Sample records for blade fatigue damage

  1. Monitoring low cycle fatigue damage in turbine blade using vibration characteristics

    NASA Astrophysics Data System (ADS)

    Kumar, Sandeep; Roy, Niranjan; Ganguli, Ranjan

    2007-01-01

    A finite element based approach is used to simulate the evolution of low cycle fatigue damage in a turbine blade. The turbine blade is modelled as a rotating Timoshenko beam with taper and twist. A damage growth model for low cycle fatigue damage developed using a continuum mechanics approach is integrated with the finite element model. Numerical results are obtained to study the effect of damage growth on the rotating frequencies. It is found that low cycle fatigue causes sufficient degradation in blade stiffness for changes in rotating frequency to be used as an indicator to track damage growth. Continuum damage mechanics models in conjunction with finite element analysis are used to develop thresholds for damage indicators. By placing suitable threshold on the frequency change, it is possible to detect the onset of the final stage of damage in the structure before failure occurs.

  2. Mitigation of FOD and Corrosion Fatigue Damage in 17-4 PH Stainless Steel Compressor Blades with Surface Treatment

    Microsoft Academic Search

    Paul S. Prevéy; N. Jayaraman; Ravi Ravindranath

    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

  3. Research on fatigue damage detection for wind turbine blade based on high-spatial-resolution DPP-BOTDA

    NASA Astrophysics Data System (ADS)

    Xu, Jinlong; Dong, Yongkang; Li, Hui

    2014-03-01

    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.

  4. Damage tolerance based life prediction in gas turbine engine blades under vibratory high cycle fatigue

    SciTech Connect

    Walls, D.P.; deLaneuville, R.E.; Cunningham, S.E. [United Technologies Pratt and Whitney, West Palm Beach, FL (United States)

    1997-01-01

    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.

  5. Mitigation Of Fretting Fatigue Damage In Blade And Disk Pressure Faces With Low Plasticity Burnishing

    Microsoft Academic Search

    Paul S. Prevéy; N. Jayaraman; Michael Shepard

    2007-01-01

    Low Plasticity Burnishing (LPB) is now established as a surface enhancement technology capable of introducing through-thickness compressive residual stresses in the edges of gas turbine engine blades and vanes to mitigate foreign object damage (FOD). The \\

  6. Determining equivalent damage loading for full-scale wind turbine blade fatigue tests

    Microsoft Academic Search

    G. Freebury; W. Musial

    2000-01-01

    This paper describes a simplified method for converting wind turbine rotor design loads into equivalent-damage, constant-amplitude loads and load ratios for both flap and lead-lag directions. It is an iterative method that was developed at the National Renewable Energy Laboratory (NREL) using Palmgren-Miner's linear damage principles. The general method is unique because it does not presume that any information about

  7. Fatigue analysis and testing of wind turbine blades

    NASA Astrophysics Data System (ADS)

    Greaves, Peter Robert

    This thesis focuses on fatigue analysis and testing of large, multi MW wind turbine blades. The blades are one of the most expensive components of a wind turbine, and their mass has cost implications for the hub, nacelle, tower and foundations of the turbine so it is important that they are not unnecessarily strong. Fatigue is often an important design driver, but fatigue of composites is poorly understood and so large safety factors are often applied to the loads. This has implications for the weight of the blade. Full scale fatigue testing of blades is required by the design standards, and provides manufacturers with confidence that the blade will be able to survive its service life. This testing is usually performed by resonating the blade in the flapwise and edgewise directions separately, but in service these two loads occur at the same time.. A fatigue testing method developed at Narec (the National Renewable Energy Centre) in the UK in which the flapwise and edgewise directions are excited simultaneously has been evaluated by comparing the Palmgren-Miner damage sum around the blade cross section after testing with the damage distribution caused by the service life. A method to obtain the resonant test configuration that will result in the optimum mode shapes for the flapwise and edgewise directions was then developed, and simulation software was designed to allow the blade test to be simulated so that realistic comparisons between the damage distributions after different test types could be obtained. During the course of this work the shortcomings with conventional fatigue analysis methods became apparent, and a novel method of fatigue analysis based on multi-continuum theory and the kinetic theory of fracture was developed. This method was benchmarked using physical test data from the OPTIDAT database and was applied to the analysis of a complete blade. A full scale fatigue test method based on this new analysis approach is also discussed..

  8. Turbine blade thermal fatigue testing Pratt and Whitney aircraft hollow core blades

    NASA Technical Reports Server (NTRS)

    Ingram, J.; Gross, L.

    1985-01-01

    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.

  9. Simulation of fatigue failure in composite axial compressor blades

    Microsoft Academic Search

    Qubo Li; Janusz Piechna; Norbert Müeller

    2011-01-01

    Centrifugal forces are generated by a spinning impeller, of magnitudes that create large stresses. Aerodynamic forces are also imparted on an impeller blade, which varies with time and position. These two forces play different roles during compressor events. Damage accumulated from these events results in the fatigue failure of impeller material and structure. Therefore, it is important to design an

  10. Fatigue strength of gas turbine compressor blades

    Microsoft Academic Search

    V. T. Troshchenko; A. V. Prokopenko

    2000-01-01

    An experimental procedure has been developed for the investigation of fatigue and crack growth resistance of materials and real compressor blades. Methods for the determination of stress intensity factors in specimens and in blades with cracks have been justified. Investigations have been performed into the influence of manufacturing residual stresses and surface defects in the form of simulators of dents,

  11. Jumplike fatigue crack growth in compressor blades

    NASA Astrophysics Data System (ADS)

    Limar', L. V.; Demina, Yu. A.; Botvina, L. R.

    2014-04-01

    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.

  12. Fatigue failure of a compressor blade

    Microsoft Academic Search

    N. J. Lourenço; M. L. A. Graça; L. A. L. Franco; O. M. M. Silva

    2008-01-01

    A helicopter in a commercial flight was substantially damaged during a hard landing following a loss of engine power at Northwest region of Brazil. The pilot and passengers reported no injuries. Initial investigations pointed out absence of any damages by foreign objects. The accident was due to the failure of a blade from compressor section. Failure analysis of 4th stage

  13. Approach to the fatigue analysis of vertical-axis wind-turbine blades

    SciTech Connect

    Veers, P.S.

    1981-01-01

    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.

  14. Approach to the fatigue analysis of vertical-axis wind-turbine blades

    SciTech Connect

    Veers, P.S.

    1981-09-01

    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.

  15. Structural fatigue test results for large wind turbine blade sections

    NASA Technical Reports Server (NTRS)

    Faddoul, J. R.; Sullivan, T. L.

    1982-01-01

    In order to provide quantitative information on the operating life capabilities of wind turbine rotor blade concepts for root-end load transfer, a series of cantilever beam fatigue tests was conducted. Fatigue tests were conducted on a laminated wood blade with bonded steel studs, a low cost steel spar (utility pole) with a welded flange, a utility pole with additional root-end thickness provided by a swaged collar, fiberglass spars with both bonded and nonbonded fittings, and, finally, an aluminum blade with a bolted steel fitting (Lockheed Mod-0 blade). Photographs, data, and conclusions for each of these tests are presented. In addition, the aluminum blade test results are compared to field failure information; these results provide evidence that the cantilever beam type of fatigue test is a satisfactory method for obtaining qualitative data on blade life expectancy and for identifying structurally underdesigned areas (hot spots).

  16. Fatigue damage detection using cyclostationarity

    NASA Astrophysics Data System (ADS)

    Boungou, D.; Guillet, F.; Badaoui, M. El; Lyonnet, P.; Rosario, T.

    2015-06-01

    In this paper, we present the second-order of cyclostationarity to detect and diagnose the fatigue damage of the stainless steel 316l subjected to low cycle fatigue (LCF). LCF is defined by repetitive cycling in a low stress and a short period. The vibration response of material subjected to LCF provides information linked to the solicitation and to the fatigue damage. Thus, we considered a cantilever beam with breathing cracks and assumed that under the solicitation, breathing cracks generates non-linearity in the stiffness of the material and this one decreases with the damage. We used the second-order of the cyclostationarity to reveal this non-linearity and showed that the fatigue provide a random component in the signal, which increases with the fatigue damage. Thus, in the specific case of a material subjected to LCF, with a non-linear stiffness, we propose a new methodology to detect and diagnose the fatigue damage using a vibration signal. This methodology is based on the second order of the cyclostationarity.

  17. High sensitive methods for health monitoring of compressor blades and fatigue detection.

    PubMed

    Wito?, Miros?aw

    2013-01-01

    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

  18. High Sensitive Methods for Health Monitoring of Compressor Blades and Fatigue Detection

    PubMed Central

    Wito?, Miros?aw

    2013-01-01

    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

  19. Loading Analysis of Composite Wind Turbine Blade for Fatigue Life Prediction of Adhesively Bonded Root Joint

    NASA Astrophysics Data System (ADS)

    Salimi-Majd, Davood; Azimzadeh, Vahid; Mohammadi, Bijan

    2015-06-01

    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.

  20. Impact damage and fatigue behavior of gamma TiAl

    SciTech Connect

    Harding, T.S.; Jones, J.W. [Univ. of Michigan, Ann Arbor, MI (United States); Pollock, T.M.; Steif, P.S.; Rubal, M.P. [Carnegie Mellon Univ., Pittsburgh, PA (United States)

    1997-12-31

    The relationship between impact damage and the fatigue behavior of gamma titanium aluminide has been examined. Axial fatigue specimens fabricated from cast Ti-47.9Al-2Cr-2Nb alloy and Ti-47.3Al-2.2Nb-0.5Mn-0.4W-0.4Mo-0.23Si alloy were impacted under controlled conditions with various indentor shapes to simulate manufacturing related damage in low pressure turbine blades. Damage was quantified and related to impact parameters. A measure of the ambient temperature fatigue strength in the damaged specimens was obtained by standard fatigue testing employing a step-loading approach. Fractographic studies were performed to differentiate impact damage from subsequent fatigue crack growth and to elucidate the mechanisms responsible for the dependence of fatigue strength on the severity of impact damage. A threshold-based fracture mechanics analysis of crack advance from damage zones, and its use in fatigue failure strength prediction, has been developed.

  1. Selection of Wind Turbine Blade Materials for Fatigue Resistance

    E-print Network

    Selection of Wind Turbine Blade Materials for Fatigue Resistance John Mandell Montana StateE glass and similar compositions · High Performance Glass (WindStrand) C b· Carbon #12;Tensile Fatigue E Gl (2 f b i )E-Glass (2 fabrics), WindStrand, Carbon ; Epoxy Resins; Stress Based (top) and Stress

  2. Nonlinear fatigue damage accumulation under random loading

    Microsoft Academic Search

    W. Q. Zhu; M. X. Jiang

    1996-01-01

    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

  3. Full-scale fatigue tests of CX-100 wind turbine blades. Part II: analysis

    NASA Astrophysics Data System (ADS)

    Taylor, Stuart G.; Jeong, Hyomi; Jang, Jae Kyeong; Park, Gyuhae; Farinholt, Kevin M.; Todd, Michael D.; Ammerman, Curtt M.

    2012-04-01

    This paper presents the initial analysis results of several structural health monitoring (SHM) methods applied to two 9- meter CX-100 wind turbine blades subjected to fatigue loading at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). The first blade was a pristine blade, manufactured to standard CX-100 design specifications. The second blade was manufactured for the University of Massachusetts, Lowell (UMass), with intentional simulated defects within the fabric layup. Each blade was instrumented with a variety of sensors on its surface. The blades were subject to harmonic excitation at their first natural frequency with steadily increasing loading until ultimately reaching failure. Data from the sensors were collected between and during fatigue loading sessions. The data were measured at multi-scale frequency ranges using a variety of data acquisition equipment, including off-the-shelf systems and prototype data acquisition hardware. The data were analyzed to identify fatigue damage initiation and to assess damage progression. Modal response, diffuse wave-field transfer functions in time and frequency domains, and wave propagation methods were applied to assess the condition of the turbine blade. The analysis methods implemented were evaluated in conjunction with hardware-specific performance for their efficacy in enabling the assessment of damage progression in the blade. The results of this assessment will inform the selection of specific data to be collected and analysis methods to be implemented for a CX-100 flight test to be conducted in collaboration with Sandia National Laboratory at the U.S. Department of Agriculture's (USDA) Conservation and Production Research Laboratory (CPRL) in Bushland, Texas.

  4. Structural damage identification in wind turbine blades using piezoelectric active sensing with ultrasonic validation

    SciTech Connect

    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

    2010-01-01

    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.

  5. Microstructural evaluation of cumulative fatigue damage below the fatigue limit

    Microsoft Academic Search

    C. Fukuoka; Y. G. Nakagawa

    1996-01-01

    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, θ, which increase with fatigue damage accumulation, are measured by the Selected Area Diffraction (SAD) method. The misorientation difference, θ, of the sample failed just above the fatigue limit

  6. Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis

    NASA Astrophysics Data System (ADS)

    Lillo Gallardo, Patricio Andres

    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.

  7. Wind turbine blade fatigue tests: lessons learned and application to SHM system development

    SciTech Connect

    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

    2012-06-28

    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.

  8. Microstructural evaluation of cumulative fatigue damage below the fatigue limit

    SciTech Connect

    Fukuoka, C.; Nakagawa, Y.G. [IHI, Tokyo (Japan). Research Inst.] [IHI, Tokyo (Japan). Research Inst.

    1996-05-01

    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.

  9. Fretting fatigue in dovetail blade roots: Experiment and analysis

    Microsoft Academic Search

    R. Rajasekaran; D. Nowell

    2006-01-01

    A biaxial fatigue experiment is described which is capable of simulating the loading experienced by a dovetail blade root in an aircraft gas turbine. A comprehensive stress analysis of the experimental configuration has been undertaken and a semi-analytical approach has been developed to provide accurate estimates of surface tractions and subsurface stress fields. The forces (normal and shear) and moment

  10. Fatigue of Wind Blade Laminates:Fatigue of Wind Blade Laminates: Effects of Resin and Fabric Structure

    E-print Network

    , environmental effects · Strength Based: standard joint geometryg j g y like lap shear; test includes crack Simulation Ic, IIc #12;3. Blade adhesives · Bulk adhesive strength, fatigue,g , g , fracture toughness;5. Property Data for Analysis · 3-D static properties of 100 mm thick glass/epoxy Laminate Elastic Constants1

  11. Microcrack growth behavior and life in high temperature low cycle fatigue of blade root and disc joint for turbines

    Microsoft Academic Search

    Nobuhiro Isobe; Shuhei Nogami

    2009-01-01

    Low cycle fatigue tests were carried out at a temperature of 600°C using a component specimen of 12%-Cr steel, which simulates a blade root and disc joint for turbines. The growth behavior of micro-cracks in the joint region of the specimens was investigated to clarify the damage mechanism of blade-root joints used in high temperature environments and to improve life

  12. A fatigue damage model for crack propagation

    SciTech Connect

    Chow, C.L. [Univ. of Michigan, Dearborn, MI (United States); Wei, Y. [Pacific Technique Development Co., Ltd., Moscow (Russian Federation)

    1996-12-31

    This paper presents a fatigue damage model for crack propagation in characterizing the fatigue crack growth behavior of cracked structures. Special emphasis is placed on the numerical simulation of cyclic loading and the dependence of the numerical results on the finite element mesh discretization. A practical method for predicting fatigue crack propagation in engineering structures is proposed. The predicted results are compared favorably with those measured experimentally from fatigue testing a center cracked panel of 2024-T3(Alclad) aluminum plates.

  13. Nonlinear fatigue damage accumulation under random loading

    SciTech Connect

    Zhu, W.Q.; Jiang, M.X. [Zhejiang Univ., Hangzhou (China). Dept. of Mechanics

    1996-05-01

    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.

  14. How surface damage removal affects fatigue life

    NASA Technical Reports Server (NTRS)

    Jeelani, S.; Scott, M. A.

    1988-01-01

    The effect of the removal of work hardened surface layers from specimens of 2024-T4 aluminum alloy and AISI-4130 steel on their fatigue lives has been investigated. Specimens were fatigued at selected stress levels for a given number of cycles, and the surface layer was removed followed by subsequent fatigue cycling. Results confirm that when a material is subjected to fatigue loading, damage accumulates in the surface layers in the form of work hardening. Removal of the surface layer brings the specimen back to its pre-fatigued condition.

  15. DAMAGE DETECTION METHODS ON WIND TURBINE BLADE TESTING WITH WIRED AND WIRELESS ACCELEROMETER SENSORS

    E-print Network

    Paris-Sud XI, Université de

    DAMAGE DETECTION METHODS ON WIND TURBINE BLADE TESTING WITH WIRED AND WIRELESS ACCELEROMETER for nonstationary blade excitations. KEYWORDS : Structural Health Monitoring, Damage Detection, Wind Turbine, Wireless sensing, Wavelets. INTRODUCTION Detecting damage in wind turbine blades is a very

  16. Novelty detection applied to vibration data from a CX-100 wind turbine blade under fatigue loading

    NASA Astrophysics Data System (ADS)

    Dervilis, N.; Choi, M.; Antoniadou, I.; Farinholt, K. M.; Taylor, S. G.; Barthorpe, R. J.; Park, G.; Worden, K.; Farrar, C. R.

    2012-08-01

    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.

  17. Blade reliability collaborative : collection of defect, damage and repair data.

    SciTech Connect

    Ashwill, Thomas D.; Ogilvie, Alistair B.; Paquette, Joshua A.

    2013-04-01

    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.

  18. Analysis of Fretting Fatigue Strength of Integral Shroud Blade for Steam Turbine

    NASA Astrophysics Data System (ADS)

    Kaneko, Yasutomo; Tomii, Masayuki; Ohyama, Hiroharu; Kurimura, Takayuki

    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.

  19. Identification of Foreign Objects Damaging Compressor Blades in Turbojet Engines

    NASA Technical Reports Server (NTRS)

    Spakowski, A E; Graab, J

    1957-01-01

    Damage to the compressor blades of turbojet engines due to ingestion of foreign objects is a growing problem, the solution of which has been made more difficult by the large percentage of damaging materials that have remained unknown. A rapid emission spectroscopic method was devised to identify the chemical composition of these foreign objects. Results on laboratory-prepared specimens and blades from damaged engines show that the method can be utilized to determine the nature of the ingested foreign objects.

  20. Neural network representation of fatigue damage dynamics

    Microsoft Academic Search

    Chen-Jung Li; Asok Ray

    1995-01-01

    This paper proposes a neural network implementation of a model of fatigue damage dynamics which allows the damage information on critical plant components to be integrated with the plant dynamics for both online life prediction and off-line control synthesis. The aim is to alleviate the problem of slow computation via conventional numerical methods. The results of simulation experiments reveal that

  1. Contactless Diagnostics of Turbine Blade Vibration and Damage

    NASA Astrophysics Data System (ADS)

    Procházka, Pavel; Van?k, František

    2011-07-01

    The study deals with the contactless diagnostic method used for the identification of steam turbine blade strain, vibration and damage. The tip-timing method based on the evaluation of time differences of blade passages in different rotor revolutions has been modified and improved to provide more precise and reliable results. A new approach to the analysis of the amplitude and time differences of impulse signals generated by a blade passage has been applied. Amplitudes and frequencies of vibrations and static position of blades ascertained by the diagnostic process are used to establish the state of blade damage. A contactless diagnostic system VDS-UT based on magneto-resistive sensors was developed in the Institute of Thermomechanics Academy of Sciences of the Czech Republic. The system provides on-line monitoring of vibration amplitudes and frequencies of all blades and notification of possible blade damage. Evaluation of the axial and circumferential components of the deflections by measuring the amplitude of blade impulse signals results in an overall improvement of the method. Using magneto-resistive sensors, blade elongation and untwisting can be determined as well.

  2. Fatigue damage considering whipping arising from slamming

    SciTech Connect

    Hansen, P.F. [Technical Univ. of Denmark, Lyngby (Denmark). Dept. of Ocean Engineering; Thayamballi, A.K. [American Bureau of Shipping, New York, NY (United States)

    1995-12-31

    In floating vessels, there are many load processes that contribute to fatigue. Among these, present day fatigue design methods emphasize low-frequency wave-induced loads. The exact level of fatigue damage contributed by the load processes neglected, e.g. slamming-induced whipping, is at this time largely unknown. Full-scale measurements appear to indicate that the slamming-induced whipping stresses may be significant for certain vessel types, locations, and loading conditions. Further, the consideration of whipping is in principle important for design of the more slender, higher speed vessels, for systematic studies of slamming-induced fatigue damage, and for applications such as failure analysis. There thus exists a need for a fatigue damage calculation procedure addressing slamming. In this paper the authors outline and summarize the results of a study to develop a new integrated procedure for obtaining the statistics of the combined slamming and wave-induced stress response and resulting fatigue damage, accounting for phasing, hog-sag non-linearities, clustering, and hull flexibility. They also provide example calculations for a vessel.

  3. Wind turbine blade fatigue tests: lessons learned and application to SHM system development

    Microsoft Academic Search

    Stuart G. Taylor; Kevin M. Farinholt; Hyomi Jeong; JaeKyung Jang; Gyu Hae Park; Michael D. Todd; Charles R. Farrar; Curtt N. Ammerman

    2012-01-01

    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

  4. ADVANCED COMPOSITE WIND TURBINE BLADE DESIGN BASED ON DURABILITY AND DAMAGE TOLERANCE

    SciTech Connect

    Galib Abumeri; Frank Abdi (PhD)

    2012-02-16

    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

  5. Analysis of relationships governing wear fatigue damage. Report 1

    Microsoft Academic Search

    L. A. Sosnovskii

    1995-01-01

    Wear-fatigue damage is classified and described. The main terms of tribometry are given. Complex damage is analyzed from the dialectic position and Wöhler curves in fatigue (mechanical), fretting fatigue, frictionmechanical, and contact-mechanical fatigue is schematized. The general form of the exponential equation for describing these curves is presented.

  6. The effect of temperature on fatigue damage of FRP composites

    Microsoft Academic Search

    H. Mivehchi; A. Varvani-Farahani

    2010-01-01

    The present study intends to investigate the effect of temperature on cumulative fatigue damage (D) of laminated fibre-reinforced polymer (FRP) composites. The effect of temperature on fatigue damage is formulated based\\u000a on Ramkrishnan–Jayaraman and Varvani-Farahani–Shirazi residual stiffness fatigue damage models. The models are further developed\\u000a to assess the fatigue damage of FRP composites at various temperatures (T). This task is

  7. Early Fatigue Damage Detection in Composite Materials

    Microsoft Academic Search

    J. J. Nevadunsky; J. J. Lucas; M. J. Salkind

    1975-01-01

    Detection of early fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for ±45° Glass\\/Epoxy, and ±45°\\/0° Graphite\\/Glass\\/Epoxy. Dynamic axial modulus and temperature were monitored continuously with a correlation between temperature rise and modulus decrease observed. The modulus decrease and temperature rise are indicative of irreversible damage in these materials.Torsional modulus measurements and coin tap tests

  8. Thermal fatigue and oxidation data for directionally solidified MAR-M 246 turbine blades

    NASA Technical Reports Server (NTRS)

    Hill, V. L.; Humphreys, V. E.

    1980-01-01

    Thermal fatigue and oxidation data were obtained for 11 plasma spray coated and 13 uncoated directionally solidified and single crystal MAR-M 246 blades. Blade coatings on the airfoil included several metal-oxide thermal barrier layers based on Al2O3, Cr2O3, or ZrO2. The 24 turbine blades were tested simultaneously for 3000 cycles in fluidized beds maintained at 950 and 25 C using a symmetrical 360 set thermal cycle. In 3000 cycles, only uncoated turbine blades exhibited cracking on the trailing edge near the platform; 3 of the 13 uncoated blades did not crack. Cracking occurred over the range 400 to 2750 cycles, with single crystal blades indicating the poorest thermal fatigue resistance. Oxidation of the uncoated blades was limited in 3000 cycles. All coatings indicated microscopically visible spalling at the trailing edge radius after 3000 cycles. Severe general spalling on the airfoil was observed for two multilayered coatings.

  9. Fatigue damage assessment of unidirectional GRP and CFRP composites

    Microsoft Academic Search

    Morteza Panbechi

    2005-01-01

    The present thesis has developed an energy-based critical plane fatigue damage parameter to assess the fatigue damage of unidirectional GRP and CFRP composites. The proposed model is based on the physics and the mechanism of fatigue cracking within three damage regions of the matrix (I), the fiber-matrix interface (II), and the fiber (III) in unidirectional GRP and CFRP composites as

  10. Nondestructive evaluation of thick-composite fatigue damage

    Microsoft Academic Search

    Robert E. Green

    1995-01-01

    This paper describes the results of the comparison of a variety of nondestructive evaluation techniques to monitor the development of fatigue damage in thick graphite\\/epoxy composites. Three inch long, one inch square cross-section test specimens were fatigue tested in compression. Most specimens incorporated stress (strain) concentration notches at their mid- section in order to localize the primary fatigue damage regions

  11. Creep, creep-fatigue, and cavitation damage

    Microsoft Academic Search

    Majumdar

    1986-01-01

    Available creep and creep-fatigue data of type 304 stainless steel are re-examined in the light of some recently generated basic cavitation data on the same material. This basic study has shown creep damage to be a highly inhomogeneous phenomenon, both in space and in time. Thus a small fraction of boundaries are so intensely cavitated by about 10--25% of life

  12. Fatigue life variability and reliability analysis of a wind turbine blade

    NASA Astrophysics Data System (ADS)

    Veers, P. S.; Sutherland, H. J.; Ashwill, T. D.

    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.

  13. Use of the WEST-1 wind turbine simulator to predict blade fatigue load distribution

    NASA Technical Reports Server (NTRS)

    Janetzke, D. C.

    1983-01-01

    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.

  14. 77 FR 4890 - Damage Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures, and Damage Tolerance...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-01

    ...its regulations to require evaluation of fatigue and residual static strength of composite rotorcraft structures using a damage tolerance...its regulations to require evaluation of fatigue and residual static strength of composite rotorcraft structures using a damage...

  15. CHARACTERIZATION OF A MOBILE OSCILLATORY FATIGUE OPERATOR FOR WIND TURBINE BLADE TESTING

    SciTech Connect

    Donohoo, P.E.; Cotrell, J.

    2008-01-01

    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.

  16. Fretting Fatigue of Single Crystal\\/Polycrystalline Nickel Subjected to Blade\\/Disk Contact Loading

    Microsoft Academic Search

    J. F. Matlik; H. Murthy; T. N. Farris

    2002-01-01

    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

  17. Estimation of fatigue damage and fatigue life of components under random loading

    Microsoft Academic Search

    W. F. Wu; H. Y. Liou; H. C. Tse

    1997-01-01

    To examine the applicability of methods proposed in the estimation of fatigue damage and fatigue life of components under random loading, a batch of specimens made of 7075-T651 aluminium alloy has been studied and some of the results are reported in the present paper. The paper describes different methods and rules in the calculation of fatigue damage, especially when random

  18. Production section: Influence of plastic predeformation on the fatigue strength of compressor blades with defects

    SciTech Connect

    Ezhov, V.N.; Sidyachenko, V.M. [Institute of Strength of Materials, Kiev (Ukraine)

    1995-06-01

    We study the influence of plastic predeformation by bending to create deep residual compressive stresses on the fatigue strength of 13Kh11N2V2MF steel specimens and compressor blades with cut and stamped V-shaped and semicircular defects, and also the use of design-based redistribution of the stresses in the blade ({open_quotes}offsetting{close_quotes} toward the edges) for the retardation of cracks in the stress concentrators. It is found that plastic predeformation increases the fatigue strength by about 20%, while {open_quotes}offsetting{close_quotes} with the creation of a compressive mean stress {sigma}{sub m} = -300 MPa in the defect region increases the fatigue strength by 2-2.5 times. We examine schemes for calculating the fatigue strength with account for the residual and mean stresses, and also examine the defect creation technique. Recommendations are made for increasing the strength of compressor blades with defects.

  19. DETECTION OF IMPULSE-LIKE AIRBORNE SOUND FOR DAMAGE IDENTIFICATION IN ROTOR BLADES OF WIND TURBINES

    E-print Network

    Boyer, Edmond

    DETECTION OF IMPULSE-LIKE AIRBORNE SOUND FOR DAMAGE IDENTIFICATION IN ROTOR BLADES OF WIND TURBINES burdens of wind turbines. To detect damage of rotor blades, several research projects focus on an acoustic, rotor blade, wind turbine INTRODUCTION There are several publications of non destructive damage

  20. Stochastic fatigue damage modeling under variable amplitude loading

    Microsoft Academic Search

    Yongming Liu; Sankaran Mahadevan

    2007-01-01

    A general methodology for stochastic fatigue life prediction under variable amplitude loading is proposed in this paper. The methodology combines a nonlinear fatigue damage accumulation rule and a stochastic S–N curve representation technique to achieve this objective. The nonlinear damage accumulation rule proposed in this paper improves the deficiencies inherent in the linear damage accumulation rule and still maintains its

  1. Experimental damage mechanics of microelectronic solder joints under fatigue loading

    Microsoft Academic Search

    C. Basaran; H. Tang; S. Nie

    2004-01-01

    Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling are very different. Elastic modulus degradation under thermal cycling, which is considered

  2. Experimental damage mechanics of microelectronic solder joints under fatigue loading

    Microsoft Academic Search

    C. Basaran; H. Tang; S. Nie

    2005-01-01

    Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling is very different. Elastic modulus degradation under thermal cycling, which is considered

  3. Effects of FOD on the fatigue crack initiation of ballistically impacted titanium-aluminum(6)-vanadium(4) simulated engine blades

    NASA Astrophysics Data System (ADS)

    Birkbeck, Janine C.

    Nicks and dents caused by foreign object damage (FOD) in leading edges of turbine engine blades often provide crack initiation sites that may grow under high cycle fatigue (HCF) conditions and lead to reduced life. Leading edge specimens simulating the geometry of these engine blades were fabricated from STOA Ti-6Al-4V. The leading edges were then ballistically impacted with small steel spheres and the subsequent damage was characterized with SEM according to the crater dimensions (depth and length), material lost, cracks and extrusions. A few specimens were sectioned after impact and SEM of the area beneath the impacts revealed adiabatic shear bands as well as a surface impact transformation layer with a fine transformed microstructure. These shear bands contained micro-cracks, tears and some shrinkage porosity, which indicated the magnitude of the localized high temperatures achieved during the impact. The remaining specimens were subjected to tension-tension axial HCF testing using a step loading fatigue procedure. Fatigue fracture initiation always occurred at the exit side of the impact crater and at the crater center. Extrusions, loss of material and cracks caused by the impact did not correlate well with the normalized fatigue strength. However, SEM of the fractured surfaces beneath the impacts revealed adiabatic shear band traces as well as a surface impact transformation layer exhibiting a fine texture at the fracture initiation sites. Only a moderate correlation existed between the depth of the impact crater and the normalized fatigue stress. No correlation existed between the crater length and the normalized fatigue strength. The failure of several craters with the smaller crater depth strongly suggested that factors not related to the crater geometry were involved. The fatigue limit stress model was able to predict the fatigue limit for craters less than 0.4 mm deep. However, this model underestimated the fatigue strength loss for deeper craters, indicating that another mechanism, such as microstructural damage played an important role. Considering the presence of the transformed microstructure and adiabatic shear bands, the use of slower strain rate methods for producing FOD on the leading edge of a test specimen may need to be re-evaluated.

  4. Full-scale fatigue tests of CX-100 wind turbine blades. Part I: testing

    NASA Astrophysics Data System (ADS)

    Farinholt, Kevin M.; Taylor, Stuart G.; Park, Gyuhae; Ammerman, Curtt M.

    2012-04-01

    This paper overviews the test setup and experimental methods for structural health monitoring (SHM) of two 9-meter CX-100 wind turbine blades that underwent fatigue loading at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). The first blade was a pristine blade, which was manufactured to standard specifications for the CX-100 design. The second blade was manufactured for the University of Massachusetts, Lowell with intentional simulated defects within the fabric layup. Each blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. The blades underwent harmonic excitation at their first natural frequency using the Universal Resonant Excitation (UREX) system at NREL. Blades were initially excited at 25% of their design load, and then with steadily increasing loads until each blade reached failure. Data from the sensors were collected between and during fatigue loading sessions. The data were measured over multi-scale frequency ranges using a variety of acquisition equipment, including off-the-shelf systems and specially designed hardware developed at Los Alamos National Laboratory (LANL). The hardware systems were evaluated for their aptness in data collection for effective application of SHM methods to the blades. The results of this assessment will inform the selection of acquisition hardware and sensor types to be deployed on a CX-100 flight test to be conducted in collaboration with Sandia National Laboratory at the U.S. Department of Agriculture's (USDA) Conservation and Production Research Laboratory (CPRL) in Bushland, Texas.

  5. Blade fatigue life assessment with application to VAWTs

    NASA Astrophysics Data System (ADS)

    Veers, P. S.

    1982-05-01

    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.

  6. Fretting Fatigue of Single Crystal/Polycrystalline Nickel Subjected to Blade/Disk Contact Loading

    NASA Astrophysics Data System (ADS)

    Matlik, J. F.; Murthy, H.; Farris, T. N.

    2002-01-01

    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.

  7. Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Swanson, Gregory R.

    2000-01-01

    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.

  8. Damage tolerance and structural monitoring for wind turbine blades.

    PubMed

    McGugan, M; Pereira, G; Sørensen, B F; Toftegaard, H; Branner, K

    2015-02-28

    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

  9. Modeling Fatigue Damage in Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.

    2009-10-30

    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.

  10. On damage diagnosis for a wind turbine blade using pattern recognition

    NASA Astrophysics Data System (ADS)

    Dervilis, N.; Choi, M.; Taylor, S. G.; Barthorpe, R. J.; Park, G.; Farrar, C. R.; Worden, K.

    2014-03-01

    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.

  11. Fatigue damage prediction for combined random and static mean stresses

    Microsoft Academic Search

    Ronald G. Lambert

    1993-01-01

    Closed form analytical expressions have been derived and are proposed for use to predict accumulated fatigue damage and fatigue life of structural elements subjected to a combination of fully reversed narrow-band Gaussian random and static mean stresses. Such mean stresses can significantly alter fatigue life. The proposed method of combining random alternating and mean stresses shows excellent agreement with published

  12. Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Arakere, N. K.; Swanson, G.

    2002-01-01

    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

  13. Surface Texture of Fretting Fatigue Damaged Shot Peened Titanium

    SciTech Connect

    Martinez, S. A.; Blodgett, M. P. [Air Force Research Laboratory, Wright Patterson Air Force Base, OH 45433 (United States); Sathish, S. [University of Dayton Research Institute, 300 College Park, Dayton, OH 45467-0127 (United States); Mall, S. [Air Force Institute of Technology, Wright Patterson Air Force Base, OH 45433 (United States)

    2006-03-06

    Fretting fatigue damage occurs at the contact between two surfaces, when a static load perpendicular to the interface and a cyclic load parallel to the surfaces are present. The fretting fatigue damage occurring on the surface is known to be responsible for initiation of surface breaking cracks and dramatic reduction of fatigue life of the materials and components. Many premature failures of the engine components of advanced fighter aircrafts have been attributed to the fretting fatigue damage. Though fretting fatigue damage occurs at the surface, NDE techniques have limited success in detecting early stages of damage. This paper presents a methodology based on optical profiling of the surface to evaluate the progression of damage in fretting fatigue damaged specimens of shot peened Ti-6Al-4V. Surface topography measurements performed using a white light interference microscope were analyzed to identify the surface texture parameters sensitive to progressive damage. Results of the relation between the number of fretting fatigue cycles, surface texture parameters, residual stress and the changing microstructure are presented. Potential of the optical surface profiling as a nondestructive evaluation tool for characterization of the fretting fatigue damage is discussed.

  14. Implementation of a Biaxial Resonant Fatigue Test Method on a Large Wind Turbine Blade

    SciTech Connect

    Snowberg, D.; Dana, S.; Hughes, S.; Berling, P.

    2014-09-01

    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.

  15. Fatigue strength and life of compressor blades for marine gas turbine engines

    Microsoft Academic Search

    V. T. Troshchenko; A. V. Prokopenko

    1999-01-01

    An experimental procedure has been developed for the investigation of fatigue and crack growth resistance of materials and\\u000a real compressor blades. Methods for the determination of stress intensity factors in specimens and in blades with cracks have\\u000a been justified. Investigations have been performed on the influence of manufacturing residual stresses and surface defects\\u000a in the form of simulators of dents,

  16. Damage and fatigue described by a fractional derivative model

    NASA Astrophysics Data System (ADS)

    Caputo, Michele; Fabrizio, Mauro

    2015-07-01

    As in [1], damage is associated with fatigue that a material undergoes. In this paper, because we work with viscoelastic solids represented by a fractional model, damage is described by the order of the fractional derivative, which represents the phase field satisfying Ginzburg-Landau equation, which describes the evolution of damage. Finally, in our model, damage is caused, not only by fatigue, but also directly by a source related to environmental factors and described by a positive time function.

  17. Computed speckle decorrelation (CSD) for the study of fatigue damage

    Microsoft Academic Search

    J. Scott Steckenrider; James W. Wagner

    1995-01-01

    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,

  18. Conditioning monitoring by microstructural evaluation of cumulative fatigue damage

    Microsoft Academic Search

    C. Fukuoka; Y. G. Nakagawa; J. J. Lance; R. N. Pangborn

    1996-01-01

    The objective of this work is to evaluate the damage induced below and above the fatigue limit (Delta sigma 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

  19. Conditioning monitoring by microstructural evaluation of cumulative fatigue damage

    Microsoft Academic Search

    C. Fukuoka; Y. G. Nakagawa; J. J. Lance; R. N. Pangborn

    1996-01-01

    The objective of this work is to evaluate the damage induced below and above the fatigue limit (??\\u000a \\u000a t\\u000a =360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate\\u000a by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell\\u000a misorientation

  20. Conditioning monitoring by microstructural evaluation of cumulative fatigue damage

    NASA Astrophysics Data System (ADS)

    Fukuoka, C.; Nakagawa, Y. G.; Lance, J. J.; Pangborn, R. N.

    1996-12-01

    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.

  1. Conditioning monitoring by microstructural evaluation of cumulative fatigue damage

    SciTech Connect

    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

    1996-12-01

    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.

  2. A new method for dual-axis fatigue testing of large wind turbine blades using resonance excitation and spectral loading

    Microsoft Academic Search

    Darris L. White

    2003-01-01

    The demand for cost effective renewable energy sources has resulted in the continual refinement of modern wind turbine designs. These refinements generally result in larger wind turbines and wind turbine blades. In order to reduce maintenance expenses, and improve quality and reliability, each new blade design must be subjected to a high cycle fatigue test. With blades expected to soon

  3. Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine

    NASA Astrophysics Data System (ADS)

    Shanyavskiy, A. A.

    2014-01-01

    In-service Very-High-Cycle-Fatigue (VHCF) regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17 and superalloy GS6K, respectively, was considered. Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades. Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface. This material behavior reflected lifetime limit that was reached by the criterion VHCF. In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet. This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology. In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream. Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations. Recommendations to continue aircrafts airworthiness were made for in-service blades.

