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Sample records for blade fatigue life

  1. 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.

  2. 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.

  3. 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.

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

    SciTech Connect

    Walls, D.P.; deLaneuville, R.E.; Cunningham, S.E.

    1997-01-01

    A novel fracture mechanics approach has been used to predict crack propagation lives in gas turbine engine blades subjected to vibratory high cycle fatigue (HCF). The vibratory loading included both a resonant mode and a nonresonant mode, with one blade subjected to only the nonresonant mode and another blade to both modes. A life prediction algorithm was utilized to predict HCF propagation lives for each case. The life prediction system incorporates a boundary integral element (BIE) derived hybrid stress intensity solution, which accounts for the transition from a surface crack to corner crack to edge crack. It also includes a derivation of threshold crack length from threshold stress intensity factors to give crack size limits for no propagation. The stress intensity solution was calibrated for crack aspect ratios measured directly from the fracture surfaces. The model demonstrates the ability to correlate predicted missions to failure with values deduced from fractographic analysis. This analysis helps to validate the use of fracture mechanics approaches for assessing damage tolerance in gas turbine engine components subjected to combined steady and vibratory stresses.

  5. 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.

  6. 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).

  7. Fatigue analysis and testing of wind turbine blades

    NASA Astrophysics Data System (ADS)

    Greaves, Peter Robert

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

  8. 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. 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.

  10. 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.

  11. Jumplike fatigue crack growth in compressor blades

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    It is shown that power relations between the two main fractographic characteristics of fracture surfaces forming during jumplike fatigue crack growth, namely, the crack depth and the corresponding crack front length, can be used to estimate the fracture stress during vibration tests of the compressor blades of an aviation gas turbine engine, which are made of VT3-1 titanium alloy.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. Methodologies for predicting fatigue life

    NASA Astrophysics Data System (ADS)

    Holman, R. K.; Liaw, P. K.

    1997-07-01

    This article reviews the basic techniques employed in fatigue life prediction. The stress-life, local-strain, and fracture-mechanics methods as applied to life prediction under constant amplitude loading and variable amplitude loading are discussed. Life prediction methodology under variable maplitude loading is also discussed, with particular emphasis on the linear-damage accumulation approach, or Miner's rule. Finally, a discussion of various cycle-counting techniques for variable amplitude loading is given.

  4. 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.

  5. 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..

  6. 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.

  7. Wind machine fatigue analysis and life prediction

    NASA Astrophysics Data System (ADS)

    Waldon, C. A.

    Wind machines are, inherently, generators of fatigue. This is true for all types and sizes. Testing at the Rocky Flats Small Wind Systems Test Center has shown that fatigue is the dominant mode of structural failure and its prediction the hardest task for the manufacturer. The objective of this paper is to present a technique, developed by the author, for measuring fatigue and predicting fatigue life for different wind regimes. Presented herein are techniques for locating high stress measuring points, obtaining data, using computer programs for calculating fatigue reduction, and predicting fatigue life. This paper also presents current work which extends the life prediction technique to other wind regimes.

  8. Turbine blade nonlinear structural and life analysis

    NASA Technical Reports Server (NTRS)

    Mcknight, R. L.; Laflen, J. H.; Halford, G. R.; Kaufman, A.

    1982-01-01

    The utility of advanced structural analysis and life prediction techniques was evaluated for the life assessment of a commercial air-cooled turbine blade with a history of tip cracking. Three dimensional, nonlinear finite element structural analyses were performed for the blade tip region. The computed strain-temperature history of the critical location was imposed on a uniaxial strain controlled test specimen to evaluate the validity of the structural analysis method. Experimental results indicated higher peak stresses and greater stress relaxation than the analytical predictions. Life predictions using the Strainrange Partitioning and Frequency Modified approaches predicted 1200 to 4420 cycles and 2700 cycles to crack initiation, respectively, compared to an observed life of 3000 cycles.

  9. Fatigue life of laser cut metals

    NASA Technical Reports Server (NTRS)

    Martin, M. R.

    1986-01-01

    Fatigue tests were conducted to determine the actual reduction in fatigue life due to weight removal for balancing by: hand grinding, low power (20 watt) Nd:glass laser, and high power (400 watt) Nd:YAG laser.

  10. 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.

  11. 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.

  12. 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.

  13. Fatigue life prediction in bending from axial fatigue information

    NASA Technical Reports Server (NTRS)

    Manson, S. S.; Muralidharan, U.

    1982-01-01

    Bending fatigue in the low cyclic life range differs from axial fatigue due to the plastic flow which alters the linear stress-strain relation normally used to determine the nominal stresses. An approach is presented to take into account the plastic flow in calculating nominal bending stress (S sub bending) based on true surface stress. These functions are derived in closed form for rectangular and circular cross sections. The nominal bending stress and the axial fatigue stress are plotted as a function of life (N sub S) and these curves are shown for several materials of engineering interest.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  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. 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

  1. 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.

  2. 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.

  3. 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.

  4. Fatigue life program using strain-life methods

    NASA Astrophysics Data System (ADS)

    Skelly, Michael V.

    1993-03-01

    A user friendly program was developed to calculate fatigue life using Strain-Life equations, given either a stress history or a strain history. Additionally, the material parameters and associated stress concentration factors can be varied. Since certain material constants, such as cyclic strength coefficient (K') and cyclic strain hardening exponent (n') vary during a material's fatigue life, the program is capable of either keeping them constant or varying them as a function of elapsed cycles. The program was then utilized to examine the effects of varying K' and n' on the calculated fatigue life of aluminum 7075-T6 under a typical flight load history.

  5. 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.

  6. 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.

  7. Low-cycle fatigue of TiNi shape memory alloy and formulation of fatigue life

    SciTech Connect

    Tobushi, Hisaaki; Nakahara, Takafumi; Shimeno, Yoshirou; Hashimoto, Takahiro

    2000-04-01

    The low-cycle fatigue of a TiNi shape memory alloy was investigated by the rotating-bending fatigue tests in air, in water and in silicone oil. (1) The influence of corrosion fatigue in water does not appear in the region of low-cycle fatigue. (2) The temperature rise measured through an infrared thermograph during the fatigue test in air is four times as large as that measured through a thermocouple. (3) The fatigue life at an elevated temperature in air coincides with the fatigue life at the same elevated temperature in water. (4) The shape memory processing temperature does not affect the fatigue life. (5) The fatigue equation is proposed to describe the fatigue life depending on strain amplitude, temperature and frequency. The fatigue life is estimated well by the proposed equation.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Considerations concerning fatigue life of metal matrix composites

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, V. M.; Bartolotta, Paul A.

    1993-01-01

    Since metal matrix composites (MMC) are composed from two very distinct materials each having their own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMC's were analyzed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fiber fracture and matrix were also quantitatively defined.

  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. Theoretical Estimation of Fatigue Crack Initiation Life for Metallic Materials

    NASA Astrophysics Data System (ADS)

    Li, Chunwang; Sun, Qiang; Yang, Youshe; Li, Jing; Zhang, Guibin; Zhang, Zhongping

    2013-03-01

    The main purpose of this paper is to theoretically estimate fatigue crack initiation life of metallic materials using the three-parameter model. For this purpose, correlations between the three parameters and conventional mechanical properties are established. The three parameters are fatigue ductility coefficient, fatigue ductility exponent, and theoretical strain endurance limit. Based on the correlations, the three parameters can be theoretically estimated, and thus the fatigue crack initiation life of metallic materials can be predicted in the absence of fatigue test data.

  15. Fatigue, Creep-Fatigue, and Thermomechanical Fatigue Life Testing of Alloys

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.; Lerch, Bradley A.; McGaw, Michael A.

    2000-01-01

    The fatigue crack initiation resistance of an alloy is determined by conducting a series of tests over a range of values of stress amplitude or strain range. The observed number of cycles to failure is plotted against the stress amplitude or strain range to obtain a fatigue curve. The fatigue properties quoted for an alloy are typically the constants used in the equation(s) that describe the fatigue curve. Fatigue lives of interest may be as low as 10(exp 2) or higher than 10(exp 9) cycles. Because of the enormous scatter associated with fatigue, dozens of tests may be needed to confidently establish a fatigue curve, and the cost may run into several thousands of dollars. To further establish the effects on fatigue life of the test temperature, environment, alloy condition, mean stress effects, creep-fatigue effects, thermomechanical cycling, etc. requires an extraordinarily large and usually very costly test matrix. The total effort required to establish the fatigue resistance of an alloy should not be taken lightly. Fatigue crack initiation tests are conducted on relatively small and presumed to be initially crack-free, samples of an alloy that are intended to be representative of the alloy's metallurgical and physical condition. Generally, samples are smooth and have uniformly polished surfaces within the test section. Some may have intentionally machined notches of well-controlled geometry, but the surface at the root of the notch is usually not polished. The purpose of polishing is to attain a reproducible surface finish. This is to eliminate surface finish as an uncontrolled variable. Representative test specimen geometries will be discussed later. Test specimens are cyclically loaded until macroscopically observable cracks initiate and eventually grow to failure. Normally, the fatigue failure life of a specimen is defined as the number of cycles to separation of the specimen into two pieces. Alternative definitions are becoming more common, particularly for low-cycle fatigue testing, wherein some prescribed indication of impending failure due to cracking is adopted. Specific criteria will be described later. As a rule, cracks that develop during testing are not measured nor are the test parameters intentionally altered owing to the presence of cracking.

  16. Fatigue life prediction of bonded primary joints

    NASA Technical Reports Server (NTRS)

    Knauss, J. F.

    1979-01-01

    The validation of a proposed fatigue life prediction methodology was sought through the use of aluminum butt and scarf joint and graphite/epoxy butt joint specimens in a constant amplitude fatigue environment. The structural properties of the HYSOL 9313 adhesive system were obtained by mechanical test of molded heat adhesive specimens. Aluminum contoured double cantilever beam specimens were used to generate crack velocity versus stress intensity factor data. The specific objectives were: (1) to ascertain the feasibility of predicting fatigue failure of an adhesive in a primary bonded composite structure by incorporating linear elastic crack growth behavior; and (2) to ascertain if acoustic emission and/or compliance measurement techniques can be used to detect flaws.

  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 Life of Superalloy Haynes 188 in Hydrogen

    NASA Astrophysics Data System (ADS)

    Gabb, T. P.; Webster, H.; Ribeiro, G.; Gorman, T.; Gayda, J.

    2012-08-01

    The effects of hydrogen and surface finish on the mean low cycle fatigue life of Haynes 188 were studied. Specimens were prepared and fatigue tested with gage sections having low stress ground (LSG) and electro-discharge machined (EDM) surfaces. Fatigue tests were performed at temperatures of 25 to 650 C with varied strain conditions, in hydrogen and helium environments. Fatigue life decreased with increasing strain range, strain ratio, temperature, and with hydrogen atmosphere. A Smith-Watson-Topper stress parameter could be used to account for variations in strain range and strain ratio, and most strongly influenced life. Hydrogen reduced fatigue life by about 5 (80%) at 25 C, but was much less harmful at 650 C. Standard EDM finish did not consistently reduce mean fatigue life from that of LSG finish specimens. Additional tests indicated fatigue life in hydrogen was maintained for varied EDM conditions, provided specimen roughness and maximum recast layer thickness were not excessive.

  19. 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.

  20. 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.

  1. Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin; Minguet, Pierre J.

    2001-01-01

    A methodology is presented for determining the fatigue life of composite structures based on fatigue characterization data and geometric nonlinear finite element (FE) analyses. To demonstrate the approach, predicted results were compared to fatigue tests performed on specimens which represented a tapered composite flange bonded onto a composite skin. In a first step, tension tests were performed to evaluate the debonding mechanisms between the flange and the skin. In a second step, a 2D FE model was developed to analyze the tests. To predict matrix cracking onset, the relationship between the tension load and the maximum principal stresses transverse to the fiber direction was determined through FE analysis. Transverse tension fatigue life data were used to -enerate an onset fatigue life P-N curve for matrix cracking. The resulting prediction was in good agreement with data from the fatigue tests. In a third step, a fracture mechanics approach based on FE analysis was used to determine the relationship between the tension load and the critical energy release rate. Mixed mode energy release rate fatigue life data were used to create a fatigue life onset G-N curve for delamination. The resulting prediction was in good agreement with data from the fatigue tests. Further, the prediction curve for cumulative life to failure was generated from the previous onset fatigue life curves. The results showed that the methodology offers a significant potential to Predict cumulative fatigue life of composite structures.

  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. Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin

    2000-01-01

    A methodology is presented for determining the fatigue life of bonded composite skin/stringer structures based on delamination fatigue characterization data and geometric nonlinear finite element analyses. Results were compared to fatigue tests on stringer flange/skin specimens to verify the approach.

  4. High-Strength Bolt Corrosion Fatigue Life Model and Application

    PubMed Central

    Hui-li, Wang; Si-feng, Qin

    2014-01-01

    The corrosion fatigue performance of high-strength bolt was studied. Based on the fracture mechanics theory and the Gerberich-Chen formula, the high-strength bolt corrosion fracture crack model and the fatigue life model were established. The high-strength bolt crack depth and the fatigue life under corrosion environment were quantitatively analyzed. The factors affecting high-strength bolt corrosion fatigue life were discussed. The result showed that the high-strength bolt corrosion fracture biggest crack depth reduces along with the material yield strength and the applied stress increases. The material yield strength was the major factor. And the high-strength bolt corrosion fatigue life reduced along with the increase of material strength, the applied stress or stress amplitude. The stress amplitude influenced the most, and the material yield strength influenced the least. Low bolt strength and a low stress amplitude level could extend high-strength bolt corrosion fatigue life. PMID:25152916

  5. Fatigue criterion to system design, life and reliability

    NASA Technical Reports Server (NTRS)

    Zaretsky, E. V.

    1985-01-01

    A generalized methodology to structural life prediction, design, and reliability based upon a fatigue criterion is advanced. The life prediction methodology is based in part on work of Weibull and Lundberg and Palmgren. The approach incorporates the computed life of elemental stress volumes of a complex machine element to predict system life. The results of coupon fatigue testing can be incorporated into the analysis allowing for life prediction and component or structural renewal rates with reasonable statistical certainty.

  6. Fatigue criterion to system design, life and reliability

    NASA Technical Reports Server (NTRS)

    Zaretsky, E. V.

    1985-01-01

    A generalized methodology to structural life prediction, design, and reliability based upon a fatigue criterion is advanced. The life prediction methodology is based in part on work of W. Weibull and G. Lundberg and A. Palmgren. The approach incorporates the computed life of elemental stress volumes of a complex machine element to predict system life. The results of coupon fatigue testing can be incorporated into the analysis allowing for life prediction and component or structural renewal rates with reasonable statistical certainty.

  7. 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.

  8. 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.

  9. Effect of spectral shape on acoustic fatigue life estimates

    NASA Technical Reports Server (NTRS)

    Miles, R. N.

    1992-01-01

    Methods for estimating fatigue life due to random loading are briefly reviewed. These methods include a probabilistic approach in which the expected value of the rate of damage accumulation is computed by integrating over the probability density of damaging events and a method which consists of analyzing the response time history to count damaging events. It is noted that it is necessary to employ a time domain approach to perform Rainflow counting, while simple peak counting may be accomplished using the probabilistic method. Data obtained indicate that Rainflow counting produces significantly different fatigue life predictions than other methods that are commonly used in acoustic fatigue predictions. When low-frequency oscillations are present in a signal along with high-frequency components, peak counting will produce substantially shorter fatigue lives than Rainflow counting. It is concluded that Rainflow counting is capable of providing reliable fatigue life predictions for acoustic fatigue studies.

  10. Effect of spectral shape on acoustic fatigue life estimates

    NASA Astrophysics Data System (ADS)

    Miles, R. N.

    1992-03-01

    Methods for estimating fatigue life due to random loading are briefly reviewed. These methods include a probabilistic approach in which the expected value of the rate of damage accumulation is computed by integrating over the probability density of damaging events and a method which consists of analyzing the response time history to count damaging events. It is noted that it is necessary to employ a time domain approach to perform Rainflow counting, while simple peak counting may be accomplished using the probabilistic method. Data obtained indicate that Rainflow counting produces significantly different fatigue life predictions than other methods that are commonly used in acoustic fatigue predictions. When low-frequency oscillations are present in a signal along with high-frequency components, peak counting will produce substantially shorter fatigue lives than Rainflow counting. It is concluded that Rainflow counting is capable of providing reliable fatigue life predictions for acoustic fatigue studies.

  11. Fatigue life characterization for piezoelectric macrofiber composites

    NASA Astrophysics Data System (ADS)

    Henslee, Isaac A.; Miller, David A.; Tempero, Tyler

    2012-10-01

    In an effort to aid the investigation into lightweight and reliable materials for actuator design, a study was developed to characterize the temperature-dependent lifetime performance of a piezoelectric macrofiber composite (MFC). MFCs are thin rectangular patches of polyimide film, epoxy and a single layer of rectangular lead zirconium titanate (PZT) fibers. In this study, the useful life of the MFC is characterized to determine the effect of temperature on the performance of the composite as it is fatigued by cyclic piezoelectric excitation. The test specimen consists of the MFC laminated to a cantilevered stainless steel beam. Beam strain and tip displacement measurements are used as a basis for determining the performance of the MFC as it is cyclically actuated under various operating temperatures. The temperature of the beam laminate is held constant and then cycled to failure, or 250 million cycles, in order to determine the useful life of the MFC over a temperature range from - 15 to 145?C. The results of the experiments show a strong temperature dependence of the operational life for the MFC. Damage inside the composite was identified through in situ visual inspection and during post-test microstructural observation; however, no degradation in operational performance was identified as it was cyclically actuated up to the point of failure, regardless of temperature or actuation cycle number.

