the HPFTP and HPOTP are defined and potential driving forces for the blades are identified. The computer models used in blade analyses are described, with results. Similar information is given for the nozzles.
Hammett, J. C.; Hayes, C. H.; Price, J. M.; Robinson, J. K.; Teal, G. A.; Thomson, J. M.; Tilley, D. M.; Welch, C. T.
Online fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach q
.elsevier.com/locate/ijfatigue International Journal of Fatigue 29 (2007) 1100Â1114 International Journalof Fatigue #12;using acoustic emission for structural health mon- itoring and life prediction [2Â5]. Apparently, no existing model, solely based.09.011 q This work has been supported in part by the US Army Research Laboratory and the US Army Research
Ray, Asok
Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage
NASA Technical Reports Server (NTRS)
Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.
Piascik, Robert S.; Gangloff, Richard P.
Probabilistic fatigue methodology and wind turbine reliability
Wind turbines subjected to highly irregular loadings due to wind, gravity, and gyroscopic effects are especially vulnerable to fatigue damage. The objective of this study is to develop and illustrate methods for the probabilistic analysis and design of fatigue-sensitive wind turbine components. A computer program (CYCLES) that estimates fatigue reliability of structural and mechanical components has been developed. A FORM/SORM analysis is used to compute failure probabilities and importance factors of the random variables. The limit state equation includes uncertainty in environmental loading, gross structural response, and local fatigue properties. Several techniques are shown to better study fatigue loads data. Common one-parameter models, such as the Rayleigh and exponential models are shown to produce dramatically different estimates of load distributions and fatigue damage. Improved fits may be achieved with the two-parameter Weibull model. High b values require better modeling of relatively large stress ranges; this is effectively done by matching at least two moments (Weibull) and better by matching still higher moments. For this purpose, a new, four-moment {open_quotes}generalized Weibull{close_quotes} model is introduced. Load and resistance factor design (LRFD) methodology for design against fatigue is proposed and demonstrated using data from two horizontal-axis wind turbines. To estimate fatigue damage, wind turbine blade loads have been represented by their first three statistical moments across a range of wind conditions. Based on the moments {mu}{sub 1}{hor_ellipsis}{mu}{sub 3}, new {open_quotes}quadratic Weibull{close_quotes} load distribution models are introduced. The fatigue reliability is found to be notably affected by the choice of load distribution model.
Lange, C.H. [Stanford Univ., CA (United States)
Thermomechanical Fatigue Damage/Failure Mechanisms in SCS-6/Timetal 21S [0/90](Sub S) Composite
NASA Technical Reports Server (NTRS)
The thermomechanical fatigue (TMF) deformation, damage, and life behaviors of SCS6/Timetal 21S (0/90)s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650 deg C. An advanced TMF test technique was used to quantify mechanically damage progression. The technique incorporated explicit measurements of the macroscopic (1) isothermal static moduli at the temperature extremes of the TMF cycle and (2) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue life results indicated trends analogous to those established for similar unidirectional(0) reinforced titanium matrix composite systems. High stress IP and mid to low stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive (0) fiber cracking with sparse matrix damage. No surface initiated matrix cracks were present. Comparable OP TMF conditions initiated environment enhanced surface cracking and matrix cracking initiated at (90) fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and (90) F/M interfaces tended to converge and coalesce at the (0) fibers.
Castelli, Michael G.
14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.
Code of Federal Regulations, 2012 CFR
...AND COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation...catastrophic loss of the airplane, in each wing (including canards, tandem wings, and winglets...catastrophic loss of the airplane, the limit load...
14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.
Code of Federal Regulations, 2011 CFR
...AND COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation...catastrophic loss of the airplane, in each wing (including canards, tandem wings, and winglets...catastrophic loss of the airplane, the limit load...
14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.
Code of Federal Regulations, 2014 CFR
...AND COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation...catastrophic loss of the airplane, in each wing (including canards, tandem wings, and winglets...catastrophic loss of the airplane, the limit load...
14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.