  4. Analysis of SNL/MSU/DOE fatigue database trends for wind turbine blade materials.

    SciTech Connect

    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)

    2010-12-01

    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.

  5. AIAA-2003-0692 NEW FATIGUE DATA FOR W IND TURBINE BLADE M ATERIALS

    E-print Network

    1 AIAA-2003-0692 NEW FATIGUE DATA FOR W IND TURBINE BLADE M ATERIALS John F. Mandell, Daniel D to the wind turbine industry in several areas: (a) very high cycle S-N data; (b) refined Goodman Diagram; (c the expected cycle range for turbines. While the data cannot be used directly in design due to the specialized

  6. Fatigue Life Prediction of Single Crystals for Turbine Blade Applications

    Microsoft Academic Search

    Franck Gallerneau; Jean-Louis Chaboche

    1999-01-01

    This paper describes a fatigue life prediction model accounting for high temperature applications of metallic materials. The formulation of the model is for general anisotropy and multiaxiality of loading. This phenomenological model distinguishes between an initiation phase and a propagation phase, and takes into account oxidation and creep effects on fatigue life. An application of the model is given for

  7. Use of the WEST-1 wind turbine simulator to predict blade fatigue load distribution

    SciTech Connect

    Janetzke, D.C.

    1983-01-01

    The WEST-1 wind turbine simulator is an implementation of mathematical models for an aeroelastic horizontal-axis wind turbine rotor using current hybrid electronics technology. High-speed digital and analog circuitry enable the computation of complex dynamic characteristics and performance of a wind turbine in real time. 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.

  8. An experiemental and computational study of the aerodynamics of turbine blades with damage

    Microsoft Academic Search

    Alamgir M. T. Islam

    1999-01-01

    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).

  9. Fatigue strength and evaluation of creep damage during fatigue cycling of Inconel Alloy 625

    SciTech Connect

    Purohit, A.; Thiele, U.; O'Donnell, J.E.

    1983-06-01

    Evaluation of high strain rate and corresponding low strain rate tests indicate no creep-fatigue interaction. For T greater than or equal to 900/sup 0/C, creep damage predominates during the cyclic straining. For tests in which creep damage is largely suppressed - for example in high-frequency reverse bend fatigue tests - the cycles to fatigue failure were found to increase directly with the degree of suppression of creep damage. However, a practical limit exists for suppression of creep damage at 1100/sup 0/C; at that temperature, even for the high frequency reverse bend tests (approx. 1000 rpm with ..sigma.. = 12.3% s/sup -1/), the creep damage predominated over the fatigue damage.

  10. The characterization of widespread fatigue damage in fuselage structure

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Willard, Scott A.; Miller, Matthew

    1994-01-01

    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.

  11. Continuum damage mechanics analysis of fatigue crack initiation

    Microsoft Academic Search

    Baidurya Bhattacharya; Bruce Ellingwood

    1998-01-01

    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

  12. Dynamics and Fatigue Damage of Wind Turbine Rotors

    E-print Network

    6 3 RiS0-Rr512 Dynamics and Fatigue Damage of Wind Turbine Rotors during Steady Operation Peter OF WIND TURBINE ROTORS DURING STEADY OPERATION Peter Hauge Madsen, Sten Frandsen, William E. Holley-carrying capacity of a wind turbine rotor with respect to short-term strength and material fatigue are presented

  13. Damage based fatigue criterion for solders in electronic packaging

    Microsoft Academic Search

    Shengmin Wen

    2005-01-01

    A fatigue failure criterion based on physical damage mechanism is proposed for solders. A solder structure is defined as fatigued when the portion of its failed grains reaches a critical percolation threshold, since under such state the failed grains may form large cluster of cracks, leading to the structure's mechanical instability as well as electrical degradation. Mechanically the inception of

  14. Coupling Between Mesoplasticity and Damage in High-cycle Fatigue

    Microsoft Academic Search

    Laurent Flaceliere; Franck Morel; André Dragon

    2007-01-01

    The multiaxial fatigue loading in the high-cycle regime leads to localized mesoscopic plastic strain that occurs in some preferential directions of individual grains for most metallic materials. Crack initiation modeling is difficult in this fatigue regime because the scale where the mechanisms operate is not the engineering scale (macroscopic scale), and local plasticity and damage act simultaneously. This article describes

  15. Mechanisms of fatigue damage in boron/aluminum composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1980-01-01

    Tensile fatigue tests were conducted on several laminates of boron/aluminum (6061-0). In laminates with 0 deg fibers on the outside, an analysis that identifies "shakedown" conditions predicted the stress amplitude below which no fatigue damage accumulated. A fatigue damage accumulation model which relates matrix fatigue cracking and the overall laminate properties is described. A model for the saturation damage stage development is presented, that identical laminates, tested in directions 90 deg apart (such that one layup has 90 deg outer plies and the other 0 deg), have different fatigue behaviors due to the stacking sequence. The 90 deg plies on the surface develop cracks earlier than predicted by shakedown. An attempt was made to explain this stacking sequence effect. Variable load history effects on the fatigue damage response were investigated. Tests reveal that for a given stress ratio the specimen seeks the saturation damage state for the largest stress range to which it is subjected. It was also found that little damage is generated by shifting a given stress range down, whereas significant damage may be created by shifting it upward. The laminate stresses were always tensile.

  16. Quantitative study of fretting fatigue damage in shot peened titanium-aluminum-vanadium

    NASA Astrophysics Data System (ADS)

    Martinez, Sonia A.

    Fretting fatigue damage has been known to be the origin of premature failure in some of the aerospace engine components. The blade/disk assemblies, for example have been particularly susceptible to fretting induced failure. Several nondestructive evaluation techniques are being used to detect the cracks due to fretting fatigue damage. Although partial success has been achieved in detection of cracks, research is lacking in the area of detection of precursors to the development of cracks due fretting fatigue damage. The goal of the research presented in this thesis is to develop a methodology based on x-ray diffraction residual stress measurements for quantitative nondestructive characterization of accumulated fretting fatigue damage. To achieve the goal a systematic experimental study of the characteristics of the residual stress due to surface treatments of shot peening (SP), Laser Shock Peening (LSP) and Low Plasticity Burnishing (LPB), used in the aerospace industry was conducted. The residual stress in LSP and LPB was found to be complex involving shear stress and spatial non-uniformity. On the other hand in shot peening it was found to be least complex. More over it is the most cost effective and hence often used surface treatment in the industry. In order to gain an understanding of the effect of shot peening parameters on the fretting fatigue life, experiments were conducted on samples with four different peening intensities (0, 4, 7 and 10 A) and two surface coverage (100% and 400%). It was observed that the fretting fatigue life increases with the increasing peening intensity, and increase in surface coverage beyond 100% has virtually no effect. Scanning Electron Microscopic (SEM) observation of fractured surface was utilized to identify crack initiation. On all of the fretting fatigued specimens relaxation of residual stress was observed and it increased with increasing number of cycles. A complete relaxation was observed before failure. To obtain an understanding of the mechanisms leading to the residual stress relaxation samples with varying number of fretting fatigue cycles were prepared and the microstructure of the damaged region was examined using SEM and White Light Intereference Microscopy (WLIM). The SEM images show formation of platelet like structures due to delamination at early stages. On further continuation of fretting the delaminated regions act as stress concentrators and generate micro-cracks. As the fretting fatigue damage is increased the micro-cracks appear to coalesce together to create a large crack to drive the sample to failure.

  17. Drag amplification and fatigue damage in vortex-induced vibrations

    E-print Network

    Jhingran, Vikas Gopal

    2008-01-01

    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 ...

  18. Mean stress and the exhaustion of fatigue-damage resistance

    NASA Technical Reports Server (NTRS)

    Berkovits, Avraham

    1989-01-01

    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.

  19. Fatigue damage analysis of unidirectional metal matrix composites

    Microsoft Academic Search

    Serge Kruch; Nicolas Carrère; Jean-Louis Chaboche

    2006-01-01

    The paper deals with the non-linear analysis of industrial components subjected to strong thermo-mechanical cyclic loads. Two kinds of damages must be taken into account: the first one being a “constitutive damage” which will dominate the low cycle fatigue (LCF) regime and whose evolution law will be coupled to the elasto-viscoplastic model. The second one will be a “classical” fatigue

  20. Microplasticity and fatigue in a damage tolerant niobium aluminide intermetallic

    SciTech Connect

    Soboyejo, W.O.; DiPasquale, J. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering; Srivatsan, T.S. [Univ. of Akron, OH (United States). Dept. of Mechanical Engineering; Konitzer, D. [General Electric Aircraft Engines, Cincinnati, OH (United States)

    1997-12-31

    In this paper, the micromechanisms of microplasticity and fatigue are elucidated for a damage tolerant niobium aluminide intermetallic deformed to failure under both monotonic and cyclic loading. Localized microplasticity is shown to occur by the formation of slip bands at stresses as low as 9% of the bulk yield stress. Formation and presence of slip bands is also observed upon application of the first cycle of fatigue load. The deformation and cracking phenomena are discussed in light of classical fatigue crack initiation and propagation models. The implications of microplasticity are elucidated for both fatigue crack initiation and crack growth.

  1. Nonlinear Laser Ultrasonic Measurements of Localized Fatigue Damage

    NASA Astrophysics Data System (ADS)

    Blackshire, J. L.; Sathish, S.; Na, J.; Frouin, J.

    2003-03-01

    A nonlinear laser ultrasonic system was developed and used to characterize the fatigue state of a fractured Ti-6Al-4V sample with high spatial-resolution and sensitivity. The measurement system is built around a scanning heterodyne interferometer, which allows detailed displacement field images to be created and visualized for propagating surface and bulk acoustic fields on a material surface. An assessment of the local fatigue damage of the material was made using nonlinear ultrasonic interaction principles, where the local amplitudes of the fundamental and second harmonic displacement fields are monitored simultaneously. This provides a means for evaluating the local acoustical nonlinearity parameter, ?, which can be related to the accumulation of fatigue damage in a material. A large increase in ? was observed between the unfatigued area (near the grip section) and the heavily fatigued area (gauge section) for a fractured dogbone specimen. The measurements show the potential for spatially-resolving the local fatigue state of a material using laser ultrasonics.

  2. Wind turbine blade damage detection using an active sensing approach

    NASA Astrophysics Data System (ADS)

    Ruan, Jiabiao; Ho, Siu Chun Michael; Patil, Devendra; Li, Mo; Song, Gangbing

    2014-10-01

    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.

  3. Fatigue damage mechanisms in boron-aluminium composite laminates

    NASA Technical Reports Server (NTRS)

    Dvorak, G. J.; Johnson, W. S.

    1980-01-01

    The relationship between fatigue and shakedown in metal matrix composites is investigated theoretically and experimentally for unidirectional and laminated 6061 Al-B materials. It is shown that no fatigue damage takes place if the applied stress range is such that the material remains elastic, or shakes down, i.e., resumes elastic cyclic straining after a small number of plastic strain cycles. Fatigue damage occurs only in specimens subjected to stress ranges which cause sustained cyclic plastic straining in the aluminum matrix. If the applied stress range is smaller than that required for fatigue failure, after about 10 to the 6th cycles a saturation damage state is reached which remains essentially unchanged with increasing number of cycles.

  4. Model of flexural fatigue damage accumulation for cortical bone.

    PubMed

    Griffin, L V; Gibeling, J C; Martin, R B; Gibson, V A; Stover, S M

    1997-07-01

    Analytical models that predict modulus degradation in cortical bone subjected to uniaxial fatigue loading in tension and compression are presented. On the basis of experimental observations, damage was modeled as self-limiting for tension but not for compression. These mechanistic uniaxial damage models were then developed into a model for flexural fatigue of cortical bone based on laminated beam theory. The unknown coefficients in the uniaxial damage models were obtained by successfully fitting the resulting equations to uniaxial fatigue data from the literature on human cortical bone in tension and compression. Then, the predictions of the flexural model for the behavior of human cortical bone were compared with experimental results from a small but independent set of specimens tested at three different ranges of load in our laboratory. The behavior of the modulus degradation curves and the flexural fatigue lives of the specimens were in excellent agreement with the predictions of the model. PMID:9379272

  5. Role of foreign-object damage on thresholds for high-cycle fatigue in Ti6Al4V

    Microsoft Academic Search

    J. O. Peters; B. L. Boyce; A. W. Thompson; R. O. Ritchie; O. Roder

    2000-01-01

    The increasing incidence of military aircraft engine failures that can be traced to high-cycle fatigue (HCF) has prompted\\u000a a reassessment of the design methodologies for HCF-critical components, such as turbine blades and disks. Because of the high-frequency\\u000a vibratory loading involved, damagetolerant design methodologies based on a threshold for no crack growth offer a preferred\\u000a approach. As impact damage from ingested

  6. Root damage analysis of aircraft engine blade subject to ice impact

    NASA Technical Reports Server (NTRS)

    Reddy, E. S.; Abumeri, G. H.; Chamis, C. C.; Murthy, P. L. N.

    1992-01-01

    The blade root response due to ice impact on an engine blade is simulated using the NASA in-house code BLASIM. The ice piece is modeled as an equivalent spherical object impacting on the leading edge of the blade and has the velocity opposite to that of the aircraft with direction parallel to the engine axis. The effect of ice impact is considered to be an impulse load on the blade with its amplitude computed based on the momentum transfer principle. The blade response due to the impact is carried out by modal superposition using the first three modes. The maximum dynamic stresses at the blade root are computed at the quarter cycle of the first natural frequency. A combined stress failure function based on modified distortion energy is used to study the spanwise bending damage response at the blade root. That damage function reaches maximum value for very low ice speeds and increases steeply with increases in engine speed.

  7. Deformation and fatigue behavior of SSME turbopump blade materials

    NASA Technical Reports Server (NTRS)

    Milligan, Walter W.; Antolovich, Stephen D.

    1987-01-01

    Directionally solidified and single crystal superalloys which are intended for use as turbopump blade materials are anisotropic both elastically and plastically. Therefore, isotropic constitutive models must be modified. Several models which are now being developed are based on metallurgical theories of deformation in these types of alloys. However, these theories have not been fully justified, and the temperature and strain regimes over which they may be valid are poorly defined. The objective of this work is to study the deformation behavior of the alloys, in order to determine the validity of these models and to thereby support the ongoing research efforts in solid mechanics.

  8. FATIGUE BEHAVIOR OF IMPACT DAMAGED PRESTRESSED CONCRETE BRIDGE GIRDER REPAIRED

    E-print Network

    as an alternative to traditional strengthening techniques (external post-tensioning and externally bonded steelFATIGUE BEHAVIOR OF IMPACT DAMAGED PRESTRESSED CONCRETE BRIDGE GIRDER REPAIRED WITH CFRP SHEETS Abstract Replacement of damaged prestressed concrete bridge girders due to accidental impact by overheight

  9. Sequential law in multiaxial fatigue, a new damage indicator

    Microsoft Academic Search

    G. Mesmacque; S. Garcia; A. Amrouche; C. Rubio-Gonzalez

    2005-01-01

    One of the largest difficulties in fatigue damage is to find a representative ‘Damage indicator’ which can be easily connected with the Wöhler curve taken as known data of the material. The most used model is the Miner's rule but this does not take into account the loading history, so for the same loading level the experimental results are higher

  10. Experimental and theoretical studies for fatigue damage of short fiber reinforced metal

    Microsoft Academic Search

    Wei Shen; Dongning Chu; Lihua Peng; Jiachi Xu

    1995-01-01

    The fatigue damage variable D which is defined by the post-fatigue strain (PFFS) is introduced to study the overall damage-failure process of metal matrix composite (MMC) under cyclic loading. A fatigue damage evolution derived by means of the definition of fatigue damage and used to predict the fatigue life is presented in this paper.In addition, information on the crack propagation,

  11. Multiaxial and thermomechanical fatigue considerations in damage tolerant design

    NASA Technical Reports Server (NTRS)

    Leese, G. E.; Bill, R. C.

    1985-01-01

    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.

  12. Monitoring Fatigue Damage Accumulation with Rayleigh Wave Harmonic Generation Measurements

    NASA Astrophysics Data System (ADS)

    Barnard, D. J.; Brasche, L. J. H.; Raulerson, D.; Degtyar, A. D.

    2003-03-01

    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.

  13. Plasticity-damage based micromechanical modelling in high cycle fatigue

    NASA Astrophysics Data System (ADS)

    Monchiet, Vincent; Charkaluk, Eric; Kondo, Djimedo

    2006-02-01

    A micro-macro approach of multiaxial fatigue in unlimited endurance is proposed. It allows one to take into account plasticity and damage mechanisms which occur at the scale of Persistent Slip Bands (PSB). The proposed macroscopic fatigue criterion, which corresponds to microcracks nucleation at the PSB-matrix interface, is derived for different homogenization schemes (Sachs, Lin-Taylor and Kröner). The role of a mean stress and of the hydrostatic pressure in high cycle fatigue is shown; in particular, in the case of Lin-Taylor scheme and linear isotropic hardening rule at microscale, one recovers the linear dependance in pressure postulated by K. Dang Van for the macroscopic fatigue criterion. This dependence is related here to the damage micro-mechanism. Finally, the particular case of affine loading is presented as an illustration. To cite this article: V. Monchiet et al., C. R. Mecanique 334 (2006).

  14. Nondestructive Evaluation of Fiberglass Reinforced Plastic Subjected to Combined Localized Heat Damage and Fatigue Damage Using Acoustic Emission

    Microsoft Academic Search

    H. Nayeb-Hashemi; P. Kasomino; Nader Saniei

    1999-01-01

    The effect of fatigue damage to unidirectional fiberglass composite specimens with prior contact heat damage was investigated. After damaging the specimens by contacting them to a hot tip at 360°C, the specimens were subjected to fatigue loading at cyclic stress amplitude corresponding to 65% of the specimens' ultimate tensile strength. The fatigue experiments was halted after 3,000 cycles. The specimens

  15. Reduction in fiber damage thresholds due to static fatigue

    NASA Astrophysics Data System (ADS)

    Setchell, R. E.

    1995-01-01

    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.

  16. On the application of the KitagawaTakahashi diagram to foreign-object damage and high-cycle fatigue

    E-print Network

    Hutchinson, John W.

    the fatigue strength of fan and compressor blades, principally by causing stress-raising notches [5 for evaluating the detrimental effect of FOD on HCF failures in Ti­ 6Al­4V blade alloys. Ó 2002 Elsevier Science High-cycle fatigue (HCF) of turbine engine disk and blade components represents one of the major

  17. Fatigue damage assessment of various welded joints under uniaxial loading based on energy methods

    Microsoft Academic Search

    F. Pakandam; A. Varvani-Farahani

    2011-01-01

    The present study intends to evaluate fatigue damage of different welded joints under uniaxial loading condition and its response on fatigue lifetime. The main variables influencing the fatigue life of a welded joint are: applied stress amplitude, material properties, geometrical stress concentration factor. Energy approaches were employed to evaluate the fatigue damage of various weld joints under uniaxial loading conditions.

  18. Meinhard Kuna Andreas Ricoeur of Fatigue, Damage

    E-print Network

    Qin, Qinghua

    Banks-Sills and Yael Motola What Do We Know About Surface Charges on Cracks in Ferroelectric Ceramics-particle Ferroelectric Ceramics .............. 67 Li Yu, Shouwen Yu, and Dietmar Gross xi #12;xii Contents and Poling on Fatigue Behavior of PZT Ceramics with Single-Edge Crack by Three-Point Bending

  19. Active sensing of fatigue damage using embedded ultrasonics

    NASA Astrophysics Data System (ADS)

    Zagrai, Andrei; Kruse, Walter A.; Gigineishvili, Vlasi

    2009-03-01

    Embedded ultrasonics has demonstrated considerable utility in structural health monitoring of aeronautical vehicle. This active sensing approach has been widely used to detect and monitor cracks, delaminations, and disbonds in a broad spectrum of metallic and composite structures. However, application of the embedded ultrasonics for active sensing of incipient damage before fracture has received limited attention. The aim of this study was to investigate the suitability of embedded ultrasonics and nonlinear acoustic signatures for monitoring pre-crack fatigue damage in aerospace structural material. A harmonic load was applied to structural specimens in order to induce fatigue damage accumulation and growth. Specimens of simple geometry were considered and piezoelectric active sensors were employed for generation and reception of elastic waves. The elastic wave signatures were analyzed in the frequency domain using nonlinear impedance and nonlinear resonance methods. A relationship between fatigue severity and linear as well as nonlinear acoustic signatures was investigated and considered in the damage classification procedure. Practical aspects of the active sensing of the fatigue damage before fracture were discussed and prospective avenues for future research were suggested.

  20. ADVANCED COMPOSITE; WIND TURBINE BLADE DESIGN BASED ON DURABILITY AND DAMAGE TOLERANCE

    Microsoft Academic Search

    Galib Abumeri; Frank Abdi

    2012-01-01

    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

  1. QUANTITATIVE DAMAGE ASSESSMENT OF HYBRID COMPOSITE WIND TURBINE BLADES BY ENERGY BASED ACOUSTIC EMISSION SOURCE

    E-print Network

    Boyer, Edmond

    QUANTITATIVE DAMAGE ASSESSMENT OF HYBRID COMPOSITE WIND TURBINE BLADES BY ENERGY BASED ACOUSTIC of safety [3]. The wind turbine blades usually use several composite materials such as glass fiber ourself with energy contour mapping concept. Firstly, we acquired energy based contour map database

  2. Early detection of fatigue damage in composite materials

    NASA Technical Reports Server (NTRS)

    Salkind, M. J.

    1975-01-01

    Early detection of fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for glass/epoxy, graphite/glass/epoxy, and graphite/epoxy composites. Modulus and temperature were monitored and a correlation between them observed. Axial modulus and torsional modulus changes were a function of the laminate orientation. Torsional modulus measurements and coin tap tests were performed at 0, 1 million, 5 million, and 10 million cycles, on axial fatigue specimens. Three distinct regions were noted. In the primary region a small but rapid change in stiffness was noted in the first few thousand cycles. This was followed by a secondary region of little or no stiffness change. The tertiary region was characterized by an increasing rate of stiffness change leading to fracture. NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-ray radiography were evaluated for fatigue damage detection.

  3. A Fatigue Damage Parameter for Life Assessment of Off-axis Unidirectional GRP Composites

    Microsoft Academic Search

    A. Varvani-Farahani; H. Haftchenari; M. Panbechi

    2006-01-01

    The present study develops a fatigue damage parameter to assess the fatigue damage of unidirectional glass fiber reinforced plastic (GRP) composites. The proposed parameter is based on the physics and the mechanism of fatigue cracking within three damage regions of matrix (I), fiber-matrix interface (II), and fiber (III) in these materials as the number of cycles progresses. In region I,

  4. Fatigue of foam core sandwich beams—2: effect of initial damage

    Microsoft Academic Search

    M. Burman; D. Zenkert

    1997-01-01

    This paper addresses the influence of sub-surface core damage in sandwich beams subjected to fatigue loading. Using results from static and fatigue tests of undamaged beams a model for the prediction of the fatigue life of damaged beams are proposed. Sandwich beams subjected to transverse loading inducing a shear stress field in the core material with two typical sub-surface damages,

  5. EXPERIMENTAL INVESTIGATION OF FATIGUE DAMAGE IN COMPOSITE STRUCTURES CONSIDERING SECOND HARMONIC LAMB WAVES

    E-print Network

    Paris-Sud XI, Université de

    EXPERIMENTAL INVESTIGATION OF FATIGUE DAMAGE IN COMPOSITE STRUCTURES CONSIDERING SECOND HARMONIC parameter is an appropriate tool to detect micro-structural damages like plasticity and fatigue in metal as well as thermal fatigue and impact damages in composites. In this work the second harmonic generation

  6. High-frequency, high-temperature fretting-fatigue experiments

    Microsoft Academic Search

    J. F. Matlik; T. N. Farris; F. K. Haake; G. R. Swanson; G. C. Duke

    2006-01-01

    Fretting fatigue is a structural damage mechanism observed when two contacting bodies are subjected to an oscillatory loading. A critical location for fretting fatigue 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 associated with such turbomachinery components can accelerate the fretting fatigue damage

  7. Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates

    NASA Technical Reports Server (NTRS)

    Johnson, W. Steven; Rhymer, Donald W.; St.Clair, Terry L. (Technical Monitor)

    2000-01-01

    Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350 F, 177 C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the "advanced" HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension-tension (R = 0.1) and tension-compression (R=-0.2). The advanced HTCL under did not demonstrate a significant improvement in fatigue life, in either tension-tension or tension-compression loading. However, the advanced HTCL proved much more damage tolerant. The R = 0.1 tests revealed the advanced HTCL to increase the fatigue life following initial titanium ply damage up to 10X that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue (R = -0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.

  8. A study of cyclic fatigue, damage initiation, damage propagation, and fracture of welded titanium alloy plate

    Microsoft Academic Search

    T. S. Srivatsan; U. Bathini; A. Patnaik; T. Quick

    2010-01-01

    In this paper, the influence of test specimen orientation and microstructure on cyclic stress-amplitude controlled fatigue response, damage initiation, damage propagation and fracture behavior of samples taken from a welded plate of titanium alloy is presented and discussed. Test specimens from the chosen alloy were prepared from an as-welded plate of the material with the stress axis both parallel (longitudinal)

  9. Investigation of Spur Gear Fatigue Damage Using Wear Debris

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Morales, Wilfredo; Afjeh, Abdollah A.

    2003-01-01

    A new diagnostic tool for detecting and assess- ing su$ace fatigue damage to spur gears was developed. This diagnostic tool was evaluated by analyzing metallic oil wear debris generated during fatigue tests that were performed using a spur gearbox rig. During each test, readings from an on-line oil debris sensor were monitored and recorded for assessment of gear pitting damage. The debris measured by the oil debris sensor was used to identify "membership functions" to build a simple fuzzy logic model. Using fuzzy logic techniques on the oil debris data, threshold limits were defined that discriminated between different stages of pitting wear. Results showed that oil wear debris data combined with fuzzy logic analysis techniques was a good predictor of pitting damage on spur gears.

  10. Reduction in fiber damage thresholds due to static fatigue

    NASA Astrophysics Data System (ADS)

    Setchell, Robert E.

    1995-07-01

    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.

  11. Inspecting for widespread fatigue damage: Is partial debonding the key?

    NASA Technical Reports Server (NTRS)

    Brewer, John

    1994-01-01

    Experimental and analytical results indicate that cracks can initiate, grow, and coalesce more rapidly in fuselage lap joints that have experienced partial or complete debonding. Computational analysis in this paper shows that stress concentrations and stress intensity factors at the rivet holes are far less severe when the bond is intact. Debonding hastens the initiation of widespread fatigue cracks and significantly increases crack growth rate. Thus, debonded regions serve as "breeding grounds" for widespread fatigue damage. Therefore, the effectiveness of lap joint inspection programs may be enhanced if detailed inspections are focused on areas in which debonding has been detected.

  12. Analysis of Fretting Fatigue Strength of Integral Shroud Blade for Steam Turbine

    Microsoft Academic Search

    Yasutomo Kaneko; Masayuki Tomii; Hiroharu Ohyama; Takayuki Kurimura

    2008-01-01

    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

  13. Modeling of fatigue behavior and damage tolerance\\/durability in fiber metal laminates

    Microsoft Academic Search

    Po-Yu Chang

    2008-01-01

    This dissertation presents the investigation into the fatigue behavior and damage tolerance of fiber metal laminates-S2-glass fiber reinforced aluminum laminates (Glare). Glare laminates exhibit excellent fatigue resistant behavior and damage tolerance based on the experimental work. Methodologies are established to predict the crack initiation life, crack path angle, crack growth rate under constant-amplitude and block-spectrum fatigue loading. The multiple-site-fatigue damage

  14. Detect, troubleshoot gas-turbine blade failures

    SciTech Connect

    Meher-Homji, C.B. [Boyce Engineering International Inc., Houston, TX (United States)

    1995-12-01

    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.

  15. Lamb Wave Assessment of Fatigue and Thermal Damage in Composites

    NASA Technical Reports Server (NTRS)

    Seale, Michael D.; Smith, Barry T.; Prosser, W. H.

    2004-01-01

    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.

  16. A damage model for estimating low cycle fatigue lives under nonproportional multiaxial loading

    Microsoft Academic Search

    Takamoto Itoh; Toshiki Miyazaki

    2003-01-01

    This paper develops a damage model for the evaluation of low cycle fatigue lives under complex cyclic multiaxial loadings. One of the authors has proposed the equivalent strain parameter for the life prediction of the nonproportional low cycle fatigue. This strain parameter can evaluate the dependence of fatigue lives on strain history and material, and correlates the fatigue lives within

  17. Analysis of widespread fatigue damage in structural joints

    SciTech Connect

    Farris, T.N.; Grandt, A.F. Jr.; Harish, G.; Wang, H.L. [Purdue Univ., West Lafayette, IN (United States)

    1996-12-31

    This paper reviews basic research being conducted to determine the onset of widespread fatigue damage found on structural members in aging aircraft. Fretting fatigue studies are being conducted to predict the onset of small cracks at fastener holes or other structural members with contacting surfaces. Experiments and analysis are directed at determining the effect of various parameters such as magnitude of tangential and normal forces transferred, interface friction and rivet patterns on the local contact stresses. Multiaxial fatigue theory then relates the localized stress state to nucleation life. Once regions of multiple site damage (MSD) have formed by fretting (or other sources of cracking), the next goal is to determine the consequences of such MSD on the fatigue life and residual strength of the joint. An elastic model is employed to determine load transfer at various fastener locations in the joint. The analysis accounts for panel thicknesses, fastener patterns and effects of fastener hole cracking on load transfer. A fracture mechanics analysis then incorporates this information to compute the growth, coalescence, and final fracture of MSD in lap joint configurations. Comparisons between analysis and experimental results are provided in the paper.

  18. Thermal fatigue damage of Cu-Cr-Zr alloys

    NASA Astrophysics Data System (ADS)

    Chatterjee, Arya; Mitra, R.; Chakraborty, A. K.; Rotti, C.; Ray, K. K.

    2013-11-01

    The primary aim of this investigation is to examine thermal fatigue damage (TFD) in Cu-Cr-Zr alloys used in High Heat Flux components of Tokamak and its subsystems. Thermal fatigue experiments have been carried out between 290 °C and 30 °C, which is analogous to the condition of service application on two Cu-Cr-Zr alloys having different aging treatments. The extents of TFD have been examined by standard measurements of electrical conductivity, lattice strain, residual stress and dynamic elastic modulus, supplemented by characterizations of microstructure and determination of hardness and tensile properties. The results lead to infer that the relative amounts of damage are different in the two alloys which are further dependent on their aging conditions; the reasons for the observed difference have been explained. The operative mechanisms of TFD are revealed to be as formation and subsequent coalescence of microvoids, and/or initiation and growth of microcracks.

  19. A stress invariant based criterion to estimate fatigue damage under multiaxial loading

    Microsoft Academic Search

    A. Cristofori; L. Susmel; R. Tovo

    2008-01-01

    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

  20. Nonlinear ultrasonics for in situ damage detection during high frequency fatigue

    Microsoft Academic Search

    Anish Kumar; Christopher J. Torbet; J. Wayne Jones; Tresa M. Pollock

    2009-01-01

    In this paper, we report the use of the feedback signal of an ultrasonic fatigue system to dynamically deduce fatigue damage accumulation via changes in the nonlinear ultrasonic parameter. The applicability of this parameter in comparison to the resonant frequency for assessment of fatigue damage accumulation in a wrought aluminum alloy has been demonstrated, without the need for coupling fluids

  1. Use of atomic force microscopy for characterizing damage evolution during fatigue

    Microsoft Academic Search

    Laurent Cretegny

    2000-01-01

    A study of the development of surface fatigue damage in PH 13-8 Mo stainless steel and copper by atomic force microscopy (AFM) was performed. AFM observations allow highly automated, quantitative characterization of surface deformation with a resolution of 5 nm or better, which is ideal for understanding fatigue damage evolution. A secondary objective was to establish a correlation between fatigue

  2. Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis

    E-print Network

    Victoria, University of

    Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite experienced in candi- date Canadian wind turbine deployment locations. The thesis then narrows its focus simulate boundary conditions, applied loading and thermal stresses for a 1.5 MW wind turbine. It is shown

  3. Fatigue and damage tolerance evaluation of an aircraft spoiler

    NASA Astrophysics Data System (ADS)

    Hurlebaus, Stefan; Gaul, Lothar

    2005-05-01

    The spoilers on an aircraft are responsible for several tasks, including execution of roll maneuvers, lift dumping (aerodynamic "spoiling"), and braking. The examined spoiler is manufactured from carbon fiber reinforced composite material and is attached to the wing by four bearing hinges and one actuator hinge. Correct spoiler design involves knowledge of the loads acting on the spoiler, calculation of stresses and strains, and examination of possible failures. Additionally, the fatigue and damage tolerance evaluation of such a spoiler has to follow established certification protocols. This study defines a load cycle based on in-service loadings, including aerodynamic loading, wing bending, inertial loading, and actuator loading. A finite element model of the spoiler is used to calculate the reaction forces in the hinges and the strain in the carbon fiber components occurring during the load cycle. The Miner Rule is used to calculate the fatigue life of the hinges based on the computed stress. A damage tolerance evaluation is then performed assuming that different hinges have failed. Finally, a certification test for fatigue and damage tolerance evaluation of a spoiler is discussed.

  4. Blasim: A computational tool to assess ice impact damage on engine blades

    NASA Astrophysics Data System (ADS)

    Reddy, E. S.; Abumeri, G. H.; Chamis, C. C.

    1993-04-01

    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.

  5. Composite Wind Turbine Blade Effects of Defects: Part B--Progressive Damage Modeling of Fiberglass/Epoxy

    E-print Network

    Composite Wind Turbine Blade Effects of Defects: Part B-- Progressive Damage Modeling of Fiberglass for the reliability of modern composite wind turbine blades. The DOE has sponsored a comprehensive study to a wind turbine blade reliability infrastructure. To support this development of a reliability

  6. Damage detection method for wind turbine blades based on dynamics analysis and mode shape difference curvature information

    NASA Astrophysics Data System (ADS)

    Wang, Yanfeng; Liang, Ming; Xiang, Jiawei

    2014-10-01

    Blades are among the key components of wind turbines. Blade damage is one of the most common types of structural defects and can cause catastrophic structural failure. Therefore, it is highly desirable to detect and diagnose blade damage as early as possible. In this paper, we propose a method for blade damage detection and diagnosis. This method incorporates finite element method (FEM) for dynamics analysis (modal analysis and response analysis) and the mode shape difference curvature (MSDC) information for damage detection/diagnosis. Finite element models of wind turbine blades have been built and modified via frequency comparison with experimental data and the formula for the model updating technique. Our numerical simulation results have demonstrated that the proposed technique can detect the spatial locations of damages for wind turbine blades. Changes in natural frequencies and modes for smaller size blades with damage are found to occur at lower frequencies and lower modes than in the larger sized blade case. The relationship between modal parameters and damage information (location, size) is very complicated especially for larger size blades. Moreover, structure and dynamic characters for larger size blades are different from those for smaller sized blades. Therefore, dynamic response analysis for a larger sized wind turbine blade with a multi-layer composite material based on aerodynamic loads’ (including lift forces and drag forces) calculation has been carried out and improved the efficiency and precision to damage detection by combining (MSDC) information. This method provides a low cost and efficient non-destructive tool for wind turbine blade condition monitoring.

  7. Fatigue damage evaluation of a high pressure tube steel using cyclic strain energy density

    Microsoft Academic Search

    S. K. Koh

    2002-01-01

    In order to evaluate the fatigue damage of a high pressure tube steel, strain-controlled fatigue tests using uniaxial specimens were performed. Based on fatigue test results from different strain ratios of ?2, ?1, 0, 0.5, 0.75, the fatigue damage of the tube steel was represented by using a cyclic strain energy density. The high pressure tube steel exhibited cyclic softening

  8. Damage mechanics characterization on fatigue behavior of a solder joint material

    SciTech Connect

    Chow, C.L.; Yang, F. [Univ. of Michigan, Dearborn, MI (United States). Dept. of Mechanical Engineering; Fang, H.E. [Sandia National Labs., Albuquerque, NM (United States). Computational Physics Dept.

    1998-08-01

    This paper presents the first part of a comprehensive mechanics approach capable of predicting the integrity and reliability of solder joint material under fatigue loading without viscoplastic damage considerations. A separate report will be made to present a comprehensive damage model describing life prediction of the solder material under thermomechanical fatigue loading. The method is based on a theory of damage mechanics which makes possible a macroscopic description of the successive material deterioration caused by the presence of microcracks/voids in engineering materials. A damage mechanics model based on the thermodynamic theory of irreversible processes with internal state variables is proposed and used to provide a unified approach in characterizing the cyclic behavior of a typical solder material. With the introduction of a damage effect tensor, the constitutive equations are derived to enable the formulation of a fatigue damage dissipative potential function and a fatigue damage criterion. The fatigue evolution is subsequently developed based on the hypothesis that the overall damage is induced by the accumulation of fatigue and plastic damage. This damage mechanics approach offers a systematic and versatile means that is effective in modeling the entire process of material failure ranging from damage initiation and propagation leading eventually to macro-crack initiation and growth. As the model takes into account the load history effect and the interaction between plasticity damage and fatigue damage, with the aid of a modified general purpose finite element program, the method can readily be applied to estimate the fatigue life of solder joints under different loading conditions.

  9. The impact of surface integrity by hard turning vs. grinding on fatigue damage mechanisms in rolling contact

    Microsoft Academic Search

    Y. B. Guo; A. W. Warren

    2008-01-01

    The fundamental knowledge of fatigue damage mechanism is necessary for understanding manufacturing process effects. The traditional method of artificially created surface defects may accelerate crack propagation and fatigue. However, the artificial defects will change the surface integrity and therefore alter the nature of fatigue damage, and thus, the fatigue damage in the presence of artificial defects in literature may not

  10. Assessment of material fatigue damage using nonlinear vibro-modulation technique

    Microsoft Academic Search

    Andrei Zagrai; Dimitri Donskoy; Alexander Chudnovsky; Hudson Wu

    2001-01-01

    Heavy periodic loads exerted on structural materials often lead to fatigue damage (material degradation at microscale) which may finally trigger irreversible fracture process. Conventional NDT techniques detect only the latter, and there is an increasing need for new tools to assess fatigue damage at the earliest possible stage, i.e., before fracture. This paper presents experimental results of early damage characterization

  11. TEMPORAL INFORMATION OF LINEAR AND NONLINEAR LAMB WAVES FOR FATIGUE DAMAGE LOCALIZATION: ANALYSIS AND SYNTHESIS

    E-print Network

    Boyer, Edmond

    widely applied to locate gross damage in plate structures, which may greatly facilitate the localization Lamb waves for fatigue damage characterization are compared. Case studies are conducted on aluminum fatigue damage in various conditions, enhancing the adaptivity of structural health monitoring for real

  12. Fatigue damage model for injection-molded short glass fibre reinforced thermoplastics

    Microsoft Academic Search

    H. Nouri; F. Meraghni; P. Lory

    2009-01-01

    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

  13. REAL-TIME FATIGUE DAMAGE MONITORING VIA IN SITU ULTRASONIC SENSING

    Microsoft Academic Search

    Shalabh Guptayand; Asok Rayz

    Estimation of structural damage and quantification of structural integrity are crit- ical for safe and reliable operation of human-engineered complex systems. Fatigue damage is one of the most commonly encountered sources of structural degradation in mechanical systems. Detection of incipient fatigue damage is essential for averting widespread crack growth that leads to catastrophic failures. This chapter presents online in situ

  14. The effect of yield strength and ductility to fatigue damage

    NASA Technical Reports Server (NTRS)

    Yeh, H. Y.

