Science.gov

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. 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.

  3. 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.

    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.

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

    SciTech Connect

    Freebury, G.; Musial, W.

    2000-03-13

    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 the materials or blade structural properties is precisely known. According to this method, the loads are never converted to stresses. Instead, a family of M-N curves (moment vs. cycles) is defined with reasonable boundaries for load-amplitude and slope. An optimization program iterates and converges on the constant amplitude test load and load ratio that minimizes the sensitivity to the range of M-N curves for each blade section. The authors constrained the general method to match the NedWind 25 design condition for the Standards, Measurements, and Testing (SMT) blade testing pro gram. SMT participants agreed to use the fixed S-N slope of m = 10 from the original design to produce consistent test-loads among the laboratories. Unconstrained, the general method suggests that slightly higher test loads should be used for the NedWind 25 blade design spectrum. NedWind 25 blade test loads were computed for lead-lag and flap under single-axis and two-axis loading.

  5. 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..

  6. Fatigue life estimation procedure for a turbine blade under transient loads

    NASA Astrophysics Data System (ADS)

    Vyas, N. S.; Rao, J. S.

    1992-06-01

    A technique for fatigue damage assessment during variable speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes, and Miner's rule is employed to estimate the cumulation of fatigue.

  7. Subrupture Tendon Fatigue Damage

    PubMed Central

    Laudier, Damien M.; Shine, Jean H.; Basta-Pljakic, Jelena; Jepsen, Karl J.; Schaffler, Mitchell B.; Flatow, Evan L.

    2016-01-01

    The mechanical and microstructural bases of tendon fatigue, by which damage accumulates and contributes to degradation, are poorly understood. To investigate the tendon fatigue process, rat flexor digitorum longus tendons were cyclically loaded (1–16 N) until reaching one of three levels of fatigue damage, defined as peak clamp-to-clamp strain magnitudes representing key intervals in the fatigue life: i) Low (6.0%–7.0%); ii) Moderate (8.5%–9.5%); and iii) High (11.0%–12.0%). Stiffness, hysteresis, and clamp-to-clamp strain were assessed diagnostically (by cyclic loading at 1–8 N) before and after fatigue loading and following an unloaded recovery period to identify mechanical parameters as measures of damage. Results showed that tendon clamp-to-clamp strain increased from pre- to post-fatigue loading significantly and progressively with the fatigue damage level (p≤0.010). In contrast, changes in both stiffness and hysteresis were significant only at the High fatigue level (p≤0.043). Correlative microstructural analyses showed that Low level of fatigue was characterized by isolated, transverse patterns of kinked fiber deformations. At higher fatigue levels, tendons exhibited fiber dissociation and localized ruptures of the fibers. Histomorphometric analysis showed that damage area fraction increased significantly with fatigue level (p≤0.048). The current findings characterized the sequential, microstructural events that underlie the tendon fatigue process and indicate that tendon deformation can be used to accurately assess the progression of damage accumulation in tendons. PMID:18683881

  8. 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.

  9. Composite blade damaging under impact

    NASA Astrophysics Data System (ADS)

    Menouillard, T.; Rthor, J.; Bung, H.; Suffis, A.

    2006-08-01

    Composites materials are now being used in primary aircraft structures, and other domains because of numerous advantages. A part of a continuous in-flight operating costs, gas turbine engine manufacturers are always looking for ways to decrease engine weight. This is the case of compressor blades which have to satisfy, for example, the standard bird strike or debris in order to measure the crashworthiness. Bird strike impacts are actually among the most challenging loads that composite blades must accommodate. Thus for the further development of composite structures, it becomes important to have available predictive tools for simulating the response of composite structures under crash or impact loads, which will allow to evaluate damage state in the structure in function of time. A composites damage model, without mesh dependency, is presented, and allows to obtain agreement with impact experiment. Examples of finite element simulations for the impact response of blade based on this materials model are developped. These numerical results correspond to a bird strike on an equivalent composites blade, and insists on damage evolution in structure.

  10. Application of the US high cycle fatigue data base to wind turbine blade lifetime predictions

    SciTech Connect

    Sutherland, H.J.; Mandell, J.F.

    1996-10-01

    This paper demonstrates a methodology for predicting the service lifetime of wind turbine blades using the high-cycle fatigue data base for typical US blade materials developed by Mandell, et al. (1995). The first step in the analysis is to normalize the data base (composed primarily of data obtained from specialized, relatively small coupons) with fatigue data from typical industrial laminates to obtain a Goodman Diagram that is suitable for analyzing wind turbine blades. The LIFE2 fatigue analysis code for wind turbines is then used for the fatigue analysis of a typical turbine blade with a known load spectrum. In the analysis, a linear damage model, Miner`s Rule, is used to demonstrate the prediction of the service lifetime for a typical wind turbine blade under assumed operating strain ranges and stress concentration factors. In contrast to typical European data, the asymmetry in this data base predicts failures under typical loads to be compressive.

  11. Probabilistic Fatigue Damage Program (FATIG)

    NASA Technical Reports Server (NTRS)

    Michalopoulos, Constantine

    2012-01-01

    FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

  12. Ultrasonic Evaluation of Fatigue Damage

    NASA Astrophysics Data System (ADS)

    Bayer, P.; Singher, L.; Notea, A.

    2004-02-01

    Despite the fact that most engineers and designers are aware of fatigue, many severe breakdowns of industrial plant and machinery still occur due to fatigue. In effect, it's been estimated that fatigue causes at least 80% of the failures in modern engineering components. From an operational point of view, the detection of fatigue damage, preferably at a very early stage, is a critically important consideration in order to prevent possible catastrophic equipment failure and associated losses. This paper describes the investigation involving the use of ultrasonic waves as a potential tool for early detection of fatigue damage. The parameters investigated were the ultrasonic wave velocities (longitudinal and transverse waves) and attenuation coefficient before fatigue damage and after progressive stages of fatigue. Although comparatively small uncertainties were observed, the feasibility of utilizing the velocity of ultrasonic waves as a fatigue monitor was barely substantiated within actual research conditions. However, careful measurements of the ultrasonic attenuation parameter had demonstrated its potential to provide an early assessment of damage during fatigue.

  13. 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.

  14. Thermographic measurement of fatigue damage

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. D.

    1979-01-01

    The paper presents a thermographic technique developed to measure the extent of fatigue damage in composite materials during fatigue loading. It is noted that heat generated by cyclic loading of fatigue damaged material raises the surface temperature. These temperatures were measured with an infrared camera and were used as boundary conditions in a finite element heat transfer program, which has been developed especially to calculate the extent of the heat generation zone, and thereby to define the fatigue damage zone. It is reported that the finite element program was verified by comparing calculated heat generation with the actual heat generation for a simple heat transfer problem that had a closed form solution. Damage zones are calculated for several boron/epoxy fatigue specimens from thermograms of specimens. The calculated damage zones were compared with damage detected by C-scan, X-ray, and scanning electron microscope (SEM) examinations. It is concluded that the analysis was effective in locating the boundaries of the fatigue damage zones.

  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. A review of damage detection methods for wind turbine blades

    NASA Astrophysics Data System (ADS)

    Li, Dongsheng; Ho, Siu-Chun M.; Song, Gangbing; Ren, Liang; Li, Hongnan

    2015-03-01

    Wind energy is one of the most important renewable energy sources and many countries are predicted to increase wind energy portion of their whole national energy supply to about twenty percent in the next decade. One potential obstacle in the use of wind turbines to harvest wind energy is the maintenance of the wind turbine blades. The blades are a crucial and costly part of a wind turbine and over their service life can suffer from factors such as material degradation and fatigue, which can limit their effectiveness and safety. Thus, the ability to detect damage in wind turbine blades is of great significance for planning maintenance and continued operation of the wind turbine. This paper presents a review of recent research and development in the field of damage detection for wind turbine blades. Specifically, this paper reviews frequently employed sensors including fiber optic and piezoelectric sensors, and four promising damage detection methods, namely, transmittance function, wave propagation, impedance and vibration based methods. As a note towards the future development trend for wind turbine sensing systems, the necessity for wireless sensing and energy harvesting is briefly presented. Finally, existing problems and promising research efforts for online damage detection of turbine blades are discussed.

  18. 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

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

    PubMed Central

    Witoś, Mirosław

    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

  20. 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.

  1. Environmental and mechanical fatigue of composite wind turbine blades

    SciTech Connect

    Caprile, C.; Sala, G.; Buzzi, A.; Botta, G.; Cavaliere, M.

    1995-11-01

    The problem relevant to fatigue design and analysis of wind turbine blades made of composite materials is studied taking into account the mid-size single-blade wind turbine. Static and fatigue load conditions are defined; hygrothermal conditions are identified as well, in terms of yearly statistical distribution of wind speed and air temperature, relative humidity, solar radiation and atmospheric pressure daily variations; the occurrence of low-energy impacts due to hailstones is also considered. A FEM structural analysis is carried out to compute stress and strain distributions all along the blade: hot spots are identified; the stress critical values, along with fatigue spectra, are used to design fatigue tests. Some preliminary tests are performed on composite specimens previously dry and wet conditioned, as well as on low-energy impacted coupons, considering both mechanical and hygrothermal effects; finally some preliminary fatigue tests on both adhesive and riveted composite joints are carried out.

  2. Analysis of aeroelastic loads and their contributions to fatigue damage

    NASA Astrophysics Data System (ADS)

    Bergami, L.; Gaunaa, M.

    2014-12-01

    The paper presents an analysis of the aeroelastic loads on a wind turbine in normal operation. The characteristic of the loads causing the highest fatigue damage are identified, so to provide indications to the development of active load alleviation systems for smart- rotor applications. Fatigue analysis is performed using rain-flow counting and Palmgren-Miner linear damage assumption; the contribution to life-time fatigue damage from deterministic load variations is quantified, as well as the contributions from operation at different mean wind speeds. A method is proposed to retrieve an estimation of the load frequencies yielding the highest fatigue contributions from the bending moment spectra. The results are in good agreement with rain-flow counting analysis on filtered time series, and, for the blade loads, show dominant contributions from frequencies close to the rotational one; negligible fatigue contributions are reported for loads with frequencies above 2 Hz.

  3. Inspection and monitoring of wind turbine blade-embedded wave defects during fatigue testing

    DOE PAGESBeta

    Niezrecki, Christopher; Avitabile, Peter; Chen, Julie; Sherwood, James; Lundstrom, Troy; LeBlanc, Bruce; Hughes, Scott; Desmond, Michael; Beattie, Alan; Rumsey, Mark; et al

    2014-05-20

    The research we present in this article focuses on a 9-m CX-100 wind turbine blade, designed by a team led by Sandia National Laboratories and manufactured by TPI Composites Inc. The key difference between the 9-m blade and baseline CX-100 blades is that this blade contains fabric wave defects of controlled geometry inserted at specified locations along the blade length. The defect blade was tested at the National Wind Technology Center at the National Renewable Energy Laboratory using a schedule of cycles at increasing load level until failure was detected. Our researchers used digital image correlation, shearography, acoustic emission, fiber-opticmore » strain sensing, thermal imaging, and piezoelectric sensing as structural health monitoring techniques. Furthermore, this article provides a comparison of the sensing results of these different structural health monitoring approaches to detect the defects and track the resultant damage from the initial fatigue cycle to final failure.« less

  4. Inspection and monitoring of wind turbine blade-embedded wave defects during fatigue testing

    SciTech Connect

    Niezrecki, Christopher; Avitabile, Peter; Chen, Julie; Sherwood, James; Lundstrom, Troy; LeBlanc, Bruce; Hughes, Scott; Desmond, Michael; Beattie, Alan; Rumsey, Mark; Klute, Sandra M.; Pedrazzani, Renee; Werlink, Rudy; Newman, John

    2014-05-20

    The research we present in this article focuses on a 9-m CX-100 wind turbine blade, designed by a team led by Sandia National Laboratories and manufactured by TPI Composites Inc. The key difference between the 9-m blade and baseline CX-100 blades is that this blade contains fabric wave defects of controlled geometry inserted at specified locations along the blade length. The defect blade was tested at the National Wind Technology Center at the National Renewable Energy Laboratory using a schedule of cycles at increasing load level until failure was detected. Our researchers used digital image correlation, shearography, acoustic emission, fiber-optic strain sensing, thermal imaging, and piezoelectric sensing as structural health monitoring techniques. Furthermore, this article provides a comparison of the sensing results of these different structural health monitoring approaches to detect the defects and track the resultant damage from the initial fatigue cycle to final failure.

  5. Application of the U.S. high cycle fatigue data base to wind turbine blade lifetime predictions

    SciTech Connect

    Sutherland, H.J.; Mandell, J.F.

    1995-12-01

    This paper demonstrates a methodology for predicting the service lifetime of wind turbine blades using the high-cycle fatigue data base for typical U.S. blade materials developed by Mandell, et al. (1995). The first step in the analysis is to normalize the data base (composed primarily of data obtained from specialized, relatively small coupons) with fatigue data from typical industrial laminates to obtain a Goodman Diagram that is suitable for analyzing wind turbine blades. The LIFE2 fatigue analysis code for wind turbines is then used for the fatigue analysis of a typical turbine blade with a known load spectrum. In the analysis, a linear damage model, Miner`s Rule, is used to demonstrate the prediction of the service lifetime for a typical wind turbine blade under assumed operating strain ranges and stress concentration factors. In contrast to typical European data, the asymmetry in this data base predicts failures under typical loads to be compressive.

  6. Non-Harmonic Fourier Analysis for bladed wheels damage detection

    NASA Astrophysics Data System (ADS)

    Neri, P.; Peeters, B.

    2015-11-01

    The interaction between bladed wheels and the fluid distributed by the stator vanes results in cyclic loading of the rotating components. Compressors and turbines wheels are subject to vibration and fatigue issues, especially when resonance conditions are excited. Even if resonance conditions can be often predicted and avoided, high cycle fatigue failures can occur, causing safety issues and economic loss. Rigorous maintenance programs are then needed, forcing the system to expensive shut-down. Blade crack detection methods are beneficial for condition-based maintenance. While contact measurement systems are not always usable in exercise conditions (e.g. high temperature), non-contact methods can be more suitable. One (or more) stator-fixed sensor can measure all the blades as they pass by, in order to detect the damaged ones. The main drawback in this situation is the short acquisition time available for each blade, which is shortened by the high rotational speed of the components. A traditional Discrete Fourier Transform (DFT) analysis would result in a poor frequency resolution. A Non-Harmonic Fourier Analysis (NHFA) can be executed with an arbitrary frequency resolution instead, allowing to obtain frequency information even with short-time data samples. This paper shows an analytical investigation of the NHFA method. A data processing algorithm is then proposed to obtain frequency shift information from short time samples. The performances of this algorithm are then studied by experimental and numerical tests.

  7. 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.

  8. Fatigue Failure of Space Shuttle Main Engine Turbine Blades

    NASA Technical Reports Server (NTRS)

    Swanson, Gregrory R.; Arakere, Nagaraj K.

    2000-01-01

    Experimental validation of finite element modeling of single crystal turbine blades is presented. Experimental results from uniaxial high cycle fatigue (HCF) test specimens and full scale Space Shuttle Main Engine test firings with the High Pressure Fuel Turbopump Alternate Turbopump (HPFTP/AT) provide the data used for the validation. The conclusions show the significant contribution of the crystal orientation within the blade on the resulting life of the component, that the analysis can predict this variation, and that experimental testing demonstrates it.

  9. Characteristics of the fretting fatigue damage threshold

    NASA Astrophysics Data System (ADS)

    Adibnazari, Saeed; Hoeppner, David W.

    1992-11-01

    It has been found that different variables, such as normal pressure and maximum fatigue stress, affect the fretting fatigue damage threshold, but the degree to which the fretting fatigue damage threshold is influenced by these variables varies from material to material. This is evidenced by the fact that increasing the maximum fatigue stress and keeping the rest of the variables constant through the test caused the damage threshold of 7075-T6 aluminum alloy to disappear, but did not change the damage threshold of Ti-6Al-4V titanium alloy. Increasing the normal pressure from 20.7 to 34.5 MPa and keeping other test variables constant, caused the damage threshold of 7075-T6 aluminum alloy to change from 30 to 20 percent of fretting fatigue life. An explanation is given for this behavior by presenting a model that links the fretting fatigue damage threshold to fretting-induced damage that is capable of nucleating cracks.

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

    SciTech Connect

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

    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.

  11. 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.

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

    SciTech Connect

    Claytor, Thomas N; Ammerman, Curtt N; Park, Gyu Hae; Farinholt, Kevin M; Farrar, Charles R; Atterbury, Marie K

    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.

  13. Structural changes and damage of single-crystal turbine blades during life tests of an aviation gas turbine engine

    NASA Astrophysics Data System (ADS)

    Ospennikova, O. G.; Orlov, M. R.; Kolodochkina, V. G.; Nazarkin, R. M.

    2015-04-01

    The irreversible structural changes of the single-crystal ZhS32-VI nickel superalloy blades of a high-pressure turbine that occur during life tests of a gas turbine engine are studied. The main operation damages in the hottest section of the blade airfoil are found to be the fracture of the heat-resistant coating in the leading edge and the formation of thermomechanical fatigue cracks. The possibility of reconditioning repair of the blades is considered.

  14. Nonlinear fatigue damage accumulation under random loading

    SciTech Connect

    Zhu, W.Q.; Jiang, M.X.

    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.

  15. 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.

  16. 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.

  17. The relationship between observed fatigue damage and life estimation models

    NASA Technical Reports Server (NTRS)

    Kurath, Peter; Socie, Darrell F.

    1988-01-01

    Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.

  18. Fatigue damage considering whipping arising from slamming

    SciTech Connect

    Hansen, P.F.; Thayamballi, A.K.

    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.

  19. Thermography detection on the fatigue damage

    NASA Astrophysics Data System (ADS)

    Yang, Bing

    It has always been a great temptation in finding new methods to in-situ "watch" the material fatigue-damage processes so that in-time reparations will be possible, and failures or losses can be minimized to the maximum extent. Realizing that temperature patterns may serve as fingerprints for stress-strain behaviors of materials, a state-of-art infrared (IR) thermography camera has been used to "watch" the temperature evolutions of both crystalline and amorphous materials "cycle by cycle" during fatigue experiments in the current research. The two-dimensional (2D) thermography technique records the surface-temperature evolutions of materials. Since all plastic deformations are related to heat dissipations, thermography provides an innovative method to in-situ monitor the heat-evolution processes, including plastic-deformation, mechanical-damage, and phase-transformation characteristics. With the understanding of the temperature evolutions during fatigue, thermography could provide the direct information and evidence of the stress-strain distribution, crack initiation and propagation, shear-band growth, and plastic-zone evolution, which will open up wide applications in studying the structural integrity of engineering components in service. In the current research, theoretical models combining thermodynamics and heat-conduction theory have been developed. Key issues in fatigue, such as in-situ stress-strain states, cyclic softening and hardening observations, and fatigue-life predictions, have been resolved by simply monitoring the specimen-temperature variation during fatigue. Furthermore, in-situ visulizations as well as qualitative and quantitative analyses of fatigue-damage processes, such as Luders-band evolutions, crack propagation, plastic zones, and final fracture, have been performed by thermography. As a method requiring no special sample preparation or surface contact by sensors, thermography provides an innovative and convenient method to in-situ monitor and analyze the mechanical-damage processes of materials and components.

  20. 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.

  1. Nondestructive characterization of fatigue damage with thermography

    NASA Astrophysics Data System (ADS)

    Roesner, Henrik; Sathish, Shamachary; Meyendorf, Norbert

    2001-08-01

    A thermal imaging NDE method has been developed for nondestructive characterization of early stages of fatigue damage. The method is based on evaluation of the thermal effects induced in a material by a short-term mechanical loading. The mechanical loading causes in addition to thermoelastic temperature change, an increase due to heat dissipation that depends upon the microstructure of the material in a characteristic manner. The origin of this heat dissipation is the mechanical damping process. Utilizing the initial temperature rise due to a short-term mechanical loading, the dissipated energy per cycle was evaluated as a thermal parameter. This new thermal NDE parameter allows a quantitative characterization of the mechanical hysteresis, without the need for calibration to eliminate influences of thermal boundary conditions. The measurement of the thermal NDE parameters has been performed on Ti-6Al-4V dog-bone specimens, fatigued in low cycle fatigue (LCF) as well as in high cycle fatigue (HCF) experiments. Characteristic dependence of the NDE parameters on the already accumulated fatigue damage has been observed. The advantage of the thermal method is the applicability to components under service conditions because of simplicity, rapid measurements (a few seconds) and the ability of locally resolved evaluations.

  2. Eulerian laser Doppler vibrometry: Online blade damage identification on a multi-blade test rotor

    NASA Astrophysics Data System (ADS)

    Oberholster, A. J.; Heyns, P. S.

    2011-01-01

    Laser Doppler vibrometry enables the telemetry-free measurement of online turbomachinery blade vibration. Specifically, the Eulerian or fixed reference frame implementation of laser vibrometry provides a practical solution to the condition monitoring of rotating blades. The short data samples that are characteristic of this measurement approach do however negate the use of traditional frequency domain signal processing techniques. It is therefore necessary to employ techniques such as time domain analysis and non-harmonic Fourier analysis to obtain useful information from the blade vibration signatures. The latter analysis technique allows the calculation of phase angle trends which can be used as indicators of blade health deterioration, as has been shown in previous work for a single-blade rotor. This article presents the results from tests conducted on a five-blade axial-flow test rotor at different rotor speeds and measurement positions. With the aid of artificial neural networks, it is demonstrated that the parameters obtained from non-harmonic Fourier analysis and time domain signal processing on Eulerian laser Doppler vibrometry signals can successfully be used to identify and quantify blade damage from among healthy blades. It is also shown that the natural frequencies of individual blades can be approximated from the Eulerian signatures recorded during rotor run-up and run-down.

  3. On-line fan blade damage detection using neural networks

    NASA Astrophysics Data System (ADS)

    Oberholster, A. J.; Heyns, P. S.

    2006-01-01

    This paper presents a methodology for monitoring the on-line condition of axial-flow fan blades with the use of neural networks. In developing this methodology, the first stage was to utilise neural networks trained on features extracted from on-line blade vibration signals measured on an experimental test structure. Results from a stationary experimental modal analysis of the structure were used for identifying global blade mode shapes and their corresponding frequencies. These in turn were used to assist in identifying vibration-related features suitable for neural network training. The features were extracted from on-line blade vibration and strain signals which were measured using a number of sensors. The second stage in the development of the methodology entails utilising neural networks trained on numerical Frequency Response Function (FRF) features obtained from a Finite Element Model (FEM) of the test structure. Frequency domain features obtained from on-line experimental measurements were used to normalise the numerical FRF features prior to neural network training. Following training, the networks were tested using experimental frequency domain features. This approach makes it unnecessary to damage the structure in order to train the neural networks. The paper shows that it is possible to classify damage for several fan blades by using neural networks with on-line vibration measurements from sensors not necessarily installed on the damaged blades themselves. The significance of this is that it proves the possibility to perform on-line fan blade damage classification using less than one sensor per blade. Even more significant is the demonstration that an on-line damage detection system for a fan can be developed without having to damage the actual structure.

  4. Brittleness Effect on Rock Fatigue Damage Evolution

    NASA Astrophysics Data System (ADS)

    Nejati, Hamid Reza; Ghazvinian, Abdolhadi

    2014-09-01

    The damage evolution mechanism of rocks is one of the most important aspects in studying of rock fatigue behavior. Fatigue damage evolution of three rock types (onyx marble, sandstone and soft limestone) with different brittleness were considered in the present study. Intensive experimental tests were conducted on the chosen rock samples and acoustic emission (AE) sensors were used in some of them to monitor the fracturing process. Experimental tests indicated that brittleness strongly influences damage evolution of rocks in the course of static and dynamic loading. AE monitoring revealed that micro-crack density induced by the applied loads during different stages of the failure processes increases as rock brittleness increases. Also, results of fatigue tests on the three rock types indicated that the rock with the most induced micro-cracks during loading cycles has the least fatigue life. Furthermore, the condition of failure surfaces of the studied rocks samples, subjected to dynamic and static loading, were evaluated and it was concluded that the roughness of failure surfaces is influenced by loading types and rock brittleness. Dynamic failure surfaces were rougher than static ones and low brittle rock demonstrate a smoother failure surface compared to high brittle rock.

  5. Fatigue Testing of 9 m Carbon Fiber Wind Turbine Research Blades

    SciTech Connect

    Paquette, J.; van Dam, J.; Hughes, S.; Johnson, J.

    2008-01-01

    Fatigue testing was conducted on Carbon Experimental and Twist-Bend Experimental (CX-100 and TX-100) 9-m wind turbine research blades. The CX-100 blade was designed to investigate the use of a carbon spar cap to reduce weight and increase stiffness while being incorporated using conventional manufacturing techniques. The TX-100 blade used carbon in the outboard portion of the skin to produce twist-bend coupling to passively alleviate aerodynamic loads. In the fatigue tests, the CX-100 blade was loaded by a single hydraulic cylinder while the TX-100 blade was loaded via a hydraulically-actuated resonant loading system called the Universal Resonant Exciter. The blades were outfitted with approximately 30 strain gages as well as displacement and load sensors. Both blades survived to cycle counts sufficient to demonstrate a 20-year operational life. The CX-100 blade failed at approximately 1.6 million cycles because of a buckle and crack that formed and grew just outboard of max-chord. The TX-100 blade failed because of a crack that grew from the termination point of the spar cap at the midspan of the blade. This paper covers the results of the fatigue tests.

  6. Uncertainty Analysis in Fatigue Life Prediction of Gas Turbine Blades Using Bayesian Inference

    NASA Astrophysics Data System (ADS)

    Li, Yan-Feng; Zhu, Shun-Peng; Li, Jing; Peng, Weiwen; Huang, Hong-Zhong

    2015-12-01

    This paper investigates Bayesian model selection for fatigue life estimation of gas turbine blades considering model uncertainty and parameter uncertainty. Fatigue life estimation of gas turbine blades is a critical issue for the operation and health management of modern aircraft engines. Since lots of life prediction models have been presented to predict the fatigue life of gas turbine blades, model uncertainty and model selection among these models have consequently become an important issue in the lifecycle management of turbine blades. In this paper, fatigue life estimation is carried out by considering model uncertainty and parameter uncertainty simultaneously. It is formulated as the joint posterior distribution of a fatigue life prediction model and its model parameters using Bayesian inference method. Bayes factor is incorporated to implement the model selection with the quantified model uncertainty. Markov Chain Monte Carlo method is used to facilitate the calculation. A pictorial framework and a step-by-step procedure of the Bayesian inference method for fatigue life estimation considering model uncertainty are presented. Fatigue life estimation of a gas turbine blade is implemented to demonstrate the proposed method.

  7. 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.

  8. 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.

  9. 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.

  10. Cumulative fatigue damage behavior of MAR M-247

    NASA Astrophysics Data System (ADS)

    McGaw, Michael A.; Halford, Gary R.; Kalluri, Sreeramesh

    1991-05-01

    The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.

  11. 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.

  12. Effect of Impact Damage on the Fatigue Response of TiAl Alloy-ABB-2

    NASA Technical Reports Server (NTRS)

    Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Nazmy, M. Y.; Staubli, M.; Clemens, D. R.

    2001-01-01

    The ability of gamma-TiAl to withstand potential foreign or domestic object damage is a technical risk to the implementation of gamma-TiAl in low pressure turbine (LPT) blade applications. In the present study, the impact resistance of TiAl alloy ABB-2 was determined and compared to the impact resistance of Ti(48)Al(2)Nb(2)Cr. Specimens were impacted with four different impact conditions with impact energies ranging from 0.22 to 6.09 J. After impacting, the impact damage was characterized by crack lengths on both the front and backside of the impact. Due to the flat nature of gamma-TiAl's S-N (stress vs. cycles to failure) curve, step fatigue tests were used to determine the fatigue strength after impacting. Impact damage increased with increasing impact energy and led to a reduction in the fatigue strength of the alloy. For similar crack lengths, the fatigue strength of impacted ABB-2 was similar to the fatigue strength of impacted Ti(48)Al(2)Nb(2)Cr, even though the tensile properties of the two alloys are significantly different. Similar to Ti(48)Al(2)Nb(2)Cr, ABB-2 showed a classical mean stress dependence on fatigue strength. The fatigue strength of impacted ABB-2 could be accurately predicted using a threshold analysis.

  13. 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

  14. 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.

  15. 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.

  16. Cumulative creep fatigue damage in 316 stainless steel

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1989-01-01

    The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.

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

    SciTech Connect

    Galib Abumeri; Frank Abdi

    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 relationships obtained from testing of the blade with baseline neat material were compared to the ones from analytical simulation using neat resin and using silica nanoparticles in the resin. Multi-scale PFA results for the neat material construction matched closely those from test for both load displacement and location and type of damage and failure. AlphaSTAR demonstrated that wind blade structures made from advanced composite materials can be certified with multi-scale progressive failure analysis by following building block verification approach.

  18. Damage tolerance and structural monitoring for wind turbine blades

    PubMed Central

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

    2015-01-01

    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

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

    PubMed

    McGugan, M; Pereira, G; Srensen, 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

  20. 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.

  1. Aspect of cumulative fatigue damage under multiaxial strain cycling.

    NASA Technical Reports Server (NTRS)

    Zamrik, S. Y.; Tang, P. Y.

    1972-01-01

    The concept of order of loading and its effect on cumulative fatigue damage under multiaxial strain cyclings was investigated. The effect is illustrated through nonlinear relationships between biaxial fatigue damage and cycle-ratio diagrams. Uniaxial theories such as Miner's method, the convergence method, and the double linear damage rule in its special and generalized form, were examined and extended to the biaxial case through the octahedral shear strain theory. The generalized double linear damage rule was found more applicable to biaxial cumulative fatigue damage.

  2. Finite element based damage assessment of composite tidal turbine blades

    NASA Astrophysics Data System (ADS)

    Fagan, Edward M.; Leen, Sean B.; Kennedy, Ciaran R.; Goggins, Jamie

    2015-07-01

    With significant interest growing in the ocean renewables sector, horizontal axis tidal current turbines are in a position to dominate the marketplace. The test devices that have been placed in operation so far have suffered from premature failures, caused by difficulties with structural strength prediction. The goal of this work is to develop methods of predicting the damage level in tidal turbines under their maximum operating tidal velocity. The analysis was conducted using the finite element software package Abaqus; shell models of three representative tidal turbine blades are produced. Different construction methods will affect the damage level in the blade and for this study models were developed with varying hydrofoil profiles. In order to determine the risk of failure, a user material subroutine (UMAT) was created. The UMAT uses the failure criteria designed by Alfred Puck to calculate the risk of fibre and inter-fibre failure in the blades. The results show that degradation of the stiffness is predicted for the operating conditions, having an effect on the overall tip deflection. The failure criteria applied via the UMAT form a useful tool for analysis of high risk regions within the blade designs investigated.

  3. A study of cumulative fatigue damage in AISI 4130 steel

    NASA Technical Reports Server (NTRS)

    Jeelani, S.; Musial, M.

    1986-01-01

    Experimental data were obtained using AISI 4130 steel under stress ratios of -1 and 0. A study of cumulative fatigue damage using Miner's and Kramer's equations for stress ratios of -1 and 0 for low-high, low-high-mixed, high-low, and high-low-mixed stress sequences has revealed that there is a close agreement between the theoretical and experimental values of fatigue damage and fatigue life. Kramer's equation predicts less conservative and more realistic cumulative fatigue damage than the popularly used Miner's rule does.

  4. 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.

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

    SciTech Connect

    Mandell, John F.; Ashwill, Thomas D.; Wilson, Timothy J.; Sears, Aaron T.; Agastra, Pancasatya; Laird, Daniel L.; Samborsky, Daniel D.

    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.

  6. Fatigue testing of low-cost fiberglass composite wind turbine blade materials

    NASA Astrophysics Data System (ADS)

    Hofer, K. E.; Bennett, L. C.

    1981-11-01

    The static and fatigue behavior of transverse filament tape (TFT) fiberglass/epoxy and TFT/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.

  7. Fatigue testing of low-cost fiberglass composite wind turbine blade materials

    NASA Technical Reports Server (NTRS)

    Hofer, K. E.; Bennett, L. C.

    1981-01-01

    The static and fatigue behavior of transverse filament tape (TFT) fiberglass/epoxy and TFT/polyester composites was established by the testing of specimens cut from panels fabricated by a filament winding process used for the construction of large experimental wind turbine blades.

  8. Fatigue damage accumulation in various metal matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1987-01-01

    The purpose of this paper is to review some of the latest understanding of the fatigue behavior of continuous fiber reinforced metal matrix composites. The emphasis is on the development of an understanding of different fatigue damage mechanisms and why and how they occur. The fatigue failure modes in continuous fiber reinforced metal matrix composites are controlled by the three constituents of the system: fiber, matrix, and fiber/matrix interface. The relative strains to fatigue failure of the fiber and matrix will determine the failure mode. Several examples of matrix, fiber, and self-similar damage growth dominated fatigue damage are given for several metal matrix composite systems. Composite analysis, failure modes, and damage modeling are discussed. Boron/aluminum, silicon-carbide/aluminum, FP/aluminum, and borsic/titanium metal matrix composites are discussed.

  9. Fatigue damage accumulation in various metal matrix composites

    SciTech Connect

    Johnson, W.S.

    1987-03-01

    The purpose of this paper is to review some of the latest understanding of the fatigue behavior of continuous fiber reinforced metal matrix composites. The emphasis is on the development of an understanding of different fatigue damage mechanisms and why and how they occur. The fatigue failure modes in continuous fiber reinforced metal matrix composites are controlled by the three constituents of the system: fiber, matrix, and fiber/matrix interface. The relative strains to fatigue failure of the fiber and matrix will determine the failure mode. Several examples of matrix, fiber, and self-similar damage growth dominated fatigue damage are given for several metal matrix composite systems. Composite analysis, failure modes, and damage modeling are discussed. Boron/aluminum, silicon-carbide/aluminum, FP/aluminum, and borsic/titanium metal matrix composites are discussed.

  10. Active sensing of fatigue damage using embedded ultrasonics

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    Dynamic measurements are widely used for structural condition assessment and damage detection. A wide range of studies are available on vibration-based detection and identification of fatigue cracks in simple and complex structures. This research explores the application of the electromechanical impedance method and nonlinear resonance measurements to high frequency detection of incipient fatigue damage in aluminum alloy specimens. The electromechanical impedance method relies on the coupling between the mechanical properties of a structure and the electrical properties of attached piezoelectric wafer active sensors (PWAS). This coupling allows structural properties to be inferred from the electrical impedance signature of the sensor. In this study, the electromechanical impedance method is utilized for assessment of material deterioration under cyclic fatigue loads. Aluminum specimens were subjected to increasing fatigue cycles at stress amplitudes below the yield point, and electromechanical impedance signatures were taken at discrete levels of fatigue damage. Linear and nonlinear features of the impedance signatures were compared for different damage conditions. The results show a downward frequency shift of impedance peaks with increasing fatigue load. This frequency shift is observed before visible crack development and fracture. Nonlinear resonance tests were applied to fatigued aluminum samples. PWAS were utilized for transmission and reception of elastic waves at increasing amplitude levels. Variations in structural dynamic characteristics were considered for different excitation conditions and increasing damage severity. This paper discusses damage detection capabilities of each method and provides perspectives for utilizing information on incipient damage for predicting structural performance under known operational loads.

  11. 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.

  12. Modal characteristics of turbine blade packets under lacing wire damage induced mistuning

    NASA Astrophysics Data System (ADS)

    Chatterjee, Animesh; Kotambkar, Mangesh S.

    2015-05-01

    Effect of mistuning on turbo machine blade vibration in a packeted blade-disk system has become an important area of research in the recent past, mainly due to the critical applications in aero engines and power plant turbines. It has been shown that even a small mistuning can lead to stress build up through mode localization under forced vibration. Such mistuning can come from initial geometric blade to blade variation due to manufacturing tolerances or from a crack growing in the bladed disk system during operational life stages. The literature review indicates that researchers have mainly considered blade damage as a cause of mistuning. However, lacing wire damage, although not as catastrophic as blade damage, are more frequent in occurrences and often act as a precursor to subsequent blade damage. Detection of lacing wire damage is therefore equally important. Present work has investigated nature of mistuning induced by lacing wire damage and its effect on the characteristic modal properties. A damage severity index has been introduced and effect of damage on the blade group natural frequencies is investigated. Scope of developing a damage identification methodology in packeted blade-disk system is also discussed.

  13. Resolution of tower shadow models for downwind mounted rotors and its effects on the blade fatigue

    NASA Astrophysics Data System (ADS)

    Reiso, M.; Muskulus, M.

    2014-12-01

    A simulation study on the wind field resolution in computer load simulations has been conducted, both in transversal/vertical and longitudinal direction, to determine the effect on blade fatigue loading. Increasing the transversal/vertical resolution decreased the loading significantly, while only small changes to the load, at very low frequencies were found for increased longitudinal resolution. Next the influence of the tower shadow for a downwind mounted rotor was investigated, with respect to blade fatigue loading. The influence of different components to the total tower shadow effect was studied, both for a monopile and a truss tower, latter at inclination 0 and 22.5 degrees with respect to the incoming wind direction. Four components were considered, both individually and in combinations: mean wind speed, mean velocity deficit, unsteady motions from vortex shedding, and turbulence. The mean velocity deficit and turbulence were the main contributors to blade fatigue loading, and the unsteady motions can be neglected for the truss tower. For the monopile, neglecting the unsteady motions resulted in an underestimation of fatigue loading in the order of 3 percent.

  14. 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.

  15. 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.

  16. 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.

  17. Environmental influence on the fatigue behavior of wind turbine rotor blades

    SciTech Connect

    Bruijn, J.C.M. de

    1995-11-01

    Generally, the lifetime of Wind Turbine blades is limited by the (mechanical) fatigue resistance, which in turn is lowered by environmental aspects such as humidity and temperature (changes). At this time, not much knowledge on the combined influence of both fatigue and environmental aspects is available, which leads to arbitrary safety factors being used by Wind Turbine designers and manufacturers, which in turn results in low cost effectiveness. To predict the life time under both fatigue and environmental loading, KEMA has developed an accelerated (50x) environmental test for Wind Turbine blades. This test is based on climatological data from different sites in the Netherlands for periods up to four years. The acceleration factors were taken from the procedures proposed in ASTM D-1183 and EN-STAFF, and based on some common knowledge. The accelerated weathering test was evaluated using data on total moisture content and moisture profile from actual glass reinforced polyester blades weathered for a prolonged period outdoors. The accelerated environmental test was adapted where necessary using WW8GAIN, a software program to simulate the effect of humidity and temperature changes on the moisture content and moisture profile for composite materials. The resulting accelerated test procedure has been used to pre-condition a number of test specimens which are thereafter tested in fatigue loading according to a constant amplitude and WISPER-spectrum. Preliminary tests indicate that the precondition on its own does not significantly influence the life time of the glass fiber reinforced samples. However, when samples are continuously kept in contact with water during fatigue loading a drastic reduction of the life time is found correspondingly to a considerably larger design safety factor than the factor 1.25 currently used.

  18. 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.

  19. 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.

  20. Reduction in fiber damage thresholds due to static fatigue

    SciTech Connect

    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.

  1. A history dependent damage model for low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Leis, B. N.

    1984-01-01

    This paper examines damage assessment and accumulation. A nonlinear damage postulate is advanced that embodies the dependence of the damage rate on cycle-dependent changes in the bulk microstructure and the surface topography. The postulate is analytically formulated in terms of the deformation history dependence of the bulk behavior. This formulation is used in conjunction with baseline data in accordance with the damage postulate to predict the low cycle fatigue resistance of OFE copper. Close comparison of the predictions with observed behavior suggests the postulate offers a viable basis for nonlinear damage analysis.

  2. High Cycle Fatigue Crack Initiation Study of Case Blade Alloy Rene 125

    NASA Technical Reports Server (NTRS)

    Kantzos, P.; Gayda, J.; Miner, R. V.; Telesman, J.; Dickerson, P.

    2000-01-01

    This study was conducted in order to investigate and document the high cycle fatigue crack initiation characteristics of blade alloy Rene 125 as cast by three commercially available processes. This alloy is typically used in turbine blade applications. It is currently being considered as a candidate alloy for high T3 compressor airfoil applications. This effort is part of NASA's Advanced Subsonic Technology (AST) program which aims to develop improved capabilities for the next generation subsonic gas turbine engine for commercial carriers. Wrought alloys, which are customarily used for airfoils in the compressor, cannot meet the property goals at the higher compressor exit temperatures that would be required for advanced ultra-high bypass engines. As a result cast alloys are currently being considered for such applications. Traditional blade materials such as Rene 125 have the high temperature capabilities required for such applications. However, the implementation of cast alloys in compressor airfoil applications where airfoils are typically much thinner does raise some issues of concern such as thin wall castability, casting cleaningness, and susceptibility to high-cycle fatigue (HCF) loading.