  12. Creep-fatigue life prediction of in situ composite solders

    SciTech Connect

    Kuo, C.G.; Sastry, S.M.L.; Jerina, K.L.

    1995-12-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni{sub 3}Sn{sub 4} and Cu{sub 6}Sn{sub 5} are incorporated into eutectic tin-lead alloy by rapid solidification processes to form in situ composite solders. In this study, the in situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage mechanism of in situ composite solders is proposed to be growth of cavities. A constrained cavity growth model is applied to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed processes can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, based on a critical cavity size of failure. Calculated lives are compared to experimental data under several fatigue histories, which include fully reversed stress-controlled fatigue, zero-tension stress-controlled fatigue, stress-controlled fatigue with tension hold time, fully reversed strain-controlled fatigue, and zero-tension strain-controlled fatigue. The model predicts the creep-fatigue lives within a factor of 2 with the incorporation of an appropriate compressive healing factor in most cases. Discrepancy between calculated lives and experimental results is discussed.

  13. 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.

  14. 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.

  15. Development of an improved method of consolidating fatigue life data

    NASA Technical Reports Server (NTRS)

    Leis, B. N.; Sampath, S. G.

    1978-01-01

    A fatigue data consolidation model that incorporates recent advances in life prediction methodology was developed. A combined analytic and experimental study of fatigue of notched 2024-T3 aluminum alloy under constant amplitude loading was carried out. Because few systematic and complete data sets for 2024-T3 were available in the program generated data for fatigue crack initiation and separation failure for both zero and nonzero mean stresses. Consolidations of these data are presented.

  16. Reinforced wind turbine blades--an environmental life cycle evaluation.

    PubMed

    Merugula, Laura; Khanna, Vikas; Bakshi, Bhavik R

    2012-09-01

    A fiberglass composite reinforced with carbon nanofibers (CNF) at the resin-fiber interface is being developed for potential use in wind turbine blades. An energy and midpoint impact assessment was performed to gauge impacts of scaling production to blades 40 m and longer. Higher loadings force trade-offs in energy return on investment and midpoint impacts relative to the base case while remaining superior to thermoelectric power generation in these indicators. Energy-intensive production of CNFs forces impacts disproportionate to mass contribution. The polymer nanocomposite increases a 2 MW plant's global warming potential nearly 100% per kWh electricity generated with 5% CNF by mass in the blades if no increase in electrical output is realized. The relative scale of impact must be compensated by systematic improvements whether by deployment in higher potential zones or by increased life span; the trade-offs are expected to be significantly lessened with CNF manufacturing maturity. Significant challenges are faced in evaluating emerging technologies including uncertainty in future scenarios and process scaling. Inventories available for raw materials and monte carlos analysis have been used to gain insight to impacts of this development. PMID:22857256

  17. Fatigue Life Estimation under Cumulative Cyclic Loading Conditions

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    The cumulative fatigue behavior of a cobalt-base superalloy, Haynes 188 was investigated at 760 C in air. Initially strain-controlled tests were conducted on solid cylindrical gauge section specimens of Haynes 188 under fully-reversed, tensile and compressive mean strain-controlled fatigue tests. Fatigue data from these tests were used to establish the baseline fatigue behavior of the alloy with 1) a total strain range type fatigue life relation and 2) the Smith-Wastson-Topper (SWT) parameter. Subsequently, two load-level multi-block fatigue tests were conducted on similar specimens of Haynes 188 at the same temperature. Fatigue lives of the multi-block tests were estimated with 1) the Linear Damage Rule (LDR) and 2) the nonlinear Damage Curve Approach (DCA) both with and without the consideration of mean stresses generated during the cumulative fatigue tests. Fatigue life predictions by the nonlinear DCA were much closer to the experimentally observed lives than those obtained by the LDR. In the presence of mean stresses, the SWT parameter estimated the fatigue lives more accurately under tensile conditions than under compressive conditions.

  18. 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.

  19. Residual fatigue life estimation using a nonlinear ultrasound modulation method

    NASA Astrophysics Data System (ADS)

    Piero Malfense Fierro, Gian; Meo, Michele

    2015-02-01

    Predicting the residual fatigue life of a material is not a simple task and requires the development and association of many variables that as standalone tasks can be difficult to determine. This work develops a modulated nonlinear elastic wave spectroscopy method for the evaluation of a metallic components residual fatigue life. An aluminium specimen (AA6082-T6) was tested at predetermined fatigue stages throughout its fatigue life using a dual-frequency ultrasound method. A modulated nonlinear parameter was derived, which described the relationship between the generation of modulated (sideband) responses of a dual frequency signal and the linear response. The sideband generation from the dual frequency (two signal output system) was shown to increase as the residual fatigue life decreased, and as a standalone measurement method it can be used to show an increase in a materials damage. A baseline-free method was developed by linking a theoretical model, obtained by combining the Paris law and the Nazarov-Sutin crack equation, to experimental nonlinear modulation measurements. The results showed good correlation between the derived theoretical model and the modulated nonlinear parameter, allowing for baseline-free material residual fatigue life estimation. Advantages and disadvantages of these methods are discussed, as well as presenting further methods that would lead to increased accuracy of residual fatigue life detection.

  20. Fatigue life prediction under service load considering strengthening effect of loads below fatigue limit

    NASA Astrophysics Data System (ADS)

    Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

    2014-11-01

    Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule (PMR), this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories: damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages: stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule (MMR), and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are -3.78% and -1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.

  1. Fatigue life prediction under service load considering strengthening effect of loads below fatigue limit

    NASA Astrophysics Data System (ADS)

    Zhao, Lihui; Zheng, Songlin; Feng, Jinzhi

    2014-09-01

    Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule (PMR), this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories: damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages: stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule (MMR), and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are -3.78% and -1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.

  2. Life Extending Control. [mechanical fatigue in reusable rocket engines

    NASA Technical Reports Server (NTRS)

    Lorenzo, Carl F.; Merrill, Walter C.

    1991-01-01

    The concept of Life Extending Control is defined. Life is defined in terms of mechanical fatigue life. A brief description is given of the current approach to life prediction using a local, cyclic, stress-strain approach for a critical system component. An alternative approach to life prediction based on a continuous functional relationship to component performance is proposed. Based on cyclic life prediction, an approach to life extending control, called the Life Management Approach, is proposed. A second approach, also based on cyclic life prediction, called the implicit approach, is presented. Assuming the existence of the alternative functional life prediction approach, two additional concepts for Life Extending Control are presented.

  3. Development of a fatigue-life methodology for composite structures subjected to out-of-plane load components

    NASA Technical Reports Server (NTRS)

    Sumich, Mark; Kedward, Keith T.

    1991-01-01

    The efforts to identify and implement a fatigue life methodology applicable to demonstrate delamination failures for use in certifying composite rotor blades are presented. The RSRA/X-Wing vehicle was a proof-of-concept stopped rotor aircraft configuration which used rotor blades primarily constructed of laminated carbon fiber. Delamination of the main spar during ground testing demonstrated that significant interlaminar stresses were produced. Analysis confirmed the presence of out-of-plane load components. The wear out (residual strength) methodology and the requirements for its implementation are discussed.

  4. Rotorcraft fatigue life-prediction: Past, present, and future

    NASA Technical Reports Server (NTRS)

    Everett, Richard A., Jr.; Elber, W.

    1994-01-01

    In this paper the methods used for calculating the fatigue life of metallic dynamic components in rotorcraft is reviewed. In the past, rotorcraft fatigue design has combined constant amplitude tests of full-scale parts with flight loads and usage data in a conservative manner to provide 'safe life' component replacement times. This is in contrast to other industries, such as the automobile industry, where spectrum loading in fatigue testing is a part of the design procedure. Traditionally, the linear cumulative damage rule has been used in a deterministic manner using a conservative value for fatigue strength based on a one in a thousand probability of failure. Conservatism on load and usage are also often employed. This procedure will be discussed along with the current U.S. Army fatigue life specification for new rotorcraft which is the so-called 'six nines' reliability requirement. In order to achieve the six nines reliability requirement the exploration and adoption of new approaches in design and fleet management may also be necessary if this requirement is to be met with a minimum impact on structural weight. To this end a fracture mechanics approach to fatigue life design may be required in order to provide a more accurate estimate of damage progression. Also reviewed in this paper is a fracture mechanics approach for calculating total fatigue life which is based on a crack-closure small crack considerations.

  5. A numerical approach to evaluate the fatigue life of monolimb.

    PubMed

    Chen, Nian-Zhong; Lee, Winson C C; Zhang, Ming

    2006-04-01

    Monolimb refers to a transtibial prosthesis with the prosthetic socket and the shank being molded into one piece of thermoplastic material. Shank flexibility of a monolimb can improve gait and comfort. However, fatigue failure of monolimbs under cyclic walking load is an important concern. This study is to evaluate the fatigue life of a monolimb designed for a transtibial amputee, based on finite element analysis, the statistical Miner's rule and reliability analysis. Stress uncertainty due to modeling error and the scatter in fatigue test data were considered. Results indicated that the accuracy of fatigue life evaluation of monolimb depends significantly on the precision of stress estimation. In addition, relationship between fatigue failure probability and the number of walking steps was suggested providing a reference for clinicians to determine the interval of the inspection for the monolimb. PMID:16112888

  6. Prestraining and Its Influence on Subsequent Fatigue Life

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.

  7. A parametric physics based creep life prediction approach to gas turbine blade conceptual design

    NASA Astrophysics Data System (ADS)

    Smith, Marcus Edward Brockbank

    The required useful service lives of gas turbine components and parts are naturally one of the major design constraints limiting the gas turbine design space. For example, the required service life of a turbine blade limits the firing temperature in the combustor, which in turn limits the performance of the gas turbine. For a cooled turbine blade, it also determines the necessary cooling flow, which has a strong impact on the turbine efficiency. In most gas turbine design practices, the life prediction is only emphasized during or after the detailed design has been completed. Limited life prediction efforts have been made in the early design stages, but these efforts capture only a few of the necessary key factors, such as centrifugal stress. Furthermore, the early stage prediction methods are usually hard coded in the gas turbine system design tools and hidden from the system designer's view. The common failure mechanisms affecting the service life, such as creep, fatigue and oxidation, are highly sensitive to the material temperatures and/or stresses. Calculation of these temperatures and stresses requires that the geometry, material properties, and operating conditions be known; information not typically available in early stages of design. Even without awareness of the errors, the resulting inaccuracy in the life prediction may mislead the system designers when examining a design space which is bounded indirectly by the inaccurate required life constraints. Furthermore, because intensive creep lifing analysis is possible only towards the end of the design process, any errors or changes will cost the engine manufacturer significant money; money that could be saved if more comprehensive creep lifing predictions were possible in the early stages of design. A rapid, physics-based life prediction method could address this problem by enabling the system designer to investigate the design space more thoroughly and accurately. Although not meant as a final decision method, the realistic trends will help to reduce risk, by providing greater insight into the bounded space at an earlier stage of the design. The method proposed by this thesis was developed by first identifying the missing pieces in the system conceptual design tools. Then, by bringing some key features from later stages of design and analysis forward through 0/1/2Ds dimensional modeling and simulation, the method allows estimation of the geometry, material selection, and the loading stemming from the operating conditions. Finally, after integration with a system design platform, the method provides a rapid and more complete way to allow system designers to better investigate the required life constraints. It also extracts the creep life as a system level metric to allow the designers to see the impact of their design decisions on life. The method was first applied to a cooled gas turbine blade and could be further developed for other critical parts. These new developments are integrated to allow the system designers to better capture the blade creep life as well as its impact on the overall design.

  8. A comparison of fatigue life prediction methodologies for rotorcraft

    NASA Technical Reports Server (NTRS)

    Everett, R. A., Jr.

    1990-01-01

    Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.

  9. 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.

  10. 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.

  11. Dramatic increase in fatigue life in hierarchical graphene composites.

    PubMed

    Yavari, F; Rafiee, M A; Rafiee, J; Yu, Z-Z; Koratkar, N

    2010-10-01

    We report the synthesis and fatigue characterization of fiberglass/epoxy composites with various weight fractions of graphene platelets infiltrated into the epoxy resin as well as directly spray-coated on to the glass microfibers. Remarkably only ?0.2% (with respect to the epoxy resin weight and ?0.02% with respect to the entire laminate weight) of graphene additives enhanced the fatigue life of the composite in the flexural bending mode by up to 1200-fold. By contrast, under uniaxial tensile fatigue conditions, the graphene fillers resulted in ?3-5-fold increase in fatigue life. The fatigue life increase (in the flexural bending mode) with graphene additives was ?1-2 orders of magnitude superior to those obtained using carbon nanotubes. In situ ultrasound analysis of the nanocomposite during the cyclic fatigue test suggests that the graphene network toughens the fiberglass/epoxy-matrix interface and prevents the delamination/buckling of the glass microfibers under compressive stress. Such fatigue-resistant hierarchical materials show potential to improve the safety, reliability, and cost effectiveness of fiber-reinforced composites that are increasingly the material of choice in the aerospace, automotive, marine, sports, biomedical, and wind energy industries. PMID:20863061

  12. Surface Fatigue Life of High Temperature Gear Materials

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.

    1994-01-01

    Three high temperature gear materials were evaluated using spur gear surface fatigue tests. These materials were, VASCO max 350, VASCO matrix 2, and nitralloy N and were evaluated for possible use in high temperature gear applications. The fatigue life of the three high temperature gear materials were compared with the life of the standard AISI 9310 aircraft gear material. Surface fatigue tests were conducted at a lubricant inlet temperature of 321 K (120 F), a lubricant outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), a speed of 10,000 rpm, and with a synthetic paraffinic lubricant. The life of the nitralloy N was approximately the same as the AISI 9310, the life of the VASCO max 350 was much less than the AISI 9310 while the life of the VASCO matrix 2 was several times the life of the AISI 9310. The VASCO max 350 also showed very low fracture toughness with approximately half of the gears failed by tooth fracture through the fatigue spall. The VASCO matrix 2 had approximately 10-percent fracture failure through the fatigue spalls indicating moderate to good fracture toughness.

  13. A self-healing polymer composite for extended fatigue life

    SciTech Connect

    Brown, E. N.; Jones, A. S.; White, S. R.; Sottos, Nancy R.

    2004-01-01

    A novel approach is explored for improving the fatigue life of thermosetting polymers through the addition of self-healing functionality. Thermosetting polymers are used in a wide variety of applications, but are susceptible to the initiation and propagation of small cracks deep within the structure where detection is difficult and repair is virtually impossible. The material under investigation is an epoxy matrix composite, which utilizes embedded microcapsules to store a healing agent and an embedded catalyst. A propagating crack exposes particles of catalyst and ruptures the microcapsules, which release healing agent into the crack plane. Polymerization of the healing agent is triggered by contact with the catalyst. Fatigue crack retardation and arrest from self-healing functionality result from crack-tip shielding mechanisms, such as hydrodynamic pressure and artificial-crack closure. In situ healing is observed to significantly extended fatigue life or permanently arrested fatigue crack growth over a wide range of loading conditions.

  14. Thermomechanical fatigue, oxidation, and Creep: Part II. Life prediction

    NASA Astrophysics Data System (ADS)

    Neu, R. W.; Sehitoglu, Huseyin

    1989-09-01

    A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation), and creep damage. The model handles different strain-temperature phasings (i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings). Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature phasings. An oxide growth (oxide damage) model is based on the repeated microrupture process of oxide observed from microscopic measurements. A creep damage expression, which is stress-based, is coupled with a unified constitutive equation. A set of interrupted tests was performed to provide valuable damage progression information. Tests were performed in air and in helium atmospheres to isolate creep damage from oxidation damage.

  15. X-43A Rudder Spindle Fatigue Life Estimate and Testing

    NASA Technical Reports Server (NTRS)

    Glaessgen, Edward H.; Dawicke, David S.; Johnston, William M.; James, Mark A.; Simonsen, Micah; Mason, Brian H.

    2005-01-01

    Fatigue life analyses were performed using a standard strain-life approach and a linear cumulative damage parameter to assess the effect of a single accidental overload on the fatigue life of the Haynes 230 nickel-base superalloy X-43A rudder spindle. Because of a limited amount of information available about the Haynes 230 material, a series of tests were conducted to replicate the overload and in-service conditions for the spindle and corroborate the analysis. Both the analytical and experimental results suggest that the spindle will survive the anticipated flight loads.