Code of Federal Regulations, 2013 CFR
...AND COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation...catastrophic loss of the airplane, in each wing (including canards, tandem wings, and winglets...catastrophic loss of the airplane, the limit load...
Peripheral and central fatigue after muscle-damaging exercise is muscle length dependent and inversely related.
Healthy untrained men performed 10 series of 12 knee eccentric extension repetitions (EE) at 160 degrees /s. The maximal voluntary isometric contraction force of the quadriceps muscle, the maximal rate of electrically induced torque development (RTD) and relaxation (RTR), isokinetic concentric torque at 30 degrees /s, the electrostimulation-induced torque at 20 and 100Hz frequencies were established before and after EE at shorter and longer muscle lengths. Besides, voluntary activation (VA) index and central activation ratio (CAR) were tested. There was more peripheral fatigue than central after EE. We established more central fatigue as well as low frequency fatigue at a shorter muscle length compared to the longer muscle length. Relative RTD as well as relative RTR, improved after EE and did not depend on the muscle length. Finally, central fatigue is inversely significantly related with the eccentric torque reduction during eccentric exercise and with the changes in muscle torque induced by low frequency stimulation. PMID:20347333
Skurvydas, Albertas; Brazaitis, Marius; Kamandulis, Sigitas; Sipaviciene, Saule
Development of criteria for fatigue repairs in bridge girders damaged by out-of-plane distortion
Numerous highway bridge girders across the United States have experienced fatigue cracking due to repetitive out-of-plane distortion at unstiffened web gaps caused by poorly designed diaphragm connection details. Due to the widespread nature...
Wilson, Scott David
Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include hold times up to 9000 s at maximum tensile strain were conducted at 950 degrees C. The fatigue resistance decreased when a hold time was added at peak tensile strain, owing to the mechanisms resulting in a change in fracture mode from transgranular in pure fatigue to intergranular in creep–fatigue. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep–fatigue resistance. An analysis of the evolving failure modes was facilitated by interrupting tests during cycling for ex situ microstructural investigation.
L.J. Carroll; M.C. Carroll; C. Cabet; R.N. Wright
Study on determination of durability analysis process and fatigue damage parameter for rubber component
Rubber components, which have been widely used in the automotive industry as anti-vibration components for many years, are\\u000a subjected to fluctuating loads, often failing due to the nucleation and growth of defects or cracks. To prevent such failures,\\u000a it is necessary to understand the fatigue failure mechanism for rubber materials and to evaluate the fatigue life for rubber\\u000a components. The
Seong-In Moon; Il-Je Cho; Chang-Su Woo; Wan-Doo Kim
The effect of surface modification on fretting fatigue in Ti Alloy turbine components
NASA Astrophysics Data System (ADS)
Severe fretting damage has been observed on the pressure surfaces of fan and compressor blade dovetails/disks in an aerospace gas turbine engine. A study has been carried out to evaluate the effect of an ion implantation technique in combination with the presently used surface treatments, such as shot peening and coating, on the fretting fatigue life of titanium alloy gas turbine engine components. The results from fretting fatigue tests, residual stress measurements, and nanoindentation tests were used to quantitatively evaluate the effect of various surface treatments on the fretting fatigue life of the fan blade and disk materials. Results from microstructural characterization and analyses of elemental and phase distributions within the implanted region are used to understand the effect of ion implantation on the surface properties of the alloys. Finally, an attempt has been made to evaluate the potential for improving the fretting fatigue life of the engine components using various surface modification techniques.
Chakravarty, S.; Andrews, R. G.; Painaik, P. C.; Koul, A. K.
Investigation of waviness in wind turbine blades: Structural health monitoring
NASA Astrophysics Data System (ADS)
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.