    1973-01-01

    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.

  15. Damage assessment in CFRP laminates exposed to impact fatigue loading

    NASA Astrophysics Data System (ADS)

    Tsigkourakos, George; Silberschmidt, Vadim V.; Ashcroft, I. A.

    2011-07-01

    Demand for advanced engineering composites in the aerospace industry is increasing continuously. Lately, carbon fibre reinforced polymers (CFRPs) became one of the most important structural materials in the industry due to a combination of characteristics such as: excellent stiffness, high strength-to-weight ratio, and ease of manufacture according to application. In service, aerospace composite components and structures are exposed to various transient loads, some of which can propagate in them as cyclic impacts. A typical example is an effect of the wind gusts during flight. This type of loading is known as impact fatigue (IF); it is a repetition of low-energy impacts. Such loads can cause various types of damage in composites: fibre breaking, transverse matrix cracking, de-bonding between fibres and matrix and delamination resulting in reduction of residual stiffness and loss of functionality. Furthermore, this damage is often sub-surface, which reinforces the need for more regular inspection. The effects of IF are of major importance due its detrimental effect on the structural integrity of components that can be generated after relatively few impacts at low force levels compared to those in a standard fatigue regime. This study utilises an innovative testing system with the capability of subjecting specimens to a series of repetitive impacts. The primary subject of this paper is to assess the damaging effect of IF on the behaviour of drilled CFRP specimens, exposed to such loading. A detailed damage analysis is implemented utilising an X-ray micro computed tomography system. The main findings suggested that at early stages of life damage is governed by o degree splits along the length of the specimens resulting in a 20% reduction of stiffness. The final failure damage scenario indicated that transverse crasks in the 90 degree plies are the main reason for complete delamination which can be translated to a 50% stiffness reduction.

  16. An energy-based fatigue damage parameter for off-axis unidirectional FRP composites

    Microsoft Academic Search

    A. Varvani-Farahani; H. Haftchenari; M. Panbechi

    2007-01-01

    An energy-based fatigue damage parameter has been developed to assess the fatigue damage of unidirectional glass-reinforced plastic (GRP) and carbon-fiber reinforced plastic (CFRP) composites. The proposed parameter is based on the physics and the mechanism of fatigue cracking within three damage regions of matrix (I), fiber–matrix interface (II), and fiber (III) in these materials as the number of cycles progresses.

  17. Effect of loading parameters on the fatigue behavior of impact damaged composite laminates

    Microsoft Academic Search

    Milan Mitrovic; H. Thomas Hahn; Greg P. Carman; Peter Shyprykevich

    1999-01-01

    The long-term mechanical fatigue of AS4\\/3501-6 graphite\\/epoxy quasi-isotropic laminates has been investigated to determine the influence of loading parameters on impact-induced delamination growth during constant amplitude, block, and spectrum fatigue loading. From the observed fatigue damage growth it is suggested that conservative damage tolerance criteria in the presence of barely visible impact damage should be based on static loading tests

  18. Fatigue damage of APC2 composite assessed from material degradation and non-destructive evaluation data

    Microsoft Academic Search

    Sp. G Pantelakis; Em. Ch Kyriakakis

    1999-01-01

    Quasi-isotropic 45° APC-2 specimens are fatigued under constant amplitude stress reversal load condition. Fatigue induced degradation of the mechanical properties is correlated to data obtained from non-destructive evaluation. C-scan readings were used to define a generic damage severity factor D. It refers to the current fatigue damage state and accounts for the varying severity of damage at the different specimen

  19. Online fatigue damage monitoring by ultrasonic measurements: A symbolic dynamics approach

    Microsoft Academic Search

    Shalabh Gupta; Asok Ray; Eric Keller

    2007-01-01

    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

  20. Model-Trained Neural Networks and Electronic Holography Demonstrated to Detect Damage in Blades

    NASA Technical Reports Server (NTRS)

    Decker, Arthur J.; Fite, E. Brian; Mehmed, Oral; Thorp, Scott A.

    1998-01-01

    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.

  1. Prediction of sand particle trajectories and sand erosion damage on helicopter rotor blades

    NASA Astrophysics Data System (ADS)

    Shin, Bong Gun

    Therefore, in this dissertation, accurate and time-efficient methodologies were developed for performing sand particle tracking and predicting sand erosion damage on actual helicopter rotor blades under realistic hover and vertical lift conditions. In this dissertation, first, injection (release) conditions of solid particles with new injection parameter, sand particle mass flow rate (SPmFR), were specified to deal with the effect of non-uniform and unsteady flow conditions surrounding at each injection point from which solid particles are released. The SPmFR defines the number of solid particles released from the same injection position per unit time. Secondly, a general definition of erosion rate, "mass or volume loss from the metal surface due to the impact of a unit "mass" of solid particles" was also modified by multiplying with SPmFR in order to solve the limitation for predicting erosion damage on actual helicopter rotor blade. Next, a suitable empirical particle rebound model and an erosion damage model for spherical sand particles with diameters ranging from 10 microm to 500 microm impacting on the material Ti-6A1-4V, the material of helicopter rotor blade, were developed. Finally, C++ language based codes in the form of User Defined Functions (UDFs) were developed and implemented into the commercially available multi-dimensional viscous flow solver ANSYS-FLUENT in order to develop and integrate with the general purpose flow solver, ANSYS-FLUENT, for a specific Lagrangian particle trajectory computing algorithm and rebound and erosion quantification purposes. In the erosion simulation, a reasonably accurate fluid flow solution is necessary. In order to validate the numerical results obtained in this dissertation, computations for flow-only around 2D RAE2822 airfoil and 3D rotating rotor blade (NACA0012) without any sand particle were performed. In the comparison of these results with experimental results, it is found that the flow solutions are in good agreement with the experimental data. Next, second computational validation for flow around the SC1095 airfoil for various turbulence models were performed in order to select a suitable turbulence model. These results concluded that numerical results with k -- o SST model have a reasonably best accuracy. Relative inflow conditions to the blade section of helicopter rotor blades are highly dependent upon rotor blade geometric conditions and helicopter rotor operational conditions. Therefore, in this dissertation, 3D erosion simulations for four different rotating blades with uniform airfoil profile (SC1095) were performed in order to understand the details of erosion mechanism. These results indicate that erosion patterns including maximum erosion rate position and the extent of erosion damaged area on the blade section were highly dependent upon a spanwise twist distribution. It is found that the magnitude of erosion damage on the blade section is affected by not a spanwise twist but a swept tip. Next, in this dissertation, UH-60A helicopter rotor blades rotating in the computational domain for various collective pitch angles and climb velocities were simulated. These results indicate that overall erosion characteristics for helicopter rotor blades can be considered to be not dependent upon these operational parameters though there is a little difference in the magnitude of erosion damage and the maximum erosion rate position. These results concluded that a hover condition can be chosen as a reference operational condition for predicting erosion characteristics or for investigating erosion reduction methods. The final phase of this research is a generalization for particle trajectories and erosion characteristics on 3D helicopter rotor blades in order to reduce very expensive erosion computational cost. The generalized results show that aerodynamic and erosion characteristics for a 3D rotor blade can be predicted by using the 2D airfoil results for corresponding relative inflow angle of attack with coefficient for inflow velocity magnitude and

  2. Time-dependent damage in predictions of fatigue behaviour of normal and healing ligaments

    NASA Astrophysics Data System (ADS)

    Thornton, Gail M.; Bailey, Soraya J.; Schwab, Timothy D.

    2015-06-01

    Ligaments are dense fibrous tissues that connect bones across a joint and are exposed daily to creep and fatigue loading. Ligaments are tensile load-bearing tissues; therefore, fatigue loading will have a component of time-dependent damage from the non-zero mean stress and cycle-dependent damage from the oscillating stress. If time-dependent damage is not sufficient to completely predict the fatigue response, then cycle-dependent damage could be an important contributor. Using data from normal ligaments (current study and Thornton et al., Clin. Biomech. 22:932-940, 2007a) and healing ligaments (Thornton and Bailey, J. Biomech. Eng. 135:091004-1-091004-6, 2013), creep data was used to predict the fatigue response considering time-dependent damage. Relationships between creep lifetime and test stress or initial strain were modelled using exponential or power-law regression. In order to predict fatigue lifetimes, constant rates of damage were assumed and time-varying stresses were introduced into the expressions for time-dependent damage from creep. Then, the predictions of fatigue lifetime were compared with curvefits to the fatigue data where exponential or power-law regressions were used to determine the relationship between fatigue lifetime and test stress or initial strain. The fatigue prediction based on time-dependent damage alone greatly overestimated fatigue lifetime suggesting that time-dependent damage alone cannot account for all of the damage accumulated during fatigue and that cycle-dependent damage has an important role. At lower stress and strain, time-dependent damage was a greater relative contributor for normal ligaments than healing ligaments; however, cycle-dependent damage was a greater relative contributor with incremental increases in stress or strain for normal ligaments than healing ligaments.

  3. New creep-fatigue damage model based on the frequency modified strain range method

    SciTech Connect

    Kim, Y.J.; Seok, C.S.; Park, J.J. [Sung Kyun Kwan Univ., Suwon (Korea, Republic of). Dept. of Mechanical Engineering

    1996-12-01

    For mechanical systems operating at high temperature, damage due to the interaction effect of creep and fatigue plays an important role. The objective of this paper is to propose a modified creep-fatigue damage model which separately analyzes the pure creep damage due to the hold time and the creep-fatigue interaction damage during the startup and the shutdown period. The creep damage was calculated by the general creep damage equation and the creep-fatigue interaction damage was calculated by the modified equation which is based on the frequency modified strain range method with strain rate term. In order to verify the proposed model, a series of high temperature low cycle fatigue tests were performed. The test specimens were made from Inconel-718 superalloy and the test parameters were wave form and hold time. A good agreement between the predicted lives based on the proposed model and experimentally obtained ones was obtained.

  4. Determination of Turbine Blade Life from Engine Field Data

    NASA Technical Reports Server (NTRS)

    Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.

    2012-01-01

    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.

  5. OPERATIONAL MODAL ANALYSIS AND WAVELET TRANSFORMATION FOR DAMAGE IDENTIFICATION IN WIND TURBINE BLADES

    E-print Network

    Paris-Sud XI, Université de

    OPERATIONAL MODAL ANALYSIS AND WAVELET TRANSFORMATION FOR DAMAGE IDENTIFICATION IN WIND TURBINE-frequency modes. KEYWORDS : Wind Turbine Blades, Debonding, Wavelet Transformation, Operational Modal Analysis. INTRODUCTION While failure can happen in any structural component of the wind turbine, one of the most common

  6. LOSS OF ROTOR ISOTROPY AS A BLADE DAMAGE INDICATOR FOR WIND TURBINE STRUCTURE HEALTH MONITORING SYSTEMS

    E-print Network

    Paris-Sud XI, Université de

    are used to detect and localise the damage. However, in this study, we use a pragmatic view: we are looking developed, e.g., [7, 8]. However, here we also use a pragmatic approach: the goal is not to perform the following investigation strategy: Section 1 sets up a lumped-mass model of a three-bladed rotor, simple

  7. Effective AE source location of damages in the wind turbine blade

    NASA Astrophysics Data System (ADS)

    Yoon, D. J.; Han, B. H.

    2012-05-01

    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.

  8. DAMAGE DETECTION IN A WIND TURBINE BLADE BASED ON TIME SERIES Simon Hoell, Piotr Omenzetter

    E-print Network

    Boyer, Edmond

    , the consequences are growing sizes of wind turbines (WTs) and erections in remote places, such as off-shore, and multivariate AR models have been used for condition monitoring of a 5 MW offshore wind energy converter [6DAMAGE DETECTION IN A WIND TURBINE BLADE BASED ON TIME SERIES METHODS Simon Hoell, Piotr Omenzetter

  9. Damage Detection in Wind Turbine Blade Panels Using Three Different SHM Techniques

    Microsoft Academic Search

    Marcin Luczak; Bart Peeters; Michael Döhler; Laurent Mevel; Wieslaw Ostachowicz; Pawel Malinowski; Tomasz Wandowski; Kim Branner

    \\u000a A comparison of three different damage detection methods is made on three nominally identical glass reinforced composite panels,\\u000a similar to the load carrying laminate in a wind turbine blade. Sensor data were recorded in the healthy state and after the\\u000a introduction of damage by means of a four–point bending quasi–static test. Acceleration sensors, PZT transducers and the piezoelectric\\u000a excited Lamb

  10. Effect of fatigue damage on the dynamic tensile behavior of 6061-T6 aluminum alloy and AISI 4140T steel

    Microsoft Academic Search

    U. Sánchez-Santana; C. Rubio-González; G. Mesmacque; A. Amrouche

    2009-01-01

    Usually material properties are determined from damage free materials, but it is not well known how these properties vary with respect to previous fatigue damage. In the present work the dynamic response of fatigue damaged 6061-T6 aluminum alloy and AISI 4140T steel specimens subjected to impact loading was investigated. Samples subjected to previous damage under high cycle fatigue and low

  11. A unified multiaxial fatigue damage model for isotropic and anisotropic materials

    Microsoft Academic Search

    Yongming Liu; Sankaran Mahadevan

    2007-01-01

    A unified multiaxial fatigue damage model based on a characteristic plane approach is proposed in this paper, integrating both isotropic and anisotropic materials into one framework. Compared with most available critical plane-based models for multiaxial fatigue problem, the physical basis of the characteristic plane does not rely on the observations of the fatigue crack in the proposed model. The cracking

  12. EXPERIMENTAL IDENTIFICATION OF FATIGUE DAMAGE MODEL FOR SHORT GLASS FIBRE REINFORCED THERMOPLASTIC COMPOSITES

    Microsoft Academic Search

    H. Nouri; H. Chalal; F. Meraghni; P. Lory

    A polycyclic fatigue damage model for short glass fibre reinforced thermoplastics is developed and implemented into ABAQUS FE code using UMAT subroutine. The MNL model is introduced here in terms of damage rates:

  13. Effects of fatigue induced damage on the longitudinal fracture resistance of cortical bone.

    PubMed

    Fletcher, Lloyd; Codrington, John; Parkinson, Ian

    2014-07-01

    As a composite material, cortical bone accumulates fatigue microdamage through the repetitive loading of everyday activity (e.g. walking). The accumulation of fatigue microdamage is thought to contribute to the occurrence of fragility fractures in older people. Therefore it is beneficial to understand the relationship between microcrack accumulation and the fracture resistance of cortical bone. Twenty longitudinally orientated compact tension fracture specimens were machined from a single bovine femur, ten specimens were assigned to both the control and fatigue damaged groups. The damaged group underwent a fatigue loading protocol to induce microdamage which was assessed via fluorescent microscopy. Following fatigue loading, non-linear fracture resistance tests were undertaken on both the control and damaged groups using the J-integral method. The interaction of the crack path with the fatigue induced damage and inherent toughening mechanisms were then observed using fluorescent microscopy. The results of this study show that fatigue induced damage reduces the initiation toughness of cortical bone and the growth toughness within the damage zone by three distinct mechanisms of fatigue-fracture interaction. Further analysis of the J-integral fracture resistance showed both the elastic and plastic component were reduced in the damaged group. For the elastic component this was attributed to a decreased number of ligament bridges in the crack wake while for the plastic component this was attributed to the presence of pre-existing fatigue microcracks preventing energy absorption by the formation of new microcracks. PMID:24715332

  14. Investigation of Gear and Bearing Fatigue Damage Using Debris Particle Distributions

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Lewicki, David G.; Decker, Harry J.

    2004-01-01

    A diagnostic tool was developed for detecting fatigue damage to spur gears, spiral bevel gears, and rolling element bearings. This diagnostic tool was developed and evaluated experimentally by collecting oil debris data from fatigue tests performed in the NASA Glenn Spur Gear Fatigue Rig, Spiral Bevel Gear Test Facility, and the 500hp Helicopter Transmission Test Stand. During each test, data from an online, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results indicate oil debris alone cannot discriminate between bearing and gear fatigue damage.

  15. A study of cumulative fatigue damage in titanium 6Al-4V alloy

    NASA Technical Reports Server (NTRS)

    Jeelani, S.; Ghebremedhin, S.; Musial, M.

    1986-01-01

    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.

  16. Delayed Exercise Promotes Remodeling in Sub-Rupture Fatigue Damaged Tendons

    PubMed Central

    Bell, R.; Boniello, M.R.; Gendron, N.R.; Flatow, E.L.; Andarawis-Puri, N.

    2015-01-01

    Tendinopathy is a common musculoskeletal injury whose treatment is limited by ineffective therapeutic interventions. Previously we have shown that tendons ineffectively repair early sub-rupture fatigue damage. In contrast, physiological exercise has been shown to promote remodeling of healthy tendons but its utility as a therapeutic to promote repair of fatigue damaged tendons remains unknown. Therefore, the objective of this study was to assess the utility of exercise initiated 1 and 14 days after onset of fatigue damage to promote structural repair in fatigue damaged tendons. We hypothesized that exercise initiated 14 days after fatigue loading would promote remodeling as indicated by a decrease in area of collagen matrix damage, increased procollagen I and decorin, while decreasing proteins indicative of tendinopathy. Rats engaged in 6-week exercise for 30 min/day or 60 min/day starting 1 or 14 days after fatigue loading. Initiating exercise 1-day after onset of fatigue injury led to exacerbation of matrix damage, particularly at the tendon insertion. Initiating exercise 14 days after onset of fatigue injury led to remodeling of damaged regions in the midsubstance and collagen synthesis at the insertion. Physiological exercise applied after the initial biological response to injury has dampened can potentially promote remodeling of damaged tendons. PMID:25732052

  17. Stochastic Measure of Fatigue Crack Damage for Health Monitoring of Ductile Alloy Structures

    Microsoft Academic Search

    Asok Ray

    2004-01-01

    This paper models a stochastic measure of fatigue crack damage in ductile alloys that are commonly encountered in structures and machinery components of complex mechanical systems such as land, air, ocean, and space vehicles. The constitutive equations of the damage measure are built upon the physics of fracture mechanics and are substantiated by Karhunen-Loeve decomposition of fatigue test data where

  18. Numerical Modeling of Fatigue Damage and Fissure Propagation under Cyclic Loadings

    Microsoft Academic Search

    F. Bogard; P. Lestriez; Y. Q. Guo

    2008-01-01

    The purpose of this work is to develop a numerical simulation procedure in order to predict the evolution of the fatigue damage and rupture in mechanical parts (such as rolling bearings and gears) under cyclic loadings. The study of the fatigue damage evolution, from the first defect appearance until the part's failure, is primordial in view of the preventive maintenance.

  19. Statistical pattern analysis of ultrasonic signals for fatigue damage detection in mechanical structures

    Microsoft Academic Search

    Shalabh Gupta; Dheeraj S. Singh; Asok Ray

    2008-01-01

    This paper addresses online monitoring of fatigue damage in polycrystalline alloy structures based on statistical pattern analysis of ultrasonic sensor signals. The real-time data-driven method for fatigue damage monitoring is based on the concepts derived from statistical mechanics, symbolic dynamics and statistical pattern identification. The underlying concept is detection and identification of small changes in statistical patterns of ultrasonic data

  20. Knee joint neuromuscular activation performance during muscle damage and superimposed fatigue

    Microsoft Academic Search

    Claire Minshull; Roger Eston; David Rees; Nigel Gleeson

    2012-01-01

    This study examined the concurrent effects of exercise-induced muscle damage and superimposed acute fatigue on the neuromuscular activation performance of the knee flexors of nine males (age: 26.7±6.1 years; height 1.81±0.05 m; body mass 81.2±11.7 kg [mean±s]). Measures were obtained during three experimental conditions: (i) ‘fatigue-muscle damage’, involving acute fatiguing exercise performed on each assessment occasion plus a single episode

  1. Characteristics of fatigue life and damage accumulation of short fiber-reinforced polymer composites

    SciTech Connect

    Yokobori, A.T. Jr. [Tohoku Univ., Sendai (Japan). Dept. of Mechatronics and Precision Engineering; Takeda, Hidetoshi [Idemitsu Petrochemical Co., Chiba (Japan); Adachi, Takeshi; Ha, J.C. [Ishinomaki Senshu Univ., Miyagi (Japan); Yokobori, Takeo [Teikyo Univ., Utsunomiya City, Tochigi (Japan). School of Science and Engineering

    1996-12-31

    The relation between fatigue life and damage accumulation of fiber-reinforced polymer composite (FRP) is not yet clarified. For practical use of FRP, it is necessary to relate the fatigue life to the mechanism of damage accumulation. Damage formation is controlled by the mechanical behavior of the interface between the matrix and fiber. The authors used short glass fiber-reinforced polycarbonate composite in the experiments. By using an in situ (real time) observational fatigue testing machine, they investigated the relationship between fatigue life and damage accumulation. From these results, the fatigue life of this material was found to be dominated by damage accumulation which results from microfracture at the interface between the matrix and fiber. This microfracture is controlled by a cycle-dependent mechanism.

  2. Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions

    NASA Astrophysics Data System (ADS)

    Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Sloss, Clayton

    2014-10-01

    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.

  3. Fiber-Optic Defect and Damage Locator System for Wind Turbine Blades

    SciTech Connect

    Dr. Vahid Sotoudeh; Dr. Richard J. Black; Dr. Behzad Moslehi; Mr. Aleks Plavsic

    2010-10-30

    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.

  4. SUBSPACE-BASED DETECTION OF FATIGUE DAMAGE ON JACKET SUPPORT STRUCTURES OF OFFSHORE WIND TURBINES

    E-print Network

    Paris-Sud XI, Université de

    SUBSPACE-BASED DETECTION OF FATIGUE DAMAGE ON JACKET SUPPORT STRUCTURES OF OFFSHORE WIND TURBINES-based Damage Detec- tion (SSDD) method on model structures for an utilization of this approach on offshore wind damage in real size structural components of offshore wind turbines. KEYWORDS : Damage detection

  5. Damage Assessment of CFRP [90/±45/0] Composite Laminates over Fatigue Cycles

    NASA Astrophysics Data System (ADS)

    Ahmadzadeh, G. R.; Shirazi, A.; Varvani-Farahani, A.

    2011-12-01

    The present paper develops a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon fiber reinforced polymer (CFRP) [90/±45/0] composite laminates with various stacking sequences. The damage model is constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional plies of 90°, 0° and angle-ply laminates of ±45° as the number of cycles progresses. The proposed model accumulates damages of constituent plies constructing [90/±45/0] laminates by means of weighting factor ? 90, ? 0 and ? 45. These weighting factors were defined based on the damage progress over fatigue cycles within the plies 90°, 0° and ±45° of the composite laminates. Damage model has been verified using CFRP [90/±45/0] laminates samples made of graphite/epoxy 3501-6/AS4. Experimental fatigue damage data of [90/±45/0] composite laminates have fell between the predicted damage curves of 0°, 90° plies and ±45°, 0/±45° laminates over life cycles at various stress levels. Predicted damage results for CFRP [90/±45/0] laminates showed good agreement with experimental data. Effect of stacking sequence on the model of stiffness reduction has been assessed and it showed that proposed fatigue damage model successfully recognizes the changes in mechanism of fatigue damage development in quasi-isotropic composite laminates.

  6. Impact behavior of filament-wound graphite/epoxy fan blades. [foreign object damage to turbofan engines

    NASA Technical Reports Server (NTRS)

    Bowles, K. J.

    1978-01-01

    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.

  7. Structural and Mechanical Effects of In Vivo Fatigue Damage Induction on Murine Tendon

    PubMed Central

    Sereysky, Jedd B.; Andarawis-Puri, Nelly; Jepsen, Karl J.; Flatow, Evan L.

    2013-01-01

    The purpose of this study was to develop and validate an in vivo mouse model of tendon fatigue and use this model to investigate and quantify the physical manifestations of fatigue damage in mouse tendon. Patellar tendons of C57BL/6J mice were fatigue loaded at 2 Hz to three endpoints (4 N peak force per cycle for 1 h, 6 N for 1 h, and 4 N for 2 h), during which hysteresis, tangent stiffness, and peak strain of each cycle were measured. Damage accumulation was then quantified using in situ histology, and each tendon was loaded monotonically to failure. Histological damage increased significantly in all three groups (?2-fold), and monotonic stiffness decreased significantly in the 6 N, 1 h and 4 N, 2-h groups (~25%), suggesting that damage initially manifests as changes to the collagen structure of the tendon and subsequently as changes to the function. For the fatigue loading protocols used in this study, none of the evaluated real-time parameters from fatigue loading correlated with damage area fraction measured structural damage or monotonic stiffness, suggesting that they are not suited to serve as proxies for damage accumulation. In future studies, this model will be used to compare the biological response of mouse tendon to fatigue damage across genetic strains. PMID:22072573

  8. Analytical Methodology for Predicting the Onset of Widespread Fatigue Damage in Fuselage Structure

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.; Newman, James C., Jr.; Piascik, Robert S.; Starnes, James H., Jr.

    1996-01-01

    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.

  9. Fatigue damage accumulation and property degradation in flat versus cylindrical specimens 

    E-print Network

    Andrews, Kristine Bachtel

    1992-01-01

    investigated the influence of drilling-induced defects on the fatigue life of a pin bearing joint in a flat toughened carbon epoxy system [23]. Chan and Ochoa examined edge delamination resistance by a critical ply termination [24). They determined... and property degradation in flat and cylindrical graphite/epoxy composite specimens. A primary goal is to determine the extent that geometry influences fatigue life. The means to achieve this goal are comparisons of accumulated fatigue damage and property...

  10. Damage progression during static and fatigue loading in metal matrix composites, volumes 1-3

    Microsoft Academic Search

    Bakuckas

    1991-01-01

    The objective is to gain a rational understanding of the damage initiation and progression in a variety of metal matrix composites (MMC) during both static and fatigue loading. An extensive two prong investigation involving experimental and analytical phases was undertaken in order to characterize damage progression in center notched MMC. Experimentally, the crack tip damage growth was studied utilizing several

  11. Fatigue Damage in CFRP Woven Fabric Composites through Dynamic Modulus Measurements

    SciTech Connect

    Chiaki Miyasaka; K. L. Telschow

    2004-07-01

    Advanced fiber reinforced composite materials offer substantial advantages over metallic materials for the structural applications subjected to fatigue loading. With the increasing use of these composites, it is required to understand their mechanical response to cyclic loading (1)-(4). Our major concern in this work is to macroscopically evaluate the damage development in composites during fatigue loading. For this purpose, we examine what effect the fatigue damage may have on the material properties and how they can be related mathematically to each other. In general, as the damage initiates in composite materials and grows during cyclic loading, material properties such as modulus, residual strength and strain would vary and, in many cases, they may be significantly reduced because of the progressive accumulation of cracks. Therefore, the damage can be characterized by the change in material properties, which is expected to be available for non-destructive evaluation of the fatigue damage development in composites. Here, the tension-tension fatigue tests are firstly conducted on the plain woven fabric carbon fiber composites for different loading levels. In the fatigue tests, the dynamic elastic moduli are measured on real-time, which will decrease with an increasing number of cycles due to the degradation of stiffness. Then, the damage function presenting the damage development during fatigue loading is determined from the dynamic elastic moduli thus obtained, from which the damage function is formulated in terms of a number of cycles and an applied loading level. Finally, the damage function is shown to be applied for predicting the remaining lifetime of the CFRP composites subjected to two-stress level fatigue loading.

  12. A damage assessment model for cadaveric cortical bone subjected to fatigue cycles

    Microsoft Academic Search

    A. Varvani-Farahani; H. Najmi

    2010-01-01

    A model is developed to evaluate the fatigue damage of cadaveric human cortical bone by incorporating stiffness reduction of bone materials as the number of fatigue cycles progresses. The structure of cortical bone has been characterized as a natural fiber-reinforced composite material consists of Haversian osteons (fibers) embedded in interstitial bone (matrix) and separated by weak cement line interfaces.The proposed

  13. Optimum inspection planning for minimizing fatigue damage detection delay of ship hull structures

    Microsoft Academic Search

    Sunyong Kim; Dan M. Frangopol

    2011-01-01

    Fatigue is one of the main factors which can produce cracks, and lead to failure of ships. For these structures, damage occurrence and propagation due to fatigue are affected by the action of sea water waves and the sea environment as well as operation, fabrication, and modeling of ship structures under uncertainties. In order to efficiently maintain the safety of

  14. OBSERVATION AND PREDICTION OF LOCAL DAMAGE PATTERNS UNDER TENSION AND TORSION HIGH CYCLE FATIGUE

    Microsoft Academic Search

    L. FLACELIERE; F. MOREL

    This paper aims at comparing the experimental fatigue strength of samples loaded in high cycle fatigue (HCF) and the predictions employing a damage model dedicated to the HCF. The material studied, a mild steel C36, is tested for lifetime ranging from 105 to 106 cycles. Some observations (by SEM) are carried out during the tests performed under fully reversed tension

  15. Fatigue and residual strength characteristics of fiber metal laminates subjected to incidental damage

    Microsoft Academic Search

    Robert Fredell; Ad Vlot; Marc Verbruggen

    1992-01-01

    The fatigue and residual strength characteristics of the fiber metal laminates GLARE and ARALL, following damage typically encountered in the service environment, were investigated. Comparative impact tests showed a gereral trend of increasing impact resistance from carbon thermoplastic composites (poorest) to ARALL, monolithic aluminum 2024-T3, and GLARE 3 (best). Fatigue and residual strength tests carried out on impact and scratch

  16. Fatigue damage prognosis of a cruciform structure under biaxial random and flight profile loading

    Microsoft Academic Search

    Subhasish Mohanty; Aditi Chattopadhyay; Pedro Peralta; Dan Quech

    2010-01-01

    The accurate estimation of fatigue life of metallic structural components in service environments is still a challenge for the aircraft designer or fleet manager. Majority of the current available fatigue life prediction models has deficiency to accurately predict damage under random or flight profile service loads. The inherent accuracy is due to the stochastic nature of crack propagation in metallic

  17. Symbolic time series analysis of ultrasonic signals for fatigue damage monitoring in polycrystalline alloys

    NASA Astrophysics Data System (ADS)

    Gupta, Shalabh; Ray, Asok; Keller, Eric

    2006-07-01

    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 anomaly detection algorithm is based on time series analysis of ultrasonic data and is built upon the principles of symbolic dynamics, information theory and statistical signal processing. Experiments have been conducted for both constant amplitude and block loading of 7075-T6 aluminium alloy compact specimens on a special-purpose test apparatus that is equipped with ultrasonics sensors and a travelling optical microscope for fatigue damage monitoring.

  18. Microstructural evaluation of cumulative fatigue damage in a plant component sample

    SciTech Connect

    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

    1996-12-31

    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.

  19. Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1988-01-01

    A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

  20. Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1989-01-01

    A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

  1. Fatigue Damage Evaluation of Friction Stir Spot Welded Cross-Tension Joints Under Repeated Two-Step Force Amplitudes

    NASA Astrophysics Data System (ADS)

    Joy-A-Ka, Sutep; Ogawa, Yuki; Akebono, Hiroyuki; Kato, Masahiko; Sugeta, Atsushi; Sun, Yufeng; Fujii, Hidetoshi

    2015-06-01

    This paper investigates an approach to evaluate the fatigue damage of FSSW cross-tension specimens under two-step force amplitude conditions. In fatigue tests with repeated two-step force amplitude, the fatigue limit of the welded joint disappeared. However, the fatigue damage evaluation using the modified Miner's rule erred too much on the side of safety, as the modified Miner's rule tends to overestimate the damage by applied forces below the fatigue limit. Thus, it was determined that, within the testing conditions used in this study, the fatigue damage evaluation using Haibach's method yielded an accurate evaluation. In the case where significant plastic deformation caused by the applied force occurred near the welded zone, the cumulative fatigue damage value based on Miner's rule was often larger than unity. Therefore, it is important to consider a cumulative damage estimation that takes into account the effect of pre-strain from the high force amplitude.

  2. A continuum damage modeling of quasi-static fatigue strength of plain concrete

    Microsoft Academic Search

    S. H. Mai; F. Le-Corre; G. Foret; B. Nedjar

    A three-dimensional phenomenological model is developed to describe the fatigue behavior of concrete. The approach is based on the framework of continuum damage mechanics where the fatigue model is derived by means of Marigo’s formulation where the yield concept is replaced by a loading–unloading irreversibility concept allowing to account for damage accumulation even for loading levels below the yield surface.

  3. Introduction of a fretting-fatigue mapping concept: Development of a dual crack nucleation – crack propagation approach to formalize fretting-fatigue damage

    Microsoft Academic Search

    S. Fouvry; K. J. Kubiak

    2009-01-01

    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

  4. Microstructure: Property correlation. [multiaxial fatigue damage evolution in waspaloy

    NASA Technical Reports Server (NTRS)

    Jayaraman, N.

    1990-01-01

    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.

  5. Creep dominates tensile fatigue damage of the cement-bone interface.

    PubMed

    Kim, Do-Gyoon; Miller, Mark A; Mann, Kenneth A

    2004-05-01

    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

  6. Nondestructive evaluation of fatigue damage on low alloy steel by magnetomechanical acoustic emission technique

    SciTech Connect

    Hiraasawa, T.; Saito, K.; Komura, I. [Toshiba Corp., Yokohama (Japan)

    1995-08-01

    A modified magnetomechanical acoustic emission (MAE) technique, denoted Pulse-MAE, in which the magnetization by current pulse was adopted, was newly developed and its applicability was assessed for the nondestructive detection and evaluation of fatigue damage in reactor pressure vessel steel SFVV2 and SA508 class2. MAE signals were measured with both conventional MAE and Pulse-MAE technique for fatigue damaged specimens having several damage fractions, and peak voltage ratio Vp/Vo, where Vp and Vo were the peak voltage for damaged and undamaged specimen respectively, was chosen as a measure. Vp/Vo was found to increase monotonously at the early stage of fatigue process and the rate of increase in Vp/Vo during the fatigue process was larger in Pulse-MAE than conventional MAE. Therefore, Pulse-MAE technique proved to have higher sensitivity for the detection of fatigue damage compared with the conventional MAE and to have the potential of a practical technique for nondestructive detection and evaluation of fatigue damage in actual components.

  7. Knee joint neuromuscular activation performance during muscle damage and superimposed fatigue.

    PubMed

    Minshull, Claire; Eston, Roger; Rees, David; Gleeson, Nigel

    2012-01-01

    This study examined the concurrent effects of exercise-induced muscle damage and superimposed acute fatigue on the neuromuscular activation performance of the knee flexors of nine males (age: 26.7 ± 6.1 years; height 1.81 ± 0.05 m; body mass 81.2 ± 11.7 kg [mean±s]). Measures were obtained during three experimental conditions: (i) 'fatigue-muscle damage', involving acute fatiguing exercise performed on each assessment occasion plus a single episode of eccentric exercise performed on the first occasion and after the fatigue trial; (ii) 'fatigue', involving the fatiguing exercise only; and (iii) 'control' consisting of no exercise. Assessments were performed prior to (pre) and at 1 h, 24 h, 48 h, 72 h, and 168 h relative to the muscle damaging eccentric exercise. Repeated-measures analyses of variance (ANOVAs) showed that muscle damage elicited reductions of up to 38%, 24% and 65% in volitional peak force, electromechanical delay and rate of force development compared to baseline and controls, respectively (F ([10, 80]) = 2.3 to 4.6; P < 0.05) with further impairments (6.2% to 30.7%) following acute fatigue (F ([2, 16]) = 4.3 to 9.1; P < 0.05). By contrast, magnetically-evoked electromechanical delay was not influenced by muscle damage and was improved during the superimposed acute fatigue (?14%; F ([2, 16]) = 3.9; P < 0.05). The safeguarding of evoked muscle activation capability despite compromised volitional performance might reveal aspects of capabilities for emergency and protective responses during episodes of fatigue and antecedent muscle damaging exercise. PMID:22574708

  8. Risk assessment of Cumberland unit 2 L-O blades

    SciTech Connect

    Lam, T.C.T. [Stress Technology Inc., Rochester, NY (United States); Puri, A. [Tennessee Valley Authority, Chattanooga, TN (United States)

    1996-12-31

    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.

  9. Evaluation of fatigue damage using a magnetic measurement technique

    Microsoft Academic Search

    C. C. H. Lo; F. Tang; D. C. Jiles; S. B. Biner

    1999-01-01

    A series of strain-controlled fatigue tests were performed on 0.1 wt% C Fe-C alloy samples under different strain amplitudes. The measured coercivity of these samples was found to behave differently in the initial and final stages of fatigue. In the intermediate stage of fatigue it was found that coercivity tended to increase, while initial and maximum permeabilities tended to decrease.

  10. Fatigue damage prognosis of a cruciform structure under biaxial random and flight profile loading

    NASA Astrophysics Data System (ADS)

    Mohanty, Subhasish; Chattopadhyay, Aditi; Peralta, Pedro; Quech, Dan

    2010-04-01

    The accurate estimation of fatigue life of metallic structural components in service environments is still a challenge for the aircraft designer or fleet manager. Majority of the current available fatigue life prediction models has deficiency to accurately predict damage under random or flight profile service loads. The inherent accuracy is due to the stochastic nature of crack propagation in metallic structure. In addition, currently no generic prediction model available accounting the load interaction effects due to variable loading. In the present paper we discus the use of a Generic Bayesian framework based Gaussian process approach to probabilistically predict the fatigue damage under complex random and flight profile loading.

  11. Fatigue Damage Tolerance of Bainitic and Pearlitic Rail Steels

    Microsoft Academic Search

    Heshmat A. Aglan; Mahmood Fateh

    2006-01-01

    The microstructure-properties relationships, fatigue crack growth, and fracture surface morphology of J6 bainitic and premium pearlitic rail steels are studied. Specimens are cut from the middle of each railhead along the longitudinal direction of the rail using electrical discharge machining. Fatigue crack propagation tests are conducted under load control conditions using a servo hydraulic material testing system. A simple form

  12. Mechanisms of fatigue damage and crack growth in advanced materials

    Microsoft Academic Search

    Robert O. Ritchie

    2001-01-01

    In terms of in-service failures, cyclic fatigue is the most prevalent form of fracture. Despite the wealth of information on fatigue failures in traditional structural materials such as (ductile) metals and alloys, far less is understood about the susceptibility of the newer advanced materials, such as (brittle) intermetallics, ceramics and their composites. In this presentation, the mechanics and mechanisms of

  13. Structural health monitoring and condition based fatigue damage prognosis of complex metallic structures

    NASA Astrophysics Data System (ADS)

    Mohanty, Subhasish

    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.