  16. Volume effects on fatigue life of equine cortical bone.

    PubMed

    Bigley, R F; Gibeling, J C; Stover, S M; Hazelwood, S J; Fyhrie, D P; Martin, R B

    2007-01-01

    Materials, including bone, often fail due to loading in the presence of critical flaws. The relative amount, location, and interaction of these flaws within a stressed volume of material play a role in determining the failure properties of the structure. As materials are generally imperfect, larger volumes of material have higher probabilities of containing a flaw of critical size than do smaller volumes. Thus, larger volumes tend to fail at fewer cycles compared with smaller volumes when fatigue loaded to similar stress levels. A material is said to exhibit a volume effect if its failure properties are dependent on the specimen volume. Volume effects are well documented in brittle ceramics and composites and have been proposed for bone. We hypothesized that (1) smaller volumes of cortical bone have longer fatigue lives than similarly loaded larger volumes and (2) that compared with microstructural features, specimen volume was able to explain comparable amounts of variability in fatigue life. In this investigation, waisted rectangular specimens (n=18) with nominal cross-sections of 3x4 mm and gage lengths of 10.5, 21, or 42 mm, were isolated from the mid-diaphysis of the dorsal region of equine third metacarpal bones. These specimens were subjected to uniaxial load controlled fatigue tests, with an initial strain range of 4000 microstrain. The group having the smallest volume exhibited a trend of greater log fatigue life than the larger volume groups. Each volume group exhibited a significant positive correlation between the logarithm of fatigue life and the cumulative failure probability, indicating that the data follow the two-parameter Weibull distribution. Additionally, log fatigue life was negatively correlated with log volume, supporting the hypothesis that smaller stressed volumes of cortical bone possess longer fatigue lives than similarly tested larger stressed volumes. PMID:17632110

  17. NASA GRC Fatigue Crack Initiation Life Prediction Models

    NASA Technical Reports Server (NTRS)

    Arya, Vinod K.; Halford, Gary R.

    2002-01-01

    Metal fatigue has plagued structural components for centuries, and it remains a critical durability issue in today's aerospace hardware. This is true despite vastly improved and advanced materials, increased mechanistic understanding, and development of accurate structural analysis and advanced fatigue life prediction tools. Each advance is quickly taken advantage of to produce safer, more reliable, more cost effective, and better performing products. In other words, as the envelope is expanded, components are then designed to operate just as close to the newly expanded envelope as they were to the initial one. The problem is perennial. The economic importance of addressing structural durability issues early in the design process is emphasized. Tradeoffs with performance, cost, and legislated restrictions are pointed out. Several aspects of structural durability of advanced systems, advanced materials and advanced fatigue life prediction methods are presented. Specific items include the basic elements of durability analysis, conventional designs, barriers to be overcome for advanced systems, high-temperature life prediction for both creep-fatigue and thermomechanical fatigue, mean stress effects, multiaxial stress-strain states, and cumulative fatigue damage accumulation assessment.

  18. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1988-01-01

    A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  19. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1989-01-01

    A major objective of the fatigue and fracture efforts under the NASA Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  20. Non-destructive measurement and role of surface residual stress monitoring in residual life assessment of a steam turbine blading material

    NASA Astrophysics Data System (ADS)

    Prabhu-Gaunkar, Gajanana; Rawat, M. S.; Prasad, C. R.

    2014-02-01

    Steam turbine blades in power generation equipment are made from martensitic stainless steels having high strength, good toughness and corrosion resistance. However, these steels are susceptible to pitting which can promote early failures of blades in the turbines, particularly in the low pressure dry/wet areas by stress corrosion and corrosion fatigue. Presence of tensile residual stresses is known to accelerate failures whereas compressive stresses can help in delaying failures. Shot peening has been employed as an effective tool to induce compressive residual stresses which offset a part of local surface tensile stresses in the surface layers of components. Maintaining local stresses at stress raisers, such as pits formed during service, below a threshold level can help in preventing the initiation microcracks and failures. The thickness of the layer in compression will, however, depend of the shot peening parameters and should extend below the bottom of corrosion pits. The magnitude of surface compressive drops progressively during service exposure and over time the effectiveness of shot peening is lost making the material susceptible to micro-crack initiation once again. Measurement and monitoring of surface residual stress therefore becomes important for assessing residual life of components in service. This paper shows the applicability of surface stress monitoring to life assessment of steam turbine blade material based on data generated in laboratory on residual surface stress measurements in relation to fatigue exposure. An empirical model is proposed to calculate the remaining life of shot peened steam turbine blades in service.

  1. A criterion for high-cycle fatigue life and fatigue limit prediction in biaxial loading conditions

    NASA Astrophysics Data System (ADS)

    Pejkowski, ?ukasz; Skibicki, Dariusz

    2015-12-01

    This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The criterion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S-N curves: tension-compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promising. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the non-proportionality of loading.

  2. Creep fatigue life prediction for engine hot section materials (isotropic)

    NASA Technical Reports Server (NTRS)

    Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

    1985-01-01

    The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

  3. Fatigue life estimates for helicopter loading spectra

    NASA Technical Reports Server (NTRS)

    Khosrovaneh, A. K.; Dowling, N. E.; Berens, A. P.; Gallagher, J. P.

    1989-01-01

    Helicopter loading histories applied to notch metal samples are used as examples, and their fatigue lives are calculated by using a simplified version of the local strain approach. This simplified method has the advantage that it requires knowing the loading history in only the reduced form of ranges and means and number of cycles from the rain-flow cycle counting method. The calculated lives compare favorably with test data.

  4. Relationship between fatigue life in the creep-fatigue region and stress-strain response

    NASA Technical Reports Server (NTRS)

    Berkovits, A.; Nadiv, S.

    1988-01-01

    On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the two more pairs of stress strain parameters must be ascertained.

  5. Life prediction for bridged fatigue cracks

    SciTech Connect

    Cox, B.N.

    1994-08-01

    One of the more promising classes of composites touted for high temperature applications, and certainly the most available, is that of relatively brittle matrices, either ceramic or intermetallic, reinforced by strong, aligned, continuous fibers. Under cyclic loading in the fiber direction, these materials develop matrix cracks that often run perpendicular to the fibers, while the fibers remain intact in the crack wake, supplying bridging tractions across the fracture surfaces. The bridging tractions shield the crack tip from the applied load, dramatically reducing the crack velocity from that expected in an unreinforced material subjected to the same value, {Delta}K{sub a}, of the cyclic applied stress intensity factor. An important issue in reliability is the prediction of the growth rates of the bridged cracks. The growth rates of matrix fatigue cracks bridged by sliding fibers are now commonly predicted by models based on the micromechanics of frictional interfaces. However, there exist many reasons, both theoretical and experimental, for suspecting that the most popular micromechanical models are probably wrong in detail in the context of fatigue cracks. Furthermore, a review of crack growth data reveals that the validity of the micromechanics-based predictive model has never been tested and may never be tested. In this paper, two alternative approaches are suggested to the engineering problem of predicting the growth rates of bridged cracks without explicit recourse to micromechanics. Instead, it is shown that the material properties required to analyze bridging effects can be deduced directly from crack growth data. Some experiments are proposed to test the validity of the proposals.

  6. Fatigue life analysis of a turboprop reduction gearbox

    NASA Technical Reports Server (NTRS)

    Lewicki, D. G.; Black, J. D.; Savage, M.; Coy, J. J.

    1985-01-01

    A fatigue life analysis of the Allison T56/501 turboprop reduction gearbox was developed. The life and reliability of the gearbox was based on the lives and reliabilities of the main power train bearings and gears. The bearing and gear lives were determined using the Lundberg-Palmgren theory and a mission profile. The five planet bearing set had the shortest calculated life among the various gearbox components, which agreed with field experience where the planet bearing had the greatest incidences of failure. The analytical predictions of relative lives among the various bearings were in reasonable agreement with field experience. The predicted gearbox life was in excellent agreement with field data when the material life adjustment factors alone were used. The gearbox had a lower predicted life in comparison with field data when no life adjustment factors were used or when lubrication life adjustment factors were used either alone or in combination with the material factors.

  7. 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.

  8. Ductility normalized-strain-range partitioning life relations for creep-fatigue life predictions

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Saltsman, J. F.; Hirschberg, M. H.

    1978-01-01

    Techniques utilizing strainrange partitioning may be used to estimate the effects of the environment on the high-temperature, low-cycle, creep-fatigue resistance of alloys. Three levels of ductility-normalized strainrange-partitioning life relations are discussed: (1) strainrange partitioning relations from ductility data, (2) strainrange partitioning relations scaled by ductility ratios, and (3) strainrange partitioning life relations with measured PP lines. The procedures have demonstrated good agreement with available creep-fatigue data.

  9. Tension fatigue analysis and life prediction for composite laminates

    NASA Technical Reports Server (NTRS)

    Obrien, T. K.; Rigamonti, M.; Zanotti, C.

    1988-01-01

    A tension fatigue life prediction methodology for composite laminates is presented. Tension fatigue tests were conducted on quasi-isotropic and orthotropic glass epoxy, graphite epoxy, and glass/graphite epoxy hybrid laminates. Edge delamination onset data were used to generate plots of strain energy release rate as a function of cycles to delamination onset. These plots were then used along with strain energy release rate analyses of delaminations initiating at matrix cracks to predict local delamination onset. Stiffness loss was measured experimentally to account for the accumulation of matrix cracks and for delamination growth. Fatigue failure was predicted by comparing the increase in global strain resulting from stiffness loss to the decrease in laminate failure strain resulting from delaminations forming at matrix cracks through the laminate thickness. Good agreement between measured and predicted lives indicated that the through-thickness damage accumulation model can accurately describe fatigue failure for laminates where the delamination onset behavior in fatigue is well characterized, and stiffness loss can be monitored in real time to account for damage growth.

  10. Multiaxial plasticity and fatigue life prediction in coiled tubing

    SciTech Connect

    Tipton, S.M.

    1996-12-31

    Coiled tubing is being used increasingly in the oil well drilling and servicing industry. Continuous steel tubing of structural dimensions (up to 89 mm or 3.5 in. in diameter) is wound onto a large-diameter reel for repeated deployment into and out of a well bore. The bending strain range associated with each wrap-unwrap cycle can exceed 3% with lives well below 100 cycles. During constant internal pressure fatigue testing, tubing has been observed to grow in diameter by as much as 30%. This paper describes an analytical model to predict the fatigue behavior of coiled tubing subjected to variable pressure service conditions. The approach utilizes standard low-cycle fatigue data but requires additional experimental results from constant pressure fatigue testing. The algorithm is based on estimates of biaxial ratcheting from an incremental plasticity model using a hybrid associated flow rule, a modified kinematic hardening rule with multiple von Mises yield surfaces, and a specialized limit surface concept. An empirical damage parameter was formulated based on constant pressure fatigue data using mean and fluctuating von Mises equivalent strain components occurring throughout the life of a section of tubing. This parameters is used with the Palmgren-Miner definition of cumulative damage to track damage that is accumulating nonlinearly under constant or variable pressure histories. Modifications to standard incremental plasticity components and implementation assumptions used to apply the model are presented and discussed. The predictive capability of the model is demonstrated relative to data generated under constant and variable pressure histories.

  11. Simplified fatigue life analysis for traction drive contacts

    NASA Technical Reports Server (NTRS)

    Rohn, D. A.; Loewenthal, S. H.; Coy, J. J.

    1980-01-01

    A simplified fatigue life analysis for traction drive contacts of arbitrary geometry is presented. The analysis is based on the Lundberg-Palmgren theory used for rolling-element bearings. The effects of torque, element size, speed, contact ellipse ratio, and the influence of traction coefficient are shown. The analysis shows that within the limits of the available traction coefficient, traction contacts exhibit longest life at high speeds. Multiple, load-sharing roller arrangements have an advantageous effect on system life, torque capacity, power-to-weight ratio and size.

  12. Thermomechanical Fatigue of Ductile Cast Iron and Its Life Prediction

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Thermomechanical fatigue (TMF) behaviors of ductile cast iron (DCI) were investigated under out-of-phase (OP), in-phase (IP), and constrained strain-control conditions with temperature hold in various temperature ranges: 573 K to 1073 K, 723 K to 1073 K, and 433 K to 873 K (300 °C to 800 °C, 450 °C to 800 °C, and 160 °C to 600 °C). The integrated creep-fatigue theory (ICFT) model was incorporated into the finite element method to simulate the hysteresis behavior and predict the TMF life of DCI under those test conditions. With the consideration of four deformation/damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement, (iii) creep, and (iv) oxidation, as revealed from the previous study on low cycle fatigue of the material, the model delineates the contributions of these physical mechanisms in the asymmetrical hysteresis behavior and the damage accumulation process leading to final TMF failure. This study shows that the ICFT model can simulate the stress-strain response and life of DCI under complex TMF loading profiles (OP and IP, and constrained with temperature hold).

  13. 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.

  14. Advances in fatigue life prediction methodology for metallic materials

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1992-01-01

    The capabilities of a plasticity-induced crack-closure model to predict small- and large-crack growth rates, and in some cases total fatigue life, for four aluminum alloys and three titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading are described. Equations to calculate a cyclic-plastic-zone corrected effective stress-intensity factor range from a cyclic J-integral and crack-closure analysis of large cracks were reviewed. The effective stress-intensity factor range against crack growth rate relations were used in the closure model to predict small- and large-crack growth under variable-amplitude and spectrum loading. Using the closure model and microstructural features, a total fatigue life prediction method is demonstrated for three aluminum alloys under various load histories.

  15. Creep fatigue life prediction for engine hot section materials (isotropic)

    NASA Technical Reports Server (NTRS)

    Moreno, V.

    1983-01-01

    The Hot Section Technology (HOST) program, creep fatigue life prediction for engine hot section materials (isotropic), is reviewed. The program is aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components. Significant results include: (1) cast B1900 and wrought IN 718 selected as the base and alternative materials respectively; (2) fatigue test specimens indicated that measurable surface cracks appear early in the specimen lives, i.e., 15% of total life at 871 C and 50% of life at 538 c; (3) observed crack initiation sites are all surface initiated and are associated with either grain boundary carbides or local porosity, transgrannular cracking is observed at the initiation site for all conditions tested; and (4) an initial evaluation of two life prediction models, representative of macroscopic (Coffin-Mason) and more microscopic (damage rate) approaches, was conducted using limited data generated at 871 C and 538 C. It is found that the microscopic approach provides a more accurate regression of the data used to determine crack initiation model constants, but overpredicts the effect of strain rate on crack initiation life for the conditions tested.

  16. 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.

  17. Relationship between fatigue life in the creep-fatigue region and stress-strain response

    NASA Technical Reports Server (NTRS)

    Berkovits, A.; Nadiv, S.

    1988-01-01

    On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the elastic modulus. For plasticity/creep interaction conditions (PC and CP) two more pairs of stress strain parameters must be ascertained.

  18. 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.

  19. Effect on interference fits on roller bearing fatigue life

    NASA Technical Reports Server (NTRS)

    Coe, H. H.; Zaretsky, E. V.

    1986-01-01

    An analysis was performed to determine the effects of inner-ring speed and press fits on roller bearing fatigue life. The effects of the resultant hoop and radial stresses on the principal stresses were considered. The maximum shear stresses below the Hertzian contact were determined for different conditions of inner-ring speed and load, and were applied to a conventional roller bearing life analysis. The effect of mean stress was determined using Goodman diagram approach. Hoop stresses caused by press fits and centrifugal force can reduce bearing life by as much as 90 percent. Use of a Goodman diagram predicts life reductions of 20 to 30 percent. The depth of the maximum shear stress remains virtually unchanged.

  20. Gas penetrant inspection: A low cost solution to infant mortality and higher turbine blade life

    SciTech Connect

    Glatz, J.; Mahon, A.; Paglieri, R.

    1995-12-31

    A small percentage of turbine blades fail or crack prematurely due to casting flaws. This problem is generic and occurs in gas turbine engines. Research with gas penetrants has identified routine liquid fluorescent penetrant inspection (FPI) errors as the cause. The Krypton Evaluation Technique (KET), a gas penetrant nondestructive inspection method, effectively identifies the potentially low lifers in FPI approved turbine blades. Replacing one of the 3 FPI`S, now performed on all new turbine blades, with a KET inspection is a much lower cost alternative to the current industry-wide multiple FPI quality assurance strategy. This best practice recommendation protects the end users from unexpected failures and premature cracking and allows them to achieve higher blade life. This logic would also apply to overhauled and repaired parts.

  1. Estimation of fatigue life of railway bridges under traffic loads

    NASA Astrophysics Data System (ADS)

    Frba, L.

    1980-06-01

    Random modelling of railway bridge loading enables fatigue damage to be calculated on the basis of the cumulative damage theory of Palmgren-Miner and the classification of the stress-time history by means of the "rain-flow" counting method. The results of calculations are the mean value of the damage and the standard deviation of the stresses, and thus an estimation of the bridge fatigue life. Accordingly the bridge life is dependent on the number of stress cycles and their distribution, the standard deviation of stresses, and on the shape of the Whler curve. Bridge life increasing span and decreases with an increasing traffic load. Results are presented as obtained in a detailed study of the effects on the bridge life of different parameters (vehicle speed, damping of bridge vibrations, variability in length and time of the moving load and its magnitude, number of stress cycles and their distribution). The equivalent damage method (the ?T-method) in the integral form enables one to compare the effects of the traffic loads with those of the standard loading.

  2. 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.

  3. Fatigue-life behavior and matrix fatigue crack spacing in unnotched SCS-6/Timetal 21S metal matrix composites

    NASA Technical Reports Server (NTRS)

    Ward, G. T.; Herrmann, D. J.; Hillberry, B. M.

    1993-01-01

    Fatigue tests of the SCS-6/Timetal 21S composite system were performed to characterize the fatigue behavior for unnotched conditions. The stress-life behavior of the unnotched (9/90)2s laminates was investigated for stress ratios of R = 0.1 and R = 0.3. The occurrence of matrix cracking was also examined in these specimens. This revealed multiple matrix crack initiation sites throughout the composite, as well as evenly spaced surface cracks along the length of the specimens. No difference in fatigue lives were observed for stress ratios of R = 0.1 and R = 0.3 when compared on a stress range basis. The unnotched SCS-6/Timetal 21S composites had shorter fatigue lives than the SCS-6/Ti-15-3 composites, however the neat Timetal 21S matrix material had a longer fatigue life than the neat Ti-15-3.