Fatigue and Damage Tolerance Analysis of a Hybrid Composite Tapered Flexbeam
NASA Technical Reports Server (NTRS)
The behavior of nonlinear tapered composite flexbeams under combined axial tension and cyclic bending loading was studied using coupon test specimens and finite element (FE) analyses. The flexbeams used a hybrid material system of graphite/epoxy and glass/epoxy and had internal dropped plies, dropped in an overlapping stepwise pattern. Two material configurations, differing only in the use of glass or graphite plies in the continuous plies near the midplane, were studied. Test specimens were cut from a full-size helicopter tail-rotor flexbeam and were tested in a hydraulic load frame under combined constant axialtension load and transverse cyclic bending loads. The first determination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group in the tapered region of the flexbeam, near the thick end. Delaminations grew slowly and stably, toward the thick end of the flexbeam, at the interfaces above and below the dropped-ply region. A 2D finite element model of the flexbeam was developed. The model was analyzed using a geometrically non-linear analysis with both the ANSYS and ABAQUS FE codes. The global responses of each analysis agreed well with the test results. The ANSYS model was used to calculate strain energy release rates (G) for delaminations initiating at two different ply-ending locations. The results showed that delaminations were more inclined to grow at the locations where they were observed in the test specimens. Both ANSYS and ABAQUS were used to calculate G values associated with delamination initiating at the observed location but growing in different interfaces, either above or below the ply-ending group toward the thick end, or toward the thin end from the tip of the resin pocket. The different analysis codes generated the same trends and comparable peak values, within 5-11 % for each delamination path. Both codes showed that delamination toward the thick region was largely mode II, and toward the thin region was predominantly mode I. The calculated peak G-values from either analysis predict delamination is most likely to occur along the same interface where it was observed in the test specimens. Calculated peak G values were used with material characterization data to calculate a curve relating the fatigue life of the specimens, N, to the applied transverse load, V, for a given constant axial load.
Murri, Gretchen B.; Schaff, Jeffrey R.; Dobyns, Al
Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics
NASA Technical Reports Server (NTRS)
Safe-life and damage-tolerant design philosophies of high performance structures have driven the development of various methods to evaluate nondestructively the accumulation of damage in such structures resulting from cyclic loading. Although many techniques have proven useful, none has been able to provide an unambiguous, quantitative assessment of damage accumulation at each stage of fatigue from the virgin state to fracture. A method based on nonlinear acoustics is shown to provide such a means to assess the state of metal fatigue. The salient features of an analytical model are presented of the microelastic-plastic nonlinearities resulting from the interaction of an acoustic wave with fatigue-generated dislocation substructures and cracks that predictably evolve during the metal fatigue process. The interaction is quantified by the material (acoustic) nonlinearity parameter extracted from acoustic harmonic generation measurements. The parameters typically increase monotonically by several hundred percent over the fatigue life of the metal, thus providing a unique measure of the state of fatigue. Application of the model to aluminum alloy 2024-T4, 410Cb stainless steel, and IN100 nickel-base superalloy specimens fatigued using different loading conditions yields good agreement between theory and experiment. Application of the model and measurement technique to the on-site inspection of steam turbine blades is discussed.
Cantrell, John H., Jr.
Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics
NASA Astrophysics Data System (ADS)
Safe-life and damage-tolerant design philosophies of high performance structures have driven the development of various methods to evaluate nondestructively the accumulation of damage in such structures resulting from cyclic loading. Although many techniques have proven useful, none has been able to provide an unambiguous, quantitative assessment of damage accumulation at each stage of fatigue from the virgin state to fracture. A method based on nonlinear acoustics is shown to provide such a means to assess the state of metal fatigue. The salient features of an analytical model are presented of the microelastic-plastic nonlinearities resulting from the interaction of an acoustic wave with fatigue-generated dislocation substructures and cracks that predictably evolve during the metal fatigue process. The interaction is quantified by the material (acoustic) nonlinearity parameter ? extracted from acoustic harmonic generation measurements. The ? parameters typically increase monotonically by several hundred percent over the fatigue life of the metal, thus providing a unique measure of the state of fatigue. Application of the model to aluminum alloy 2024-T4 and 410 Cb stainless steel specimens fatigued using different loading conditions yields good agreement between theory and experiment. Application of the model and measurement technique to the on-site inspection of steam turbine blades is discussed.