  3. 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

    ... Composite Rotorcraft Structures'' (76 FR 74655), published December 1, 2011, and ``Damage Tolerance and Fatigue Evaluation for Metallic Structures'' (76 FR 75435), published December 2, 2011. In the ``Composite... Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures'' (76 FR 74655). On December 2,...

  4. Finite element prediction of fatigue damage growth in cancellous bone.

    PubMed

    Hambli, Ridha; Frikha, Sana; Toumi, Hechmi; Tavares, João Manuel R S

    2016-04-01

    Cyclic stresses applied to bones generate fatigue damage that affects the bone stiffness and its elastic modulus. This paper proposes a finite element model for the prediction of fatigue damage accumulation and failure in cancellous bone at continuum scale. The model is based on continuum damage mechanics and incorporates crack closure effects in compression. The propagation of the cracks is completely simulated throughout the damaged area. In this case, the stiffness of the broken element is reduced by 98% to ensure no stress-carrying capacities of completely damaged elements. Once a crack is initiated, the propagation direction is simulated by the propagation of the broken elements of the mesh. The proposed model suggests that damage evolves over a real physical time variable (cycles). In order to reduce the computation time, the integration of the damage growth rate is based on the cycle blocks approach. In this approach, the real number of cycles is reduced (divided) into equivalent blocks of cycles. Damage accumulation is computed over the cycle blocks and then extrapolated over the corresponding real cycles. The results show a clear difference between local tensile and compressive stresses on damage accumulation. Incorporating stiffness reduction also produces a redistribution of the peak stresses in the damaged region, which results in a delay in damage fracture. PMID:26077722

  5. Damage and fatigue in cross-linked rubbers

    NASA Astrophysics Data System (ADS)

    Melnikov, Alexei

    Damage and fatigue of elastomers have not been fundamentally understood because of the complex nature of these materials. All currently existing models are completely phenomenological. Therefore two problems have been investigated in this research to address those fundamental issues. The first problem was creating an innovative concept with a mathematical modeling, which would be able to describe the damage using molecular characteristics of elastomers. The second problem is developing new approaches to study fatigue, and especially impact fatigue of elastomers. The following results have been obtained in this research. A theoretical model of damage has been developed which involves the basic molecular characteristics of cross-linked elastomers and takes into account the effects of viscoelasticity and stress-induced crystallization. This model was found very reliable and successful in description of numerous quasi-static simple extension experiments for monotonous and repeating loadings. It also roughly predicts in molecular terms the failure of elastomers with various degrees of cross-linking. Quasi-impact fatigue tests with different geometry of an indenter have also been performed. Some microscopic features of rubber damage have been investigated using optical microscopy and SEM. In particular, the accumulation of a completely de-vulcanized, liquid-like substance was observed under intense, multi-cycle impacts. All the findings discovered in quasi-impact experiments are consistent with the damage model predictions.

  6. Optimization of fatigue damage indication in ferromagnetic low carbon steel

    NASA Astrophysics Data System (ADS)

    Tom, Ivan; Kov?k, Ond?ej; Kadlecov, Jana; Vrtesy, Gbor

    2015-09-01

    Fatigue damage was investigated by the method of magnetic adaptive testing (MAT), which is based on the systematic measurement and evaluation of minor magnetic hysteresis loops. A large number of magnetic measurements were performed on a single reference series of low carbon steel flat samples, which were fatigued by cyclic bending in an identical way, up to an increasing level of fatigue damage. The measurements of the magnetic properties of these samples were repeated under varied conditions, including speed of magnetization of the samples, sample temperature during the measurement, choice of the evaluated signal, frequency of the voltage sampling, and range of the applied amplitudes of the magnetizing field/current. Special attention was turned to the influence of the thickness of the non-ferromagnetic spacers positioned between the surface of the samples and the flat fronts of the attached magnetizing yokes. On one hand, the spacers decrease the values of the induced signal and its derivatives, but on the other hand they substantially increase the reproducibility of the measurement and positively influence the shapes of the resulting degradation curves. Optimum conditions for the magnetic measurement of the fatigue damage were searched, found, and recommended. The results indicate the reliable applicability of MAT to detect early stages of the material fatigue, and to predict its residual lifetime.

  7. Evaluation of service-induced damage and restoration of cast turbine blades

    NASA Astrophysics Data System (ADS)

    Persson, C.; Persson, P.-O.

    1993-08-01

    Conventionally cast turbine blades of Inconel 713C, from a military gas turbine aircraft engine, have been investigated with regard to service-induced microstructural damage and residual creep life time. For cast turbine blades, service life is defined by statistical values. The statistical methods can prove to be uneconomical, because safe limits must be stated with regard to the statistical probability that some blades will have higher damage than normal. An alternative approach is to determine the service-induced microstructural damage on each blade, or a representative number of blades, to better optimize blade us-age. Ways to use service-induced ? rafting and void formation as quantified microstructural damage pa-rameters in a service lifetime prediction model are suggested. The damage parameters were quantified, in blades with different service exposure levels, and correlated to remaining creep life evaluated from creep test specimens taken from different positions of serviced blades. Results from tests with different rejuvenation treatments, including hot isostatic pressing andJor heat treatment, are discussed briefly.

  8. 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.

  9. Interaction between impact damage and fatigue in fibre reinforced plastics

    NASA Astrophysics Data System (ADS)

    Beheshty, M. H.

    This study has been designed to investigate the interaction between impact damage and fatigue, which is necessarily a complex one and of current interest to the aerospace industry, and to predict the fatigue response for virgin and impact-damaged materials by using a constant-life model. In order to achieve these goals, measurements have been made of the residual tensile and compressive strengths after low-velocity impacts of 1, 2, 3 and 5 Joules of two modem carbon-fibre composites, viz., HTA/982A and HTA/913, and a glass-fibre laminate, E-Glass/913, all having the common lay-up [(45,02)2]s. The impact damage was assessed by transient thermography, ultrasonic C-scan and optical microscopy. The modes of failure under low-velocity impacts of 1-3J were found to be matrix cracking and mainly delamination. Only a 5J impact energy event caused some fibre fractures in CFRP laminates. Measurement of post-impact mechanical properties has shown that impact damage in the range 1-5J had little effect on the residual tensile strength although the compressive strength was markedly reduced. Replicate stress/life fatigue data were obtained at different stress ratios, R, for sound and impact-damaged materials. Results show that impact energies in the range 1-3J had no effect on the tensile fatigue behaviour at R = +0.l. At R = -1.5 and +10, on the other hand, the stress/life curves are markedly affected. And as the compression component of stress increases the slope of the S/N curve decreases, which indicates less sensitivity to fatigue. The fatigue tests results have been analysed by using a constant-life model previously developed at Bath. A new relationship between constant-life model parameters and material properties has been found. The model has been modified to predict the fatigue response of fibre composite materials in the virgin condition and after damage by low-velocity impact by using only the tensile and compressive strengths of composite in question. Results show that there is a good agreement between predicted S/N curves with experimental stress/life data for virgin and impact- damaged CFRP laminates.

  10. 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.

  11. Sliding Contact Fatigue Damage in Layered Ceramic Structures

    PubMed Central

    Kim, Jae-Won; Kim, Joo-Hyung; Thompson, Van P.; Zhang, Yu

    2016-01-01

    Porcelain veneered restorations often chip and fracture from repeated occlusal loading, making fatigue studies relevant. Most fatigue studies are limited to uniaxial loading without sliding motion. We hypothesize that biaxial loading (contact-load-slide-liftoff, simulating a masticatory cycle) as compared to uniaxial loading accelerates the fatigue of layered ceramics. Monolithic glass plates were epoxy joined to polycarbonate substrates as a transparent model for an all-ceramic crown on dentin. Uniaxial and biaxial cyclic contact was applied through a hard sphere in water with a mouth-motion machine. The uniaxial (contact-load-hold-liftoff) and traditional R-ratio fatigue (indenter never leaves the specimen surface) produced a similar lifespan, while biaxial fatigue was more severe. The accelerated crack growth rate in biaxial fatigue is attributed to enhanced tensile stresses at the trailing edges of a moving indenter. Fracture mechanics descriptions for damage evolution in brittle materials loaded repeatedly with a sliding sphere are provided. Clinical relevance is addressed. PMID:17959894

  12. 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.

  13. Fatigue damage development of various CFRP-laminates

    NASA Technical Reports Server (NTRS)

    Schulte, K.; Baron, CH.

    1988-01-01

    The chronic strength and fatigue behavior of a woven carbon-fiber reinforced laminate in a balanced eight-shaft satin weave style was compared to nonwoven laminates with an equivalent cross-ply layup. Half the fibers were arranged in the direction of the load and the other half perpendicular to it. Two types of nonwoven laminates consisting of continuous fibers and aligned discontinuous fibers, both produced from carbon fiber prepregs, were studied. The cross-ply laminate with continuous fiber showed the best characteristics with regard to both static strength and fatigue. The similarities and differences in damage mechanisms in the laminates are described.

  14. Effects of Materials Parameters and Design Details on the Fatigue of Composite Materials for Wind Turbine Blades

    SciTech Connect

    Mandell, J.F.; Samborsky, D.D.; Sutherland, H.J.

    1999-03-04

    This paper presents an analysis of the results of nine years of fatigue testing represented in the USDOE/Montana State University (DOE/MSU) Composite Materials Fatigue Database. The focus of the program has been to explore a broad range of glass-fiber-based materials parameters encompassing over 4500 data points for 130 materials systems. Significant trends and transitions in fatigue resistance are shown as the fiber content and fabric architecture are varied. The effects of structural details including ply drops, bonded stiffeners, and other geometries that produce local variations in fiber packing and geometry are also described. Fatigue tests on composite beam structures are then discussed; these show generally good correlation with coupon fatigue data in the database. Goodman diagrams for fatigue design are presented, and their application to predicting the service lifetime of blades is described.

  15. Continuum Fatigue Damage Modeling for Use in Life Extending Control

    NASA Technical Reports Server (NTRS)

    Lorenzo, Carl F.

    1994-01-01

    This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.

  16. Fatigue damage prognosis using affine arithmetic

    NASA Astrophysics Data System (ADS)

    Gbaguidi, Audrey; Kim, Daewon

    2014-02-01

    Among the essential steps to be taken in structural health monitoring systems, damage prognosis would be the field that is least investigated due to the complexity of the uncertainties. This paper presents the possibility of using Affine Arithmetic for uncertainty propagation of crack damage in damage prognosis. The structures examined are thin rectangular plates made of titanium alloys with central mode I cracks and a composite plate with an internal delamination caused by mixed mode I and II fracture modes, under a harmonic uniaxial loading condition. The model-based method for crack growth rates are considered using the Paris Erdogan law model for the isotropic plates and the delamination growth law model proposed by Kardomateas for the composite plate. The parameters for both models are randomly taken and their uncertainties are considered as defined by an interval instead of a probability distribution. A Monte Carlo method is also applied to check whether Affine Arithmetic (AA) leads to tight bounds on the lifetime of the structure.

  17. Damage localization in a residential-sized wind turbine blade by use of the SDDLV method

    NASA Astrophysics Data System (ADS)

    Johansen, R. J.; Hansen, L. M.; Ulriksen, M. D.; Tcherniak, D.; Damkilde, L.

    2015-07-01

    The stochastic dynamic damage location vector (SDDLV) method has previously proved to facilitate effective damage localization in truss- and plate-like structures. The method is based on interrogating damage-induced changes in transfer function matrices in cases where these matrices cannot be derived explicitly due to unknown input. Instead, vectors from the kernel of the transfer function matrix change are utilized; vectors which are derived on the basis of the system and state-to-output mapping matrices from output-only state-space realizations. The idea is then to convert the kernel vectors associated with the lowest singular values into static pseudo-loads and apply these alternately to an undamaged reference model with known stiffness matrix. By doing so, the stresses in the potentially damaged elements will, theoretically, approach zero. The present paper demonstrates an application of the SDDLV method for localization of structural damages in a cantilevered residential-sized wind turbine blade. The blade was excited by an unmeasured multi-impulse load and the resulting dynamic response was captured through accelerometers mounted along the blade. The static pseudo-loads were applied to a finite element (FE) blade model, which was tuned against the modal parameters of the actual blade. In the experiments, an undamaged blade configuration was analysed along with different damage scenarios, hereby testing the applicability of the SDDLV method.

  18. Recovery of Fatigue Damage and Life Prediction by Laser Irradiation Healing Treatment for Copper Film

    NASA Astrophysics Data System (ADS)

    Guo, Yu-Bo; Shang, De-Guang; Liu, Xiao-Dong; Ren, Chong-Gang; Liu, Feng-Zhu; Zhang, Li-Hong; Sun, Yu-Juan

    2015-01-01

    A fatigue life prediction method was investigated after healing fatigue damage by excimer laser irradiation treatment for the damaged copper film. First, the variations of residual fatigue life and strain range for the damaged specimens after laser irradiation healing treatment were analyzed. The results showed that the fatigue damage can be effectively healed by laser irradiation for copper film. The presented healing phenomenon during laser irradiation process showed that the recovery of fatigue damage can result in the improvement in fatigue life for the damaged copper film. Then, based on the fact that the strain concentration factor of copper film had not been changed before and after laser irradiation treatment, a residual fatigue life prediction method was proposed by the local stress transformation. The predicted residual fatigue lives by the proposed method agreed well with the experimental results for copper film after laser irradiation treatment.

  19. 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.

  20. Damage detection of engine bladed-disks using multivariate statistical analysis

    NASA Astrophysics Data System (ADS)

    Fang, X.; Tang, J.

    2006-03-01

    The timely detection of damage in aero-engine bladed-disks is an extremely important and challenging research topic. Bladed-disks have high modal density and, particularly, their vibration responses are subject to significant uncertainties due to manufacturing tolerance (blade-to-blade difference or mistuning), operating condition change and sensor noise. In this study, we present a new methodology for the on-line damage detection of engine bladed-disks using their vibratory responses during spin-up or spin-down operations which can be measured by blade-tip-timing sensing technique. We apply a principle component analysis (PCA)-based approach for data compression, feature extraction, and denoising. The non-model based damage detection is achieved by analyzing the change between response features of the healthy structure and of the damaged one. We facilitate such comparison by incorporating the Hotelling's statistic T2 analysis, which yields damage declaration with a given confidence level. The effectiveness of the method is demonstrated by case studies.

  1. Nonlinear ultrasound modelling and validation of fatigue damage

    NASA Astrophysics Data System (ADS)

    Fierro, G. P. Malfense; Ciampa, F.; Ginzburg, D.; Onder, E.; Meo, M.

    2015-05-01

    Nonlinear ultrasound techniques have shown greater sensitivity to microcracks and they can be used to detect structural damages at their early stages. However, there is still a lack of numerical models available in commercial finite element analysis (FEA) tools that are able to simulate the interaction of elastic waves with the materials nonlinear behaviour. In this study, a nonlinear constitutive material model was developed to predict the structural response under continuous harmonic excitation of a fatigued isotropic sample that showed anharmonic effects. Particularly, by means of Landau's theory and Kelvin tensorial representation, this model provided an understanding of the elastic nonlinear phenomena such as the second harmonic generation in three-dimensional solid media. The numerical scheme was implemented and evaluated using a commercially available FEA software LS-DYNA, and it showed a good numerical characterisation of the second harmonic amplitude generated by the damaged region known as the nonlinear response area (NRA). Since this process requires only the experimental second-order nonlinear parameter and rough damage size estimation as an input, it does not need any baseline testing with the undamaged structure or any dynamic modelling of the fatigue crack growth. To validate this numerical model, the second-order nonlinear parameter was experimentally evaluated at various points over the fatigue life of an aluminium (AA6082-T6) coupon and the crack propagation was measured using an optical microscope. A good correlation was achieved between the experimental set-up and the nonlinear constitutive model.

  2. 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.

  3. Evaluation of the New B-REX Fatigue Testing System for Multi-Megawatt Wind Turbine Blades: Preprint

    SciTech Connect

    White, D.; Musial, W.; Engberg, S.

    2004-12-01

    The National Renewable Energy Laboratory (NREL) recently developed a new hybrid fatigue testing system called the Blade Resonance Excitation (B-REX) test system. The new system uses 65% less energy to test large wind turbine blades in half the time of NREL's dual-axis forced-displacement test method with lower equipment and operating costs. The B-REX is a dual-axis test system that combines resonance excitation with forced hydraulic loading to reduce the total test time required while representing the operating strains on the critical inboard blade stations more accurately than a single-axis test system. The analysis and testing required to fully implement the B-REX was significant. To control unanticipated blade motion and vibrations caused by dynamic coupling between the flap, lead-lag, and torsional directions, we needed to incorporate additional test hardware and control software. We evaluated the B-REX test system under stable operating conditions using a combination of various sensors. We then compared our results with results from the same blade, tested previously using NREL's dual-axis forced-displacement test method. Experimental results indicate that strain levels produced by the B-REX system accurately replicated the forced-displacement method. This paper describes the challenges we encountered while developing the new blade fatigue test system and the experimental results that validate its accuracy.

  4. Damage Detection Based on Static Strain Responses Using FBG in a Wind Turbine Blade.

    PubMed

    Tian, Shaohua; Yang, Zhibo; Chen, Xuefeng; Xie, Yong

    2015-01-01

    The damage detection of a wind turbine blade enables better operation of the turbines, and provides an early alert to the destroyed events of the blade in order to avoid catastrophic losses. A new non-baseline damage detection method based on the Fiber Bragg grating (FBG) in a wind turbine blade is developed in this paper. Firstly, the Chi-square distribution is proven to be an effective damage-sensitive feature which is adopted as the individual information source for the local decision. In order to obtain the global and optimal decision for the damage detection, the feature information fusion (FIF) method is proposed to fuse and optimize information in above individual information sources, and the damage is detected accurately through of the global decision. Then a 13.2 m wind turbine blade with the distributed strain sensor system is adopted to describe the feasibility of the proposed method, and the strain energy method (SEM) is used to describe the advantage of the proposed method. Finally results show that the proposed method can deliver encouraging results of the damage detection in the wind turbine blade. PMID:26287200

  5. Damage Detection Based on Static Strain Responses Using FBG in a Wind Turbine Blade

    PubMed Central

    Tian, Shaohua; Yang, Zhibo; Chen, Xuefeng; Xie, Yong

    2015-01-01

    The damage detection of a wind turbine blade enables better operation of the turbines, and provides an early alert to the destroyed events of the blade in order to avoid catastrophic losses. A new non-baseline damage detection method based on the Fiber Bragg grating (FBG) in a wind turbine blade is developed in this paper. Firstly, the Chi-square distribution is proven to be an effective damage-sensitive feature which is adopted as the individual information source for the local decision. In order to obtain the global and optimal decision for the damage detection, the feature information fusion (FIF) method is proposed to fuse and optimize information in above individual information sources, and the damage is detected accurately through of the global decision. Then a 13.2 m wind turbine blade with the distributed strain sensor system is adopted to describe the feasibility of the proposed method, and the strain energy method (SEM) is used to describe the advantage of the proposed method. Finally results show that the proposed method can deliver encouraging results of the damage detection in the wind turbine blade. PMID:26287200

  6. Estimation of fatigue damage parameters using guided wave technique

    NASA Astrophysics Data System (ADS)

    Rathod, V. T.; Roy Mahapatra, D.

    2014-03-01

    In the present work we have considered the problem of monitoring a fatigue crack growth in a thin plate specimen. The problem is first solved analytically by modeling the structure with a cyclic plastic zone around the crack. The damaged region is modeled as a visco-elastic zone and other regions are modeled as elastic zones. Using the one-dimensional guided wave model, the reflected and transmitted energies of the guided waves from the fatigue crack and plastic zone are studied. Experimental study of the reflected and transmitted energies is done using guided waves generated and received by piezoelectric wafers. The reflected and transmitted energies are derived at various cycles of fatigue loading till the failure of the structure. Validation of the results from the analytical model is done by comparing the results obtained from the experiments. The reflected and transmitted energy is related to the size of crack size or the magnitude of loading. Using crack size and the nature of loading, a method is proposed to estimate the fatigue life using fracture mechanics approach.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

  8. 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.

  9. 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.

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

    SciTech Connect

    Chow, C.L.; Yang, F.; Fang, H.E.

    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.

  11. Periostin Deficiency Increases Bone Damage and Impairs Injury Response to Fatigue Loading in Adult Mice

    PubMed Central

    Bonnet, Nicolas; Gineyts, Evelyne; Ammann, Patrick; Conway, Simon J.; Garnero, Patrick; Ferrari, Serge

    2013-01-01

    Bone damage removal and callus formation in response to fatigue loading are essential to prevent fractures. Periostin (Postn) is a matricellular protein that mediates adaptive response of cortical bone to loading. Whether and how periostin influences damage and the injury response to fatigue remains unknown. We investigated the skeletal response of Postn-/- and Postn+/+ mice after fatigue stimulus by axial compression of their tibia. In Postn+/+ mice, cracks number and surface (CsNb, CsS) increased 1h after fatigue, with a decrease in strength compared to non-fatigued tibia. At 15 days, CsNb had started to decline, while CtTV and CtBV increased in fatigued vs non-fatigued tibia, reflecting a woven bone response that was present in 75% of the fatigued bones. Cortical porosity and remodelling also prominently increased in the fatigued tibia of Postn+/+ mice. At 30 days, paralleling a continuous removal of cortical damage, strength of the fatigued tibia was similar to the non-fatigue tibia. In Postn-/- mice, cracks were detectable even in the absence of fatigue, while the amount of collagen crosslinks and tissue hardness was decreased compared to Postn+/+. Fatigue significantly increased CsNb and CsS in Postn-/-, but was not associated with changes in CtTV and CtBV, as only 16% of the fatigued bones formed some woven bone. Cortical porosity and remodelling did not increase either after fatigue in Postn-/- , and the level of damage remained high even after 30 days. As a result, strength remained compromised in Postn-/- mice. Contrary to Postn+/+ , which osteocytic lacunae showed a change in the degree of anisotropy (DA) after fatigue, Postn-/- showed no DA change. Hence periostin appears to influence bone materials properties, damage accumulation and repair, including local modeling/remodeling processes in response to fatigue. These observations suggest that the level of periostin expression could influence the propensity to fatigue fractures. PMID:24167618

  12. Selection and measurement of the 'bearing fatigue damage parameter' in CFRP laminate bolted joints

    NASA Astrophysics Data System (ADS)

    Liu, Da; Ying, Bing-Zhang; Gau, Wei-Gwei

    The cumulative damage (CD) problem can be resolved in terms of a damage parameter which must obey certain conditions. Such a damage parameter can be used with residual strength as well as residual stiffness theory. This paper debates the 'bearing fatigue damage' in CFRP laminates around loaded holes according to the above two theories. It describes damage initiation and propagation by the bearing strength of loaded holes as well as perpetuity deformation of circular holes. This paper gives a selection of the measurement methods of the bearing fatigue damage parameter, a new concept of the fatigue damage point, and lists experimental data.

  13. 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.

    2015-08-01

    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.

  14. 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

  15. Damage assessment for wind turbine blades based on a multivariate statistical approach

    NASA Astrophysics Data System (ADS)

    García, David; Tcherniak, Dmitri; Trendafilova, Irina

    2015-07-01

    This paper presents a vibration based structural health monitoring methodology for damage assessment on wind turbine blades made of composite laminates. Normally, wind turbine blades are manufactured by two half shells made by composite laminates which are glued together. This connection must be carefully controlled due to its high probability to disbond which might result in collapse of the whole structure. The delamination between both parts must be monitored not only for detection but also for localisation and severity determination. This investigation consists in a real time monitoring methodology which is based on singular spectrum analysis (SSA) for damage and delamination detection. SSA is able to decompose the vibratory response in a certain number of components based on their covariance distribution. These components, known as Principal Components (PCs), contain information about of the oscillatory patterns of the vibratory response. The PCs are used to create a new space where the data can be projected for better visualization and interpretation. The method suggested is applied herein for a wind turbine blade where the free-vibration responses were recorded and processed by the methodology. Damage for different scenarios viz different sizes and locations was introduced on the blade. The results demonstrate a clear damage detection and localization for all damage scenarios and for the different sizes.

  16. 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.

  17. Unified continuum damage model for matrix cracking in composite rotor blades

    SciTech Connect

    Pollayi, Hemaraju; Harursampath, Dineshkumar

    2015-03-10

    This paper deals with modeling of the first damage mode, matrix micro-cracking, in helicopter rotor/wind turbine blades and how this effects the overall cross-sectional stiffness. The helicopter/wind turbine rotor system operates in a highly dynamic and unsteady environment leading to severe vibratory loads present in the system. Repeated exposure to this loading condition can induce damage in the composite rotor blades. These rotor/turbine blades are generally made of fiber-reinforced laminated composites and exhibit various competing modes of damage such as matrix micro-cracking, delamination, and fiber breakage. There is a need to study the behavior of the composite rotor system under various key damage modes in composite materials for developing Structural Health Monitoring (SHM) system. Each blade is modeled as a beam based on geometrically non-linear 3-D elasticity theory. Each blade thus splits into 2-D analyzes of cross-sections and non-linear 1-D analyzes along the beam reference curves. Two different tools are used here for complete 3-D analysis: VABS for 2-D cross-sectional analysis and GEBT for 1-D beam analysis. The physically-based failure models for matrix in compression and tension loading are used in the present work. Matrix cracking is detected using two failure criterion: Matrix Failure in Compression and Matrix Failure in Tension which are based on the recovered field. A strain variable is set which drives the damage variable for matrix cracking and this damage variable is used to estimate the reduced cross-sectional stiffness. The matrix micro-cracking is performed in two different approaches: (i) Element-wise, and (ii) Node-wise. The procedure presented in this paper is implemented in VABS as matrix micro-cracking modeling module. Three examples are presented to investigate the matrix failure model which illustrate the effect of matrix cracking on cross-sectional stiffness by varying the applied cyclic load.

  18. 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.

  19. 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.

  20. 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.

  1. Damage assessment of small-scale wind turbine blade using piezoelectric sensors

    NASA Astrophysics Data System (ADS)

    Rim, Mi-Sun; Kim, Sang-Woo; Kim, Eun-Ho; Lee, In

    2012-04-01

    Real-time structural health monitoring (SHM) systems are applied many fields. Recently, the interest about wind energy was increased by the demand of clean energy in the world and many researches were actively performed for applying SHM technology to wind turbine systems. Piezoelectric sensor is one kind of sensor which is widely used for SHM system to assess damage creation. In this paper, the small scale wind turbine blade was fabricated and health monitoring of the blade was performed using the piezoelectric sensor. The quasi-static bending test of the blade was carried out and the PVDF (Polyvinylidene fluoride) sensors, which are polymer type piezoelectric materials, were used for health monitoring. Two-cycle test was performed; the load was applied during 350 sec and removed at the first cycle, and load was applied again until the blade was broken completely at the second cycle. The voltage of PVDF sensors were measured during the quasi-static bending test in order to find out the moment when the damage occurrence started. The voltage of the sensor critically changed at the moment of damage occurred.

  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. A SMALL-SCALE DAMAGE APPROACH TO PREDICT FATIGUE CRACK GROWTH IN CERAMIC MATERIALS

    SciTech Connect

    Nguyen, Ba Nghiep; Koeppel, Brian J.; Khaleel, Mohammad A.

    2006-05-19

    This paper proposes a small-scale damage modeling approach to predict fatigue crack growth in ceramic materials. A fatigue damage model is formulated that uses two variables. One variable is the scalar damage variable governing the reduction of stiffness, and the other is the number of cycles. The damage evolution law is obtained based on thermodynamics of continuous media and a damage criterion containing a damage threshold function that depends on the damage variable and the cyclic loading parameters. The model has been implemented into the ABAQUS finite element code via user-subroutines and has been used in a modified boundary layer (MBL) modeling approach to analyze fatigue crack growth in a small fracture process zone situated at an initial crack tip. The model application is illustrated through an analysis of fatigue crack growth in an yttria-stabilized tetragonal zirconia material.

  4. Damage estimates for European and US sites using the US high-cycle fatigue data base

    SciTech Connect

    Sutherland, H.J.

    1996-02-01

    This paper uses two high-cycle fatigue data bases, US blade materials and one for European materials the service lifetime of a wind turbine blade sit WISPER load spectrum for northern European sit 19921 and the WISPER protocol load spectrum farm sites. The US data base, developed by Mandell, et al. (1995), contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. Further, the analyses demonstrate that the European and the US fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the US data base predicting significantly shorter service lifetimes than the European data base.

  5. Multiple damage identification on a wind turbine blade using a structural neural system

    NASA Astrophysics Data System (ADS)

    Kirikera, Goutham R.; Schulz, Mark J.; Sundaresan, Mannur J.

    2007-04-01

    A large number of sensors are required to perform real-time structural health monitoring (SHM) to detect acoustic emissions (AE) produced by damage growth on large complicated structures. This requires a large number of high sampling rate data acquisition channels to analyze high frequency signals. To overcome the cost and complexity of having such a large data acquisition system, a structural neural system (SNS) was developed. The SNS reduces the required number of data acquisition channels and predicts the location of damage within a sensor grid. The sensor grid uses interconnected sensor nodes to form continuous sensors. The combination of continuous sensors and the biomimetic parallel processing of the SNS tremendously reduce the complexity of SHM. A wave simulation algorithm (WSA) was developed to understand the flexural wave propagation in composite structures and to utilize the code for developing the SNS. Simulation of AE responses in a plate and comparison with experimental results are shown in the paper. The SNS was recently tested by a team of researchers from University of Cincinnati and North Carolina A&T State University during a quasi-static proof test of a 9 meter long wind turbine blade at the National Renewable Energy Laboratory (NREL) test facility in Golden, Colorado. Twelve piezoelectric sensor nodes were used to form four continuous sensors to monitor the condition of the blade during the test. The four continuous sensors are used as inputs to the SNS. There are only two analog output channels of the SNS, and these signals are digitized and analyzed in a computer to detect damage. In the test of the wind turbine blade, multiple damages were identified and later verified by sectioning of the blade. The results of damage identification using the SNS during this proof test will be shown in this paper. Overall, the SNS is very sensitive and can detect damage on complex structures with ribs, joints, and different materials, and the system relatively inexpensive and simple to implement on large structures.

  6. 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.

  7. Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage

    NASA Technical Reports Server (NTRS)

    Manson, S. S.; Halford, G. R.

    1980-01-01

    Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is provided for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are provided for determining the two phases of life. The procedure involves two steps, each similar to the conventional application of the commonly used linear damage rule. When the sum of cycle ratios based on phase 1 lives reaches unity, phase 1 is presumed complete, and further loadings are summed as cycle ratios on phase 2 lives. When the phase 2 sum reaches unity, failure is presumed to occur. No other physical properties or material constants than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons of both methods are discussed.

  8. Fatigue damage to pig erythrocytes during repeated swelling and shrinkage.

    PubMed

    Zou, Lili; Ding, Weiping; Sun, Sijie; Tang, Fangqiong; Gao, Dayong

    2015-10-01

    During the removal of cryoprotectants from cryopreserved-thawed blood with the dialysis-based or dilution-filtration method, due to the change in the extracellular osmolality, erythrocytes usually undergo repeated swelling and shrinkage. However, the erythrocyte fatigue damage induced by this repeated volume change has not yet been studied. In this work, by successively loading hypotonic and hypertonic solutions, we mimicked the repeated swelling and shrinkage of pig erythrocytes and then examined the effect of the number of cycle loops on the steady-state volume and the mortality of the pig erythrocytes. The results suggest that because of cell leakage in the swelling process, the steady-state volume of the pig erythrocytes after one cycle is smaller than the volume before the cycle, even though the cell performs a self-protective regulatory procedure. If the number of cycle loops is increased, the repeated swelling and shrinkage will cause a continuous decrease in the steady-state volume, and the ability of the pig erythrocytes to resist osmotic damage will decrease; as a result, the mortality of the pig erythrocytes increases as the number of cycle loops increases. The viability of the cells is also affected by the hypotonic and isotonic processing times: a short processing time may contribute to a decrease in the mortality of the pig erythrocytes. This work is of significance to optimizing the process of removing cryoprotectants. PMID:26143742

  9. Fatigue damage in cross-ply titanium metal matrix composites containing center holes

    NASA Technical Reports Server (NTRS)

    Bakuckas, J. G., Jr.; Johnson, W. S.; Bigelow, C. A.

    1992-01-01

    The development of fatigue damage in (0/90) sub SCS-6/TI-15-3 laminates containing center holes was studied. Stress levels required for crack initiation in the matrix were predicted using an effective strain parameter and compared to experimental results. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state of damage consisting of matrix cracks and fiber matrix debonding was obtained which reduced the composite modulus. Matrix cracks were bridged by the 0 deg fibers. The fatigue limit (stress causing catastrophic fracture of the laminates) was also determined. The static and post fatigue residual strengths were accurately predicted using a three dimensional elastic-plastic finite element analysis. The matrix damage that occurred during fatigue loading significantly reduced the notched strength.

  10. Advanced nondestructive examination technologies for measuring fatigue damage in nuclear power plant components

    SciTech Connect

    MacDonald, P.E.; Shah, V.N.; Akers, D.W.

    1995-12-01

    This paper presents recent results from an ongoing project at the Idaho National Engineering Laboratory (INEL) to develop advanced nondestructive methods to characterize the aging degradation of nuclear power plant pressure boundary components. One of the advanced methods, positron annihilation, is being developed for in situ characterization of fatigue damage in nuclear power plant piping and other components. This technique can detect and correlate the microstructural changes that are precursors of fatigue cracking in austenitic stainless steel components. In fact, the initial INEL test results show that the method can detect fatigue damage in stainless steel ranging from a few percent of the fatigue life up to 40 percent.

  11. Fatigue Damage Identification in Composite Structures Through Ultrasonics and Wavelet Transform Signal Processing

    NASA Astrophysics Data System (ADS)

    La Saponara, V.; Lestari, W.; Winkelmann, C.; Arronche, L.; Tang, H.-Y.

    2011-06-01

    This is an investigation on the damage behavior of fiberglass/epoxy specimens with embedded piezoelectrics under axial tensile fatigue. The specimen's local and global damage states are complicated by the specimen's own stretching under loading, which varies as a function of damage. A signal processing technique based on wavelet transforms is presented: denoised signals are processed with Gabor wavelet transforms, and the area of one of the contours is tracked throughout the fatigue life.

  12. Cumulative creep-fatigue damage evolution in an austenitic stainless steel

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1992-01-01

    A model of cumulative creep-fatigue damage has been developed which is based on the use of damage curve equations to describe the evolution of creep-fatigue damage for four basic creep-fatigue cycle types. These cycle types correspond to the four fundamental cycles of the Strain Range Partitioning Life Prediction approach of Manson, Halford, and Hirschberg. A concept referred to as Damage Coupling is introduced to analytically account for the differences in the nature of the damage introduced by each cycle type. For application of this model, the cumulative creep-fatigue damage behavior of type 316 stainless steel at 816 C has been experimentally established for the two-level loading cases involving fatigue and creep-fatigue, in various permutations. The tests were conducted such that the lower life (high strain) cycling was applied first, for a controlled number of cycles, and the higher life (lower strain) cycling was conducted at the second level, to failure. The proposed model correlated the majority of the observed cumulative creep-fatigue data.

  13. 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.

  14. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... requirements is impractical for a particular structure. This structure must be shown, by analysis supported by... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... (b) of this section, for each part of the structure that could contribute to a catastrophic...

  15. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... requirements is impractical for a particular structure. This structure must be shown, by analysis supported by... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... (b) of this section, for each part of the structure that could contribute to a catastrophic...

  16. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... requirements is impractical for a particular structure. This structure must be shown, by analysis supported by... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... (b) of this section, for each part of the structure that could contribute to a catastrophic...

  17. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... requirements is impractical for a particular structure. This structure must be shown, by analysis supported by... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... (b) of this section, for each part of the structure that could contribute to a catastrophic...

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

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... structure. 23.573 Section 23.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Structure Fatigue Evaluation § 23.573 Damage tolerance and fatigue evaluation of structure. (a) Composite airframe structure. Composite airframe structure must be evaluated under this paragraph instead of §§...

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

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... structure. 23.573 Section 23.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Structure Fatigue Evaluation § 23.573 Damage tolerance and fatigue evaluation of structure. (a) Composite airframe structure. Composite airframe structure must be evaluated under this paragraph instead of §§...

  20. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... structure. 23.573 Section 23.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Structure Fatigue Evaluation § 23.573 Damage tolerance and fatigue evaluation of structure. (a) Composite airframe structure. Composite airframe structure must be evaluated under this paragraph instead of §§...

  1. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Damage tolerance and fatigue evaluation of structure. 23.573 Section 23.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation §...

  2. 14 CFR 23.573 - Damage tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... structure. 23.573 Section 23.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Structure Fatigue Evaluation § 23.573 Damage tolerance and fatigue evaluation of structure. (a) Composite airframe structure. Composite airframe structure must be evaluated under this paragraph instead of §§...

  3. 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.

  4. 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.

  5. Fatigue damage monitoring for basalt fiber reinforced polymer composites using acoustic emission technique

    NASA Astrophysics Data System (ADS)

    Wang, Wentao; Li, Hui; Qu, Zhi

    2012-04-01

    Basalt fiber reinforced polymer (BFRP) is a structural material with superior mechanical properties. In this study, unidirectional BFRP laminates with 14 layers are made with the hand lay-up method. Then, the acoustic emission technique (AE) combined with the scanning electronic microscope (SEM) technique is employed to monitor the fatigue damage evolution of the BFRP plates in the fatigue loading tests. Time-frequency analysis using the wavelet transform technique is proposed to analyze the received AE signal instead of the peak frequency method. A comparison between AE signals and SEM images indicates that the multi-frequency peaks picked from the time-frequency curves of AE signals reflect the accumulated fatigue damage evolution and fatigue damage patterns. Furthermore, seven damage patterns, that is, matrix cracking, delamination, fiber fracture and their combinations, are identified from the time-frequency curves of the AE signals.

  6. Fatigue-Induced Damage in Zr-Based Bulk Metallic Glasses

    PubMed Central

    Chuang, Chih-Pin; Yuan, Tao; Dmowski, Wojciech; Wang, Gong-Yao; Freels, Matt; Liaw, Peter K.; Li, Ran; Zhang, Tao

    2013-01-01

    In the present work, we investigate the effect of fatigue on the fatigue behavior and atomic structure of Zr-based BMGs. Fatigue experiments on the failed-by-fatigue samples indicate that the remnants generally have similar or longer fatigue life than the as-cast samples. Meanwhile, the pair-distribution-function (PDF) analysis of the as-cast and post-fatigue samples showed very small changes of local atomic structures. These observations suggest that the fatigue life of the 6-mm in-diameter Zr-based BMG is dominated by the number of pre-existing crack-initiation sites in the sample. Once the crack initiates in the specimen, the fatigue-induced damage is accumulated locally on these initiated sites, while the rest of the region deforms elastically. The results suggest that the fatigue failure of BMGs under compression-compression fatigue experiments is a defect-controlled process. The present work indicates the significance of the improved fatigue resistance with decreasing the sample size. PMID:23999496

  7. 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.

  8. Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Halford, Gary R.

    1992-01-01

    Post failure fractographic and metallographic studies were conducted on Haynes 188 specimens fatigued under bithermal and thermomechanical loading conditions between 316 and 760 C. Bithermal fatigue specimens examined included those tested under high strain rate in-phase and out-phase, tensile creep in-phase, and compressive creep out-of-phase loading conditions. Specimens tested under in-phase and out-of-phase thermomechanical fatigue were also examined. The nature of failure mode (transgrandular versus intergranular), the topography of the fracture surface, and the roles of oxidation and metallurgical changes were studied for each type of bithermal and thermomechanical test.

  9. A coupled/uncoupled deformation and fatigue damage algorithm utilizing the finite element method

    NASA Technical Reports Server (NTRS)

    Wilt, Thomas E.; Arnold, Steven M.

    1994-01-01

    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 which fully couples the fatigue damage calculations with the finite element deformation solution. An axisymmetric stress analysis was performed on a circumferentially reinforced ring, wherein both the matrix cladding and the composite core were assumed to behave elastic-perfectly plastic. The composite core behavior was represented using Hill's anisotropic continuum based plasticity model, and similarly, the matrix cladding was represented by an isotropic plasticity model. Results are presented in the form of S-N curves and damage distribution plots.

  10. Fatigue damage of steam turbine shaft at asynchronous connections of turbine generator to electrical network

    NASA Astrophysics Data System (ADS)

    Bovsunovsky, A. P.