  4. Lubricant and additive effects on spur gear fatigue life

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Zaretsky, E. V.; Scibbe, H. W.

    1985-01-01

    Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided into four batches each of which had a different additive content. Lubricants tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulfur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt % sulfur and 0.1 wt % phosphorus EP additives in the lubricant had reactive films that were 200 to 400 (0.8 to 1.6 microns) thick.

  5. Lubricant and additive effects on spur gear fatigue life

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Zaretsky, E. V.; Scibbe, H. W.

    1986-01-01

    Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricants was divided into four batches each of which had a different additive content. Lubricant tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulfur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwar additives. Gears tested with a 0.1 wt pct sulfur and 0.1 wt pct phosphorus EP additives in the lubricant had reactive films that were 200 to 400 (0.8 to 1.6 microns) thick.

  6. Development of a Generic Creep-Fatigue Life Prediction Model

    NASA Technical Reports Server (NTRS)

    Goswami, Tarun

    2002-01-01

    The objective of this research proposal is to further compile creep-fatigue data of steel alloys and superalloys used in military aircraft engines and/or rocket engines and to develop a statistical multivariate equation. The newly derived model will be a probabilistic fit to all the data compiled from various sources. Attempts will be made to procure the creep-fatigue data from NASA Glenn Research Center and other sources to further develop life prediction models for specific alloy groups. In a previous effort [1-3], a bank of creep-fatigue data has been compiled and tabulated under a range of known test parameters. These test parameters are called independent variables, namely; total strain range, strain rate, hold time, and temperature. The present research attempts to use these variables to develop a multivariate equation, which will be a probabilistic equation fitting a large database. The data predicted by the new model will be analyzed using the normal distribution fits, the closer the predicted lives are with the experimental lives (normal line 1 to 1 fit) the better the prediction. This will be evaluated in terms of a coefficient of correlation, R 2 as well. A multivariate equation developed earlier [3] has the following form, where S, R, T, and H have specific meaning discussed later.

  7. 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.

  8. Modeling fatigue crack growth for life-extending control

    NASA Astrophysics Data System (ADS)

    Patankar, Ravindra Prakash

    1999-12-01

    This dissertation presents a nonlinear dynamic model of fatigue crack growth in the state-space setting under variable amplitude cyclic load. The model is especially suited to the needs of real-time decision-making for life-extending control. The state variables are crack length and crack opening stress. The model is capable of capturing the effects of a single-cycle overload, block loads, random loads, and irregular sequences through a fading memory algorithm. Model predictions are in good agreement with experimental data on 7075-T6 and 2024-T3 aluminum alloys. Compiled results also demonstrate that the proposed model compares well with one of the most comprehensive models, FASTRAN-II that is used by the aircraft industry. Specifically, the state-space model recursively computes the crack opening stress via a simple functional relationship based on the principle of fading memory and does not require the storage of the stress history for its execution. Therefore, savings in both computation time and memory requirements are significant. The need for a reliable damage model for life-extending control is addressed with reference to the colossal inaccuracies that could occur in controller synthesis for a reusable rocket engine if a simplistic damage model is used under variable-amplitude load conditions. The seemingly counter-intuitive notion of overload injection could be gainfully utilized for life-extending optimization. The proof of this concept is demonstrated on a laboratory test apparatus by life-extension of test specimens with intentionally injected overload pulses at specific intervals. A stochastic model of fatigue crack growth under variable-amplitude load is proposed using the framework of the state-space model. The stochastic model is validated with four sets of constant-amplitude load test data and a set under variable-amplitude load test. The crack growth process is observed to be nearly deterministic for a cyclic load applied to a given specimen, provided that its microstructure does not undergo any major change. Therefore, a reliable deterministic model is a prerequisite for a stochastic model of fatigue crack growth. The stochastic model of fatigue crack growth does not require expensive computations to obtain a solution to the stochastic difference equations.

  9. Fatigue Life Methodology for Tapered Composite Flexbeam Laminates

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; O''Brien, T. Kevin; Rousseau, Carl Q.

    1997-01-01

    The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to nonlinear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending loads. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse flexbeam tip-displacement and flapping angle. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.

  10. Fatigue Life Methodology for Tapered Composite Flexbeam Laminates

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; OBrien, T. Kevin; Rousseau, Carl Q.

    1997-01-01

    The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to non-linear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse displacement. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.

  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. 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.

  13. Fatigue

    MedlinePLUS

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  14. Structural health monitoring of wind towers: residual fatigue life estimation

    NASA Astrophysics Data System (ADS)

    Benedetti, M.; Fontanari, V.; Battisti, L.

    2013-04-01

    In a recent paper (Benedetti et al 2011 Smart Mater. Struct. 20 055009), the authors investigated the possibility of detecting cracks in critical sites of onshore wind towers using a radial arrangement of strain sensors around the tower periphery in the vicinity of the base welded joint. Specifically, the strain difference between adjacent strain sensors is used as a damage indicator. The number of sensors to be installed is determined by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule. In this companion paper, we address these issues by investigating possible strategies for residual fatigue life assessment and management of onshore wind towers once the crack has been detected. For this purpose, fracture mechanics tests are carried out using welded samples to quantify the resistance to fatigue crack growth as well as the elastic-plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality.

  15. Fatigue life of organic fiber/epoxy pressure vessels

    NASA Technical Reports Server (NTRS)

    Hamstad, M. A.; Chiao, T. T.; Patterson, R. G.

    1975-01-01

    The cyclic fatigue life of 10.2-cm-diam cylindrical pressure vessels has been studied. The vessels were made of an organic fiber/epoxy composite. To determine the typical strength distribution of the vessels, 25 of them were internally pressurized until they burst. Twenty-five vessels were then tested under sinusoidal cycling at 1 Hz between 4% and 91% of the mean burst strength. An additional twenty-five vessels were tested between 4% and 91% with a rectangular pressure pulse at 1/3 Hz. A limited number of vessels were tested for stress rupture at the 91% level. Cyclic life was found to depend on time at peak load as well as the number of stress cycles.

  16. Rainflow counting algorithm for the LIFE2 fatigue analysis code

    NASA Astrophysics Data System (ADS)

    Schluter, L. L.; Sutherland, H. J.

    The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. In this formulation, each stress cycle is counted or binsed according to the magnitude of its mean stress and alternating stress components and by the operating condition of the turbine. A set of numerical algorithms are described that were incorporated into the LIFE2 code. These algorithms determine the cycle count matrices for a turbine component using stress-time histories of the imposed stress states. Example problems are used to illustrate the use of these algorithms.

  17. NASALIFE - Component Fatigue and Creep Life Prediction Program

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, John Z.; Murthy, Pappu L. N.; Mital, Subodh K.

    2014-01-01

    NASALIFE is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although the primary focus was for CMC components, the underlying methodologies are equally applicable to other material systems as well. The program references empirical data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method or a peak counting type method. Lastly, damage due to cyclic loading and creep is combined with Minor's Rule to determine damage due to cyclic loading, damage due to creep, and the total damage per mission and the number of potential missions the component can provide before failure.

  18. Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability

    NASA Technical Reports Server (NTRS)

    Zaretsky, Erwin V.; Lewicki, David G.; Savage, Michael; Vlcek, Brian L.

    2007-01-01

    Two computational models to determine the fatigue life and reliability of a commercial turboprop gearbox are compared with each other and with field data. These models are (1) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising the system and (2) two-parameter Weibull distribution function for bearings and gears comprising the system using strict-series system reliability to combine the calculated individual component lives in the gearbox. The Monte Carlo simulation included the virtual testing of 744,450 gearboxes. Two sets of field data were obtained from 64 gearboxes that were first-run to removal for cause, were refurbished and placed back in service, and then were second-run until removal for cause. A series of equations were empirically developed from the Monte Carlo simulation to determine the statistical variation in predicted life and Weibull slope as a function of the number of gearboxes failed. The resultant L(sub 10) life from the field data was 5,627 hr. From strict-series system reliability, the predicted L(sub 10) life was 774 hr. From the Monte Carlo simulation, the median value for the L(sub 10) gearbox lives equaled 757 hr. Half of the gearbox L(sub 10) lives will be less than this value and the other half more. The resultant L(sub 10) life of the second-run (refurbished) gearboxes was 1,334 hr. The apparent load-life exponent p for the roller bearings is 5.2. Were the bearing lives to be recalculated with a load-life exponent p equal to 5.2, the predicted L(sub 10) life of the gearbox would be equal to the actual life obtained in the field. The component failure distribution of the gearbox from the Monte Carlo simulation was nearly identical to that using the strict-series system reliability analysis, proving the compatibility of these methods.

  19. An Energy Based Fatigue Life Prediction Framework for In-Service Structural Components

    SciTech Connect

    H. Ozaltun; M. H.H. Shen; T. George; C. Cross

    2011-06-01

    An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in service gas turbine materials. The purpose of the life prediction framework is to account aging effect caused by cyclic loadings on fatigue strength of gas turbine engines structural components which are usually designed for very long life. Previous studies indicate the total strain energy dissipated during a monotonic fracture process and a cyclic process is a material property that can be determined by measuring the area underneath the monotonic true stress-strain curve and the sum of the area within each hysteresis loop in the cyclic process, respectively. The energy-based fatigue life prediction framework consists of the following entities: (1) development of a testing procedure to achieve plastic energy dissipation per life cycle and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials. The accuracy of the remaining fatigue life prediction method was verified by comparison between model approximation and experimental results of Aluminum 6061-T6. The comparison shows promising agreement, thus validating the capability of the framework to produce accurate fatigue life prediction.

  20. From cleanliness to rolling fatigue life of bearings -- A new approach

    SciTech Connect

    Lormand, G.; Meynaud, P.; Vincent, A.; Baudry, G.; Girodin, D.; Dudragne, G.

    1998-12-31

    One of the main causes of in-service spalling of bearing steels is fatigue crack initiation from non-metallic inclusions. At the present time, while the relationship between endurance and cleanliness of bearing steels is obvious, no quantitative relationship between them has been established. The aim of this paper is to present a new quantitative method which predicts the rolling fatigue life distribution of bearings. This approach is based on a model of fatigue crack initiation in the vicinity of an inclusion in the steel matrix and on a simple fatigue crack propagation relationship. This basic model is used in a statistical approach to describe the scatter of fatigue lives using the distribution of inclusions in the Hertzian zone. The fairly good agreement with fatigue results shows that this approach constitutes a real future tool for predicting the influence of the main material parameters on the fatigue life distribution of bearings.

  1. Estimation of fatigue strain-life curves for austenitic stainless steels in light water reactor environments.

    SciTech Connect

    Chopra, O. K.; Smith, J. L.

    1998-02-12

    The ASME Boiler and Pressure Vessel Code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels (SSs) in light water reactor (LWR) environments. Unlike those of carbon and low-alloy steels, environmental effects on fatigue lives of SSs are more pronounced in low-dissolved-oxygen (low-DO) water than in high-DO water, This paper summarizes available fatigue strain vs. life data on the effects of various material and loading variables such as steel type, DO level, strain range, and strain rate on the fatigue lives of wrought and cast austenitic SSs. Statistical models for estimating the fatigue lives of these steels in LWR environments have been updated with a larger data base. The significance of the effect of environment on the current Code design curve has been evaluated.

  2. Probabilistic fatigue life prediction model for alloys with defects: applied to A206

    SciTech Connect

    Kapoor, Rajeev; Sree Hari Rao, V.; Mishra, Rajiv S.; Baumann, John A.; Grant, Glenn J.

    2011-05-31

    Presented here is a model for the prediction of fatigue life based on the statistical distribution of pores, intermetallic particles and grains. This has been applied to a cast Al alloy A206, before and after friction stir processing (FSP). The model computes the probability to initiate a small crack based on the probability of finding combinations of defects and grains on the surface. The crack initiation and propagation life of small cracks due to these defect and grain combinations are computed and summed to obtain the total fatigue life. The defect and grain combinations are ranked according to total fatigue life and the failure probability computed. Bending fatigue experiments were carried out on A206 before and after FSP. FSP eliminated the porosity, broke down the particles and refined the microstructure. The model predicted the fatigue life of A206 before and after FSP well. The cumulative probability distribution vs. fatigue life was fitted to a three parameter Weibull distribution function. The scatter reduced after FSP and the threshold of fatigue life increased. The potential improvement in the fatigue life of A206 for a microstructure consisting of a finer distribution of particle sizes after FSP was predicted using the model.

  3. Creep fatigue life prediction for engine hot section materials (isotropic)

    NASA Technical Reports Server (NTRS)

    Nelson, R. S.; Levan, G. W.; Harvey, P. R.

    1992-01-01

    This Final Report covers the activities completed under the optional program of the NASA HOST Contract, NAS3-23288. The initial effort of the optional program was report-in NASA CR189221, which consisted of high temperature strain controlled fatigue tests to study the effects of thermomechanical fatigue, multiaxial loading, reactive environments, and imposed stresses. The baseline alloy used in the tests included B1900+Hf (with or without coating) and wrought INCO 718. Tests conducted on B1900+Hf included environmental tests using various atmospheres (75 psig oxygen, purified argon, or block exposures) and specimen tests of wrought INCO 718 included tensile, creep, stress rupture, TMF, multiaxial, and mean stress tests. Results of these testings were used to calibrate a CDA model for INCO 718 alloy and to develop modifications or corrections to the CDA model to handle additional failure mechanisms. The Socie parameter was found to provide the best correlation for INCO multiaxial loading. Microstructural evaluations consisting of optical, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) techniques, and surface replication techniques to determine crack initiation lives provided data which were used to develop life prediction models.

  4. Fatigue life under random load history derived from exceedance curves using different algorithms

    NASA Astrophysics Data System (ADS)

    Prakash, Raghu V.; Sunder, R.

    1993-07-01

    Low cycle fatigue life and crack growth rates were analytically estimated for random load sequences, generated from three combat aircraft load exceedance curves using different algorithms, including simulated rainflow cycle count, extreme-to-extreme excursions, upper to lower bound excursions and unrestricted peak-trough excursions. Also, the response of a fatigue meter to a random load sequence was simulated. Fatigue damage for the different load histories was computed using material constants for an Al-Cu alloy. Computed fatigue damage was relatively insensitive to the algorithm used for load sequence generation from combat aircraft load exceedance curves. Fatigue meter data based damage estimates were, however, sometimes unconservative.

  5. Fatigue Life Estimation of an Aircaft Engine Under Different Load Spectrums

    NASA Astrophysics Data System (ADS)

    Huang, Hong-Zhong; Gong, Jie; Zuo, Ming J.; Zhu, Shun-Peng; Liao, Qiang

    2012-12-01

    Aircraft engine components are subjected to variable amplitude load conditions usually they tend to experience fatigue damage. Many fatigue damage accumulation theories have been put forward to predict the fatigue lives of structure components. Under different load spectra, the aircraft engine has different working life. In this paper, based on the linear damage rule, the fatigue life of an aircraft engine was estimated by considering the load spectrum difference factor. According to one aircraft engine used for different load spectrums, the relationship between the load spectrum and the life is discussed. Moreover, the fatigue life of this engine used in A-type bomber is estimated based on the different load spectrum of the B-type bomber. A good agreement is found between the estimated results and real life data.

  6. Development of a Composite Delamination Fatigue Life Prediction Methodology

    NASA Technical Reports Server (NTRS)

    OBrien, Thomas K.

    2009-01-01

    Delamination is one of the most significant and unique failure modes in composite structures. Because of a lack of understanding of the consequences of delamination and the inability to predict delamination onset and growth, many composite parts are unnecessarily rejected upon inspection, both immediately after manufacture and while in service. NASA Langley is leading the efforts in the U.S. to develop a fatigue life prediction methodology for composite delamination using fracture mechanics. Research being performed to this end will be reviewed. Emphasis will be placed on the development of test standards for delamination characterization, incorporation of approaches for modeling delamination in commercial finite element codes, and efforts to mature the technology for use in design handbooks and certification documents.

  7. Experimental fatigue life investigation of cylindrical thrust chambers

    NASA Technical Reports Server (NTRS)

    Quentmeyer, R. J.

    1977-01-01

    The thrust chambers studied in the investigation have been designed for a possible use in the Space Shuttle main engine. An annular combustion chamber configuration was used, consisting of an annular injector, a liquid hydrogen cooled outer cylinder, which served as the test section, and a contoured water cooled centerbody which formed the throat. Twenty-two cylinders were fabricated by milling cooling channels into liners fabricated from the material to be evaluated. The three materials chosen for the liners include OFHC copper, Amzirc, and NARloy-Z. The cylinders were cyclically tested until failure occurred due to fatigue cracks in the hot-gas-side wall. It was found that cylinders with liners fabricated from NARloy-Z and aged Amzirc had the best cyclic life characteristics.