Cantrell, John H.
Characterization of Damage Progression in SCS-6/timetal 21S (0)4 Under Thermomechanical Fatigue Loadings
NASA Technical Reports Server (NTRS)
A detailed experimental investigation was performed at a single maximum cyclic stress (sigma max) level to physically characterize the progression of thermomechanical fatigue (lW) damage in continuously reinforced (0 deg) SCS-6/Timetal 21S, a titanium matrix composite. In-phase (IP) and out of-phase (OP) loadings were investigated at sigma max = 1000 MPa with a temperature cycle from 150 to 6500 C. Damage progression, in terms of macroscopic property degradation, was experimentally quantified through an advanced TMF test methodology which incorporates explicit measurements of the isothermal static moduli at the TMF temperature extremes and the coefficient of thermal expansion (CTE) as functions of the TMF cycles. Detailed characterization of the physical damage progression at the microstructural level was performed by interrupting multiple TMF tests at various stages of mechanical property degradation and analyzing the microstructure through extensive destructive metallography. Further, the extent of damage was also quantified through residual static strength measurements. Results indicated that damage initiation occurred very early in cyclic life (N less than 0.1Nf) for both the IP and OP TMF loadings. IP TMF damage was found to be dominated by fiber breakage with a physical damage progression in the microstructure which was difficult to quantify. OP TMF loadings produced matrix cracking exclusively associated with surface initiations. Here, damage progression was easily distinguished in terms of both the number of cracks and their relative inward progressions toward the outer fiber rows with increased cycling. The point at which the leading cracks reached the outer fiber rows (when localized fiber/matrix de-bonding and matrix crack bridging occurred) appeared to be reflected in the macroscopic property degradation curves.
Castelli, Michael G.
Application of piezoelectric active-sensors for SHM of wind turbine blades
The goal of this study is to characterize the dynamic response of a CX-100 wind blade and the design parameters of SHM techniques as they apply to wind turbine blades, and to investigate the performance of high-frequency active-sensing SHM techniques, including lamb wave and frequency response functions, as a way to monitor the health of a wind turbine blade. The results of the dynamic characterization will be used to validate a numerical model and understand the effect of structural damage on the performance of the blades. The focus of SHM study is to assess and compare the performance of each method in identifying incipient damage, with a special consideration given to field deployability. For experiments, a 9-m CX-100 blade was used. Overall, the methods yielded sufficient damage detection to warrant further investigation into field deployment. This paper also summarizes the SHM results of a full-scale fatigue test of 9-m CX-100 blade using piezoelectric active-sensors.
Park, Gyuhae [Los Alamos National Laboratory; Taylor, Stuart G. [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory
The benefits of applying low plasticity burnishing (LPB) to 17-4PH Stainless Steel (H1100) on both the fatigue and corrosion fatigue performance were compared with the shot peened (SP) and low stress ground (LSG) conditions. LPB treatment dramatically improved both the high cycle fatigue (HCF) performance and fatigue strength. The baseline LSG and SP treatments showed similar fatigue strengths of about
Paul S. Prevéy; N. Jayaraman
Development of the Non-Destructive Evaluation System Using an Eddy Current Probe for Detection of Fatigue Damage in a Stainless Steel
The non-destructive evaluation system which is developed using an eddy current probe to evaluate fatigue damage in an austenitic stainless steel is reported in this paper. This probe is composed of the ferrite core and two pick-up coils connected differentially. The eddy current induced by the excitation coil is disarranged by nonuniform distribution of electromagnetic characteristics due to fatigue damage. The structural function of the eddy current probe proposed, enable to detect the eddy current disarrangement by fatigue damage. This probe detects the change of electromagnetic characteristics in the direction of X. In this paper, SUS304, a austenitic stainless steel was used as the sample. The experimental results show that the output voltage of the probe clearly depends on the number of stress cycles.