    2015-07-01

    The investigations of cracks growth in the fractured turbine rotors point out at theirs fatigue nature. The main reason of turbine shafts fatigue damage is theirs periodical startups which are typical for steam turbines. Each startup of a turbine is accompanied by the connection of turbine generator to electrical network. During the connection because of the phase shift between the vector of electromotive force of turbine generator and the vector of supply-line voltage the short-term but powerful reactive shaft torque arises. This torque causes torsional vibrations and fatigue damage of turbine shafts of different intensity. Based on the 3D finite element model of turbine shaft of the steam turbine K-200-130 and the mechanical properties of rotor steel there was estimated the fatigue damage of the shaft at its torsional vibrations arising as a result of connection of turbine generator to electric network.

  11. Differential continuum damage mechanics models for creep and fatigue of unidirectional metal matrix composites

    NASA Technical Reports Server (NTRS)

    Arnold, S. M.; Kruch, S.

    1991-01-01

    Three multiaxial isothermal continuum damage mechanics models for creep, fatigue, and creep/fatigue interaction of a unidirectional metal matrix composite volume element are presented, only one of which will be discussed in depth. Each model is phenomenological and stress based, with varying degrees of complexity to accurately predict the initiation and propagation of intergranular and transgranular defects over a wide range of loading conditions. The development of these models is founded on the definition of an initially transversely isotropic fatigue limit surface, static fracture surface, normalized stress amplitude function and isochronous creep damage failure surface, from which both fatigue and creep damage evolutionary laws can be obtained. The anisotropy of each model is defined through physically meaningful invariants reflecting the local stress and material orientation. All three transversely isotropic models have been shown, when taken to their isotropic limit, to directly simplify to previously developed and validated creep and fatigue continuum damage theories. Results of a nondimensional parametric study illustrate (1) the flexibility of the present formulation when attempting to characterize a large class of composite materials, and (2) its ability to predict anticipated qualitative trends in the fatigue behavior of unidirectional metal matrix composites. Additionally, the potential for the inclusion of various micromechanical effects (e.g., fiber/matrix bond strength, fiber volume fraction, etc.), into the phenomenological anisotropic parameters is noted, as well as a detailed discussion regarding the necessary exploratory and characterization experiments needed to utilize the featured damage theories.

  12. Fatigue properties of MA 6000E, a gamma-prime strengthened ODS alloy. [Oxide Dispersion Strengthened Ni-base alloy for gas turbine blade applications

    NASA Technical Reports Server (NTRS)

    Kim, Y. G.; Merrick, H. F.

    1980-01-01

    MA 6000E is a corrosion resistant, gamma-prime strengthened ODS alloy under development for advanced turbine blade applications. The high temperature, 1093 C, rupture strength is superior to conventional nickel-base alloys. This paper addresses the fatigue behavior of the alloy. Excellent properties are exhibited in low and high cycle fatigue and also thermal fatigue. This is attributed to a unique combination of microstructural features, i.e., a fine distribution of dispersed oxides and other nonmetallics, and the highly elongated grain structure which advantageously modify the deformation characteristics and crack initiation and propagation modes from that characteristic of conventional gamma-prime hardened superalloys.

  13. Finite Element Analysis on the Impact-Induced Damage of Composite Fan Blades Subjected to a Bird Strike

    NASA Astrophysics Data System (ADS)

    Nishikawa, Masaaki; Hemmi, Kei; Park, Sangchul; Nadabe, Takeaki; Takeda, Nobuo

    Carbon fiber-reinforced composites have been recently applied for engine fan blades, because of their high specific strength. In the design of the fan blade, the bird-strike impact is one of the greatest concerns, since impact-induced damage can lead to the engine stall. This study presented a numerical method to analyze the bird-strike impact as a soft-body impact on cantilevered composite panel. Especially, we coupled a stabilized dynamic contact analysis, which enables predicting impact force on the panel appropriately, with laminate damage analysis to predict the impact-induced progressive damage in the composite. This method was verified through the comparison with the experimental results. With the numerical method, we investigated the effect of impact condition, blade thickness and shape on the impact-induced damage in composite fan blade subjected to a bird strike. An intermediate blade thickness and a large blade curvature help improving the bird-striking impact resistance of the composite.

  14. Control of Compressive Fatigue Delamination Propagation of Impact Damaged Composites Using Discrete Thermoplastic Interleaves

    NASA Astrophysics Data System (ADS)

    Yasaee, M.; Killock, C.; Hartley, J.; Bond, I. P.

    2015-10-01

    A delamination damage control and management concept is demonstrated showing how, through selective placement of discrete thermoplastic film interleaves, it is possible to manipulate the formation of impact damage and control its subsequent propagation during compressive fatigue cyclic loading. Under cyclic loading the gradual growth of impact damaged delamination was shown to be arrested by the discretely embedded interleaved strips. This technique then resulted in the growth of delamination away from the arrested sites effectively moving the damage zones and thus confirming the concept of delamination damage control. By managing the propagation of delamination, significant improvements to the compression after impact fatigue life of the composite were achieved. The proposed method is cost-effective and can be implemented with minimal disturbance to the global laminated composite properties. With an optimised design approach to managing delamination damage, safe `damage tolerant' composite structures can be realised with significant weight saving benefits.

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

    SciTech Connect

    Lam, T.C.T.; Puri, A.

    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.

  16. Experimental damage detection in a wind turbine blade model using principal components of response correlation functions

    NASA Astrophysics Data System (ADS)

    Hoell, S.; Omenzetter, P.

    2015-07-01

    The utilization of vibration signals for structural damage detection (SDD) is appealing due to the strong theoretical foundation of such approaches, ease of data acquisition and processing efficiency. Different methods are available for defining damage sensitive features (DSFs) based on vibrations, such as modal analysis or time series methods. The present paper proposes the use of partial autocorrelation coefficients of acceleration responses as DSFs. Principal component (PC) analysis is used to transform the initial DSFs to scores. The resulting scores from the healthy and damaged states are used to select the PCs which are most sensitive to damage. These are then used for making decisions about the structural state by means of statistical hypothesis testing conducted on the scores. The approach is applied to experiments with a laboratory scale wind turbine blade (WTB) made of glass-fibre reinforced epoxy composite. Damage is non-destructively simulated by attaching small masses and the WTB is excited with the help of an electrodynamic shaker using band-limited white noise. The SDD results for the selected subsets of PCs show a clear improvement of the detectability of early damages compared to other DSF selections.

  17. 77 FR 30877 - Aging Airplane Program: Widespread Fatigue Damage; Technical Amendment

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-24

    ... Airplane Program: Widespread Fatigue Damage,'' (75 FR 69746). In that final rule the FAA revised the... actions (see Damage Tolerance Data for Repairs and Alterations, 72 FR 70486). Change to Table 1 of Sec... Jet Series 705), 2D24 60 (Regional Jet Series 900) Embraer: ERJ 170 60 ERJ 190 60 Fokker: F.28...

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

    NASA Astrophysics Data System (ADS)

    Zagrai, Andrei; Donskoy, Dimitri; Chudnovsky, Alexander; Wu, Hudson

    2001-05-01

    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 using an innovative nonlinear vibro-modulation technique (VMT) [Donskoy et al., NDT&E Int. 34 (2001)]. In the experiments, fatigue damage was initiated in steel, aluminum, and carbon-carbon composite specimens during strain-controlled three-point bending high-cycling fatigue tests. The damage progress was independently monitored using dataflow from the testing machine and the real-time nonlinear vibro-modulation measurements. The tests demonstrated that the reduction in the specimens' stiffness (direct indication of damage accumulation) correlates well with the increase in the VMT's nonlinear damage index. These results confirm that VMT could offer new opportunities for early damage detection and remaining life prediction. [Work supported by NAVAIR.

  19. The fatigue damage behavior of a single crystal superalloy

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1988-01-01

    The uniaxial fatigue behavior of a single crystal superalloy, PWA 1480, is described. Both monotonic tensile and constant amplitude fatigue tests were conducted at room temperature, in an effort to assess the applicability of polycrystalline-based fatigue life prediction methods to a single crystal superalloy. The observed constant amplitude behavior correlated best using a stress-based life criterion. Nearly all specimens failed at surface or slightly subsurface microporosity; this is thought to be responsible for the unusually large amount of scatter in the test results. An additional term is developed in the stress-life equation for the purpose of accounting for the effect of microporosity on fatigue life. The form chosen is a function of the effective area of the failure-producing microporosity projected on a plane perpendicular to the loading axis, as well as the applied stress. This additional term correlated the data to within factors of two on life. Although speculative, extrapolation of the microporosity relation to zero micropore area indicates that approximately an order of magnitude improvement in fatigue life should result.

  20. Fatigue crack initiation and damage evolution of unnotched titanium matrix composites

    NASA Astrophysics Data System (ADS)

    Her, Yung-Chiun

    Fatigue crack initiation, multiplication, matrix crack density evolution, and stiffness reduction of several unnotched SCS-6 silicon carbide fiber-reinforced titanium and titanium aluminide matrix composites have been investigated experimentally and analytically. The effects of the thickness of the interfacial reaction layer and fiber coating on fatigue crack initiation life, crack growth rate, and fatigue damage evolution of the composites were examined. Growth behavior of small fatigue cracks in TMCs was also studied carefully. It was found that fatigue crack initiation and multiplication of TMCs are strongly influenced by the thickness of the interfacial reaction layer. Fatigue crack will not develop from the micro-notches in the interfacial reaction layer until the thickness of the reaction layer exceeds a critical value. Matrix crack growth rate is affected by the applied stress level, however, it appears to be independent of the matrix material and heat treatment. The combined effects of fatigue crack multiplication and propagation result in stiffness degradation of the composites. The Ag/Ta duplex fiber coating significantly improves the transverse tensile and flexural creep resistance of the SCS-6/Ti-25-10 composite. However, the Ag/Ta-coated composite exhibits a shorter crack initiation life, higher number of matrix cracks, and higher crack growth rate than the uncoated composite. The embrittlement of the residual Ag/Ta layer suggests that Ag is not an effective diffusion barrier to prevent the interdiffusion of atomic species across the interface. The high interfacial cracking density and high interfacial bond strength in the Ag/Ta-coated SCS-6/Tisb3Al composite are believed to be responsible for its poor fatigue damage tolerance. For titanium alloys, the threshold intensity factor range, Delta Ksbth, for small fatigue cracks in the matrix alloys of TMCs has been determined to be between 0.9 ˜ 1.0 MPa*msp{1/2} which is much lower than that for long fatigue cracks which is ˜5 MPa*msp{1/2}. The crack growth rate fluctuates widely while the cracks are short, and converges gradually with crack growth. The transition from short fatigue crack to long fatigue crack in the SCS-6/Ti-15-3 composite has been found to occur when the crack length is in the range of 400 to 1000 mum. Finally, an interface-controlled fatigue cracking model incorporating a modified shear-lag model, the strain-life equation, and a fiber bridging model is developed to predict the fatigue crack initiation life, matrix crack growth rate, saturated matrix crack spacing, normalized matrix crack density, and residual stiffness of the composites. The predicted fatigue properties correlate well with experimental results.

  1. 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.

  2. An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components

    SciTech Connect

    Fernandes, B.; Gaydecki, P.; Burdekin, F. Michael

    2005-04-09

    A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth{sup TM} technology to a PC.

  3. 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.

  4. Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Naik, R. A.; Pollock, W. D.

    1990-01-01

    The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) will be discussed. Results from titanium matrix/silicon-carbide fiber composites will be the primary topic of discussion. Results have been obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers has been indentified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow many fiber spacings in the matrix materials without breaking fibers.

  5. Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Naik, R. A.; Pollock, W. D.

    1990-01-01

    The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) is discussed. Results from titanium matrix silicon carbide fiber composites is the primary topic of discussion. Results were obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers was identified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow in the matrix materials without breaking fibers.

  6. Fatigue damage of notched boron/epoxy laminates under constant amplitude loading

    NASA Technical Reports Server (NTRS)

    Roderick, G. L.; Whitcomb, J. D.

    1976-01-01

    Fatigue damage in (0, + or - 45) and (0, + or - 45,90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy. In addition, limited tests for residual strength and stiffness were performed. The results of this study suggest that in boron/epoxy laminates the 45-degree plies play a key role in the fatigue process of boron/epoxy laminates that contain them. The fatigue process in the + or - 45-degree plies starts as intralaminar matrix cracks.

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

    SciTech Connect

    Zhang, Jianfeng; Xuan, Fu-Zhen

    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.

  8. Fatigue

    MedlinePLUS

    ... sense, fatigue is defined as a lack of energy, a subjective feeling of being tired. Fatigue also ... muscular dystrophies as muscles weaken and require greater energy to perform the same activities. Types of fatigue ...

  9. 75 FR 69745 - Aging Airplane Program: Widespread Fatigue Damage

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-15

    .... ``Rotable'' parts 4. Use of LOVs for financial evaluations IV. Regulatory Notices and Analyses I. Executive...\\ Structural fatigue characteristics of airplanes are understood only up to the point where analyses and... the anticipated LOV in the 20-year analysis period. The retirement of this one airplane will result...

  10. Fatigue damage localization using time-domain features extracted from nonlinear Lamb waves

    NASA Astrophysics Data System (ADS)

    Hong, Ming; Su, Zhongqing; Lu, Ye; Cheng, Li

    2014-03-01

    Nonlinear guided waves are sensitive to small-scale fatigue damage that may hardly be identified by traditional techniques. A characterization method for fatigue damage is established based on nonlinear Lamb waves in conjunction with the use of a piezoelectric sensor network. Theories on nonlinear Lamb waves for damage detection are first introduced briefly. Then, the ineffectiveness of using pure frequency-domain information of nonlinear wave signals for locating damage is discussed. With a revisit to traditional gross-damage localization techniques based on the time of flight, the idea of using temporal signal features of nonlinear Lamb waves to locate fatigue damage is introduced. This process involves a time-frequency analysis that enables the damage-induced nonlinear signal features, which are either undiscernible in the original time history or uninformative in the frequency spectrum, to be revealed. Subsequently, a finite element modeling technique is employed, accounting for various sources of nonlinearities in a fatigued medium. A piezoelectric sensor network is configured to actively generate and acquire probing Lamb waves that involve damageinduced nonlinear features. A probability-based diagnostic imaging algorithm is further proposed, presenting results in diagnostic images intuitively. The approach is experimentally verified on a fatigue-damaged aluminum plate, showing reasonably good accuracy. Compared to existing nonlinear ultrasonics-based inspection techniques, this approach uses a permanently attached sensor network that well accommodates automated online health monitoring; more significantly, it utilizes time-domain information of higher-order harmonics from time-frequency analysis, and demonstrates a great potential for quantitative characterization of small-scale damage with improved localization accuracy.

  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. A probabilistic approach to the evaluation of fatigue damage in a space propulsion system injector element

    NASA Technical Reports Server (NTRS)

    Rajagopal, K. R.; Keremes, J.; Ho, H.; Orient, G.

    1992-01-01

    The fatigue damage of a space propulsion system component is computed using probabilistic structural analysis methods. The analysis takes into account the variations in static and dynamic loads, the uncertainty in structural damping, and the scatter in material fatigue resistance. The key elements of the probabilistic approach include: (1) a numerical engine model for describing the global component interface loads consistent with engine balance, (2) models for computing the local mode boundary conditions on the component, (3) a static structural analysis model that captures the strains at a damage critical location as a function of engine performance variables, (4) a finite element model for assessment of the random amplitude stress response due to random base and pressure excitations with uncertain power and correlation length, and (5) advanced first order reliability methods for computing the probabilities associated with the fatigue damage.

  13. The application of the load-stroke hysteresis technique for evaluating fatigue damage development

    SciTech Connect

    Baxter, T.; Reifsnider, K.L.

    1994-12-31

    A new experimental method was developed to measure hysteresis loss during a fatigue test from the load and stroke signals of a standard servo-hydraulic materials testing system. The method was used to characterize changes in properties and performance induced by long-term cyclic loading. Advantages of the load-stroke hysteresis measurement include: (1) contact with the specimen is not required, (2) the fatigue test is not interrupted for data collection, (3) the measured quantity (the hysteresis loop area) is directly related to the (damage) events that alter material properties and life, and (4) a quantitative measure of damage extent and development rate is obtained. The method was used to evaluate damage development during fatigue tests of polymeric composite laminates with unidirectional and angle-ply fiber orientations. The hysteresis loop measurements were used to identify the different stages of damage development and the different damage mechanisms (matrix cracking, delamination, and fiber fracture) in the material systems. The results from the hysteresis technique were correlated with conventional NDE methods such as dynamic signal analysis and specimen surface temperature measurements. It was found that the load-stroke hysteresis technique was especially sensitive to the fiber fracture, the most difficult type of damage process to interrogate in-situ. The hysteresis technique may provide a valuable method for predicting fatigue failure in composite specimens.

  14. Evaluation of Creep-Fatigue Damage Based on Simplified Model Test Approach

    SciTech Connect

    Wang, Yanli; Li, Tianlei; Sham, Sam; Jetter, Robert I

    2013-01-01

    Current methods used in the ASME Code, Subsection NH for the evaluation of creep-fatigue damage are based on the separation of elevated temperature cyclic damage into two parts, creep damage and fatigue damage. This presents difficulties in both evaluation of test data and determination of cyclic damage in design. To avoid these difficulties, an alternative approach was identified, called the Simplified Model Test or SMT approach based on the use of creep-fatigue hold time test data from test specimens with elastic follow-up conservatively designed to bound the response of general structural components of interest. A key feature of the methodology is the use of the results of elastic analysis directly in design evaluation similar to current methods in the ASME Code, Subsection NB. Although originally developed for current material included in Subsection NH, recent interest in the application of Alloy 617 for components operating at very high temperatures has caused renewed interest in the SMT approach because it provides an alternative to the proposed restriction on the use of current Subsection NH simplified methods at very high temperatures. A comprehensive review and assessment of five representative simplified methods for creep-fatigue damage evaluation is presented in Asayama [1]. In this review the SMT methodology was identified as the best long term approach but the need for test data precluded its near term implementation. Asayama and Jetter [2] is a summary of the more comprehensive report by Asayama [1] with a summary of the SMT approach presented by Jetter [3].

  15. Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, Andrew L.

    1998-01-01

    This dissertation focuses on the characterization of the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin, woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The residual elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed noticeable reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment composing the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.

  16. Development of a new fatigue damage growth model for polymer matrix composites

    NASA Astrophysics Data System (ADS)

    Atodaria, Devrajsinh R.

    The objective of this research is to develop a new fatigue crack growth model for fiber reinforced polymer composites. This new model takes into account the progressive damage that occurs at each load increment in fatigue cycling through a weighted average stress intensity factor. The fatigue crack growth rate is modeled using a power law equation; however, the fatigue damage controlling parameters used in this equation are the stress intensity range as well as the weighted stress intensity factor. The model was developed and verified using three different polymer matrix composites, namely, a randomly oriented short carbon fiber reinforced thermoplastic (PEEK), a polyester sheet molding compound composite containing randomly oriented short glass fibers and a plain weave glass fabric reinforced epoxy. Fatigue crack growth experiments were conducted using either a compact tension specimen or a double cantilever beam specimen. The stress intensity approach is used for the first two composites. The strain energy release rate approach is used for the woven fabric reinforced epoxy matrix composite since delamination growth was the primary mode of fatigue failure in these laminates and delamination growth can be better modeled using the strain energy release rate. In all cases, it was observed that the proposed model given by the following equation can represent the fatigue crack growth rate at different load ratio in a unified equation${da/ dN}=B(Ksbsp{average}{gamma}.Delta Ksp{1-gamma})sp {p}where, B, gamma$ and p are the model constants determined from the fatigue crack growth rate data. The fatigue crack growth rate predicted with this single power law equation for each load ratio gives a close agreement with the experimental data for all three composites under study.

  17. Multiaxial low-cycle fatigue damage evaluation using a. c. potential method for alloy 738LC superalloy

    SciTech Connect

    Isono, Yoshitada; Sakane, Masao; Ohnami, Masateru . Dept. of Mechanical Engineering); Fujiyama, Kazunari . Heavy Apparatus Engineering Lab.)

    1994-10-01

    This paper studies tension/torsion multiaxial low-cycle fatigue lives and creep-fatigue damage evaluation for Alloy 738LC superalloy. Tension/torsion creep-fatigue tests were carried out using hollow cylinder specimens and multiaxial creep-fatigue lives were obtained. The Mises' equivalent strain correlated the multiaxial low cycle fatigue lives within a factor of two scatter band. An a.c. potential method is developed to detect the creep-fatigue damage associated with crack nucleation and extension. A.c. potentials at high frequencies accurately detect the creep-fatigue damage from the early stage of life while those at low frequencies detect that in the final stage of life. A.c. potentials at high frequencies detect the crack density, defined as the total crack length per unit area, and maximum crack length more sensitivity than those at low frequencies.

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

    SciTech Connect

    Wu, Weiliang Qu, Wenzhong E-mail: xiaoli6401@126.com; Xiao, Li E-mail: xiaoli6401@126.com; Shen, Yanfeng Giurgiutiu, Victor

    2015-03-31

    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.

  19. 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.

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

  1. Second Harmonic Generation Imaging and Fourier Transform Spectral Analysis Reveal Damage in Fatigue-Loaded Tendons

    PubMed Central

    Fung, David T.; Sereysky, Jedd B.; Basta-Pljakic, Jelena; Laudier, Damien M.; Huq, Rumana; Jepsen, Karl J.; Schaffler, Mitchell B.; Flatow, Evan L.

    2016-01-01

    Conventional histologic methods provide valuable information regarding the physical nature of damage in fatigue-loaded tendons, limited to thin, two-dimensional sections. We introduce an imaging method that characterizes tendon microstructure three-dimensionally and develop quantitative, spatial measures of damage formation within tendons. Rat patellar tendons were fatigue loaded in vivo to low, moderate, and high damage levels. Tendon microstructure was characterized using multiphoton microscopy by capturing second harmonic generation signals. Image stacks were analyzed using Fourier transform-derived computations to assess frequency-based properties of damage. Results showed 3D microstructure with progressively increased density and variety of damage patterns, characterized by kinked deformations at low, fiber dissociation at moderate, and fiber thinning and out-of-plane discontinuities at high damage levels. Image analysis generated radial distributions of power spectral gradients, establishing a “fingerprint” of tendon damage. Additionally, matrix damage was mapped using local, discretized orientation vectors. The frequency distribution of vector angles, a measure of damage content, differed from one damage level to the next. This study established an objective 3D imaging and analysis method for tendon microstructure, which characterizes directionality and anisotropy of the tendon microstructure and quantitative measures of damage that will advance investigations of the microstructural basis of degradation that precedes overuse injuries. PMID:20232150

  2. Fatigue analysis of multiple site damage at a row of holes in a wide panel

    NASA Technical Reports Server (NTRS)

    Buhler, Kimberley; Grandt, Alten F., Jr.; Moukawsher, E. J.

    1994-01-01

    This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.

  3. Cumulative damage and the response of human bone in two-step loading fatigue.

    PubMed

    Zioupos, P; Casinos, A

    1998-09-01

    It has already been shown that in fatigue tests in vitro human cortical bone accumulates damage in the form of microcracks and that the total number of microcracks generated prior to the creation of the fatal macrocrack, and their effect (softening) on the material properties, depends on the level of applied stress. At each stress level the amount of accumulated damage has also been shown to be a non-linear function of the cycle number (Zioupos et al., 1996a, b; Pattin et al., 1996). The theoretical implications of the previous findings and two possible models for cumulative damage were put to the test here by performing tensile fatigue tests in two-step level (high/low or low/high) loading on human cortical bone specimens. The results indicate that the accumulation of damage in-vitro is highly dependent on the level of stress and the stress history. Usual linear expressions for fatigue lifetime predictions, like the Palmgren-Miner rule, substantially over or underestimate the outcome depending on whether the stress was applied in a high/low or a low/high sequence, respectively. In view of these discrepancies we conclude that predicting the fatigue lifetime of any bone in vivo under variable loading and complex history regimes is an extremely difficult task to which the study of accumulation of damage can offer a significant but, perhaps, still limited contribution. PMID:9802783

  4. Fatigue analysis of multiple site damage at a row of holes in a wide panel

    NASA Astrophysics Data System (ADS)

    Buhler, Kimberley; Grandt, Alten F., Jr.; Moukawsher, E. J.

    1994-09-01

    This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.

  5. Modeling nonlinearities of ultrasonic waves for fatigue damage characterization: theory, simulation, and experimental validation.

    PubMed

    Hong, Ming; Su, Zhongqing; Wang, Qiang; Cheng, Li; Qing, Xinlin

    2014-03-01

    A dedicated modeling technique for comprehending nonlinear characteristics of ultrasonic waves traversing in a fatigued medium was developed, based on a retrofitted constitutive relation of the medium by considering the nonlinearities originated from material, fatigue damage, as well as the "breathing" motion of fatigue cracks. Piezoelectric wafers, for exciting and acquiring ultrasonic waves, were integrated in the model. The extracted nonlinearities were calibrated by virtue of an acoustic nonlinearity parameter. The modeling technique was validated experimentally, and the results showed satisfactory consistency in between, both revealing: the developed modeling approach is able to faithfully simulate fatigue crack-incurred nonlinearities manifested in ultrasonic waves; a cumulative growth of the acoustic nonlinearity parameter with increasing wave propagation distance exists; such a parameter acquired via a sensing path is nonlinearly related to the offset distance from the fatigue crack to that sensing path; and neither the incidence angle of the probing wave nor the length of the sensing path impacts on the parameter significantly. This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously. PMID:24156928

  6. Observations of fatigue crack initiation and damage growth in notched titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Naik, R. A.; Johnson, W. S.

    1990-01-01

    The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.

  7. Observations of fatigue crack initiation and damage growth in notched titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Naik, Rajiv A.; Johnson, W. S.

    1991-01-01

    The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.

  8. Fatigue life prediction of rotor blade composites: Validation of constant amplitude formulations with variable amplitude experiments

    NASA Astrophysics Data System (ADS)

    Westphal, T.; Nijssen, R. P. L.

    2014-12-01

    The effect of Constant Life Diagram (CLD) formulation on the fatigue life prediction under variable amplitude (VA) loading was investigated based on variable amplitude tests using three different load spectra representative for wind turbine loading. Next to the Wisper and WisperX spectra, the recently developed NewWisper2 spectrum was used. Based on these variable amplitude fatigue results the prediction accuracy of 4 CLD formulations is investigated. In the study a piecewise linear CLD based on the S-N curves for 9 load ratios compares favourably in terms of prediction accuracy and conservativeness. For the specific laminate used in this study Boerstra's Multislope model provides a good alternative at reduced test effort.

  9. Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation

    SciTech Connect

    Cantrell, John H.

    2006-09-15

    Self-organized substructural arrangements of dislocations formed during cyclic stress-induced fatigue of metals produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter {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 [Proc. R. Soc. London, Ser. A 460, 757 (2004)] 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 fatigue damage included in the total 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% from the virgin state to roughly 95% full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, during the last 5% of fatigue life the model predicts a rapid monotonic increase of {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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. A nonlinear history-dependent damage model for low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Leis, B. N.

    1988-01-01

    A nonlinear damage postulate that embodies the dependence of the damage rate on cycle-dependent changes in the bulk microstructure and the surface topography is examined. The postulate is analytically formulated in terms of the deformation history dependence of the bulk behavior. This formulation is used in conjunction with baseline data in accordance with the damage postulate to predict the low cycle fatigue resistance of OFE copper. Close comparison of the predictions with experimentally observed behavior suggests that the postulate offers a viable basis for nonlinear damage analysis.

  15. 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.

  16. Nondestructive determination of fatigue crack damage in composites using vibration tests.

    NASA Technical Reports Server (NTRS)

    Dibenedetto, A. T.; Gauchel, J. V.; Thomas, R. L.; Barlow, J. W.

    1972-01-01

    The vibration response of glass reinforced epoxy and polyester laminates was investigated. The complex modulus and the damping capacity were measured as fatigue crack damage accumulated. Changes in the Young's modulus as well as the damping capacity correlated with the amount of crack damage. The damping was especially sensitive to debonding of the reinforcement from the resin matrix. Measurement of these vibration response changes shows promise as a means to nondestructively test the structural integrity of filament-reinforced composite structural members.

  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. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Metallic damage tolerance and fatigue evaluation of commuter category airplanes. 23.574 Section 23.574 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES...

  19. 14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance... structure is able to withstand the repeated loads of variable magnitude expected in-service. In establishing... rotorcraft structure and: (1) Identify all PSEs considered in the fatigue evaluation; (2) Identify the...

  20. 14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance... structure is able to withstand the repeated loads of variable magnitude expected in-service. In establishing... rotorcraft structure and: (1) Identify all PSEs considered in the fatigue evaluation; (2) Identify the...

  1. 14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance... structure is able to withstand the repeated loads of variable magnitude expected in-service. In establishing... rotorcraft structure and: (1) Identify all PSEs considered in the fatigue evaluation; (2) Identify the...

  2. 14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance... structure is able to withstand the repeated loads of variable magnitude expected in-service. In establishing... rotorcraft structure and: (1) Identify all PSEs considered in the fatigue evaluation; (2) Identify the...

  3. 14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance... structure is able to withstand the repeated loads of variable magnitude expected in-service. In establishing... rotorcraft structure and: (1) Identify all PSEs considered in the fatigue evaluation; (2) Identify the...

  4. 14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance... structure is able to withstand the repeated loads of variable magnitude expected in-service. In establishing... rotorcraft structure and: (1) Identify all PSEs considered in the fatigue evaluation; (2) Identify the...

  5. 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

  6. Structural damage detection in wind turbine blades based on time series representations of dynamic responses

    NASA Astrophysics Data System (ADS)

    Hoell, Simon; Omenzetter, Piotr

    2015-03-01

    The development of large wind turbines that enable to harvest energy more efficiently is a consequence of the increasing demand for renewables in the world. To optimize the potential energy output, light and flexible wind turbine blades (WTBs) are designed. However, the higher flexibilities and lower buckling capacities adversely affect the long-term safety and reliability of WTBs, and thus the increased operation and maintenance costs reduce the expected revenue. Effective structural health monitoring techniques can help to counteract this by limiting inspection efforts and avoiding unplanned maintenance actions. Vibration-based methods deserve high attention due to the moderate instrumentation efforts and the applicability for in-service measurements. The present paper proposes the use of cross-correlations (CCs) of acceleration responses between sensors at different locations for structural damage detection in WTBs. CCs were in the past successfully applied for damage detection in numerical and experimental beam structures while utilizing only single lags between the signals. The present approach uses vectors of CC coefficients for multiple lags between measurements of two selected sensors taken from multiple possible combinations of sensors. To reduce the dimensionality of the damage sensitive feature (DSF) vectors, principal component analysis is performed. The optimal number of principal components (PCs) is chosen with respect to a statistical threshold. Finally, the detection phase uses the selected PCs of the healthy structure to calculate scores from a current DSF vector, where statistical hypothesis testing is performed for making a decision about the current structural state. The method is applied to laboratory experiments conducted on a small WTB with non-destructive damage scenarios.

  7. Locating fatigue damage using temporal signal features of nonlinear Lamb waves

    NASA Astrophysics Data System (ADS)

    Hong, Ming; Su, Zhongqing; Lu, Ye; Sohn, Hoon; Qing, Xinlin

    2015-08-01

    The temporal signal features of linear guided waves, as typified by the time-of-flight (ToF), have been exploited intensively for identifying damage, with proven effectiveness in locating gross damage in particular. Upon re-visiting the conventional, ToF-based detection philosophy, the present study extends the use of temporal signal processing to the realm of nonlinear Lamb waves, so as to reap the high sensitivity of nonlinear Lamb waves to small-scale damage (e.g., fatigue cracks), and the efficacy of temporal signal processing in locating damage. Nonlinear wave features (i.e., higher-order harmonics) are extracted using networked, miniaturized piezoelectric wafers, and reverted to the time domain for damage localization. The proposed approach circumvents the deficiencies of using Lamb wave features for evaluating undersized damage, which are either undiscernible in time-series analysis or lacking in temporal information in spectral analysis. A probabilistic imaging algorithm is introduced to supplement the approach, facilitating the presentation of identification results in an intuitive manner. Through numerical simulation and then experimental validation, two damage indices (DIs) are comparatively constructed, based, respectively, on linear and nonlinear temporal features of Lamb waves, and used to locate fatigue damage near a rivet hole of an aluminum plate. Results corroborate the feasibility and effectiveness of using temporal signal features of nonlinear Lamb waves to locate small-scale fatigue damage, with enhanced accuracy compared with linear ToF-based detection. Taking a step further, a synthesized detection strategy is formulated by amalgamating the two DIs, targeting continuous and adaptive monitoring of damage from its onset to macroscopic formation.

  8. Fatigue damage study in aluminum-2024 T3 alloys

    NASA Technical Reports Server (NTRS)

    Ferguson, Milton W.

    1992-01-01

    The grain structure of aluminum 2024, a commonly used commercial alloy is investigated, and these findings are correlated with the fatigue property of the material. Samples of aluminum 2024 were polished and etched in different reagents. Optical micrographs (at 500X) of samples etched in Keller's reagent revealed grain boundaries as well as some particles present in the microstructure. Normal x-ray scans of samples etched for different intervals of time in Keller's reagent indicate no significant variations in diffraction peak positions; however, the width of the rocking curve increased with the time of etching. These results are consistent with the direct dependence of the width of the rocking curve on the range of grain orientation. Etching removes the preferred orientation layer of the sample produced by polishing; thereby, causing the width to increase.

  9. Fatigue

    MedlinePLUS

    ... like chemotherapy and radiation Recovering from major surgery Anxiety, stress, or depression Staying up too late Drinking too much alcohol or too many caffeinated drinks Pregnancy One disorder that causes extreme fatigue is chronic fatigue syndrome ( ...

  10. Numerical fatigue life assessment of cardiovascular stents: A two-scale plasticity-damage model

    NASA Astrophysics Data System (ADS)

    Santos, H. A. F. A.; Auricchio, F.; Conti, M.

    2013-07-01

    Cardiovascular disease has become a major global health care problem in the last decades. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, numerical approaches for fatigue life assessment of stents have gained special interest in the engineering community. Numerical fatigue life predictions can be used to modify the design and prevent failure without making and testing numerous physical devices, thus preventing from undesired fatigue failures. We present a numerical fatigue life model for the analysis of cardiovascular balloon-expandable stainless steel stents that can hopefully provide useful information either to be used for product improvement or for clinicians to make life-saving decisions. This model incorporates a two-scale continuum damage mechanics model and the so-called Soderberg fatigue failure criterion. We provide numerical results for both Palmaz-Schatz and Cypher stent designs and demonstrate that a good agreement is found between the numerical and the available experimental results.

  11. 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.

  12. Experimental Evaluation of Fatigue Damage Progression in Postbuckled Single Stringer Composite Specimens

    NASA Technical Reports Server (NTRS)

    Bisagni, Chiara; Davila, Carlos G.; Rose, Cheryl A.; Zalameda, Joseph N.

    2014-01-01

    The durability and damage tolerance of postbuckled composite structures are not yet completely understood, and remain difficult to predict due to the nonlinearity of the geometric response and its interaction with local damage modes. A research effort was conducted to investigate experimentally the quasi-static and fatigue damage progression in a single-stringer compression (SSC) specimen. Three specimens were manufactured with a hat-stiffener, and an initial defect was introduced with a Teflon film embedded between one flange of the stringer and the skin. One of the specimens was tested under quasi-static compressive loading, while the remaining two specimens were tested by cycling in postbuckling. The tests were performed at the NASA Langley Research Center under controlled conditions and with instrumentation that allows a precise evaluation of the postbuckling response and of the damage modes. Three-dimensional digital image correlation VIC-3D systems were used to provide full field displacements and strains on the skin and the stringer. Passive thermal monitoring was conducted during the fatigue tests using an infrared camera that showed the location of the delamination front while the specimen was being cycled. The live information from the thermography was used to stop the fatigue tests at critical stages of the damage evolution to allow detailed ultrasonic scans.

  13. 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.

  14. 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.

  15. Nondestructive indication of fatigue damage and residual lifetime in ferromagnetic construction materials

    NASA Astrophysics Data System (ADS)

    Tom, Ivan; Kov?k, Ond?ej; Vrtesy, Gbor; Kadlecov, Jana

    2014-06-01

    A new revolutionary attitude toward investigation of fatigue damage in cyclically loaded steel samples is reported. The measurement is based on the method of magnetic adaptive testing, which--in contrast to traditional magnetic hysteresis investigations--picks up the relevant information from systematic measurement and evaluation of whole minor magnetic hysteresis loops and their derivatives. Satisfactory correlations between nondestructively measured magnetic descriptors and actual lifetime of the fatigued material were found. The presented method is able to serve as a powerful tool for indication of changes, which occur in the structure of the inspected objects during their industrial service lifetime, as long as they are manufactured from ferromagnetic materials.

  16. A model for predicting damage induced fatigue life of laminated composite structural components

    NASA Technical Reports Server (NTRS)

    Allen, David H.; Lo, David C.; Georgiou, Ioannis T.; Harris, Charles E.

    1990-01-01

    This paper presents a model for predicting the life of laminated composite structural components subjected to fatigue induced microstructural damage. The model uses the concept of continuum damage mechanics, wherein the effects of microcracks are incorporated into a damage dependent lamination theory instead of treating each crack as an internal boundary. Internal variables are formulated to account for the effects of both matrix cracks and internal delaminations. Evolution laws for determining the damage variables as functions of ply stresses are proposed, and comparisons of predicted damage evolution are made to experiment. In addition, predicted stiffness losses, as well as ply stresses are shown as functions of damage state for a variety of stacking sequences.

  17. Post-Impact Fatigue Damage Monitoring Using Fiber Bragg Grating Sensors

    PubMed Central

    Shin, Chow-Shing; Liaw, Shien-Kuei; Yang, Shi-Wei

    2014-01-01

    It has been shown that impact damage to composite materials can be revealed by embedded Fiber Bragg Gratings (FBG) as a broadening and splitting of the latter's characteristic narrow peak reflected spectrum. The current work further subjected the impact damaged composite to cyclic loading and found that the FBG spectrum gradually submerged into a rise of background intensity as internal damages progressed. By skipping the impact, directing the impact to positions away from the FBG and examining the extracted fibers, we concluded that the above change is not a result of deterioration/damage of the sensor. It is caused solely by the damages initiated in the composite by the impact and aggravated by fatigue loading. Evolution of the grating spectrum may therefore be used to monitor qualitatively the development of the incurred damages. PMID:24594609

  18. Acoustography as a means of monitoring damage in composites during static or fatigue loading

    NASA Astrophysics Data System (ADS)

    Chen, A. S.; Almond, D. P.; Harris, B.

    2001-02-01

    The integration of an acoustography ultrasonic imaging system with a mechanical testing machine is described. The apparatus is designed for real-time ultrasonic imaging of impact damage growth in composite material samples subjected to either static or fatigue loading. Experimental results are presented of the damage growth to failure of an aerospace standard carbon-fibre composite sample subjected to compressive cyclic loading. Experimental results for static loading show a reversible increase and decrease in damage area, indicating an opening and closing of delamination defects, which points to the possibility of an under-estimation of defect size by the conventional ultrasonic testing of unloaded components.

  19. The effect of cement creep and cement fatigue damage on the micromechanics of the cement-bone interface

    PubMed Central

    Waanders, Daan; Janssen, Dennis; Mann, Kenneth A.; Verdonschot, Nico

    2010-01-01

    The cement-bone interface provides fixation for the cement mantle within the bone. The cement-bone interface is affected by fatigue loading in terms of fatigue damage, or micro cracks, and creep, both mostly in the cement. This study investigates how fatigue damage and cement creep separately affect the mechanical response of the cement-bone interface at various load levels in terms of plastic displacement and crack formation. Two FEA models were created, which were based on micro-computed tomography data of two physical cement-bone interface specimens. These models were subjected to tensile fatigue loads with four different magnitudes. Three deformation modes of the cement were considered; only creep, only damage or creep and damage. The interfacial plastic deformation, the crack reduction as a result of creep and the interfacial stresses in the bone were monitored. The results demonstrate that, although some models failed early, the majority of plastic displacement was caused by fatigue damage, rather than cement creep. However, cement creep does decrease the crack formation in the cement up to 20%. Finally, while cement creep hardly influences the stress levels in the bone, fatigue damage of the cement considerably increases the stress levels in the bone. We conclude that at low load levels the plastic displacement is mainly caused by creep. At moderate to high load levels, however, the plastic displacement is dominated by fatigue damage and is hardly affected by creep, although creep reduced the number of cracks in moderate to high load region. PMID:20692663

  20. 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.