  8. The application of strain field intensity method in the steel bridge fatigue life evaluation

    NASA Astrophysics Data System (ADS)

    Zhao, Xuefeng; Wang, Yanhong; Cui, Yanjun; Cao, Kaisheng

    2012-04-01

    Asce's survey shows that 80%--90% bridge damage were associated with fatigue and fracture problems. With the operation of vehicle weight and traffic volume increases constantly, the fatigue of welded steel bridge is becoming more and more serious in recent years. A large number of studies show that most prone to fatigue damage of steel bridge is part of the welding position. Thus, it's important to find a more precise method to assess the fatigue life of steel bridge. Three kinds of fatigue analysis method is commonly used in engineering practice, such as nominal stress method, the local stress strain method and field intensity method. The first two methods frequently used for fatigue life assessment of steel bridge, but field intensity method uses less ,and it widely used in fatigue life assessment of aerospace and mechanical. Nominal stress method and the local stress strain method in engineering has been widely applied, but not considering stress gradient and multiaxial stress effects, the accuracy of calculation stability is relatively poor, so it's difficult to fully explain the fatigue damage mechanism. Therefore, it used strain field intensity method to evaluate the fatigue life of steel bridge. The fatigue life research of the steel bridge based on the strain field method and the fatigue life of the I-section plate girder was analyzed. Using Ansys on the elastoplastic finite element analysis determined the dangerous part of the structure and got the stress-strain history of the dangerous point. At the same time, in order to divide the unit more elaborate introduced the sub-structure technology. Finally, it applies K.N. Smith damage equation to calculate the fatigue life of the dangerous point. In order to better simulating the actual welding defects, it dug a small hole in the welding parts. It dug different holds from different view in the welding parts and plused the same load to calculate its fatigue life. Comparing the results found that the welding defect in different parts had different influence on the fatigue life. Simultaneously, it based on S-N curve the I-shaped beam and combined with Palmgren - Miner linear cumulative damage theory to calculate the fatigue life of the dangerous part. The corresponding calculation results proved the superiority of the strain field intensity method.

  9. Effect of lubricant extreme pressure additives on rolling element fatigue life

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Zaretsky, E. V.

    1973-01-01

    The effects of surface active additives on rolling-element fatigue life were investigated with the five-ball fatigue tester at conditions where classical subsurface initiated rolling-element fatigue is the sole mode of failure. Test balls of AISI 52100, AISI M-50, and AISI 1018 were run with an acid-treated white oil containing either 2.5 percent sulfurized terpene, 1 percent didodecyl phosphite, or 5 percent chlorinated wax. In general, it was found that the influence of surface active additives was detrimental to rolling-element fatigue life. The chlorinated-wax additive significantly reduced fatigue life by a factor of 7. The base oil with the 2.5 percent sulfurized-terpene additive can reduce fatigue life by as much as 50 percent. No statistical change in fatigue life occurred with the base oil having the 1 percent didodecyl-phosphite additive. The additives used with the base oil did not change the ranking of the bearing steels where rolling-element fatigue life was of subsurface origin.

  10. Fatigue

    MedlinePLUS

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  11. Transverse Tension Fatigue Life Characterization Through Flexure Testing of Composite Materials

    NASA Technical Reports Server (NTRS)

    OBrien, T. Kevin; Chawan, Arun D.; Krueger, Ronald; Paris, Isabelle

    2001-01-01

    The transverse tension fatigue life of S2/8552 glass-epoxy and IM7/8552 carbon-epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass-epoxy laminates. Results showed that 90-degree bend specimens with polished machined edges and polished tension-side surfaces, where bending failures where observed, had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law was examined using the carbon-epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice-versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S-N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S-N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives.

  12. Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life

    NASA Technical Reports Server (NTRS)

    Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

    2008-01-01

    Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

  13. Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life

    NASA Technical Reports Server (NTRS)

    Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

    2012-01-01

    Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

  14. Probabilistic fatigue life prediction using ultrasonic inspection data considering equivalent initial flaw size uncertainty

    NASA Astrophysics Data System (ADS)

    Guan, X.; Zhang, J.; Kadau, K.; Zhou, S. K.

    2013-01-01

    This study presents a systematical method for probabilistic fatigue life prediction using ultrasonic inspection data. A probabilistic model to correlate the ultrasonic inspection reported size and the actual size is proposed based on historical data of rotor flaw sizing. Both of the reported size and the actual size are quantified in terms of the equivalent reflector diameter. The equivalent initial flaw size (EIFS) is then calculated based on the actual size for fatigue propagation analysis. All major uncertainties, such as EIFS uncertainty, fatigue crack growth model parameter uncertainty, and experimental data measurement uncertainty are explicitly included in the fatigue life prediction. Bayesian parameter estimation is used to estimate fatigue crack growth model parameters and measurement uncertainties using a limited number of fatigue testing data points. The overall procedure is demonstrated using a Cr-Mo-V rotor segment with ultrasonic inspection data. Interpretations of the probabilistic prediction results are given.

  15. Evaluation of Pressurization Fatigue Life of 1441 Al-li Fuselage Panel

    NASA Technical Reports Server (NTRS)

    Bird, R. Keith; Dicus, Dennis I.; Fridlyander, Joseph; Davydov, Valentin

    1999-01-01

    A study was conducted to evaluate the pressurization fatigue life of fuselage panels with skins fabricated from 1441 Al-Li, an attractive new Russian alloy. The study indicated that 1441 Al-Li has several advantages over conventional aluminum fuselage skin alloy with respect to fatigue behavior. Smooth 1441 Al-Li sheet specimens exhibited a fatigue endurance limit similar to that for 1163 Al (Russian version of 2024 Al) sheet. Notched 1441 Al-Li sheet specimens exhibited greater fatigue strength and longer fatigue life than 1163 Al. In addition, Tu-204 fuselage panels fabricated by Tupolev Design Bureau using Al-Li skin and ring frames with riveted 7000-series aluminum stiffeners had longer pressurization fatigue lives than did panels constructed from conventional aluminum alloys. Taking into account the lower density of this alloy, the results suggest that 1441 Al-Li has the potential to improve fuselage performance while decreasing structural weight.

  16. Grain boundary oxidation and its effects on high temperature fatigue life

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Oshida, Yoshiki

    1986-01-01

    Fatigue lives at elevated temperatures are often shortened by creep and/or oxidation. Creep causes grain boundary void nucleation and grain boundary cavitation. Grain boundary voids and cavities will accelerate fatigue crack nucleation and propagation, and thereby shorten fatigue life. The functional relationships between the damage rate of fatigue crack nucleation and propagation and the kinetic process of oxygen diffusion depend on the detailed physical processes. The kinetics of grain boundary oxidation penetration was investigated. The statistical distribution of grain boundary penetration depth was analyzed. Its effect on high temperature fatigue life are discussed. A model of intermittent micro-ruptures of grain boundary oxide was proposed for high temperature fatigue crack growth. The details of these studies are reported.

  17. Effect of carbide distribution on rolling-element fatigue life of AMS 5749

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Bamberger, E. N.

    1983-01-01

    Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.

  18. Fatigue Life of Titanium Alloys Fabricated by Additive Layer Manufacturing Techniques for Dental Implants

    NASA Astrophysics Data System (ADS)

    Chan, Kwai S.; Koike, Marie; Mason, Robert L.; Okabe, Toru

    2013-02-01

    Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.

  19. Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.

    PubMed

    Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati; Koting, Suhana

    2014-01-01

    Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406

  20. Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness

    PubMed Central

    Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati

    2014-01-01

    Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400?kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406

  1. Statistical analysis of fatigue strain-life data for carbon and low-alloy steels

    SciTech Connect

    Keisler, J.; Chopra, O.K.

    1995-03-01

    The existing fatigue strain vs life (S-N) data, foreign and domestic, for carbon and low-alloy steels used in the construction of nuclear power plant components have been compiled and categorized according to material, loading, and environmental conditions. A statistical model has been developed for estimating the effects of the various test conditions on fatigue life. The results of a rigorous statistical analysis have been used to estimate the probability of initiating a fatigue crack. Data in the literature were reviewed to evaluate the effects of size, geometry, and surface finish of a component on its fatigue life. The fatigue S-N curves for components have been determined by applying design margins for size, geometry, and surface finish to crack initiation curves estimated from the model.

  2. Ultrasonic attenuation as an indicator of fatigue life of graphite/epoxy fiber composite

    NASA Technical Reports Server (NTRS)

    Williams, J. H., Jr.; Doll, B.

    1979-01-01

    The narrow band ultrasonic longitudinal wave velocity and attenuation were measured as a function of the transfiber compression-compression fatigue of unidirectional graphite/epoxy composites. No change in velocity was detected at any point in fatigue life. For specimens fatigued at 80% of static strength, there was generally a 5% to 10% increase in attenuation, however, this increase does not appear to be a satisfactory indicator of fatigue life. On the other hand, there appears to be a correlation between initial attenuation (measured prior to cycling) and cycles to fracture. Initial attenuation as measured at 1.5 MHz and 2.0 MHz appears to be a good indicator of relative fatigue life.

  3. Low-cycle fatigue life of steel P92 under gradual loading

    NASA Astrophysics Data System (ADS)

    Cie?la, M.; Junak, G.

    2012-05-01

    The aim of the study was to determine low-cycle fatigue life characteristics of P92 steel used in the power unit components that work under the highest effort. Steel service life was determined in the tests for total fixed strain ??t ranges from 0.6 to 1.2 % and with application of two-stage sequence loading. Low-cycle fatigue tests were conducted at room temperature and at 550 C on MTS-810 testing machine. The tests under sequence loading were carried out for two strain ranges: ??t = 0.6 and 1.2 %. Sinusoidal load cycles of a coefficient R = -1 were used. Low-cycle fatigue life characteristics were developed with consideration of loading sequence impact. It was found out the fatigue life of an element under sequence loading is strictly correlated with its history of strain, which determines the degree of material microstructure damage. Higher degree of steel damage was found in two-stage tests, in which the larger range of strain ??t = 1.2 % was used as the first one. Fractography analyses of scrap revealed the patterns of fatigue lines and bands typical for this process as well as numerous secondary cracks occurred to the boundaries of former austenite grains. Analytic method of predicting low-cycle fatigue life of an element under two-stage sequence loading is presented. For this purpose, an energy criterion for the material life developed for tests carried out in conditions of low-cycle fatigue was used.

  4. Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

    NASA Technical Reports Server (NTRS)

    Miles, R. N.

    1992-01-01

    This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

  5. Effects of LWR environments on fatigue life of carbon and low-alloy steels

    SciTech Connect

    Chopra, O.K.; Shack, W.J.

    1995-03-01

    SME Boiler and Pressure Vessel Code provides construction of nuclear power plant components. Figure I-90 Appendix I to Section III of the Code specifies fatigue design curves for structural materials. While effects of environments are not explicitly addressed by the design curves, test data suggest that the Code fatigue curves may not always be adequate in coolant environments. This paper reports the results of recent fatigue tests that examine the effects of steel type, strain rate, dissolved oxygen level, strain range, loading waveform, and surface morphology on the fatigue life of A 106-Gr B carbon steel and A533-Gr B low-alloy steel in water.

  6. Predictive analysis of metal fatigue in the high cyclic life range

    NASA Technical Reports Server (NTRS)

    Manson, S. S.

    1979-01-01

    This report summarizes various aspects of predictive approaches in high cycle fatigue, hcf. The distinction between hcf and low cycle fatigue, lcf, is discussed in relation to the transition life and strainrange, and curves are presented to establish regions wherein each range predominates depending on the properties of any material of interest. The role of loading order on hcf in cumulative damage analysis is also discussed, together with mean stress effects and their relaxation. Also briefly discussed are high temperature fatigue and ultra-high cycle fatigue.

  7. Description of a computerized method for predicting thermal fatigue life of metals

    NASA Technical Reports Server (NTRS)

    Spera, D. A.; Cox, E. C.

    1975-01-01

    A computer program is described which can be used to predict the thermal fatigue life of metals and structural components from conventional metal properties. A unique feature of TFLIFE is that it calculates lives according to several different failure criteria for the same input data. These criteria are surface crack initiation, interior crack initiation, and complete fracture of both unnotched and notched fatigue specimens. Sample output tables are shown, together with results for two typical problems: (1) Thermal-mechanical fatigue of bar specimens of the tantalum alloy T-111, and (2) thermal-stress fatigue of wedge specimens of the nickel alloy B-1900.

  8. Fatigue Life Methodology for Tapered Hybrid Composite Flexbeams

    NASA Technical Reports Server (NTRS)

    urri, Gretchen B.; Schaff, Jeffery R.

    2006-01-01

    Nonlinear-tapered flexbeam specimens from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. Two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) associated with simulated delamination growth in the flexbeams are presented from both codes. These results compare well with each other and suggest that the initial delamination growth from the tip of the ply-drop toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves for comparison with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared well with the test results.

  9. Fatigue Life Analysis of Tapered Hybrid Composite Flexbeams

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.; Schaff, Jeffery R.; Dobyns, Alan L.

    2002-01-01

    Nonlinear-tapered flexbeam laminates from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. The two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) obtained from the above codes using the virtual crack closure technique (VCCT) at a resin crack location in the flexbeams are presented for both hybrid material types. These results compare well with each other and suggest that the initial delamination growth from the resin crack toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves and compared with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared reasonably well with the test results.

  10. Tensile, Fracture, Fatigue Life, and Fatigue Crack Growth Rate Behavior of Structural Materials for the ITER Magnets: The European Contribution

    NASA Astrophysics Data System (ADS)

    Nyilas, A.; Nikbin, K.; Portone, A.; Sborchia, C.

    2004-06-01

    Fatigue crack growth rates (FCGR) are determined for R ratios between 0.1 - 0.7 at 7 K for three full-size Mock-up Models of the ITER Toroidal Field coil case produced by modified Type 316LN alloys. A representative forged block of Model 3 is additionally manufactured to determine its improved spatial tensile properties and compare it to former Model 3 data. From the new candidate jacket materials, developed for the ITER Central Solenoid coil, a batch is investigated to assess the fatigue life behavior at 7 K. Furthermore, the 4 K test facility, a 630 kN load capacity hydraulic machine has been used to allow fatigue life investigations under four point bending of the full-size jackets with artificial surface flaws. Cyclic life results have been assessed for the heat affected zone, weld, and base metal. The results are used in the fatigue analysis of the coil. Residual stresses resulting from jacket welding have been determined using two different techniques. First by distortion measurements of sliced pieces of the weld section and secondly by neutron diffraction measurements. In addition, tensile and fracture tests have been performed at 7 K with Al 7075, a candidate alloy for the pre-compression system of the CS coil.

  11. 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.

  12. Childhood Adversity and Cumulative Life Stress: Risk Factors for Cancer-Related Fatigue

    PubMed Central

    Bower, Julienne E.; Crosswell, Alexandra D.; Slavich, George M.

    2013-01-01

    Fatigue is a common symptom in healthy and clinical populations, including cancer survivors. However, risk factors for cancer-related fatigue have not been identified. On the basis of research linking stress with other fatigue-related disorders, we tested the hypothesis that stress exposure during childhood and throughout the life span would be associated with fatigue in breast cancer survivors. Stress exposure was assessed using the Stress and Adversity Inventory, a novel computer-based instrument that assesses for 96 types of acute and chronic stressors that may affect health. Results showed that breast cancer survivors with persistent fatigue reported significantly higher levels of cumulative lifetime stress exposure, including more stressful experiences in childhood and in adulthood, compared to a control group of nonfatigued survivors. These findings identify a novel risk factor for fatigue in the growing population of cancer survivors and suggest targets for treatment. PMID:24377083

  13. Assessment of Solder Joint Fatigue Life Under Realistic Service Conditions

    NASA Astrophysics Data System (ADS)

    Hamasha, Sa'd.; Jaradat, Younis; Qasaimeh, Awni; Obaidat, Mazin; Borgesen, Peter

    2014-12-01

    The behavior of lead-free solder alloys under complex loading scenarios is still not well understood. Common damage accumulation rules fail to account for strong effects of variations in cycling amplitude, and random vibration test results cannot be interpreted in terms of performance under realistic service conditions. This is a result of the effects of cycling parameters on materials properties. These effects are not yet fully understood or quantitatively predictable, preventing modeling based on parameters such as strain, work, or entropy. Depending on the actual spectrum of amplitudes, Miner's rule of linear damage accumulation has been shown to overestimate life by more than an order of magnitude, and greater errors are predicted for other combinations. Consequences may be particularly critical for so-called environmental stress screening. Damage accumulation has, however, been shown to scale with the inelastic work done, even if amplitudes vary. This and the observation of effects of loading history on subsequent work per cycle provide for a modified damage accumulation rule which allows for the prediction of life. Individual joints of four different Sn-Ag-Cu-based solder alloys (SAC305, SAC105, SAC-Ni, and SACXplus) were cycled in shear at room temperature, alternating between two different amplitudes while monitoring the evolution of the effective stiffness and work per cycle. This helped elucidate general trends and behaviors that are expected to occur in vibrations of microelectronics assemblies. Deviations from Miner's rule varied systematically with the combination of amplitudes, the sequences of cycles, and the strain rates in each. The severity of deviations also varied systematically with Ag content in the solder, but major effects were observed for all the alloys. A systematic analysis was conducted to assess whether scenarios might exist in which the more fatigue-resistant high-Ag alloys would fail sooner than the lower-Ag ones.

  14. Fatigue life assessment of top tensioned risers under vortex-induced vibrations

    NASA Astrophysics Data System (ADS)

    Li, Xiaomin; Guo, Haiyan; Meng, Fanshun

    2010-03-01

    The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain. The long-term stress histories of the riser under VIVs are calculated and the mean stresses, the number of stress cycles and amplitudes are determined by the rainflow counting method. The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser. The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled. Finally the influences of the riser’s parameters such as flexural rigidity, top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.