Oka, M. [Department of Computer and Control Engineering, Oita National College of Technology, 1666 Maki, Oita, 870-0152 (Japan); Yakushiji, T. [Department of Mechanical Engineering, Oita National College of Technology, 1666 Maki, Oita, 870-0152 (Japan); Tsuchida, Y.; Enokizono, M. [Faculty of Engineering, Oita University, 700 Dannoharu, Oita, 870-1192 (Japan)
Development of the Non-Destructive Evaluation System Using an Eddy Current Probe for Detection of Fatigue Damage in a Stainless Steel
NASA Astrophysics Data System (ADS)
The non-destructive evaluation system which is developed using an eddy current probe to evaluate fatigue damage in an austenitic stainless steel is reported in this paper. This probe is composed of the ferrite core and two pick-up coils connected differentially. The eddy current induced by the excitation coil is disarranged by nonuniform distribution of electromagnetic characteristics due to fatigue damage. The structural function of the eddy current probe proposed, enable to detect the eddy current disarrangement by fatigue damage. This probe detects the change of electromagnetic characteristics in the direction of X. In this paper, SUS304, a austenitic stainless steel was used as the sample. The experimental results show that the output voltage of the probe clearly depends on the number of stress cycles.
Oka, M.; Yakushiji, T.; Tsuchida, Y.; Enokizono, M.
Successful Solutions to SSME/AT Development Turbine Blade Distress
NASA Technical Reports Server (NTRS)
As part of the High-Pressure Fuel Turbopump/Alternate Turbopump (HPFTP/AT) turbine blade development program, unique turbine blade design features were implemented to address 2nd stage turbine blade high cycle fatigue distress and improve turbine robustness. Features included the addition of platform featherseal dampers, asymmetric blade tip seal segments, gold plating of the blade attachments, and airfoil tip trailing edge modifications. Development testing shows these features have eliminated turbine blade high cycle fatigue distress and consequently these features are currently planned for incorporation to the flight configuration. Certification testing will begin in 1999. This presentation summarizes these features.
Montgomery, Stuart K.
Failure of a low pressure turbine rotor blade of an aeroengine
During a test run of an aeroengine, a low-pressure turbine rotor blade had failed. The turbine blades were made of Ni-base superalloy of CM 247 LC grade and fabricated by DS investment casting. The blades were coated with platinum aluminide. Investigation revealed that the blade had failed by fatigue. It was concluded that the coating on the blade had developed
S. K. Bhaumik; M. Sujata; M. A. Venkataswamy; M. A. Parameswara
Systematic error in mechanical measures of damage during four-point bending fatigue of cortical bone
Accumulation of fatigue microdamage in cortical bone specimens is commonly measured by a modulus or stiffness degradation after normalizing tissue heterogeneity by the initial modulus or stiffness of each specimen measured during a preloading step. In the first experiment, the initial specimen modulus defined using linear elastic beam theory (LEBT) was shown to be nonlinearly dependent on the preload level,
Matthew D. Landrigan; Ryan K. Roeder
Quantitative Assessment of Fatigue Damage Accumulation in Wavy Slip Metals from Acoustic Harmonic Generation
NASA Technical Reports Server (NTRS)
A comprehensive, analytical treatment is presented of the microelastic-plastic nonlinearities resulting from the interaction of a stress perturbation with dislocation substructures (veins and persistent slip bands) and cracks that evolve during high-cycle fatigue of wavy slip metals. The nonlinear interaction is quantified by a material (acoustic) nonlinearity parameter beta extracted from acoustic harmonic generation measurements. The contribution to beta from the substructures is obtained from the analysis of Cantrell [Cantrell, J. H., 2004, Proc. R. Soc. London A, 460, 757]. The contribution to beta from cracks is obtained by applying the Paris law for crack propagation to the Nazarov-Sutin crack nonlinearity equation [Nazarov, V. E., and Sutin, A. M., 1997, J. Acoust. Soc. Am. 102, 3349]. The nonlinearity parameter resulting from the two contributions is predicted to increase monotonically by hundreds of percent during fatigue from the virgin state to fracture. The increase in beta during the first 80-90 percent of fatigue life is dominated by the evolution of dislocation substructures, while the last 10-20 percent is dominated by crack growth. The model is applied to the fatigue of aluminium alloy 2024-T4 in stress-controlled loading at 276MPa for which experimental data are reported. The agreement between theory and experiment is excellent.