  1. Optimal selection of autoregressive model coefficients for early damage detectability with an application to wind turbine blades

    NASA Astrophysics Data System (ADS)

    Hoell, Simon; Omenzetter, Piotr

    2016-03-01

    Data-driven vibration-based damage detection techniques can be competitive because of their lower instrumentation and data analysis costs. The use of autoregressive model coefficients (ARMCs) as damage sensitive features (DSFs) is one such technique. So far, like with other DSFs, either full sets of coefficients or subsets selected by trial-and-error have been used, but this can lead to suboptimal composition of multivariate DSFs and decreased damage detection performance. This study enhances the selection of ARMCs for statistical hypothesis testing for damage presence. Two approaches for systematic ARMC selection, based on either adding or eliminating the coefficients one by one or using a genetic algorithm (GA) are proposed. The methods are applied to a numerical model of an aerodynamically excited large composite wind turbine blade with disbonding damage. The GA out performs the other selection methods and enables building multivariate DSFs that markedly enhance early damage detectability and are insensitive to measurement noise.

  2. Acoustic emission and fatigue damage induced in plasma-sprayed hydroxyapatite coating layers.

    PubMed

    Laonapakul, Teerawat; Otsuka, Yuichi; Nimkerdphol, Achariya Rakngarm; Mutoh, Yoshiharu

    2012-04-01

    In order to improve the adhesive strength of hydroxyapatite (HAp) coatings, grit blasting with Al(2)O(3) powder and then wet blasting with HAp/Ti mixed powders was carried out on a commercially pure Ti (cp-Ti) substrate. Subsequently, an HAp/Ti bond coat layer and HAp top coat layer were deposited by plasma spraying. Fatigue tests of the HAp-coated specimens were carried out under four-point bending. Acoustic emission (AE) signals during the entire fatigue test were monitored to investigate the fatigue cracking behavior of the HAp-coated specimens. The HAp-coated specimens could survive up to 10(7) cycles without spallation of the HAp coating layers at the stress amplitude of 120 MPa. The HAp-coated specimens without HAp/Ti bond coat layer showed shorter fatigue life and easy crack nucleation compared to the HAp-coated specimens with HAp/Ti bond coat layer. The delamination and spallation of the HAp top coat with HAp/Ti bond coat on cp-Ti was not observed until the crack propagated into the cp-Ti during the final fracture stage of the fatigue cycle. Therefore, the HAp/Ti bond coat layer was found to greatly improve the fatigue damage resistance of the HAp coating layer. Three stages of the fatigue failure behavior of the HAp top coat with HAp/Ti bond coat on a cp-Ti substrate can be clearly estimated by the AE monitoring technique. These stages are cracks nucleating and propagating in the coating layer, cracks propagating in the substrate, and cracks propagating unstably to final fracture. PMID:22402159

  3. Fatigue damage at room temperature in aluminium single crystals. 4: Secondary slip

    SciTech Connect

    Zhai, T.; Briggs, G.A.D.; Martin, J.W.

    1996-09-01

    Two Al single crystals were fatigued in push-pull in air at room temperature, at a constant shear stress amplitude of 4 MPa, zero mean stress and frequency of 20 Hz. Secondary slip lines were observed in the matrix, macrobands and PSBs (mainly in extrusions and intrusions) on the side-surfaces of the two specimens. At the later stage of the fatigue test (after 5 {times} 10{sup 6} cycles), in addition to extrusions and intrusions which were probably formed by local persistent secondary slip in PSBs, short cracks were also usually observed on the side-surfaces mainly along the interface between the matrix and the extrusions in the PSBs. It is suggested that an internal stress at each slip offset (caused by net irreversible secondary slip in the extrusions within PSBs due to lattice rotation on the side-surface), is mainly responsible for crack initiation in the extrusions. Secondary slip takes place commonly to assist lattice rotation during fatigue, and plays a significant role in fatigue damage at room temperature, especially in the later stage of fatigue, in Al single crystals.

  4. Monitoring of fatigue damage in composite lap-joints using guided waves and FBG sensors

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Adhesive bonding is being increasingly employed in many applications as it offers possibility of light-weighting and efficient multi-material joining along with reduction in time and cost of manufacturing. However, failure initiation and progression in critical components like joints, specifically in fatigue loading is not well understood, which necessitates reliable NDE and SHM techniques to ensure structural integrity. In this work, concurrent guided wave (GW) and fiber Bragg grating (FBG) sensor measurements were used to monitor fatigue damage in adhesively bonded composite lap-joints. In the present set-up, one FBG sensor was strategically embedded in the adhesive bond-line of a lap-joint, while two other FBGs were bonded on the surface of the adherends. Full spectral responses of FBG sensors were collected and compared at specific intervals of fatigue loading. In parallel, guided waves were actuated and sensed using PZT wafers mounted on the composite adherends. Experimental results demonstrated that time-of-flight (ToF) of the fundamental modes transmitted through the bond-line and spectral response of FBG sensors were sensitive to fatigue loading and damage. Combination of guided wave and FBG measurements provided the desired redundancy and synergy in the data to evaluate the degradation in bond-line properties. Measurements taken in the presence of continuously applied load replicated the in-situ/service conditions. The approach shows promise in understanding the behavior of bonded joints subjected to complex loading.

  5. Applications of matched field processing to damage detection in composite wind turbine blades

    NASA Astrophysics Data System (ADS)

    Tippmann, Jeffery D.; Lanza di Scalea, Francesco

    2015-03-01

    There are many structures serving vital infrastructure, energy, and national security purposes. Inspecting the components and areas of the structure most prone to failure during maintenance operations by using non- destructive evaluation methods has been essential in avoiding costly, but preventable, catastrophic failures. In many cases, the inspections are performed by introducing acoustic, ultrasonic, or even thermographic waves into the structure and then evaluating the response. Sometimes the structure, or a component, is not accessible for active inspection methods. Because of this, there is a growing interest to use passive methods, such as using ambient noise, or sources of opportunity, to produce a passive impulse response function similar to the active approach. Several matched field processing techniques most notably used in oceanography and seismology applications are examined in more detail. While sparse array imaging in structures has been studied for years, all methods studied previously have used an active interrogation approach. Here, structural damage detection is studied by use of the reconstructed impulse response functions in ambient noise within sparse array imaging techniques, such as matched-field processing. This has been studied in experiments on a 9-m wind turbine blade.

  6. Effect of Buckling Modes on the Fatigue Life and Damage Tolerance of Stiffened Structures

    NASA Technical Reports Server (NTRS)

    Davila, Carlos G.; Bisagni, Chiara; Rose, Cheryl A.

    2015-01-01

    The postbuckling response and the collapse of composite specimens with a co-cured hat stringer are investigated experimentally and numerically. These specimens are designed to evaluate the postbuckling response and the effect of an embedded defect on the collapse load and the mode of failure. Tests performed using controlled conditions and detailed instrumentation demonstrate that the damage tolerance, fatigue life, and collapse loads are closely tied with the mode of the postbuckling deformation, which can be different between two nominally identical specimens. Modes that tend to open skin/stringer defects are the most damaging to the structure. However, skin/stringer bond defects can also propagate under shearing modes. In the proposed paper, the effects of initial shape imperfections on the postbuckling modes and the interaction between different postbuckling deformations and the propagation of skin/stringer bond defects under quasi-static or fatigue loads will be examined.

  7. A recursive Bayesian approach for fatigue damage prognosis: An experimental validation at the reliability component level

    NASA Astrophysics Data System (ADS)

    Gobbato, Maurizio; Kosmatka, John B.; Conte, Joel P.

    2014-04-01

    Fatigue-induced damage is one of the most uncertain and highly unpredictable failure mechanisms for a large variety of mechanical and structural systems subjected to cyclic and random loads during their service life. A health monitoring system capable of (i) monitoring the critical components of these systems through non-destructive evaluation (NDE) techniques, (ii) assessing their structural integrity, (iii) recursively predicting their remaining fatigue life (RFL), and (iv) providing a cost-efficient reliability-based inspection and maintenance plan (RBIM) is therefore ultimately needed. In contribution to these objectives, the first part of the paper provides an overview and extension of a comprehensive reliability-based fatigue damage prognosis methodology previously developed by the authors for recursively predicting and updating the RFL of critical structural components and/or sub-components in aerospace structures. In the second part of the paper, a set of experimental fatigue test data, available in the literature, is used to provide a numerical verification and an experimental validation of the proposed framework at the reliability component level (i.e., single damage mechanism evolving at a single damage location). The results obtained from this study demonstrate (i) the importance and the benefits of a nearly continuous NDE monitoring system, (ii) the efficiency of the recursive Bayesian updating scheme, and (iii) the robustness of the proposed framework in recursively updating and improving the RFL estimations. This study also demonstrates that the proposed methodology can lead to either an extent of the RFL (with a consequent economical gain without compromising the minimum safety requirements) or an increase of safety by detecting a premature fault and therefore avoiding a very costly catastrophic failure.

  8. Modeling of thermo-mechanical fatigue and damage in shape memory alloy axial actuators

    NASA Astrophysics Data System (ADS)

    Wheeler, Robert W.; Hartl, Darren J.; Chemisky, Yves; Lagoudas, Dimitris C.

    2015-04-01

    The aerospace, automotive, and energy industries have seen the potential benefits of using shape memory alloys (SMAs) as solid state actuators. Thus far, however, these actuators are generally limited to non-critical components or over-designed due to a lack of understanding regarding how SMAs undergo thermomechanical or actuation fatigue and the inability to accurately predict failure in an actuator during use. The purpose of this study was to characterize the actuation fatigue response of Nickel-Titanium-Hafnium (NiTiHf) axial actuators and, in turn, use this characterization to predict failure and monitor damage in dogbone actuators undergoing various thermomechanical loading paths. Calibration data was collected from constant load, full cycle tests ranging from 200-600MPa. Subsequently, actuator lifetimes were predicted for four additional loading paths. These loading paths consisted of linearly varying load with full transformation (300-500MPa) and step loads which transition from zero stress to 300-400MPa at various martensitic volume fractions. Thermal cycling was achieved via resistive heating and convective cooling and was controlled via a state machine developed in LabVIEW. A previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current and local stress and actuation strain states, was utilized. This form allows the model to be utilized for specimens undergoing complex loading paths. Agreement between experiments and simulations is discussed.

  9. Evaluation of plane bending fatigue damage in metallic plates using the thin-film flux-gate magnetic sensor

    NASA Astrophysics Data System (ADS)

    Oka, M.; Yakushiji, T.; Tsuchida, Y.; Enokizono, M.

    2002-05-01

    To estimate the amount of fatigue damage in metallic plates such as steel and stainless steel, we have investigated the relationship between the amount of plane bending fatigue damage and residual magnetization. The magnetic flux density in the Z component (Bz) at 1 mm above a specimen caused by residual magnetization is measured by using a thin-film flux-gate magnetic sensor. From the results of our experiment, the magnetic flux density has clear dependence on the increase of bending stress and the number of stress cycles in austenitic stainless steel. The distribution of Bz on steel plates is changed by the amount of plane bending fatigue damage. But, the relationship between the change of Bz and the number of stress cycles is not clear in the case of steel plates. In this paper, the relationship between the amount of plane bending fatigue damage and residual magnetization in metallic plates is discussed.

  10. A continuum damage model of fatigue-induced damage in laminated composites

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.; Allen, David H.

    1988-01-01

    A model is presented which predicts the stress-strain behavior of continuous fiber reinforced laminated composites in the presence of microstructural damage. The model is based on the concept of continuum damage mechanics and uses internal state variables to characterize the various damage modes. The associated internal state variable growth laws are mathematical models of the loading history induced development of microstructural damage. The model is demonstrated by using it to predict the response of damaged AS-4/3502 graphite/epoxy laminate panels.

  11. 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.

  12. Systematic error in mechanical measures of damage during four-point bending fatigue of cortical bone.

    PubMed

    Landrigan, Matthew D; Roeder, Ryan K

    2009-06-19

    Accumulation of fatigue microdamage in cortical bone specimens is commonly measured by a modulus or stiffness degradation after normalizing tissue heterogeneity by the initial modulus or stiffness of each specimen measured during a preloading step. In the first experiment, the initial specimen modulus defined using linear elastic beam theory (LEBT) was shown to be nonlinearly dependent on the preload level, which subsequently caused systematic error in the amount and rate of damage accumulation measured by the LEBT modulus degradation. Therefore, the secant modulus is recommended for measurements of the initial specimen modulus during preloading. In the second experiment, different measures of mechanical degradation were directly compared and shown to result in widely varying estimates of damage accumulation during fatigue. After loading to 400,000 cycles, the normalized LEBT modulus decreased by 26% and the creep strain ratio decreased by 58%, but the normalized secant modulus experienced no degradation and histology revealed no significant differences in microcrack density. The LEBT modulus was shown to include the combined effect of both elastic (recovered) and creep (accumulated) strain. Therefore, at minimum, both the secant modulus and creep should be measured throughout a test to most accurately indicate damage accumulation and account for different damage mechanisms. Histology revealed indentation of tissue adjacent to roller supports, with significant sub-surface damage beneath large indentations, accounting for 22% of the creep strain on average. The indentation of roller supports resulted in inflated measures of the LEBT modulus degradation and creep. The results of this study suggest that investigations of fatigue microdamage in cortical bone should avoid the use of four-point bending unless no other option is possible. PMID:19394019

  13. 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.

    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.

  14. Estimation of the damaging energy under creep-fatigue interaction conditions in 1Cr-Mo-V steel

    SciTech Connect

    Jeong, C.Y.; Nam, S.W.

    1999-02-05

    1Cr-Mo-V steel is widely used in power-generating plants for components which operate at high temperatures. Since many components used in power plants are subjected to complex loading cycles at high temperatures, high temperature low-cycle fatigue (LCF) experiments with hold time can be very meaningful tests for understanding the creep-fatigue interaction phenomenon under complex loading conditions. Therefore, in the study of creep-fatigue interaction, a damage formation mechanism is important in understanding a prediction for fatigue lives. In this study an estimation of the damaging energy is tried by using the power law relation between the fatigue life and the hysteresis loop energy, and the quantitative values of it are compared with the fractured area per cycle, with a scanning electron microscope (SEM) analysis.

  15. Structural health monitoring of wind turbine blades

    NASA Astrophysics Data System (ADS)

    Rumsey, Mark A.; Paquette, Joshua A.

    2008-03-01

    As electric utility wind turbines increase in size, and correspondingly, increase in initial capital investment cost, there is an increasing need to monitor the health of the structure. Acquiring an early indication of structural or mechanical problems allows operators to better plan for maintenance, possibly operate the machine in a de-rated condition rather than taking the unit off-line, or in the case of an emergency, shut the machine down to avoid further damage. This paper describes several promising structural health monitoring (SHM) techniques that were recently exercised during a fatigue test of a 9 meter glass-epoxy and carbon-epoxy wind turbine blade. The SHM systems were implemented by teams from NASA Kennedy Space Center, Purdue University and Virginia Tech. A commercial off-the-shelf acoustic emission (AE) NDT system gathered blade AE data throughout the test. At a fatigue load cycle rate around 1.2 Hertz, and after more than 4,000,000 fatigue cycles, the blade was diagnostically and visibly failing at the out-board blade spar-cap termination point at 4.5 meters. For safety reasons, the test was stopped just before the blade completely failed. This paper provides an overview of the SHM and NDT system setups and some current test results.

  16. Transition from dislocation glide to creep controlled damage in fatigued thin Cu films

    NASA Astrophysics Data System (ADS)

    Trinks, C.; Volkert, C. A.

    2013-09-01

    The ultra-high cycle fatigue behavior of supported Cu films with thicknesses between 40 and 360 nm has been investigated using a novel atomic force microscope (AFM)-based resonance method. The damage created under strain controlled fatigue loading is investigated as a function of applied strain, film thickness, and cycle numbers up to 5 1010. For films thicker than 100 nm, extrusions and boundary cracks limit the fatigue performance but only appear above a threshold in the applied strain amplitude which scales inversely with the square root of the film thickness. The extrusion formation is attributed to dislocation activation. The grain boundary cracks are replaced by grain boundary grooves in films of 100 nm and thinner. The grooves are believed to form by diffusion mediated creep processes, similar to observations at higher temperatures but here driven by cyclic stresses and capillarity, and become detectable once the accumulated plastic strain exceeds a critical value. These results indicate that due to creep processes, thinner films can be less resistant to fatigue than thicker films, particularly for large cycle numbers.

  17. Fatigue damage estimate comparisons for northern European and US wind farm loading environments

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.; Kelley, N. D.

    Typical loading histories associated with wind turbine service environments in northern Europe and within a large wind farm in the continental US were recently compared by Kelley using the WISPER (Ten Have) loading standard and its development protocol. In this study, an equivalent load spectrum for a US wind farm was developed by applying the WISPER development protocol to representative service load histories collected from two adjacent turbines operating within a large wind farm in San Gorgonio Pass, California. The results of this study showed that turbines operating in the California wind farm experience many more loading cycles with larger peak-to-peak values for the same mean wind speed classification than their European counterparts. In this paper, the impact of the two WISPER-protocol fatigue-load spectra on service lifetime predictions are used to compare and contrast the impact of the two loading environments with one another. The service lifetime predictions are made using the LIFE2 Fatigue Analysis Code (Sutherland and Schluter), with the fatigue properties of typical fiber glass composite blade materials. Additional analyses, based on rainflow counted time histories from the San Gorgonio turbines, are also used in the comparisons. In general, these results indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. The authors conclude that there are fundamental differences in the two service environments.

  18. Fatigue damage estimate comparisons for northern European and U.S. wind farm loading environments

    SciTech Connect

    Sutherland, H.J.; Kelley, N.D.

    1995-05-01

    Typical loading histories associated with wind turbine service environments in northern Europe and within a large wind farm in the continental US were recently compared by Kelley (1995) using the WISPER [Ten Have, 1992] loading standard and its development protocol. In this study, an equivalent load spectrum for a US wind farm was developed by applying the WISPER development protocol to representative service load histories collected from two adjacent turbines operating within a large wind farm in San Gorgonio Pass, California. The results of this study showed that turbines operating in the California wind farm experience many more loading cycles with larger peak-to-peak values for the same mean wind speed classification than their European counterparts. In this paper, the impact of the two WISPER-protocol fatigue-load spectra on service lifetime predictions are used to compare and contrast the impact of the two loading environments with one another. The service lifetime predictions are made using the LIFE2 Fatigue Analysis Code [Sutherland and Schluter, 1989] with the fatigue properties of typical fiber glass composite blade materials. Additional analyses, based on rainflow counted time histories from the San Gorgonio turbines, are also used in the comparisons. In general, these results indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a US wind farm site; i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a US wind farm site. The authors conclude that there are fundamental differences in the two service environments.

  19. Fatigue damage of notched boron/epoxy laminates under constant-amplitude loading

    NASA Technical Reports Server (NTRS)

    Roderick, G. L.; Whitcomb, J. D.

    1977-01-01

    Fatigue damage in (0, plus or minus 45) and (0, plus or minus 45, 90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy. In addition, limited tests for residual strength and stiffness were performed. Initially, fatigue damage in both (0, plus or minus 45) and (0, plus or minus 45, 90) laminates occurred as intralaminar cracks around the edge of the hole. Then, whenever further damage developed, intralaminar cracks in the plus or minus 45-deg plies began to propagate from the edge of the hole. Finally, in both types of laminates, primarily plus or minus 45-deg fibers broke (prior to two-piece failure) where intralaminar cracks in the plus or minus 45-deg plies had occurred. In the (0, plus or minus 45) laminates, the 45-deg plies developed intralaminar and transthickness cracks along lines parallel to the loading axis and tangent to the hole in the test specimen. This damage, which was most pronounced under compressive loads, had little effect on either strength or stiffness. In contrast, in the (0, plus or minus 45, 90) laminates, the plus or minus 45-deg plies developed intralaminar cracks transverse to the loading axis.

  20. Fatigue

    MedlinePLUS

    ... sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of not caring ... and drink plenty of water throughout the day. Exercise regularly. Learn better ways to relax. Try yoga ...

  1. The welding method repair and improving of low pressure steam turbine blades damaged by erosion

    SciTech Connect

    Mazur, Z.; Kubiak, J.; Cristalinas, V.M.

    1994-12-31

    The development of a welding technology for the butt welding of 6B cobalt-bearing Stellite solid bar-nose erosion shields to the leading edges of low pressure steam turbine moving blades is described. The welded solid bar-nose design was incorporated to improve erosion resistance and eliminate shield loss associated with the previously brazed shields. The repair technology and refurbishment of the L-O blades of a 300 MW steam turbine is fully described. The repair process included the blade geometry measurement by a 3D digital measuring machine, the design of a welded joint between the Stellite solid bar-nose and the blade leading edge, cutting off of worn blade leading edges, manufacture of the solid Stellite inserts, deposition of welds, stress relief, and blade polishing to recover the original profile. Finally quality control including natural frequency tests before and after the repair, and x-ray tests were applied. Also, the special jigs and tools for fabrication were designed.

  2. Evaluation of fatigue damage accumulation in composites via linear and nonlinear guided wave methods

    NASA Astrophysics Data System (ADS)

    Zhao, Jinling; Chillara, Vamshi; Cho, Hwanjeong; Qiu, Jinhao; Lissenden, Cliff

    2016-02-01

    For non-destructive evaluation (NDE) of fatigue damage accumulation in composites, this research proposed a combined linear and a nonlinear ultrasonic guided wave method. For the linear Lamb waves approach, a laser-generation based imaging system (LGBI) is utilized to measure the phase velocities of guided waves in composites. The elastic moduli of the specimen are then obtained by inverting the measured phase velocities using genetic algorithms (GAs). The variation of the above two parameters (phase velocity and elastic moduli), together with the guided wave amplitudes, are then observed during the fatigue process. Nonlinear second harmonics in composites are studied theoretically and numerically. A third-order strain energy function of transversely isotropic materials is expressed by five invariants of the Green-Lagrange strain tensor. Results enable intelligent selection of primary modes for cumulative second harmonics generation. Meanwhile, finite element simulations are conducted to characterize second harmonics in light of the theory.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Bolander, Nathan; Haynes, Chris; Toms, Allison M.

    2011-01-01

    Research was performed to determine if a diagnostic tool for detecting fatigue damage of helicopter tapered roller bearings can be used to determine remaining useful life (RUL). The taper roller bearings under study were installed on the tail gearbox (TGB) output shaft of UH- 60M helicopters, removed from the helicopters and subsequently installed in a bearing spall propagation test rig. The diagnostic tool was developed and evaluated experimentally by collecting oil debris data during spall progression tests on four bearings. During each test, data from an on-line, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results from the four bearings tested indicate that measuring the debris generated when a bearing outer race begins to spall can be used to indicate bearing damage progression and remaining bearing life.

  8. A method for the assessment of operational severity for a high pressure turbine blade of an aero-engine

    NASA Astrophysics Data System (ADS)

    Haslam, Anthony; Abu, Abdullahi; Laskaridis, Panagiotis

    2015-12-01

    This paper provides a tool for the estimation of the operational severity of a high pressure turbine blade of an aero engine. A multidisciplinary approach using aircraft/ engine performance models which provide inputs to a thermo-mechanical fatigue damage model is presented. In the analysis, account is taken of blade size, blade metal temperature distribution, relevant heat transfer coefficients and mechanical and thermal stresses. The leading edge of the blade is selected as the critical part in the estimation of damage severity for different design and operational parameters. The study also suggests a method for production of operational severity data for the prediction of maintenance intervals.

  9. 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 1010C. 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, 100C, 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.

  10. 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.

  11. 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.

  12. Activation of Bone Remodeling after Fatigue: Differential Response to Linear Microcracks and Diffuse Damage

    PubMed Central

    Herman, B.C.; Cardoso, L.; Majeska, R.J.; Jepsen, K.J.; Schaffler, M.B

    2010-01-01

    Recent experiments point to two predominant forms of fatigue microdamage in bone: linear microcracks (tens to a few hundreds microns in length) and diffuse damage (patches of diffuse stain uptake in fatigued bone comprised of clusters of sublamellar-sized cracks). The physiological relevance of diffuse damage in activating bone remodeling is not known. In this study microdamage amount and type were varied to assess whether linear or diffuse microdamage have similar effects on the activation of intracortical resorption. Activation of resorption was correlated to the number of linear microcracks (Cr.Dn) in the bone (R2=0.60, p<0.01). In contrast, there was no activation of resorption in response to diffuse microdamage alone. Furthermore, there was no significant change in osteocyte viability in response to diffuse microdamage, suggesting that osteocyte apoptosis, which is know to activate remodeling at typical linear microcracks in bone, does not result from sublamellar damage. These findings indicate that inability of diffuse microdamage to activate resorption may be due to lack of a focal injury response. Finally, we found that duration of loading does not affect the remodeling response. In conclusion, our data indicate that osteocytes activate resorption in response to linear microcracks but not diffuse microdamage, perhaps due to lack of a focal injury-induced apoptotic response. PMID:20633708

  13. Fatigue damage characterization of braided and woven fiber reinforced polymer matrix composites at room and elevated temperatures

    NASA Astrophysics Data System (ADS)

    Montesano, John

    The use of polymer matrix composites (PMC) for manufacturing primary load-bearing structural components has significantly increased in many industrial applications. Specifically in the aerospace industry, PMCs are also being considered for elevated temperature applications. Current aerospace-grade composite components subjected to fatigue loading are over-designed due to insufficient understanding of the material failure processes, and due to the lack of available generic fatigue prediction models. A comprehensive literature survey reveals that there are few fatigue studies conducted on woven and braided fabric reinforced PMC materials, and even fewer at elevated temperatures. It is therefore the objective of this study to characterize and subsequently model the elevated temperature fatigue behaviour of a triaxial braided PMC, and to investigate the elevated temperature fatigue properties of two additional woven PMCs. An extensive experimental program is conducted using a unique test protocol on the braided and woven composites, which consists of static and fatigue testing at various test temperatures. The development of mechanically-induced damage is monitored using a combination of non-destructive techniques which included infrared thermography, fiber optic sensors and edge replication. The observed microscopic damage development is quantified and correlated to the exhibited macroscopic material behaviour at all test temperatures. The fiber-dominated PMC materials considered in this study did not exhibit notable time- or temperature-dependent static properties. However, fatigue tests reveal that the local damage development is in fact notably influenced by temperature. The elevated temperature environment increases the toughness of the thermosetting polymers, which results in consistently slower fatigue crack propagation rates for the respective composite materials. This has a direct impact on the stiffness degradation rate and the fatigue lives for the braided and woven composites under investigation. The developed analytical fatigue damage prediction model, which is based on actual observed damage mechanisms, accurately predicted the development of damage and the corresponding stiffness degradation for the braided PMC, for all test temperatures. An excellent correlation was found between the experimental and the predicted results to within a 2% accuracy. The prediction model adequately captured the local temperature-induced phenomenon exhibited by the braided PMC material. The results presented in this study are novel for a braided composite material subjected to elevated temperature fatigue.

  14. Estimation of Temperature Conductivity Coefficient Impact upon Fatigue Damage of Material

    NASA Astrophysics Data System (ADS)

    Bibik, V.; Galeeva, A.

    2015-09-01

    In the paper we consider the peculiarities of adhesive wear of cutting tools. Simulation of heat flows in the cutting zone showed that, as thermal conduction and heat conductivity of tool material grow, the heat flows from the front and back surfaces to tool holder will increase and so, the temperature of the contact areas of the tool will lower. When estimating the adhesive wear rate of cemented-carbide tool under the cutting rates corresponding to the cutting temperature of up to 900 C, it is necessary to take the fatigue character of adhesive wear into consideration. The process of accumulation and development of fatigue damage is associated with micro- and macroplastic flowing of material, which is determined by the processes of initiation, motion, generation, and elimination of line defects - dislocations. Density of dislocations grows with increase of the loading cycles amount and increase of load amplitude. Growth of dislocations density leads to loosening of material, formation of micro- and macrocracks. The heat capacity of material grows as the loosening continues. In the given paper the authors prove theoretically that temperature conductivity coefficient which is associated with heat capacity of material, decreases as fatigue wear grows.

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

    NASA Technical Reports Server (NTRS)

    Ferguson, Milton W.

    1994-01-01

    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.

  16. Fatigue crack growth spectrum simplification: Facilitation of on-board damage prognosis systems

    NASA Astrophysics Data System (ADS)

    Adler, Matthew Adam

    2009-12-01

    Better lifetime predictions of systems subjected to fatigue loading are needed in support of the optimization of the costs of life-cycle engineering. In particular, the climate is especially encouraging for the development of safer aircraft. One issue is that aircraft experience complex fatigue loading and current methods for the prediction of fatigue damage accumulation rely on intensive computational tools that are not currently carried onboard during flight. These tools rely on complex models that are made more difficult by the complicated load spectra themselves. This presents an overhead burden as offline analysis must be performed at an offsite facility. This architecture is thus unable to provide online, timely information for on-board use. The direct objective of this research was to facilitate the real-time fatigue damage assessments of on-board systems with a particular emphasis on aging aircraft. To achieve the objective, the goal of this research was to simplify flight spectra. Variable-amplitude spectra, in which the load changes on a cycle-by-cycle basis, cannot readily be supported by an onboard system because the models required to predict fatigue crack growth during variable-amplitude loading are too complicated. They are too complicated because variable-amplitude fatigue crack growth analysis must be performed on a cycle-by-cycle basis as no closed-form solution exists. This makes these calculations too time-consuming and requires impractical, heavy onboard systems or offsite facilities. The hypothesis is to replace a variable-amplitude spectrum with an equivalent constant-amplitude spectrum. The advantage is a dramatic reduction in the complexity of the problem so that damage predictions can be made onboard by simple, fast calculations in real-time without the need to add additional weight to the aircraft. The intent is to reduce the computational burden and facilitate on-board projection of damage evolution and prediction for the accurate monitoring and management of aircraft. A spectrum reduction method was proposed and experimentally validated that reduces a variable-amplitude spectrum to a constant-amplitude equivalent. The reduction from a variable-amplitude (VA) spectrum to a constant-amplitude equivalent (CAE) was proposed as a two-part process. Preliminary spectrum reduction is first performed by elimination of those loading events shown to be too negligible to significantly contribute to fatigue crack growth. This is accomplished by rainflow counting. The next step is to calculate the appropriate, equivalent maximum and minimum loads by means of a root-mean-square average. This reduced spectrum defines the CAE and replaces the original spectrum. The simplified model was experimentally shown to provide the approximately same fatigue crack growth as the original spectrum. Fatigue crack growth experiments for two dissimilar aircraft spectra across a wide-range of stress-intensity levels validated the proposed spectrum reduction procedure. Irrespective of the initial K-level, the constant-amplitude equivalent spectra were always conservative in crack growth rate, and were so by an average of 50% over the full range tested. This corresponds to a maximum 15% overestimation in driving force Delta K. Given other typical sources of scatter that occur during fatigue crack growth, a consistent 50% conservative prediction on crack growth rate is very satisfying. This is especially attractive given the reduction in cost gained by the simplification. We now have a seamless system that gives an acceptably good approximation of damage occurring in the aircraft. This contribution is significant because in a very simple way we now have given a path to bypass the current infrastructure and ground-support requirements. The decision-making is now a lot simpler. In managing an entire fleet we now have a workable system where the strength is in no need for a massive, isolated computational center. The fidelity of the model gives credence because experimental data show that the approximate spectrum model captures the essential spectrum response. The discrepancy between the models is such that an experimental parameter is sufficient to converge the models. The proposed spectrum reduction procedure significantly mitigates the computational burden and allows for the probabilistic assessment of fatigue in real-time. This, in turn, provides support for crack-growth monitoring systems in facilitation of aircraft prognosis and fleet management.

  17. An overview of elevated temperature damage mechanisms and fatigue behavior of a unidirectional SCS-6/Ti-15-3 composite

    NASA Technical Reports Server (NTRS)

    Castelli, Michael G.; Gayda, John

    1993-01-01

    The fatigue behavior of a unidirectionally reinforced titanium matrix composite (TMC), SiC/Ti-15-3, was thoroughly characterized to support life prediction modeling of advanced TMC disks designed for gas turbine engine applications. The results of this coupon-level experimental investigation are reviewed. On a stress basis, the isothermal fatigue behavior of the (0 deg) TMC revealed significant improvements over the unreinforced matrix. In contrast, the (90 deg) TMC exhibited degraded properties and lives for similar comparisons. This was attributed to the weak fiber/matrix interfacial bond. Encasing the (0 deg) TMC with a Ti-15-3 case did not affect isothermal fatigue lives at higher strain levels. However, at lower strain levels, rapid initiation and propagation of large fatigue cracks in the case degraded the fatigue lives. Thermomechanical fatigue (TMF) lives were significantly reduced for the (0 deg) TMC when compared to isothermal lives. At high strains, in-phase TMF produced extremely short lives. This degradation was attributed to fiber overload failures brought about by stress relaxation in the matrix. At low strains, out-of-phase TMF conditions became life limiting. Environment-assisted surface cracking was found to accelerate fatigue failure. This produced extensive matrix damage with minimal fiber damage. For the (90 deg) TMC, TMF conditions did not promote an additional degradation in cyclic life beyond that observed under isothermal conditions.

  18. 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.

  19. Experimental Investigations on Fatigue Damage and Residual Properties of Interacting Notched Woven E-Glass/Epoxy Composite

    NASA Astrophysics Data System (ADS)

    Bhaskara Rao, Pathakokila; Rama Krishna, Avasarala; Ramji, Koona; Satya Devi, Ambadipudi

    2015-10-01

    The interacting notched laminates of plain weave E-glass fiber reinforced with epoxy were fatigued at predetermined frequency in tension-tension to investigate the fatigue damage and residual properties. The results from stress-life curves summarize that damage growing around the notches due to stress concentration is the underlying cause for the variation in fatigue strengths among the geometrically different specimens considered. The residual strength and modulus decay with respect to cycle number at 50 % of the ultimate tensile strength were investigated. It is evident from the experimental data that the residual strength decreases with cycle number and increases due to redistribution of stress around the notches. The detailed study of the damage development under cyclic loads also explains the causes of modulus reduction for all the laminate geometries.

  20. An advanced test technique to quantify thermomechanical fatigue damage accumulation in composite materials

    NASA Technical Reports Server (NTRS)

    Castelli, Michael G.

    1993-01-01

    A mechanical test technique was developed to assist in quantifying the accumulation of damage in composite materials during thermomechanical fatigue (TMF) cycling. This was accomplished by incorporating definitive elastic mechanical property measurements into an ongoing load-controlled TMF test without disturbing the test specimen or significantly altering the test conditions. The technique allows two fundamental composite properties consisting of the isothermal elastic static moduli and the macroscopic coefficient of thermal expansion (CTE) to be measured and collected as functions of the TMF cycles. The specific implementation was incorporated into the commonly employed idealized in-phase and out-of-phase TMF cycles. However, the techniques discussed could be easily implemented into any form of load-controlled TMF mission cycle. By quantifying the degradations of these properties, tremendous insights are gained concerning the progression of macroscopic composite damage and often times the progression of damage within a given constituent. This information should also be useful for the characterization and essential for the verification of analytical damage modeling methodologies. Several examples utilizing this test technique are given for three different fiber lay-ups of titanium metal matrix composites.

  1. An advanced test technique to quantify thermomechanical fatigue damage accumulation in composite materials. Final report

    SciTech Connect

    Castelli, M.G.

    1993-08-01

    A mechanical test technique was developed to assist in quantifying the accumulation of damage in composite materials during thermomechanical fatigue (TMF) cycling. This was accomplished by incorporating definitive elastic mechanical property measurements into an ongoing load-controlled TMF test without disturbing the test specimen or significantly altering the test conditions. The technique allows two fundamental composite properties consisting of the isothermal elastic static moduli and the macroscopic coefficient of thermal expansion (CTE) to be measured and collected as functions of the TMF cycles. The specific implementation was incorporated into the commonly employed idealized in-phase and out-of-phase TMF cycles. However, the techniques discussed could be easily implemented into any form of load-controlled TMF mission cycle. By quantifying the degradations of these properties, tremendous insights are gained concerning the progression of macroscopic composite damage and often times the progression of damage within a given constituent. This information should also be useful for the characterization and essential for the verification of analytical damage modeling methodologies. Several examples utilizing this test technique are given for three different fiber lay-ups of titanium metal matrix composites.

  2. The effect of lamination-induced stresses on fatigue damage development at internal flaws

    NASA Technical Reports Server (NTRS)

    Reifsnider, K. L.

    1981-01-01

    The effects of stresses induced by the lamination of off-axis plies to O-deg lamina on the development of damage during the fatigue loading of the O-deg plies are discussed. The transverse normal stresses in the plane of the laminae and the laminate created by the laminating constraints when an axial force is applied to the laminate are calculated in terms of a differential Poisson ratio between the ply in question in the unconstrained and constrained states, and significant differences in the constraint environments of an unnotched specimen joined to plies of 45 and 90 deg inclination are noted which correspond to an increase in longitudinal splitting in the 90 deg case and a marked decrease in longitudinal splitting in the 45 deg case. If a notch is present, shear and crack-opening damage is found to be very effectively suppressed in 45-deg laminates, and less so in the 90-deg case. It is pointed out that whereas the 45-deg laminate represents the least damage situation, it does not have the greatest notched strength. It is concluded that an understanding and prediction of damage development in laminates requires knowledge of the stress fields caused by the lamination constraints.

  3. Integrated approach for stress based lifing of aero gas turbine blades

    NASA Astrophysics Data System (ADS)

    Abu, Abdullahi Obonyegba

    In order to analyse the turbine blade life, the damage due to the combined thermal and mechanical loads should be adequately accounted for. This is more challenging when detailed component geometry is limited. Therefore, a compromise between the level of geometric detail and the complexity of the lifing method to be implemented would be necessary. This research focuses on how the life assessment of aero engine turbine blades can be done, considering the balance between available design inputs and adequate level of fidelity. Accordingly, the thesis contributes to developing a generic turbine blade lifing method that is based on the engine thermodynamic cycle; as well as integrating critical design/technological factors and operational parameters that influence the aero engine blade life. To this end, thermo-mechanical fatigue was identified as the critical damage phenomenon driving the life of the turbine blade.. The developed approach integrates software tools and numerical models created using the minimum design information typically available at the early design stages. Using finite element analysis of an idealised blade geometry, the approach captures relevant impacts of thermal gradients and thermal stresses that contribute to the thermo-mechanical fatigue damage on the gas turbine blade. The blade life is evaluated using the Neu/Sehitoglu thermo-mechanical fatigue model that considers damage accumulation due to fatigue, oxidation, and creep. The leading edge is examined as a critical part of the blade to estimate the damage severity for different design factors and operational parameters. The outputs of the research can be used to better understand how the environment and the operating conditions of the aircraft affect the blade life consumption and therefore what is the impact on the maintenance cost and the availability of the propulsion system. This research also finds that the environmental (oxidation) effect drives the blade life and the blade coolant side was the critical location. Furthermore, a parametric and sensitivity study of the Neu/Sehitoglu model parameters suggests that in addition to four previously reported parameters, the sensitivity of the phasing to oxidation damage would be critical to overall blade life..

  4. Fatigue life estimation procedures for the endurance of a cardiac valve prosthesis: stress/life and damage-tolerant analyses.

    PubMed

    Ritchie, R O; Lubock, P

    1986-05-01

    Projected fatigue life analyses are performed to estimate the endurance of a cardiac valve prosthesis under physiological environmental and mechanical conditions. The analyses are conducted using both the classical stress-strain/life and the fracture mechanics-based damage-tolerant approaches, and provide estimates of expected life in terms of initial flaw sizes which may pre-exist in the metal prior to the valve entering service. The damage-tolerant analysis further is supplemented by consideration of the question of "short cracks," which represents a developing area in metal fatigue research, not commonly applied to data in standard engineering design practice. PMID:3724103

  5. Characterization of exposure dependent fatigue crack growth kinetics and damage mechanisms for aluminum alloys

    NASA Astrophysics Data System (ADS)

    Ro, Yunjo

    The effect of environmental exposure [given by the ratio of water vapor pressure to the loading frequency (PH2O/f)] on fatigue crack growth rates (FCGR) and damage mechanisms has been investigated for Al-Cu-Li/Mg alloys tested at constant stress intensity range (DeltaK = KMAX - KMIN). Different exposure dependences of the FCGR are explained by H-embrittlement and 3 rate-limiting processes that are similar for each alloy and aging condition. It is shown that the dislocation slip character (heterogeneous planar vs. wavy) controls FCGR at low to moderate exposures, rather than alloy composition and strengthening precipitate reactivity. However, the benefit of planar slip is significantly reduced at higher exposures. An SEM-based electron backscattered diffraction (EBSD)/stereology method was used to successfully quantify changes in fatigue fracture surface crystallography as a function of exposure for a peak aged Al-Cu-Li alloy and an under-aged Al-Cu-Mg alloy. Near-{111} slip band cracking (SBC) observed under high vacuum conditions is gradually replaced by near-{001}/{011} and high index, {hkl}, cracking planes as PH2O/f is increased. The complete absence of near-{111} SBC at higher exposures suggests H enhanced decohesion rather than slip based damage process enhanced by H. This conclusion was substantiated by direct TEM observation. Focused Ion Beam (FIB) milling was used to produce thin foils for TEM, which successfully revealed the underlying dislocation structure at the crack surface and within surrounding materials in under-aged Al-Cu-Mg tested at exposure conditions of 10 -8 and 50 Pasec. Both conditions exhibit a similar layer of dislocation cells just below the fracture surface which abruptly changes to localized slip bands away from the fracture surface, confirming the presence of a strain gradient at the crack tip. However, the thickness of the substructure layer and slip band width observed at 10-8 Pasec was larger than those observed at 50 Pasec. This infers that less plastic strain accumulation is necessary to produce a fatigue crack extension at high exposures. The dislocation substructure observations also clarify the interpretation of facet crystallography. For instance, the high-index {hkl} crack surface planes produced at higher exposures may be caused by H-enhanced inter/intra-cell structure cracking, based on the observation that the low index crack surface deviates with cell formation just underneath of crack surface. In conclusion, near-{001}/{011) and {hkl} crack surfaces, and lowered plastic strain accumulation in the moist environment imply that fatigue crack growth rates are enhanced by multiple manifestations of H-enhanced decohesion.