  14. APPLICATION OF POSITRON ANNIHILATION TO FATIGUE AND PLASTIC DAMAGE DETECTION IN SA508 AND TYPE 304 STEELS

    Microsoft Academic Search

    M. UCHIDA; K. YOSHIDA; Y. G. NAKAGAWA; A. J. ALLEN; A. D. WHAPHAM

    1992-01-01

    The positron annihilation(PA) lineshape analysis method was applied to evaluate the fatigue damage in SA508 Ierritic steel and type 304 stainless steel, and the damage distribution in a type 304 sample plastically deformed by 3-point bending. The PA was found to be effective to detect early stages of the fatigue damage (less than 25% of the cycles to failure) in

  15. Fatigue damage analysis and life assessment under variable amplitude loading conditions

    Microsoft Academic Search

    A. Varvani-Farahani; M. Sharma; M. R. Kianoush

    2005-01-01

    An earlier developed critical plane-energy based damage parameter has been further developed to assess the life of engineering components subjected to variable service loading conditions. In damage analysis, the effects of materials memory, small cycles and loading sequence on the hysteresis stress–strain loops of materials have been included. The parameter successfully correlated fatigue lives of a low carbon steel and

  16. Continuum damage mechanics for hysteresis and fatigue of quasi-brittle materials and structures

    Microsoft Academic Search

    R. Desmorat; F. Ragueneau; H. Pham

    2007-01-01

    For a material exhibiting hysteresis such as quasi-brittle materials, it is natural to consider that hysteresis and fatigue are related to each other. One shows in the present work that damage, from the continuum damage mechanics point of view, may be seen as the link between both phenomena. One attempts, hence, to set up a unified modelling of hysteresis and

  17. Evaluation of micro-damage accumulation in holed plain-woven CFRP composite under fatigue loading

    NASA Astrophysics Data System (ADS)

    Ying, Jia; Nishikawa, Masaaki; Hojo, Masaki

    2014-03-01

    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.

  18. Nondestructive detection of creep and creep-fatigue damages in welded joints by ultrasonic technique

    SciTech Connect

    Okazaki, M. [Nagaoka Univ. of Technology (Japan). Dept. of Mechanical Engineering; Hashimoto, M. [Babcock Hitachi K.K., Kure (Japan). Kure Research Center

    1995-12-01

    The non-destructive detection of creep and creep-fatigue damages was studied by employing an ultrasonic technique, taking account of the applicability to welded joints. Particular attention was paid to the change of ultrasonic wave attenuation and that of the anisotropy during the creep and creep-fatigue failures. The experimental results, using the welded joint of 2 1/4 Cr-1 Mo steel and the dissimilar metal welded joint between 2 1/4 Cr-1 Mo and Type 316 steels, showed that the development process of creep damage ad that of creep-fatigue one were successfully reflected on the change of the ultrasonic attenuation as follows: the ultrasonic wave attenuation remarkably increased with creep and the creep-fatigue damages, especially at the final rupture zone, while the change was not noticeable at the other zones accompanying with negligible damage. In addition, the attenuation exhibited a comparable change to the other useful engineering parameters, such as the A-parameter; i.e., the change was satisfied,or competent for detection. These results indicate that the ultrasonic attenuation properties provide the useful information to detect the creep and creep-fatigue damages nondestructively, as well as to find out the dangerous sites to failure, in welded joints.

  19. Swept Blade Aero-Elastic Model for a Small Wind Turbine (Presentation)

    SciTech Connect

    Damiani, R.; Lee, S.; Larwood, S.

    2014-07-01

    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.

  20. Simplification of Fatigue Test Requirements for Damage Tolerance of Composite Interstage Launch Vehicle Hardware

    NASA Technical Reports Server (NTRS)

    Nettles, A. T.; Hodge, A. J.; Jackson, J. R.

    2010-01-01

    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.

  1. Methodology for Predicting the Onset of Widespread Fatigue Damage in Lap-Splice Joints

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Harris, C. E.; Piascik, R. S.; Dawicke, D. S.

    1998-01-01

    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).

  2. A Stiffness Degradation Based Fatigue Damage Model for FRP Composites of (0\\/ ? ) Laminate Systems

    Microsoft Academic Search

    Alireza Shirazi; A. Varvani-Farahani

    2010-01-01

    The present study develops a stiffness reduction—based model to characterize fatigue damage in unidirectional 0? and ?° plies\\u000a and (0\\/?) laminates of fiber-reinforced polymer (FRP) composites. The proposed damage model was constructed based on (i) cracking\\u000a mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding\\u000a stiffness reduction of unidirectional composite

  3. Fatigue damage initiation and growth from artificial defects in Zr-based metallic glass

    Microsoft Academic Search

    B. C. Menzel; R. H. Dauskardt

    2008-01-01

    An array of well-defined and micrometer-sized circular and line defects were produced on the surface of Zr-based bulk metallic glass bend specimens using a focused ion beam (FIB) in order to study the effect of the defect size, orientation and shape on fatigue damage initiation and growth. Damage evolution was recorded using a surface-replicating technique. Damage was observed to initiate

  4. Application of positron annihilation line-shape analysis to fatigue damage for nuclear plant materials

    Microsoft Academic Search

    Noriyoshi Maeda; Noriko Nakamura; Misako Uchida; Yoshio Ohta; Kazuo Yoshida

    1996-01-01

    Positron annihilation line-shape analysis is sufficiently sensitive to detect microstructural defects such as vacancies and dislocations. We are developing a portable positron annihilation system and applying this technique to fatigue damage in type 316 stainless steel and SA508 low alloy steel. The positron annihilation technique was found to be sensitive in the early fatigue life, i.e. up to 10% of

  5. The fatigue behaviour and damage development of 3D woven sandwich composites

    Microsoft Academic Search

    H. Judawisastra; J. Ivens; I. Verpoest

    1998-01-01

    In this paper, the bending fatigue behaviour and damage development during fatigue of polyurethane (PUR)-epoxy 3D woven sandwich composites is investigated. 3D sandwich fabrics are produced by a velvet weaving technique. It allows relatively easy production of delamination-resistant sandwich panels, compared to more traditional sandwich structures with honeycomb or foam cores. In this paper, the 3D sandwich fabrics made of

  6. Development of advanced structural analysis methodologies for predicting widespread fatigue damage in aircraft structures

    Microsoft Academic Search

    Charles E. Harris; James H. Starnes Jr.; James C. Newman Jr.

    1995-01-01

    NASA is developing a 'tool box' that includes a number of advanced structural analysis computer codes which, taken together, represent the comprehensive fracture mechanics capability required to predict the onset of widespread fatigue damage. These structural analysis tools have complementary and specialized capabilities ranging from a finite-element-based stress-analysis code for two- and three-dimensional built-up structures with cracks to a fatigue

  7. Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth

    NASA Technical Reports Server (NTRS)

    Dawicke, D. S.; Newman, J. C., Jr.

    1992-01-01

    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.

  8. Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime

    SciTech Connect

    Zhang, Jianfeng; Xuan, Fu-Zhen, E-mail: fzxuan@ecust.edu.cn [MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China)

    2014-05-28

    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.

  9. Mitigation of fatigue damage in self-healing vascular materials A.R. Hamilton a,b,1

    E-print Network

    Sottos, Nancy R.

    Mitigation of fatigue damage in self-healing vascular materials A.R. Hamilton a,b,1 , N.R. Sottos b: Self-healing Fatigue Vascular network a b s t r a c t The fatigue response of an epoxy matrix and polymerize, and the effect of healing is minimal. The self-healing response is most effective at impeding

  10. Standardization of fretting fatigue test methods and equipment

    SciTech Connect

    Attia, M.H.; Waterhouse, R.B.

    1992-01-01

    Papers contained in this book are grouped under the topics of the fundamental aspects of fretting fatigue testing (conceptual framework and mechanics of contact), methods and equipment for fretting fatigue testing, environmental and surface conditions, and nonconventional materials and test methods. Papers are presented on the problems of fretting fatigue testing, a critical appraisal of testing methods in fretting fatigue, the determination and control of contact pressure distribution in fretting fatigue, and fretting fatigue analysis of strength improvement models with grooving or knurling on a contact surface. Other papers include a critical review of fretting fatigue investigations at the Royal Aerospace Establishment, techniques for the characterization of fretting fatigue damage, improving fretting fatigue strength at elevated temperatures by shot peening in steam turbine steel, the fretting fatigue properties of a blade steel in air and vapor environments, and fretting fatigue of carbon-fiber-reinforced epoxy laminates.

  11. Thermo-elastic nondestructive evaluation of fatigue damage in PMR-15 resin

    NASA Astrophysics Data System (ADS)

    Welter, J. T.; Sathish, S.; Tandon, G. P.; Schehl, N.; Cherry, M.; Nalladega, V.; Lindgren, E. A.; Hall, R.

    2012-05-01

    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.

  12. Computational Fluid Dynamics Analysis of Blade Tip Clearances on Hemodynamic Performance and Blood Damage in a Centrifugal Ventricular Assist Device

    PubMed Central

    Wu, Jingchun; Paden, Bradley E.; Borovetz, Harvey S.; Antaki, James F.

    2011-01-01

    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 ?m. 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 ?m. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 ?m compared to 50 ?m and 200 ?m. 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

  13. Computational fluid dynamics analysis of blade tip clearances on hemodynamic performance and blood damage in a centrifugal ventricular assist device.

    PubMed

    Wu, Jingchun; Paden, Bradley E; Borovetz, Harvey S; Antaki, James F

    2010-05-01

    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

  14. Non-destructive estimation of fatigue damage for steel by Barkhausen noise analysis

    SciTech Connect

    Tomita, Yasumitsu; Hashimoto, Kiyoshi; Osawa, Naoki [Osaka Univ. (Japan). Dept. of Naval Architecture and Ocean Engineering; Inai, Hirohisa [Mitsubishi Motors Corp., Tokyo (Japan)

    1993-12-31

    A magnetic Barkhausen noise signals are detected when magnetized domain walls move discontinuously in a ferromagnetic material. This non-uniform motion is sensitive to the microstructures of material which vary continuously with the increase of applied loading cycles. In this paper, the process of fatigue damage accumulation subjected to constant cyclic loading are explored by measuring the Barkhausen noise signal with the progress of loading cycles. The experimental results show the possibility to detect the progress of fatigue damage using the peak Barkhausen noise signal.

  15. Fatigue damage criteria - Matrix, fibers and interfaces of continuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1988-01-01

    Continuous fiber reinforced metal matrix composites (MMC) are projected for use in high temperature, stiffness critical parts that will be subjected to cyclic loadings. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four catagories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage are discussed and illustrated by examples. The emphasis is on the fatigue of unnotched laminates.

  16. Damage detection in carbon composite material typical of wind turbine blades using auto-associative neural networks

    NASA Astrophysics Data System (ADS)

    Dervilis, N.; Barthorpe, R. J.; Antoniadou, I.; Staszewski, W. J.; Worden, K.

    2012-04-01

    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.

  17. Fatigue crack damage detection using subharmonic component with nonlinear boundary condition

    NASA Astrophysics Data System (ADS)

    Wu, Weiliang; Shen, Yanfeng; Qu, Wenzhong; Xiao, Li; Giurgiutiu, Victor

    2015-03-01

    In recent years, researchers have focused on structural health monitoring (SHM) and damage detection techniques using nonlinear vibration and nonlinear ultrasonic methods. Fatigue cracks may exhibit contact acoustic nonlinearity (CAN) with distinctive features such as superharmonics and subharmonics in the power spectrum of the sensing signals. However, challenges have been noticed in the practical applications of the harmonic methods. For instance, superharmonics can also be generated by the piezoelectric transducers and the electronic equipment; super/subharmonics may also stem from the nonlinear boundary conditions such as structural fixtures and joints. It is hard to tell whether the nonlinear features come from the structural damage or the intrinsic nonlinear boundary conditions. The objective of this paper is to demonstrate the application of nonlinear ultrasonic subharmonic method for detecting fatigue cracks with nonlinear boundary conditions. The fatigue crack was qualitatively modeled as a single-degree-of-freedom (SDOF) system with non-classical hysteretic nonlinear interface forces at both sides of the crack surfaces. The threshold of subharmonic generation was studied, and the influence of crack interface parameters on the subharmonic resonance condition was investigated. The different threshold behaviors between the nonlinear boundary condition and the fatigue crack was found, which can be used to distinguish the source of nonlinear subharmonic features. To evaluate the proposed method, experiments of an aluminum plate with a fatigue crack were conducted to quantitatively verify the subharmonic resonance range. Two surface-bonded piezoelectric transducers were used to generate and receive ultrasonic wave signals. The fatigue damage was characterized in terms of a subharmonic damage index. The experimental results demonstrated that the subharmonic component of the sensing signal can be used to detect the fatigue crack and further distinguish it from inherent nonlinear boundary conditions.

  18. Monitoring Fatigue Damage in Industrial Steel by Barkhausen Noise

    Microsoft Academic Search

    J. Lamontanara; J. Chicois; P. Fleischmann; R. Fougères

    1992-01-01

    Barkhausen noise is generated by the rapid and irreversible motion of Bloch walls within ferromagnetic materials, when submitted to mechanical stresses or external magnetic field. Bloch walls motion is influenced by obstacles like dislocations, precipitates Therefore Barkhausen noise depends on the microstructure and the stress state of material, that can change during fatigue tests. Indeed the Barkhausen noise measurements can

  19. Assessment of damage and life prediction of austenitic stainless steel under high temperature creep–fatigue interaction condition

    Microsoft Academic Search

    Soo Woo Nam

    2002-01-01

    It is understood that grain boundary cavitation is one of the detrimental processes for the degradation of austenitic stainless steels that reduces the creep–fatigue life at high temperatures. A new damage function based on a model for the creep–fatigue life prediction in terms of nucleation and growth of grain boundary cavities is proposed for austenitic stainless steel. This damage function

  20. Characterization of low cycle fatigue damage in 9Cr–1Mo ferritic steel using X-ray diffraction technique

    Microsoft Academic Search

    Sanjay Rai; B. K Choudhary; T Jayakumar; K. Bhanu Sankara Rao; Baldev Raj

    1999-01-01

    X-ray diffraction (XRD) technique has been used to characterize the low cycle fatigue (LCF) damage in 9Cr–1Mo ferritic steel. In this study, full-width at half-maximum (FWHM) of the XRD peak has been measured for assessing the fatigue damage. Fully reversed total-axial-strain controlled fatigue tests have been performed at ambient temperature (300K) at strain amplitudes of ±0.25%, ±0.50% and ±0.75%. FWHM

  1. Real-time sensing of fatigue crack damage for information-based decision and control

    NASA Astrophysics Data System (ADS)

    Keller, Eric Evans

    Information-based decision and control for structures that are subject to failure by fatigue cracking is based on the following notion: Maintenance, usage scheduling, and control parameter tuning can be optimized through real time knowledge of the current state of fatigue crack damage. Additionally, if the material properties of a mechanical structure can be identified within a smaller range, then the remaining life prediction of that structure will be substantially more accurate. Information-based decision systems can rely one physical models, estimation of material properties, exact knowledge of usage history, and sensor data to synthesize an accurate snapshot of the current state of damage and the likely remaining life of a structure under given assumed loading. The work outlined in this thesis is structured to enhance the development of information-based decision and control systems. This is achieved by constructing a test facility for laboratory experiments on real-time damage sensing. This test facility makes use of a methodology that has been formulated for fatigue crack model parameter estimation and significantly improves the quality of predictions of remaining life. Specifically, the thesis focuses on development of an on-line fatigue crack damage sensing and life prediction system that is built upon the disciplines of Systems Sciences and Mechanics of Materials. A major part of the research effort has been expended to design and fabricate a test apparatus which allows: (i) measurement and recording of statistical data for fatigue crack growth in metallic materials via different sensing techniques; and (ii) identification of stochastic model parameters for prediction of fatigue crack damage. To this end, this thesis describes the test apparatus and the associated instrumentation based on four different sensing techniques, namely, traveling optical microscopy, ultrasonic flaw detection, Alternating Current Potential Drop (ACPD), and fiber-optic extensometry-based compliance, for crack length measurements.

  2. A Stiffness Degradation Based Fatigue Damage Model for FRP Composites of (0/ ?) Laminate Systems

    NASA Astrophysics Data System (ADS)

    Shirazi, Alireza; Varvani-Farahani, A.

    2010-04-01

    The present study develops a stiffness reduction—based model to characterize fatigue damage in unidirectional 0? and ?° plies and (0/?) laminates of fiber-reinforced polymer (FRP) composites. The proposed damage model was constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional composite laminates as the number of cycles progresses. The proposed model enabled damage assessment of FRP (0/?) composite laminates by integrating the fatigue damage values of 0? and ?° plies. A weighting factor ? was introduced to partition the efficiency of load carrying plies of 0° and ?° in the (0/?) composite lamina. The fatigue damage curves of unidirectional FRP composite samples with off-axis angles of 0?, 30?, 45?, and 90? and composite laminate systems of (0?/30?), (0?/45?) and (0?/90?) predicted based on the proposed damage model were found in good agreement with experimental data reported at various cyclic stress levels and stress ratios in the literature.

  3. Experimental and analytical study of fatigue damage in notched graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. D.

    1979-01-01

    Both tension and compression fatigue behaviors were investigated in four notched graphite/epoxy laminates. After fatigue loading, specimens were examined for damage type and location using visual inspection, light microscopy, scanning electron microscopy, ultrasonic C-scans, and X-radiography. Delamination and ply cracking were found to be the dominant types of fatigue damage. In general, ply cracks did not propagate into adjacent plies of differing fiber orientation. To help understand the varied fatigue observations, the interlaminar stress distribution was calculated with finite element analysis for the regions around the hole and along the straight free edge. Comparison of observed delamination locations with the calculated stresses indicated that both interlaminar shear and peel stresses must be considered when predicting delamination. The effects of the fatigue cycling on residual strength and stiffness were measured for some specimens of each laminate type. Fatigue loading generally caused only small stiffness losses. In all cases, residual strengths were greater than or equal to the virgin strengths.

  4. Thermography Inspection for Early Detection of Composite Damage in Structures During Fatigue Loading

    NASA Technical Reports Server (NTRS)

    Zalameda, Joseph N.; Burke, Eric R.; Parker, F. Raymond; Seebo, Jeffrey P.; Wright, Christopher W.; Bly, James B.

    2012-01-01

    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.

  5. Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

    NASA Technical Reports Server (NTRS)

    Jones, David J.; Kurath, Peter

    1988-01-01

    Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

  6. Evidence of Fatigue Damage in the Local Structure of Zr-based Bulk Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Louca, Despina; Tong, Peng; Liaw, Peter; Wang, Gongyao; Yokoyama, Yoshihiko; Llobet, Anna; Spence, Rick

    2011-03-01

    Bulk metallic glasses (BMG) are particularly vulnerable to fatigue damage, where catastrophic failure may occur without observable macroscopic changes. The local atomic structure of two BMGs with compositions of Zr 50 Cu 40 Al 10 and Zr 60 Cu 30 Al 10 was investigated by synchrotron X-ray and neutron diffraction via the pair density function analysis. Under a load of 1600 MPa, the number of compression cycles ranged from 0 -- 107 at 10 Hz. At room temperature, a subtle but irreversible change is observed in the local structure due to fatigue. Upon cooling down to 10 K, however, a significant structural re-organization is observed especially in the short range that is proportional to the number of fatigue cycles. The effect becomes more pronounced with increasing the number of loading cycles. The changes are beyond the usual narrowing from reducing thermal vibrations. The results indicate that hardening occurs after fatigue.

  7. Dependence of Microelastic-plastic Nonlinearity of Martensitic Stainless Steel on Fatigue Damage Accumulation

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.

    2006-01-01

    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.

  8. Sensing damage in carbon fiber polymer-matrix composites during fatigue by electrical resistance measurement

    NASA Astrophysics Data System (ADS)

    Wang, Xiaojun; Chung, Deborah D. L.

    1998-07-01

    Self-monitoring of static/fatigue damage and dynamic strain in a continuous crossply carbon fiber polymer-matrix composite by electrical resistance (R) measurement was achieved. With a static/cyclic tensile stress along the 0 degree direction, R in this direction and R perpendicular to the fiber layers were measured.Upon static tension to failure, R in the 0 direction first decreased and then increased, while R perpendicular to the fiber layers increased monotonically. Upon cyclic tension, R decreased reversibly, while R perpendicular to the fiber layers increased reversibly, though R in both directions changed irreversibly by a small amount after the first cycle. Upon fatigue testing at a maximum stress of 57 percent of the fracture stress, R irreversibly increased both in spurts and continuously, due to 0 degree fiber breakage, which started at 15 percent of the fatigue life, while R irreversibly increased both in spurts and continuously, due to delamination, which started at 33 percent of the fatigue life. The peak R in a cycle irreversibly decreased, while the minimum R at the end of a cycle irreversibly increased during the first 0.1 percent of the fatigue life, due to irreversible increases in the degree of 0 fiber alignment. R became noisy starting at 87 percent of the fatigue life, whereas R became noisy starting at 50 percent of the fatigue life. For a unidirectional composite, R increased reversibly upon tension and decreased reversibly upon compression in the 0 direction, due to piezoresistivity.

  9. Structural and Damage Assessment of Multi-Section Modular Hybrid Composite Wind Turbine Blade 

    E-print Network

    Nanami, Norimichi

    2014-07-25

    computational design concept that includes a multi-section modular hybrid composite wind turbine blade with successful joints while maintaining structural integrity and stability requirements. The configuration of the blade will simplify manufacturing...

  10. Under-filled BGA solder joint vibration fatigue damage

    Microsoft Academic Search

    T. E. Wong; F. W. Palmieri; H. S. Fenger

    2002-01-01

    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

  11. A micro-damage healing model that improves prediction of fatigue life in asphalt mixes

    Microsoft Academic Search

    Rashid K. Abu Al-Rub; Masoud K. Darabi; Dallas N. Little; Eyad A. Masad

    2010-01-01

    The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative

  12. In-situ fatigue damage monitoring using symbolic dynamic filtering of ultrasonic signals

    Microsoft Academic Search

    D S Singh; S Gupta; A Ray

    2009-01-01

    This article presents a data-driven method of pattern identification forin-situ monitor- ing of fatigue damage in polycrystalline alloys that are commonly used in aerospace structures. The concept is built upon analytic signal space partitioning of ultrasonic data sequences for sym- bolic dynamic filtering of the underlying information. The statistical patterns of evolving damage are generated for real-time monitoring of the

  13. Role of brain macrophages on IL1? and fatigue following eccentric exercise-induced muscle damage

    Microsoft Academic Search

    Martin D. Carmichael; J. Mark Davis; E. Angela Murphy; James A. Carson; N. Van Rooijen; Eugene Mayer; Abdul Ghaffar

    2010-01-01

    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

  14. Numerical prediction of fatigue damage in steel catenary riser due to vortex-induced vibration

    Microsoft Academic Search

    Yun GAO; Zhi ZONG; Lei SUN

    2011-01-01

    For studying the characteristics of Steel Catenary Riser (SCR), a simplified pinned-pinned cable model of vibration is established. The natural frequencies, the normalized mode shapes and mode curvatures of the SCR are calculated. The fatigue damage of the SCR can be obtained by applying the modal superposition method combined with the parameters of – curve. For analyzing the relation between

  15. Numerical study on fatigue damage properties of cavitation erosion for rigid metal materials

    Microsoft Academic Search

    Guogang Wang; Guang Ma; Dongbai Sun; Hongying Yu; Huimin Meng

    2008-01-01

    Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated

  16. Nonlinear differential equation for fatigue damage evolution, using a micromechanical model

    Microsoft Academic Search

    Eli Altus

    2002-01-01

    A 1-D discrete (cycle by cycle) micromechanical fatigue model, which represents a material made from an ensemble of elements having statistical (Weibull) strength distribution, has been developed in previous works. In the present study, the recursive type equations have been transformed into a continuous form, leading to a nonlinear second order differential equation of damage evolution (stiffness reduction), for which

  17. A Modified Nonlinear Damage Accumulation Model for Fatigue Life Prediction Considering Load Interaction Effects

    PubMed Central

    Huang, Hong-Zhong; Yuan, Rong

    2014-01-01

    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

  18. Determination of Turbine Blade Life from Engine Field Data

    NASA Technical Reports Server (NTRS)

    Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.

    2013-01-01

    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.

  19. Fatigue-damage evolution and damage-induced reduction of critical current of a Nb3Al superconducting composite

    NASA Astrophysics Data System (ADS)

    Ochiai, S.; Sekino, F.; Sawada, T.; Ohno, H.; Hojo, M.; Tanaka, M.; Okuda, H.; Koganeya, M.; Hayashi, K.; Yamada, Y.; Ayai, N.; Watanabe, K.

    2003-09-01

    We have studied the fatigue-damage mechanism of a Nb3Al superconducting composite at room temperature, and the influences of the fatigue damages introduced at room temperature on the critical current at 4.2 K and the residual strength at room temperature. The main (largest) fatigue crack arose first in the clad copper and then extended into the inner core with an increasing number of stress cycles. The cracking of the Nb3Al filaments in the core region occurred at a late stage (around 60-90% of the fatigue life). Once the fracture of the core occurred, it extended very quickly, resulting in a quick reduction in critical current and the residual strength with increasing stress cycles. Such a behaviour was accounted for by the crack growth calculated from the S-N curves (the relation of the maximum stress to the number of stress cycles at failure) combined with the Paris law. The size and distribution of the subcracks along the specimen length, and therefore the reduction in critical current of the region apart from the main crack, were dependent on the maximum stress level. The large subcracks causing fracture of the Nb3Al filaments were formed when the maximum stress was around 300-460 MPa, resulting in large reduction in critical current, but not when the maximum stress was outside such a stress range.

  20. ASSESSING FATIGUE DAMAGE IN GRP COMPONENTS USING INFRA RED TECHNIQUES

    Microsoft Academic Search

    J. M. Dulieu-Barton; T. R. Emery; P. R. Cunningham

    Full-field data captured equating to the real-time stress state in a composite material has the ability to provide useful information to understand stress redistribution due to damage. One process that offers this capability is Thermoelastic Stress Analysis (TSA) (1). The process has been used to investigate damage in composite materials by calculating a ratio of the stress states recorded from

  1. Deformation history and load sequence effects on cumulative fatigue damage and life predictions

    NASA Astrophysics Data System (ADS)

    Colin, Julie

    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

  2. A Coupled/Uncoupled Computational Scheme for Deformation and Fatigue Damage Analysis of Unidirectional Metal-Matrix Composites

    NASA Technical Reports Server (NTRS)

    Wilt, Thomas E.; Arnold, Steven M.; Saleeb, Atef F.

    1997-01-01

    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.

  3. Tensile and bending thermo-mechanical fatigue testing on cylindrical and flat specimens of CMSX-4 for design of turbine blades

    Microsoft Academic Search

    J. Xu; S. Reuter; W. Rothkegel

    2008-01-01

    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

  4. Procedure and results of the investigation of full-scale lock joints of blades of compressors of gas-turbine engines for fretting fatigue

    Microsoft Academic Search

    G. V. Tsybanev; Yu. S. Nalimov; O. N. Gerasimchuk

    1997-01-01

    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

  5. Fatigue damage in superalloys determined using Doppler broadening positron annihilation

    NASA Technical Reports Server (NTRS)

    Hoeckelman, Donald; Leighly, H. P., Jr.

    1990-01-01

    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.

  6. Real Time Fatigue Damage Growth Assessment of a Composite Three-Stringer Panel Using Passive Thermography

    NASA Technical Reports Server (NTRS)

    Zalameda, Joseph N.; Burke, Eric R.; Horne, Michael R.; Bly, James B.

    2015-01-01

    Fatigue testing of advanced composite structures is critical to validate both structural designs and damage prediction models. In-situ inspection methods are necessary to track damage onset and growth as a function of load cycles. Passive thermography is a large area, noncontact inspection technique that is used to detect composite damage onset and growth in real time as a function of fatigue cycles. The thermal images are acquired in synchronicity to the applied compressive load using a dual infrared camera acquisition system for full (front and back) coverage. Image processing algorithms are investigated to increase defect contrast areas. The thermal results are compared to non-immersion ultrasound inspections and acoustic emission data.

  7. Low cost corrosion damage mitigation and improved fatigue performance of low plasticity burnished 7075-T6

    NASA Astrophysics Data System (ADS)

    Prevéy, Paul S.; Cammett, John

    2001-10-01

    Low plasticity burnishing (LPB) has been investigated as a surface enhancement process and corrosion mitigation method for aging aircraft structural applications. Compressive residual stresses reaching the alloy yield strength and extending to a depth of 1.25 mm (0.050 in.) deeper than typical corrosion damage is achievable. Excellent surface finish can be achieved with no detectable metallurgical damage to surface and subsurface material. Salt fog exposures of 100 and 500 h reduced the fatigue strength at 2×106 cycles by 50%. The LPB of the corroded surface, without removal of the corrosion product or pitted material, restored the 2×106 fatigue strength to greater than that of the original machined surface. The fatigue strength of the corroded material in the finite life regime (104 to 106 cycles) after LPB was 140 MPa (20 ksi) higher than the original uncorroded alloy and increased the life by an order of magnitude. Ease of adaptation to computer numerical control (CNC) machine tools allows LPB processing at costs and speeds comparable to machining operations. Low plasticity burnishing offers a promising new technology for mitigation of corrosion damage and improved fatigue life of aircraft structural components with significant cost and time savings over current practices.

  8. Mechanical and magnetic hysteresis as indicators of the origin and inception of fatigue damage in steel

    Microsoft Academic Search

    Sheng Bao; Wei-liang Jin; Ming-feng Huang

    2010-01-01

    N\\u000a 2 and N\\u000a 3 are known as the transition points of the three principal stages of fatigue: initial accommodation, accretion of damage and\\u000a terminal fatigue. Many experiments show that the ratios of N\\u000a 2\\/N\\u000a f and N\\u000a 3\\/N\\u000a f tend to be stable even though the specific N\\u000a 2 and N\\u000a 3 values may fluctuate widely. The primary goal

  9. A comparison of damage mechanisms for SCS-6/Timetal 21-S subjected to various thermomechanical fatigue cycles

    SciTech Connect

    Calcaterra, J.R.; Johnson, W.S. [Georgia Inst. of Technology, Atlanta, GA (United States). School of Materials Science and Engineering

    1995-12-31

    The work of investigators from Wright Laboratories, NASA LARC and NASA LERC concerning the thermomechanical fatigue behavior of SCS-6/Timetal 21-S is reviewed. The review is centered on damage mechanisms, which are dependent on test type, temperature range, and load range. Test types cause different forms of damage due to the interaction of mechanical, time and environmental effects. In general, isothermal fatigue is dominated by matrix cracking, unless the stress range is high enough to cause fiber damage. In-phase fatigue is dominated by fiber cracking while out-of-phase fatigue is dominated by matrix damage. Spectrum loading is combination of load types but seems to be dominated by matrix cracking. Investigators disagree on the exact types of damage mechanisms. Most disagreements arise from differences in stiffness loss data and the analytical tools used.

  10. Detecting damage in non-uniform beams using the dereverberated transfer function response

    Microsoft Academic Search

    A. S. Purekar; D. J. Pines

    2000-01-01

    Delamination damage in composite rotorcraft flexbeams caused by excessive vibratory and fatigue loads can lead to degradation in flapwise and lagwise performance of the rotor blade. In addition, delaminations can result in rapid fatigue failure of these tailored composite elements leading to catastrophic results. A novel damage detection strategy is evaluated in this work which attempts to exploit the dereverberated

  11. Reliability and fatigue damage modes of zirconia and titanium abutments.

    PubMed

    Mitsias, Miltiadis E; Silva, Nelson R F A; Pines, Mitchel; Stappert, Christian; Thompson, Van P

    2010-01-01

    The fracture strength and accelerated fatigue reliability of metal and zirconia abutment systems were tested. Implants with either titanium (Ti, n = 9) or zirconia abutments(Zr, n = 18) were restored with metal crowns. Loads were applied as either a monotonic load to failure or mouth-motion cycles using a step-stress accelerated life testing method. At failure, monotonic loads were 1,475 +/- 625 N for Ti and 690 +/- 430 N for Zr. In step-stress testing, the Ti group was truncated at 70,000 cycles and a 900-N load with no fractures. In the Zr group, eight specimens survived and seven failed, with a maximum load of 400 N. Strength and reliability were significantly higher for the Ti abutments compared to the Zr. Int J Prosthodont 2010;23:56-59. PMID:20234894

  12. Ultrasonic detection of fatigue damage in glass-epoxy composites

    SciTech Connect

    Simpson, W.A. Jr.; McClung, R.W.

    1990-01-01

    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.

  13. 75 FR 69745 - Aging Airplane Program: Widespread Fatigue Damage

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-15

    ...validity of the engineering data that supports the structural...structure may be performed to obtain data for calibration and validation...Hughes Technical Center, Atlantic City, New Jersey. The Scope...requirements of the Damage Tolerance Data Rule NPRM \\19\\ be...

  14. Application of positron annihilation lineshape analysis to fatigue damage and thermal embrittlement for nuclear plant materials

    SciTech Connect

    Uchida, M.; Ohta, Y.; Nakamura, N. [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan); Yoshida, K. [Ishikawajima-Harima Heavy Industries Co., Ltd., Kanagawa (Japan)

    1995-08-01

    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.

  15. Inuence of foreign-object damage on crack initiation and early crack growth during high-cycle fatigue of Ti6Al4V

    E-print Network

    Ritchie, Robert

    of small surface fatigue cracks in a Ti±6Al±4V alloy, processed for typical turbine blade applications; Ti±6Al±4V 1. Introduction The high-cycle fatigue (HCF) of aircraft gas-turbine engine components has) and (iii) fretting. All these Engineering Fracture Mechanics 67 (2000) 193±207 www

  16. Fatigue Damage Characterization by NDT in Polypropylene/Glass Fibre Composites

    NASA Astrophysics Data System (ADS)

    Reis, Paulo N. B.; Ferreira, José A. M.; Richardson, Mel O. W.

    2011-10-01

    This paper presents the results of a study on glass-fibre-reinforced polypropylene composite in which the fatigue damage was investigated in terms of residual stiffness and temperature rise. Thermographic and acoustic emission techniques were used to aid the interpretation the fatigue damage mechanisms. Different laminates were tested. For one series, all the layers have one of the two fibre directions oriented with the axis of the plate. For the other two series layer distribution was obtained with the following laminate orientation in respect to the axis of the sheet: +45°/0°/-45°/0°/+45°/0°/-45° and +30°/-30°/+30°/0°/+30°/-30°/+30°. It was possible to conclude that the residual stiffness and temperature rise can be used to predict final failure of a structure and/or component. With thermographic technique it is possible to obtain temperature maps and the precise site where the failure will occur.

  17. Experimental study on fatigue performance and damage model of aluminum alloy welding joints for high-speed train car body

    NASA Astrophysics Data System (ADS)

    Wang, Wenjing; Li, Qiang; Liu, Zhiming; Wang, Binjie

    2010-03-01

    In order to realize lightweight, security and comfort, the aluminum alloy profile becomes the first choice of the high speed train carbody. The fatigue experiments are carried on the typical welding joins such as butt, fillet, cruciform and lap joins. The fatigue limits and P-S-N curves are obtained. The non-linearity cumulative damage model is proposed taking loading sequences for consideration and the two-level loading experiments on butt and fillet joints are studied to verify the feasibility of the damage model. The fatigue life of carbody is predicted based on the proposed damage model and the online dynamic stress test results. The results show that the fatigue life calculated by non-linearity damage model is close to that by modified Miner law and 22% less than that by Miner law.

  18. Experimental study on fatigue performance and damage model of aluminum alloy welding joints for high-speed train car body

    NASA Astrophysics Data System (ADS)

    Wang, Wenjing; Li, Qiang; Liu, Zhiming; Wang, Binjie

    2009-12-01

    In order to realize lightweight, security and comfort, the aluminum alloy profile becomes the first choice of the high speed train carbody. The fatigue experiments are carried on the typical welding joins such as butt, fillet, cruciform and lap joins. The fatigue limits and P-S-N curves are obtained. The non-linearity cumulative damage model is proposed taking loading sequences for consideration and the two-level loading experiments on butt and fillet joints are studied to verify the feasibility of the damage model. The fatigue life of carbody is predicted based on the proposed damage model and the online dynamic stress test results. The results show that the fatigue life calculated by non-linearity damage model is close to that by modified Miner law and 22% less than that by Miner law.

  19. Optimization of the method of cold rolling of axial-flow compressor blades taking into consideration the fatigue characteristics

    Microsoft Academic Search

    V. P. Egorov; I. V. Kornet; V. M. Kapralov; V. A. Matviichuk

    1989-01-01

    Conclusions 1.A method has been developed for evaluation of the deformability of blank materials in rolling of thin profile compressor blades which provides the capability of designating the basic parameters of the process of cold rolling of blades. With the use of the proposed method it is possble to intensify the process of cold rolling of blades by reducing the

  20. A Fatigue Damage Model for the Fiber-reinforced Composite of Haversian Cadaveric Cortical Bone

    Microsoft Academic Search

    A. Varvani-Farahani; H. Najmi

    2008-01-01

    A model is developed to assess the fatigue damage of cadaveric human cortical bone as a fiber-reinforced composite by incorporating stiffness degradation of bone materials as the number of loading cycles progresses. This study characterizes the cortical bone structure as a natural fiber-reinforced composite material consisting of Haversian osteons (fibers) embedded in interstitial bone (matrix) and separated by weak cement-line

  1. Effects of local fibre waviness on damage mechanisms and fatigue behaviour of biaxially loaded tube specimens

    Microsoft Academic Search

    F. Schmidt; M. Rheinfurth; P. Horst; G. Busse

    Damage development in and final failure process of glass fibre winding specimens during biaxial fatigue loading are investigated. The phenomena in nominally defect-free tubes and specimens exhibiting local fibre waviness in one layer are compared. A subset of wound tubes is analysed using non-destructive testing methods, i.e. air-coupled guided waves, thermography, optical fracture analysis by a high-speed camera, and discrete

  2. Interfaces and fatigue damage in a metastable beta titanium matrix composite

    Microsoft Academic Search

    W. O Soboyejo; B. M Rabeeh; P Kantzos

    1995-01-01

    The results of a systematic study of the effects of interfacial microstructure on fatigue damage in a metastable ? Ti?15V?3Cr?3Al?3Sn\\/SiC (SCS-9) composite are presented. Interfacial microstructure is controlled by heat treatment in the ? phase field of the matrix, which promotes coarsening of the fiber-matrix interface without significant changes in the metastable ? matrix microstructure (grain size). The effects of

  3. Fretting fatigue of Ti–6Al–4V under flat-on-flat contact

    Microsoft Academic Search

    Alisha L. Hutson; Ted Nicholas; Rick Goodman

    1999-01-01

    A fretting fatigue test system has been developed to simulate the fretting fatigue damage that occurs in turbine engine blade attachments. The test system employs a flat-on-flat contact with blending radii, which reproduces the nominal levels of normal and internal shear stresses present in dovetails. These stress states are achieved through the application of the normal loads required to grip

  4. Parameters identification of fatigue damage model for short glass fiber reinforced polyamide (PA6GF30) using digital image correlation

    Microsoft Academic Search

    F. Meraghni; H. Nouri; N. Bourgeois; C. Czarnota; P. Lory

    2011-01-01

    The work deals with the parameters identification and the experimental validation of a phenomenological model for fatigue anisotropic damage in short glass fiber reinforced polyamide (PA6-GF30). The damage fatigue model has been formulated in terms of strain energy and was implemented into the finite element code ABAQUS\\/Standard through a user defined material subroutine UMAT. The present paper focuses mainly on

  5. Applications of a new magnetic monitoring technique to in situ evaluation of fatigue damage in ferrous components

    SciTech Connect

    Jiles, D.C.; Biner, S.B.; Govindaraju, M.R.; Chen, Z.J. [Iowa State Univ. of Science and Technology, Ames, IA (United States). Center for Nondestructive Evaluation

    1994-06-01

    This project consisted of research into the use of magnetic inspection methods for the estimation of fatigue life of nuclear pressure vessel steel. Estimating the mechanical and magnetic properties of ferromagnetic materials are closely interrelated, therefore, measurements of magnetic properties could be used to monitor the evolution of fatigue damage in specimens subjected to cyclic loading. Results have shown that is possible to monitor the fatigue damage nondestructively by magnetic techniques. For example, in load-controlled high-cycle fatigue tests, it has been found that the plastic strain and coercivity accumulate logarithmically during the fatigue process. Thus a quantitative relationship between coercivity and the number of fatigue cycles could be established based on two empirical coefficients, which can be determined from the test conditions and material properties. Also it was found that prediction of the onset of fatigue failure in steels was possible under certain conditions. In strain-controlled low cycle fatigue, critical changes in Barkhausen emissions, coercivity and hysteresis loss occurred in the last ten to twenty percent of fatigue life.