  15. Rolling-element fatigue life with two synthetic cycloaliphatic traction fluids

    NASA Technical Reports Server (NTRS)

    Loewenthal, S. H.; Parker, R. J.

    1976-01-01

    The life potential of two synthetic cycloaliphatic hydrocarbon traction fluids in rolling element fatigue was evaluated in a five ball fatigue tester. Life comparisons with a MIL-L-23699 qualified tetraester oil showed that the traction test oils had good fatigue life performance, comparable to that of the tetraester oil. No statistically significant life differences between the traction fluids and the tetraester oil were exhibited under the accelerated fatigue test conditions. Erratic operating behavior was occasionally encountered during tests with the antiwear additive containing traction fluid for reasons thought to be related to excessive chemical activity under high contact pressure. This behavior occasionally resulted in premature test termination due to excessive surface distress and overheating.

  16. Residual stress evaluation and fatigue life prediction in the welded joint by x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Yoo, Keun Bong; Hwang, Kwon Tae; Chang, Jung Chel; Kim, Jae Hoon

    2009-07-01

    In the fossil power plant, the reliability of the components which consist of the many welded parts depends on the quality of welding. The residual stress is occurred by the heat flux of high temperature during weld process. This decreases the mechanical properties as the strength of fatigue and fracture. The residual stress of the welded part in the recently constructed power plants has been the cause of a variety of accidents. The objective of this study is measurement of the residual stress and the full width at half maximum intensity (FWHM) by X-ray diffraction method and to estimate the feasibility of this application for fatigue life assessment of the high-temperature pipeline. The materials used for the study is P92 steel for the use of high temperature pipe on super critical condition. The test results were analyzed by the distributed characteristics of residual stresses and FWHM in x-ray diffraction intensity curve. Also, X-ray diffraction tests using specimens simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the ratio of the FWHM due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.

  17. Joint design for improved fatigue life of diffusion-bonded box-stiffened panels

    NASA Technical Reports Server (NTRS)

    Davis, R. C.; Moses, P. L.; Kanenko, R. S.

    1985-01-01

    Simple photoelastic models were used to identify a cross-section geometry that would eliminate the severe stress concentrations at the bond line between box stiffeners diffusion bonded to a panel skin. Experimental fatigue-test data from titanium test specimens quantified the allowable stress in terms of cycle life for various joint geometries. It is shown that the effect of stress concentration is reduced and an acceptable fatigue life is achieved.

  18. Ductility normalized-strainrange partitioning life relations for creep-fatigue life predictions

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Saltsman, J. F.; Hirschberg, M. H.

    1977-01-01

    Procedures based on Strainrange Partitioning (SRP) are presented for estimating the effects of environment and other influences on the high temperature, low cycle, creep fatigue resistance of alloys. It is proposed that the plastic and creep, ductilities determined from conventional tensile and creep rupture tests conducted in the environment of interest be used in a set of ductility normalized equations for making a first order approximation of the four SRP inelastic strainrange life relations. Different levels of sophistication in the application of the procedures are presented by means of illustrative examples with several high temperature alloys. Predictions of cyclic lives generally agree with observed lives within factors of three.

  19. 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.

  20. Increasing fatigue life of weld repaired rotating elements

    SciTech Connect

    Welsch, W.

    1998-07-01

    The paper discusses the use of controlled shot peening to regain the fatigue strength lost on rotating elements due to welding during original manufacture, welding used for salvaging expensive components due to mishaps during final machining, and weld repair after years of successful service. Weld repair of rotating components is becoming more popular due to improved welding techniques and non-destructive testing capabilities. Confidence in weld repair has further been heightened by the ability to regain the fatigue strength lost by welding and actually raise the fatigue strength close to that of the original homogeneous metal.

  1. 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.

  2. The Effect of Hole Quality on the Fatigue Life of 2024-T3 Aluminum Alloy Sheet

    NASA Technical Reports Server (NTRS)

    Everett, Richard A., Jr.

    2004-01-01

    This paper presents the results of a study whose main objective was to determine which type of fabrication process would least affect the fatigue life of an open-hole structural detail. Since the open-hole detail is often the fundamental building block for determining the stress concentration of built-up structural parts, it is important to understand any factor that can affect the fatigue life of an open hole. A test program of constant-amplitude fatigue tests was conducted on five different sets of test specimens each made using a different hole fabrication process. Three of the sets used different mechanical drilling procedures while a fourth and fifth set were mechanically drilled and then chemically polished. Two sets of specimens were also tested under spectrum loading to aid in understanding the effects of residual compressive stresses on fatigue life. Three conclusions were made from this study. One, the residual compressive stresses caused by the hole-drilling process increased the fatigue life by two to three times over specimens that were chemically polished after the holes were drilled. Second, the chemical polishing process does not appear to adversely affect the fatigue life. Third, the chemical polishing process will produce a stress-state adjacent to the hole that has insignificant machining residual stresses.

  3. Evaluation of tilting disc valves after fatigue life testing: preliminary results within a comparison program.

    PubMed

    Barbaro, V; Boccanera, G; Daniele, C; Grigioni, M; Palombo, A

    1995-09-01

    A fatigue life test, by accelerating the beat rate, simulates several years of virtual life of a prosthetic heart valve in a short period of time. The correlation between the in vivo life of a valve and in vitro testing expectations is as yet not well established, but reproducible test conditions yield precious information about wear and failure. The paper reports a qualitative analysis of mechanical valve wear as part of a comparison program designed to investigate the significance of fatigue testing with the ultimate aim of defining standard guidelines for these type of tests. Two tilting disc valves (29 mm) were subjected to 16 years of fatigue life simulated by means of a Rowan Ash fatigue tester (accelerated rate of 1,200 bpm). Fatigue-induced effects on valve disc and ring surfaces were observed under a monitor microscope to identify wear sites and patterns. A high speed cinematographic system was used to investigate the mechanisms responsible for the wear (wear modes). Valve closure was inspected at a 6,000 frame/s rate. Because of disc rotation during the tilting movement, the points of contact between disc and ring are distributed all around the disc edge but focally on the ring. On both sides of the disc, the surfaces present ring-like concentric grooves. After 16 years of fatigue life the valves showed neither severe wear nor alteration of their fluidodynamic behavior in the pulsatile flow test. PMID:8687299

  4. Life prediction of thermal-mechanical fatigue using strain-range partitioning

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    The applicability is described of the method of Strainrange Partitioning to the life prediction of thermal-mechanical strain-cycling fatigue. An in-phase test on 316 stainless steel is analyzed as an illustrative example. The observed life is in excellent agreement with the life predicted by the method using the recently proposed Step-Stress Method of experimental partitioning, the Interation Damage Rule, and the life relationships determined at an isothermal temperature of 705 C. Implications of the study are discussed relative to the general thermal fatigue problem.

  5. Fatigue in multiple sclerosis is related to disability, depression and quality of life.

    PubMed

    Pittion-Vouyovitch, S; Debouverie, M; Guillemin, F; Vandenberghe, N; Anxionnat, R; Vespignani, H

    2006-04-15

    Fatigue in multiple sclerosis is a frequent and disabling symptom that can interfere in daily functioning. The aim of this study is to demonstrate the relationship between fatigue and disability, disease course, depression and quality of life. We administered French valid versions of the Fatigue Impact Scale (EMIF-SEP), the short form of the Beck depression inventory (13 items) and the SF-36 to 237 out of 312 patients with clinically definite multiple sclerosis with EDSSfatigue on each scale of quality of life of the SF-36. These data confirm that fatigue is correlated with disability, but cognitive and psychological dimensions of fatigue remain independent. Fatigue is also associated with depression and quality of life. PMID:16434057

  6. Effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK).

    PubMed

    Simsiriwong, Jutima; Shrestha, Rakish; Shamsaei, Nima; Lugo, Marcos; Moser, Robert D

    2015-11-01

    In this study, the effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK) was investigated. Due to the versatility of its material properties, the semi-crystralline PEEK polymer has been increasingly adopted in a wide range of applications particularly as a biomaterial for orthopedic, trauma, and spinal implants. To obtain the cyclic behavior of PEEK, uniaxial fully-reversed strain-controlled fatigue tests were conducted at ambient temperature and at 0.02 mm/mm to 0.04 mm/mm strain amplitudes. The microstructure of PEEK was obtained using the optical and the scanning electron microscope (SEM) to determine the microstructural inclusion properties in PEEK specimen such as inclusion size, type, and nearest neighbor distance. SEM analysis was also conducted on the fracture surface of fatigue specimens to observe microstructural inclusions that served as the crack incubation sites. Based on the experimental strain-life results and the observed microstructure of fatigue specimens, a microstructure-sensitive fatigue model was used to predict the fatigue life of PEEK that includes both crack incubation and small crack growth regimes. Results show that the employed model is applicable to capture microstructural effects on fatigue behavior of PEEK. PMID:26301567

  7. Multiaxial Fatigue Life Prediction for Steels Based on Some Simple Approximations

    NASA Astrophysics Data System (ADS)

    Li, Jing; Yao, Zhi-feng; Zhang, Zhong-ping

    2015-01-01

    The Roessle-Fatemi's hardness method (HM) and Muralidharan-Manson's modified universal slopes method (MUSM) were employed to determine the uniaxial fatigue properties of steels from easily obtained tensile properties. Both methods give good life predictions, while the Roessle-Fatemi's HM is somewhat better. Furthermore, for predicting multiaxial fatigue lives of steels in the absence of any fatigue data, the Li's modified Wang-Brown model (MWB) was used in combination with the HM method (MWB-HM) as well as the MUSM method (MWB-MUSM), respectively. Correlation between the yield strength and the Brinell hardness was also developed to estimate the multiaxial fatigue lives of steels based only on hardness and elasticity modulus. It is shown that multiaxial fatigue lives were predicted fairly well by all the methods, and the MWB-MUSM method is slightly more accurate. In addition, a computer-based procedure for multiaxial fatigue life assessment incorporating MWB-MUSM approach was proposed and implemented to predict the fatigue life of an intermediate compressor casing. The predicted results are promising.

  8. 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 ...

  9. 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

  10. Empirical modeling of environment-enhanced fatigue crack propagation in structural alloys for component life prediction

    NASA Technical Reports Server (NTRS)

    Richey, Edward, III

    1995-01-01

    This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The approach couples empirical modeling of environmental FCP with corrosion fatigue experiments. Three different computer models have been developed and incorporated in the DOS executable program. UVAFAS. A multiple power law model is available, and can fit a set of fatigue data to a multiple power law equation. A model has also been developed which implements the Wei and Landes linear superposition model, as well as an interpolative model which can be utilized to interpolate trends in fatigue behavior based on changes in loading characteristics (stress ratio, frequency, and hold times).

  11. Application of an Energy-Based Life Prediction Model to Bithermal and Thermomechanical Fatigue

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, V. M.; Kalluri, Sreeramesh; Halford, Gary R.

    1994-01-01

    The inelastic hysteresis energy applied to the material in a cycle is used as the basis for predicting nonisothermal fatigue life of a wrought cobalt-base superalloy, Haynes 188, from isothermal fatigue data. Damage functions that account for hold-time effects and time-dependent environmental phenomena such as oxidation and hot corrosion are proposed in terms of the inelastic hysteresis energy per cycle. The proposed damage functions are used to predict the bithermal and thermomechanical fatigue lives of Haynes 188 between 316 and 760 C from isothermal fatigue data. Predicted fatigue lives of all but two of the nonisothermal tests are within a factor of 1.5 of the experimentally observed lives.

  12. 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.

  13. Life Prediction and Stress Evolvement for Low Cycle Fatigue in PWR Primary Pipe Material

    NASA Astrophysics Data System (ADS)

    Fei, Xue; Wei-wei, Yu; Zhao-xi, Wang; Wen-xin, Ti; Lei, Lin; Xin-ming, Men

    2010-05-01

    The low cycle fatigue (LCF) behavior of primary pipe material Z3CN20.09M cast stainless stell (CASS) was studied at room temperature (RT) and elevated temperature of 350 C by conducting total axial stain controlled tests in air with strain amplitude in the range 0.175% to 0.8%. Based on the test results, the cyclic stress response of material was analyzed, and a dynamic strain aging (DSA) phenomena was discovered at 350 C. Besides, the evaluation of elastic modulus during cyclic tests was studied, and the effect of elastic modulus on parameters of low cycle fatigue was investigated based on the Manson-Coffin model. It is shown that elastic modulus for Z3CN20.09M decreases constantly during the whole fatigue life, but fluctuates more frequently at elevated temperature. Both the static and dynamic elastic modulus result in a same life trend in low cycle fatigue, but the elastic modulus affects the precision of fatigue life prediction to some extent when the fatigue life exceeded 105.

  14. 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.

  15. Baseline-free estimation of residual fatigue life using a third order acoustic nonlinear parameter.

    PubMed

    Amura, Mikael; Meo, Michele; Amerini, F

    2011-10-01

    Prediction of crack growth and fatigue life estimation of metals using linear/nonlinear acousto-ultrasound methods is an ongoing issue. It is known that by measuring nonlinear parameters, the relative accumulated fatigue damage can be evaluated. However, there is still a need to measure two crack propagation states to assess the absolute residual fatigue life. A procedure based on the measurement of a third-order acoustic nonlinear parameter is presented to assess the residual fatigue life of a metallic component without the need of a baseline. The analytical evaluation of how the cubic nonlinear-parameter evolves during crack propagation is presented by combining the Paris law to the Nazarov-Sutin crack equation. Unlike other developed models, the proposed model assumes a crack surface topology with variable geometrical parameters. Measurements of the cubic nonlinearity parameter on AA2024-T351 specimens demonstrated high sensitivity to crack propagation and excellent agreement with the predicted theoretical behavior. The advantages of using the cubic nonlinearity parameter for fatigue cracks on metals are discussed by comparing the relevant results of a quadratic nonlinear parameter. Then the methodology to estimate crack size and residual fatigue life without the need of a baseline is presented, and advantages and limitations are discussed. PMID:21973336

  16. Fatigue-Life Prediction Methodology Using Small-Crack Theory

    NASA Technical Reports Server (NTRS)

    Newmann, James C., Jr.; Phillips, Edward P.; Swain, M. H.

    1997-01-01

    This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional state-of-stress effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta K(eff)) under constant-amplitude loading. Some modifications to the delta k(eff)-rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well.

  17. Quality of life, fatigue, depression and cognitive impairment in Lyme neuroborreliosis.

    PubMed

    Dersch, Rick; Sarnes, Antonia A; Maul, Monika; Hottenrott, Tilman; Baumgartner, Annette; Rauer, Sebastian; Stich, Oliver

    2015-11-01

    The prognosis and impact of residual symptoms on quality of life in patients with Lyme neuroborreliosis (LNB) is subject to debate. The aim of this study was to assess quality of life, fatigue, depression, cognitive impairment and verbal learning in patients with definite LNB and healthy controls in a case-control study. We retrospectively identified all patients diagnosed with definite LNB between 2003 and 2014 in our tertiary care center. Healthy controls were recruited from the same area. Patients and healthy controls were assessed for quality of life [Short Form (36) with subscores for physical and mental components (PCS, MCS)], fatigue (fatigue severity scale), depression (Beck depression inventory), verbal memory and learning and cognitive impairment (mini-mental state examination). 53 patients with definite LNB could be identified, of which 30 partook in the follow-up assessment. Estimates for quality of life, fatigue, depression, verbal memory and cognitive impairment did not differ statistically significantly between 30 patients with LNB and 35 healthy controls. Patients with residual symptoms had lower scores for quality of life (PCS) compared to patients without residual symptoms. Our results do not support the hypothesis that a considerable proportion of patients with antibiotically treated LNB develop a 'post Lyme syndrome' consisting of debilitating fatigue or cognitive impairment or have severe limitations of quality of life. However, some patients experience residual symptoms of LNB. PMID:26410742

  18. Mathematical Model of Load Pass and Prediction of Fatigue Life on Bolt Threads with Reduced Lead

    NASA Astrophysics Data System (ADS)

    Asayama, Yukiteru

    A mathematical model is proposed in order to elucidate the mechanism that the fatigue strength of external threads increases by reducing the lead on a thread system such as a bolt and nut. The model is constructed from the concept that a local strain proportional to the reducing degree of the lead, although the local strain is at first produced in the bolt thread farthest from the bearing surface of the nut, is induced in each thread root with an increase of applied load. The fatigue life predicted from the mathematical model shows good agreement with the experimental fatigue life of cadmium-plated external threads with the reduced lead on the material having strength as high as 1270MPa. The model can provide useful suggestions for the design of fasteners for aerospace, which are required to satisfy severe requirements of fatigue strengths and dimensions.

  19. Fatigue life prediction of an intermetallic matrix composite at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Bartolotta, Paul A.

    1991-01-01

    A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the Universal Slopes method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio, number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.

  20. A comparison of reliability and conventional estimation of safe fatigue life and safe inspection intervals

    NASA Technical Reports Server (NTRS)

    Hooke, F. H.