  6. Modeling of thermal effects when investigating the thermal fatigue life of the blades of a gas-turbine engine

    NASA Astrophysics Data System (ADS)

    Kravchuk, L. V.

    1982-10-01

    Problems associated with the modeling of the thermal state of gas turbine blades during testing on a gasdynamic test stand are discussed with emphasis on those cases where similarity of the boundary conditions of heat transfer cannot be achieved. A blading design method is proposed which makes it possible to obtain thermal and stressed states close to those observed under actual service conditions in the regions of thermal stress concentration. The required local heat flows are achieved by programmed control of the gas flow temperature.

  7. Ductile Damage and Fatigue Behavior of Semi-Finished Tailored Blanks for Sheet-Bulk Metal Forming Processes

    NASA Astrophysics Data System (ADS)

    Besserer, Hans-Bernward; Hildenbrand, Philipp; Gerstein, Gregory; Rodman, Dmytro; Nürnberger, Florian; Merklein, Marion; Maier, Hans Jürgen

    2016-01-01

    To produce parts from sheet metal with thickened functional elements, bulk forming operations can be employed. For this new process class, the term sheet-bulk metal forming has been established recently. Since sheet-bulk metal forming processes such as orbital forming generates triaxial stress and strain states, ductile damage is induced in the form of voids in the microstructure. Typical parts will experience cyclic loads during service, and thus, the influence of ductile damage on the fatigue life of parts manufactured by orbital forming is of interest. Both the formation and growth of voids were characterized following this forming process and then compared to the as-received condition of the ferritic deep drawing steel DC04 chosen for this study. Subsequent to the forming operation, the specimens were fatigued and the evolution of ductile damage and the rearrangement of the dislocation networks occurring during cyclic loading were determined. It was shown, that despite an increased ductile damage due to the forming process, the induced strain hardening has a positive effect on the fatigue life of the material. However, by analyzing the fatigued specimens a development of the ductile damage by an increasing number of voids and a change in the void shape were detected.

  8. Damage Monitoring of Unidirectional C/SiC Ceramic-Matrix Composite under Cyclic Fatigue Loading using A Hysteresis Loss Energy-Based Damage Parameter at Room and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    The damage evolution of unidirectional C/SiC ceramic-matrix composite (CMC) under cyclic fatigue loading has been investigated using a hysteresis loss energy-based damage parameter at room and elevated temperatures. The experimental fatigue hysteresis modulus and fatigue hysteresis loss energy versus cycle number have been analyzed. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the interface shear stress corresponding to different cycle number and peak stress has been estimated. The experimental evolution of fatigue hysteresis loss energy and fatigue hysteresis loss energy-based damage parameter versus cycle number has been predicted for unidirectional C/SiC composite at room and elevated temperatures. The predicted results of interface shear stress degradation, stress-strain hysteresis loops corresponding to different number of applied cycles, fatigue hysteresis loss energy and fatigue hysteresis loss energy-based damage parameter as a functions of cycle number agreed with experimental data. It was found that the fatigue hysteresis energy-based parameter can be used to monitor the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs.

  9. 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.

  10. Experimental Verification of a Progressive Damage Model for IM7/5260 Laminates Subjected to Tension-Tension Fatigue

    NASA Technical Reports Server (NTRS)

    Coats, Timothy W.; Harris, Charles E.

    1995-01-01

    The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve structurally efficient and economical designs. The purpose of this research is to experimentally verify the application of a continuum damage model to predict progressive damage development in a toughened material system. Damage due to monotonic and tension-tension fatigue was documented for IM7/5260 graphite/bismaleimide laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables to predict stiffness loss in unnotched laminates. A damage dependent finite element code predicted the stiffness loss for notched laminates with good agreement to experimental data. It was concluded that the continuum damage model can adequately predict matrix damage progression in notched and unnotched laminates as a function of loading history and laminate stacking sequence.

  11. Nonlinear ultrasonic measurements with EMATs for detecting pre-cracking fatigue damage

    NASA Astrophysics Data System (ADS)

    Cobb, A.; Capps, M.; Duffer, C.; Feiger, J.; Robinson, K.; Hollingshaus, B.

    2012-05-01

    This paper describes an approach for measuring material degradation using nonlinear acoustics. The importance of this measurement is that prior efforts have shown that the degree of acoustic nonlinearity increases as a function of fatigue damage accumulation. By exploiting this physical mechanism, there is the potential to develop methods for measuring the remaining life of critical components. The challenge with existing approaches for measuring acoustic nonlinearity is that primarily they have only been shown to be successful in a laboratory setting. This paper presents a potential approach for field measurement of acoustic nonlinearity that utilizes Rayleigh waves generated from electromagnetic acoustic transducers (EMATs). Rayleigh waves have unique advantages because the sound propagates along the surface, allowing for application on complex engineering structures. EMATs were used in place of traditional piezoelectric transducers because the sound is generated directly in the metallic structure, eliminating the need for sound coupling fluids that are a source of variability. Custom EMATs were developed and nonlinearity measurements were performed on 410 stainless steel specimens that were subjected to a fatigue process. Some experiments showed an increase in the acoustic nonlinearity of up to 500% compared to the unfatigued value. Other experiments had too much scatter and did not show this relationship consistently due to unanticipated challenges in producing repeatable measurements. Lessons learned from the project effort will be presented to potentially improve the repeatability of the measurement approach. If the scatter can be reduced, this EMAT-based technique could result in a field deployable prognosis tool.

  12. 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

    2010-01-01

    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 [Ed. 's note: See Appendix A-Definitions D were deduced from the time-averaged vibration data and used with the ODM to evaluate their performance for gear fault detection. The NA4 parameter showed to be a very good condition indicator for the detection of gear tooth surface pitting failures. The FM4 and RMS parameters perfomu:d average to below average in detection of gear tooth surface pitting failures. The ODM sensor was successful in detecting a significant 8lDOunt of debris from all the gear tooth pitting fatigue failures. Excluding outliers, the average cumulative mass at the end of a test was 40 mg.

  13. Re-examination of cumulative fatigue damage analysis - An engineering perspective

    NASA Technical Reports Server (NTRS)

    Manson, S. S.; Halford, G. R.

    1986-01-01

    A method which has evolved in the laboratories for the past 20 yr is re-examined with the intent of improving its accuracy and simplicity of application to engineering problems. Several modifications are introduced both to the analytical formulation of the Damage Curve Approach, and to the procedure for modifying this approach to achieve a Double Linear Damage Rule formulation which immensely simplifies the calculation. Improvements are also introduced in the treatment of mean stress for determining fatigue life of the individual events that enter into a complex loading history. While the procedure is completely consistent with the results of numerous two level tests that have been conducted on many materials, it is still necessary to verify applicability to complex loading histories. Caution is expressed that certain phenomenon can also influence the applicability - for example, unusual deformation and fracture modes inherent in complex loading especially if stresses are multiaxial. Residual stresses at crack tips, and metallurgical factors are also important in creating departures from the cumulative damage theories; examples of departures are provided.

  14. Re-examination of cumulative fatigue damage analysis: An engineering perspective

    NASA Technical Reports Server (NTRS)

    Manson, S. S.; Halford, G. R.

    1986-01-01

    A method which has evolved in our laboratories for the past 20 yr is re-examined with the intent of improving its accuracy and simplicity of application to engineering problems. Several modifications are introduced both to the analytical formulation of the Damage Curve Approach, and to the procedure for modifying this approach to achieve a Double Linear Damage Rule formulation which immensely simplifies the calculation. Improvements are also introduced in the treatment of mean stress for determining fatigue life of the individual events that enter into a complex loading history. While the procedure is completely consistent with the results of numerous two level tests that have been conducted on many materials, it is still necessary to verify applicability to complex loading histories. Caution is expressed that certain phenomena can also influence the applicability - for example, unusual deformation and fracture modes inherent in complex loading - especially if stresses are multiaxial. Residual stresses at crack tips, and metallurgical factors are also important in creating departures from the cumulative damage theories; examples of departures are provided.

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

    PubMed Central

    Zuluaga-Ramrez, Pablo; Arconada, lvaro; Frvel, Malte; Belenguer, Toms; Salazar, Flix

    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

  16. Torsional and biaxial (tension-torsion) fatigue damage mechanisms in Waspaloy at room temperature

    NASA Technical Reports Server (NTRS)

    Jayaraman, N.; Ditmars, M. M.

    1989-01-01

    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 and nonproportional cyclic conditions. The deformation behavior under these different cyclic conditions was 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, nonproportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under nonproportional cyclic conditions, deformation was through multiple slip, as opposed to 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.

  17. Optical sensing of the fatigue damage state of CFRP under realistic aeronautical load sequences.

    PubMed

    Zuluaga-Ramrez, Pablo; Arconada, lvaro; Frvel, Malte; Belenguer, Toms; Salazar, Flix

    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

  18. Residual strength and crack propagation tests on C-130 airplane center wings with service-imposed fatigue damage

    NASA Technical Reports Server (NTRS)

    Snider, H. L.; Reeder, F. L.; Dirkin, W. J.

    1972-01-01

    Fourteen C-130 airplane center wings, each containing service-imposed fatigue damage resulting from 4000 to 13,000 accumulated flight hours, were tested to determine their fatigue crack propagation and static residual strength characteristics. Eight wings were subjected to a two-step constant amplitude fatigue test prior to static testing. Cracks up to 30 inches long were generated in these tests. Residual static strengths of these wings ranged from 56 to 87 percent of limit load. The remaining six wings containing cracks up to 4 inches long were statically tested as received from field service. Residual static strengths of these wings ranged from 98 to 117 percent of limit load. Damage-tolerant structural design features such as fastener holes, stringers, doublers around door cutouts, and spanwise panel splices proved to be effective in retarding crack propagation.

  19. Simulation of long-term fatigue damage in bioprosthetic heart valves: effects of leaflet and stent elastic properties.

    PubMed

    Martin, Caitlin; Sun, Wei

    2014-08-01

    One of the major failure modes of bioprosthetic heart valves (BHVs) is noncalcific structural deterioration due to fatigue of the tissue leaflets; yet, the mechanisms of fatigue are not well understood. BHV durability is primarily assessed based on visual inspection of the leaflets following accelerated wear testing. In this study, we developed a computational framework to simulate BHV leaflet fatigue, which is both efficient and quantitative, making it an attractive alternative to traditional accelerated wear testing. We utilize a phenomenological soft tissue fatigue damage model developed previously to describe the stress softening and permanent set of the glutaraldehyde-treated bovine pericardium leaflets in BHVs subjected to cyclic loading. A parametric study was conducted to determine the effects of altered leaflet and stent elastic properties on the fatigue of the leaflets. The simulation results show that heterogeneity of the leaflet elastic properties, poor leaflet coaptation, and little stent-tip deflection may accelerate leaflet fatigue, which agrees with clinical findings. Therefore, the developed framework may be an invaluable tool for evaluating leaflet durability in new tissue valve designs, including traditional BHVs as well as new transcatheter valves. PMID:24092257

  20. Simulation of long-term fatigue damage in bioprosthetic heart valves: effects of leaflet and stent elastic properties

    PubMed Central

    Martin, Caitlin

    2014-01-01

    One of the major failure modes of bioprosthetic heart valves (BHVs) is noncalcific structural deterioration due to fatigue of the tissue leaflets; yet, the mechanisms of fatigue are not well understood. BHV durability is primarily assessed based on visual inspection of the leaflets following accelerated wear testing. In this study, we developed a computational framework to simulate BHV leaflet fatigue, which is both efficient and quantitative, making it an attractive alternative to traditional accelerated wear testing. We utilize a phenomenological soft tissue fatigue damage model developed previously to describe the stress softening and permanent set of the glutaraldehyde-treated bovine pericardium leaflets in BHVs subjected to cyclic loading. A parametric study was conducted to determine the effects of altered leaflet and stent elastic properties on the fatigue of the leaflets. The simulation results show that heterogeneity of the leaflet elastic properties, poor leaflet coaptation, and little stent-tip deflection may accelerate leaflet fatigue, which agrees with clinical findings. Therefore, the developed framework may be an invaluable tool for evaluating leaflet durability in new tissue valve designs, including traditional BHVs as well as new transcatheter valves. PMID:24092257

  1. High-fidelity Modeling of Local Effects of Damage for Derated Offshore Wind Turbines

    NASA Astrophysics Data System (ADS)

    Richards, Phillip W.; Griffith, D. Todd; Hodges, Dewey H.

    2014-06-01

    Offshore wind power production is an attractive clean energy option, but the difficulty of access can lead to expensive and rare opportunities for maintenance. As part of the Structural Health and Prognostics Management (SHPM) project at Sandia National Laboratories, smart loads management (controls) are investigated for their potential to increase the fatigue life of offshore wind turbine rotor blades. Derating refers to altering the rotor angular speed and blade pitch to limit power production and loads on the rotor blades. High- fidelity analysis techniques like 3D finite element modeling (FEM) should be used alongside beam models of wind turbine blades to characterize these control strategies in terms of their effect to mitigate fatigue damage and extend life of turbine blades. This study will consider a commonly encountered damage type for wind turbine blades, the trailing edge disbond, and show how FEM can be used to quantify the effect of operations and control strategies designed to extend the fatigue life of damaged blades. The Virtual Crack Closure Technique (VCCT) will be used to post-process the displacement and stress results to provide estimates of damage severity/criticality and provide a means to estimate the fatigue life under a given operations and control strategy.

  2. Comparison of strength and load-based methods for testing wind turbine blades

    SciTech Connect

    Musial, W.D.; Clark, M.E.; Egging, N.

    1996-11-01

    The purpose of this paper is to compare two methods of blade test loading and show how they are applied in an actual blade test. Strength and load-based methods were examined to determine the test load for an Atlantic Orient Corporation (AOC) 15/50 wind turbine blade for fatigue and static testing. Fatigue load-based analysis was performed using measured field test loads extrapolated for extreme rare events and scaled to thirty-year spectra. An accelerated constant amplitude fatigue test that gives equivalent damage at critical locations was developed using Miner`s Rule and the material S-N curves. Test load factors were applied to adjust the test loads for uncertainties, and differences between the test and operating environment. Similar analyses were carried, out for the strength-based fatigue test using the strength of the blade and the material properties to determine the load level and number of constant amplitude cycles to failure. Static tests were also developed using load and strength criteria. The resulting test loads were compared and contrasted. The analysis shows that, for the AOC 15/50 blade, the strength-based test loads are higher than any of the static load-based cases considered but were exceeded in the fatigue analysis for a severe hot/wet environment.

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

    SciTech Connect

    Park, Gyuhae; Taylor, Stuart G; Farinholt, Kevin M; Farrar, Charles R

    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.

  4. Detection of Tight Fatigue Cracks at the Root of Dampers in Fan Blades Using Sonic IR Inspection: A Feasibility Demonstration

    NASA Astrophysics Data System (ADS)

    Hassan, W.; Homma, C.; Wen, Z.; Vensel, F.; Hogan, B.

    2007-03-01

    The results of a feasibility demonstration for the detection of tight cracks at the root of dampers in fan blades are presented. The primary purpose of these dampers is to reduce undesired vibrations of the fan blades during operation. Unfortunately cracks can develop at the root of these dampers in a very tight radius which renders their detection using other NDE techniques like Fluorescent Penetrant Inspection (FPI) and Eddy Current (EC) rather unreliable and sometimes not possible. SONIC Infra Red (IR) is proposed as an alternate effective detection technique in such situations. An optimized SONIC IR inspection technique using the SIEMAT and Smart SIEMAT systems is presented. An empirical study was conducted to determine the optimal excitation position for the ultrasonic horn that results in the highest crack detectability. Finite Element Modeling (FEM) was then used to further understand the actual vibrational modes that are needed to ensure detectability of such cracks and to validate the empirical results. A preliminary result from the Smart SIEMAT system that is based on a resonance frequency excitation is also included.

  5. Modelling of pavement materials on steel decks using the five-point bending test: Thermo mechanical evolution and fatigue damage

    NASA Astrophysics Data System (ADS)

    Arnaud, L.; Houel, A.

    2010-06-01

    This paper deals with the modelling of wearing courses on steel orthotropic decks such as the Millau viaduct in France. This is of great importance when dealing with durability: due to the softness of such a support, the pavement is subjected to considerable strains that may generate top-down cracks in the layer at right angles of the orthotropic plate stiffeners and shear cracks at the interface between pavement and steel. Therefore, a five-point bending fatigue test was developed and improved since 2003 at the ENTPE laboratory, to test different asphalt concrete mixes. This study aims at modelling the mechanical behavior of the wearing course throughout the fatigue test by a finite element method (Comsol Multiphysics software). Each material - steel, sealing sheet, asphalt concrete layer - is considered and modelled. The modelling of asphalt concrete is complex since it is a heterogeneous material, a viscoelastic medium and it thermosensitive. The actual characteristics of the asphalt concrete (thermo physical parameter and viscoelastic complex modulus) are determined experimentally on cylindrical cores. Moreover, a damage law based on Miner's damage is included in the model. The modelling of the fatigue test leads to encouraging results. Finally, results from the model are compared to the experimental data obtained from the five-point bending fatigue test device. The experimental data are very consistent with the numerical simulation.

  6. Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material

    NASA Technical Reports Server (NTRS)

    Vandermey, Nancy E.; Morris, Don H.; Masters, John E.

    1991-01-01

    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.

  7. 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

  8. Stochastic propagation of an array of parallel cracks: Exploratory work on matrix fatigue damage in composite laminates

    SciTech Connect

    Williford, R.E.

    1989-09-01

    Transverse cracking of polymeric matrix materials is an important fatigue damage mechanism in continuous-fiber composite laminates. The propagation of an array of these cracks is a stochastic problem usually treated by Monte Carlo methods. However, this exploratory work proposes an alternative approach wherein the Monte Carlo method is replaced by a more closed-form recursion relation based on fractional Brownian motion.'' A fractal scaling equation is also proposed as a substitute for the more empirical Paris equation describing individual crack growth in this approach. Preliminary calculations indicate that the new recursion relation is capable of reproducing the primary features of transverse matrix fatigue cracking behavior. Although not yet fully tested or verified, this cursion relation may eventually be useful for real-time applications such as monitoring damage in aircraft structures.

  9. 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.

  10. Blade Manufacturing Improvement: Remote Blade Manufacturing Demonstration

    SciTech Connect

    ASHWILL, THOMAS D.

    2003-05-01

    The objective of this program was to investigate manufacturing improvements for wind turbine blades. The program included a series of test activities to evaluate the strength, deflection, performance, and loading characteristics of the prototype blades. The original contract was extended in order to continue development of several key blade technologies identified in the project. The objective of the remote build task was to demonstrate the concept of manufacturing wind turbine blades at a temporary manufacturing facility in a rural environment. TPI Composites successfully completed a remote manufacturing demonstration in which four blades were fabricated. The remote demonstration used a manufacturing approach which relied upon material ''kits'' that were organized in the factory and shipped to the site. Manufacturing blades at the wind plant site presents serious logistics difficulties and does not appear to be the best approach. A better method appears to be regional manufacturing facilities, which will eliminate most of the transportation cost, without incurring the logistical problems associated with fabrication directly onsite. With this approach the remote facilities would use commonly available industrial infrastructure such as enclosed workbays, overhead cranes, and paved staging areas. Additional fatigue testing of the M20 root stud design was completed with good results. This design provides adhesive bond strength under fatigue loading that exceeds that of the fastener. A new thru-stud bonding concept was developed for the M30 stud design. This approach offers several manufacturing advantages; however, the test results were inconclusive.

  11. 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.

  12. 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.

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

    SciTech Connect

    Dunn, Martin L.; Talmage, Mellisa J.; 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

    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.

  14. 14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... structure. 25.571 Section 25.571 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25.571 Damage—tolerance and fatigue evaluation of structure. (a) General. An evaluation of the...

  15. 14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... structure. 25.571 Section 25.571 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25.571 Damage—tolerance and fatigue evaluation of structure. (a) General. An evaluation of the...

  16. 14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... structure. 25.571 Section 25.571 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25.571 Damage—tolerance and fatigue evaluation of structure. Link to an amendment published at 75...

  17. 14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... structure. 25.571 Section 25.571 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25.571 Damage—tolerance and fatigue evaluation of structure. (a) General. An evaluation of the...

  18. 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 120C to yield a glass transition temperature of 127C. 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 (-196C to 35C) 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.

  19. Analysis of the causes of fracture of turbine blades in a gas-compressor unit

    NASA Astrophysics Data System (ADS)

    Rybalko, V. G.; Novgorodov, D. V.

    2015-10-01

    The problems of the fatigue life of gas-compressor unit blades are discussed. In particular, the results of fractographic investigation are used to formulate the specific features of fracture of stamped lowpressure turbine blades made of an EI893 alloy, which exhibit the maximum number of damages in a five-year period. In 80% cases, fracture begins with the formation of a brittle zone in the leading edge of a blade airfoil because of the resonance phenomena caused by a break in the stiffness of the blade-turbine disk joint. This conclusion is supported by pronounced traces of fretting corrosion in the contact surfaces of the joint of a failed blade and a disk.

  20. Tungsten fiber reinforced FeCralY: A first generation composite turbine blade material

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Winsa, E. A.; Westfall, L. J.; Signorelli, R. A.

    1979-01-01

    Tungsten-fiber/FeCrAlY (W/FeCrAlY) was identified as a promising aircraft engine, first generation, turbine blade composite material. Based on available data, W/FeCrAlY should have the stress-rupture, creep, tensile, fatigue, and impact strengths required for turbine blades operating from 1250 to 1370 K. It should also have adequate oxidation, hot corrosion, and thermal cycling damage resistance as well as high thermal conductivity. Concepts for potentially low cost blade fabrication were developed. These concepts were used to design a first stage JT9D convection cooled turbine blade having a calculated 50 K use-temperature advantage over the directionally solidified superalloy blade.

  1. Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1992-01-01

    Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

  2. Development of an Image-based Multi-Scale Finite Element Approach to Predict Fatigue Damage in Asphalt Mixtures

    NASA Astrophysics Data System (ADS)

    Arshadi, Amir

    Image-based simulation of complex materials is a very important tool for understanding their mechanical behavior and an effective tool for successful design of composite materials. In this thesis an image-based multi-scale finite element approach is developed to predict the mechanical properties of asphalt mixtures. In this approach the "up-scaling" and homogenization of each scale to the next is critically designed to improve accuracy. In addition to this multi-scale efficiency, this study introduces an approach for consideration of particle contacts at each of the scales in which mineral particles exist. One of the most important pavement distresses which seriously affects the pavement performance is fatigue cracking. As this cracking generally takes place in the binder phase of the asphalt mixture, the binder fatigue behavior is assumed to be one of the main factors influencing the overall pavement fatigue performance. It is also known that aggregate gradation, mixture volumetric properties, and filler type and concentration can affect damage initiation and progression in the asphalt mixtures. This study was conducted to develop a tool to characterize the damage properties of the asphalt mixtures at all scales. In the present study the Viscoelastic continuum damage model is implemented into the well-known finite element software ABAQUS via the user material subroutine (UMAT) in order to simulate the state of damage in the binder phase under the repeated uniaxial sinusoidal loading. The inputs are based on the experimentally derived measurements for the binder properties. For the scales of mastic and mortar, the artificially 2-Dimensional images of mastic and mortar scales were generated and used to characterize the properties of those scales. Finally, the 2D scanned images of asphalt mixtures are used to study the asphalt mixture fatigue behavior under loading. In order to validate the proposed model, the experimental test results and the simulation results were compared. Indirect tensile fatigue tests were conducted on asphalt mixture samples. A comparison between experimental results and the results from simulation shows that the model developed in this study is capable of predicting the effect of asphalt binder properties and aggregate micro-structure on mechanical behavior of asphalt concrete under loading.

  3. Lamb wave-based damage quantification and probability of detection modeling for fatigue life assessment of riveted lap joint

    NASA Astrophysics Data System (ADS)

    He, Jingjing; Wang, Dengjiang; Zhang, Weifang

    2015-03-01

    This study presents an experimental and modeling study for damage detection and quantification in riveted lap joints. Embedded lead zirconate titanate piezoelectric (PZT) ceramic wafer-type sensors are employed to perform in-situ non-destructive testing during fatigue cyclical loading. A multi-feature integration method is developed to quantify the crack size using signal features of correlation coefficient, amplitude change, and phase change. In addition, probability of detection (POD) model is constructed to quantify the reliability of the developed sizing method. Using the developed crack size quantification method and the resulting POD curve, probabilistic fatigue life prediction can be performed to provide comprehensive information for decision-making. The effectiveness of the overall methodology is demonstrated and validated using several aircraft lap joint specimens from different manufactures and under different loading conditions.

  4. THE DEVELOPMENT OF MICROSTRUCTURAL DAMAGE DURING HIGH TEMPERATURE CREEP-FATIGUE OF A NICKEL ALLOY

    SciTech Connect

    L.J. Carroll; M.C. Carroll; C. Cabet; R.N. Wright

    2013-02-01

    Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include hold times up to 9000 s at maximum tensile strain were conducted at 950 degrees C. The fatigue resistance decreased when a hold time was added at peak tensile strain, owing to the mechanisms resulting in a change in fracture mode from transgranular in pure fatigue to intergranular in creep–fatigue. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep–fatigue resistance. An analysis of the evolving failure modes was facilitated by interrupting tests during cycling for ex situ microstructural investigation.

  5. 77 FR 50576 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; OMB Approval of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-22

    ... and Fatigue Evaluation of Composite Rotorcraft Structures,'' published in the Federal Register (76 FR... impractical. In a correction document (77 FR 4890), published February 1, 2012, the FAA revised the...

  6. 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.

  7. Thermomechanical Fatigue Damage/Failure Mechanisms in SCS-6/Timetal 21S [0/90](Sub S) Composite

    NASA Technical Reports Server (NTRS)

    Castelli, Michael G.

    1994-01-01

    The thermomechanical fatigue (TMF) deformation, damage, and life behaviors of SCS6/Timetal 21S (0/90)s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650 deg C. An advanced TMF test technique was used to quantify mechanically damage progression. The technique incorporated explicit measurements of the macroscopic (1) isothermal static moduli at the temperature extremes of the TMF cycle and (2) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue life results indicated trends analogous to those established for similar unidirectional(0) reinforced titanium matrix composite systems. High stress IP and mid to low stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive (0) fiber cracking with sparse matrix damage. No surface initiated matrix cracks were present. Comparable OP TMF conditions initiated environment enhanced surface cracking and matrix cracking initiated at (90) fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and (90) F/M interfaces tended to converge and coalesce at the (0) fibers.

  8. Probabilistic fatigue methodology and wind turbine reliability

    SciTech Connect

    Lange, C.H.

    1996-05-01

    Wind turbines subjected to highly irregular loadings due to wind, gravity, and gyroscopic effects are especially vulnerable to fatigue damage. The objective of this study is to develop and illustrate methods for the probabilistic analysis and design of fatigue-sensitive wind turbine components. A computer program (CYCLES) that estimates fatigue reliability of structural and mechanical components has been developed. A FORM/SORM analysis is used to compute failure probabilities and importance factors of the random variables. The limit state equation includes uncertainty in environmental loading, gross structural response, and local fatigue properties. Several techniques are shown to better study fatigue loads data. Common one-parameter models, such as the Rayleigh and exponential models are shown to produce dramatically different estimates of load distributions and fatigue damage. Improved fits may be achieved with the two-parameter Weibull model. High b values require better modeling of relatively large stress ranges; this is effectively done by matching at least two moments (Weibull) and better by matching still higher moments. For this purpose, a new, four-moment {open_quotes}generalized Weibull{close_quotes} model is introduced. Load and resistance factor design (LRFD) methodology for design against fatigue is proposed and demonstrated using data from two horizontal-axis wind turbines. To estimate fatigue damage, wind turbine blade loads have been represented by their first three statistical moments across a range of wind conditions. Based on the moments {mu}{sub 1}{hor_ellipsis}{mu}{sub 3}, new {open_quotes}quadratic Weibull{close_quotes} load distribution models are introduced. The fatigue reliability is found to be notably affected by the choice of load distribution model.

  9. 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.

  10. Load Mitigation with Bending/Twist-coupled Blades on Rotors using Modern Control Strategies

    NASA Astrophysics Data System (ADS)

    Lobitz, Don W.; Veers, Paul S.

    2003-04-01

    The prospect of installing blades that twist as they bend and/or extend on horizontal axis wind turbines provides opportunities for enhanced energy capture and/or load mitigation. Although this coupling could be achieved in either an active or a passive manner, the passive approach is much more attractive owing to its simplicity and economy. As an example, a blade design might employ coupling between bending and twisting, so that as the blade bends owing to the action of the aerodynamic loads, it also twists, modifying the aerodynamic performance in some way. For reducing loads the blades are designed to twist towards feather as they bend. For variable-speed pitch-controlled rotors, dynamic computer simulations with turbulent inflow show that twist coupling substantially decreases fatigue damage over all wind speeds, without reducing average power. Maximum loads also decrease modestly. For constant-speed stall-controlled and variable-speed stall-controlled rotors, significant decreases in fatigue damage are observed at the lower wind speeds and smaller decreases at the higher wind speeds. Maximum loads also decrease slightly. As a general observation, whenever a rotor is operating in the linear aerodynamic range (lower wind speeds for stall control and all wind speeds for pitch control), substantial reductions in fatigue damage are realized.

  11. A supervised vibration-based statistical methodology for damage detection under varying environmental conditions & its laboratory assessment with a scale wind turbine blade

    NASA Astrophysics Data System (ADS)

    Gómez González, A.; Fassois, S. D.

    2016-03-01

    The problem of vibration-based damage detection under varying environmental conditions and uncertainty is considered, and a novel, supervised, PCA-type statistical methodology is postulated. The methodology employs vibration data records from the healthy and damaged states of a structure under various environmental conditions. Unlike standard PCA-type methods in which a feature vector corresponding to the least important eigenvalues is formed in a single step, the postulated methodology uses supervised learning in which damaged-state data records are employed to sequentially form a feature vector by appending a transformed scalar element at a time under the condition that it optimally, among all remaining elements, improves damage detectability. This leads to the formulation of feature vectors with optimized sensitivity to damage, and thus high damage detectability. Within this methodology three particular methods, two non-parametric and one parametric, are formulated. These are validated and comparatively assessed via a laboratory case study focusing on damage detection on a scale wind turbine blade under varying temperature and the potential presence of sprayed water. Damage detection performance is shown to be excellent based on a single vibration response sensor and a limited frequency bandwidth.

  12. 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.

  13. Characterization of Damage Progression in SCS-6/timetal 21S (0)4 Under Thermomechanical Fatigue Loadings

    NASA Technical Reports Server (NTRS)

    Castelli, Michael G.

    1994-01-01

    A detailed experimental investigation was performed at a single maximum cyclic stress (sigma max) level to physically characterize the progression of thermomechanical fatigue (lW) damage in continuously reinforced (0 deg) SCS-6/Timetal 21S, a titanium matrix composite. In-phase (IP) and out of-phase (OP) loadings were investigated at sigma max = 1000 MPa with a temperature cycle from 150 to 6500 C. Damage progression, in terms of macroscopic property degradation, was experimentally quantified through an advanced TMF test methodology which incorporates explicit measurements of the isothermal static moduli at the TMF temperature extremes and the coefficient of thermal expansion (CTE) as functions of the TMF cycles. Detailed characterization of the physical damage progression at the microstructural level was performed by interrupting multiple TMF tests at various stages of mechanical property degradation and analyzing the microstructure through extensive destructive metallography. Further, the extent of damage was also quantified through residual static strength measurements. Results indicated that damage initiation occurred very early in cyclic life (N less than 0.1Nf) for both the IP and OP TMF loadings. IP TMF damage was found to be dominated by fiber breakage with a physical damage progression in the microstructure which was difficult to quantify. OP TMF loadings produced matrix cracking exclusively associated with surface initiations. Here, damage progression was easily distinguished in terms of both the number of cracks and their relative inward progressions toward the outer fiber rows with increased cycling. The point at which the leading cracks reached the outer fiber rows (when localized fiber/matrix de-bonding and matrix crack bridging occurred) appeared to be reflected in the macroscopic property degradation curves.

  14. Quantitative Assessment of Fatigue Damage Accumulation in Wavy Slip Metals from Acoustic Harmonic Generation

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.

    2006-01-01

    A comprehensive, analytical treatment is presented of the microelastic-plastic nonlinearities resulting from the interaction of a stress perturbation with dislocation substructures (veins and persistent slip bands) and cracks that evolve during high-cycle fatigue of wavy slip metals. The nonlinear interaction is quantified by a material (acoustic) nonlinearity parameter beta extracted from acoustic harmonic generation measurements. The contribution to beta from the substructures is obtained from the analysis of Cantrell [Cantrell, J. H., 2004, Proc. R. Soc. London A, 460, 757]. The contribution to beta from cracks is obtained by applying the Paris law for crack propagation to the Nazarov-Sutin crack nonlinearity equation [Nazarov, V. E., and Sutin, A. M., 1997, J. Acoust. Soc. Am. 102, 3349]. The nonlinearity parameter resulting from the two contributions is predicted to increase monotonically by hundreds of percent during fatigue from the virgin state to fracture. The increase in beta during the first 80-90 percent of fatigue life is dominated by the evolution of dislocation substructures, while the last 10-20 percent is dominated by crack growth. The model is applied to the fatigue of aluminium alloy 2024-T4 in stress-controlled loading at 276MPa for which experimental data are reported. The agreement between theory and experiment is excellent.

  15. High cycles fatigue damage of CFRP plates clamped by bolts for axial coupling joint with off-set angle during rotation

    NASA Astrophysics Data System (ADS)

    Ooka, Kazuaki; Okubo, Kazuya; Fujii, Toru; Umeda, Shinichi; Fujii, Masayuki; Sugiyama, Tetsuya

    2014-03-01

    This study discussed the change of residual fracture torque and the fatigue damage process of thin CFRP plates clamped by bolts for axial coupling joint, in which flexible deformation was allowed in the direction of off-set angle by the deflection of the CFRP plates while effective stiffness was obtained in rotational direction. Mechanically laminated 4 layers of the CFRP plates were repeatedly deflected during the rotation of axial coupling, when two axes were jointed with 3 degree of off-set angle, in which number of revolution was 1,800 rpm (30Hz of loading frequency). At first, the fracture morphology of specimen and the residual fracture torque was investigated after 1.0107 cycles of repeated revolutions. The reduction ratio of spring constant was also determined by simple bending test after the fatigue. The residual fracture torque of the joint was determined on the rotational test machine after 1.0107 cycles of fatigue. After rotations of cyclic fatigue, fiber breaking and wear of matrix were observed around the fixed parts compressed by washers for setting bolts. The reduction of spring constant of the CFRP plates was caused by the initiation of cyclic fatigue damages around the fixed parts, when the axial coupling joint was rotated with off-set angle. It was found that residual fracture torque of the joint was related with the specific fatigue damage of the CFRP observed in this study.

  16. 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.

  17. Detection of Fatigue Damage Prior to Crack Initiation withScanning SQUID Microscopy

    SciTech Connect

    Lee, Tae-Kyu; Morris Jr., J.W.; Lee, Seungkyun; Clarke, John

    2005-11-07

    The remanence fields of fatigued ferritic steel specimens were measured using a scanning microscope based on a high transition temperature Superconducting Quantum Interference Device (SQUID). The results show an overall increase of remanence until dislocation density saturates and an additional local remanence increase after saturation during cyclic loading. Because of the combined magnetic and spatial resolution of the SQUID microscope, these local changes of dislocation structures can be detected before a crack actually initiates, and identify the sites where crack nucleation will occur.

  18. 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.

  19. Monitoring Thermal Fatigue Damage In Nuclear Power Plant Materials Using Acoustic Emission

    SciTech Connect

    Meyer, Ryan M.; Ramuhalli, Pradeep; Watson, Bruce E.; Pitman, Stan G.; Roosendaal, Timothy J.; Bond, Leonard J.

    2012-04-26

    Proactive aging management of nuclear power plant passive components requires technologies to enable monitoring and accurate quantification of material condition at early stages of degradation (i.e., pre-macrocrack). Acoustic emission (AE) is well-suited to continuous monitoring of component degradation and is proposed as a method to monitor degradation during accelerated thermal fatigue tests. A key consideration is the ability to separate degradation responses from external sources such as water spray induced during thermal fatigue testing. Water spray provides a significant background of acoustic signals, which can overwhelm AE signals caused by degradation. Analysis of AE signal frequency and energy is proposed in this work as a means for separating degradation signals from background sources. Encouraging results were obtained by applying both frequency and energy filters to preliminary data. The analysis of signals filtered using frequency and energy provides signatures exhibiting several characteristics that are consistent with degradation accumulation in materials. Future work is planned to enable verification of the efficacy of AE for thermal fatigue crack initiation detection. While the emphasis has been placed on the use of AE for crack initiation detection during accelerated aging tests, this work also has implications with respect to the use of AE as a primary tool for early degradation monitoring in nuclear power plant materials. The development of NDE tools for characterization of aging in materials can also benefit from the use of a technology such as AE which can continuously monitor and detect crack initiation during accelerated aging tests.

  20. Monitoring thermal fatigue damage in nuclear power plant materials using acoustic emission

    NASA Astrophysics Data System (ADS)

    Meyer, R. M.; Ramuhalli, P.; Watson, B. E.; Pitman, S. G.; Roosendaal, T. J.; Bond, L. J.

    2012-04-01

    Proactive aging management of nuclear power plant passive components requires technologies to enable monitoring and accurate quantification of material condition at early stages of degradation (i.e., pre-macrocrack). Acoustic emission (AE) is well-suited to continuous monitoring of component degradation and is proposed as a method to monitor degradation during accelerated thermal fatigue tests. A key consideration is the ability to separate degradation responses from external sources such as water spray induced during thermal fatigue testing. Water spray provides a significant background of acoustic signals, which can overwhelm AE signals caused by degradation. Analysis of AE signal frequency and energy is proposed in this work as a means for separating degradation signals from background sources. Encouraging results were obtained by applying both frequency and energy filters to preliminary data. The analysis of signals filtered using frequency and energy provides signatures exhibiting several characteristics that are consistent with degradation accumulation in materials. Future work is planned to enable verification of the efficacy of AE for thermal fatigue crack initiation detection. While the emphasis has been placed on the use of AE for crack initiation detection during accelerated aging tests, this work also has implications with respect to the use of AE as a primary tool for early degradation monitoring in nuclear power plant materials. The development of NDE tools for characterization of aging in materials can also benefit from the use of a technology such as AE which can continuously monitor and detect crack initiation during accelerated aging tests.

  1. 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.

  2. Successful Solutions to SSME/AT Development Turbine Blade Distress

    NASA Technical Reports Server (NTRS)

    Montgomery, Stuart K.

    1999-01-01

    As part of the High-Pressure Fuel Turbopump/Alternate Turbopump (HPFTP/AT) turbine blade development program, unique turbine blade design features were implemented to address 2nd stage turbine blade high cycle fatigue distress and improve turbine robustness. Features included the addition of platform featherseal dampers, asymmetric blade tip seal segments, gold plating of the blade attachments, and airfoil tip trailing edge modifications. Development testing shows these features have eliminated turbine blade high cycle fatigue distress and consequently these features are currently planned for incorporation to the flight configuration. Certification testing will begin in 1999. This presentation summarizes these features.