  6. Structural-Response Analysis, Fatigue-Life Prediction, and Material Selection for 1 MW Horizontal-Axis Wind-Turbine Blades

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Arakere, G.; Subramanian, E.; Sellappan, V.; Vallejo, A.; Ozen, M.

    2010-08-01

    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.

  7. In vitro fatigue behavior of the equine third metacarpus: remodeling and microcrack damage analysis.

    PubMed

    Martin, R B; Stover, S M; Gibson, V A; Gibeling, J C; Griffin, L V

    1996-09-01

    We studied remodeling and microcrack damage in specimens of Thoroughbred racehorse third metacarpal bone that had been subjected to monotonic or fatigue failure. We asked three questions. What effects does mechanical loading have on histologically observable microcrack damage? Are there regional variations in remodeling of the equine cannon bone, and do these variations correlate with mechanical properties? To what extent are remodeling and microcrack damage age-dependent? Machined beams from the medial, lateral, and dorsal cortices were loaded to fracture in four-point bending monotonically, or cyclically at a load initially producing 10,000 microstrain. Specimens were then bulk-stained in basic fuchsin, and cross sections were prepared from loaded and load-free regions of each beam. Current and past remodeling, porosity, and microcrack density and length were determined histomorphometrically. Strained and unstained microcracks were observed. Unstained cracks were associated with regions of woven bone and appeared to be damaged Sharpey's fibers. Their density (approximately 30/mm2) did not increase after failure, but their length (approximately 25 microns) did, especially near the surfaces of the beam. Stained cracks were wider and longer than unstained cracks and were located primarily near the fracture surface and on the compressed side of the beam. Stained cracks after failure were more numerous in those beams having a higher elastic modulus, a shorter fatigue life, or greater deformation at failure. The extent of past remodeling increased with age, especially in the medial region; the rate of current remodeling generally declined with age, but not in the dorsal region, which has the best fatigue resistance. In summary, while remodeling varied with age and region, its effects on bone structure did not appear to influence microdamage. Basic fuchsin staining of damage in fractured equine bone was independent of age and region and confined to near the fracture surfaces. Distributed microdamage consisted only of what appeared to be subtle disruptions of Sharpey's fibers. PMID:8893774

  8. Three-dimensional constitutive model considering transformation-induced damage and resulting fatigue failure in shape memory alloys

    NASA Astrophysics Data System (ADS)

    Hartl, Darren J.; Chemisky, Yves; Meraghni, Fodil

    2014-03-01

    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.

  9. Modeling of long-term fatigue damage of soft tissue with stress softening and permanent set effects

    PubMed Central

    Martin, Caitlin; Sun, Wei

    2012-01-01

    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

  10. Performance optimization of a diagnostic system based upon a simulated strain field for fatigue damage characterization

    NASA Astrophysics Data System (ADS)

    Sbarufatti, C.; Manes, A.; Giglio, M.

    2013-11-01

    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.

  11. An experimental investigation of homogeneous fatigue damage in a random short-fiber composite under combined tension-torsion loading

    SciTech Connect

    Dasgupta, A.

    1989-01-01

    An experimental study is conducted to examine the effects of the state of stress on the fundamental nature of distributed fatigue damage in a random short fiber composite. The project consists of two different tasks: first, to develop a new experimental method, for conducting combined shear and axial fatigue damage in composites which are difficult to fabricate in axisymmetric configurations; and second, to study the evolution of the multiaxial fatigue damage in the material. A sandwich specimen, consisting of SMC composite skins bonded to an aluminum honeycomb core, is proposed. Anisotropic finite element analyses are used to obtained detailed stress and deformation fields in the composite facing and in the core of specimens with optimum geometry. The macroscopic fatigue damage is defined and measured as the relative change in the elastic stiffness tensor of the composite. Multiaxial extensometry is developed for strain measurements, and an approximate analytical technique is evolved for online prediction of the multiaxial stress state in the damaged material. Measurements of residual modulus are conducted, after multiaxial fatiguing, to provide additional information on the residual stiffness of the composite. The magnitude and rate of stiffness degradation are found to depend not only on the level of stress but also on the state of stress. Combined stress states are found to be particularly detrimental to the degradation rate of shear modulus. Microscopic damage parameters such as crack length distribution and crack orientation distribution are monitored through non-destructive replication and subsequent quantitative microscopy techniques.

  12. A study of fatigue damage mechanisms in Waspaloy from 25 to 800 C

    NASA Technical Reports Server (NTRS)

    Lerch, B. A.; Jayaraman, N.; Antolovich, S. D.

    1984-01-01

    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.

  13. Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.; Dempsey, Paula J.; Heath, Gregory F.; Shanthakumaran, Perumal

    2009-01-01

    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.

  14. Development of advanced structural analysis methodologies for predicting widespread fatigue damage in aircraft structures

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.; Starnes, James H., Jr.; Newman, James C., Jr.

    1995-01-01

    NASA is developing a 'tool box' that includes a number of advanced structural analysis computer codes which, taken together, represent the comprehensive fracture mechanics capability required to predict the onset of widespread fatigue damage. These structural analysis tools have complementary and specialized capabilities ranging from a finite-element-based stress-analysis code for two- and three-dimensional built-up structures with cracks to a fatigue and fracture analysis code that uses stress-intensity factors and material-property data found in 'look-up' tables or from equations. NASA is conducting critical experiments necessary to verify the predictive capabilities of the codes, and these tests represent a first step in the technology-validation and industry-acceptance processes. NASA has established cooperative programs with aircraft manufacturers to facilitate the comprehensive transfer of this technology by making these advanced structural analysis codes available to industry.

  15. Symbolic time series analysis of ultrasonic data for early detection of fatigue damage

    NASA Astrophysics Data System (ADS)

    Gupta, Shalabh; Ray, Asok; Keller, Eric

    2007-02-01

    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 proposed method has been evaluated relative to existing pattern recognition tools, such as neural networks and principal component analysis, for detection of small changes in the statistical characteristics of the observed data sequences. This concept is experimentally validated on a special-purpose test apparatus for 7075-T6 aluminium alloy specimens, where the anomalies accrue from small fatigue crack growth.

  16. Study of the Applicability of Eddy Current NDT for Fatigue Damage Evaluation in Aluminum Alloy 2024-T3

    Microsoft Academic Search

    Tanius R. Mansur; Nelson N. Atanázio Filho; Paulo T. V. Gomes; Denis H. B. Scaldaferr; Vlamir C. E. Almeida; Antônio E. Aguiar; Geraldo A. Scoralick; André L. Nogueira; Donizete A. Alencar

    Mechanical components are generally expected to be damaged by fatigue processes along their lifetime. Since the maximum allowable stress value is reached, some irrecoverable and cumulative damage appears in materials. That process is related with the nucleation of superficial or volumetric discontinuities (micro-cracks or micro-cavities) and begins when any localized stress is greater than the material yield stress. For components

  17. An investigation of rolling-sliding contact fatigue damage of carburized gear steels

    NASA Astrophysics Data System (ADS)

    Kramer, Patrick C.

    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.

  18. Fatigue damage assessment of high-usage in-service aircraft fuselage structure

    NASA Astrophysics Data System (ADS)

    Mosinyi, Bao Rasebolai

    As the commercial and military aircraft fleets continue to age, there is a growing concern that multiple-site damage (MSD) can compromise structural integrity. Multiple site damage is the simultaneous occurrence of many small cracks at independent structural locations, and is the natural result of fatigue, corrosion, fretting and other possible damage mechanisms. These MSD cracks may linkup and form a fatigue lead crack of critical length. The presence of MSD also reduces the structure's ability to withstand longer cracks. The objective of the current study is to assess, both experimentally and analytically, MSD formation and growth in the lap joint of curved panels removed from a retired aircraft. A Boeing 727-232 airplane owned and operated by Delta Air Lines, and retired at its design service goal, was selected for the study. Two panels removed from the left-hand side of the fuselage crown, near stringer 4L, were subjected to extended fatigue testing using the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration (FAA) William J. Hughes Technical Center. The state of MSD was continuously assessed using several nondestructive inspection (NDI) methods. Damage to the load attachment points of the first panel resulted in termination of the fatigue test at 43,500 fatigue cycles, before cracks had developed in the lap joint. The fatigue test for the second panel was initially conducted under simulated in-service loading conditions for 120,000 cycles, and no cracks were detected in the skin of the panel test section. Artificial damage was then introduced into the panel at selected rivets in the critical (lower) rivet row, and the fatigue loads were increased. Visually detectable crack growth from the artificial notches was first seen after 133,000 cycles. The resulting lead crack grew along the lower rivet row, eventually forming an 11.8" long unstable crack after 141,771 cycles, at which point the test was terminated. Posttest fractograpic examinations of the crack surfaces were conducted, revealing the presence of subsurface MSD at the critical rivet row of the lap joint. Special attention was also given to the stringer clips that attach the fuselage frames to the stringers, since they also experienced cracking during the fatigue tests. The performance of the different conventional and emerging NDI methods was also assessed, and some of the emerging NDI methods were quite effective in detecting and measuring the length of subsurface cracks. Delta Air Lines conducted a separate destructive investigation on the state of damage along the right-hand side of the fuselage, near stringer 4R. A comparison of these two studies showed that the lap joint on the left hand-side of the aircraft, along stringer 4L, had better fatigue life than the one on the opposite side, along stringer 4R. The cause of the difference in fatigue life was investigated by close examination of the rivet installation qualities, and was found to be a result of better rivet installation along the lap joint at stringer 4L. Finite element models for both the skin and substructures of the panels were developed and geometrically nonlinear finite element analyses were conducted to verify the loading conditions and to determine near-field parameters governing MSD initiation and growth. Fatigue crack growth predictions based on the NASGRO equation were in good agreement with the experimental crack growth data for through-the-thickness cracks. For subsurface cracks, simulation of crack growth was found to correlate better with fractography data when an empirical crack growth model was used. The results of the study contribute to the understanding of the initiation and growth of MSD in the inner skin layer of a lap joint, and provide valuable data for the evaluation and validation of analytical methodologies to predict MSD initiation and growth and a better understanding on the effect of manufacturing quality on damage accumulation along the lap joint.

  19. Multitechnique monitoring of fatigue damage in adhesively bonded composite lap-joints

    NASA Astrophysics Data System (ADS)

    Karpenko, Oleksii; Koricho, Ermias; Khomenko, Anton; Dib, Gerges; Haq, Mahmoodul; Udpa, Lalita

    2015-03-01

    The requirement for reduced structural weight has driven the development of adhesively bonded joints. However, a major issue preventing their full acceptance is the initiation of premature failure in the form of a disbond between adherends, mainly due to fatigue, manufacturing flaws or impact damage. This work presents the integrated approach for in-situ monitoring of degradation of the adhesive bond in the GFRP composite lap-joint using ultrasonic guided waves and dynamic measurements from strategically embedded FBG sensors. Guided waves are actuated with surface mounted piezoelectric elements and mode tuning is used to provide high sensitivity to the degradation of the adhesive layer parameters. Composite lap-joints are subjected to fatigue loading, and data from piezoceramic transducers are collected at regular intervals to evaluate the progression of damage. Results demonstrate that quasi-static loading affects guided wave measurements considerably, but FBG sensors can be used to monitor the applied load levels and residual strains in the adhesive bond. The proposed technique shows promise for determining the post-damage stiffness of adhesively bonded joints.

  20. Characterization of Fatigue Damage for Bonded Composite Skin/Stringer Configurations

    NASA Technical Reports Server (NTRS)

    Paris, Isabelle; Cvitkovich, Michael; Krueger, Ronald

    2008-01-01

    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.

  1. High-temperature, high-frequency fretting fatigue of a single crystal nickel alloy

    Microsoft Academic Search

    John Frederick Matlik

    2004-01-01

    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

  2. Fatigue damage of ball bearing steel: Influence of phases dispersed in the martensitic matrix

    NASA Astrophysics Data System (ADS)

    Vincent, L.; Coquillet, B.; Guiraldenq, P.

    1980-06-01

    The specific behavior of dispersed phases as nonmetallic inclusions or carbides is defined through rotating beam fatigue tests for several martensitic matrices of ball bearing steel. An accurate study of nucleation in sublayers shows the major part played by such parameters of damaging as the shape, size, chemical nature and internal boundaries of defects and also applied stresses. To attempt an explanation of the specific harmfulness of those weak points, we consider the combination formed by the defect and its surrounding matrix and define the concept of the “minimal true initiating stress”.

  3. Experimental study on fatigue performance and damage model of aluminum alloy welding joints for high-speed train car body

    Microsoft Academic Search

    Wenjing Wang; Qiang Li; Zhiming Liu; Binjie Wang

    2009-01-01

    In order to realize lightweight, security and comfort, the aluminum alloy profile becomes the first choice of the high speed train carbody. The fatigue experiments are carried on the typical welding joins such as butt, fillet, cruciform and lap joins. The fatigue limits and P-S-N curves are obtained. The non-linearity cumulative damage model is proposed taking loading sequences for consideration

  4. Life assessment and repair of fatigue damaged high strength aluminium alloy structure using a peening rework method

    Microsoft Academic Search

    L. Molent; S. Barter; B. Main

    2008-01-01

    This paper discusses a holistic assessment and rework\\/repair process for fatigue damaged structure based on estimating the depth of any potential cracking, its removal and subsequently improving the fatigue resistance of the region by peening the area using tightly controlled conditions. The process was developed to be generally applicable to parts of the F\\/A-18 aircraft’s aluminium alloy 7050 centre barrel

  5. ACTIVE AERODYNAMIC BLADE CONTROL DESIGN FOR LOAD REDUCTION ON LARGE WIND TURBINES

    Microsoft Academic Search

    David G. Wilson; Dale E. Berg; Mathew F. Barone; Jonathan C. Berg; Brian R. Resor; Don W. Lobitz

    Through numerical simulations that use trailing edge flaps as active aerodynamic load control devices on wind turbines that range from 0.6MW-5MW rated power, a 20-32% reduction in blade root flap bending moments was achieved. This allows the turbine blade lengths to be increased, without exceeding origi- nal fatigue damage on the system, resulting in larger swept ro- tor area. This

  6. Estimating the strength of turbine rotor blades taking into account operational damage

    Microsoft Academic Search

    V. T. Kozyrev

    1977-01-01

    Conclusions 1.The law of equality of the action of opposite forces was used as the basis for determining the ratio of residual surface compressive stresses to subsurface tensile stresses in a hardened compressor rotor blade for the case of thin and thick cross sections.2.Equations were derived which relate components of the stress state due to service loads to components of

  7. Nondestructive evaluation of fatigue damage in aluminum 2024 by x-ray diffraction

    SciTech Connect

    Ferguson, M.W.

    1994-12-01

    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.

  8. Fatigue

    MedlinePLUS

    ... organs. Your body also changes the way it processes foods and nutrients. All of these changes are stressful for your body and may lead to fatigue. Physical and psychological changes during pregnancy can also cause mental and ...

  9. Particle impact on metal substrates with application to foreign object damage to aircraft engines

    Microsoft Academic Search

    X. Chen; John W. Hutchinson

    2002-01-01

    Foreign object damage (FOD) occurs when hard, millimeter-sized objects such as gravel or sand are ingested into aircraft jet engines. Particles impacting turbine blades at velocities up to about 300m\\/s produce small indentation craters which can become sites for fatigue crack initiation, severely limiting the lifetime of the blade. A framework for analyzing FOD and its effect on fatigue cracking

  10. Acoustic fatigue characterization of carbon/carbon panels

    NASA Technical Reports Server (NTRS)

    Rizzi, S. A.; Clevenson, S. A.; Daniels, E. F.

    1992-01-01

    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.

  11. Neural Network Modelling of Oscillatory Loads and Fatigue Damage Estimation of Helicopter Components

    NASA Astrophysics Data System (ADS)

    Cabell, R. H.; Fuller, C. R.; O'Brien, W. F.

    1998-01-01

    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.

  12. Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Xue, D.; Shi, Y.

    2013-01-01

    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.

  13. 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)

    Tippmann, Jeffery D.; Lanza di Scalea, Francesco

    2014-03-01

    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.

  14. 75 FR 793 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-06

    ...require evaluation of fatigue and residual static strength of composite rotorcraft structures...FAA to avoid catastrophic failure due to static or fatigue loads. The proposal would...show that catastrophic failure due to static and fatigue loads, considering the...

  15. Fatigue damage detection in carbon-fiber-reinforced composites using an intensity-based optical fiber sensor

    NASA Astrophysics Data System (ADS)

    Badcock, Rodney A.; Fernando, Gerard F.

    1995-04-01

    The detection of fatigue damage within composite materials is vital for the safe use of these materials in engineering structures. Embedded fiber-optic sensors have been identified as suitable for damage detection in these materials, as they have minimal interference with bulk composite properties. The relationship between fatigue damage within a composite material and the associated moduli changes have been used to characterize damage development and progression. An intensity based fiber-optic strain sensor has been designed and evaluated for damage detection in composite laminates. This intensity sensor has the ability to monitor rapid strain changes without loss of the reference level. This sensor utilizes relatively simple and inexpensive instrumentation. In this study the fiber-optic strain sensor has been embedded within a 16 layer cross-ply carbon/epoxy laminate. The response of the sensor has been compared to that obtained from strain gauges and an extensometer. The composite coupons with the embedded sensors have also been subjected to tension-tension and tension- compression fatigue. The stiffness decay of the composite during fatigue loading was monitored in real-time.

  16. Analysis of fatigue crack growth behavior in niobium–hydrogen alloys using the unified approach to fatigue damage

    Microsoft Academic Search

    K Sadananda; R Sreenivasan

    2001-01-01

    Evaluation of fatigue crack growth behavior in Nb–H alloys was done using the Unified Approach to Fatigue Crack Growth developed earlier. It shows that the mechanism of hydrogen embrittlement changes with crack growth rate, load ratio and hydrogen concentration. The analysis provides an example where the changes in the governing mechanisms can be easily followed using the ?K* vs Kmax*

  17. FUNDAMENTALS OF THE DEEP ROLLING OF COMPRESSOR BLADES FOR TURBO AIRCRAFT ENGINES

    Microsoft Academic Search

    S. Mader; F. Klocke

    The weakening of the fatigue strength of turbine blades due to local impa caused by foreign objects (Foreign Object Damage - FOD) represents i3 safety risk in modern aviation. It is possible to employ deep rolling to courat component weakening in a particularly effective way. In order to derive a possible process parameter-set in advance, fundamental knowledge regarding the elastic

  18. Fatigue damage evolution and property degradation of a SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite

    SciTech Connect

    Wang, P.C.; Jeng, S.M.; Yang, J.M. [Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering] [Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering; Russ, S.M. [Wright Lab., Wright-Patterson AFB, OH (United States). Materials Directorate] [Wright Lab., Wright-Patterson AFB, OH (United States). Materials Directorate

    1996-08-01

    The fatigue damage evolution and property degradation of a SCS-6/Ti-22Al-23Nb orthorhombic titanium aluminide composite under low cycle fatigue loading at room temperature was investigated. The fatigue test was conducted under a load-controlled mode with a load ratio (R) of 0.1, a frequency of 10 Hz, and a maximum applied stress ranging from 600 to 945 MPa. The stiffness reduction as well as the evolution of microstructural damage which includes matrix crack length, matrix crack density and interfacial debonding length as a function of fatigue cycles, and applied stresses were measured. An analytical model and a computer simulation were also developed to predict the residual stiffness and the post-fatigued tensile strength as a function of microstructural damage. Finally, a steady-state crack growth model proposed by Marshall et al. was used to predict the interfacial frictional stress and the critical crack length. Correlation between the theoretical predictions and experimental results were also discussed.

  19. SHM of wind turbine blades using piezoelectric active-sensors

    SciTech Connect

    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

    2010-01-01

    This paper presents a variety of structural health monitoring (SHM) techniques, based on the use of piezoelectric active-sensors, used to determine the structural integrity of wind turbine blades. Specifically, Lamb wave propagations, frequency response functions, and time series based methods are utilized to estimate the condition of wind turbine blades. For experiments, a 1m section of a 9m CX100 blade is used. Overall, these three methods yielded a sufficient damage detection capability to warrant further investigation into field deployment. A full-scale fatigue test of a CX-100 wind turbine blade is also conducted. This paper summarizes considerations needed to design such SHM systems, experimental procedures and results, and practical implementation issues that can be used as guidelines for future investigations.

  20. Optical Sensing of the Fatigue Damage State of CFRP under Realistic Aeronautical Load Sequences

    PubMed Central

    Zuluaga-Ramírez, Pablo; Arconada, Álvaro; Frövel, Malte; Belenguer, Tomás; Salazar, Félix

    2015-01-01

    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

  1. Healing of fatigue damage in NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    F-X Wagner, M.; Nayan, N.; Ramamurty, U.

    2008-09-01

    Progressive accumulation of stress-induced martensite during cyclic loading of NiTi shape memory alloys results in both structural and functional fatigue. We present experimental data demonstrating that periodic annealing of the fatigued samples above the austenite finish temperature ('healing') retransforms the residual martensite back into the parent phase, and therefore enhances the fatigue life (stress-controlled testing, structural fatigue) or partly reverses the changes in the pseudo-elastic hysteresis (strain-controlled testing, functional fatigue).

  2. Predicting sequence effects and cumulative damage in fatigue using a unified model for crack initiation and growth

    SciTech Connect

    Miller, A.K.

    1983-01-01

    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.

  3. Cross-flow VIV-induced fatigue damage of deepwater steel catenary riser at touch-down point

    NASA Astrophysics Data System (ADS)

    Wang, Kun-peng; Tang, Wen-yong; Xue, Hong-xiang

    2014-03-01

    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.

  4. Prediction of damage evolution in continuous fiber metal matrix composites subjected to fatigue loading

    SciTech Connect

    Allen, D.; Helms, K.; Lagoudas, D. [Texas A& M Univ., College Station, TX (United States)] [and others

    1995-08-01

    A life prediction model is being developed by the authors for application to metal matrix composites (MMC`s). The systems under study are continuous silicon carbide fibers imbedded in titanium matrix. The model utilizes a computationally based framework based on thermodynamics and continuum mechanics, and accounts for matrix inelasticity, damage evolution, and environmental degradation due to oxidation. The computational model utilizes the finite element method, and an evolutionary analysis of a unit cell is accomplished via a time stepping algorithm. The computational scheme accounts for damage growth such as fiber-matrix debonding, surface cracking, and matrix cracking via the inclusion of cohesive zone elements in the unit cell. These elements are located based on experimental evidence also obtained by the authors. The current paper outlines the formulation utilized by the authors to solve this problem, and recent results are discussed. Specifically, results are given for a four-ply unidirectional composite subjected to cyclic fatigue loading at 650{degrees}C both in air and inert gas. The effects of oxidation on the life of the composite are predicted with the model, and the results are compared to limited experimental results.

  5. Corrosion fatigue of steam turbine-blading alloys in operational environments. Final report. [Ti-6Al-4V

    SciTech Connect

    Cunningham, J.W.; Dowling, N.E.; Heymann, F.J.; Jonas, O.; Kunsman, L.D.; Pebler, A.R.; Swaminathan, V.P.; Willertz, L.E.; Rust, T.M.

    1984-09-01

    The corrosion fatigue strengths of Type 403 and 17-4 PH stainless steel and several processing variations of Ti-6Al-4V were determined in various steam turbine environments. Steam and turbine deposits were analyzed to establish test environments. Pure 80/sup 0/C water base line data was determined and compared to saturated aqueous solutions of NaCl, Na/sub 2/SO/sub 4/, Na/sub 3/PO/sub 4/, Na/sub 2/SiO/sub 3/ and some mixtures of these. The pH and oxygen content were also varied. Fatigue strengths at 20 kHz and 100 Hz were established for 10/sup 9/ and 10/sup 7/ cycles, respectively. The corrosion fatigue effect of notches, shot peening and mean stress were measured. Acidic, high oxygen 22% NaCl solutions were found to be extremely aggressive, causing Type 403 to lose 87% of its pure water fatigue strength; more basic solutions and other chemical species were less severe. The Ti-6Al-4V alloys were only mildly affected in most environments although NaOH plus SiO/sub 2/ was found to dissolve this alloy. The effect of the environments on 17-4 PH was intermediate between Type 403 and Ti-6Al-4V.

  6. Fretting Stresses in Single Crystal Superalloy Turbine Blade Attachments

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Swanson, Gregory

    2000-01-01

    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.

  7. Critical plane-energy based approach for assessment of biaxial fatigue damage where the stress-time axes are at different frequencies

    Microsoft Academic Search

    A. Varvani-Farahani

    2003-01-01

    A new fatigue parameter has been developed to assess the fatigue lives under in-phase and out-of-phase biaxial constant amplitude fatigue stressing where the stresses are at different frequencies. In this parameter, the normal and shear stress and strain ranges have been calculated from the largest stress and strain Mohr's circles. The total damage accumulation in a block loading history has

  8. Experimental analysis of behavior and damage of sandwich composite materials in three-point bending. Part 2. Fatigue test results and damage mechanisms

    Microsoft Academic Search

    A. Bezazi; A. El Mahi; J.-M. Berthelot; B. Bezzazi

    2009-01-01

    The analysis of stiffness degradation and the identification of damage mechanisms during and after fatigue tests of sandwich\\u000a panels with PVC foam cores have been performed. The sandwich panels with cross-ply laminates skins made of glass fiber and\\u000a epoxy resin were manufactured by vacuum moulding and subjected to three-point bending tests. Two PVC cores of similar type\\u000a but with differing

  9. Helicopter rotor blade design for minimum vibration

    NASA Technical Reports Server (NTRS)

    Taylor, R. B.

    1984-01-01

    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.

  10. The normalized coffin manson plot in terms of a new damage function based on grain boundary cavitation under creep fatigue condition

    Microsoft Academic Search

    Soo Woo Nam; Young Cheol Yoon; Baig Gyu Choi; Je Min Lee; Jin Wan Hong

    1996-01-01

    A new damage function based on a model for the creep-fatigue life prediction in terms of nucleation and growth of grain boundary cavities is proposed. This damage function is a combination of the terms related to the cavitational damage in the life prediction equation and is generally applicable to the materials in which failure is controlled by the grain boundary

  11. Corrosion fatigue of steam turbine-blading alloys in operational environments. Final report. [Ti6Al4V

    Microsoft Academic Search

    J. W. Cunningham; N. E. Dowling; F. J. Heymann; O. Jonas; L. D. Kunsman; A. R. Pebler; V. P. Swaminathan; L. E. Willertz; T. M. Rust

    1984-01-01

    The corrosion fatigue strengths of Type 403 and 17-4 PH stainless steel and several processing variations of Ti-6Al-4V were determined in various steam turbine environments. Steam and turbine deposits were analyzed to establish test environments. Pure 80°C water base line data was determined and compared to saturated aqueous solutions of NaCl, NaâSOâ, NaâPOâ, NaâSiOâ and some mixtures of these. The

  12. On the application of the Kitagawa–Takahashi diagram to foreign-object damage and high-cycle fatigue

    Microsoft Academic Search

    J. O. Peters; B. L. Boyce; X. Chen; J. M. McNaney; J. W. Hutchinson; R. O. Ritchie

    2002-01-01

    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

  13. Fatigue crack growth from foreign object damage under combined low and high cycle loading. Part I: Experimental studies

    Microsoft Academic Search

    J. Ding; R. F. Hall; J. Byrne; J. Tong

    2007-01-01

    The study aims to understand small crack growth behaviour in Ti–6Al–4V plate specimens after foreign object damage (FOD), under combined low and high cycle fatigue (LCF\\/HCF) loading conditions. The loading block studied represents one of the simplest loading sequences experienced by aero-engines and each block includes a single LCF cycle at a load ratio (R) of 0.01 with 1000 HCF

  14. Structural and Damage Assessment of Multi-Section Modular Hybrid Composite Wind Turbine Blade

    E-print Network

    Nanami, Norimichi

    2014-07-25

    %, and natural gas use by 11% through 2030 [2]. Due to the aftermath of the 2011 Tohoku earthquake and tsunami that resulted in severe damage to several nuclear reactors at Fukushima Daiichi Nuclear Power Plant, the Japanese government put the use of nuclear... power on hold. The event may have more profound implications for the future of world nuclear power. The support of clean energy is demanded due to the possible 2 ramifications of Fukushima for the long-term global developments and government...

  15. Effects of successive judo matches on fatigue and muscle damage markers.

    PubMed

    Detanico, Daniele; Dal Pupo, Juliano; Franchini, Emerson; Dos Santos, Saray G

    2015-04-01

    This study aimed to investigate the acute effects of simulated judo matches on fatigue and muscle damage markers. Twenty male judo athletes participated in this study. The athletes performed three 5-minute judo matches separated by 15 minutes of passive rest between each match. The following measurements were performed before and after each match: shoulder external/internal rotation isokinetic torque and countermovement jump (CMJ). Blood samples were taken before the first match and after the third match for serum creatine kinase (CK) and lactate dehydrogenase (LDH) analysis. T-tests for dependent samples and analysis of variance for repeated measures were used to compare the variables over the time; the level of significance was set at 0.05. An overall effect of the successive matches on shoulder internal (PTIN) and external (PTEX) rotation peak torque and CMJ performance was observed. PTIN and PTEX showed significant decreases in postmatch 2 and postmatch 3 when compared with the baseline (p < 0.01). Also, CMJ height declined in postmatch 2 and postmatch 3 (p < 0.01) when compared with the baseline. Serum CK and LDH activity increased significantly after the third match (p < 0.01). It was concluded that 3 successive judo matches induced a decline of peak torque and muscle power in the upper and lower limbs, respectively, and also provoked an increase of muscle damage markers. These findings may provide important knowledge for coaches and physical trainers to improve judo-specific strength training in both the upper and lower limbs. PMID:25426512

  16. HIGH-CYCLE FATIGUE AND TIME-DEPENDENT FAILURE IN METALLIC ALLOYS FOR PROPULSION SYSTEMS AFOSR F49620-96-1-0478

    Microsoft Academic Search

    R. O. Ritchie; S. Suresh; J. W. Hutchinson; W. W. Milligan; A. W. Thompson

    The objective of the AFOSR-MURI High-Cycle Fatigue program is to characterize and model the limiting damage states at the onset of high-cycle fatigue to facilitate mechanistic understanding as a basis for life prediction. Efforts have been focused on the influence of foreign object damage (FOD) and fretting on a Ti-6Al-4V blade alloy and a polycrystalline Ni-base disk alloy. Accomplishments from

  17. 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)

    Hammett, J. C.; Hayes, C. H.; Price, J. M.; Robinson, J. K.; Teal, G. A.; Thomson, J. M.; Tilley, D. M.; Welch, C. T.

    1983-01-01

    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.

  18. The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)

    NASA Technical Reports Server (NTRS)

    Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.

    2000-01-01

    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.

  19. The mechanics and tribology of fretting fatigue with application to riveted lap joints

    Microsoft Academic Search

    Matthew Paul Szolwinski

    1998-01-01

    Fretting is the synergistic combination of wear, corrosion, and fatigue damage mechanisms driven by the partial slip of contacting surfaces. The surface microslip and near-surface contact stresses associated with fretting can lead to severe reduction in service lifetimes of contacting components as diversified as bearings, turbine blades and mechanically-fastened joints, both structural and biological. This tribologically induced degradation has come

  20. Atomistic modeling of nanowires, small-scale fatigue damage in cast magnesium, and materials for MEMS.

    SciTech Connect

    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)

    2006-10-01

    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.

  1. Effect of microstructure on pitting and corrosion fatigue of 17-4 PH turbine blade steel in chloride environments

    SciTech Connect

    Syrett, B.C.; Viswanathan, R.

    1982-02-01

    Depending on its heat treatment, 17-4 PH stainless steel may contain significant levels of reformed austenite and untempered martensite in a matrix of tempered martensite. Shot peening can cause changes in the microstructure of the surface layers by transforming the austenite to untempered martensite. The effect of these microstructural varations on the resistance of 17-4 PH stainless steel to pitting and corrosion fatigue has been determined in simulated steam turbine environments. The results of two electrochemical tests (large amplitude cyclic voltammetry and the pit propagation rate (PPR) test) indicate that tempering temperature and shot peening have only minor effects on resistance to pit initiation and propagation in any one of three aqueous chloride environments. However, the susceptibility of this stainless steel to corrosion fatigue in one of these environments (6 wt % FeCl/sub 3/) was reduced by increasing the tempering temperature from 538/sup 0/C (1000/sup 0/F) to 649/sup 0/C (1200/sup 0/F).

  2. Role of brain macrophages on IL-1beta and fatigue following eccentric exercise-induced muscle damage.

    PubMed

    Carmichael, Martin D; Davis, J Mark; Murphy, E Angela; Carson, James A; Van Rooijen, N; Mayer, Eugene; Ghaffar, Abdul

    2010-05-01

    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 on brain IL-1beta and fatigue following eccentric exercise-induced muscle damage. Mice were assigned to six groups: Downhill saline (DWNSAL), downhill clodronate (DWNCLD), uphill saline (UPSAL), uphill clodronate (UPCLD), non-running saline (CONSAL) or non-running clodronate (CONCLD). Mice were given intracerebroventricular (ICV) (10 microL) injections of clodronate-filled liposomes (CLD) to deplete macrophages, or saline-filled liposomes (SAL) and run on a treadmill at 22m/min and -14% (DWN) or 14% (UP) grade for 150 min. A subset of uphill and downhill running mice (n=40) was then run to fatigue on a treadmill at 36m/min, 8% grade at 24h after the uphill and downhill runs. A second subset of uphill, downhill, and control mice (n=30) was sacrificed 24h after the run for analysis of brain IL-1beta concentration. Histological examination confirmed previous reports that CLD administration reduced perivascular and meningeal macrophage subsets in the brain. CLD reduced IL-1beta concentration in the cortex of DWN mice (P<0.05), which was associated with enhanced treadmill performance 24h after both uphill and downhill runs (P<0.05) although the magnitude was greater following the downhill run. These results suggest that brain macrophages can contribute to the increase in brain IL-1beta and fatigue that are associated with recovery from exercise-induced muscle damage. PMID:20051263

  3. Self-sealing of thermal fatigue and mechanical damage in fiber-reinforced composite materials

    NASA Astrophysics Data System (ADS)

    Moll, Jericho L.

    Fiber reinforced composite tanks provide a promising method of storage for liquid oxygen and hydrogen for aerospace applications. The inherent thermal fatigue of these vessels leads to the formation of microcracks, which allow gas phase leakage across the tank walls. In this dissertation, self-healing functionality is imparted to a structural composite to effectively seal microcracks induced by both mechanical and thermal loading cycles. Two different microencapsulated healing chemistries are investigated in woven glass fiber/epoxy and uni-weave carbon fiber/epoxy composites. Self-healing of mechanically induced damage was first studied in a room temperature cured plain weave E-glass/epoxy composite with encapsulated dicyclopentadiene (DCPD) monomer and wax protected Grubbs' catalyst healing components. A controlled amount of microcracking was introduced through cyclic indentation of opposing surfaces of the composite. The resulting damage zone was proportional to the indentation load. Healing was assessed through the use of a pressure cell apparatus to detect nitrogen flow through the thickness direction of the damaged composite. Successful healing resulted in a perfect seal, with no measurable gas flow. The effect of DCPD microcapsule size (51 microm and 18 microm) and concentration (0--12.2 wt%) on the self-sealing ability was investigated. Composite specimens with 6.5 wt% 51 microm capsules sealed 67% of the time, compared to 13% for the control panels without healing components. A thermally stable, dual microcapsule healing chemistry comprised of silanol terminated poly(dimethyl siloxane) plus a crosslinking agent and a tin catalyst was employed to allow higher composite processing temperatures. The microcapsules were incorporated into a satin weave E-glass fiber/epoxy composite processed at 120°C to yield a glass transition temperature of 127°C. Self-sealing ability after mechanical damage was assessed for different microcapsule sizees (25 microm and 42 microm) and concentrations (0--11 vol%). Incorporating 9 vol% 42 microm capsules or 11 vol% 25 microm capsules into the composite matrix leads to 100% of the samples sealing. The effect of microcapsule concentration on the short beam strength, storage modulus, and glass transition temperature of the composite specimens was also investigated. The thermally stable tin catalyzed poly(dimethyl siloxane) healing chemistry was then integrated into a [0/90]s uniweave carbon fiber/epoxy composite. Thermal cycling (-196°C to 35°C) of these specimens lead to the formation of microcracks, over time, formed a percolating crack network from one side of the composite to the other, resulting in a gas permeable specimen. Crack damage accumulation and sample permeability was monitored with number of cycles for both self-healing and traditional non-healing composites. Crack accumulation occurred at a similar rate for all sample types tested. A 63% increase in lifetime extension was achieved for the self-healing specimens over traditional non-healing composites.

  4. Positron lifetime measurements as a non-destructive technique to monitor fatigue damage

    Microsoft Academic Search

    Byrne

    1975-01-01

    In the fatigue cycling of initially hard copper, self consistent ; positron lifetime and x-ray particle size measurements followed the softening ; process and revealed a new feature which may be the final development of ; microvoids before fracture. In the cyclic fatigue of initially soft 4340 steel ; closely spaced concurrent measurements of these parameters are now in progress.