    1972-01-01

    Both the conventional and reliability analyses for determining safe fatigue life are predicted on a population having a specified (usually log normal) distribution of life to collapse under a fatigue test load. Under a random service load spectrum, random occurrences of load larger than the fatigue test load may confront and cause collapse of structures which are weakened, though not yet to the fatigue test load. These collapses are included in reliability but excluded in conventional analysis. The theory of risk determination by each method is given, and several reasonably typical examples have been worked out, in which it transpires that if one excludes collapse through exceedance of the uncracked strength, the reliability and conventional analyses gave virtually identical probabilities of failure or survival.

  1. Roller-burnishing to improve fatigue life in beta-titanium alloys

    SciTech Connect

    Berg, A.; Drechsler, A.; Wagner, L.

    1999-07-01

    The possibilities for using roller-burnishing to improve fatigue behavior in the beta titanium alloys Ti-3Al-8V-6Cr-4Mo-4Zr (Beta C) and Ti-10V-2Fe-3Al (10-2-3) are examined. While roller burnishing does not significantly increase the endurance limit in Beta C, fatigue lifetimes at high cyclic stresses can be increased by up to one order of magnitude. In 10-2-3, the endurance limit can be increased by roughly 100 MPa, while fatigue life at high cyclic stresses is only marginally improved.

  2. Effect of viscosity on rolling-element fatigue life at cryogenic temperature with fluorinated ether lubricants

    NASA Technical Reports Server (NTRS)

    Dietrich, M. W.; Zaretsky, E. V.

    1975-01-01

    Rolling-element fatigue tests were conducted with 12.7-mm-(1/2-in.-) diameter AISI 52100 steel balls in the NASA five-ball fatigue tester, with a maximum hertz stress of 5500 mN/m2 (800 000 psi), a shaft speed of 4750 rpm, lubricant temperature of 200 K (360 R), a contact angle of 20 deg, using four fluorinated ether lubricants of varying viscosities. No statistically significant differences in rolling-element fatigue life occurred using the four viscosity levels. Elastohydrodynamic calculations indicate that values of the lubricant film parameter were approximately 2 or greater.

  3. High compressive pre-strains reduce the bending fatigue life of nitinol wire.

    PubMed

    Gupta, Shikha; Pelton, Alan R; Weaver, Jason D; Gong, Xiao-Yan; Nagaraja, Srinidhi

    2015-04-01

    Prior to implantation, Nitinol-based transcatheter endovascular devices are subject to a complex thermo-mechanical pre-strain associated with constraint onto a delivery catheter, device sterilization, and final deployment. Though such large thermo-mechanical excursions are known to impact the microstructural and mechanical properties of Nitinol, their effect on fatigue properties is still not well understood. The present study investigated the effects of large thermo-mechanical pre-strains on the fatigue of pseudoelastic Nitinol wire using fully reversed rotary bend fatigue (RBF) experiments. Electropolished Nitinol wires were subjected to a 0%, 8% or 10% bending pre-strain and RBF testing at 0.3-1.5% strain amplitudes for up to 10(8) cycles. The imposition of 8% or 10% bending pre-strain resulted in residual set in the wire. Large pre-strains also significantly reduced the fatigue life of Nitinol wires below 0.8% strain amplitude. While 0% and 8% pre-strain wires exhibited distinct low-cycle and high-cycle fatigue regions, reaching run out at 10(8) cycles at 0.6% and 0.4% strain amplitude, respectively, 10% pre-strain wires continued to fracture at less than 10(5) cycles, even at 0.3% strain amplitude. Furthermore, over 70% fatigue cracks were found to initiate on the compressive pre-strain surface in pre-strained wires. In light of the texture-dependent tension-compression asymmetry in Nitinol, this reduction in fatigue life and preferential crack initiation in pre-strained wires is thought to be attributed to compressive pre-strain-induced plasticity and tensile residual stresses as well as the formation of martensite variants. Despite differences in fatigue life, SEM revealed that the size, shape and morphology of the fatigue fracture surfaces were comparable across the pre-strain levels. Further, the mechanisms underlying fatigue were found to be similar; despite large differences in cycles to failure across strain amplitudes and pre-strain levels, cracks initiated from surface inclusions in nearly all wires. Compressive pre-strain-induced damage may accelerate such crack initiation, thereby reducing fatigue life. The results of the present study indicate that large compressive pre-strains are detrimental to the fatigue properties of Nitinol, and, taken together, the findings underscore the importance of accounting for thermo-mechanical history in the design and testing of wire-based percutaneous implants. PMID:25625888

  4. Evaluation of the EHL Film Thickness and Extreme Pressure Additives on Gear Surface Fatigue Life

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.; Shimski, John

    1994-01-01

    Surface pitting fatigue life tests were conducted with seven lubricants, using AISI 9310 spur gears. The test lubricants can be classified as synthetic polyol-esters with various viscosities and additive packages. The lubricant with a viscosity that provided a specific film thickness greater than one and with an additive package produced gear surface fatigue lives that were 8.6 times that for lubricants with a viscosity that provided specific film thickness less than one. Lubricants with the same viscosity and similar additive packages gave equivalent gear surface fatigue lives.

  5. Ratcheting and low cycle fatigue behavior of SA333 steel and their life prediction

    NASA Astrophysics Data System (ADS)

    Paul, Surajit Kumar; Sivaprasad, S.; Dhar, S.; Tarafder, S.

    2010-06-01

    Ratcheting and low cycle fatigue (LCF) experiments have been conducted at 25 C temperature in laboratory environment under different loading conditions. SA333 steel exhibits cyclic hardening throughout its life during LCF. It is found that ratcheting strain increases with both increasing mean stress and stress amplitude. It has also been noticed that plastic strain amplitude and plastic strain energy decrease with increase in mean stress at constant stress amplitude. Ratcheting and LCF life in the range of 10 2-10 5 cycles have been predicted with the help of a mean stress-based fatigue lifing equation.

  6. Use of strainrange partitioning to predict high temperature low-cycle fatigue life. [of metallic materials

    NASA Technical Reports Server (NTRS)

    Hirschberg, M. H.; Halford, G. R.

    1976-01-01

    The fundamental concepts of the strainrange partitioning approach to high temperature, low low-cycle fatigue are reviewed. Procedures are presented by which the partitioned strainrange versus life relationships for any material can be generated. Laboratory tests are suggested for further verifying the ability of the method of strainrange partitioning to predict life.

  7. A Fatigue Life Prediction Model of Welded Joints under Combined Cyclic Loading

    NASA Astrophysics Data System (ADS)

    Goes, Keurrie C.; Camarao, Arnaldo F.; Pereira, Marcos Venicius S.; Ferreira Batalha, Gilmar

    2011-01-01

    A practical and robust methodology is developed to evaluate the fatigue life in seam welded joints when subjected to combined cyclic loading. The fatigue analysis was conducted in virtual environment. The FE stress results from each loading were imported to fatigue code FE-Fatigue and combined to perform the fatigue life prediction using the S x N (stress x life) method. The measurement or modelling of the residual stresses resulting from the welded process is not part of this work. However, the thermal and metallurgical effects, such as distortions and residual stresses, were considered indirectly through fatigue curves corrections in the samples investigated. A tube-plate specimen was submitted to combined cyclic loading (bending and torsion) with constant amplitude. The virtual durability analysis result was calibrated based on these laboratory tests and design codes such as BS7608 and Eurocode 3. The feasibility and application of the proposed numerical-experimental methodology and contributions for the technical development are discussed. Major challenges associated with this modelling and improvement proposals are finally presented.

  8. Reliability of fatigue life predictions for tubular joints with load pattern recognition

    SciTech Connect

    Kanegaonkar, H.B.

    1994-12-31

    All parametric formulae for Stress Concentration Factors (SCFs) classify the tubular joints according to the geometry and standard load patterns. Thus the SCFs are purely dependent on geometry, and loadings on the joint braces are ignored which keeps the uncertainty in the SCFs at the same level as the geometric uncertainty. It is shown that the SCFs with load pattern recognition if associated with standard formats for fatigue analysis of offshore platform connection would create theoretical anomalies and practical unsuitability. Particularly, it is shown that these SCFs if associated with deterministic fatigue analysis would violate the basic assumption viz. one-to-one correspondence between the wave height and hotspot stress range. It is shown that multiple values of wave heights may give rise to same stress range. This non compliance of the basic tenet of deterministic fatigue analysis can have significant effect on predicted fatigue life of joints in splash zone. The reliability analysis of fatigue life calculations using SCFs according to load pattern recognition is performed using First Order Second Moment technique. It is shown that fatigue life reliability is less in this case by orders of magnitude compared to one with standard SCFs.

  9. Improvement of fatigue life of an aluminum alloy by overstressing

    NASA Technical Reports Server (NTRS)

    STRICKLEY G W

    1942-01-01

    Fatigue tests were made on some 1.375-inch-diameter and 0.300-inch diameter specimens of a 17S-T aluminum alloy rod. One test of a large specimen was run continuously to failure at a maximum stress of 22,000 pounds per square inch. In two other tests of large specimens, thin surface layers were removed periodically until failure occurred. The same nominal maximum stress of 22,000 pounds per square inch was used throughout the two tests and the load on the fatigue machine was lowered accordingly after the removal of each surface layer. As each test progressed the stress in the metal of the final surface area therefore was increased after the removal of each surface layer. Because of the stresses used, this metal was overstressed, that is, stressed above its endurance limit. All the remaining specimens were subjected to similar over- stressing conditions but no metal was removed and a low initial stress was increased periodically to a final maximum value of 22,000 pounds per square inch as each test progressed. It was found that the fatigue resistance of 17S-T aluminum alloy can be increased by moderate overstressing. Apparently the increase in fatigue lift obtained in the tests of specimens from which layers were removed was the result of overstressing rather than from the removal of damaged surface layers.

  10. Probabilistic Fatigue Life Analysis of High Density Electronics Packaging

    NASA Technical Reports Server (NTRS)

    Moore, N. R.; Kolawa, E. A.; Sutharshana, S.; Newlin, L. E.; Creager, M.

    1996-01-01

    The fatigue of thin film metal interconnections in high density electronics packaging subjected to thermal cycling has been evaluated using a probabilistic fracture mechanics methodology. This probabilistic methodology includes characterization of thin film stress using an experimentally calibrated finite element model and simulation of flaw growth in the thin films using a stochastic crack growth model.

  11. Acoustic fatigue life prediction for non-linear structures

    NASA Technical Reports Server (NTRS)

    Sun, J. Q.; Miles, R. N.

    1991-01-01

    Using an approach based on a time domain analysis, a method of equivalent linearization is applied for an estimation of the strain response of complex nonlinear structures having nearly arbitrary complexity. Fatigue lives estimated for a nonlinear beam with random excitation using the approximate method were compared with results obtained using a conventional numerical simulation, yielding nearly identical results.

  12. Effect of grinding conditions on the fatigue life of titanium 5Al-2.5Sn alloy

    NASA Technical Reports Server (NTRS)

    Rangaswamy, P.; Terutung, H.; Jeelani, S.

    1991-01-01

    An investigation into the effect of grinding conditions on the fatigue life of titanium 5Al-2.5Sn is presented. Damage to surface integrity and changes in the residual stresses distribution are studied to assess changes in fatigue life. A surface grinding machine, operating at speeds ranging from 2000 to 6000 fpm and using SiC wheels of grit sizes 60 and 120, was used to grind flat subsize specimens of 0.1-in. thickness. After grinding, the specimens were fatigued at a chosen stress and compared with the unadulterated material. A standard profilometer, a microhardness tester, and a scanning electron microscope were utilized to examine surface characteristics and measure roughness and hardness. Increased grinding speed in both wet and dry applications tended to decrease the fatigue life of the specimens. Fatigue life increased markedly at 2000 fpm under wet conditions, but then decreased at higher speeds. Grit size had no effect on the fatigue life.

  13. 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

  14. Major Effects of Nonmetallic Inclusions on the Fatigue Life of Disk Superalloy Demonstrated

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Kantzos, Peter T.; Bonacuse, Peter J.; Barrie, Robert L.

    2002-01-01

    The fatigue properties of modern powder metallurgy disk alloys can vary because of the different steps of materials and component processing and machining. Among these variables, the effects of nonmetallic inclusions introduced during the powder atomization and handling processes have been shown to significantly degrade low-cycle fatigue life. The levels of inclusion contamination have, therefore, been reduced to less than 1 part per million in state-of-the-art nickel disk powder-processing facilities. Yet the large quantities of compressor and turbine disks weighing from 100 to over 1000 lb have enough total volume and surface area for these rare inclusions to still be present and limit fatigue life. The objective of this study was to investigate the effects on fatigue life of these inclusions, as part of the Crack Resistant Disk Materials task within the Ultra Safe Propulsion Project. Inclusions were carefully introduced at elevated levels in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were then performed on extracted test specimens at 650 C. Analyses were performed to compare the low-cycle fatigue lives and failure initiation sites as functions of inclusion content and fatigue conditions. Powder of the nickel-base superalloy U720 was atomized in argon at Special Metals Corporation, Inc., using production-scale high-cleanliness powder-processing facilities and handling practices. The powder was then passed through a 270-mesh screen. One portion of this powder was set aside for subsequent consolidation without introduced inclusions. Two other portions of this powder were seeded with alumina inclusions. Small, polycrystalline soft (Type 2) inclusions of about 50 mm diameter were carefully prepared and blended into one powder lot, and larger hard (Type 1) inclusions of about 150 mm mean diameter were introduced into the other seeded portion of powder. All three portions of powder were then sealed in separate containers, hot isostatically pressurized, extruded, forged into subscale disks, and heat treated. Low-cycle-fatigue specimens were then extracted, machined, and tested. Fatigue tests were performed at 650 C in closed-loop servohydraulic testing machines using induction heating and axial extensometers. All tests were continued to failure, and fractographic evaluations were performed on all specimens to determine the crack initiation sites. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface, as shown for each type of inclusion in the following bar chart. The inclusions significantly reduced fatigue life from unseeded material levels, as shown in the bar chart. These effects were found to depend on the strain range, strain ratio, and inclusion size. Tests at lower strain ranges and higher strain ratios resulted in larger effects of inclusions on life. Inclusion effects on life were thereby maximized in tests at the lowest strain range of 0.6 percent and the most positive strain ratio of 0.5. Under these conditions, small Type 2 inclusions reduced life substantially-- about 20 times, whereas large Type 1 inclusions dramatically reduced life 100 times. These results clearly demonstrate that it is essential to include the effects of inclusions for realistic predictions of disk fatigue life. Important issues, including temperature dependence, crack initiation versus propagation, surface treatments, realistic disk features and machining, and realistic disk spin testing will be addressed to accurately model inclusion effects on disk fatigue life. Fatigue life varied from well over 105 cycles for no inclusions to a little over 103 cycles for 100-micrometer inclusions. A single crack initiating at a surface-connected seeded inclusion caused failure in each case.

  15. Prevalence of fatigue in patients with multiple sclerosis and its effect on the quality of life

    PubMed Central

    Nagaraj, Karthik; Taly, Arun B.; Gupta, Anupam; Prasad, Chandrajit; Christopher, Rita

    2013-01-01

    Objective: This prospective study was carried out to observe the prevalence of fatigue in patients with multiple sclerosis (MS) and its effect on quality-of-life (QoL). Study Design and Setting: Prospective observational study in a University Tertiary Research Hospital in India. Patients and Methods: A total of 31 patients (25 females) with definite MS according to McDonald's criteria presented in out-patient/admitted in the Department of Neurology (between February 2010 and December 2011) were included in the study. Disease severity was evaluated using the Kurtzke's expanded disability status scale (EDSS). Fatigue was assessed using Krupp's fatigue severity scale (FSS). QoL was assessed by the World Health Organization QoL-BREF questionnaire. Results: The mean age of patients was 30.1 9.1 years. The mean age at first symptom was 25.23 6.4 years. The mean number of relapses was 4.7 3.6 in the patients. The mean duration of illness was 4.9 4.4 years. The mean EDSS score was 3.5 2.2. Mean fatigue score was 38.7 18.5 (cut-off value 36 in FSS). The prevalence of fatigue in patients with MS was 58.1% (18/31). MS patients with fatigue were significantly more impaired (P < 0.05) on all QoL domains (i.e., physical, psychosocial, social, and environment) than MS patients without fatigue. Conclusion: Prevalence of fatigue was found to be high in the MS patients in the study. All four domains of QoL were significantly more impaired in the group with fatigue than in those without fatigue. PMID:24250159

  16. Creep fatigue life prediction for engine hot section materials (isotropic). Annual report

    SciTech Connect

    Moreno, V.; Nissley, D.; Lin, L.J.

    1985-03-01

    The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

  17. Reduction factors for creep strength and fatigue life of modified 9 Cr-1 Mo steel weldments

    SciTech Connect

    Blass, J.J.; Battiste, R.L.; O'Connor, D.G.

    1991-01-01

    The provisions of ASME B PV Code Case N-47 currently include reduction factors for creep strength and fatigue life of weldments. To provide experimental confirmation of such factors for modified 9 Cr-1 Mo steel, tests of tubular specimens were conducted at 538{degree}C (1000{degree}F). Three creep-rupture specimens with longitudinal welds were tested in tension; and, of three with circumferential welds, two were tested in tension and one in torsion. In each specimen with a circumferential weld, a nonuniform axial distribution of strain was easily visible. The test results were compared to an existing empirical model of creep-rupture life. For the torsion test, the comparison was based on a definition of equivalent normal stress recently adopted in Code Case N-47. Some 27 fatigue specimens, with longitudinal, circumferential, or no welds, were tested under axial or torsional strain control. In specimens with welds, fatigue cracking initiated at fusion lines. In axial tests cracks grew in the circumferential direction, and in torsional tests cracks grew along fusion lines. The test results were compared to empirical models of fatigue life based on two definition of equivalent normal strain range. The results have provided some needed confirmation of the reduction factors for creep strength and fatigue life of modified 9 Cr-1 Mo steel weldments currently under consideration by ASME Code committees. 8 refs., 5 figs.