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

    SciTech Connect

    Park, Gyuhae; Taylor, Stuart G.; Farinholt, Kevin M; Farrar, Charles R

    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.

  4. 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.

    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.

  5. Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-08-01

    Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

  6. Infrared thermal wave nondestructive testing for rotor blades in wind turbine generators non-destructive evaluation and damage monitoring

    NASA Astrophysics Data System (ADS)

    Zhao, Shi bin; Zhang, Cun-lin; Wu, Nai-ming; Duan, Yu-xia; Li, Hao

    2009-07-01

    The rotor blades are key components in wind turbine generators. A visual inspection of the laminated shells for delaminations, air pockets, missing/disoriented fabric etc. is in most cases also not possible due to the manufacturing process, so Non-destructive testing and evaluation (NDT & E) techniques for assessing the integrity of rotor blades structure are essential to both reduce manufacturing costs and out of service time of wind turbine generators due to maintenance. Nowadays, Infrared Thermal Wave Nondestructive Testing (Pulsed thermography) is commonly used for assessing composites. This research work utilizes Infrared Thermal Wave Nondestructive Testing system (EchoTherm, Thermal Wave Imaging, Inc.) to inspect a specimen with embedded defects (i.e. foreign matter and air inclusions) in different depth which is a part of rotor blades in wind turbine generators, we have successfully identified defects including foreign matter and air inclusions, and discovered a defective workmanship. The system software allows us to simultaneously view and analyze the results for an entire transition.

  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. 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

  9. An advanced method for tracking the evolution of fatigue damage in reusable space propulsion systems

    NASA Technical Reports Server (NTRS)

    Rajagopal, K. R.; Orient, G.; Newell, J. F.; Mcgaw, M.

    1991-01-01

    NASA-Lewis is actively involved in the general effort to research, develop, test, and evaluate advanced theoretical, analytical, experimental, and probabilistic analysis concepts required for life prediction of liquid rocket engines at the subcomponent, component, and engine system levels. The models developed are oriented toward use in advanced health monitoring systems of space propulsion systems. It is planned to demonstrate the methodology considering a representative set of three components such as a main injector element, a combustion chamber liner, and a turbopump blade. This paper describes the initial development and application of this method to a specific location in the main injector element of the SSME. Further enhancements and various elements of the framework will be completed as the work proceeds in subsequent years.

  10. An advanced method for tracking the evolution of fatigue damage in reusable space propulsion systems

    NASA Astrophysics Data System (ADS)

    Rajagopal, K. R.; Orient, G.; Newell, J. F.; McGaw, M.

    NASA-Lewis is actively involved in the general effort to research, develop, test, and evaluate advanced theoretical, analytical, experimental, and probabilistic analysis concepts required for life prediction of liquid rocket engines at the subcomponent, component, and engine system levels. The models developed are oriented toward use in advanced health monitoring systems of space propulsion systems. It is planned to demonstrate the methodology considering a representative set of three components such as a main injector element, a combustion chamber liner, and a turbopump blade. This paper describes the initial development and application of this method to a specific location in the main injector element of the SSME. Further enhancements and various elements of the framework will be completed as the work proceeds in subsequent years.

  11. Turbine Blade Research

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Under contract with the New York State Energy Research and Development Authority, GE's Energy Systems Programs Department used a COSMIC program in assessing the problem of blade erosion in a PFB (pressurized fluid bed) environment. Data provided by this program and an associated program enabled the company engineers to determine gas velocities and the velocities of the particles striking the blades, calculations necessary for predicting blade erosion and potential damage. The assessment resulted in a new estimate for the allowable dust load for a modern heavy duty gas turbine.

  12. 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

  13. Incipient Crack Detection in Composite Wind Turbine Blades

    SciTech Connect

    Taylor, Stuart G.; Choi, Mijin; Jeong, Hyomi; Jang, Jae Kyeong; Park, Gyuhae; Farinholt, Kevin; Farrar, Charles R.; Ammerman, Curtt N.; Todd, Michael D.; Lee, Jung-Ryul

    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.

  14. Fatigue damage at room temperature in aluminium single crystals. 3: Lattice rotation

    SciTech Connect

    Zhai, T.; Martin, J.W.; Briggs, G.A.D.; Wilkinson, A.J.

    1996-09-01

    Lattice rotation was observed in different scales in aluminium single crystals fatigued in push-pull in air at room temperature, a constant shear stress amplitude 4 MPa, zero mean stress and frequency of 20 Hz. Using the channelling contrast technique in SEM, contrast of grey and dark bands consistent in dimensions with those of PSBs was observed on the surface sectioned parallel to the Burgers vector b in an Al single crystal after 1.2 {times} 10{sup 6} cycles, suggesting that there was lattice misorientation (rotation or tilt) between PSBs and the matrix in the specimen. It might be caused by local net material movement due to irreversible slip or non-uniform deformation in PSBs. Lattice rotation (about 6) always appeared between a macroband and the matrix relative to the normals of two perpendicular surfaces of the specimens, as a result of net irreversible slip in one direction of b in PSBs. Often more cracks were found in a positive macroband than a negative one. Deformation bands coarser than PSBs and smaller than macrobands were also found on the surface containing b by the scanning acoustic microscope. They deviated slightly from the direction of the PSBs and were probably formed to release the internal stresses between macrobands and the matrix due to macroband formation. The macroband effect is likely a general metallographic characteristic of unidirectional fatigue in planar-slip metal single crystals. The lattice rotation was probably one of the key factors controlling crack initiation and early propagation in the Al single crystals.

  15. On the feasibility of nonlinear assessment of fatigue damage in hardened IN718 specimens based on non-collinear shear wave mixing

    NASA Astrophysics Data System (ADS)

    Zhang, Ziyin; Nagy, Peter B.; Hassan, Waled

    2016-02-01

    Recent studies have shown that various ultrasonic wave mixing techniques can be exploited for assessing the nonlinearity of both intact and damaged materials. It has been reported that one particular type of ultrasonic wave mixing, non-collinear shear wave mixing, is sensitive to the excess nonlinearity caused by plastic deformation and low-cycle fatigue in Al2014-T4 aluminum alloy. In this study we investigated the feasibility of using the same non-collinear shear wave mixing technique to detect plastic deformation and fatigue damage in fully hardened IN718 engine alloy specimens. We implemented numerous technical improvements over the earlier developed non-collinear shear wave mixing system to improve its detection sensitivity and image resolution. In spite of these enhancements, we found that in fully hardened IN718 this technique is sensitive only to plastic deformation and, to a much lesser degree, to highly accelerated low-cycle fatigue, but it is not sensitive to either typical low-cycle fatigue or high-cycle fatigue. These observations highlight a potential deficiency in our current understanding of nonlinear material-wave interaction and suggest that further research is needed to explain why certain classes of dislocation networks remain hidden from this type of inspection.

  16. Structural Tailoring of SSME Blades (vanes)

    NASA Technical Reports Server (NTRS)

    Rubinstein, R.

    1985-01-01

    The engine blade design optimization program STAEBL (Structural Tailoring of Engine Blades) is available at the NASA Lewis computer facility. The analysis capabilities of this program were extended to typical loading conditions for SSME turbopump blades including thermal and pressure loading. Input files for representative SSME blade designs were developed and sample optimization studies for these blades completed. The structural tailoring program combines a general optimization package and a finite element blade analysis package. The analysis package's capabilities include natural frequency, maximum stress, and forced response computation, and fatigue life and flutter analysis. Optimization is performed using the feasible directions method. The current design is modified by perturbing the design variables so that the design constraints are satisfied while the objective function, such as blade weight, is reduced at the maximum rate. The program's geometric design variables include blade thickness distribution, thickness to chord ratios, and root chord.

  17. Effect of ply constraint on fatigue damage development in composite material laminates

    NASA Technical Reports Server (NTRS)

    Stinchcomb, W. W.; Reifsnider, K. L.; Yeung, P.; Masters, J.

    1981-01-01

    It is shown that the effects of constraint on the response of composite materials can be classified as (1) in-plane effects, and (2) through-the-thickness effects; with in-plane constraint being the principal contributor to notched strength and changes in notched strength under quasi-static loading. It is also determined that the constraint situations that produce the greatest static strength do not minimize the extent of damage that develops under either static or cyclic loading, and that through-the-thickness constraint controls the pattern and spacing of transverse cracks in the characteristic damage state that determines those of strength and stress in unnotched laminates. It is concluded that the mode and the extent of damage in notched and unnotched constrained plies is governed by the stress state in those plies, as determined by the constraining ones, and the relationship of stress and strength states.

  18. Assessment technology for turbine blades

    SciTech Connect

    McCloskey, T.H.; Rieger, N.F.

    1995-08-01

    Blade failures are the leading cause of steam turbine unavailability for large fossil fuel power plants in the US, costing utilities over $200 million per year in maintenance and lost revenue. In low-pressure (LP) turbines, the major concern is failure of blades by corrosion fatigue in the last or next-to-last stage. To reduce the incidence of these failures, industry efforts have included development and testing of blade evaluation tools, new blading materials, and blade coatings. In intermediate-pressure (IP) and high-pressure (HP) turbines, solid particle erosion is a major concern. To address this problem, industry work has included reducing the source of the solid particles, removing the particles upstream of the turbine, protecting the turbine from the effects of the particular matter, and adjusting operation.

  19. Early stage fatigue damage occurs in bovine tendon fascicles in the absence of changes in mechanics at either the gross or micro-structural level

    PubMed Central

    Shepherd, Jennifer H.; Riley, Graham P.; Screen, Hazel R.C.

    2014-01-01

    Many tendon injuries are believed to result from repetitive motion or overuse, leading to the accumulation of micro-damage over time. In vitro fatigue loading can be used to characterise damage during repeated use and investigate how this may relate to the aetiology of tendinopathy. This study considered the effect of fatigue loading on fascicles from two functionally distinct bovine tendons: the digital extensor and deep digital flexor. Micro-scale extension mechanisms were investigated in fascicles before or after a period of cyclic creep loading, comparing two different measurement techniques the displacement of a photo-bleached grid and the use of nuclei as fiducial markers. Whilst visual damage was clearly identified after only 300 cycles of creep loading, these visual changes did not affect either gross fascicle mechanics or fascicle microstructural extension mechanisms over the 900 fatigue cycles investigated. However, significantly greater fibre sliding was measured when observing grid deformation rather than the analysis of nuclei movement. Measurement of microstructural extension with both techniques was localised and this may explain the absence of change in microstructural deformation in response to fatigue loading. Alternatively, the data may demonstrate that fascicles can withstand a degree of matrix disruption with no impact on mechanics. Whilst use of a photo-bleached grid to directly measure the collagen is the best indicator of matrix deformation, nuclei tracking may provide a better measure of the strain perceived directly by the cells. PMID:25001495

  20. Early stage fatigue damage occurs in bovine tendon fascicles in the absence of changes in mechanics at either the gross or micro-structural level.

    PubMed

    Shepherd, Jennifer H; Riley, Graham P; Screen, Hazel R C

    2014-10-01

    Many tendon injuries are believed to result from repetitive motion or overuse, leading to the accumulation of micro-damage over time. In vitro fatigue loading can be used to characterise damage during repeated use and investigate how this may relate to the aetiology of tendinopathy. This study considered the effect of fatigue loading on fascicles from two functionally distinct bovine tendons: the digital extensor and deep digital flexor. Micro-scale extension mechanisms were investigated in fascicles before or after a period of cyclic creep loading, comparing two different measurement techniques - the displacement of a photo-bleached grid and the use of nuclei as fiducial markers. Whilst visual damage was clearly identified after only 300 cycles of creep loading, these visual changes did not affect either gross fascicle mechanics or fascicle microstructural extension mechanisms over the 900 fatigue cycles investigated. However, significantly greater fibre sliding was measured when observing grid deformation rather than the analysis of nuclei movement. Measurement of microstructural extension with both techniques was localised and this may explain the absence of change in microstructural deformation in response to fatigue loading. Alternatively, the data may demonstrate that fascicles can withstand a degree of matrix disruption with no impact on mechanics. Whilst use of a photo-bleached grid to directly measure the collagen is the best indicator of matrix deformation, nuclei tracking may provide a better measure of the strain perceived directly by the cells. PMID:25001495

  1. A thermodynamics based damage mechanics framework for fatigue analysis of microelectronics solder joints with size effects

    NASA Astrophysics Data System (ADS)

    Gomez, Juan

    Experimental observations of an increase in resistance with decreasing specimen size and under the presence of non-uniform plastic deformation fields have pushed the development for small scale plasticity theories since the early 90's. The observed phenomenon has been explained in terms of an accumulation of a density of geometrically necessary dislocations, which is required in order to accommodate nonuniform plastic deformation fields. This extra density of dislocations, contributes to the additional hardening observed in small scale specimens under imposed non-uniform plastic deformations. The density of geometrically necessary dislocations has been related to the gradients of plastic strain which are imposed either by the loading conditions or the geometry of the specimen. The proposed set of theories has promoted the idea that there is an additional material parameter, namely a plastic length scale. Within these theories when the material is under the presence of a non-uniform plastic deformation field and once typical structural dimensions approaches the material length scale there is an increase in resistance. Such a class of mathematical framework is currently known as strain gradient plasticity (SGP) theory. On the other hand, the current trend towards miniaturization in the microelectronics industry has raised questions about the true behavior of small structural systems. In this dissertation we address such a problem but from the perspective of eutectic solder alloys. Eutectic solder alloys as frequently used in the microelectronics industry exhibit considerable rate dependent response even at room temperature. Moreover for this type of material, the problem of interest is the response under cyclic loadings induced by thermomechanical fatigue leading to the classical case of creep-fatigue interaction. Several experimental and theoretical studies have been developed in order to generate robust constitutive descriptions for this class of applications. For a structure whose size is close to a 100mum or larger several and relatively simple to implement constitutive models are now available in the literature, and it can be generally stated that the level of understanding has reached a mature level. However, the same problem when the size of the structure is below this characteristic dimension has not been studied before. In other words, the available constitutive models completely neglect the incidence of size effects when evaluating the true behavior of the material at small scales. (Abstract shortened by UMI.)

  2. 14 CFR 35.37 - Fatigue limits and evaluation.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention... fatigue failure mode leading to hazardous propeller effects. (b) The fatigue limits must take into...

  3. 14 CFR 35.37 - Fatigue limits and evaluation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention... fatigue failure mode leading to hazardous propeller effects. (b) The fatigue limits must take into...

  4. 14 CFR 35.37 - Fatigue limits and evaluation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention... fatigue failure mode leading to hazardous propeller effects. (b) The fatigue limits must take into...

  5. 14 CFR 35.37 - Fatigue limits and evaluation.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention... fatigue failure mode leading to hazardous propeller effects. (b) The fatigue limits must take into...

  6. 14 CFR 35.37 - Fatigue limits and evaluation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention... fatigue failure mode leading to hazardous propeller effects. (b) The fatigue limits must take into...

  7. 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.

  8. Reducing fatigue damage for ships in transit through structured decision making

    USGS Publications Warehouse

    Nichols, J.M.; Fackler, P.L.; Pacifici, K.; Murphy, K.D.; Nichols, J.D.

    2014-01-01

    Research in structural monitoring has focused primarily on drawing inference about the health of a structure from the structure’s response to ambient or applied excitation. Knowledge of the current state can then be used to predict structural integrity at a future time and, in principle, allows one to take action to improve safety, minimize ownership costs, and/or increase the operating envelope. While much time and effort has been devoted toward data collection and system identification, research to-date has largely avoided the question of how to choose an optimal maintenance plan. This work describes a structured decision making (SDM) process for taking available information (loading data, model output, etc.) and producing a plan of action for maintaining the structure. SDM allows the practitioner to specify his/her objectives and then solves for the decision that is optimal in the sense that it maximizes those objectives. To demonstrate, we consider the problem of a Naval vessel transiting a fixed distance in varying sea-state conditions. The physics of this problem are such that minimizing transit time increases the probability of fatigue failure in the structural supports. It is shown how SDM produces the optimal trip plan in the sense that it minimizes both transit time and probability of failure in the manner of our choosing (i.e., through a user-defined cost function). The example illustrates the benefit of SDM over heuristic approaches to maintaining the vessel.

  9. 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.

  10. 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.

  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. Isothermal Damage and Fatigue Behavior of SCS-6/Timetal 21S [0/90](Sub S) Composite at 650 Deg C

    NASA Technical Reports Server (NTRS)

    Castelli, Michael G.

    1994-01-01

    The isothermal fatigue damage and life behaviors of SCS-6/Timetal 21S (0/90)s were investigated at 650 C. Strain ratcheting and degradation of the composite's static elastic modulus were carefully monitored as functions of cycles to indicate damage progression. Extensive fractographic and metallographic analyses were conducted to determine damage/failure mechanisms. Resulting fatigue lives show considerable reductions in comparison to (0) reinforced titanium matrix composites subjected to comparable conditions. Notable stiffness degradations were found to occur after the first cycle of loading, even at relatively low maximum stress levels, where cyclic lives are greater than 25,000 cycles. This was attributed to the extremely weak fiber/matrix bond which fails under relatively low transverse loads. Stiffness degradations incurred on first cycle loadings and degradations thereafter were found to increase with increasing maximum stress. Environmental effects associated with oxidation of the (90) fiber interfaces clearly played a role in the damage mechanisms as fracture surfaces revealed environment assisted matrix cracking along the (90) fibers. Metallographic analysis indicated that all observable matrix fatigue cracks initiated at the (90) fiber/matrix interfaces. Global de-bonding in the loading direction was found along the (90) fibers. No surface initiated cracks were evident and minimal if any (0) fiber cracking was visible.

  13. Distrubance Tracking and Blade Load Control of Wind Turbines in Variable-Speed Operation: Preprint

    SciTech Connect

    Stol, K. A.

    2003-01-01

    A composite state-space controller was developed for a multi-objective problem in the variable-speed operation of wind turbines. Disturbance Tracking Control theory was applied to the design of a torque controller to optimize energy capture under the influence of persistent wind disturbances. A limitation in the theory for common multi-state models is described, which led to the design of a complementary pitch controller. The goal of the independent blade pitch design was to minimize blade root fatigue loads. Simulation results indicate an 11% reduction in fatigue damage using the proposed controllers, compared to a conventional torque-only design. Meanwhile, energy capture is almost identical, partly because of nonlinear effects.

  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.; Kusnick, Joshua F.; Barrett, Natalie C.; Adams, Douglas E.; 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. Fiber composite fan blade impact improvement program

    NASA Technical Reports Server (NTRS)

    Oller, T. L.

    1976-01-01

    The results of a 20-month program, designed to investigate parameters which effect the foreign object damage resulting from ingestion of birds into fan blades are described. Work performed on this program included the design, fabrication, and impact testing of QCSEE fan blades to demonstrate improvement in resistance relative to existing blades and also the design and demonstration of a pin root attachment concept.

  16. Field Measurement of the Acoustic Nonlinearity Parameter in Turbine Blades

    NASA Technical Reports Server (NTRS)

    Hinton, Yolanda L.; Na, Jeong K.; Yost, William T.; Kessel, Gregory L.

    2000-01-01

    Nonlinear acoustics techniques were used to measure fatigue in turbine blades in a power generation plant. The measurements were made in the field using a reference based measurement technique, and a reference sample previously measured in the laboratory. The acoustic nonlinearity parameter showed significant increase with fatigue in the blades, as indicated by service age and areas of increased stress. The technique shows promise for effectively measuring fatigue in field applications and predicting subsequent failures.

  17. 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.

  18. Analysis of the Static and Fatigue Strenght of a Damage Tolerant 3D-Reinforced Joining Technology on Composite Single Lap Joints

    NASA Astrophysics Data System (ADS)

    Nogueira, A. C.; Drechsler, K.; Hombergsmeier, E.

    2012-07-01

    The increasing usage of carbon fiber reinforced plastics (CFRP) in aerospace together with the constant drive for fuel efficiency and lightweight design have imposed new challenges in next generation structural assemblies and load transfer efficient joining methods. To address this issue, an innovative technology, denominated Redundant High Efficiency Assembly (RHEA) joints, is introduced as a high-performance lightweight joint that combines efficient load transfer with good damage tolerance. A review of the ongoing research involving the RHEA joint technology, its through-thickness reinforcement concept and the results of quasi-static and fatigue tensile investigations of single lap shear specimens are exposed and discussed. Improvements in ultimate static load, maximum joint deformation, damage tolerance and fatigue life are encountered when comparing the performance of the RHEA lap shear joints to co-bonded reference specimens.

  19. 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

  20. 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

  1. Effect of interstitial content on high-temperature fatigue crack propagation and low-cycle fatigue of Alloy 720

    SciTech Connect

    Bashir, S. ); Thomas, M.C. . Allison Gas Turbine Div.)

    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 intended for use as turbine blades, large carbide and borides stringers formed and acted as preferred crack initiators. Stringering was attributed to relatively higher boron and carbon levels. These interstitial 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-cycle 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 modification. The fatigue crack propagation rate was reduced by a concurrent reduction of both carbon and boron 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.

  2. 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 Allisons 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.

  3. 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.

  4. Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions

    NASA Astrophysics Data System (ADS)

    Fujiyama, Kazunari; Kimachi, Hirohisa; Tsuboi, Toshiki; Hagiwara, Hiroyuki; Ogino, Shotaro; Mizutani, Yoshiki

    EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values KAMave and GOSave were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As KAM values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters M?KAMnet and M??KAMave were introduced as the sum of product of the noise subtracted KAMnet and the absolute change from initial value ?KAMave with dislocation movement distance divided by pixel size. M??KAMave parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

  5. Piezoelectric Vibration Damping Study for Rotating Composite Fan Blades

    NASA Technical Reports Server (NTRS)

    Min, James B.; Duffy, Kirsten P.; Choi, Benjamin B.; Provenza, Andrew J.; Kray, Nicholas

    2012-01-01

    Resonant vibrations of aircraft engine blades cause blade fatigue problems in engines, which can lead to thicker and aerodynamically lower performing blade designs, increasing engine weight, fuel burn, and maintenance costs. In order to mitigate undesirable blade vibration levels, active piezoelectric vibration control has been investigated, potentially enabling thinner blade designs for higher performing blades and minimizing blade fatigue problems. While the piezoelectric damping idea has been investigated by other researchers over the years, very little study has been done including rotational effects. The present study attempts to fill this void. The particular objectives of this study were: (a) to develop and analyze a multiphysics piezoelectric finite element composite blade model for harmonic forced vibration response analysis coupled with a tuned RLC circuit for rotating engine blade conditions, (b) to validate a numerical model with experimental test data, and (c) to achieve a cost-effective numerical modeling capability which enables simulation of rotating blades within the NASA Glenn Research Center (GRC) Dynamic Spin Rig Facility. A numerical and experimental study for rotating piezoelectric composite subscale fan blades was performed. It was also proved that the proposed numerical method is feasible and effective when applied to the rotating blade base excitation model. The experimental test and multiphysics finite element modeling technique described in this paper show that piezoelectric vibration damping can significantly reduce vibrations of aircraft engine composite fan blades.

  6. Disease Activity and Damage are not Associated with Increased Levels of Fatigue in Systemic Lupus Erythematosus Patients from LUMINA LXVII, a Multiethnic Cohort

    PubMed Central

    Burgos, Paula I.; Alarcn, Graciela S.; McGwin, Gerald; Crews, Kendra Q.; Reveille, John D.; Vil, Luis M.

    2009-01-01

    Objective To determine the factors associated with increased levels of fatigue over the course of the disease in systemic lupus erythematosus (SLE) patients from LUMINA (Lupus in Minorities: Nature versus Nurture), a longitudinal multiethnic cohort. Methods Patients with SLE (American College of Rheumatology revised and updated criteria), age ?16 years, disease duration ? 5 years at entry into the cohort (T0), of Hispanic (Texan or Puerto Rican), African America or Caucasian ethnicity, were studied. The association between socioeconomic-demographic, health behaviors, behavioral and psychological, functional and clinical characteristics and fatigue was examined using generalized estimating equations to account for the longitudinal nature of the data. Results Five-hundred and fifteen patients (~91% female) contributed 2,609 visits to these analyses; there were: 93 (18.1%) Texan Hispanics, 101 (19.6%) Puerto Rican Hispanics, 169 (32.8%) African Americans, and 152 (29.5%) Caucasians; the patients mean (SD) age and follow up time were 37.2 (12.0) and 4.7 (3.2) years, respectively. Variables associated with increased levels of fatigue in the multivariable analyses were Caucasian ethnicity, the presence of constitutional symptoms(fever, weight loss), higher levels of pain, of abnormal illness-related behaviors and of helplessness (ps between 0.0018 and <0.0001). Conclusions The presence of pain, abnormal illness-related behaviors, helplessness and constitutional manifestations were associated with increased levels of fatigue; however, lupus specific measures, such as disease activity and damage were not. Interventions aimed at decreasing fatigue need to take into account these findings. PMID:19714612

  7. Method for cumulative damage summation through an understanding of the kinetics of stage-I crack propagation under stress controlled fatigue of copper single crystals

    NASA Astrophysics Data System (ADS)

    Jameel, Mohammad Ahsan

    The understanding of the cyclic deformation processes and their interaction with the kinetics of stage-I crack growth under stress control is rudimentary in copper single crystals. This understanding is necessary to conceive a method for summing damage under variable amplitude loading. In this thesis a detailed investigation of the cyclic stress strain response and stage-I crack growth kinetics under both constant and variable amplitude stress control has been undertaken. It is found that the cyclic stress strain response of copper single crystals depends upon the starting conditions of the test. The absence or presence of PSB's in a crystal can be controlled by varying the startup. If PSB's exist in the crystal then the cyclic stress strain response does not show saturation behavior and instead the plastic strain increases throughout life. On the other hand the cyclic stress strain response saturates if PSB's do not exist in the crystal. The increase in plastic strain in crystals containing a population of PSB's is tied to the nucleation of new PSB's. Thus, the volume fraction of PSB's, and hence the nucleation sites for cracks, keeps increasing throughout life under stress control as opposed to under strain control where the volume fraction of PSB's at a certain strain is fixed. Since PSB's are nucleation sites for cracks, the population of cracks is found to be much larger in stress control than under strain control. The growth of this population of cracks is proportional to the cumulative strain under both constant and variable amplitude fatigue except that under variable amplitude fatigue the constant of proportionality is modified. The population reaches a critical density, and the fatigue life is said to be exhausted, when the average separation of the cracks is equal to the strain relaxation region (an idea developed by Ma and Laird). Methods for summing damage under constant and variable amplitude stress controlled fatigue are proposed that predict the number of cycles necessary to achieve the critical population density.

  8. An integrated approach to wind turbine fatigue analysis

    SciTech Connect

    Laino, D.J.; Hansen, A.C.

    1997-08-01

    The wind turbine dynamics codes YawDyn and ADAMS have been interfaced with the LIFE2 code for fatigue life estimation via a new interface program, Dyn2LIFE. This work is sponsored by the National Renewable Energy Laboratory (NREL) with the intent of making it straightforward and practical for wind turbine designers to determine those aspects of their design and wind environment that will cause the most fatigue damage. Several parameters suspected of affecting turbine fatigue life are investigated through a model of the NREL Phase III Combined Experiment Rotor. This study proved the Dyn2LIFE code useful in creating LIFE2 input from YawDyn and ADAMS output, and also revealed some areas of possible expansion and improvement. Results from this study of a steel blade root suggest changes affecting the normal operation of the turbine alter fatigue life more than rare, high load events. Understanding how the material fatigue characteristics affect lifetime estimates is discussed in terms of the S-N curve utilized in this study. This paper presents the first results from an ongoing project. In the future, the authors plan to analyze a variety of turbine configurations to help identify those variables which may have the greatest influence on fatigue life.

  9. Damage-Tolerant Composites Made By Stitching Carbon Fabrics

    NASA Technical Reports Server (NTRS)

    Dow, Marvin B.; Smith, Donald L.

    1992-01-01

    Work conducted at NASA Langley Research Center to investigate stitching combined with resin transfer molding to make composites more tolerant of damage and potentially cost competitive with metals. Composite materials tailored for damage tolerance by stitching layers of dry carbon fabric with closely spaced threads to provide reinforcement through thickness. Epoxy resin then infused into stitched preforms, and epoxy was cured. Various stitching patterns and thread materials evaluated by use of flat plate specimens. Also, blade-stiffened structural elements fabricated and tested. Stitched flat laminates showed outstanding damage tolerance, excellent compression strength in notched specimens, and acceptable fatigue behavior. Development of particular interest to aircraft and automotive industries.

  10. Structural Testing of the Blade Reliability Collaborative Effect of Defect Wind Turbine Blades

    SciTech Connect

    Desmond, M.; Hughes, S.; Paquette, J.

    2015-06-08

    Two 8.3-meter (m) wind turbine blades intentionally constructed with manufacturing flaws were tested to failure at the National Wind Technology Center (NWTC) at the National Renewable Energy Laboratory (NREL) south of Boulder, Colorado. Two blades were tested; one blade was manufactured with a fiberglass spar cap and the second blade was manufactured with a carbon fiber spar cap. Test loading primarily consisted of flap fatigue loading of the blades, with one quasi-static ultimate load case applied to the carbon fiber spar cap blade. Results of the test program were intended to provide the full-scale test data needed for validation of model and coupon test results of the effect of defects in wind turbine blade composite materials. Testing was part of the Blade Reliability Collaborative (BRC) led by Sandia National Laboratories (SNL). The BRC seeks to develop a deeper understanding of the causes of unexpected blade failures (Paquette 2012), and to develop methods to enable blades to survive to their expected operational lifetime. Recent work in the BRC includes examining and characterizing flaws and defects known to exist in wind turbine blades from manufacturing processes (Riddle et al. 2011). Recent results from reliability databases show that wind turbine rotor blades continue to be a leading contributor to turbine downtime (Paquette 2012).

  11. 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.

  12. Mechanical characterization of composite repairs for fiberglass wind turbine blades

    NASA Astrophysics Data System (ADS)

    Chawla, Tanveer Singh

    While in service, wind turbine blades experience various modes of loading. An example is impact loading in the form of hail or bird strikes, which might lead to localized damage or formation of cracks a few plies deep on the blade surface. One of the methods to conduct repairs on wind turbine blades that are damaged while in service is hand lay-up of the repair part after grinding out the damaged portion and some of its surrounding area. The resin used for such repairs usually differs from the parent plate resin in composition and properties such as gel time, viscosity, etc. As a result the properties of the repaired parts are not the same as that of the undamaged blades. Subsequent repetitive loading can be detrimental to weak repairs to such an extent so as to cause delamination at the parent-repair bondline causing the repairs to eventually fall off the blade. Thus the strength and toughness of the repair are of critical importance. Initial part of this work consists of an effort to increase repair strength by identifying an optimum hand layup repair resin for fiberglass wind turbine blades currently being manufactured by a global company. As delamination of the repair from the parent blade is a major concern and unidirectional glass fibers along with a polymer resin are used to manufacture blades under consideration, testing method detailed in ASTM D 5528 (Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites) was followed to determine propagation fracture toughness values of the prospective vinyl ester repair resin candidates. These values were compared to those for a base polyester repair resin used by the company. Experimental procedure and results obtained from the above mentioned testing using double cantilever beam (DCB) specimens are detailed. Three new repair resins were shortlisted through mode I testing. It was also found that variation in the depth of the ground top ply of the parent part affects the propagation fracture toughness values of the repair. Repairs conducted on surfaces with partially ground top plies possess higher fracture toughness values than those conducted on surfaces with complete top plies ground off. The three top repair resin candidates were then evaluated against the base repair resin under fatigue loading. The specimen configuration and testing method were chosen so as to be able to test hand layup repairs under tension -- tension cyclic loading. It was observed that all three new repair resins perform better than the base repair resin. The selection of the optimum repair resin was based on results from mode I and fatigue testing. Global manufacturing regulations and standards were also of prime concern. The final new repair resin is being used by the company in all of its plants over the globe. The balance of this work involves study of the effect of mixed mode I -- mode II loading on the strength of repairs conducted on fiber reinforced composite parts using hand lay-up technique. The specimens for this part were similar to those manufactured for mode I testing but with different dimensions and layup. They were made and tested in accordance with ASTM D 6671 (Standard Test Method for Mixed Mode I -- Mode II Interlaminar Fracture Toughness of Unidirectional Fiber Reinforced Polymer Matrix Composites). Comparison was made between the fracture toughness of the above chosen optimum repair resin and the base repair resin. At least two levels of mode mixture GII/G (Mode II fracture toughness / Mode I and II fracture toughness) were examined. Also, two levels of grinding were considered (complete ply vs. partial ply ground off) in order to establish the influence of varying top-ply grinding depths on the strength of hand layup repairs conducted on fiberglass composite structures. The results of this work have the potential to improve the repair process for current fiberglass wind turbine blades.

  13. Characterisation of the fatigue life, dynamic creep and modes of damage accumulation within mitral valve chordae tendineae.

    PubMed

    Gunning, Gillian M; Murphy, Bruce P

    2015-09-01

    Mitral valve prolapse is often caused by either elongated or ruptured chordae tendineae (CT). In many cases, rupture is spontaneous, meaning there is no underlying cause. We hypothesised that spontaneous rupture may be due to mechanical fatigue. To investigate this hypothesis, we tested porcine marginal CT: in uniaxial tension, and in fatigue at a range of peak stresses (n=12 at 15, 10 and 7.5MPa respectively, n=6 at 5MPa). The rupture surfaces of failed CT were observed histologically, under polarised light microscopy, and SEM. The cycles to failure for 15, 10, 7.5 and 5 MPa peak stresses were: (averageSD): 50774366, 4951356414, 99927108908, 19709969103. A Weibull plot was constructed and from this, the number of cycles at 50% probability of failure was established in order to approximate the fatigue life, which was found to be 2.43MPa at 10 million cycles. The rate of creep increases exponentially with increasing peak stress. Under histological examination it was observed that CT which have been fatigued at low stress partially lose their organised collagen structure and can sustain micro-cracks that can be linked to increases in the creep rate. Furthermore our SEM images closely matched descriptions from the literature of spontaneous in vivo rupture. In conclusion, we believe that the mechanical test results we present strongly suggest that spontaneous chordal rupture and chordal elongation in vivo can be caused by mechanical fatigue. PMID:26087111

  14. 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.

  15. Panel resonant behavior of wind turbine blades.

    SciTech Connect

    Paquette, Joshua A.; Griffith, Daniel Todd

    2010-03-01

    The principal design drivers in the certification of wind turbine blades are ultimate strength, fatigue resistance, adequate tip-tower clearance, and buckling resistance. Buckling resistance is typically strongly correlated to both ultimate strength and fatigue resistance. A composite shell with spar caps forms the airfoil shape of a blade and reinforcing shear webs are placed inside the blade to stiffen the blade in the flap-wise direction. The spar caps are dimensioned and the shear webs are placed so as to add stiffness to unsupported panel regions and reduce their length. The panels are not the major flap-wise load carrying element of a blade; however, they must be designed carefully to avoid buckling while minimizing blade weight. Typically, buckling resistance is evaluated by consideration of the load-deflection behavior of a blade using finite element analysis (FEA) or full-scale static testing of blades under a simulated extreme loading condition. The focus of this paper is on the use of experimental modal analysis to measure localized resonances of the blade panels. It can be shown that the resonant behavior of these panels can also provide a means to evaluate buckling resistance by means of analytical or experimental modal analysis. Further, panel resonances have use in structural health monitoring by observing changes in modal parameters associated with panel resonances, and use in improving panel laminate model parameters by correlation with test data. In recent modal testing of wind turbine blades, a set of panel modes were measured. This paper will report on the findings of these tests and accompanying numerical and analytical modeling efforts aimed at investigating the potential uses of panel resonances for blade evaluation, health monitoring, and design.

  16. Test evaluation of a laminated wood wind turbine blade concept

    NASA Technical Reports Server (NTRS)

    Faddoul, J. R.

    1981-01-01

    A series of tests conducted on a root end section of a laminated wood wind turbine blade are reported. The blade to hub transition of the wood blade uses steel studs cast into the wood D spar with a filled epoxy. Both individual studs and a full scale, short length, root section were tested. Results indicate that the bonded stud concept is more than adequate for both the 30 year life fatigue loads and for the high wind or hurricane gust loads.

  17. 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.

  18. Microstructural aspects of fatigue in Ni-base superalloys.

    PubMed

    Antolovich, Stephen D

    2015-03-28

    Nickel-base superalloys are primarily used as components in jet engines and land-based turbines. While compositionally complex, they are microstructurally simple, consisting of small (50-1000?nm diameter), ordered, coherent Ni(3)(Al,Ti)-type L1(2) or Ni(3)Nb-type DO(22) precipitates (called ?(') and ?(''), respectively) embedded in an FCC substitutional solid solution consisting primarily of Ni and other elements which confer desired properties depending upon the application. The grain size may vary from as small as 2??m for powder metallurgy alloys used in discs to single crystals the actual size of the component for turbine blades. The fatigue behaviour depends upon the microstructure, deformation mode, environment and cycle time. In many cases, it can be controlled or modified through small changes in composition which may dramatically change the mechanism of damage accumulation and the fatigue life. In this paper, the fundamental microstructural, compositional, environmental and deformation mode factors which affect fatigue behaviour are critically reviewed. Connections are made across a range of studies to provide more insight. Modern approaches are pointed out in which the wealth of available microstructural, deformation and damage information is used for computerized life prediction. The paper ends with a discussion of the very important and highly practical subject of thermo-mechanical fatigue (TMF). It is shown that physics-based modelling leads to significantly improved life prediction. Suggestions are made for moving forward on the critical subject of TMF life prediction in notched components. PMID:25713453

  19. 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.

  20. 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.

  1. Modifications on A-F hardening rule to assess ratcheting response of materials and its interaction with fatigue damage under uniaxial stress cycles

    NASA Astrophysics Data System (ADS)

    Ahmadzadehrishehri, Gholamreza

    Ratcheting deformation is accumulated progressively over three distinct stages in materials undergoing asymmetrical cyclic stresses. The present thesis evaluates the triphasic ratcheting response of materials from two stand points: (i) Mechanistic approach at which stages of ratcheting progress over stress cycles was related to mechanistic parameters such as stress level, lifespan, mechanical properties and the softening/hardening response of materials. Mechanistic approach formulated in this thesis was employed to assess ratcheting strain over triphasic stages in various steel and copper alloys under uniaxial stress cycles. Good agreements were achieved between the predicted ratcheting strain values based on the proposed formulation and those of experimentally reported. (ii) Kinematic hardening rule approach at which the hardening rule was characterized by the yield surface translation mechanism and the corresponding plastic modulus calculated based on the consistency condition. Various cyclic plasticity models were employed to assess ratcheting response of materials under different loading conditions. The Armstrong-Frederick (A-F) hardening rule was taken as the backbone of ratcheting analysis developed in this thesis mainly due to less complexity and number of coefficients in the hardening rule as compared with other earlier developed hardening rules in the literature. To predict triphasic ratcheting strain over stress cycles, the A-F hardening rule has been further developed by means of new strain rate coefficients gamma 2 and delta. These coefficients improved the hardening rule capability to calibrate and control the rate of ratcheting over its progressive stages. The modified hardening formulation holds the coefficients of the hardening rule to control stress-strain hysteresis loops generated over stress cycles during ratcheting process plus the ratcheting rates over stages I, II, and III. These coefficients were calibrated and defined based on the applied stress levels. The constructed calibration curves were employed to determine strain rate coefficients required to assess ratcheting response of materials under uniaxial loading conditions at various cyclic stress levels. The predicted ratcheting strain values based on the modified hardening rule were found in good agreements with the experimentally obtained ratcheting data over stages I and II under uniaxial loading conditions. The capability of the modified hardening rule to assess ratcheting deformation of materials under multi-step uniaxial loading spectra was also assessed. Subsequent load steps were considerably affected by previous load steps in multi-step loading conditions. Ratcheting strains for low-high stress steps were successfully predicted by the modified hardening rule. High-low loading sequences however resulted in an overestimated reversed ratcheting strain in the later load steps. The modified hardening rule proposed in this thesis was then employed to predict the ratcheting strain and its concurrent interaction with fatigue damage over stress cycles in steel alloys. The interaction of ratcheting and fatigue damage was defined based on mechanistic parameters involving the effects of mean stress, stress amplitude, and cyclic softening/hardening response of materials. The extent of ratcheting effect on the overall damage of steel samples was defined by means of the product of the average ratcheting strain rate over the stress cycles and the applied maximum cyclic stress, while fatigue damage was analysed based on earlier developed energy-based models of Xia-Ellyin and Smith-Watson-Topper. Overall damage induced by both ratcheting and fatigue was calibrated through a weighting factor at various ratios of mean stress/cyclic amplitude stress (sigmam/sigmaa). The estimated lives based on the proposed algorithm at different mean stresses and stress amplitudes showed good agreements as compared with experiments.