  5. OVERVIEW OF LOW PLASTICITY BURNISHING FOR MITIGATION OF FATIGUE DAMAGE MECHANISMS

    Microsoft Academic Search

    Paul S. Prevéy; N. Jayaraman; John Cammett

    2005-01-01

    Surface enhancement technologies such as shot peening (SP), laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. LPB provides thermally stable compression and can be performed in conventional machine shop environments on CNC machine tools. LPB enables

  6. A generalised damage model for constant amplitude fatigue loading of adhesively bonded joints

    Microsoft Academic Search

    H. Khoramishad; A. D. Crocombe; K. B. Katnam; I. A. Ashcroft

    2010-01-01

    The fatigue resistance of adhesively bonded joints is an important aspect of reliable structural design in many sectors. In this paper, the effect of load ratio on the fatigue behaviour of adhesively bonded joints was investigated using both experimental and numerical approaches. Single lap joints were tested under cyclic loading at different load ratios and load levels to characterise their

  7. Mechanics and mechanisms of fatigue damage and crack growth in advanced materials

    E-print Network

    Ritchie, Robert

    , such as ceramics, intermetallics and their respective composites for structural applications where cyclic loading 94720-1760, USA Abstract The mechanisms of fatigue-crack propagation in ceramics and intermetallics by Elsevier Science Ltd. Keywords: Fatigue-crack growth; Crack-tip shielding; Ceramics; Intermetallics 1

  8. Measuring the damage factor of materials with the thin-walled cylinder torsion test and the low-cycle fatigue test

    Microsoft Academic Search

    Mingzhe Shi

    1993-01-01

    An expression is derived for the damage factor, D, and a method for measuring D is proposed which employs the thin-walled cylinder torsion test. Results of torsion tests for steels 35 and 45 are presented as an example. The values of the critical damage factor, Dc, for steel 45 are also determined using low-cycle fatigue tests with controlled strain amplitude.

  9. Stochastic Damage Evolution under Static and Fatigue Loading in Composites with Manufacturing Defects 

    E-print Network

    Huang, Yongxin

    2012-07-16

    In this dissertation, experimental investigations and theoretical studies on the stochastic matrix cracking evolution under static and fatigue loading in composite laminates with defects are presented. The presented work demonstrates a methodology...

  10. Development of criteria for fatigue repairs in bridge girders damaged by out-of-plane distortion 

    E-print Network

    Wilson, Scott David

    1994-01-01

    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...

  11. Peripheral and central fatigue after muscle-damaging exercise is muscle length dependent and inversely related.

    PubMed

    Skurvydas, Albertas; Brazaitis, Marius; Kamandulis, Sigitas; Sipaviciene, Saule

    2010-08-01

    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

  12. Estimating fatigue lifetime of steel weldments locally damaged by variable amplitude multiaxial stress fields

    Microsoft Academic Search

    Luca Susmel

    2010-01-01

    The present investigation aims to prove that the so-called Modified Wöhler Curve Method applied along with the Theory of Critical Distances (formalised in the form of the Point Method) can successfully be used also to estimate fatigue lifetime of steel welded joints subjected to both uniaxial and proportional\\/non-proportional multiaxial variable amplitude load histories. The accuracy and reliability of our fatigue

  13. Microstructure-dependent fatigue damage process zone and notch sensitivity index

    Microsoft Academic Search

    Gbadebo Owolabi; Benedict Egboiyi; Li Shi; Horace Whitworth

    The development of simulation methods for calculating notch root parameters for purposes of estimating the fatigue life of\\u000a notched components is a critical aspect of designing against fatigue failures. At present, however, treatment of the notch\\u000a root stress and plastic strain field gradients, coupled with intrinsic length scales of grains or other material attributes,\\u000a has yet to be developed. Ultimately,

  14. Cumulative Damage of Fiber-Reinforced Elastomer Composites under Fatigue Loading

    Microsoft Academic Search

    B. L. Lee; D. S. Liu

    1994-01-01

    Fracture mechanisms under fatigue loading were assessed in the case of nylon fiber-reinforced elastomer matrix composite which represents the actual carcass of bias aircraft tires. Under uniaxial tension, the angle-plied carcass composite specimens were subjected to a considerably large interply shear strain before failure. The composite specimens exhibited semi-infinite fatigue life when stress amplitude was below a threshold level, i.e.,

  15. An investigation of the fracture and fatigue crack growth behavior of forged damage-tolerant niobium aluminide intermetallics

    Microsoft Academic Search

    F. Ye; C. MerCer; W. O. Soboyejo

    1998-01-01

    The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class\\u000a of forged damage-tolerant niobium aluminide (Nb3Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti\\u000a (10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic

  16. The effect of surface modification on fretting fatigue in Ti Alloy turbine components

    NASA Astrophysics Data System (ADS)

    Chakravarty, S.; Andrews, R. G.; Painaik, P. C.; Koul, A. K.

    1995-04-01

    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.

  17. The normalized coffin manson plot in terms of a new damage function based on grain boundary cavitation under creep fatigue condition

    Microsoft Academic Search

    Soo Woo Nam; Young Cheol Yoon; Baig Gyu Choi; Je Min Lee; Jin Wan Hong

    1996-01-01

    A new damage function based on a model for the creep-fatigue life prediction in terms of nucleation and growth of grain boundary\\u000a cavities is proposed. This damage function is a combination of the terms related to the cavitational damage in the life prediction\\u000a equation and is generally applicable to the materials in which failure is controlled by the grain boundary

  18. Fatigue and Damage Tolerance Analysis of a Hybrid Composite Tapered Flexbeam

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; Schaff, Jeffrey R.; Dobyns, Al

    2001-01-01

    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.

  19. Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics

    NASA Technical Reports Server (NTRS)

    Cantrell, John H., Jr.

    2008-01-01

    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.

  20. Application of piezoelectric active-sensors for SHM of wind turbine blades

    SciTech Connect

    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

    2010-10-04

    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.

  1. Characterisation of foreign object damage (FOD) and early fatigue crack growth in laser shock peened Ti–6Al–4V aerofoil specimens

    Microsoft Academic Search

    S. Spanrad; J. Tong

    2011-01-01

    Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage.In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge

  2. Modeling interfacial conditions in nominally flat contacts for application to fretting fatigue of turbine engine components

    Microsoft Academic Search

    P. A McVeigh; G Harish; T. N Farris; M. P Szolwinski

    1999-01-01

    The area of contact between the blade root and disk in high-performance turbomachinery has been identified as a critical area for the nucleation of fatigue damage leading to premature and often catastrophic component failures. The interaction of small-scale relative displacements or microslip at the contact surfaces and sharp gradients in the near-surface contact stress field drives a damage process known

  3. LOW PLASTICITY BURNISHING (LPB) TREATMENT TO MITIGATE FOD AND CORROSION FATIGUE DAMAGE IN 17-4 PH STAINLESS STEEL

    Microsoft Academic Search

    Paul S. Prevéy; N. Jayaraman

    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

  4. Acoustic Emission and Damage Monitoring During Fatigue of C-SiC Composites at Room Temperature

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Deemer, Chris; Cuneo, Jacques; Smith, Aron; Koenig, John

    2003-01-01

    Fatigue experiments were performed at room temperature for C-fiber reinforced chemical vapor infiltrated (CVI Sic) matrix and melt-infiltrated (MI) matrix composites. The goal was to associate some nondestructive parameter or acoustic emission characteristic with the processes that lead to fatigue failure. Failure only occurred at loads very close to the ultimate. However, correlations between the acoustic data and the eventual failure of the composites could be made. These will be presented with respect to health monitoring of these types of composites.

  5. Damage Theory Applied to Flexural Fatigue Tests on Conventional and Asphalt Rubber Hot Mixes

    Microsoft Academic Search

    Luiz G. R. Mello; Kamil E. Kaloush; Márcio M. Farias

    2010-01-01

    Application of the Continuum Damage Theory (CDT) to evaluate the evolution of internal damage in Hot Mix Asphalt (HMA) is investigated in this paper. The CDT leads to the formulation of a characteristic curve relating normalized pseudo-stiffness and the internal damage variable, and this curve is supposed to be unique for each material. The uniqueness of the characteristic curve was

  6. A Non-Uniformly Under-Sampled Blade Tip-Timing Signal Reconstruction Method for Blade Vibration Monitoring

    PubMed Central

    Hu, Zheng; Lin, Jun; Chen, Zhong-Sheng; Yang, Yong-Min; Li, Xue-Jun

    2015-01-01

    High-speed blades are often prone to fatigue due to severe blade vibrations. In particular, synchronous vibrations can cause irreversible damages to the blade. Blade tip-timing methods (BTT) have become a promising way to monitor blade vibrations. However, synchronous vibrations are unsuitably monitored by uniform BTT sampling. Therefore, non-equally mounted probes have been used, which will result in the non-uniformity of the sampling signal. Since under-sampling is an intrinsic drawback of BTT methods, how to analyze non-uniformly under-sampled BTT signals is a big challenge. In this paper, a novel reconstruction method for non-uniformly under-sampled BTT data is presented. The method is based on the periodically non-uniform sampling theorem. Firstly, a mathematical model of a non-uniform BTT sampling process is built. It can be treated as the sum of certain uniform sample streams. For each stream, an interpolating function is required to prevent aliasing in the reconstructed signal. Secondly, simultaneous equations of all interpolating functions in each sub-band are built and corresponding solutions are ultimately derived to remove unwanted replicas of the original signal caused by the sampling, which may overlay the original signal. In the end, numerical simulations and experiments are carried out to validate the feasibility of the proposed method. The results demonstrate the accuracy of the reconstructed signal depends on the sampling frequency, the blade vibration frequency, the blade vibration bandwidth, the probe static offset and the number of samples. In practice, both types of blade vibration signals can be particularly reconstructed by non-uniform BTT data acquired from only two probes. PMID:25621612

  7. A non-uniformly under-sampled blade tip-timing signal reconstruction method for blade vibration monitoring.

    PubMed

    Hu, Zheng; Lin, Jun; Chen, Zhong-Sheng; Yang, Yong-Min; Li, Xue-Jun

    2015-01-01

    High-speed blades are often prone to fatigue due to severe blade vibrations. In particular, synchronous vibrations can cause irreversible damages to the blade. Blade tip-timing methods (BTT) have become a promising way to monitor blade vibrations. However, synchronous vibrations are unsuitably monitored by uniform BTT sampling. Therefore, non-equally mounted probes have been used, which will result in the non-uniformity of the sampling signal. Since under-sampling is an intrinsic drawback of BTT methods, how to analyze non-uniformly under-sampled BTT signals is a big challenge. In this paper, a novel reconstruction method for non-uniformly under-sampled BTT data is presented. The method is based on the periodically non-uniform sampling theorem. Firstly, a mathematical model of a non-uniform BTT sampling process is built. It can be treated as the sum of certain uniform sample streams. For each stream, an interpolating function is required to prevent aliasing in the reconstructed signal. Secondly, simultaneous equations of all interpolating functions in each sub-band are built and corresponding solutions are ultimately derived to remove unwanted replicas of the original signal caused by the sampling, which may overlay the original signal. In the end, numerical simulations and experiments are carried out to validate the feasibility of the proposed method. The results demonstrate the accuracy of the reconstructed signal depends on the sampling frequency, the blade vibration frequency, the blade vibration bandwidth, the probe static offset and the number of samples. In practice, both types of blade vibration signals can be particularly reconstructed by non-uniform BTT data acquired from only two probes. PMID:25621612

  8. Fatigue damage to a pseudo-?-titanium alloy in the 10–33Hz frequency range

    Microsoft Academic Search

    A. Ya. Krasovskii; Yu. N. Petrov; G. N. Nadezhdin; L. E. Matokhnyuk; V. L. Svechnikov; T. Ya. Yakovleva

    1982-01-01

    The frequency of cyclic loading is an extremely important factor affecting the fatigue fracture of metals. Frequency exerts an effect because sign-changing deformation may be accompanied by several phenomena, especially heating of the material. However, relatively few works have examined the role of frequency in structural changes in the sonic and ultrasonic ranges [I-3]. Due to their low level of

  9. Post-impact fatigue damage growth in fiber–metal laminates

    Microsoft Academic Search

    J. F Laliberté; C Poon; P. V Straznicky; A Fahr

    2002-01-01

    Fiber–metal laminates (FMLs) are a family of hybrid materials currently being considered for use in airframe structural applications. Post-impact fatigue strength tests were carried out on several varieties of GLAss REinforced (GLARE) aluminum laminates. The panels were impacted in a drop weight impact tower located at the Institute for Aerospace Research of the National Research Council of Canada. Observations made

  10. Analysis of the effects of controlled shot peening on fatigue damage of high strength aluminium alloys

    Microsoft Academic Search

    S. Curtis; E. R. de los Rios; C. A. Rodopoulos; A. Levers

    2003-01-01

    The use of two micro-mechanical models for notch sensitivity and fatigue life allowed the development of boundary conditions that would evaluate potential life improvement after controlled shot peening (CSP) in high strength aluminium alloys. The boundary conditions describe the state of equal weight between surface roughening and residual stresses and the implication of material and loading parameters. From the boundary

  11. Deformation history and load sequence effects on cumulative fatigue damage and life predictions

    Microsoft Academic Search

    Julie Colin

    2010-01-01

    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

  12. Fatigue damage assessment by the continuous examination of the magnetomechanical and mechanical behavior

    Microsoft Academic Search

    Lode Vandenbossche; Luc Dupré

    2009-01-01

    To evaluate the material degradation of ferritic steels caused by low cycle stress-induced fatigue, the continuous examination of changes in the magnetomechanical behavior during the cyclic mechanical loading is proposed, and this is validated by comparing with the continuous examination of changes in the mechanical stress-strain behavior. In this context two magnetomechanical examination methods are investigated, differing only in the

  13. Effect of BCAA intake during endurance exercises on fatigue substances, muscle damage substances, and energy metabolism substances.

    PubMed

    Kim, Dong-Hee; Kim, Seok-Hwan; Jeong, Woo-Seok; Lee, Ha-Yan

    2013-12-01

    The increase rate of utilization of branched-chain amino acids (BCAA) by muscle is reduced to its plasma concentration during prolonged exercise leading to glycogen. BCAA supplementation would reduce the serum activities of intramuscular enzymes associated with muscle damage. To examine the effects of BCAA administration on fatigue substances (serotonin, ammonia and lactate), muscle damage substances (CK and LDH) and energy metabolism substances (FFA and glucose) after endurance exercise. Subjects (n = 26, college-aged males) were randomly divided into an experimental (n = 13, EXP) and a placebo (n = 13, CON) group. Subjects both EXP and CON performed a bout of cycle training (70% VO2max intensity) to exhaustion. Subject in the EXP were administrated BCAA (78ml/kg·w) prior to the bout of cycle exercise. Fatigue substances, muscle damage substances and energy metabolism substances were measured before ingesting BCAAs and placebos, 10 min before exercise, 30 min into exercise, immediately after exercise, and 30 min after exercise. Data were analyzed by two-way repeated measure ANCOVA, correlation and statistical significance was set at p < 0.05. The following results were obtained from this study; 1. In the change of fatigue substances : Serotonin in the EXP tended to decreased at the 10 min before exercise, 30 min into exercise, post exercise, and recovery 30 min. Serotonin in the CON was significantly greater than the EXP at the10 min before exercise and recovery 30. Ammonia in the EXP was increased at the 10 min before exercise, 30 min into exercise, and post exercise, but significantly decreased at the recovery 30min (p < 0.05). Ammonia in the CON was significantly lower than the EXP at the 10 min before exercise, 30 min into exercise, and post exercise (p < 0.05). Lactate in the EXP was significantly increased at the 30 min into exercise and significantly decreased at the post exercise and recovery 30 min. Lactate in the CON was significantly lower than the EXP at the post exercise (p < 0.05). 2. In the change of muscle damage substances : CK in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. CK in the CON was greater than the EXP. LDH in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. LDH in the CON was higher than the EXP. 3. In the change of energy metabolism substances :Glucose in the EXP tended to decrease at the 10 min before exercise, 30 min into exercise, post exercise and recovery 30 min. Glucose in the CON was significantly greater than the EXP at the recovery 30 min (p < .05). FFA in both EXP and CON was increased at the post exercise and recovery 30 min. % increase for FFA in the EXP was greater than the CON at the post exercise and recovery 30 min. 4. The relationship of the fatigue substances, muscle damage substances and energy metabolism substances after endurance exercise indicated strongly a positive relationship between LDH and ammonia and a negative relationship between LDH and FFA in the EXP. Also, there were a strong negative relationship between glucose and FFA and a positive relationship between glucose and serotonin in the EXP. There was a strong positive relationship between CK and LDH and a strong negative relationship between FFA and glucose in the CON. These results indicate that supplementary BCAA decreased serum concentrations of the intramuscular enzymes as CK and LDH following exhaustive exercise. This observation suggests that BCAA supplementation may reduce the muscle damage associated with endurance exercise. PMID:25566428

  14. Effect of BCAA intake during endurance exercises on fatigue substances, muscle damage substances, and energy metabolism substances

    PubMed Central

    Kim, Dong-Hee; Kim, Seok-Hwan; Jeong, Woo-Seok; Lee, Ha-Yan

    2013-01-01

    The increase rate of utilization of branched-chain amino acids (BCAA) by muscle is reduced to its plasma concentration during prolonged exercise leading to glycogen. BCAA supplementation would reduce the serum activities of intramuscular enzymes associated with muscle damage. To examine the effects of BCAA administration on fatigue substances (serotonin, ammonia and lactate), muscle damage substances (CK and LDH) and energy metabolism substances (FFA and glucose) after endurance exercise. Subjects (n = 26, college-aged males) were randomly divided into an experimental (n = 13, EXP) and a placebo (n = 13, CON) group. Subjects both EXP and CON performed a bout of cycle training (70% VO2max intensity) to exhaustion. Subject in the EXP were administrated BCAA (78ml/kg·w) prior to the bout of cycle exercise. Fatigue substances, muscle damage substances and energy metabolism substances were measured before ingesting BCAAs and placebos, 10 min before exercise, 30 min into exercise, immediately after exercise, and 30 min after exercise. Data were analyzed by two-way repeated measure ANCOVA, correlation and statistical significance was set at p < 0.05. The following results were obtained from this study; 1. In the change of fatigue substances : Serotonin in the EXP tended to decreased at the 10 min before exercise, 30 min into exercise, post exercise, and recovery 30 min. Serotonin in the CON was significantly greater than the EXP at the10 min before exercise and recovery 30. Ammonia in the EXP was increased at the 10 min before exercise, 30 min into exercise, and post exercise, but significantly decreased at the recovery 30min (p < 0.05). Ammonia in the CON was significantly lower than the EXP at the 10 min before exercise, 30 min into exercise, and post exercise (p < 0.05). Lactate in the EXP was significantly increased at the 30 min into exercise and significantly decreased at the post exercise and recovery 30 min. Lactate in the CON was significantly lower than the EXP at the post exercise (p < 0.05). 2. In the change of muscle damage substances : CK in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. CK in the CON was greater than the EXP. LDH in the EXP was decreased at the 10 min before exercise and increased at the 30 min into exercise and then decreased at the post exercise and recovery 30 min. LDH in the CON was higher than the EXP. 3. In the change of energy metabolism substances :Glucose in the EXP tended to decrease at the 10 min before exercise, 30 min into exercise, post exercise and recovery 30 min. Glucose in the CON was significantly greater than the EXP at the recovery 30 min (p < .05). FFA in both EXP and CON was increased at the post exercise and recovery 30 min. % increase for FFA in the EXP was greater than the CON at the post exercise and recovery 30 min. 4. The relationship of the fatigue substances, muscle damage substances and energy metabolism substances after endurance exercise indicated strongly a positive relationship between LDH and ammonia and a negative relationship between LDH and FFA in the EXP. Also, there were a strong negative relationship between glucose and FFA and a positive relationship between glucose and serotonin in the EXP. There was a strong positive relationship between CK and LDH and a strong negative relationship between FFA and glucose in the CON. These results indicate that supplementary BCAA decreased serum concentrations of the intramuscular enzymes as CK and LDH following exhaustive exercise. This observation suggests that BCAA supplementation may reduce the muscle damage associated with endurance exercise. PMID:25566428

  15. Blade fragment energy analysis

    NASA Technical Reports Server (NTRS)

    Oconnor, M. A., Jr.

    1977-01-01

    Two classes of fan blade fragments were considered in an analysis of blade fragment energy. The first, of relatively small size (.15 pound) and energy, tends to rebound from the fan and case when liberated in an FOD encounter. These small fragments have relatively low secondary damage potential and are less demanding in terms of protection. The larger fan blade fragments are ejected in a more direct release trajectory with higher energy and hence can represent a higher potential hazard. Simplified analytical methods were used to describe blade fragment energy transfer kinematics, establish fragment energy levels, evaluate damage potential and configure protection. The approach, methodology, and application are discussed as a possible building block for other applications. Development of effective local protection using Kevlar is also discussed. Analysis methods developed and applied to the rebound fragment problem and to the large direct release fragment problem are described.

  16. Incipient Crack Detection in Composite Wind Turbine Blades

    SciTech Connect

    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

    2012-08-28

    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.

  17. Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads

    NASA Technical Reports Server (NTRS)

    Stinchcomb, W. W.; Henneke, E. G.; Reifsnider, K. L.; Kress, G. R.

    1985-01-01

    The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

  18. Nondestructive detection of fatigue damage in austenitic stainless steel by positron annihilation

    Microsoft Academic Search

    Petra Schaaff; Uwe Holzwarth

    2005-01-01

    Austenitic stainless steel specimens have been examined by positron-lifetime measurements at various stages until failure\\u000a during fatigue tests at constant stress or plastic strain amplitudes. A positron-source-detector assembly has been mounted\\u000a on the servohydraulic testing machines that allowed truly non-destructive positron annihilation studies without removing the\\u000a specimens from the load train. Positrons were generated by a 72Se\\/72 As source with

  19. Monitoring and modeling stress corrosion and corrosion fatigue damage in nuclear reactors

    NASA Astrophysics Data System (ADS)

    Andresen, P. L.; Ford, F. P.; Solomon, H. D.; Taylor, D. F.

    1990-12-01

    Despite the serious impact of stress-corrosion cracking and corrosion fatigue, the relevant design and operational guidelines for light-water nuclear reactors are often just rules of thumb which identify susceptibility or codes which only quantify the effects of stress. However, quantitative understanding of the crack advance process is unfolding for several alloy types, and modeling now permits accurate prediction of crack growth over a wide range of material, environmental and stress conditions.

  20. Thermomechanical fatigue—damage mechanisms and mechanism-based life prediction methods

    Microsoft Academic Search

    H.-J. Christ; A. Jung; H. J. Maier; R. Teteruk

    2003-01-01

    An existing extensive database on the isothermal and thermomechanical fatigue behaviour of high-temperature titanium alloy\\u000a EVII 834 and dispersoid-strengthened aluminum alloy X8019 in SiC particle-reinforced as well as unreinv conditions was used\\u000a to evaluate both the adaptability of fracture mechanics approaches to TMF and the resulting predictive capabilities of determining\\u000a material life by crack propagation consideration. Selection of the correct

  1. Nondestructive monitoring of fatigue damage evolution in austenitic stainless steel by positron-lifetime measurements

    Microsoft Academic Search

    Uwe Holzwarth; Petra Schaaff

    2004-01-01

    Positron-lifetime measurements have been performed on austenitic stainless steel during (i) stress- and (ii) strain-controlled fatigue experiments for different applied stress and strain amplitudes, respectively. For this purpose a generator-detector assembly with a 72Se\\/72As positron generator [maximum activity 25 muCi (0.9 MBq)] has been mounted on mechanical testing machines in order to measure the positron lifetime without removing the specimens

  2. Fatigue life until small cracks in aircraft structures: Durability and damage tolerance

    NASA Technical Reports Server (NTRS)

    Schijve, J.

    1994-01-01

    Crack initiation in notched elements occurs very early in the fatigue life. This is also true for riveted lap joints, an important fatigue critical element of a pressurized fuselage structure. Crack nucleation in a riveted lap joint can occur at different locations, depending on the riveting operation. It can occur at the edge of the rivet hole, at a small distance away from the hole, but still with subsequent crack growth through the hole, and ahead of the hole with a crack no longer passing through the hole. Moreover, crack nucleation can occur in the top row at the countersunk holes (outer sheet) or in the bottom row at the non-countersunk holes. Fractographic evidence is shown. The initial growth of the small cracks occurs as an (invisible) part through crack. As a consequence, predictions on the crack initiation life are problematic. After a though crack is present, the major part of the fatigue life has been consumed. There is still an apparent lack of empirical data on crack growth and residual strength of riveted lap joints, five years after the Aloha accident. Such data are very much necessary for further developments of prediction models. Some test results are presented.

  3. An investigation of the fracture and fatigue crack growth behavior of forged damage-tolerant niobium aluminide intermetallics

    SciTech Connect

    Ye, F.; Mercer, C.; Soboyejo, W.O. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering

    1998-09-01

    The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class of forged damage-tolerant niobium aluminide (Ng, Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti (10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic percentages unless stated otherwise. The 10Ti and 25Ti alloys exhibit fracture toughness levels between 10 and 20 MPa{radical}m at room temperature. Fracture in these alloys occurs by brittle cleavage fracture modes. In contrast, a ductile dimpled fracture mode is observed at room-temperature for the alloy containing 40 at. pct Ti. The 40Ti alloy also exhibits exceptional combinations of room-temperature strength (695 to 904 MPa), ductility (4 to 30 pct), fracture toughness (40 to 100 MPa{radical}m), and fatigue crack growth resistance (comparable to Ti-6Al-4V, monolithic Nb, and inconel 718). The implications of the results are discussed for potential structural applications of the 40Ti alloy in the intermediate-temperature ({approximately}700 C to 750 C) regime.

  4. LOW COST CORROSION DAMAGE MITIGATION AND IMPROVED FATIGUE PERFORMANCE OF LOW PLASTICITY BURNISHED 7075-T6

    Microsoft Academic Search

    Paul S. Prevéy; John Cammett

    2000-01-01

    Low plasticity burnishing (LPB) has been investigated as a surface enhancement process and corrosion mitigation method for aging aircraft structural applications. Compressive residual stresses reaching the alloy yield strength and extending to a depth of 1.25 mm (0.050 in.), deeper than typical corrosion damage, is achievable. Excellent surface finish can be achieved with no detectable metallurgical damage to surface and

  5. Structural tailoring of engine blades (STAEBL) user's manual

    NASA Technical Reports Server (NTRS)

    Brown, K. W.

    1985-01-01

    This User's Manual contains instructions and demonstration case to prepare input data, run, and modify the Structural Tailoring of Engine Blades (STAEBL) computer code. STAEBL was developed to perform engine fan and compressor blade numerical optimizations. This blade optimization seeks a minimum weight or cost design that satisfies realistic blade design constraints, by tuning one to twenty design variables. The STAEBL constraint analyses include blade stresses, vibratory response, flutter, and foreign object damage. Blade design variables include airfoil thickness at several locations, blade chord, and construction variables: hole size for hollow blades, and composite material layup for composite blades.

  6. Structural tailoring of engine blades (STAEBL) theoretical manual

    NASA Technical Reports Server (NTRS)

    Brown, K. W.

    1985-01-01

    This Theoretical Manual includes the theories included in the Structural Tailoring of Engine Blades (STAEBL) computer program which was developed to perform engine fan and compressor blade numerical optimizations. These blade optimizations seek a minimum weight or cost design that satisfies practical blade design constraints, by controlling one to twenty design variables. The STAEBL constraint analyses include blade stresses, vibratory response, flutter, and foreign object damage. Blade design variables include airfoil thickness at several locations, blade chord, and construction variables: hole size for hollow blades, and composite material layup for composite blades.

  7. Static-transmission-error vibratory-excitation contributions from plastically deformed gear teeth caused by tooth bending-fatigue damage

    NASA Astrophysics Data System (ADS)

    Mark, W. D.; Reagor, C. P.

    2007-02-01

    To assess gear health and detect gear-tooth damage, the vibratory response from meshing gear-pair excitations is commonly monitored by accelerometers. In an earlier paper, strong evidence was presented suggesting that, in the case of tooth bending-fatigue damage, the principal source of detectable damage is whole-tooth plastic deformation; i.e. yielding, rather than changes in tooth stiffness caused by tooth-root cracks. Such plastic deformations are geometric deviation contributions to the "static-transmission-error" (STE) vibratory excitation caused by meshing gear pairs. The STE contributions caused by two likely occurring forms of such plastic deformations on a single tooth are derived, and displayed in the time domain as a function of involute "roll distance." Example calculations are provided for transverse contact ratios of Qt=1.4 and 1.8, for spur gears and for helical-gear axial contact ratios ranging from Qa=1.2 to Qa=3.6. Low-pass- and band-pass-filtered versions of these same STE contributions also are computed and displayed in the time domain. Several calculations, consisting of superposition of the computed STE tooth-meshing fundamental harmonic contribution and the band-pass STE contribution caused by a plastically deformed tooth, exhibit the amplitude and frequency or phase modulation character commonly observed in accelerometer-response waveforms caused by damaged teeth. General formulas are provided that enable computation of these STE vibratory-excitation contributions for any form of plastic deformation on any number of teeth for spur and helical gears with any contact ratios.

  8. Low cost corrosion damage mitigation and improved fatigue performance of low plasticity burnished 7075-T6

    Microsoft Academic Search

    Paul S. Preveiy; John Cammett

    2001-01-01

    Low plasticity burnishing (LPB) has been investigated as a surface enhancement process and corrosion mitigation method for\\u000a aging aircraft structural applications. Compressive residual stresses reaching the alloy yield strength and extending to a\\u000a depth of 1.25 mm (0.050 in.) deeper than typical corrosion damage is achievable. Excellent surface finish can be achieved\\u000a with no detectable metallurgical damage to surface and

  9. Damage accumulation during isothermal fatigue of Ti-SiC laminates

    SciTech Connect

    Lipetzky, P.; Dvorak, G.J.; Stoloff, N.S. [Rensselaer Polytechnic Inst., Troy, NY (United States)] [Rensselaer Polytechnic Inst., Troy, NY (United States)

    1996-11-01

    Titanium-based composites have been under investigation for the last three decades because titanium alloys have the highest strength-to-weight ratio of all common structural metals. The high strength at low to intermediate temperatures (up to 550 C), coupled with a high impact fracture energy, makes these materials candidates for applications such as gas turbine fan blades. Perhaps more important for this application is the fact that Ti composites can have high stiffness, which raises the critical vibration frequencies and lowers the necessary blade thickness and mass. Efforts to reinforce these alloys began with the inclusion of boron filaments. However, complications arose due to reactivity between Ti and the fibers. Since that time compatibility problems have been overcome by either altering the matrix composition or coating the fibers. Subsequently, interest has turned to continuous SiC reinforcements with a variety of fiber diameters, volume fractions and coatings. A full description of the experimental test methods as well as the sample manufacturing procedure was given previously. Therefore, only a brief summary is given here. Fiber volume fraction for all lay-ups was approximately 30%. Prismatic coupons were subjected to a cyclic tensile load history (load ratio = 0.1) with frequencies of 0.001 Hz and 0.1 Hz. Temperature in the entire gauge section was held constant at 650 C. Strain was measured directly from the sample using a high-temperature extensometer. Following failure, portions of the gauge section were mounted in epoxy and polished by hand on conventional diamond wheels for metallographic analysis. Because the composite section was inclined at a small angle relative to the grinding surface, a wedge of material was removed during grinding so that features from a range of depths could be viewed simultaneously.

  10. Simplified rotor load models and fatigue damage estimates for offshore wind turbines.

    PubMed

    Muskulus, M

    2015-02-28

    The aim of rotor load models is to characterize and generate the thrust loads acting on an offshore wind turbine. Ideally, the rotor simulation can be replaced by time series from a model with a few parameters and state variables only. Such models are used extensively in control system design and, as a potentially new application area, structural optimization of support structures. Different rotor load models are here evaluated for a jacket support structure in terms of fatigue lifetimes of relevant structural variables. All models were found to be lacking in accuracy, with differences of more than 20% in fatigue load estimates. The most accurate models were the use of an effective thrust coefficient determined from a regression analysis of dynamic thrust loads, and a novel stochastic model in state-space form. The stochastic model explicitly models the quasi-periodic components obtained from rotational sampling of turbulent fluctuations. Its state variables follow a mean-reverting Ornstein-Uhlenbeck process. Although promising, more work is needed on how to determine the parameters of the stochastic model and before accurate lifetime predictions can be obtained without comprehensive rotor simulations. PMID:25583872

  11. The LIFE computer code: Fatigue life prediction for vertical axis wind turbine components

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.; Ashwill, T. D.; Slack, N.

    1987-08-01

    The LIFE computer code was originally written by Veers to analyze the fatigue life of a vertical axis wind turbine (VAWT) blade. The basic assumptions built into this analysis tool are: the fatigue life of a blade component is independent of the mean stress; the frequency distribution of the vibratory stresses may be described adequately by a Rayleigh probability density function; and damage accumulates linearly (Miner's Rule). Further, the yearly distribution of wind is assumed to follow a Rayleigh distribution. The original program has been updated to run in an interactive mode on a personal computer with a BASIC interpreter and 256K RAM. Additional capabilities included in this update include: the generalization of the Rayleigh function for the wind speed distribution to a Weibull function; the addition of two constitutive rules for the evaluation of the effects of mean stress on fatigue life; interactive data input; and the inclusion of a stress concentration factor into the analysis.

  12. Development of Self-Powered Wireless Structural Health Monitoring (SHM) for Wind Turbine Blades

    NASA Astrophysics Data System (ADS)

    Lim, Dong-Won

    Wind turbine blade failure can lead to unexpected power interruptions. Monitoring wind turbine blades is important to ensure seamless electricity delivery from power generation to consumers. Structural health monitoring (SHM) enables early recognition of structural problems so that the safety and reliability of operation can be enhanced. This dissertation focuses on the development of a wireless SHM system for wind turbine blades. The sensor is comprised of a piezoelectric energy harvester (EH) and a telemetry unit. The sensor node is mounted on the blade surface. As the blade rotates, the blade flexes, and the energy harvester captures the strain energy on the blade surface. Once sufficient electricity is captured, a pulse is sent from the sensing node to a gateway. Then, a central monitoring algorithm processes a series of pulses received from all three blades. This wireless SHM, which uses commercially available components, can be retrofitted to existing turbines. The harvested energy for sensing can be estimated in terms of two factors: the available strain energy and conversion efficiency. The available strain energy was evaluated using the FAST (Fatigue, Aerodynamics, Structures, and Turbulence) simulator. The conversion efficiency was studied analytically and experimentally. An experimental set-up was designed to mimic the expected strain frequency and amplitude for rotor blades. From a series of experiments, the efficiency of a piezoelectric EH at a typical rotor speed (0.2 Hz) was approximately 0.5%. The power requirement for sending one measurement (280 muJ) can be achieved in 10 minutes. Designing a detection algorithm is challenging due to this low sampling rate. A new sensing approach-the timing of pulses from the transmitter-was introduced. This pulse timing, which is tied to the charging time, is indicative of the structural health. The SHM system exploits the inherent triple redundancy of the three blades. The timing data of the three blades are compared to discern an outlier, corresponding to a damaged blade. Two types of post-processing of pulses were investigated: (1) comparing the ratios of signal timings (i.e. transmission ratio); and (2) comparing the difference between signal timings (i.e. residuals). For either method, damage is indicated when the energy ratio or residual exceeds a threshold level. When residuals are used to detect damage, performance measures such as the false alarm rate and detection probability can also be imposed. The SHM algorithms were evaluated using strain energy data from a 2.5 MW wind turbine.

  13. The Impact of Active Aerodynamic Load Control on Fatigue and Energy Capture at Low Wind Speed Sites

    Microsoft Academic Search

    Dale E. Berg; David G. Wilson; Matthew F. Barone; Brian R. Resor; Jonathan C. Berg; Joshua A. Paquette; Jose R. Zayas; Sridhar Kota; Gregory Ervin; Dragan Maric

    Abstract † Active aerodynamic ,load control of wind turbine blades has been,heavily researched,for years by the,wind energy,research,community and,shows ,great promise ,for reducing ,turbine fatigue damage., One,way,to benefit,from this technology,is to choose,to utilize a larger,rotor ona,turbine tower ,and ,drive train to realize increased,turbine ,energy ,capture ,while keeping,the fatigue damage ,of critical turbine components,at the ,original levels. To assess this rotor-increase potential,

  14. Structural health and prognostics management for offshore wind turbines : case studies of rotor fault and blade damage with initial O&M cost modeling.

    SciTech Connect

    Myrent, Noah J. [Purdue Center for Systems Integrity, Lafayette, IN; Kusnick, Joshua F. [Purdue Center for Systems Integrity, Lafayette, IN; Barrett, Natalie C. [Purdue Center for Systems Integrity, Lafayette, IN; Adams, Douglas E. [Purdue Center for Systems Integrity, Lafayette, IN; Griffith, Daniel Todd

    2013-04-01

    Operations and maintenance costs for offshore wind plants are significantly higher than the current costs for land-based (onshore) wind plants. One way to reduce these costs would be to implement a structural health and prognostic management (SHPM) system as part of a condition based maintenance paradigm with smart load management and utilize a state-based cost model to assess the economics associated with use of the SHPM system. To facilitate the development of such a system a multi-scale modeling approach developed in prior work is used to identify how the underlying physics of the system are affected by the presence of damage and faults, and how these changes manifest themselves in the operational response of a full turbine. This methodology was used to investigate two case studies: (1) the effects of rotor imbalance due to pitch error (aerodynamic imbalance) and mass imbalance and (2) disbond of the shear web; both on a 5-MW offshore wind turbine in the present report. Based on simulations of damage in the turbine model, the operational measurements that demonstrated the highest sensitivity to the damage/faults were the blade tip accelerations and local pitching moments for both imbalance and shear web disbond. The initial cost model provided a great deal of insight into the estimated savings in operations and maintenance costs due to the implementation of an effective SHPM system. The integration of the health monitoring information and O&M cost versus damage/fault severity information provides the initial steps to identify processes to reduce operations and maintenance costs for an offshore wind farm while increasing turbine availability, revenue, and overall profit.

  15. Micro\\/meso scale fatigue damage accumulation monitoring using nonlinear acoustic vibro-modulation measurements

    Microsoft Academic Search

    Andrei Zagrai; Dimitri Donskoy; Alexander Chudnovsky; Edward Golovin; Vinod S. Agarwala

    2006-01-01

    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

  16. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...attaching structure fuselage, and pressure cabin using the damage-tolerance...1g flight combined with a cabin differential pressure equal to 1.1 times the normal...1g flight combined with a cabin differential pressure equal to 1.1 times the...

  17. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...attaching structure fuselage, and pressure cabin using the damage-tolerance...1g flight combined with a cabin differential pressure equal to 1.1 times the normal...1g flight combined with a cabin differential pressure equal to 1.1 times the...

  18. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...attaching structure fuselage, and pressure cabin using the damage-tolerance...1g flight combined with a cabin differential pressure equal to 1.1 times the normal...1g flight combined with a cabin differential pressure equal to 1.1 times the...

  19. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...attaching structure fuselage, and pressure cabin using the damage-tolerance...1g flight combined with a cabin differential pressure equal to 1.1 times the normal...1g flight combined with a cabin differential pressure equal to 1.1 times the...

  20. Effect of machining damage on low cycle fatigue crack initiation life in drilled holes in UdimetRTM 720

    NASA Astrophysics Data System (ADS)

    Magadanz, Christine M.