Cantrell, John H.
Monitoring and modeling stress corrosion and corrosion fatigue damage in nuclear reactors
Stress corrosion and corrosion fatigue are significant problems in many industries, causing economic penalties from decreased plant availability and component repair or replacement. In nuclear power reactors, environmental cracking occurs in a wide variety of components, including reactor piping and steam generator tubing, bolting materials and pressure vessels. Life assessment for these components is complicated by the belief that cracking
P. L. Andresen; F. P. Ford; H. D. Solomon; D. F. Taylor
Influence of Prior Fatigue Damage on Tensile Properties of 316L(N) Stainless Steel and Modified 9Cr-1Mo Steel
NASA Astrophysics Data System (ADS)
In the current study, the effect of prior low-cycle fatigue (LCF) damage on the tensile properties of 316L(N) stainless steel (SS) and modified 9Cr-1Mo steel were systematically investigated. The LCF tests were interrupted at 5, 10, 30, and 50 pct of the total fatigue life followed by tensile tests on the same specimens at the same strain rate (3 × 10-3 s-1) and temperatures of 300 K, 823 K, and 873 K (27 °C, 550 °C, and 600 °C). Prior strain cycling at elevated temperatures had remarkable effect on the tensile properties of both cyclically hardening and cyclically softening materials. An exponential relationship between the yield stress and the amount of pre-strain cycles is obtained for both the materials. The initial drastic change in the yield strength values up to 10 pct of fatigue life may be due to the microstructural changes that lead to hardening or softening in 316L(N) SS and modified 9Cr-1Mo steel, respectively. Saturation in the yield strength values beyond 10 pct of fatigue life has practical importance for remnant fatigue life assessment. Evolution of fatigue damage in both the 316L(N) SS and modified 9Cr-1Mo steel was analyzed using the surface replica technique.
Mariappan, K.; Shankar, Vani; Sandhya, R.; Mathew, M. D.; Bhaduri, A. K.
Incipient Crack Detection in Composite Wind Turbine Blades
This paper presents some analysis results for incipient crack detection in a 9-meter CX-100 wind turbine blade that underwent fatigue loading to failure. The blade was manufactured to standard specifications, and it underwent harmonic excitation at its first resonance using a hydraulically-actuated excitation system until reaching catastrophic failure. This work investigates the ability of an ultrasonic guided wave approach to detect incipient damage prior to the surfacing of a visible, catastrophic crack. The blade was instrumented with piezoelectric transducers, which were used in an active, pitchcatch mode with guided waves over a range of excitation frequencies. The performance results in detecting incipient crack formation in the fiberglass skin of the blade is assessed over the range of frequencies in order to determine the point at which the incipient crack became detectable. Higher excitation frequencies provide consistent results for paths along the rotor blade's carbon fiber spar cap, but performance falls off with increasing excitation frequencies for paths off of the spar cap. Lower excitation frequencies provide more consistent performance across all sensor paths.
Taylor, Stuart G. [Los Alamos National Laboratory; Choi, Mijin [Chonbuk National University, Korea; Jeong, Hyomi [Chonbuk National University, Korea; Jang, Jae Kyeong [Chonbuk National University, Korea; Park, Gyuhae [Chonnam National University, Korea; Farinholt, Kevin [Commonwealth Center for Advanced Manufacturing, VA; Farrar, Charles R. [Los Alamos National Laboratory; Ammerman, Curtt N. [Los Alamos National Laboratory; Todd, Michael D. [Los Alamos National Laboratory; Lee, Jung-Ryul [Chonbuk National University, Korea
Damage development during low cycle fatigue of carbon-black loaded SBR. [Styrene butadiene rubber containing 0, 15, 25, and 35 wt % carbon black
Fatigue of elastomers is a subject that has received con