  2. 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.

  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. Thermal-barrier-coated turbine blade study

    NASA Technical Reports Server (NTRS)

    Siemers, P. A.; Hillig, W. B.

    1981-01-01

    The effects of coating TBC on a CF6-50 stage 2 high-pressure turbine blade were analyzed with respect to changes in the mean bulk temperature, cooling air requirements, and high-cycle fatigue. Localized spallation was found to have a possible deleterious effect on low-cycle fatigue life. New blade design concepts were developed to take optimum advantage of TBCs. Process and material development work and rig evaluations were undertaken which identified the most promising combination as ZrO2 containing 8 w/o Y2O3 applied by air plasma spray onto a Ni22Cr-10Al-1Y bond layer. The bond layer was applied by a low-pressure, high-velocity plasma spray process onto the base alloy. During the initial startup cycles the blades experienced localized leading edge spallation caused by foreign objects.

  5. 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.

  6. Tensile Creep and Fatigue of Sylramic-iBN Melt-Infiltrated SiC Matrix Composites: Retained Properties, Damage Development, and Failure Mechanisms

    NASA Technical Reports Server (NTRS)

    Morscher, Greg; Gowayed, yasser; Miller, Robert; Ojard, Greg; Ahmad, Jalees; Santhosh, Unni; John, Reji

    2008-01-01

    An understanding of the elevated temperature tensile creep, fatigue, rupture, and retained properties of ceramic matrix composites (CMC) envisioned for use in gas turbine engine applications are essential for component design and life-prediction. In order to quantify the effect of stress, time, temperature, and oxidation for a state-of-the-art composite system, a wide variety of tensile creep, dwell fatigue, and cyclic fatigue experiments were performed in air at 1204 C for the SiC/SiC CMC system consisting of Sylramic-iBN SiC fibers, BN fiber interphase coating, and slurry-cast melt-infiltrated (MI) SiC-based matrix. Tests were either taken to failure or interrupted. Interrupted tests were then mechanically tested at room temperature to determine the residual properties. The retained properties of most of the composites subjected to tensile creep or fatigue were usually within 20% of the as-produced strength and 10% of the as-produced elastic modulus. It was observed that during creep, residual stresses in the composite are altered to some extent which results in an increased compressive stress in the matrix upon cooling and a subsequent increased stress required to form matrix cracks. Microscopy of polished sections and the fracture surfaces of specimens which failed during stressed-oxidation or after the room-temperature retained property test was performed on some of the specimens in order to quantify the nature and extent of damage accumulation that occurred during the test. It was discovered that the distribution of stress-dependent matrix cracking at 1204 C was similar to the as-produced composites at room temperature; however, matrix crack growth occurred over time and typically did not appear to propagate through thickness except at final failure crack. Failure of the composites was due to either oxidation-induced unbridged crack growth, which dominated the higher stress regime (> 179 MPa) or controlled by degradation of the fibers, probably caused by intrinsic creep-induced flaw growth of the fibers or internal attack of the fibers via Si diffusion through the CVI SiC and/or microcracks at the lower stress regime (< 165 MPa).

  7. Design and evaluation of low-cost stainless steel fiberglass foam blades for large wind driven generating systems

    NASA Technical Reports Server (NTRS)

    Eggert, W. S.

    1982-01-01

    A low cost wind turbine blade based on a stainless steel fiberglass foam Budd blade design concept, was evaluated for its principle characteristics, low cost features, and its advantages and disadvantages. A blade structure was designed and construction methods and materials were selected. A complete blade tooling concepts, various technical and economic analysis, and evaluations of the blade design were performed. A comprehensive fatigue test program is conducted to provide data to verify the design stress allowables.

  8. Fatigue loading of tendon

    PubMed Central

    Shepherd, Jennifer H; Screen, Hazel R C

    2013-01-01

    Tendon injuries, often called tendinopathies, are debilitating and painful conditions, generally considered to develop as a result of tendon overuse. The aetiology of tendinopathy remains poorly understood, and whilst tendon biopsies have provided some information concerning tendon appearance in late-stage disease, there is still little information concerning the mechanical and cellular events associated with disease initiation and progression. Investigating this in situ is challenging, and numerous models have been developed to investigate how overuse may generate tendon fatigue damage and how this may relate to tendinopathy conditions. This article aims to review these models and our current understanding of tendon fatigue damage. We review the strengths and limitations of different methodologies for characterizing tendon fatigue, considering in vitro methods that adopt both viable and non-viable samples, as well as the range of different in vivo approaches. By comparing data across model systems, we review the current understanding of fatigue damage development. Additionally, we compare these findings with data from tendinopathic tissue biopsies to provide some insights into how these models may relate to the aetiology of tendinopathy. Fatigue-induced damage consistently highlights the same microstructural, biological and mechanical changes to the tendon across all model systems and also correlates well with the findings from tendinopathic biopsy tissue. The multiple testing routes support matrix damage as an important contributor to tendinopathic conditions, but cellular responses to fatigue appear complex and often contradictory. PMID:23837793

  9. 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.

  10. Feasibility study of pultruded blades for wind turbine rotors

    SciTech Connect

    Migliore, P.G.; Cheney, M.C.

    2000-02-28

    In work performed under subcontract to the National Renewable Energy Laboratory (NREL), a preliminary design study and proof-of-concept field test were conducted to evaluate the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study, and a scaled 80 kW rotor was fabricated and tested as a demonstration of the concept. To examine the feasibility of pultruded blades, several issues were addressed, including power performance, tower strikes, yaw stability, stall flutter, fatigue, and rotor cost. Results showed that with proper design, rotors using pultruded blades demonstrate acceptable fatigue life and stable yaw behavior without tower strikes. Furthermore, blades using this technology may be manufactured for approximately half the cost of conventional blades. Field tests of the scaled rotor provided experimental data on power performance and loads while verifying stable yaw operation.

  11. Design, fabrication, and test of a steel spar wind turbine blade

    NASA Technical Reports Server (NTRS)

    Sullivan, T. L.; Sirocky, P. J., Jr.; Viterna, L. A.

    1979-01-01

    The design and fabrication of wind turbine blades based on 60 foot steel spars are discussed. Performance and blade load information is given and compared to analytical prediction. In addition, performance is compared to that of the original MOD-O aluminum blades. Costs for building the two blades are given, and a projection is made for the cost in mass production. Design improvements to reduce weight and improve fatigue life are suggested.

  12. A Failure Analysis Conducted on a Fractured AISI 5160 Steel Blade Which Separated from an Agricultural Rotary Cutter

    NASA Astrophysics Data System (ADS)

    Johnson, Alan A.; Storey, Randall J.

    2011-07-01

    One of the six blades of an agricultural rotary cutter used for cutting down small trees and bushes broke into two pieces while the blades were rotating. One piece was hurled from the cutter and struck a young farmer, who had been operating the machine, causing a near fatal leg injury. In the ensuing litigation against the manufacturers and marketer of the machine each litigant retained a metallurgist and other experts. The metallurgists jointly directed laboratory work on the broken blade conducted at an independent laboratory according to a protocol which they developed and which was approved by the court. As a result of the laboratory work the present authors, working for the Plaintiffs, concluded that failure of the blade occurred because it contained quench cracks introduced when it was manufactured. The Defendants' metallurgists concluded that the blade had been misassembled onto the machine and, as a result, had failed by fatigue. Eventually, the case was set for a jury trial in a Circuit Court in rural Kentucky. The jury found for the Plaintiffs and awarded them $5.9 million in damages. Part of this judgement was later reversed by the Kentucky Court of Appeals and the case was then settled without a second trial under terms which were not revealed.

  13. Self-Repairing Fatigue Damage in Metallic Structures for Aerospace Vehicles Using Shape Memory Alloy Self-healing (SMASH) Technology

    NASA Technical Reports Server (NTRS)

    Wright, M. Clara; Manuel, Michele; Wallace, Terryl; Newman, Andy; Brinson, Kate

    2015-01-01

    This DAA is for the Phase II webinar presentation of the ARMD-funded SMASH technology. A self-repairing aluminum-based composite system has been developed using liquid-assisted healing theory in conjunction with the shape memory effect of wire reinforcements. The metal matrix composite was thermodynamically designed to have a matrix with a relatively even dispersion of low-melting phase, allowing for repair of cracks at a pre-determined temperature. Shape memory alloy wire reinforcements were used within the composite to provide crack closure. Investigators focused the research on fatigue cracks propagating through the matrix in order to optimize and computer model the SMASH technology for aeronautical applications.

  14. Performance of twist-coupled blades on variable speed rotors

    SciTech Connect

    Lobitz, D.W.; Veers, P.S.; Laino, D.J.

    1999-12-07

    The load mitigation and energy capture characteristics of twist-coupled HAWT blades that are mounted on a variable speed rotor are investigated in this paper. These blades are designed to twist toward feather as they bend with pretwist set to achieve a desirable twist distribution at rated power. For this investigation, the ADAMS-WT software has been modified to include blade models with bending-twist coupling. Using twist-coupled and uncoupled models, the ADAMS software is exercised for steady wind environments to generate C{sub p} curves at a number of operating speeds to compare the efficiencies of the two models. The ADAMS software is also used to generate the response of a twist-coupled variable speed rotor to a spectrum of stochastic wind time series. This spectrum contains time series with two mean wind speeds at two turbulence levels. Power control is achieved by imposing a reactive torque on the low speed shaft proportional to the RPM squared with the coefficient specified so that the rotor operates at peak efficiency in the linear aerodynamic range, and by limiting the maximum RPM to take advantage of the stall controlled nature of the rotor. Fatigue calculations are done for the generated load histories using a range of material exponents that represent materials from welded steel to aluminum to composites, and results are compared with the damage computed for the rotor without twist-coupling. Results indicate that significant reductions in damage are achieved across the spectrum of applied wind loading without any degradation in power production.

  15. Wind Turbine Blade

    USGS Multimedia Gallery

    This photo shows one of the three 135-ft blades of a turbine before installation. Although the blades of wind turbines appear to move quite slowly to the human eye, blade tips often move at speeds faster than 100 mph. ...

  16. 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.

  17. Ceramic blade attachment system

    DOEpatents

    Boyd, Gary L. (Alpine, CA)

    1995-01-01

    A retainer ring is arranged to mount turbine blades to a turbine disk so that aerodynamic forces produced by a gas turbine engine are transferred from the turbine blades to the turbine disk to cause the turbine blades and turbine disk to rotate, but so that centrifugal forces of the turbine blades resulting from the rotation of the turbine blades and turbine disk are not transferred from the turbine blades to the turbine disk.

  18. Ceramic blade attachment system

    DOEpatents

    Boyd, G.L.

    1995-04-11

    A retainer ring is arranged to mount turbine blades to a turbine disk so that aerodynamic forces produced by a gas turbine engine are transferred from the turbine blades to the turbine disk to cause the turbine blades and turbine disk to rotate, but so that centrifugal forces of the turbine blades resulting from the rotation of the turbine blades and turbine disk are not transferred from the turbine blades to the turbine disk. 6 figures.

  19. Investigation of the fatigue and short-term mechanical properties of 13% chromium steel and titanium alloys after welding or treatment with high-frequency currents as applied to steam-turbine blades

    NASA Astrophysics Data System (ADS)

    Gonserovskii, F. G.; Nikitin, V. I.; Silevich, V. M.; Simin, O. N.

    2008-02-01

    We present the results of a study on comparing the structural strength of rotor blades made of stainless 13% chromium steels for their design versions in which wear-resistant straps made of cast VZK stellite are soldered or welded on the blade inlet edges. It is shown that treatment of VT6 alloy with high-frequency currents increases the endurance limit of the zone subjected to strengthening and makes the alloy more resistant to erosion. The worn blades of a 48-T4 titanium alloy repaired with the use of welding technologies have operational characteristics at least as good as those of newly manufactured ones.

  20. 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.

  1. Fatigue In Continuous-Fiber/Metal-Matrix Composites

    NASA Technical Reports Server (NTRS)

    Johnson, William S.

    1992-01-01

    Report describes experimental approaches to quantification of fatigue damage in metal-matrix composites (MMC's). Discusses number of examples of development of damage and failure along with associated analytical models of behavior of MMC. Objectives of report are twofold. First, present experimental procedures and techniques for conducting meaningful fatigue tests to detect and quantify fatigue damage in MMC's. Second, present examples of how fatigue damage initiated and grows in various MMC's. Report furnishes some insight into what type of fatigue damage occurs and how damage quantified.

  2. Analysis and improvement of gas turbine blade temperature measurement error

    NASA Astrophysics Data System (ADS)

    Gao, Shan; Wang, Lixin; Feng, Chi; Daniel, Ketui

    2015-10-01

    Gas turbine blade components are easily damaged; they also operate in harsh high-temperature, high-pressure environments over extended durations. Therefore, ensuring that the blade temperature remains within the design limits is very important. In this study, measurement errors in turbine blade temperatures were analyzed, taking into account detector lens contamination, the reflection of environmental energy from the target surface, the effects of the combustion gas, and the emissivity of the blade surface. In this paper, each of the above sources of measurement error is discussed, and an iterative computing method for calculating blade temperature is proposed.

  3. Evaluation of the durability of composite tidal turbine blades.

    PubMed

    Davies, Peter; Germain, Grgory; Gaurier, Benot; Boisseau, Amlie; 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

  4. 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.

  5. Influence of different wind profiles due to varying atmospheric stability on the fatigue life of wind turbines

    NASA Astrophysics Data System (ADS)

    Sathe, Ameya; Bierbooms, Wim

    2007-07-01

    Offshore wind energy is being developed on a very large scale in the European seas. The objective of developing wind energy offshore is to capture greater wind speeds than are encountered onshore and as a result more energy. With this also come more challenges in the design of wind turbines due to the hostile offshore environment. Currently the standards for offshore wind turbines prescribe a site specific design for the support structures and the design for the rotor nacelle assembly according to onshore standards. Wind turbines are designed to withstand fatigue and ultimate loads. For the fatigue loading several input conditions have been prescribed, amongst which wind profile is one of them. Wind profile is represented by power law or logarithmic law as given in the standards. A neutral stability of the atmosphere is considered while obtaining the wind profile using the logarithmic law. In this paper the atmospheric stability is varied in order to estimate different wind profiles and simulations are run in Bladed to check its influence on the fatigue damage at the blade root. The variations in the atmospheric stability has been taken into account by using some typical values of Obukhov length. From steady state simulations it has been found that atmospheric stability is important for fatigue damage. The analysis showed that variation in the distribution of atmospheric stability causes large variations in the fatigue damage for different sites. Thus, it is worthwhile to carry out a full scale study using the turbulent winds and real data for wind turbine and environmental conditions.

  6. Thermal Imaging of Medical Saw Blades and Guides

    SciTech Connect

    Dinwiddie, Ralph Barton; Steffner, Thomas E

    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.

  7. Impact resistance of current design composite fan blades tested under short-haul operating conditions

    NASA Technical Reports Server (NTRS)

    Steinhagen, C. A.; Salemme, C. T.

    1973-01-01

    Boron/epoxy and graphite/epoxy composite blades were impacted in a rotating whirligig facility with conditions closely simulating those which might be experienced by a STOL engine impacted with various foreign objects. The tip speed of the rotating blades was 800 feet per second. The blades were impacted with simulated birds, real birds, ice balls, and gravel. The results of composite blade impact tests were compared with a titanium blade tested under similar conditions. Neither composite material indicated a clear superiority over the other. Blades made from both composite materials showed more damage than the titanium blades.

  8. Analysis and Tests of Pultruded Blades for Wind Turbine Rotors

    SciTech Connect

    Cheney, M. C.; 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.

  9. Advanced turbofan blade refurbishment technique

    SciTech Connect

    Roberts, W.B.

    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.

  10. Seismic-induced impeller/blade rubs in rotating power plant components

    SciTech Connect

    Padovan, J.; Choy, F.K.; Batur, C.; Canilang, L. . Dept. of Mechanical Engineering)

    1988-11-01

    During seismic or blade/impeller loss events, the potential for rubs in rotating nuclear and fossil fuel power plant components is quite high. Generally, such events involve interactions between blade/impeller tips and machinery components. This also includes the possibility of seal casing rubs. The paper develops methodologies to: evaluate the blade impeller-casing rub event; establish the associated stress, strain and force fields; enable signature analysis defining blade/impeller/seal participation; and establish procedure enabling evaluation of blade/impeller/seal fatigue life. Additionally, the paper presents benchmarking examples of prototypical power plant components.

  11. Gas turbine blade seal

    SciTech Connect

    Chlus, W.A.

    1993-07-20

    A gas turbine engine is described having a disk and a plurality of blades, each blade having a airfoil, a blade platform, a neck, and a root, the root of each blade secured in the disk, the platform of each blade being independent of the other; a seal arrangement comprising: a rigid damper disposed in an under blade zone and in contact with adjacent platforms; and a flexible seal located downstream of the rigid damper, the seal being clipped to the rigid damper and in contact with the adjacent platforms at a location downstream of the rigid damper.

  12. 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.

  13. SSME HPFTP/AT Turbine Blade Platform Featherseal Damper Design

    NASA Technical Reports Server (NTRS)

    Montgomery, S. K.

    1999-01-01

    During the Space Shuttle Main Engines (SSM) HPFtP/AT development program, engine hot fire testing resulted in turbine blade fatigue cracks. The cracks were noted after only a few tests and a several hundred seconds versus the design goal of 60 tests and >30,000 seconds. Subsequent investigation attributed the distress to excessive steady and dynamic loads. To address these excessive turbine blade loads, Pratt & Whitney Liquid Space Propulsion engineers designed and developed retrofitable turbine blade to blade platform featherseal dampers. Since incorporation of these dampers, along with other turbine blade system improvements, there has been no observed SSME HPFTP/AT turbine blade fatigue cracking. The high time HPFTP/AT blade now has accumulated 32 starts and 19,200 seconds hot fire test time. Figure #1 illustrates the HPFTP/AT turbine blade platform featherseal dampers. The approached selected was to improve the turbine blade structural capability while simultaneously reducing loads. To achieve this goal, the featherseal dampers were designed to seal the blade to blade platform gap and damp the dynamic motions. Sealing improves the steady stress margins by increasing turbine efficiency and improving turbine blade attachment thermal conditioning. Load reduction was achieved through damping. Thin Haynes 188 sheet metal was selected based on its material properties (hydrogen resistance, elongation, tensile strengths, etc.). The 36,000 rpm wheel speed of the rotor result in a normal load of 120#/blade. The featherseals then act as micro-slip dampers during actual SSME operation. After initial design and analysis (prior to full engine testing), the featherseal dampers were tested in P&W's spin rig facility in West Palm Beach, Florida. Both dynamic strain gages and turbine blade tip displacement measurements were utilized to quantify the featherseal damper effectiveness. Full speed (36,000 rpm), room temperature rig testing verified the elimination of fundamental mode (i.e, modes 1 & 2) resonant response. The reduction in turbine blade dynamic response is shown for a typical turbine blade. This paper discusses the design and verification of these dampers. The numerous benefits associated with this design concept warrants consideration in existing and future turbomachinery applications.

  14. Effects of pre-irradiation of low-level laser therapy with different doses and wavelengths in skeletal muscle performance, fatigue, and skeletal muscle damage induced by tetanic contractions in rats.

    PubMed

    Santos, Larissa Aline; Marcos, Rodrigo Labat; Tomazoni, Shaiane Silva; Vanin, Adriane Aver; Antonialli, Fernanda Colella; Grandinetti, Vanessa dos Santos; Albuquerque-Pontes, Gianna Mes; de Paiva, Paulo Roberto Vicente; Lopes-Martins, Rodrigo lvaro Brando; de Carvalho, Paulo de Tarso Camillo; Bjordal, Jan Magnus; Leal-Junior, Ernesto Cesar Pinto

    2014-09-01

    This study aimed to evaluate the effects of low-level laser therapy (LLLT) immediately before tetanic contractions in skeletal muscle fatigue development and possible tissue damage. Male Wistar rats were divided into two control groups and nine active LLLT groups receiving one of three different laser doses (1, 3, and 10 J) with three different wavelengths (660, 830, and 905 nm) before six tetanic contractions induced by electrical stimulation. Skeletal muscle fatigue development was defined by the percentage (%) of the initial force of each contraction and time until 50 % decay of initial force, while total work was calculated for all six contractions combined. Blood and muscle samples were taken immediately after the sixth contraction. Several LLLT doses showed some positive effects on peak force and time to decay for one or more contractions, but in terms of total work, only 3 J/660 nm and 1 J/905 nm wavelengths prevented significantly (p < 0.05) the development of skeletal muscle fatigue. All doses with wavelengths of 905 nm but only the dose of 1 J with 660 nm wavelength decreased creatine kinase (CK) activity (p < 0.05). Qualitative assessment of morphology revealed lesser tissue damage in most LLLT-treated groups, with doses of 1-3 J/660 nm and 1, 3, and 10 J/905 nm providing the best results. Optimal doses of LLLT significantly delayed the development skeletal muscle performance and protected skeletal muscle tissue against damage. Our findings also demonstrate that optimal doses are partly wavelength specific and, consequently, must be differentiated to obtain optimal effects on development of skeletal muscle fatigue and tissue preservation. Our findings also lead us to think that the combined use of wavelengths at the same time can represent a therapeutic advantage in clinical settings. PMID:24651950

  15. 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.

  16. Wind turbine blade testing system using base excitation

    DOEpatents

    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).

  17. 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.

  18. Wind turbine blade shear web disbond detection using rotor blade operational sensing and data analysis.

    PubMed

    Myrent, Noah; Adams, Douglas E; Griffith, D Todd

    2015-02-28

    A wind turbine blade's structural dynamic response is simulated and analysed with the goal of characterizing the presence and severity of a shear web disbond. Computer models of a 5?MW offshore utility-scale wind turbine were created to develop effective algorithms for detecting such damage. Through data analysis and with the use of blade measurements, a shear web disbond was quantified according to its length. An aerodynamic sensitivity study was conducted to ensure robustness of the detection algorithms. In all analyses, the blade's flap-wise acceleration and root-pitching moment were the clearest indicators of the presence and severity of a shear web disbond. A combination of blade and non-blade measurements was formulated into a final algorithm for the detection and quantification of the disbond. The probability of detection was 100% for the optimized wind speed ranges in laminar, 30% horizontal shear and 60% horizontal shear conditions. PMID:25583871

  19. 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.

  20. 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.

  1. White noise response of turbine blades subjected to heat flux and thermal gradient

    SciTech Connect

    Karadag, V.; Aba, E.; Morguel, O.K.

    1997-07-01

    Design and production of the complex mechanical structures rarely result in an optimal solution. A typical example for this is a turbine blade design. Fatigue failures of the turbine blades is one of the most vexing problems of turbo-machine manufacturers, ever since the steam turbine became the main stay for power generating equipment and the gas turbines are increasingly used in air transport. Turbine blade failures due to fatigue are predominantly vibration related. The dynamic loads on the blading can arise from many different sources such as the high rotational speed, the high operating temperatures, the asymmetric aerofil tapered form of the turbine blade etc. Therefore, vibratory analysis is one of the most important stage in the designing of the turbine blades. In this study, the random response of the turbine blade to white noise excitation has been consistently calculated, including the internal damping mechanisms of the blade. Beside the damping effects, the rotational speed and the linear thermal gradient along the turbine blade are incorporated into the analysis. Pressure difference between the two surfaces of the turbine blades are modelled as white noise excitation along all over the turbine blade. The system dynamic equation of motion are derived and solved by using the combined Finite Element-Modal Analysis Method.

  2. 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.

  3. 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.

  4. 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.; Khn, 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.

  5. Nondestructive evaluation of fatigue in titanium alloys

    SciTech Connect

    Roesner, H.; Meyendorf, N.; Sathish, S.; Matikas, T.E.

    2000-07-01

    Dissipated heat has been measured by thermographic technique during fatigue experiments on Ti-6Al-4V. Surface temperature of the specimen was found sensitive to the amount of fatigue damage accumulated in the material. An increased heat dissipation due to fatigue can be related to continuous change in the microstructure (increased dislocation density, stacking faults, etc.) of the material. A method based on passive thermography can be proposed to monitor damage accumulation in Ti-6Al-4V due to cyclic loading.

  6. 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.

  7. 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.

  8. Composite fan blade

    SciTech Connect

    Farr, J.D.

    1993-08-31

    A composite fan blade is described for a prop fan engine comprising: a support disk having a plurality of hinge lugs formed therein, the disk being connected to an engine drive means; a bushing element; a fan blade formed from a first set of radially oriented unidirectional layers of fibers, the first set of layers of fibers being wrapped around the bushing element to form an elongated front side, an elongated back side, and a portion encompassing the bushing element; a blade platform formed from a second set of unidirectional layers of fibers having a first and a second end which are both wrapped around respective resin filler elements to form resin filled support pockets, the second set of unidirectional layers of fibers being wrapped around the portion of the fan blade encompassing the bushing element to place the resin filled support pockets against the portion of the fan blade encompassing the bushing element, wherein the fan blade and the blade platform form a fan blade assembly, the fan blade assembly having a plurality of hinge slots formed therein; and a pin element extending through the hinge formed by the plurality of hinge lugs in the support disk and the plurality of hinge slots in the fan blade assembly for attaching the fan blade assembly to the support disk.

  9. Multiscale Fatigue Life Prediction for Composite Panels

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.

    2012-01-01

    Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.

  10. Blade design and operating experience on the MOD-OA 200 kW wind turbine at Clayton, New Mexico

    NASA Technical Reports Server (NTRS)

    Linscott, B. S.; Shaltens, R. K.

    1979-01-01

    Two 60 foot long aluminum wind turbine blades were operated for over 3000 hours on the MOD-OA wind turbine. The first signs of blade structural damage were observed after 400 hours of operation. Details of the blade design, loads, cost, structural damage, and repair are discussed.

  11. 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.

  12. Reducing Fatigue in a Rotary Flowmeter

    NASA Technical Reports Server (NTRS)

    Rao, G.

    1987-01-01

    Redesign of vanes straightening flow of liquid in rotary flowmeter increase fatigue lives of vanes and rotor. Purpose of vanes to eliminate turbulence so proportionality between flow and rotor speed constant. Nonuniform but symmetrical, new spacing of straightener vanes prevents flow wake from strongly interacting with rotor blades. At same time, vanes ensure accurate flow-rate measurement.

  13. Corrosion fatigue of high strength fastener materials in seawater

    NASA Technical Reports Server (NTRS)

    Tipton, D. G.

    1983-01-01

    Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength of AISI 41L4O in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials was studied. The AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35N were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data are fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.

  14. Dual-axis resonance testing of wind turbine blades

    DOEpatents

    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.

  15. Application of BSTRAIN software for wind turbine blade testing

    SciTech Connect

    Musial, W D; Clark, M E; Stensland, T

    1996-07-01

    NREL currently operates the largest structural testing facility in US for testing wind turbine blades. A data acquisition system was developed to measure blade response and monitor test status; it is called BSTRAIN (Blade Structural Test Real-time Acquisition Interface Network). Software objectives were to develop a robust, easy-to-use computer program that could automatically collect data from static and fatigue blade tests without missing any significant events or overloading the computer with excess data. The program currently accepts inputs from up to 32 channels but can be expanded to over 1000 channels. In order to reduce the large amount of data collected during long fatigue tests, options for real-time data processing were developed including peak-valley series collection, peak-valley decimation, block decimation, and continuous recording of all data. Other BSTRAIN features include automated blade stiffness checks, remote terminal access to blade test status, and automated VCR control for continuous test recording. Results from tests conducted with the software revealed areas for improvement including test accuracy, post-processing analysis, and further data reduction.

  16. Fatigue analyses of the prototype Francis runners based on site measurements and simulations

    NASA Astrophysics Data System (ADS)

    Huang, X.; Chamberland-Lauzon, J.; Oram, C.; Klopfer, A.; Ruchonnet, N.

    2014-03-01

    With the increasing development of solar power and wind power which give an unstable output to the electrical grid, hydropower is required to give a rapid and flexible compensation, and the hydraulic turbines have to operate at off-design conditions frequently. Prototype Francis runners suffer from strong vibrations induced by high pressure pulsations at part load, low part load, speed-no-load and during start-stops and load rejections. Fatigue and damage may be caused by the alternating stress on the runner blades. Therefore, it becomes increasingly important to carry out fatigue analysis and life time assessment of the prototype Francis runners, especially at off-design conditions. This paper presents the fatigue analyses of the prototype Francis runners based on the strain gauge site measurements and numerical simulations. In the case of low part load, speed-no-load and transient events, since the Francis runners are subjected to complex hydraulic loading, which shows a stochastic characteristic, the rainflow counting method is used to obtain the number of cycles for various dynamic amplitude ranges. From middle load to full load, pressure pulsations caused by Rotor-stator- Interaction become the dominant hydraulic excitation of the runners. Forced response analysis is performed to calculate the maximum dynamic stress. The agreement between numerical and experimental stresses is evaluated using linear regression method. Taking into account the effect of the static stress on the S-N curve, the Miner's rule, a linear cumulative fatigue damage theory, is employed to calculate the damage factors of the prototype Francis runners at various operating conditions. The relative damage factors of the runners at different operating points are compared and discussed in detail.

  17. Active Blade Vibration Control Being Developed and Tested

    NASA Technical Reports Server (NTRS)

    Johnson, Dexter

    2003-01-01

    Gas turbine engines are currently being designed to have increased performance, lower weight and manufacturing costs, and higher reliability. Consequently, turbomachinery components, such as turbine and compressor blades, have designs that are susceptible to new vibration problems and eventual in-service failure due to high-cycle fatigue. To address this problem, researchers at the NASA Glenn Research Center are developing and testing innovative active blade vibration control concepts. Preliminary results of using an active blade vibration control system, involving a rotor supported by an active magnetic bearing in Glenn's Dynamic Spin Rig, indicate promising results (see the photograph). Active blade vibration control was achieved using feedback of blade strain gauge signals within the magnetic bearing control loop. The vibration amplitude was reduced substantially (see the graphs). Also, vibration amplitude amplification was demonstrated; this could be used to enhance structural mode identification, if desired. These results were for a nonrotating two-bladed disk. Tests for rotating blades are planned. Current and future active blade vibration control research is planned to use a fully magnetically suspended rotor and smart materials. For the fully magnetically suspended rotor work, three magnetic bearings (two radial and one axial) will be used as actuators instead of one magnetic bearing. This will allow additional degrees of freedom to be used for control. For the smart materials work, control effectors located on and off the blade will be considered. Piezoelectric materials will be considered for on-the-blade actuation, and actuator placement on a stator vane, or other nearby structure, will be investigated for off-the-blade actuation. Initial work will focus on determining the feasibility of these methods by performing basic analysis and simple experiments involving feedback control.

  18. Fracture mechanics evaluation of progressive fatigue damage in a circular-hole-notched GRP composite under combined tension/torsion loading

    NASA Astrophysics Data System (ADS)

    Takemura, Kenichi; Fujii, Toru

    Progressive failure from a circular hole in glass-fiber-reinforced plastics (GRP) under combined tension/torsion cyclic loading has been investigated. Thin-walled tubular specimens were used. The composition of the specimens was the same as in previous work. As pseudo-crack growth was observed under fatigue loading leading to the final failure, fracture mechanics methods were applied to characterize the fatigue failure process. The energy release rate was used as a parameter for progressive failure. Fatigue life under combined cyclic loading was estimated on the basis of the relationship between pseudo-crack-growth rate and energy release rate. The prediced S/N lines agree with the experimental results in all except a few cases.

  19. Multi-spectral temperature measurement method for gas turbine blade

    NASA Astrophysics Data System (ADS)

    Gao, Shan; Feng, Chi; Wang, Lixin; Li, Dong

    2016-02-01

    One of the basic methods to improve both the thermal efficiency and power output of a gas turbine is to increase the firing temperature. However, gas turbine blades are easily damaged in harsh high-temperature and high-pressure environments. Therefore, ensuring that the blade temperature remains within the design limits is very important. There are unsolved problems in blade temperature measurement, relating to the emissivity of the blade surface, influences of the combustion gases, and reflections of radiant energy from the surroundings. In this study, the emissivity of blade surfaces has been measured, with errors reduced by a fitting method, influences of the combustion gases have been calculated for different operational conditions, and a reflection model has been built. An iterative computing method is proposed for calculating blade temperatures, and the experimental results show that this method has high precision.

  20. Multi-spectral temperature measurement method for gas turbine blade

    NASA Astrophysics Data System (ADS)

    Gao, Shan; Feng, Chi; Wang, Lixin; Li, Dong

    2015-11-01

    One of the basic methods to improve both the thermal efficiency and power output of a gas turbine is to increase the firing temperature. However, gas turbine blades are easily damaged in harsh high-temperature and high-pressure environments. Therefore, ensuring that the blade temperature remains within the design limits is very important. There are unsolved problems in blade temperature measurement, relating to the emissivity of the blade surface, influences of the combustion gases, and reflections of radiant energy from the surroundings. In this study, the emissivity of blade surfaces has been measured, with errors reduced by a fitting method, influences of the combustion gases have been calculated for different operational conditions, and a reflection model has been built. An iterative computing method is proposed for calculating blade temperatures, and the experimental results show that this method has high precision.

  1. 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.

  2. 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.

  3. Vibration-based SHM System: Application to Wind Turbine Blades

    NASA Astrophysics Data System (ADS)

    Tcherniak, D.; Mlgaard, L. L.

    2015-07-01

    This study presents an vibration-based system designed for structural health monitoring of wind turbine blades. Mechanical energy is introduced by means of an electromechanical actuator mounted inside the blade. The actuator's plunger periodically hits the blade structure; the induced vibrations propagate along the blade and are measured by an array of accelerometers. Unsupervised learning is applied to the data: the vibration patterns corresponding to the undamaged blade are used to create a statistical model of the reference state. During the detection stage, the current vibration pattern is compared with the reference state, and the novelties can be associated with damage. The vibration pattern is described by the covariance matrix between the accelerometer signals. The mid-range frequencies are used: this range is above the frequencies excited by blade-wind interaction, thus ensuring a good signal-to-noise ratio. Simultaneously, the frequencies are low enough to be able to propagate the entire blade length, so good results can be obtained even using only one actuator. The system is demonstrated on a real 34m blade mounted on a test rig. Using the suggested approach, the system enables detection of, e.g., a 20cm long trailing edge opening under realistic noise conditions. It is also demonstrated that the system provides rough information about damage location. Progression of damage, if any, can also be detected.

  4. Ceramic blade attachment system

    DOEpatents

    Shaffer, James E. (Maitland, FL)

    1995-01-01

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine disc having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade and forms a turbine assembly. The turbine blade has a root portion defining a pair of sides having a pair of grooves therein. The turbine assembly includes a pair of flanges between which the turbine blades are positioned. Each of the pair of flanges has a plurality of grooves defined therein. The grooves within the pair of flanges are aligned with the grooves in the blades and have a space formed therebetween. A plurality of spherical balls are positioned within the space. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade.

  5. Ceramic blade attachment system

    DOEpatents

    Shaffer, J.E.

    1995-07-11

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine disc having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade and forms a turbine assembly. The turbine blade has a root portion defining a pair of sides having a pair of grooves therein. The turbine assembly includes a pair of flanges between which the turbine blades are positioned. Each of the pair of flanges has a plurality of grooves defined therein. The grooves within the pair of flanges are aligned with the grooves in the blades and have a space formed therebetween. A plurality of spherical balls are positioned within the space. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade. 4 figs.

  6. The SNL100-03 Blade: Design Studies with Flatback Airfoils for the Sandia 100-meter Blade.

    SciTech Connect

    Griffith, Daniel; Richards, Phillip William

    2014-09-01

    A series of design studies were performed to inv estigate the effects of flatback airfoils on blade performance and weight for large blades using the Sandi a 100-meter blade designs as a starting point. As part of the study, the effects of varying the blade slenderness on blade structural performance was investigated. The advantages and disadvantages of blad e slenderness with respect to tip deflection, flap- wise & edge-wise fatigue resistance, panel buckling capacity, flutter speed, manufacturing labor content, blade total weight, and aerodynamic design load magn itude are quantified. Following these design studies, a final blade design (SNL100-03) was prod uced, which was based on a highly slender design using flatback airfoils. The SNL100-03 design with flatback airfoils has weight of 49 tons, which is about 16% decrease from its SNL100-02 predecessor that used conventional sharp trailing edge airfoils. Although not systematically optimized, the SNL100 -03 design study provides an assessment of and insight into the benefits of flatback airfoils for la rge blades as well as insights into the limits or negative consequences of high blade slenderness resulting from a highly slender SNL100-03 planform as was chosen in the final design definition. This docum ent also provides a description of the final SNL100-03 design definition and is intended to be a companion document to the distribution of the NuMAD blade model files for SNL100-03, which are made publicly available. A summary of the major findings of the Sandia 100-meter blade development program, from the initial SNL100-00 baseline blade through the fourth SNL100-03 blade study, is provided. This summary includes the major findings and outcomes of blade d esign studies, pathways to mitigate the identified large blade design drivers, and tool development that were produced over the course of this five-year research program. A summary of large blade tec hnology needs and research opportunities is also presented.

  7. Propeller blade retention system

    NASA Technical Reports Server (NTRS)

    Elston, III, Sidney B. (Inventor); Simon, III, Victor H. (Inventor); Tseng, Wu-Yang (Inventor); Butler, Lawrence (Inventor)

    1993-01-01

    The invention concerns the mounting of propeller blades to a ring-shaped rotor. The blades are of the variable pitch type, and the shank of each blade extends through a respective hole in the rotor. Each hole contains an annular shelf which is fastened to the wall of the hole and surrounds each shank. Each shank bears a pair of bearing races which sandwich the annular shelf in order to connect the blade to the rotor. Bearing rollers are positioned between the annular shelf and the bearing races.

  8. Evaluation of flawed composite structural components under static and cyclic loading. [fatigue life of graphite-epoxy composite materials

    NASA Technical Reports Server (NTRS)

    Porter, T. R.

    1979-01-01

    The effects of initial defects on the fatigue and fracture response of graphite-epoxy composite laminates are presented. The structural laminates investigated were a typical angle ply laminate, a polar/hoop wound pressure vessel laminate, and a typical engine fan blade laminate. Defects investigated were full and half penetration circular holes, full and half penetration slits, and countersink holes. The effects of the defect size and type on the static fracture strength, fatigue performance, and residual static strength are shown as well as the results of loadings on damage propagation in composite laminates. The data obtained were used to define proof test levels as a qualification procedure in composite structure subjected to cyclic loading.

  9. Impact absorbing blade mounts for variable pitch blades

    NASA Technical Reports Server (NTRS)

    Ravenhall, R.; Salemme, C. T.; Adamson, A. P. (inventors)

    1977-01-01

    A variable pitch blade and blade mount are reported that are suitable for propellers, fans and the like and which have improved impact resistance. Composite fan blades and blade mounting arrangements permit the blades to pivot relative to a turbine hub about an axis generally parallel to the centerline of the engine upon impact of a large foreign object, such as a bird. Centrifugal force recovery becomes the principal energy absorbing mechanism and a blade having improved impact strength is obtained.

  10. 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.

  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. Condition monitoring techniques for composite wind turbine blades

    NASA Astrophysics Data System (ADS)

    Bond, Leonard J.; Aftab, Nadeem; Clayton, Brian R.; Dutton, A. G.; Irving, Andrew D.; Lipman, Norman H.

    The range of possible NDT techniques that might be applied to wind turbine blades is reviewed. Thermal techniques are selected and implemented in various active and passive modes. Theoretical modeling of 3D thermal interactions is performed using a finite difference model. Several thermal condition monitoring methods are evaluated experimentally on both composites and composite wood blades. The relative detectability of various effects using the active heating approach is shown. Internal generation of heat was detected during a full-size wood laminate blade fatigue test. Temperature differences of over 1 C were measured at the surface above the underlying butt joint some 12 hr before failure occurred at the point. The hot spot was identified as early as at two-thirds of the final blade life.

  13. Fatigue life prediction for wind turbines: A case study on loading spectra and parameter sensitivity

    SciTech Connect

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

    1992-01-01

    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.

  14. 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.

  15. Blade System Design Studies Volume I: Composite Technologies for Large Wind Turbine Blades

    SciTech Connect

    GRIFFIN, DAYTON A.; ASHWILL, THOMAS D.