    White layer is a generic term for a light etching surface layer on metal alloys that can result under extreme deformation conditions in wear, sliding or machining. While there has been some characterization of white layer due to abusive machining, the specific effect on fatigue crack initiation life has not been well documented. This study aimed to establish a relationship between the presence of white layer due to abusive machining and fatigue crack initiation life in a wrought nickel based superalloy (Udimet ® 720). Low cycle fatigue testing was conducted on large specimens containing through holes drilled with parameters aimed at creating holes with and without white layer. Initially, Acoustic Emission monitoring technologies were used to monitor for acoustic events associated with crack initiation, however, this technology was deemed unreliable for this testing. Instead, cycles to crack initiation was determined using striation density measurements on each fracture surface to estimate the number of cycles of crack propagation, which was subtracted from the total number of cycles for the specimen. A total of sixteen specimens were tested in this manner. The results suggested that the crack initiation lives of holes machined with good machining parameters were statistically longer than crack initiation lives of holes machined with poor machining parameters. The mean initiation life of the poorly machined specimens was a factor of approximately 2 times shorter than the mean initiation life of the well machined specimens. The holes machined with good machining parameters exhibited subsurface initiations which suggested that no anomalies affected crack initiation for these specimens. It was also shown that some of the poorly machined holes exhibited subsurface initiations rather than initiations at white layer damage. These holes had better surface finish than the poorly machined specimens that did fail at white layer. The mean initiation life of the poorly machined holes with subsurface initiation was 7 times longer than the mean initiation life of the holes that exhibited white layer at the crack origins. Lastly, no apparent correlation between white layer thickness and initiation life was demonstrated in this study.

  1. A Phenomenological Discrete Brittle Damage-Mechanics Model for Fatigue of MEMS Devices With Application to LIGA Ni

    Microsoft Academic Search

    Trevor S. Slack; Farshid Sadeghi; Dimitrios Peroulis

    2009-01-01

    Fatigue initiation and failure of various microelectromechanical systems (MEMS) is of significant importance as they gain widespread acceptance in sensors and electronics. This paper presents an approach for utilizing available experimental fatigue data to evaluate the fatigue lives of MEMS components. The approach is based on a phenomenological discrete material representation in which a domain is represented by a collection

  2. Quantitative damage detection and sparse sensor array optimization of carbon fiber reinforced resin composite laminates for wind turbine blade structural health monitoring.

    PubMed

    Li, Xiang; Yang, Zhibo; Chen, Xuefeng

    2014-01-01

    The active structural health monitoring (SHM) approach for the complex composite laminate structures of wind turbine blades (WTBs), addresses the important and complicated problem of signal noise. After illustrating the wind energy industry's development perspectives and its crucial requirement for SHM, an improved redundant second generation wavelet transform (IRSGWT) pre-processing algorithm based on neighboring coefficients is introduced for feeble signal denoising. The method can avoid the drawbacks of conventional wavelet methods that lose information in transforms and the shortcomings of redundant second generation wavelet (RSGWT) denoising that can lead to error propagation. For large scale WTB composites, how to minimize the number of sensors while ensuring accuracy is also a key issue. A sparse sensor array optimization of composites for WTB applications is proposed that can reduce the number of transducers that must be used. Compared to a full sixteen transducer array, the optimized eight transducer configuration displays better accuracy in identifying the correct position of simulated damage (mass of load) on composite laminates with anisotropic characteristics than a non-optimized array. It can help to guarantee more flexible and qualified monitoring of the areas that more frequently suffer damage. The proposed methods are verified experimentally on specimens of carbon fiber reinforced resin composite laminates. PMID:24763210

  3. Quantitative Damage Detection and Sparse Sensor Array Optimization of Carbon Fiber Reinforced Resin Composite Laminates for Wind Turbine Blade Structural Health Monitoring

    PubMed Central

    Li, Xiang; Yang, Zhibo; Chen, Xuefeng

    2014-01-01

    The active structural health monitoring (SHM) approach for the complex composite laminate structures of wind turbine blades (WTBs), addresses the important and complicated problem of signal noise. After illustrating the wind energy industry's development perspectives and its crucial requirement for SHM, an improved redundant second generation wavelet transform (IRSGWT) pre-processing algorithm based on neighboring coefficients is introduced for feeble signal denoising. The method can avoid the drawbacks of conventional wavelet methods that lose information in transforms and the shortcomings of redundant second generation wavelet (RSGWT) denoising that can lead to error propagation. For large scale WTB composites, how to minimize the number of sensors while ensuring accuracy is also a key issue. A sparse sensor array optimization of composites for WTB applications is proposed that can reduce the number of transducers that must be used. Compared to a full sixteen transducer array, the optimized eight transducer configuration displays better accuracy in identifying the correct position of simulated damage (mass of load) on composite laminates with anisotropic characteristics than a non-optimized array. It can help to guarantee more flexible and qualified monitoring of the areas that more frequently suffer damage. The proposed methods are verified experimentally on specimens of carbon fiber reinforced resin composite laminates. PMID:24763210

  4. Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material. Interim Report No. 86

    SciTech Connect

    Vandermey, N.E.; Morris, D.H.; Masters, J.E.

    1991-07-01

    Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

  5. Effect of interstitial content on high- temperature fatigue crack propagation and low- cycle fatigue of alloy 720

    NASA Astrophysics Data System (ADS)

    Bashir, S.; Thomas, M. C.

    1993-08-01

    Alloy 720 is a high-strength cast and wrought turbine disc alloy currently in use for temperatures up to about 650 °C in Allison’s T800, T406, GMA 2100, and GMA 3007 engines. In the original composition in-tended for use as turbine blades, large carbide and boride stringers formed and acted as preferred crack initiators. Stringering was attributed to relatively higher boron and carbon levels. These interstitials are known to affect creep and ductility of superalloys, but the effects on low-cycle fatigue and fatigue crack propagation have not been studied. Recent emphasis on the total life approach in the design of turbine discs necessitates better understanding of the interactive fatigue crack propagation and low-cycle fatigue behavior at high temperatures. The objective of this study was to improve the damage tolerance of Alloy 720 by systematically modifying boron and carbon levels in the master melt, without altering the low-cy-cle fatigue and strength characteristics of the original composition. Improvement in strain-controlled low-cycle fatigue life was achieved by fragmenting the continuous stringers via composition modifica-tion. The fatigue crack propagation rate was reduced by a concurrent reduction of both carbon and bo-ron levels to optimally low levels at which the frequency of brittle second phases was minimal. The changes in composition have been incorporated for production disc forgings.

  6. Effective strain–fatigue life data for variable amplitude fatigue

    Microsoft Academic Search

    T. H. Topper; T. S. Lam

    1997-01-01

    The usual analysis procedure for variable amplitude fatigue calculates fatigue damage based on constant amplitude strain controlled fatigue tests of smooth specimens. The resulting predictions are typically nonconservative due to a load interaction effect in variable amplitude fatigue. This paper reviews recent work which shows that large loads in a service load history decrease the crack opening stress and as

  7. Multiaxial fatigue criteria for AISI 304 and 2-1/4 Cr-1 Mo steel at 538/sup 0/C with applications to strain-range partitioning and linear summation of creep and fatigue damage

    SciTech Connect

    Blass, J.J.

    1982-01-01

    An improved multiaxial fatigue failure criterion was developed based on the results of combined axial-torsional strain cycling tests of AISI 304 and 2-1/4 Cr-1 Mo steel conducted at 538/sup 0/C (1000/sup 0/F). The formulation of this criterion involves the shear and normal components of inelastic strain range on the planes of maximum inelastic shear strain range. Optimum values of certain parameters contained in the formulation were obtained for each material by the method of least squares. The ability of this criterion to correlate the test results was compared with that of the usual (Mises) equivalent inelastic strain range criterion. An improved definition of equivalent inelastic strain range resulting from these considerations was used to generalize the theory of Strain Range Partitioning to multiaxial stress-strain conditions and was also applied to the linear summation of creep and fatigue damage.

  8. A real time neural net estimator of fatigue life

    NASA Technical Reports Server (NTRS)

    Troudet, T.; Merrill, W.

    1990-01-01

    A neural net architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the Intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopump blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines. This neural net estimator of fatigue life is seen as the enabling technology to achieve component life prognosis, and therefore would be an important part of life extending control for reusable rocket engines.

  9. STRUCTURAL INTEGRITY EVALUATION OF WIND TURBINE BLADES USING PATTERN RECOGNITION ANALYSIS ON ACOUSTIC EMISSION DATA

    Microsoft Academic Search

    A. A. Anastassopoulos; D. A. Kouroussis; V. N. Nikolaidis; A. Proust; A. G. Dutton; M. J. Blanch; L. E. Jones; P. Vionis; D. J. Lekou; D R V van Delft; P. A. Joosse

    2002-01-01

    Current Wind Turbine (W\\/T) Blade certification practices require the conduction of static and fatigue tests on new blades, in order to assess whether the blade can sustain the applied loads. Within the scopes of a current EC-funded research project, Acoustic Emission (AE) monitoring has been extensively applied during testing of various W\\/T Blades of similar design. All blades were loaded

  10. Fatigue and creep damage resistance of a thermal barrier coated superalloy for combustor liners in aero turbines

    Microsoft Academic Search

    Ashok Kumar Ray; Bangsidhar Goswami; Yogendra Nath Tiwary; Hemant Kumar Das; Deepak Kumar Das; Sashi Bhusan Kumar

    2010-01-01

    Fatigue testing of thermal barrier coated (TBC), bond coated only and bare Superni C263 superalloy was conducted at 800°C\\u000a in air. Fatigue results reveal that the endurance limits for the TBC and bond coated substrate was substantially higher than\\u000a that of the base alloy, while the opposite was found for high stress, low cyclic life times. It appears that the

  11. An experimental study of heat transfer in the rectangular coolant passages of a gas turbine rotor blade 

    E-print Network

    Uddin, Mohammed Jalal

    2000-01-01

    Modern gas turbines have high inlet temperatures to harness maximum power output, which causes different components to experience severe thermal stresses and fatigue. To achieve turbine blade durability goals, the blades are cooled with air...

  12. High and low cycle fatigue life estimation of welding steel under constant amplitude loading: Analysis of different multiaxial damage models and in-phase and out-of-phase loading effects

    Microsoft Academic Search

    C. Gómez; M. Canales; S. Calvo; R. Rivera; J. R. Valdés; J. L. Núñez

    2011-01-01

    The objective of the present work is to estimate the high and low cycle fatigue life of a type of welding steel used for construction (S355 J2 according to UNE EN 10025-2: 2006), subject to in-phase and out-of-phase multiaxial loading, by means of different classical multiaxial fatigue damage models. A complete cyclic characterization of the material is obtained, including new

  13. Gas turbine disk-blade attachment crack

    Microsoft Academic Search

    David L. Davidson

    2005-01-01

    Evaluation of a gas turbine disk revealed a crack in the blade attachment area. The subsequent effort to understand the origin\\u000a of this crack led to a series of analyses that included computing the stresses on the attachment, characterization of fatigue\\u000a crack growth, and a model for fretting fatigue crack growth. These elements were brought together to simulate the conditions

  14. Fracture analysis of compressor blade of a helicopter engine

    Microsoft Academic Search

    L. Witek; M. Wierzbi?ska; A. Pozna?ska

    2009-01-01

    This paper presents the failure analysis of the blade of a helicopter engine. From the visual examination of the fractured surface, it was possible to observe beach marks, typical of fatigue failure. The crack was initiated from the corrosion pit located on the attack edge of the blade. A non-linear finite element method was utilized to determine the stress state

  15. Load Alleviation on Wind Turbine Blades using Variable Airfoil Geometry

    E-print Network

    Load Alleviation on Wind Turbine Blades using Variable Airfoil Geometry Peter Bjørn Andersen, Mac to 40% when signal noise is added to the control. Keywords: Wind Turbine, Load Alleviation, Fatigue Loads, Trailing Edge Flaps, PID control, Signal Noise. 1 Introduction Wind turbine blades are subject

  16. Design and fabrication of integrally damped composite fan blades

    Microsoft Academic Search

    John B. Kosmatka; Geoffrey Appuhn

    1999-01-01

    The design, analysis, and fabrication methods of embedding small viscoelastic damping patches into scaled composite fan blades is presented, where the goal is to improve the blade fatigue characteristics by increasing the damping in the chord-wise modes. This discussion concentrates on improving the damping levels in a research composite shell\\/titanium spar fan blade, developed by NASA-Lewis and Pratt and Whitney.

  17. Influence of creep damage on the low cycle thermal-mechanical fatigue behavior of two tantalum base alloys

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.; Doble, G. S.

    1972-01-01

    Low cycle fatigue tests have been performed on the tantalum base alloys T-111 and ASTAR 811C with synchronized, independently programmed temperature and strain cycling. The thermal-mechanical cycles applied fell into three basic categories: these were isothermal cycling, in-phase thermal cycling, and out-of-phase thermal cycling. In-phase cycling was defined as tensile deformation associated with high temperature and compressive deformation with low temperature, while out-of-phase thermal cycling was defined as the reverse case. The in-phase thermal cycling had a pronounced detrimental influence on the fatigue life of both alloys, with the life reduction being greater in the solid solution strengthened T-111 alloy than in the carbide strengthened ASTAR 811C alloy. The out-of-phase tests also showed pronounced effects on the fatigue life of both alloys, although not as dramatic.

  18. Elevated temperature fretting fatigue of nickel based alloys

    NASA Astrophysics Data System (ADS)

    Gean, Matthew C.

    This document details the high temperature fretting fatigue of high temperature nickel based alloys common to turbine disk and blade applications. The research consists of three area of focus: Experiments are conducted to determine quantitatively the fretting fatigue lives of advanced nickel based alloys; Analytical tools are developed and used to investigate the fretting fatigue response of the material; Fractographic analysis of the experimental results is used to improve the analytical models employed in the analysis of the experiments. Sixty three fretting fatigue experiments were conducted at 649 °C using a polycrystalline Nickel specimen in contact with directionally solidified and single crystal Nickel pads. Various influences on the fretting fatigue life are investigated. Shot peened Rene' 95 had better fretting fatigue life compared to shot peened Rene' 88. Shot peening produced a 2x increase in life for Rene' 95, but only a marginal improvement in the fretting fatigue life for Rene' 88. Minor cycles in variable amplitude loading produces significant damage to the specimen. Addition of occasional overpeaks in load produces improvements in fretting fatigue life. Contact tractions and stresses are obtained through a variety of available tools. The contact tractions can be efficiently obtained for limited geometries, while FEM can provide the contact tractions for a broader class of problems, but with the cost of increased CPU requirements. Similarly, the subsurface contact stresses can be obtained using the contact tractions as a boundary condition with either a semi-analytical FFT method or FEM. It is found that to calculate contact stresses the FFT was only marginally faster than FEM. The experimental results are combined with the analysis to produce tools that are used to design against fretting fatigue. Fractographic analysis of the fracture surface indicates the nature of the fretting fatigue crack behavior. Interrupted tests were performed to analyze the crack at intermediate lives. Fretting fatigue cracks were found to have formed in less than 10% of total fretting fatigue life. In addition to the formation of the individual fretting fatigue cracks, by 10% of the total expected fretting fatigue life, the individual fretting fatigue cracks have linked together to form a through the thickness edge crack. At some point in the experiment in between 20% to 50% of total expected fretting fatigue life, the edge crack growth retards or a corner crack accelerates. The result is a corner crack forms out of the edge crack. In many experiments this corner crack is the primary crack that leads to failure. The experimental results are combined with the analytic tools to generate usefull tools for the analysis of the fretting fatigue behavior of nickel based alloys at high temperature. This analysis tool is helpfull in the design of gas turbine engines which use nickel based alloys for the turbine blades and disks.

  19. PREDICTION OF DELAM INATION IN WIND TURBINE BLADE STRUCTURAL DETAILS John F. Mandell, Douglas S. Cairns

    E-print Network

    1 PREDICTION OF DELAM INATION IN WIND TURBINE BLADE STRUCTURAL DETAILS John F. Mandell, Douglas S materials structures such as wind turbine blades. Design methodologies to prevent such failures have static and fatigue loading. INTRODUCTION Composite material structures such as wind turbine blades

  20. Developments in blade shape design for a Darrieus vertical axis wind turbine

    SciTech Connect

    Ashwill, T.D.; Leonard, T.M.

    1986-09-01

    A new computer program package has been developed that determines the troposkein shape for a Darrieus Vertical Axis Wind Turbine Blade with any geometrical configuration or rotation rate. This package allows users to interact and develop a ''buildable'' blade whose shape closely approximates the troposkein. Use of this package can significantly reduce flatwise mean bending stresses in the blade and increase fatigue life.

  1. Counterrotating aircraft propulsor blades

    NASA Technical Reports Server (NTRS)

    Nelson, Joey L. (Inventor); Elston, III, Sidney B. (Inventor); Tseng, Wu-Yang (Inventor); Hemsworth, Martin C. (Inventor)

    1993-01-01

    A propulsor blade for an aircraft engine includes an airfoil section formed in the shape of a scimitar. A metallic blade spar is interposed between opposed surfaces of the blade and is bonded to the surfaces to establish structural integrity of the blade. The metallic blade spar includes a root end allowing attachment of the blade to the engine.

  2. Fatigue Life Estimation Considering Damaging and Strengthening of Low amplitude Loads under Different Load Sequences Using Fuzzy Sets Approach

    Microsoft Academic Search

    Shun-Peng Zhu; Hong-Zhong Huang; Zhong-Lai Wang

    2011-01-01

    In this study, based on the Miner rule, a new linear damage accumulation rule is proposed to consider the strengthening and damaging of low amplitude loads with different sequences using fuzzy sets theory. This model improves the application of the traditional Miner rule, by considering not only the damaging and strengthening of low amplitude loads, but also the load sequence

  3. Boron/aluminum fan blades for SCAR engines

    NASA Technical Reports Server (NTRS)

    Stabrylla, R. G.; Carlson, R. G.

    1977-01-01

    Processing procedures were developed to enhance boron/aluminum bond behavior and foreign object damage (FOD) tolerance. Design and analysis indicated that the J101 Stage 1 fan blade meets the required frequencies without a midspan shroud. The fabricability of full size J101 blades was assessed, while six blades were fabricated and finished machined.

  4. Application of new damage indicator-based sequential law for remaining fatigue life estimation of railway bridges

    Microsoft Academic Search

    Sudath Siriwardane; Mitao Ohga; Ranjith Dissanayake; Kazuhiro Taniwaki

    2008-01-01

    Miner’s rule is generally accepted as the fatigue criteria for life estimation of railway bridges. Similarly, it has always been acknowledged as a simplification that is easy to use in design where detailed loading history is unknown. But in the case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of

  5. Fatigue Life of Damaged Bridge Deck Panels Strengthened With Carbon Fiber Hongseob Oh, Jongsung Sim, and Christian Meyer

    E-print Network

    Meyer, Christian

    , such as specific mix design parameters and environmental conditions (e.g. humidity), which complicate the fatigue, such as aircraft structures and railroad bridges are routinely designed on the basis of this theory. #12;2 In the case of reinforced concrete structures, the situation is more complicated because of the complex nature

  6. In vitro simulation of contact fatigue damage found in ultra-high molecular weight polyethylene components of knee prostheses

    Microsoft Academic Search

    J H Currier; J L Duda; D K Sperling; J P Collier; B H Currier; F E Kennedy

    1998-01-01

    An in vitro simulation of fatigue loading of ultra-high molecular weight polyethylene ( UHMWPE ) knee components was carried out on a knee simulator and on a rolling and sliding wear tester. Tibial components for the knee simulator were gamma-sterilized, implantable components taken from manufacturing inventory. The rolling\\/sliding UHMWPE discs were machined from bar stock and either gamma sterilized in

  7. Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications

    NASA Technical Reports Server (NTRS)

    Prevey, Paul S.; Shepard, Michael; Ravindranath, Ravi A.; Gabb, Timothy

    2003-01-01

    Surface enhancement technologies such as shot peening, laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. For successful integration into turbine design, the process must be affordable and compatible with the manufacturing environment. LPB provides thermally stable compression of comparable magnitude and even greater depth than other methods, and can be performed in conventional machine shop environments on CNC machine tools. LPB provides a means to extend the fatigue lives of both new and legacy aircraft engines and ground-based turbines. Improving fatigue performance by introducing deep stable layers of compressive residual stress avoids the generally cost prohibitive alternative of modifying either material or design. The X-ray diffraction based background studies of thermal and mechanical stability of surface enhancement techniques are briefly reviewed, demonstrating the importance of minimizing cold work. The LPB process, tooling, and control systems are described. An overview of current research programs conducted for engine OEMs and the military to apply LPB to a variety of engine and aging aircraft components are presented. Fatigue performance and residual stress data developed to date for several case studies are presented including: * The effect of LPB on the fatigue performance of the nickel based super alloy IN718, showing fatigue benefit of thermal stability at engine temperatures. * An order of magnitude improvement in damage tolerance of LPB processed Ti-6-4 fan blade leading edges. * Elimination of the fretting fatigue debit for Ti-6-4 with prior LPB. * Corrosion fatigue mitigation with LPB in Carpenter 450 steel. *Damage tolerance improvement in 17-4PH steel. Where appropriate, the performance of LPB is compared to conventional shot peening after exposure to engine operating temperatures.

  8. Laser thermal shock and fatigue testing system

    NASA Astrophysics Data System (ADS)

    Fantini, Vincenzo; Serri, Laura; Bianchi, P.

    1997-08-01

    Thermal fatigue consists in repeatedly cycling the temperature of a specimen under test without any other constraint and stopping the test when predefined damage aspects. The result is a lifetime in terms of number of cycles. The parameters of the thermal cycle are the following: minimum and maximum temperature, time of heating, of cooling and time at high or at low temperature. When the temperature jump is very big and fast, phenomena of thermal shock can be induced. Among the numerous techniques used to perform these tests, the laser thermal fatigue cycling is very effective when fast heating of small and localized zones is required. That's the case of test performed to compare new and repaired blades of turbogas machines or components of combustion chambers of energy power plants. In order to perform these tests a thermal fatigue system, based on 1 kW Nd-YAG laser as source of heating, has been developed. The diameter of the heated zone of the specimen irradiated by the laser is in the range 0.5 - 20 mm. The temperatures can be chosen between 200 degree(s)C and 1500 degree(s)C and the piece can be maintained at high and/or low temperature from 0 s to 300 s. Temperature are measured by two sensors: a pyrometer for the high range (550 - 1500 degree(s)C) and a contactless thermocouple for the low range (200 - 550 degree(s)C). Two different gases can be blown on the specimen in the irradiated spot or in sample backside to speed up cooling phase. A PC-based control unit with a specially developed software performs PID control of the temperature cycle by fast laser power modulation. A high resolution vision system of suitable magnification is connected to the control unit to detect surface damages on the specimen, allowing real time monitoring of the tested zone as well as recording and reviewing the images of the sample during the test. Preliminary thermal fatigue tests on flat specimens of INCONEL 738 and HAYNES 230 are presented. IN738 samples, laser cladded by powder of the same material to simulate the refurbishing of a damaged turbine blade after long-term operation, are compared to the parents. Lifetimes are decreasing when high temperature of the cycle is increased and shorter lifetimes of repaired pieces have been found. Laser and TIG welding on HY230 specimens are compared to the parent. Parent and repaired samples have no evidence of cracks after 1500 thermal cycles between 650 and 1000 degree(s)C.

  9. Fiber composite fan blade impact improvement

    NASA Technical Reports Server (NTRS)

    Graff, J.; Stoltze, L.; Varholak, E. M.

    1976-01-01

    The improved foreign object damage resistance of a metal matrix advanced composite fan blade was demonstrated. The fabrication, whirl impact test and subsequent evaluation of nine advanced composite fan blades of the "QCSEE" type design were performed. The blades were designed to operate at a tip speed of 282 m/sec. The blade design was the spar/shell type, consisting of a titanium spar and boron/aluminum composite airfoils. The blade retention was designed to rock on impact with large birds, thereby reducing the blade bending stresses. The program demonstrated the ability of the blades to sustain impacts with up to 681 g slices of birds at 0.38 rad with little damage (only 1.4 percent max weight loss) and 788 g slices of birds at 0.56 rad with only 3.2 percent max weight loss. Unbonding did not exceed 1.1 percent of the post-test blade area during any of the tests. All blades in the post-test condition were judged capable of operation in accordance with the FAA guidelines for medium and large bird impacts.

  10. High temperature low cycle fatigue

    Microsoft Academic Search

    P Rodriguez; S L Mannan

    1995-01-01

    Fatigue at high temperature is a complex phenomenon as it is influenced by a number of time-dependent processes which become\\u000a important at elevated temperatures. These processes include creep, oxidation, phase instabilities and dynamic strain ageing\\u000a (DSA), acting either independently or synergistically influence fatigue behaviour, often lowering the fatigue life. Current\\u000a design approaches employ linear summation of fatigue and creep damage

  11. Failure analysis of a third stage gas turbine blade

    Microsoft Academic Search

    S. Barella; M. Boniardi; S. Cincera; P. Pellin; X. Degive; S. Gijbels

    2011-01-01

    This paper investigates a third stage turbine blade failure in the 150MW unit of a thermal power plant. This primary event caused extensive damage to the unit, i.e. rupture of all blades present in the third and subsequent stages. The blade is made of nickel-based superalloy, Inconel 738, and the blade failure occurred at approximately 22,400 operating hours (25,600 equivalent

  12. An investigation of fatigue and fretting in a dovetail joint

    Microsoft Academic Search

    C. Ruiz; P. H. B. Boddington; K. C. Chen

    1984-01-01

    Specimens designed to reproduce the state of stress of the dovetail joint between blade and disk in a typical gas-turbine configuration have been tested in a 250-kN capacity biaxial fatigue machine. The materials tested were Ti-IMI 829 (disk and blade), Inco 901 and steel FV535 (blades only). The investigation highlights the importance of fretting at the disk\\/blade interface. A design

  13. Smart structure for small wind turbine blade

    NASA Astrophysics Data System (ADS)

    Supeni, E. E.; Epaarachchi, J. A.; Islam, M. M.; Lau, K. T.

    2013-08-01

    Wind energy is seen as a viable alternative energy option for future energy demand. The blades of wind turbines are generally regarded as the most critical component of the wind turbine system. Ultimately, the blades act as the prime mover of the whole system which interacts with the wind flow during the production of energy. During wind turbine operation the wind loading cause the deflection of the wind turbine blade which can be significant and affect the turbine efficiency. Such a deflection in wind blade not only will result in lower performance in electrical power generation but also increase of material degradation due high fatigue life and can significantly shorten the longevity for the wind turbine material. In harnessing stiffness of the blade will contribute massive weight factor and consequently excessive bending moment. To overcome this excessive deflection due to wind loading on the blade, it is feasible to use shape memory alloy (SMA) wires which has ability take the blade back to its optimal operational shape. This paper details analytical and experimental work being carried out to minimize blade flapping deflection using SMA.

  14. Elevated temperature fretting fatigue of nickel based alloys

    Microsoft Academic Search

    Matthew C. Gean

    2008-01-01

    This document details the high temperature fretting fatigue of high temperature nickel based alloys common to turbine disk and blade applications. The research consists of three area of focus: Experiments are conducted to determine quantitatively the fretting fatigue lives of advanced nickel based alloys; Analytical tools are developed and used to investigate the fretting fatigue response of the material; Fractographic

  15. Impact resistance of composite fan blades

    NASA Technical Reports Server (NTRS)

    1974-01-01

    Results are presented of a program to determine the impact resistance of composite fan blades subjected to foreign object damage (FOD) while operating under conditions simulating a short take-off and landing (STOL) engine at takeoff. The full-scale TF39 first-stage fan blade was chosen as the base design for the demonstration component since its configuration and operating tip speeds are similar to a typical STOL fan blade several composite configurations had already been designed and evaluated under previous programs. The first portion of the program was devoted toward fabricating and testing high impact resistant, aerodynamically acceptable composite blades which utilized only a single material system in any given blade. In order to increase the blade impact capability beyond this point, several mixed material (hybrid) designs were investigated using S-glass and Kevlar as well as boron and graphite fibers. These hybrid composite blades showed a marked improvement in resistance to bird impact over those blades made of a single composite material. The work conducted under this program has demonstrated substantial improvement in composite fan blades with respect to FOD resistance and has indicated that the hybrid design concept, which utilizes different types of fibers in various portions of a fan blade design depending on the particular requirements of the different areas and the characteristics of the different fibers involved, shows a significant improvement over those designs utilizing only one material system.

  16. Mixed-Mode, High-Cycle Fatigue-Crack Growth Thresholds in Ti-6Al-4V

    E-print Network

    Ritchie, Robert

    -cycle fatigue-crack growth thresholds with crack size and shape are reported for a Ti-6Al-4V turbine blade alloy and control of failure due to high cycle fatigue (HCF) in turbine engine components is currently one occur, for example, in association with fretting fatigue in the blade dovetail/disk contact section [1

  17. Fatigue Test

    MedlinePLUS

    ... About Your Fatigue 1) During the past two weeks, have you experienced persistent or frequent fatigue? Yes ... fatigue been, on average, during the past two weeks? Not at all 0 Mild fatigue 1 2 ...

  18. Growian rotor blades: Production development, construction and test

    NASA Technical Reports Server (NTRS)

    Thiele, H. M.

    1984-01-01

    Development and construction of three 50 m rotor blades for a 3 MW wind turbine are described. A hybrid concept was chosen, i.e., a load carrying inflexible steel spar and a glass fiber reinforced plastic skin. A test blade was constructed and static loading tests, dynamic vibration tests and fatigue tests on critical welds as well as at the connection between spar and blade skin were performed. All test results show good accordance with calculated values, and were taken into consideration during the construction of two rotor blades.

  19. Fatigue and corrosion in aircraft pressure cabin lap splices

    Microsoft Academic Search

    R. J. H Wanhill; M. F. J Koolloos

    2001-01-01

    Aircraft structures are susceptible to fatigue and corrosion damage, notably at joints. There may be interactions between fatigue and corrosion, especially as aircraft age. Longitudinal lap splices from several types of transport aircraft pressure cabins were disassembled and investigated for Multiple Site Damage (MSD) fatigue cracking and corrosion. The results are compared with NASA data for a full-scale fatigue test.

  20. Tension–tension fatigue behaviour of knitted fabric composites

    Microsoft Academic Search

    Surya D Pandita; Ignaas Verpoest

    2004-01-01

    The tension–tension fatigue behaviour of knitted fabric composites has been investigated. The fatigue damage of knitted fabric composites such as matrix cracks and yarn–matrix debonds was initiated from the part of the knitting loop that is perpendicular to the loading direction. The fatigue damage then propagated following the knitting structure. The fatigue properties of weft knitted fabric composites are compared

  1. Viscoelastic Vibration Dampers for Turbomachine Blades

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan

    2003-01-01

    Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines. Figure 1 depicts a basic turbomachine rotor, which includes multiple blades affixed to a hub by means of dovetail root attachments. Prior to mounting of the blades, thin layers of a viscoelastic material are applied to selected areas of the blade roots. Once the blades have been installed in the hub and the rotor is set into rotation, centrifugal force compresses these layers between the mating load-bearing surfaces of the hub and the blade root. The layers of viscoelastic material provide load paths through which the vibration energy of the blade can be dissipated. The viscoelasticity of the material converts mechanical vibration energy into shear strain energy and then from shear strain energy to heat. Of the viscoelastic materials that have been considered thus far for this application, the one of choice is a commercial polyurethane that is available in tape form, coated on one side with an adhesive that facilitates bonding to blade roots. The thickness of the tape can be chosen to suit the specific application. The typical thickness of 0.012 in. (.0.3 mm) is small enough that the tape can fit in the clearance between the mating blade-root and hub surfaces in a typical turbomachine. In an experiment, a blade was mounted in a test fixture designed to simulate the blade-end conditions that prevail in a turbocompressor. Vibrations were excited in the blade by use of an impact hammer, and damping of the vibrations was measured by use of a dynamic signal analyzer. Tests were performed without and with viscoelastic dampers installed in the dovetail root attachment. The results of the measurements, some of which are presented in Figure 2, show that the viscoelastic dampers greatly increased the rate of damping of vibrations. Accordingly, dynamic stresses on rotor blades were significantly reduced, as shown in Figure 2.

  2. Mechanisms of fretting-fatigue of titanium alloys

    Microsoft Academic Search

    R. A. Antoniou; T. C. Radtke

    1997-01-01

    The effect of continuous fretting in air at 20°C on fatigue performance has been studied for Ti-17 and T1-6Al-4V, high strength titanium alloys used for gas-turbine fan and compressor disks and blades, respectively. The effect of fretting was to reduce the fatigue stress limit from 700 MPa for plain fatigue to 200 MPa for fretting-fatigue. A number of models, supported

  3. Critical issues in high cycle fatigue

    Microsoft Academic Search

    T Nicholas

    1999-01-01

    High cycle fatigue (HCF) failures in materials used in rotating components of gas turbine engines have often been found to be attributable to fatigue loading on materials which have sustained damage from other sources. Damage can be present in the form of initial material or manufacturing defects, or can develop during service operation. Three major sources of in-service damage have

  4. On the Fatigue Analysis of Wind Turbines

    SciTech Connect

    Sutherland, Herbert J.

    1999-06-01

    Modern wind turbines are fatigue critical machines that are typically used to produce electrical power from the wind. Operational experiences with these large rotating machines indicated that their components (primarily blades and blade joints) were failing at unexpectedly high rates, which led the wind turbine community to develop fatigue analysis capabilities for wind turbines. Our ability to analyze the fatigue behavior of wind turbine components has matured to the point that the prediction of service lifetime is becoming an essential part of the design process. In this review paper, I summarize the technology and describe the ''best practices'' for the fatigue analysis of a wind turbine component. The paper focuses on U.S. technology, but cites European references that provide important insights into the fatigue analysis of wind turbines.

  5. Program for impact testing of spar-shell fan blades, test report

    NASA Technical Reports Server (NTRS)

    Ravenhall, R.; Salemme, C. T.

    1978-01-01

    Six filament-wound, composite spar-shell fan blades were impact tested in a whirligig relative to foreign object damage resulting from ingestion of birds into the fan blades of a QCSEE-type engine. Four of the blades were tested by injecting a simulated two pound bird into the path of the rotating blade and two were tested by injecting a starling into the path of the blade.

  6. Subsurface Crack Propagation in Rolling Contact Fatigue of Sintered Alloy

    Microsoft Academic Search

    Yukio Miyashita; Yoshihiro Yoshimura; Jin-Quan Xu; Makoto Horikoshi; Yoshiharu Mutoh

    2003-01-01

    Rolling contact fatigue tests of sintered alloy were carried out under two cylinder contacts. Damage of the specimen was detected by using acceleration sensor before occurrence of final failure, namely spalling failure. In order to study the damage process of contact fatigue of sintered alloy, surfaces and cross sections of the specimens were observed after contact fatigue test. Damage on

  7. Heat treatment, surface roughness and corrosion effects on the damage mechanism of mechanical components in the very high cycle fatigue regime

    Microsoft Academic Search

    Emin Bayraktar; Rubén Mora; I.-M. Garcia; Claude Bathias

    2009-01-01

    Many engineering components are subjected to combined torsion and axial loading in their working conditions, and the cyclic combined loading can result in fatigue fracture after a very long life fatigue regime. The present investigation extends over a wider range of test conditions involving surface treatment and manufacturing effects such as machining, so as to understand the fatigue properties and

  8. Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results

    Microsoft Academic Search

    D. T. Rusk; W. Hoppe; W. Braisted; N. Powar

    2009-01-01

    The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that

  9. Residual stress profiles for mitigating fretting fatigue in gas turbine engine disks

    Microsoft Academic Search

    Kwai S. Chan; Michael P. Enright; Jonathan P. Moody; Patrick J. Golden; Ramesh Chandra; Alan C. Pentz

    2010-01-01

    The driving force for fretting fatigue in engine disks is the contact stresses generated by fretting of the blade and the disk surfaces in the attachment region. This paper examines the use of different residual compressive stress profiles to counteract the undesirable effects of contact stresses and to mitigate fretting fatigue. A global finite-element analysis of the disk blade assembly

  10. Failure analysis of a large wind tunnel compressor blade

    NASA Technical Reports Server (NTRS)

    Hampton, Roy W.; Nelson, Howard G.

    1986-01-01

    A failure analysis was performed to establish the cause of a 2014-T6 aluminum compressor rotor blade failure in a large NASA-Ames wind tunnel. Metallurgical failure analysis by light photography, fractographic SEM examinations, and fatigue experiments showed that a 0.13-mm-deep scratch in the shank of the blade had acted as an initiation site for a fatigue crack, which subsequently grew by Stage II fatigue before occurrence of the final fracture by unstable crack growth. Studies of modal deformation plots and blade FEM analysis indicated that Mode-3 was the most likely mode responsible for the resonance condition which produced the vibration loading that effected crack growth. Tunnel measurements data showed that the crack growth was controlled by both the tunnel resonance and the dampening from the crack itself.

  11. Test evaluation of a laminated wood wind turbine blade concept

    SciTech Connect

    Faddoul, J.R.

    1981-05-01

    Because of the high stiffness and fatigue strength of wood (as compared to density) along with the low cost manufacturing techniques available, a laminated wood wind turbine blade application has been studied. This report presents the results of the testing performed on elements of the wood blade-to-hub transition section which uses steel studs cast into a laminated wood spar with a filled epoxy. Individual stud samples were tested for both ultimate load carrying capability and fatigue strength. A one-time pull-out load of 78,000 lb was achieved for a 15 in. long stud with a diameter of 1 in. Tension-tension fatigue indicated that peak loads on the order of 40% of ultimate could be maintained as an endurance limit (mean load = 20,000 lb, cyclic load = +-15,000 lb). Following the individual stud testing, a full-scale inboard blade section (20 ft in length) was tested.

  12. Thermal Imaging of Medical Saw Blades and Guides

    SciTech Connect

    Dinwiddie, Ralph Barton [ORNL; Steffner, Thomas E [ORNL

    2007-01-01

    Better Than New, LLC., has developed a surface treatment to reduce the friction and wear of orthopedic saw blades and guides. The medical saw blades were thermally imaged while sawing through fresh animal bone and an IR camera was used to measure the blade temperature as it exited the bone. The thermal performance of as-manufactured saw blades was compared to surface-treated blades, and a freshly used blade was used for temperature calibration purposes in order to account for any emissivity changes due to organic transfer layers. Thermal imaging indicates that the treated saw blades cut faster and cooler than untreated blades. In orthopedic surgery, saw guides are used to perfectly size the bone to accept a prosthesis. However, binding can occur between the blade and guide because of misalignment. This condition increases the saw blade temperature and may result in tissue damage. Both treated ad untreated saw guides were also studied. The treated saw guide operated at a significantly lower temperature than untreated guide. Saw blades and guides that operate at a cooler temperature are expected to reduce the amount of tissue damage (thermal necrosis) and may reduce the number of post-operative complications.

  13. Evaluation of the durability of composite tidal turbine blades.

    PubMed

    Davies, Peter; Germain, Grégory; Gaurier, Benoît; Boisseau, Amélie; Perreux, Dominique

    2013-02-28

    The long-term reliability of tidal turbines is critical if these structures are to be cost effective. Optimized design requires a combination of material durability models and structural analyses. Composites are a natural choice for turbine blades, but there are few data available to predict material behaviour under coupled environmental and cycling loading. The present study addresses this problem, by introducing a multi-level framework for turbine blade qualification. At the material scale, static and cyclic tests have been performed, both in air and in sea water. The influence of ageing in sea water on fatigue performance is then quantified, and much lower fatigue lives are measured after ageing. At a higher level, flume tank tests have been performed on three-blade tidal turbines. Strain gauging of blades has provided data to compare with numerical models. PMID:23319705

  14. Fretting Fatigue of Gamma TiAl Studied

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Lerch, Bradley A.; Draper, Susan L.

    2003-01-01

    Gamma titanium-aluminum alloy (g-TiAl) is an attractive new material for aerospace applications because of its low density and high specific strength in comparison to currently used titanium and nickel-base alloys. Potential applications for this material are compressor and low-pressure turbine blades. These blades are fitted into either the compressor or turbine disks via a dovetail connection. The dovetail region experiences a complex stress state due to the alternating centrifugal force and the natural high-frequency vibration of the blade. Because of the dovetail configuration and the complex stress state, fretting is often a problem in this area. Furthermore, the local stress state becomes more complex when the influence of the metal-metal contact and the edge of the contact is evaluated. Titanium and titanium-based alloys in the clean state exhibit strong adhesive bonds when in contact with themselves and other materials (refs. 1 and 2). This adhesion causes heavy surface damage and high friction in practical cases. Although the wear produced by fretting may be mild, the reduction in fatigue life can be substantial. Thus, there is the potential for fretting problems with these TiAl applications. Since TiAl is an emerging material, there has been limited information about its fretting behavior.

  15. Analysis and Tests of Pultruded Blades for Wind Turbine Rotors

    SciTech Connect

    Cheney, M. C. (PS Enterprises, Glastonbury, Connecticut); Olsen, T.; Quandt, G.; Archidiacono, P.

    1999-07-19

    PS Enterprises, Inc. investigated a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades. A rotor was designed, manufactured and tested in the field. A preliminary design study and proof of concept test were conducted to assess the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study and a scaled 80 kW rotor was fabricated and field tested as a demonstration of the concept. The design studies continued to support the premise that pultruded blades offer the potential for significant reductions in rotor weight and cost. The field test provided experimental performance and loads data that compared well with predictions using the FLEXDYNE aeroelastic analysis. The field test also demonstrated stable yaw behavior and the absence of stall flutter over the wind conditions tested. During the final year of the contract, several studies were conducted by a number of independent consultants to address specific technical issues related to pultruded blades that could impact the commercial viability of turbines using this technology. The issues included performance, tower strikes, yaw stability, stall flutter, fatigue, and costs. While the performance of straight pultruded blades was projected to suffer a penalty of about 13% over fully twisted and tapered blades, the study showed that an aerodynamic fairing over the inner 40% could recover 85% of that loss while still keeping the blade cost well below that of conventional blades. Other results of the study showed that with proper design, rotors using pultruded blades could operate without aeroelastic problems, have acceptable fatigue life, and cost less than half that of rotors employing conventionally manufactured blades.

  16. The effects of fretting on fatigue characteristics of a mechanically fastened aircraft joint

    NASA Astrophysics Data System (ADS)

    Shah, Akbar Hussain

    A research study to investigate the effects of fretting on fatigue characteristics of an aircraft joint was carried out. The selected joint for this study simulates the rotor head of an aircraft capable of taking off vertically. The primary function of this hub-spindle joint is to retain the main rotor blade against the centrifugal forces, both in-plane and out-of-plane bending moments and torsion caused due to the lift, drag and other aerodynamic forces imposed on the rotor blades while the aircraft is in forward flight. The primary objectives of this study were twofold; (a) Verify that the average lives of mechanically fastened joints with combined effects of fretting and fatigue will be lower compared to the average lives due to plain fatigue. (b) Discover whether fretting causes cracks to nucleate and fatigue causes those cracks to propagate. In order to verify the validity of the first hypothesis, seven test joints were tested to failure. Several S/N curves were generated against Mil-Handbook 5H data for comparable plain fatigue response of the same material. Out of the seven specimens that were tested, five were machined from Aluminum 7075-T6, and the other two were machined from Aluminum 7050-T7451. An average fretting fatigue life reduction factor Kff, of 21 was found for all these seven joints. In order to validate the second hypothesis, a detailed investigation under a scanning electron microscope of the fretted/failed surfaces was conducted. Severe fretting damage was observed in all test specimens. It was found that fretting-induced damage provided the crack nucleation sites in all test specimens that failed. These nucleation sites were in the form of fretting scars, pits and gouges providing several regions of stress concentration. Under the influence of high tensile stress fields, these sites allowed several small embryonic cracks to form, coalesce and link up to form primary and multiple cracks, which subsequently propagated under the applied cyclic loads leading to final instability, i.e., fracture. Fretting fatigue should be treated as a major threat against structural integrity of joints. Currently, there are no known analytical models available to design against fretting fatigue. It is therefore recommended that in areas of critical applications full scale tests should be conducted prior to actual use.

  17. Advanced turbofan blade refurbishment technique

    SciTech Connect

    Roberts, W.B. [Flow Application Research and Sermatech International Inc., Fremont, CA (United States)

    1995-10-01

    The purpose of the work reported here is to investigate whether the lessons learned from the work of Suder et al. can be used to reduce the in-service performance deterioration of a fan on a high bypass ratio turbofan engine. To this end, a back-to-back test was done on the fan of an RB211-22B engine with the cooperation of Delta Airlines. The fan and engine were first overhauled per normal airline practice and cell-tested to establish that the engine performance met flight acceptance standards. This test, which the engine passed, also established a performance baseline for the overhauled engine. At this point the fan blade leading edge had not been filed or scraped and the blade surfaces had not been polished because the leading edge damage and blade surface roughness fell within the acceptable limits specified by the manufacturer for normal overhaul practice. After the cell test, the fan was removed from the engine and sent to Sermatech International where the following additional operations were performed: (1) the blade surfaces were polished to a finish of 20 rms {micro}in; (2) leading edge roughness due to particle impact damage was removed and the leading edge was polished to a finish of 20 rms {micro}in; (3) the leading edge shape was rounded and the leading edge thickness was reduced over the first 5--10% of chord. Test results indicated a 0.7% drop in thrust specific fuel consumption (lb fuel/lb thrust/hr) relative to the baseline engine after the enhanced fan overhaul. Based on the results of Suder et al. (1995) it appears that 70--80% of this performance gain is due to the thin smooth leading edge and the remainder to the highly polished finish of the blade.

  18. Development of a remote-controlled fatigue test machine using a laser extensometer for investigation of irradiation effect on fatigue properties

    Microsoft Academic Search

    M. Yonekawa; T. Ishii; M. Ohmi; F. Takada; T. Hoshiya; M. Niimi; I. Ioka; Y. Miwa; H. Tsuji

    2002-01-01

    In order to investigate effects of neutron irradiation on fatigue properties of nuclear materials, a remote-controlled high temperature fatigue test machine was developed at the hot laboratory of the Japan Materials Testing Reactor (JMTR) in the Japan Atomic Energy Research Institute (JAERI). A small-sized fatigue specimen having double blades to measure strain with a laser extensometer was designed for this

  19. Fatigue in steel structures under random loading

    Microsoft Academic Search

    Henning Agerskov

    2000-01-01

    Fatigue damage accumulation in steel structures under random loading is studied. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part of the investigation, fatigue test series have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been

  20. Turbine blade

    SciTech Connect

    Butts, D.

    1993-08-03

    A blade is described for use in a gas turbine engine comprising: leading and trailing edges and first and second side walls extending there between, the side walls defining a coolant passage having a width D extending between the first and second side walls for channeling coolant there through in a direction substantially parallel to a longitudinal axis thereof, one of the side walls including a plurality of longitudinally spaced substantially straight turbulator ribs disposed substantially perpendicularly to the longitudinal axis in the coolant passage, each of the ribs having a height E and the radio E/D being greater than about 0.07; and further including a root and a first partition extending therefrom and wherein the coolant passage comprises a serpentine passage defined by the first partition and the side walls and includes a first passage extending along the leading edge and a second passage disposed substantially parallel to and in flow communication with the first passage, the ribs extending from the partition along both the first and second side walls to the leading edge in the first passage and from the first partition along both the first and second side walls in the second passage.

  1. Structural Evaluation of Exo-Skeletal Engine Fan Blades

    NASA Technical Reports Server (NTRS)

    Kuguoglu, Latife; Abumeri, Galib; Chamis, Christos C.

    2003-01-01

    The available computational simulation capability is used to demonstrate the structural viability of composite fan blades of innovative Exo-Skeletal Engine (ESE) developed at NASA Glenn Research Center for a subsonic mission. Full structural analysis and progressive damage evaluation of ESE composite fan blade is conducted through the NASA in-house computational simulation software system EST/BEST. The results of structural assessment indicate that longitudinal stresses acting on the blade are in compression. At a design speed of 2000 rpm, pressure and suction surface outer most ply stresses in longitudinal, transverse and shear direction are much lower than the corresponding composite ply strengths. Damage is initiated at 4870 rpm and blade fracture takes place at rotor speed of 7735 rpm. Damage volume is 51 percent. The progressive damage, buckling, stress and strength results indicate that the design at hand is very sound because of the factor of safety, damage tolerance, and buckling load of 6811 rpm.

  2. The critical role of environment in fatigue damage accumulation in deep-reactive ion-etched single-crystal silicon structural films

    Microsoft Academic Search

    Olivier N. Pierron; Christopher L. Muhlstein

    2006-01-01

    The importance of service environment to the fatigue resistance of n+-type, 10 ?m thick, deep-reactive ion-etched (DRIE) silicon structural films used in microelectromechanical systems (MEMS) was characterized by testing of electrostatically actuated resonators (natural frequency, f0, ?40 kHz) in controlled atmospheres. Stress-life (S-N) fatigue tests conducted in 30°C, 50% relative humidity (R.H.) air demonstrated the fatigue susceptibility of silicon films.

  3. Evaluation of wind farm effects on fatigue loads of an individual wind turbine at the EnBW Baltic 1 offshore wind farm

    NASA Astrophysics Data System (ADS)

    Bustamante, A.; Vera-Tudela, L.; Kühn, M.

    2015-06-01

    Turbulence in wake has special interest due to its strong connection with increment of fatigue loads. The aim of this paper is to evaluate the wind farm effects on fatigue loads of an individual wind turbine at the EnBW Baltic 1 offshore wind farm and compare the results with the statements suggested by IEC 61400-1 ed. 3 [1]. From measurements, the study provides strong evidence that considerable wake effects up to 15 rotor diameters (D) downstream are related to the increase of fatigue loads in the analyzed turbine. The influence of the behavior of the upstream wind turbine's thrust coefficient (CT) can be observed in the analyzed curves for turbulence intensity and damage equivalent loads (DELs) in blade root flapwise and edgewise direction.

  4. Wind turbine blade testing system using base excitation

    SciTech Connect

    Cotrell, Jason; Thresher, Robert; Lambert, Scott; Hughes, Scott; Johnson, Jay

    2014-03-25

    An apparatus (500) for fatigue testing elongate test articles (404) including wind turbine blades through forced or resonant excitation of the base (406) of the test articles (404). The apparatus (500) includes a testing platform or foundation (402). A blade support (410) is provided for retaining or supporting a base (406) of an elongate test article (404), and the blade support (410) is pivotally mounted on the testing platform (402) with at least two degrees of freedom of motion relative to the testing platform (402). An excitation input assembly (540) is interconnected with the blade support (410) and includes first and second actuators (444, 446, 541) that act to concurrently apply forces or loads to the blade support (410). The actuator forces are cyclically applied in first and second transverse directions. The test article (404) responds to shaking of its base (406) by oscillating in two, transverse directions (505, 507).

  5. Composite Fan Blade Design for Advanced Engine Concepts

    NASA Technical Reports Server (NTRS)

    Abumeri, Galib H.; Kuguoglu, Latife H.; Chamis, Christos C.

    2004-01-01

    The aerodynamic and structural viability of composite fan blades of the revolutionary Exo-Skeletal engine are assessed for an advanced subsonic mission using the NASA EST/BEST computational simulation system. The Exo-Skeletal Engine (ESE) calls for the elimination of the shafts and disks completely from the engine center and the attachment of the rotor blades in spanwise compression to a rotating casing. The fan rotor overall adiabatic efficiency obtained from aerodynamic analysis is estimated at 91.6 percent. The flow is supersonic near the blade leading edge but quickly transitions into a subsonic flow without any turbulent boundary layer separation on the blade. The structural evaluation of the composite fan blade indicates that the blade would buckle at a rotor speed that is 3.5 times the design speed of 2000 rpm. The progressive damage analysis of the composite fan blade shows that ply damage is initiated at a speed of 4870 rpm while blade fracture takes place at 7640 rpm. This paper describes and discusses the results for the composite blade that are obtained from aerodynamic, displacement, stress, buckling, modal, and progressive damage analyses. It will be demonstrated that a computational simulation capability is readily available to evaluate new and revolutionary technology such as the ESE.

  6. Dynamic analysis tool development for advanced geometry wind turbine blades

    NASA Astrophysics Data System (ADS)

    Larwood, Scott Michael

    This dissertation describes work to develop a dynamic analysis code for swept wind turbine blades. Because of their aeroelastic behavior, swept blades offer the potential to increase energy capture and lower fatigue loads. This work was an outgrowth of United States Department of Energy contract on swept blades, where the author used the Adams(TM)dynamic software. The author based the new code on the National Renewable Energy Laboratory's FAST code. The new code would allow for lower cost analysis and faster computation times for swept blades compared to Adams. The FAST revisions included the geometry and mode shapes required for the bending and twisting motion of the swept blade. The author also developed a finite-element program to determine mode shapes for the swept blade. The author verified the new code with Adams. The comparisons were favorable; however, the Adams model exhibited more twist. The differences may be attributed to differences in modeling approach. The author attempted to validate the code with field test data; however, uncertainties in the test wind speed and the turbine controller made comparison difficult. The author used the new code to perform preliminary designs of swept rotors for 1.5 MW and 3.0MWwind turbines. The designs showed a 5% increase in annual energy production and a decrease in flap-bending fatigue over the baseline straight-blade designs.

  7. A new device for fretting fatigue testing

    Microsoft Academic Search

    G. H. Majzoobi; R. Hojjati; M. Nematian; E. Zalnejad; A. R. Ahmadkhani; E. Hanifepoor

    2010-01-01

    Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loads and sliding movements at the\\u000a same time. Fretting fatigue can reduce the fatigue life of materials by half or even more. Fretting fatigue tests are usually\\u000a performed using universal hydraulic testing devices. The contact pressure is produced by a fixture, typically designed and\\u000a manufactured by researchers.

  8. Nitinol Fatigue Life for Variable Strain Amplitude Fatigue

    NASA Astrophysics Data System (ADS)

    Lin, Z.; Pike, K.; Schlun, M.; Zipse, A.; Draper, J.

    2012-12-01

    Nitinol fatigue testing results are presented for variable strain amplitude cycling. The results indicate that cycles smaller than the constant amplitude fatigue limit may contribute to significant fatigue damage when they occur in a repeating sequence of large and small amplitude cycles. The testing utilized two specimen types: stent-like diamond specimens and Z-shaped wire specimens. The diamond specimens were made from nitinol tubing with stent-like manufacturing processes and the Z-shaped wire specimens were made from heat set nitinol wire. The study explored the hypothesis that duty cycling can have an effect on nitinol fatigue life. Stent-like structures were subjected to different in vivo loadings in order to create more complex strain amplitudes. The main focus in this study was to determine whether a combination of small and large amplitudes causes additional damage that alters the fatigue life of a component.

  9. Thermal fatigue testing of thin metal films

    NASA Astrophysics Data System (ADS)

    Mönig, R.; Keller, R. R.; Volkert, C. A.

    2004-11-01

    An experimental method is described for performing thermal fatigue testing of thin films and lines on substrates. The method uses Joule heating from alternating currents to generate temperature, strain, and stress cycles in the metal structures. The apparatus has been installed in a scanning electron microscope and allows in situ observations of the fatigue damage evolution. First observations on Cu films reveal that fatigue damage forms in submicrometer thick films and is strongly affected by the film thickness and grain size. In addition, results from a special test structure confirm that the damage is caused by fatigue and not by electromigration.

  10. Wind Turbine Blade Design

    NSDL National Science Digital Library

    Kidwind Project

    Students go through the design process and the scientific method to test the effect of blade design on power output. There is an optional extension to use the data to create an optimal set of wind turbine blades.

  11. Fretting fatigue crack analysis in Ti–6Al–4V

    Microsoft Academic Search

    Alisha Hutson; Ted Nicholas; Reji John

    2005-01-01

    A study was conducted to verify the efficacy of a fracture mechanics methodology to model the crack growth behavior of fretting fatigue-nucleated cracks obtained under test conditions similar to those found in turbine engine blade attachments. Experiments were performed to produce cracked samples, and fretting fatigue crack propagation lives were calculated for each sample. Cracks were generated at 106 cycles

  12. Structural qualification testing and operational loading on a fiberglass rotor blade for the Mod-OA wind turbine

    NASA Technical Reports Server (NTRS)

    Sullivan, T. L.

    1983-01-01

    Fatigue tests were performed on full- and half-scale root end sections, first to qualify the root retention design, and second to induce failure. Test methodology and results are presented. Two operational blades were proof tested to design limit load to ascertain buckling resistance. Measurements of natural frequency, damping ratio, and deflection under load made on the operational blades are documented. The tests showed that all structural design requirements were met or exceeded. Blade loads measured during 3000 hr of field operation were close to those expected. The measured loads validated the loads used in the fatigue tests and gave high confidence in the ability of the blades to achieve design life.

  13. Fretting fatigue of laser shock peened Ti–6Al–4V

    Microsoft Academic Search

    S. Srinivasan; D. B. Garcia; M. C. Gean; H. Murthy; T. N. Farris

    2009-01-01

    The objective of this paper is to examine fretting fatigue of laser shock peened (LSP) titanium to quantify the influence of LSP on fretting fatigue life. Contact conditions such as loads and pad geometry are chosen to generate fretting fatigue stresses similar to those occurring in blade\\/disk contacts in gas turbine engines. LSP treated specimens attained 5-, 10- and 25-fold

  14. Observation, analysis and prediction of fretting fatigue in 2024-T351 aluminum alloy

    Microsoft Academic Search

    Matthew P. Szolwinski; Thomas N. Farris

    1998-01-01

    Fretting is associated with microslip at the interface of contacts experiencing oscillatory loads. One consequence of fretting is the formation and subsequent growth of cracks at the edge of contact, a phenomenon known as fretting fatigue. Fretting fatigue is an important fatigue failure mechanism in aircraft structural lap joints and turbine blade\\/disk contacts. A well-characterized, integrated fretting test system has

  15. Mechanics of fretting fatigue crack formation

    Microsoft Academic Search

    Matthew P. Szolwinski; Thomas N. Farris

    1996-01-01

    Fretting is a contact damage process arising from surface microslip associated with small-scale oscillatory motion of clamped structural members. The fretting damage process is a synergistic competition among wear, corrosive and fatigue phenomena driven by both the microslip at the contact surface and cyclic fretting contact stresses. Fretting fatigue is one mechanism of the formation of cracks in many common

  16. Hydrodynamic blade guide

    DOEpatents

    Blaedel, Kenneth L. (Dublin, CA); Davis, Pete J. (Pleasanton, CA); Landram, Charles S. (Livermore, CA)

    2000-01-01

    A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.

  17. Turbine blade damping study

    NASA Technical Reports Server (NTRS)

    Dominic, R. J.

    1984-01-01

    Research results and progress on the performance of bladed systems is reported the different topics discussed include: the study of turbine blade damping; forced vibrations of friction damped beam moistures in two dimensions; and a users manual for a computer program for dynamic analysis of bladed systems.

  18. FRACTOGRAPHIC INVESTIGATION OF THE FAILURE OF SECOND STAGE GAS TURBINE BLADES

    Microsoft Academic Search

    Hassan FARHANGI; Ali Asghar; FOULADI MOGHADAM

    This paper deals with a fracture investigation of second stage turbine blades in a 32 MW unit in a thermal power plant. The premature failure of the blades, made of nickel based superalloy Udimet 500, occurred after a service life of 50000 h and caused extensive damage to the unit. Several fractured blades were retrieved from the unit to identify

  19. Fatigue properties of jointed wood composites Part I Statistical analysis, fatigue master curves and constant life diagrams

    Microsoft Academic Search

    I. P. Bond; M. P. Ansell

    1998-01-01

    The primary aim of this work was to assess the fatigue performance of scarf-jointed laminated wood composites used to manufacture wind turbine blades and establish simple fatigue design procedures. Laminates made from poplar (Populus canadensis\\/serotina), Khaya (Khaya ivorensis) and beech (Fagus sylvatica), incorporating typical scarf joints, were assessed under reversed loading (R =-1). Scarf joints were found to be great

  20. Piezomagnetism and fatigue: II

    Microsoft Academic Search

    S. A. Guralnick; S. Bao; T. Erber

    2008-01-01

    The cumulation of damage in test specimens of AISI 1018 steel, subjected to repeated cycles of tension and compression leading to fatigue failure at Nf cycles, is correlated with the evolution of stress-strain (sigma - ?) hysteresis and piezomagnetic (B-?) hysteresis. Specifically, the sigma - ? hysteresis loop areas, when plotted as a function of the number of loading cycles

  1. Blades and Towers Modal Analysis Code (BModes): Verification of Blade Modal Analysis Capability

    SciTech Connect

    Bir, G.

    2009-01-01

    BModes is a finite-element code we developed to provide coupled modes for flexible blades, rotating or non-rotating, and for towers, onshore or offshore (supported either on floating platforms or on monopile foundations). Both the blade and the tower allow a tip attachment, which is modeled as a rigid body with mass, six moments of inertia, and a mass centroid that may be offset from the blade or tower axis. Examples of tip attachments are aerodynamic brakes for blades and nacelle-rotor subassemblies for towers. Allowable supports for the tower include tension wires, floating platforms, and shallow-water monopiles with elastic foundation. Coupled modes (implying coupling of flap, lag, axial, and torsion motions) have several applications. Examples are: modeling of major flexible components for modal-based aeroelastic codes such as FAST, validation of turbine models using experimental data, modal-based fatigue analysis, and understanding of aeroelastic-stability behavior of turbines. This paper presents verification of the blade modal analysis capability of BModes. Verification begins with simple uniform beams, rotating and non-rotating, and progresses to realistic blades. BModes-computed modes for all models are compared with analytical modes, if possible to obtain, and with modes generated by RCAS. All results, presented in terms of frequencies and mode shapes, show excellent agreement.

  2. Thermal fatigue life evaluation of CSP joints by mechanical fatigue testing

    Microsoft Academic Search

    Yoshihiko Kanda; Kunihiro Zama; Yoshiharu Kariya; Hironori Oota; Shunichi Kikuchi; Hideki Yamabe; Kazuhiko Nakamura

    2010-01-01

    The interrelation between a thermal cycle test and a mechanical shear fatigue test has been studied for CSP joints from the view point of fatigue life and the microstructural damage of solder joints. The fatigue lives in both methods are almost equivalent even though loading method is different. From the viewpoint of microstructure, the fact is attributed to that the

  3. Failure investigation of a low-pressure turbine blade

    Microsoft Academic Search

    S. J. Ghosh

    2004-01-01

    Several blades at a thermal power plant had failed during operation. Extensive visual, metallographic, and microhardness tests\\u000a indicated that the initiation of the failure had been due to cracks formed due to fretting, which subsequently propagated\\u000a in fatigue.

  4. Wireless Inductive Power Device Suppresses Blade Vibrations

    NASA Technical Reports Server (NTRS)

    Morrison, Carlos R.; Provenza, Andrew J.; Choi, Benjamin B.; Bakhle, Milind A.; Min, James B.; Stefko, George L.; Duffy, Kirsten P.; Fougers, Alan J.

    2011-01-01

    Vibration in turbomachinery can cause blade failures and leads to the use of heavier, thicker blades that result in lower aerodynamic efficiency and increased noise. Metal and/or composite fatigue in the blades of jet engines has resulted in blade destruction and loss of lives. Techniques for suppressing low-frequency blade vibration, such as gtuned circuit resistive dissipation of vibratory energy, h or simply "passive damping," can require electronics incorporating coils of unwieldy dimensions and adding unwanted weight to the rotor. Other approaches, using vibration-dampening devices or damping material, could add undesirable weight to the blades or hub, making them less efficient. A wireless inductive power device (WIPD) was designed, fabricated, and developed for use in the NASA Glenn's "Dynamic Spin Rig" (DSR) facility. The DSR is used to simulate the functionality of turbomachinery. The relatively small and lightweight device [10 lb (approx.=4.5 kg)] replaces the existing venerable and bulky slip-ring. The goal is the eventual integration of this technology into actual turbomachinery such as jet engines or electric power generators, wherein the device will facilitate the suppression of potentially destructive vibrations in fan blades. This technology obviates slip rings, which require cooling and can prove unreliable or be problematic over time. The WIPD consists of two parts: a remote element, which is positioned on the rotor and provides up to 100 W of electrical power to thin, lightweight piezoelectric patches strategically placed on/in fan blades; and a stationary base unit that wirelessly communicates with the remote unit. The base unit supplies inductive power, and also acts as an input and output corridor for wireless measurement, and active control command to the remote unit. Efficient engine operation necessitates minimal disturbance to the gas flow across the turbine blades in any effort to moderate blade vibration. This innovation makes it possible to moderate vibration on or in turbomachinery blades by providing 100 W of wireless electrical power and actuation control to thin, lightweight vibration-suppressing piezoelectric patches (eight actuation and eight sensor patches in this prototype, for a total of 16 channels) positioned strategically on the surface of, or within, titanium fan blades, or embedded in composite fan blades. This approach moves significantly closer to the ultimate integration of "active" vibration suppression technology into jet engines and other turbomachinery devices such as turbine electrical generators used in the power industry. The novel feature of this device is in its utilization of wireless technology to simultaneously sense and actively control vibration in rotating or stationary turbomachinery blades using piezoelectric patches. In the past, wireless technology was used solely for sensing and diagnostics. This technology, however, will accomplish much more, in terms of simultaneously sensing, suppressing blade vibration, and making it possible for detailed study of vibration impact in turbomachinery blades.

  5. Failure of the J79 Engine Compressor Blade Due to Stall

    Microsoft Academic Search

    Kyo-Soo Song; Seon-Gab Kim; Young-Ha Hwang

    2007-01-01

    The fractured and damaged compressor rotor blades of a J79 engine have been examined. Optical, stereoscopic, microhardness\\u000a testing, and SEM examinations were carried out to find out the causes of the fracture. The material of the blades was STS403\\u000a and blades were used without coating. From the 15th through the 17th compressor stages the rotor blades, stator vanes, combustion,\\u000a and

  6. Dual-axis resonance testing of wind turbine blades

    SciTech Connect

    Hughes, Scott; Musial, Walter; White, Darris

    2014-01-07

    An apparatus (100) for fatigue testing test articles (104) including wind turbine blades. The apparatus (100) includes a test stand (110) that rigidly supports an end (106) of the test article (104). An actuator assembly (120) is attached to the test article (104) and is adapted for substantially concurrently imparting first and second forcing functions in first and second directions on the test article (104), with the first and second directions being perpendicular to a longitudinal axis. A controller (130) transmits first and second sets of displacement signals (160, 164) to the actuator assembly (120) at two resonant frequencies of the test system (104). The displacement signals (160, 164) initiate the actuator assembly (120) to impart the forcing loads to concurrently oscillate the test article (104) in the first and second directions. With turbine blades, the blades (104) are resonant tested concurrently for fatigue in the flapwise and edgewise directions.

  7. The dependence of magnetic properties on fatigue in A533B nuclear pressure vessel steels

    Microsoft Academic Search

    Y. Bi; M. R. Govindaraju; D. C. Jiles

    1997-01-01

    Cyclic loading causes cumulative microstructural changes in materials. The magnetic properties of A533B steel are determined by both initial microstructures and microstructural changes induced by fatigue damage. From the results of a series of strain-controlled fatigue tests, the magnetic properties were found to change systematically with fatigue damage throughout the fatigue life. A linear relationship between magnetic remanence and mechanical

  8. Impact behavior of filament wound graphite/epoxy fan blades

    NASA Technical Reports Server (NTRS)

    Bowles, K. J.

    1978-01-01

    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 meters per second retained their structural integrity. Two blades were each impacted with a 454 gram slice of a 908 gram simulated bird at a tip speed of 263 meters per second and impact angles of 22 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. Results of a failure mode analysis are also discussed.

  9. Characterization of Fatigue Cracking and Healing of Asphalt Mixtures 

    E-print Network

    Luo, Xue

    2012-07-16

    Fatigue cracking is one of the most common distresses of asphalt pavements, whereas healing is a counter process to cracking which alleviates cracking damage and extends fatigue life of asphalt pavements. Most of existing methods to characterize...

  10. Thermomechanical fatigue life prediction for several solders

    Microsoft Academic Search

    Shengmin Wen

    2001-01-01

    Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage

  11. Vibration-based condition monitoring of a turbomachinery bladed system

    NASA Astrophysics Data System (ADS)

    Rehman, Anees ur

    Damage detection in mistuned turbomachinery bladed systems is addressed in this research utilising a statistical approach to vibration-based damage detection. Initially, a modal characteristics-based damage identification technique is developed by obtaining damage indices based on the differences in the Modal Assurance Criterion (MAC) that give a measure of the change in the mode shapes. These damage indices are then correlated to the depth/location of the damage and also to the level/pattern of the mistuning present. The possibility of characterising cracks from their nonlinear response is investigated by detecting and classifying nonlinearity arising from a breathing crack interface. Nonlinearity detection is achieved by obtaining the amplitude dependent Frequency Response Functions (FRFs) and classification is accomplished by obtaining their Hilbert transform (HT). The breathing crack nonlinear behaviour is numerically validated by drawing a comparison between experimental and numerical results. The Coulomb friction-induced damping at the crack interface is quantified by obtaining relationships between crack depth/coefficient of friction and damping levels/friction stress/crack face pressures.. Based on the conclusions from the breathing crack nonlinear behaviour investigations, damage detection in the mistuned bladed disc is addressed utilising outlier analysis. The effect of noise on the damage detection is studied by obtaining the maximum, mean and minimum damage detectability levels for varying noise. Both, the frequency and time domain data from the bladed disc are considered for damage detection. For the frequency domain, FRFs for varying mistuning levels in the bladed disc are obtained and damage detection is addressed when the FRF peak of the crack mode cannot be distinguished from the cluster of mistuning modes. In the time domain, the effectiveness of the developed damage detection procedure is examined for reduced data sets from the blade tips (blade tip timing)..

  12. Effect of Crystal Orientation on Analysis of Single-Crystal, Nickel-Based Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Swanson, G. R.; Arakere, N. K.

    2000-01-01

    High-cycle fatigue-induced failures in turbine and turbopump blades is a pervasive problem. Single-crystal nickel turbine blades are used because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant and complicating factor. A fatigue failure criterion based on the maximum shear stress amplitude on the 24 octahedral and 6 cube slip systems is presented for single-crystal nickel superalloys (FCC crystal). This criterion greatly reduces the scatter in uniaxial fatigue data for PWA 1493 at 1,200 F in air. Additionally, single-crystal turbine blades used in the Space Shuttle main engine high pressure fuel turbopump/alternate turbopump are modeled using a three-dimensional finite element (FE) model. This model accounts for material orthotrophy and crystal orientation. Fatigue life of the blade tip is computed using FE stress results and the failure criterion that was developed. Stress analysis results in the blade attachment region are also presented. Results demonstrate that control of crystallographic orientation has the potential to significantly increase a component's resistance to fatigue crack growth without adding additional weight or cost.

  13. Fatigue behavior and damage characteristic of ultra-fine grain low-purity copper processed by equal-channel angular pressing (ECAP)

    Microsoft Academic Search

    Changzheng Xu; Qingjuan Wang; Maosheng Zheng; Jindou Li; Meiquan Huang; Qingming Jia; Jiewu Zhu; Ludvik Kunz; Michal Buksa

    2008-01-01

    The S–N and Coffin–Manson plot, cyclic stress–strain response, changes of microstructure, and the surface morphology of ultra-fine grain (UFG) low-purity copper processed by ECAP were tested and observed in present study. And the formation mechanism of shear bands was discussed in detail. The results show that the UFG Cu represents longer lifetime under stress-controlled fatigue, but lower fatigue resistance under

  14. Effect of frequency and strain amplitude on the fatigue damage of boron\\/epoxy fiber-reinforced composite materials. Interim report

    Microsoft Academic Search

    R. S. Williams; K. L. Reifsnider; W. W. Stinchcomb; H. T. Turgay

    1975-01-01

    The results of strain-controlled axial fatigue tests on boron\\/epoxy fiber reinforced composite materials are presented in the first of a series of reports detailing such results for a large number of fatigue tests run on boron\\/epoxy and boron\\/aluminum. The report contains a complete discussion of present experimental methods used in conjunction with this research program. Data from a series of

  15. Designing against fretting fatigue in aeroengines

    Microsoft Academic Search

    C. Ruiz; D. Nowell

    2000-01-01

    Gas turbines used for aircraft propulsion incorporate a large number of mechanical joints, where fretting fatigue is an important design consideration. Chief amongst them are the dovetail and firtree joints between blades and disks, particularly in the fan assembly and in the low pressure stages of the compressor where the operating temperature is sufficiently low to exclude the possibility of

  16. Impact resistance of composite fan blades. [fiber reinforced graphite and boron epoxy blades for STOL operating conditions

    NASA Technical Reports Server (NTRS)

    Premont, E. J.; Stubenrauch, K. R.

    1973-01-01

    The resistance of current-design Pratt and Whitney Aircraft low aspect ratio advanced fiber reinforced epoxy matrix composite fan blades to foreign object damage (FOD) at STOL operating conditions was investigated. Five graphite/epoxy and five boron/epoxy wide chord fan blades with nickel plated stainless steel leading edge sheath protection were fabricated and impact tested. The fan blades were individually tested in a vacuum whirlpit under FOD environments. The FOD environments were typical of those encountered in service operations. The impact objects were ice balls, gravel, stralings and gelatin simulated birds. Results of the damage sustained from each FOD impact are presented for both the graphite boron reinforced blades. Tests showed that the present design composite fan blades, with wrap around leading edge protection have inadequate FOD impact resistance at 244 m/sec (800 ft/sec) tip speed, a possible STOL operating condition.

  17. Structural health monitoring of wind turbine blade using fiber Bragg grating sensors and fiber optic rotary joint

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Ni, Y. Q.; Ye, X. W.; Yang, H. X.; Zhu, S.

    2012-04-01

    Wind energy utilization as a reliable energy source has become a large industry in the last 20 years. Nowadays, wind turbines can generate megawatts of power and have rotor diameters that are on the order of 100 meters in diameter. One of the key components in a wind turbine is the blade which could be damaged by moisture absorption, fatigue, wind gusts or lighting strikes. The wind turbine blades should be routinely monitored to improve safety, minimize downtime, lower the risk of sudden breakdowns and associated huge maintenance and logistics costs, and provide reliable power generation. In this paper, a real-time wind turbine blade monitoring system using fiber Bragg grating (FBG) sensors with the fiber optic rotary joint (FORJ) is proposed, and applied to monitor the structural responses of a 600 W small scale wind turbine. The feasibility and effectiveness of the FORJ is validated by continuously transmitting the optical signals between the FBG interrogator at the stationary side and the FBG sensors on the rotating part. A comparison study between the measured data from the proposed system and those from an IMote2-based wireless strain measurement system is conducted.

  18. The effect of low cycle fatigue cracks and loading history on high cycle fatigue threshold

    Microsoft Academic Search

    Monty Allen Moshier

    2000-01-01

    High cycle fatigue (HCF) has been of great concern of late in light of the many HCF gas turbine engine failures experienced by the U.S. Air Force. Due to the high frequency, failures occur rapidly when components sustain damage from other sources. Low cycle fatigue (LCF) can initiate cracks that produce such damage. This study investigates the HCF threshold of

  19. Fatigue life prediction for wind turbines: A case study on loading spectra and parameter sensitivity

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.; Veers, P. S.; Ashwill, T. D.

    Wind turbines are fatigue-critical machines used to produce electrical energy from the wind. These rotating machines are subjected to environmental loadings that are highly irregular in nature. Historical examples of fatigue problems in both research and commercial wind turbine development are presented. Some example data on wind turbine environments, loadings and material properties are also shown. Before a description of how the authors have chosen to attack the cumulative damage assessment, questions are presented for the reader's reflection. The solution technique used by the authors is then presented, followed by a case study applying the procedures to an actual wind turbine blade joint. The wind turbine is the 34-meter diameter vertical axis wind turbine (VAWT) erected by Sandia National Laboratories near Bushland, Texas. The case study examines parameter sensitivities for realistic uncertainties in inputs defining the turbine environment, stress response and material properties. The fatigue lifetimes are calculated using a fatigue analysis program, called LIFE2, which was developed at Sandia. The LIFE2 code, described in some detail in an appendix, is a PC-based, menu-driven package that leads the user through the steps required to characterize the loading and material properties, then uses Miner's rule or a linear crack propagation rule to numerically calculate the time to failure. Only S-n based cumulative damage applications are illustrated here. The LIFE2 code is available to educational institutions for use as a case study in describing complicated loading histories and for use by students in examining, hands on, parameter sensitivity of fatigue life analysis.

  20. KATP channel deficiency in mouse flexor digitorum brevis causes fibre damage and impairs Ca2+ release and force development during fatigue in vitro

    PubMed Central

    Cifelli, Carlo; Bourassa, François; Gariépy, Louise; Banas, Krystyna; Benkhalti, Maria; Renaud, Jean-Marc

    2007-01-01

    Activation of the KATP channels results in faster fatigue rates as the channels depress action potential amplitude, whereas abolishing the channel activity has no effect in whole extensor digitorum longus (EDL) and soleus muscles. In this study, we examined the effects of abolished KATP channel activity during fatigue at 37°C on free intracellular Ca2+() and tetanic force using single muscle fibres and small muscle bundles from the flexor digitorum brevis (FDB). KATP channel deficient muscle fibres were obtained (i) pharmacologically by exposing wild-type fibres to glibenclamide, and (ii) genetically using null mice for the Kir6.2 gene (Kir6.2?/? mice). Fatigue was elicited using 200 ms tetanic contractions every second for 3 min. This study demonstrated for the first time that abolishing KATP channel activity at 37°C resulted in faster fatigue rates, where decreases in peak and tetanic force were faster in KATP channel deficient fibres than in control wild-type fibres. Furthermore, several contractile dysfunctions were also observed in KATP channel deficient muscle fibre. They included partially or completely supercontracted single muscle fibres, greater increases in unstimulated and unstimulated force, and lower force recovery. We propose that the observed faster rate of fatigue in KATP channel deficient fibres is because the decreases in peak and force caused by contractile dysfunctions prevail over the expected slower decreases when the channels do not depress action potential amplitude. PMID:17510189