    2002-07-01

    As part of the U.S. Department of Energy's Wind Partnerships for Advanced Component Technologies (WindPACT) program, Global Energy Concepts LLC (GEC) is performing a study concerning innovations in materials, processes and structural configurations for application to wind turbine blades in the multi-megawatt range. The project team for this work includes experts in all areas of wind turbine blade design, analysis, manufacture, and testing. Constraints to cost-effective scaling-up of the current commercial blade designs and manufacturing methods are identified, including self-gravity loads, transportation, and environmental considerations. A trade-off study is performed to evaluate the incremental changes in blade cost, weight, and stiffness for a wide range of composite materials, fabric types, and manufacturing processes. Fiberglass/carbon fiber hybrid blades are identified as having a promising combination of cost, weight, stiffness and fatigue resistance. Vacuum-assisted resin transfer molding, resin film infision, and pre-impregnated materials are identified as having benefits in reduced volatile emissions, higher fiber content, and improved laminate quality relative to the baseline wet lay-up process. Alternative structural designs are identified, including jointed configurations to facilitate transportation. Based on the results to date, recommendations are made for further evaluation and testing under this study to verify the predicted material and structural performance.

  16. 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.

  17. Fan blade protection system

    NASA Technical Reports Server (NTRS)

    Hermans, Thomas C. (Inventor); Wakeman, Thomas G. (Inventor); Hauser, Ambrose A. (Inventor)

    1993-01-01

    In one type of aircraft propulsion system, propeller blades are mounted on a ring which surrounds a turbine. An annular space exists between the turbine and the ring. If a propeller blade should break free, the unbalanced centrifugal load tends to deform the ring. The invention reduces the deformation, as by locating spacers between the turbine and the ring.

  18. Relevance of aerodynamic modelling for load reduction control strategies of two-bladed wind turbines

    NASA Astrophysics Data System (ADS)

    Luhmann, B.; Cheng, P. W.

    2014-06-01

    A new load reduction concept is being developed for the two-bladed prototype of the Skywind 3.5MW wind turbine. Due to transport and installation advantages both offshore and in complex terrain two-bladed turbine designs are potentially more cost-effective than comparable three-bladed configurations. A disadvantage of two-bladed wind turbines is the increased fatigue loading, which is a result of asymmetrically distributed rotor forces. The innovative load reduction concept of the Skywind prototype consists of a combination of cyclic pitch control and tumbling rotor kinematics to mitigate periodic structural loading. Aerodynamic design tools must be able to model correctly the advanced dynamics of the rotor. In this paper the impact of the aerodynamic modelling approach is investigated for critical operational modes of a two-bladed wind turbine. Using a lifting line free wake vortex code (FVM) the physical limitations of the classical blade element momentum theory (BEM) can be evaluated. During regular operation vertical shear and yawed inflow are the main contributors to periodic blade load asymmetry. It is shown that the near wake interaction of the blades under such conditions is not fully captured by the correction models of BEM approach. The differing prediction of local induction causes a high fatigue load uncertainty especially for two-bladed turbines. The implementation of both cyclic pitch control and a tumbling rotor can mitigate the fatigue loading by increasing the aerodynamic and structural damping. The influence of the time and space variant vorticity distribution in the near wake is evaluated in detail for different cyclic pitch control functions and tumble dynamics respectively. It is demonstrated that dynamic inflow as well as wake blade interaction have a significant impact on the calculated blade forces and need to be accounted for by the aerodynamic modelling approach. Aeroelastic simulations are carried out using the high fidelity multi body simulation software SIMPACK. The aerodynamic loads are calculated using ECN's AeroModule and NREL's BEM code Aerodynl3.

  19. Rotor loading on a three-bladed wind turbine

    NASA Astrophysics Data System (ADS)

    Madsen, Peter Hauge; Rasmussen, Flemming

    For a well designed and adjusted horizontal axis wind turbine, the turbulence in the wind is one of the primary sources of cyclic loading. Wind turbulence not only causes blade loads, but is responsible for the major part of the cyclic rotor loads which are transferred through the rotor shaft. In order to predict the cyclic part of the primary structural rotor loads, the thrust, the yaw and the tilt moment, a model was developed. The model works in the frequency domain and uses the standard engineering representation of turbulence in terms of a coherence function and a power spectrum. The model which accounts for the rotational sampling of the turbulent wind field, shows good agreement with the results of testing programs on wind turbines which are tested at The Test Station for Windmills at Risoe National Laboratory. The comparison is made in terms of both the frequency content of the turbulence induced loads as well as the associated fatigue damage. A parametric study demonstrates the effect of the tower bending and tower torsion flexibility on the magnitude of the cyclic rotor loads.

  20. Turbine blade platform seal

    DOEpatents

    Zagar, Thomas W. (Winter Springs, FL); Schiavo, Anthony L. (Oviedo, FL)

    2001-01-01

    A rotating blade group 90 for a turbo-machine having an improved device for sealing the gap 110 between the edges 112,114 of adjacent blade platforms 96,104. The gap 110 between adjacent blades 92,100 is sealed by a seal pin 20 its central portion 110 and by a seal plate 58,60 at each of the front 54 and rear 56 portions. The seal plates 58,60 are inserted into corresponding grooves 62,64 formed in the adjacent edges 112,114 of adjoining blades 92,100 and held in place by end plates 40,42. The end of the seal plates 58,60 may be chamfered 78,80 to improve the seal against the end plate 40,42. The seal pin 20 provides the required damping between the blades 92,100 and the seal plates 58,60 provide improved sealing effectiveness.

  1. Ceramic blade attachment system

    DOEpatents

    Shaffer, James E. (Maitland, FL)

    1995-01-01

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a first groove and a second groove therein. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings has a first groove and a second groove therein. The space or void formed between the first grooves and the second grooves has a plurality of spherical balls positioned therein. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade.

  2. Ceramic blade attachment system

    DOEpatents

    Shaffer, J.E.

    1995-01-10

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a first groove and a second groove therein. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings has a first groove and a second groove therein. The space or void formed between the first grooves and the second grooves has a plurality of spherical balls positioned therein. The plurality of spherical balls has a preestablished rate of thermal expansion being equal to the preestablished rate of thermal expansion of the turbine blade. 4 figures.

  3. Characterization of a nine-meter sensor-equipped wind turbine blade using a laser measuring device

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A nine-meter turbine blade was prepared for an experiment to examine the movement and fatigue patterns during operation on a 115 kW turbine. The blade, equipped with surface mounted fiber optic strain gauges, foil strain gauges, single, and triple axis accelerometers was placed on a calibration fixt...

  4. Simulated Bladed MMC Disk LCF Validation

    NASA Technical Reports Server (NTRS)

    Merrick, H. F.; Costen, M.

    1998-01-01

    The goal of this program was to evaluate the low cycle fatigue behavior of an SCS-6/Ti-6Al-4V sub-component under bi-axial loading conditions at 316 C(600 F). A simulated bladed TMC disk was designed having thirty four blades representing the number that would be used in Allied Signal's JTAGG II impeller. The outer diameter of the bladed ring was 254 mm (10.0 inch) and the inner diameter 114.3 mm (4.50 inch). The outer and inner diameter of the composite zone was 177.8 mm (7.00 inch) and 127.O mm(5.00 inch) respectively. Stress analysis showed that the fatigue life of the bladed composite ring would be about 12000 cycles for the test conditions applied. A modal analysis was conducted which showed that the blades would have sufficient life margin from dynamic excitation. The arbor design was the same as that employed in the spin-to burst test of NAS3-27027. A systematic stress analysis of each part making up the arbor was undertaken to assure the design would meet the low cycle fatigue requirements of the program. The Textron Systems grooved foil-fiber process was chosen to make the SCS-6/Ti-6Al-4V core ring based on the success they had in contract NAS3-27027. Fiber buckling, however, was observed at several locations in the first ring made which rendered it unsuitable for spin testing. The fiber buckling was attributed to cracking of the graphite tooling during the consolidation process. On this basis a second ring was made but it too contained fiber buckling defects. Analysis by Textron indicated that the fiber buckling was most likely due to poor placement of the SCS-6 fiber in the etched grooves of the Ti-6Al-4V foil. This was also a contributor to the defects in the first ring. Since there was little indication of control in the process to manufacture a quality ring a third attempt at making a ring was not undertaken.

  5. The design of propeller blade roots

    NASA Technical Reports Server (NTRS)

    Cordes, G

    1942-01-01

    Predicated on the assumption of certain normal conditions for engine and propeller, simple expressions for the static and dynamic stresses of propeller blade roots are evolved. They, in combination with the fatigue strength diagram of the employed material, afford for each engine power one certain operating point by which the state of stress serving as a basis for the design of the root is defined. Different stress cases must be analyzed, depending on the vibration tendency of engine and use of propeller. The solution affords an insight into the possible introduction of different size classes of propeller.

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

    NASA Astrophysics Data System (ADS)

    Szolwinski, Matthew Paul

    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 under close scrutiny by those responsible for maintaining aging fleets of both commercial and military aircraft. Thus a critical need exists for predicting fretting crack nucleation in riveted aluminum. aircraft joints. Fulfilling this need requires characterizing both the near-surface mechanics and intimately-related tribology of fretting. To this end, a well characterized experimental setup has been developed to generate carefully controlled and monitored fretting contacts to investigate the nature of the near-surface conditions. Included in this investigation were in-situ observations of the fretting contact stress field via a non-invasive thermal imaging technique and a characterization of the evolution of friction under partial slip conditions. With specific qualitative and quantitative understanding of these near-surface conditions, a series of fretting fatigue experiments have been conducted to validate a mechanics-based model for predicting fretting fatigue crack nucleation. Finally, efforts have been directed toward extending this understanding of fretting crack nucleation to riveted aircraft structure through modeling of the riveting process and a related experimental program designed to link riveting process parameters and fretting damage in single-lap joint structures. This work focuses specifically on determination of the residual stresses induced during rivet installation and the morphological characterization of fretting fatigue damage in the riveted test specimens manufactured under controlled conditions.

  7. Muscular fatigue.

    PubMed

    Sesbo, B; Guincestre, J-Y

    2006-07-01

    Although everyone knows fatigue personally, it is a difficult concept to define. For muscular fatigue, one must know the aspect of performance affected. The most obvious demonstrations are decreased maximal force and slowed muscular answer. Fatigue can have a central origin, by reducing cognitive performance or lowering excitation of motoneurons. Various mediators are in question (serotonin, moduline, dopamine). The fatiguing muscular contractions are accompanied by reduced discharges of motoneurons. The neuromuscular junction does not seem to be in question. Cold reduces muscular power, whereas a hot environment limits exercise by a central mechanism, which starts the normal behavioural response to stop the exercise. Fatigue can also be the consequence of overtraining. In the periphery, the electric activity of the membrane's surface is the first possible sign of failure, which explains high-frequency fatigue: the accumulation of potassium outside the cell blocks the sodic channels to block the potentials of action or slow down their propagation. With fatigue, less calcium is released and limits the number of attached actin-myosin bridges connections of actin-myosin. The slowing down of the muscular answer represents a deterioration of the function of actin-myosin bridges. On the metabolic level, the most-often evoked changes are reduced pH and increased intracellular lactate level. However, these variations cannot all describe fatigue, since patients with Mc Ardle disease do not exhibit these variations but very quickly experience tiredness. In fact, an association of small metabolic intracellular variations could explain tiredness. The fast fibres are larger than slow fibres; their metabolic needs are higher and they are thus more sensitive to tiredness. The half time of recovery is within approximately 1 min: normal values of force and power are recovered after 5 to 10 min. During endurance activities, the limiting factors are glycogen reserves and levels of oxidative enzymes. On the whole, mechanisms of fatigue must be explored to completely understand the governing phenomena. PMID:16757054

  8. Detection of nocturnal coherent turbulence in the US Great Plains and effects on wind turbine fatigue

    NASA Astrophysics Data System (ADS)

    Dvorak, M. J.; Wiersema, D. J.; Zhou, B.; Chow, F. K.

    2012-12-01

    Strong low-level jet winds that develop in the nocturnal stable boundary layer (SBL) create some of the most energetic wind energy resources in Great Plains of North America. These stratified flows, however, can cause strong wind shear and veer across wind turbine rotors. Additionally, turbulent bursting events triggered by strong vertical wind shear can lead to fatigue and damage of wind turbine blades and components, increasing maintenance costs and reducing wind turbine power production. Coherent structures which are the signature of turbulent bursting events can be observed in heavily instrumented wind farms and in high-resolution simulations. Large-scale adoption of wind energy will benefit from the ability to predict these turbulence events with limited in-situ data. By identifying signatures of these bursting events, new turbine control technologies could be used to reduce wind turbine damage and increase overall wind farm energy yield (for example using algorithms with the ability to proactively and independently pitch blades). This research analyzes SBL turbulence in the Great Plains to develop methods to identify these structures at wind farms. Nested large-eddy simulations down to about 20m horizontal resolution are performed and compared to high-resolution Doppler wind LIDAR data (1 Hz) to determine if the model is able to create similar wind and turbulence conditions. Wavelet analysis of the LIDAR and model wind fields is used to detect coherent turbulent structures at frequencies that could be potentially damaging for wind turbines and provide guidance for design of turbine control technologies.

  9. Effect of Low Temperature on Fatigue Crack Formation and Microstructure-Scale Growth from Corrosion Damage in Al-Zn-Mg-Cu

    NASA Astrophysics Data System (ADS)

    Burns, James T.; Gangloff, Richard P.

    2013-05-01

    The strong effect of cold temperature on the fatigue resistance of 7075-T651 is established. As temperature decreases from 296 K to 183 K (23 °C to -90 °C), the formation life for cracking about pit and EXCO corrosion perimeters increases, microstructure scale crack growth rates decrease in the range from 20 to 500 μm beyond the corrosion topography, and long crack growth rates similarly decline. Fatigue crack surface features correlate with reduced hydrogen embrittlement with decreasing temperature fed by localized H produced during precorrosion for pit and EXCO-proximate cracks, as well as by crack tip H produced by water vapor reaction during stressing for all crack sizes. The importance of the former H source increases with decreasing temperature for cracks sized below 200 μm. Decreasing temperature to 223 K (-50 °C) eliminates the contribution of environmental H through interaction of reduced water vapor pressure in equilibrium with ice and reduced H diffusion. The Knudsen flow model and exposure parameter, P_{{{{H}}2 {{O}}}}/f , enables improved modeling of temperature dependent crack propagation, but does not fully describe low temperature fatigue behavior due to possible rate limitation by H diffusion. Further decreases in MSC da/dN to 183 K (-90 °C) are related to reduced mobility of the corrosion-precharged H which may associate with vacancies from dissolution. Crack formation, and growth rates correlate with either elastic stress intensity range or cyclic crack tip opening displacement, and are available to predict corrosion effects on airframe fatigue for the important low temperature regime.

  10. Rotor fatigue monitoring data acquisition system

    NASA Technical Reports Server (NTRS)

    Smith, Scott M.

    1993-01-01

    The 40 by 80 Foot Wind Tunnel of the National Full Scale Aerodynamics Complex (NFAC) had a requirement to monitor rotor fatigue during a test. This test subjected various rotor components to stress levels higher than their structural fatigue limits. A data acquisition system was developed to monitor the cumulative fatigue damage of rotor components using National Instruments hardware and LabVIEW software. A full description of the data acquisition system including its configuration and salient features, is presented in this paper.

  11. Self-Tuning Impact Dampers Designed for Turbomachinery Blade Vibration Suppression

    NASA Technical Reports Server (NTRS)

    Duffy, Kirsten P.; Mehmed, Oral

    2002-01-01

    Turbomachinery blades are subject to aerodynamic forces that can lead to high-cycle-fatigue (HCF) failures. These failures will only increase as engineers begin to design blades without shrouds or as integrally bladed disks (blisks). These new designs will decrease blade damping significantly because the mechanical damping from shroud and blade joints will be eliminated. Also, it is difficult to design dampers for the engine environment with its extremely high centrifugal loads and high temperatures. The self-tuning impact damper has been designed to provide the additional damping required to avoid HCF while withstanding the harsh engine environment. In addition, the damper is placed within the engine blade itself rather than external to it.

  12. Probabilistic fatigue methodology for six nines reliability

    NASA Technical Reports Server (NTRS)

    Everett, R. A., Jr.; Bartlett, F. D., Jr.; Elber, Wolf

    1990-01-01

    Fleet readiness and flight safety strongly depend on the degree of reliability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification for new rotorcraft is the so-called six nines reliability, or a probability of failure of one in a million. The progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance is reviewed to investigate reliability-based fatigue methodology. The participants in this cooperative effort are in the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliability calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic which includes both fatigue strength and spectrum loading variability in developing a consistant reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study.

  13. Instrumented composite turbine blade for health monitoring

    NASA Astrophysics Data System (ADS)

    Robison, Kevin E.; Watkins, Steve E.; Nicholas, James; Chandrashekhara, K.; Rovey, Joshua L.

    2012-04-01

    A health monitoring approach is investigated for hydrokinetic turbine blade applications. In-service monitoring is critical due to the difficult environment for blade inspection and the cost of inspection downtime. Composite blade designs have advantages that include long life in marine environments and great control over mechanical properties. Experimental strain characteristics are determined for static loads and free-vibration loads. These experiments are designed to simulate the dynamic characteristics of hydrokinetic turbine blades. Carbon/epoxy symmetric composite laminates are manufactured using an autoclave process. Four-layer composite beams, eight-layer composite beams, and two-dimensional eight-layer composite blades are instrumented for strain. Experimental results for strain measurements from electrical resistance gages are validated with theoretical characteristics obtained from in-house finite-element analysis for all sample cases. These preliminary tests on the composite samples show good correlation between experimental and finite-element strain results. A health monitoring system is proposed in which damage to a composite structure, e.g. delamination and fiber breakage, causes changes in the strain signature behavior. The system is based on embedded strain sensors and embedded motes in which strain information is demodulated for wireless transmission.

  14. Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

    NASA Astrophysics Data System (ADS)

    Ranjan, Srikant

    2005-11-01

    Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the resolved shear stress on primary slip planes. The maximum value of Krss and DeltaKrss was found to determine the crack growth direction and the fatigue crack growth rate respectively. The fatigue crack driving force parameter, DeltaK rss, forms an important multiaxial fatigue damage parameter that can be used to predict life in superalloy components.

  15. Ceramic blade attachment system

    DOEpatents

    Boyd, Gary L. (Alpine, CA)

    1994-01-01

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a pair of recessed portions thereon. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings have a pair of grooves therein in which are positioned a pair of pins having a generally rectangular cross-section and a reaction surface thereon. A pair of cylindrical rollers interposed respective ones of the pair of reaction surfaces and the pair of recessed portions. The attachment system or turbine assembly provides an economical, reliable and effective attachment of a component having a preestablished rate of thermal expansion to a component having a greater preestablished rate of thermal expansion.

  16. Synthetic fan blade

    SciTech Connect

    Wright, J.C.

    1988-05-24

    A fan blade characterized by its efficiency of material utilization is described comprising, in combination, an elongated blade body having an outer air flow portion, an inner root portion, a transition portion between the air flow and root portions and a longitudinal axis, transverse sections defined on the blade body perpendicular to the body axis each having a neutral axis defining the minimum resistance to primary blade body bending. The material of the body is increasingly offset from the neutral axis from the intersection of the air flow and transition portions to the root portion such that the moment of inertia of the transverse sections from the intersection with the air flow portion to the root portion uniformly increases.

  17. Ceramic blade attachment system

    DOEpatents

    Boyd, G.L.

    1994-12-13

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine wheel having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine blade has a root portion having a pair of recessed portions thereon. The turbine wheel includes a plurality of openings in which the turbine blade is positioned. Each of the openings have a pair of grooves therein in which are positioned a pair of pins having a generally rectangular cross-section and a reaction surface thereon. A pair of cylindrical rollers interposed respective ones of the pair of reaction surfaces and the pair of recessed portions. The attachment system or turbine assembly provides an economical, reliable and effective attachment of a component having a preestablished rate of thermal expansion to a component having a greater preestablished rate of thermal expansion. 3 figures.

  18. Influence of alternating loads on nonlinear vibration characteristics of cracked blade in rotor system

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Jiang, Dongxiang; Chu, Fulei

    2015-09-01

    As important causes of fatigue and crack failure, alternating loads also affect vibration characteristics of cracked blades in rotor system and probably influence formulation of diagnostic rule. This work carried out analysis of nonlinear vibration of cracked blade in rotor system with crack breathing effects and alternating loads taken into account. Firstly, equations of motion are formed with Finite Element Method (FEM), and breathing crack is modeled with cracked hexahedral element (CHE) where the breathing behavior is load-dependent. Secondly, displacement responses of cracked blade are obtained, and the results with CHE and contact element are identical. The stiffness of the cracked blade is obtained with CHE and proved to be time-varying and dependent on the alternating loads. Thirdly, natural frequencies of cracked blade in stationary condition are analyzed including normal model, linear model (open crack) and nonlinear model (breathing crack), and the requirement of the inclusion of breathing effects in blades with fatigue crack is proved. Finally, influence of alternating loads on critical frequency of cracked blade in rotating condition is compared. The results show that the critical frequency is significantly affected due to the co-effects of the rotating speed and alternating loads. The proposed method can estimate nonlinear vibration characteristics of crack blade which is beneficial for the formulation of the diagnostic rule.

  19. Blade Testing Trends (Presentation)

    SciTech Connect

    Desmond, M.

    2014-08-01

    As an invited guest speaker, Michael Desmond presented on NREL's NWTC structural testing methods and capabilities at the 2014 Sandia Blade Workshop held on August 26-28, 2014 in Albuquerque, NM. Although dynamometer and field testing capabilities were mentioned, the presentation focused primarily on wind turbine blade testing, including descriptions and capabilities for accredited certification testing, historical methodology and technology deployment, and current research and development activities.

  20. Fatigue and Multiple Sclerosis

    MedlinePLUS

    ... not trying hard enough. Fatigue & lassitude Several different kinds of fatigue occur in MS. For example, people ... to these sources of fatigue, there is another kind of fatigue referred to as lassitude that is ...

  1. NREL Wind Turbine Blade Structural Testing of the Modular Wind Energy MW45 Blade: Cooperative Research and Development Final Report, CRADA Number CRD-09-354

    SciTech Connect

    Hughes, S.

    2012-05-01

    This CRADA was a purely funds-in CRADA with Modular Wind Energy (MWE). MWE had a need to perform full-scale testing of a 45-m wind turbine blade. NREL/NWTC provided the capabilities, facilities, and equipment to test this large-scale MWE wind turbine blade. Full-scale testing is required to demonstrate the ability of the wind turbine blade to withstand static design load cases and demonstrate the fatigue durability. Structural testing is also necessary to meet international blade testing certification requirements. Through this CRADA, MWE would obtain test results necessary for product development and certification, and NREL would benefit by working with an industrial partner to better understand the unique test requirements for wind turbine blades with advanced structural designs.

  2. Comparison of Measured Flapwise Structural Bending Moments on a Teetering Rotor Blade With Results Calculated From the Measured Pressure Distribution

    NASA Technical Reports Server (NTRS)

    Mayo, Alton P.

    1959-01-01

    Flapwise bending moments were calculated for a teetering rotor blade using a reasonably rapid theoretical method in which airloads obtained from wind-tunnel tests were employed. The calculated moments agreed reasonably well with those measured with strain gages under the same test conditions. The range of the tests included one hovering and two forward-flight conditions. The rotor speed for the test was very near blade resonance, and difficult-to-calculate resonance effects apparently were responsible for the largest differences between the calculated and measured harmonic components of blade bending moments. These differences, moreover, were largely nullified when the harmonic components were combined to give a comparison of the calculated and measured blade total- moment time histories. The degree of agreement shown is therefore considered adequate to warrant the use of the theoretical method in establishing and applying methods of prediction of rotor-blade fatigue loads. At the same time, the validity of the experimental methods of obtaining both airload and blade stress measurement is also indicated to be adequate for use in establishing improved methods for prediction of rotor-blade fatigue loads during the design stage. The blade stiffnesses and natural frequencies were measured and found to be in close agreement with calculated values; however, for a condition of blade resonance the use of the experimental stiffness values resulted in better agreement between calculated and measured blade stresses.

  3. Low-cost directionally-solidified turbine blades, volume 2. [TFE731-3 turbofan engine

    NASA Technical Reports Server (NTRS)

    Dennis, R. E.; Hoppin, G. S., III; Hurst, L. G.

    1979-01-01

    An endothermically heated technology was used to manufacture low cost, directionally solidified, uncooled nickel-alloy blades for the TFE731-3 turbofan engine. The MAR-M 247 and MER-M 100+Hf blades were finish processed through heat treatment, machining, and coating operations prior to 150 hour engine tests consisting of the following sequences: (1) 50 hours of simulated cruise cycling (high fatigue evaluation); (2) 50 hours at the maximum continuous power rating (stress rupture endurance (low cycle fatigue). None of the blades visually showed any detrimental effects from the test. This was verified by post test metallurgical evaluation. The specific fuel consumption was reduced by 2.4% with the uncooled blades.

  4. Dynamic response characteristics of dual flow-path integrally bladed rotors

    NASA Astrophysics Data System (ADS)

    Beck, Joseph A.; Brown, Jeffrey M.; Scott-Emuakpor, Onome E.; Cross, Charles J.; Slater, Joseph C.

    2015-02-01

    New turbine engine designs requiring secondary flow compression often look to dual flow-path integrally bladed rotors (DFIBRs) since these stages have the ability to perform work on the secondary, or bypassed, flow-field. While analogous to traditional integrally bladed rotor stages, DFIBR designs have many differences that result in unique dynamic response characteristics that must be understood to avoid fatigue. This work investigates these characteristics using reduced-order models (ROMs) that incorporate mistuning through perturbations to blade frequencies. This work provides an alternative to computationally intensive geometric-mistuning approaches for DFIBRs by utilizing tuned blade mode reductions and substructure coupling in cyclic coordinates. Free and forced response results are compared to full finite element model (FEM) solutions to determine if any errors are related to the reduced-order model formulation reduction methods. It is shown that DFIBRs have many more frequency veering regions than their single flow-path integrally blade rotor (IBR) counterparts. Modal families are shown to transition between system, inner-blade, and outer-blade motion. Furthermore, findings illustrate that while mode localization of traditional IBRs is limited to a single or small subset of blades, DFIBRs can have modal energy localized to either an inner- or outer-blade set resulting in many blades responding above tuned levels. Lastly, ROM forced response predictions compare well to full FEM predictions for the two test cases shown.

  5. Design and fabrication of integrally damped composite fan blades

    NASA Astrophysics Data System (ADS)

    Kosmatka, John B.; Appuhn, Geoffrey

    1999-06-01

    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. First, the geometry and material definition of the existing composite fan blade are presented. Second, methods for sizing and locating the damping patch are presented based upon the modal strain energy method. The layered damping patch is composed of outer layers of a TEDLAR (or KAPTON) barrier film, which encompasses a viscoelastic damping material and loose- weave scrim cloth (creep protection). Two different patch sizes and locations are discussed to provide maximum damping as well as optimal damping. Finally, procedures are outlined for fabricating the integrally damped composite fan blades. Fabricated blades will be tested at the NASA-Lewis vacuum facility.

  6. Quiet Clean Short-haul Experimental Engine (QCSEE) under-the-wing engine composite fan blade design report

    NASA Technical Reports Server (NTRS)

    Ravenhall, R.; Salemme, C. T.

    1977-01-01

    A total of 38 quiet clean short haul experimental engine under the wing composite fan blades were manufactured for various component tests, process and tooling, checkout, and use in the QCSEE UTW engine. The component tests included frequency characterization, strain distribution, bench fatigue, platform static load, whirligig high cycle fatigue, whirligig low cycle fatigue, whirligig strain distribution, and whirligig over-speed. All tests were successfully completed. All blades planned for use in the engine were subjected to and passed a whirligig proof spin test.

  7. Material development for fan blade containment casing

    NASA Astrophysics Data System (ADS)

    McMillan, A.

    2008-03-01

    This paper describes the physics reasoning and the engineering development process for the structured material system adopted for the containment system of the Trent 900 engine. This is the Rolls-Royce engine that powers the Airbus A380 double-decker aeroplane, which is on the point of entering service. The fan blade containment casing is the near cylindrical casing that surrounds the fan blades at the front of the engine. The fan blades provide the main part of the thrust of the engine; the power to the fan is provided through a shaft from the turbine. The fan is approximately three meters in diameter, with the tips of the blade travelling at a little over Mach speed. The purpose of the containment system is to catch and contain a blade in the extremely unlikely event of a part or whole blade becoming detached. This is known as a ''Fan Blade Off (FBO)'' event. The requirement is that no high-energy fragments should escape the containment system; this is essential to prevent damage to other engines or to the fuselage of the aircraft. Traditionally the containment system philosophy has been to provide a sufficiently thick solid metallic skin that the blade cannot penetrate. Obviously, this is heavy. A good choice of metal in this case is a highly ductile steel, which arrests the kinetic energy of the blade through plastic deformation, and possibly, a controlled amount of cracking. This is known as ''hard wall'' containment. More recently, to reduce weight, containment systems have incorporated a Kevlar fibre wrap. In this case, the thinner metallic wall provides some containment, which is backed up by the stretching of the Kevlar fibres. This is known as ''soft wall'' containment; but it suffers the disadvantage of requiring a large empty volume in the nacelle in to which to expand. For the Trent 900 engine, there was a requirement to make a substantial weight saving while still adopting a hard wall style of containment system. To achieve this, a hollow structured material system was developed, with much of the kinetic energy arrest provided by the mechanism of crushing. A number of structural elements were included within the containment system to maximise the area of material involved in the arrest and thereby minimise the overall weight.

  8. Peridynamic model for fatigue cracking.

    SciTech Connect

    Silling, Stewart A.; Abe Askari

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the %22remaining life%22 of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  9. Impact resistance of hybrid composite fan blade materials

    NASA Technical Reports Server (NTRS)

    Friedrich, L. A.

    1974-01-01

    Improved resistance to foreign object damage was demonstrated for hybrid composite simulated blade specimens. Transply metallic reinforcement offered additional improvement in resistance to gelatin projectile impacts. Metallic leading edge protection permitted equivalent-to-titanium performance of the hybrid composite simulated blade specimen for impacts with 1.27 cm and 2.54 cm (0.50 and 1.00 inch) diameter gelatin spheres.

  10. Calculation of trajectories of detached wind turbine blades and prediction of site risk levels associated with failures of HAWT's

    NASA Astrophysics Data System (ADS)

    Soerensen, J. N.

    1984-11-01

    The risk of a wind turbine blade or blade fragment hitting a person was calculated. For the prediction of trajectories of detached wind turbine blades, the governing equations of the full motion, which includes translation and rotation of the blade, are derived. The aerodynamic forces and moments, acting on the blade, are determined by strip theory and constructed airfoil data, which take into account that the blade can be exposed to all possible angles of the relative free stream velocity. The sensitivity of trajectories and throw distances to changes in the conditions by which the blade is detached, was studied. A statistical model by which the damage to people, under assumption of detachment of a blade/blade-fragment, can be determined is presented. The results for a 2 MW, 60 m diameter unit are shown.

  11. Tension fatigue analysis and life prediction for composite laminates

    NASA Technical Reports Server (NTRS)

    O'Brien, T. K.; Rigamonti, M.; Zanotti, C.

    1989-01-01

    A methodology is presented for the tension fatigue analysis and life prediction of composite laminates subjected to tension fatigue loading. The methodology incorporates both the generic fracture mechanics characterization of delamination and the assessment of the infuence of damage on laminate fatigue life. Tension fatigue tests were conducted on quasi-isotropic and orthotropic glass epoxy, graphite epoxy, and glass/graphite epoxy hybrid laminates, demonstrating good agreement between measured and predicted lives.

  12. Thermal Fatigue and Fracture Behavior of Ceramic Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Choi, Sung R.; Miller, Robert A.

    2001-01-01

    Thermal fatigue and fracture behavior of plasma-sprayed ceramic thermal barrier coatings has been investigated under high heat flux and thermal cyclic conditions. The coating crack propagation is studied under laser heat flux cyclic thermal loading, and is correlated with dynamic fatigue and strength test results. The coating stress response and inelasticity, fatigue and creep interactions, and interface damage mechanisms during dynamic thermal fatigue processes are emphasized.

  13. Ultrasonic absortion in fatigued materials

    NASA Astrophysics Data System (ADS)

    Dugan, S.; Arnold, W.

    2013-01-01

    Non-destructive detection of fatigue damage, allowing an estimate of the residual life-time of components, could contribute to a safe and reliable operation of components and installations. Ultrasonic absorption, i.e. the internal friction, of a material increases with increasing fatigue or creep damage and there are many theories trying to explain the physics behind this phenomenon. Measurement of ultrasonic absorption directly on components could provide information on the degree of damage. A laser ultrasonic method, using laser-generated pulses and optical detection, was applied to study ultrasonic absorption in fatigue specimens of different metals. A characteristic behavior of the ultrasonic absorption coefficient with increasing levels of fatigue damage was found for the titanium alloy Ti-6Al-4V. Another aim of this study was to relate the absorption mechanisms to the behavior of ultrasonic absorption observed in metals with complex microstructure. To achieve this, different ultrasonic absorption mechanisms were analyzed with respect to experimental data. A thermoelastic effect related to the size and elasticity of the microstructure is discussed as the origin of the increased ultrasonic absorption.

  14. National Transonic Facility Fan Blade prepreg material characterization tests

    NASA Technical Reports Server (NTRS)

    Klich, P. J.; Richards, W. H.; Ahl, E. L., Jr.

    1981-01-01

    The test program for the basic prepreg materials used in process development work and planned fabrication of the national transonic facility fan blade is presented. The basic prepreg materials and the design laminate are characterized at 89 K, room temperature, and 366 K. Characterization tests, test equipment, and test data are discussed. Material tests results in the warp direction are given for tensile, compressive, fatigue (tension-tension), interlaminar shear and thermal expansion.

  15. Effect of low-level laser therapy (GaAs 904 nm) in skeletal muscle fatigue and biochemical markers of muscle damage in rats.

    PubMed

    Leal Junior, Ernesto Cesar Pinto; Lopes-Martins, Rodrigo Alvaro Brandão; de Almeida, Patrícia; Ramos, Luciano; Iversen, Vegard V; Bjordal, Jan Magnus

    2010-04-01

    We wanted to test if pre-exercise muscle irradiation with 904 nm laser affects the development of fatigue, blood lactate levels and creatine kinase (CK) activity in a rat model with tetanic contractions. Thirty male Wistar rats were divided into five groups receiving either one of four different laser doses (0.1, 0.3, 1.0 and 3.0 J) or a no-treatment control group. Laser irradiation was performed immediately before the first contraction for treated groups. Electrical stimulation was used to induce six tetanic tibial anterior muscle contractions with 10 min intervals between them. Contractions were stopped when the muscle force fell to 50% of the peak value for each contraction; blood samples were taken before the first and immediately after the sixth contraction. The relative peak forces for the sixth contraction were significantly better (P < 0.05) in the two laser groups irradiated with highest doses [151.27% (SD +/- 18.82) for 1.0 J, 144.84% (SD +/- 34.47) for 3.0 J and 82.25% (SD +/- 11.69) for the control group]. Similar significant (P < 0.05) increases in mean performed work during the sixth contraction for the 1.0 and 3.0 J groups were also observed. Blood lactate levels were significantly lower (P < 0.05) than the control group in all irradiated groups. All irradiated groups except the 3.0 J group had significantly lower post-exercise CK activity than the control group. We conclude that pre-exercise irradiation with a laser dose of 1.0 J and 904 nm wavelength significantly delays muscle fatigue and decreases post-exercise blood lactate and CK in this rat model. PMID:20024577

  16. Non-Destructive Evaluation of Wind Turbine Blades Using an Infrared Camera

    SciTech Connect

    Beattie, A.G.; Rumsey, M.

    1998-12-17

    The use of a digital infrared as a non-destructive evaluation thermography camera (NDE) tool was ex- plored in two separate wind turbine blade fatigue tests. The fwst test was a fatigue test of part of a 13.1 meter wood-epoxy-composite blade. The second test was on a 4.25 meter pultruded fiber glass blade section driven at several mechanical resonant frequencies. The digital infrared camera can produce images of either the static temperature distribution on the surface of the specimen, or the dynamic temperature distribution that is in phase with a specific frequency on a vibrating specimen. The dynamic temperature distribution (due to thermoplastic effects) gives a measure of the sum of the principal stresses at each point on the surface. In the wood- epoxy-composite blade fatigue test, the point of ultimate failure was detected long before failure occurred. The mode shapes obtained with the digital infrared camera, from the resonant blade tests, were in very good agree- ment with the finite-element calculations. In addition, the static temperature images of the resonating blade showed two areas that contained cracks. Close-up dy- namic inf%red images of these areas showed the crack structure that agreed with subsequent dye-penetrant analysis.

  17. Effects of blade bending on aerodynamic control of fluctuating loads on teetered HAWT rotors

    SciTech Connect

    Eggers, A.J. Jr.; Ashley, H.; Rock, S.M.; Chaney, K.; Digumarthi, R.

    1996-10-01

    Active aerodynamic control, in the form of closed-loop actuation of blade-tip ailerons or all-movable blades, is investigated as a means of increasing the structural fatigue life of HAWT rotors. The rotor considered is teetered, with two blades of diameter 29.2 m., fiberglass construction and other properties representative of modern light-weight construction. The paper begins with a review of prior work which studied the problem for an essentially rigid structure. For that and the present research two loading conditions were invoked: exposure to a Rayleigh distribution of operating winds with a 15% superimposed spectrum of turbulence; and occasional exposure to 120-kt hurricanes. Accounted for herein is the effect of flatwise bending flexibility on the resulting spectra, open-loop vs. closed-loop, of root flatwise bending moment, thrust and torque. By means of Miner`s rule, the moments are converted to fatigue lives. With aerodynamic control, RMS moments for the flexible blade in turbulence are found to be less than {1/2} of those without control. At a fixed blade weight of 540 kg when hurricane loads are added, the aileron-controlled blade is designed by that limit-load condition. In contrast, the all-movable blade can be feathered in the high wind so that its life is determined by turbulent loads. Simplified fatigue analysis permits weight reductions to be estimated which yield controlled blades capable of thirty years` operation with the safety factor of 11. The resulting weights are about 400 kg for aileron control and 230 kg for the all-movable blade. However, such light-weight rotors require attention to other design considerations, such as start-stop cycles.

  18. Ceramic blade attachment system

    DOEpatents

    Frey, deceased, Gary A. (late of Poway, CA); Jimenez, Oscar D. (Escondia, CA)

    1996-01-01

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine flange having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine flange includes a first upstanding flange and a second upstanding flange having a groove formed therebetween. The turbine flange further includes a recess. Each of the first and second upstanding flanges have a plurality of bores therein. A turbine blade has a first member and a second member positioned in one of the groove and the recess. Each of the first member and the second member have a plurality of bores therein. And, a pin is positioned in respective ones of the plurality of bores in the first and second upstanding members and the first and second members and attach the blade to the turbine flange. The pin has a preestablished rate of thermal expansion being substantially equal to the rate of thermal expansion of the blade.

  19. SSME blade damper technology

    NASA Technical Reports Server (NTRS)

    Kielb, Robert E.; Griffin, Jerry H.

    1987-01-01

    Before 1975 turbine blade damper designs were based on experience and very simple mathematical models. Failure of the dampers to perform as expected showed the need to gain a better understanding of the physical mechanism of friction dampers. Over the last 10 years research on friction dampers for aeronautical propulsion systems has resulted in methods to optimize damper designs. The first-stage turbine blades on the Space Shuttle Main Engine (SSME) high-pressure oxygen pump have experienced cracking problems due to excessive vibration. A solution is to incorporate a well-designed friction dampers to attenuate blade vibration. The subject study, a cooperative effort between NASA Lewis and Carnegie-Mellon University, represents an application of recently developed friction damper technology to the SSME high-pressure oxygen turbopump. The major emphasis was the contractor's design known as the two-piece damper. Damping occurs at the frictional interface between the top half of the damper and the underside of the platforms of the adjacent blades. The lower half of the damper is an air seal to retard airflow in the volume between blade necks.

  20. Ceramic blade attachment system

    DOEpatents

    Frey, G.A.; Jimenez, O.D.

    1996-12-03

    A turbine blade having a preestablished rate of thermal expansion is attached to a turbine flange having a preestablished rate of thermal expansion being greater than the preestablished rate of thermal expansion of the turbine blade. The turbine flange includes a first upstanding flange and a second upstanding flange having a groove formed between them. The turbine flange further includes a recess. Each of the first and second upstanding flanges have a plurality of bores therein. A turbine blade has a first member and a second member positioned in one of the groove and the recess. Each of the first member and the second member have a plurality of bores therein. A pin is positioned in respective ones of the plurality of bores in the first and second upstanding members and the first and second members and attach the blade to the turbine flange. The pin has a preestablished rate of thermal expansion being substantially equal to the rate of thermal expansion of the blade. 4 figs.