  18. An engineering approach to determine the fatigue life of sheet structures under cyclic loading

    SciTech Connect

    Toribio, J. . Dept. of Engineering); Valiente, A. . Dept. of Materials Science)

    1993-01-01

    The structural integrity and the reliability of sheet structures, especially those of high risk like pressure vessels and pipes, is a relevant topic which has centered the attention of many researchers. This paper offers an engineering approach to determine the fatigue life of sheet structures under cyclic loading. The theoretical development presents a general method for calculating, by using a micro-computer, the initiation and fracture loci and the two-parameter crack growth paths as well as the integral value and therefore the fatigue life of the structure. This permits an evaluation of the influence of the different factors from the structural integrity point of view, and particularly of the material. The proposed method is applied to the computation of the fatigue life of a pressure vessel under cyclic loading produced by the thermal oscillations of the environment, allowing a study of leak before break.

  19. A study of stiffness, residual strength and fatigue life relationships for composite laminates

    NASA Technical Reports Server (NTRS)

    Ryder, J. T.; Crossman, F. W.

    1983-01-01

    Qualitative and quantitative exploration of the relationship between stiffness, strength, fatigue life, residual strength, and damage of unnotched, graphite/epoxy laminates subjected to tension loading. Clarification of the mechanics of the tension loading is intended to explain previous contradictory observations and hypotheses; to develop a simple procedure to anticipate strength, fatigue life, and stiffness changes; and to provide reasons for the study of more complex cases of compression, notches, and spectrum fatigue loading. Mathematical models are developed based upon analysis of the damage states. Mathematical models were based on laminate analysis, free body type modeling or a strain energy release rate. Enough understanding of the tension loaded case is developed to allow development of a proposed, simple procedure for calculating strain to failure, stiffness, strength, data scatter, and shape of the stress-life curve for unnotched laminates subjected to tension load.

  20. An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.

    NASA Technical Reports Server (NTRS)

    Hudson, C. M.

    1972-01-01

    Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.

  1. Fatigue degradation and life prediction of glass fabric polymer composites under tension/torsion biaxial loadings

    SciTech Connect

    Kawakami, H.; Fujii, T.J.; Morita, Y.

    1995-10-01

    Fatigue degradation and life prediction for a plain woven glass fabric reinforced polyester under tension/torsion biaxial loadings were investigated. Typical S-N diagrams were given at several biaxial ratios when the biaxial cyclic loads were proportionally applied to the specimens. A fatigue damage accumulation model based on the continuum damage mechanics theory was developed, where modulus decay ratios in tension and shear were used as indicators for damage variables (D). In the model, the damage variables are considered to be second-order tensors. Then, the maximum principal damage variable, D* is introduced. According to the similarity to the principal stress, D* is obtained as the maximum eigen value of damage tensor [D{prime}]. Under proportional tension/torsion loadings, fatigue lives were satisfactorily predicted at any biaxial stress ratios using the present model in which the fatigue characteristics only under uniaxial tension and pure torsion loadings were needed. For a certain biaxial stress ratio, the effect of loading path on the fatigue strength was examined. The experimental result does not show a strong effect of loading path on the fatigue life.

  2. Effect of electric discharge machining on the fatigue life of Inconel 718

    NASA Technical Reports Server (NTRS)

    Jeelani, S.; Collins, M. R.

    1988-01-01

    The effect of electric discharge machining on the fatigue life of Inconel 718 alloy at room temperature was investigated. Data were generated in the uniaxial tension fatigue mode at ambient temperature using flat 3.175 mm thick specimens. The specimens were machined on a wire-cut electric discharge machine at cutting speeds ranging from 0.5 to 2 mm per minute. The specimens were fatigued at a selected stress, and the resulting fatigue lives compared with that of the virgin material. The surfaces of the fatigued specimens were examined under optical and scanning electron microscopes, and the roughness of the surfaces was measured using a standard profilometer. From the results of the investigation, it was concluded that the fatigue life of the specimens machined using EDM decreased slightly as compared with that of the virgin material, but remained unchanged as the cutting speed was changed. The results are explained using data produced employing microhardness measurements, profilometry, and optical and scanning microscopy.

  3. Creep fatigue life prediction for engine hot section materials (isotropic)

    NASA Technical Reports Server (NTRS)

    Nelson, R. S.; Levan, G. W.; Schoendorf, J. F.

    1992-01-01

    A series of high temperature strain controlled fatigue tests have been completed to study the effects of thermomechanical fatigue, multiaxial loading, reactive environments, and imposed mean stresses. The baseline alloy used in these tests was cast B1900+Hf (with and without coatings); a small number of tests of wrought INCO 718 are also included. A strong path dependence was demonstrated during the thermomechanical fatigue testing, using in-phase, out-phase, and non-proportional (elliptical and 'dogleg') strain-temperature cycles. The multiaxial tests also demonstrated cycle path to be a significant variable, using both proportional and non-proportional tension-torsion loading. Environmental screening tests were conducted in moderate pressure oxygen and purified argon; the oxygen reduced the specimen lives by two, while the argon testing produced ambiguous data. Both NiCoCrAlY overlay and diffusion aluminide coatings were evaluated under isothermal and TMF conditions; in general, the lives of the coated specimens were higher that those of uncoated specimens. Controlled mean stress TMF tests showed that small mean stress changes could change initiation lives by orders of magnitude; these results are not conservatively predicted using traditional linear damage summation rules. Microstructures were evaluated using optical, SEM and TEM methods.

  4. Structural integrity and fatigue crack propagation life assessment of welded and weld-repaired structures

    NASA Astrophysics Data System (ADS)

    Alam, Mohammad Shah

    2005-11-01

    Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is assessed and necessary precaution is taken appropriately. Structural integrity includes tasks in many areas, such as structural analysis, failure analysis, nondestructive testing, corrosion, fatigue and creep analysis, metallurgy and materials, fracture mechanics, fatigue life assessment, welding metallurgy, development of repairing technologies, structural monitoring and instrumentation etc. In this research fatigue life assessment of welded and weld-repaired joints is studied both in numerically and experimentally. A new approach for the simulation of fatigue crack growth in two elastic materials has been developed and specifically, the concept has been applied to butt-welded joint in a straight plate and in tubular joints. In the proposed method, the formation of new surface is represented by an interface element based on the interface potential energy. This method overcomes the limitation of crack growth at an artificial rate of one element length per cycle. In this method the crack propagates only when the applied load reaches the critical bonding strength. The predicted results compares well with experimental results. The Gas Metal Arc welding processes has been simulated to predict post-weld distortion, residual stresses and development of restraining forces in a butt-welded joint. The effect of welding defects and bi-axial interaction of a circular porosity and a solidification crack on fatigue crack propagation life of butt-welded joints has also been investigated. After a weld has been repaired, the specimen was tested in a universal testing machine in order to determine fatigue crack propagation life. The fatigue crack propagation life of weld-repaired specimens was compared to un-welded and as-welded specimens. At the end of fatigue test, samples were cut from the fracture surfaces of typical welded and weld-repaired specimens and are examined under Scanning Electron Microscope (SEM) and characteristics features from these micrographs are explained.

  5. Fatigue life improvement of an autofrettage thick-walled pressure vessel with an external groove

    NASA Astrophysics Data System (ADS)

    Koh, Seung K.; Stephens, Ralph I.

    1992-01-01

    This report presents an investigation into a fatigue life improvement of an autofrettaged thick-walled pressure vessel with an external groove subjected to pulsating internal pressure, along with mean strain and mean stress effects on strain-controlled low cycle fatigue behavior. Linear elastic stress analysis of an autofrettaged thick-walled pressure vessel with an external groove is done using a finite element method. Autofrettage loading is performed using a thermal loading analogy. Change of external groove geometry is made using a quasi-optimization technique and finite element method to achieve longer fatigue life by relieving the stress concentration at the groove root. Surface treatment using shot peening is employed to produce compressive residual stresses at the vulnerable surface of the groove root to counteract the high tensile stresses. An evaluation of the fatigue life of an autofrettaged thick-walled pressure vessel with an external groove is done through a series of simulation fatigue tests using C-shaped specimens taken from the thick-walled pressure vessel.

  6. Fatigue management by truck drivers in real life situations: some suggestions to improve training.

    PubMed

    Fournier, Pierre-Sébastien; Montreuil, Sylvie; Brun, Jean-Pierre

    2007-01-01

    Truck driver fatigue is a major safety issue for truck drivers and the public in general. Although training prepares drivers to effectively operate a truck, it tends to minimize the importance of working constraints faced daily on-the-job and thus reduces its impact on safety and effectiveness. With experience, drivers develop skills to combat fatigue. Documenting these skills can contribute to improved training of apprentices. An ethnographic approach was used to better understand the real-life fatigue management skills of truck drivers. Participant observation was used to analyze the activity of apprentices in training and the activity of truck drivers at work. Observations indicated that training focused on time management and regulations, but did not prepare trainees to manage real-life constraints. Experienced drivers were not merely managing time; rather they were managing working constraints (including time) as a whole. To do so, they used two strategies: managing psycho-physical transformations and dynamic work planning. By integrating psycho-physical preoccupations into all aspects of work and by preparing future drivers to face real-life constraints, we could better train and prepare apprentices. Drivers do develop effective skills to combat fatigue which can improve training and better prepare future drivers to face daily constraints. These improvements can have a significant impact on fatigue and safety in the transportation industry. PMID:17942992

  7. Enhancing fatigue life of cylinder-crown integrated structure by optimizing dimension

    NASA Astrophysics Data System (ADS)

    Zhang, Weiwei; Wang, Xiaosong; Wang, Zhongren; Yuan, Shijian

    2015-03-01

    Cylinder-crown integrated hydraulic press (CCIHP) is a new press structure. The hemispherical hydraulic cylinder also functions as a main portion of crown, which has lower weight and higher section modulus compared with the conventional hydraulic cylinder and press crown. As a result, the material strength capacity is better utilized. During the engineering design of cylinder-crown integrated structure, in order to increase the fatigue life, structural optimization on the basis of the adaptive macro genetic algorithms (AMGA) is first conducted to both reduce weight and decrease peak stress. It is shown that the magnitude of the maximum principal stress is decreased by 28.6%, and simultaneously the total weight is reduced by 4.4%. Subsequently, strain-controlled fatigue test is carried out, and the stress-strain hysteresis loops and cyclic hardening curve are obtained. Based on linear fit, the fatigue properties are calculated and used for the fatigue life prediction. It is shown that the predicted fatigue life is significantly increased from 157000 to 1070000 cycles after structural optimization. Finally, according to the optimization design, a 6300 kN CCIHP has been manufactured, and priority application has been also suggested.

  8. Hold-time effects on the fatigue life of CuCrZr alloys for fusion applications

    NASA Astrophysics Data System (ADS)

    Wu, Xianglin; Pan, Xiao; Singh, Bachu N.; Li, Meimei; Stubbins, James F.

    2007-08-01

    The fatigue and creep-fatigue response of copper alloys is of interest due to the cyclic thermal-mechanical loading processes a fusion first wall will experience during operation. Creep-fatigue experiments were performed on a CuCrZr alloy with an overaged heat treatment at room temperature to determine the effects on fatigue life of a 10 s hold period applied at the maximum tension and compression points in the fatigue loading cycle. The hold period produced a reduction in the number of cycles to failure. This reduction was largest at the lowest strain amplitudes and the longest fatigue lives, the region of most interest for component design. Stress relaxation was observed during the hold periods even at room temperature where thermally-activated creep processes are not expected. The large reduction in fatigue life is apparently due to a change in the crack initiation mode from transgranular with no hold period to intergranular with a hold period.

  9. Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements

    NASA Astrophysics Data System (ADS)

    Koike, Mari; Chan, Kwai S.; Hummel, Susan K.; Mason, Robert L.; Okabe, Toru

    2013-02-01

    The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al2O3-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (α = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (α = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy ( p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.

  10. Experimental and modeling results of creep fatigue life of Inconel 617 and Haynes 230 at 850 C

    SciTech Connect

    Chen, Xiang; Sokolov, Mikhail A; Sham, Sam; ERDMAN III, DONALD L; Busby, Jeremy T; Mo, Kun; Stubbins, James

    2013-01-01

    Creep fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure for both materials decreased under creep fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep fatigue life. The linear damage summation could predict the creep fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep fatigue life prediction results for both materials.

  11. Experimental and modeling results of creep-fatigue life of Inconel 617 and Haynes 230 at 850 C

    NASA Astrophysics Data System (ADS)

    Chen, Xiang; Sokolov, Mikhail A.; Sham, Sam; Erdman, Donald L., III; Busby, Jeremy T.; Mo, Kun; Stubbins, James F.

    2013-01-01

    Creep-fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep-fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep-fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure for both materials decreased under creep-fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep-fatigue life. The linear damage summation could predict the creep-fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep-fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep-fatigue life prediction results for both materials.

  12. Daytime Sleepiness, Nighttime Sleep Quality, Stressful Life Events, and HIV-Related Fatigue

    PubMed Central

    Salahuddin, Naima; Barroso, Julie; Leserman, Jane; Harmon, James L.; Pence, Brian Wells

    2009-01-01

    In this report we describe the relationships between daytime sleepiness, nighttime sleep quality, stressful life events, and HIV-related fatigue in a sample of 128 individuals; we are reporting the baseline results of a longitudinal observational study. We examined sleep using the Pittsburg Sleep Quality Index (PSQI) (a measure of the quality of nighttime sleep), and the Epworth Sleepiness Scale (ESS), (a measure of daytime sleepiness). Recent stressful life events were measured via a methodology developed in a previous 9-year HIV study. Poor nighttime sleep was significantly correlated with fatigue intensity (r = 0.46, p < 0.05), as was daytime sleepiness (r = 0.20, p < 0.05). However, in multiple regression models, the association between stress and fatigue intensity was not explained by daytime sleepiness and was only partially explained by nighttime sleep quality. Further research is needed to better elucidate these relationships. PMID:19118766

  13. Characterization of the strain-life fatigue properties of thin sheet metal using an optical extensometer

    NASA Astrophysics Data System (ADS)

    Zhang, Shuiqiang; Mao, Shuangshuang; Arola, Dwayne; Zhang, Dongsheng

    2014-09-01

    Characterizing the strain-life fatigue behavior of thin sheet metals is often challenging since the required specimens have short gauge lengths to avoid buckling, thereby preventing the use of conventional mechanical extensometers. To overcome this obstacle a microscopic optical imaging system has been developed to measure the strain amplitude during fatigue testing using Digital Image Correlation (DIC). A strategy for rapidly recording images is utilized to enable sequential image sampling rates of at least 10 frames per second (fps) using a general digital camera. An example of a complete strain-life fatigue test for thin sheet steel under constant displacement control is presented in which the corresponding strain within the gage section of the specimen is measured using the proposed imaging system. The precision in strain measurement is assessed and methods for improving the image sampling rates in dynamic testing are discussed.

  14. A Study on the Effects of Ball Defects on the Fatigue Life in Hybrid Bearings

    NASA Technical Reports Server (NTRS)

    Tang, Ching-Yao; Foerster, Chad E.; O'Brien, Michael J.; Hardy, Brian S.; Goyal, Vinay K.; Nelson, Benjamin A.; Robinson, Ernest Y.; Ward, Peter C.; Hilton, Michael R.

    2014-01-01

    Hybrid ball bearings using silicon nitride ceramic balls with steel rings are increasingly being used in space mechanism applications due to their high wear resistance and long rolling contact fatigue life. However, qualitative and quantitative reports of the effects of ball defects that cause early fatigue failure are rare. We report on our approach to study these effects. Our strategy includes characterization of defects encountered in use, generation of similar defects in a laboratory setting, execution of full-scale bearing tests to obtain lifetimes, post-test characterization, and related finite-element modeling to understand the stress concentration of these defects. We have confirmed that at least one type of defect of appropriate size can significantly reduce fatigue life. Our method can be used to evaluate other defects as they occur or are encountered.

  15. The fatigue life of a cobalt-chromium alloy after laser welding.

    PubMed

    Al-Bayaa, Nabil Jalal Ahmad; Clark, Robert K F; Juszczyk, Andrzej S; Radford, David R

    2011-03-01

    The aim of this study was to investigate the fatigue life of laser welded joints in a commercially available cast cobalt-chromium alloy. Twenty rod shaped specimens (40 mm x 1.5 mm) were cast and sand blasted. Ten specimens were used as controls and the remaining ten were sectioned and repaired using a pulsed Nd: YAG laser welder. All specimens were subjected to fatigue testing (30N - 2Hz) in a controlled environment. A statistically significant difference in median fatigue life was found between as-cast and laser welded specimens (p < 0.001). Consequently, the technique may not be appropriate for repairing cobalt chromium clasps on removable partial dentures. Scanning electron microscopy indicated the presence of cracks, pores and constriction of the outer surface in the welded specimens despite 70% penetration of the weld. PMID:21528682

  16. 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.

  17. Fatigue, fracture, and life prediction criteria for composite materials in magnets

    SciTech Connect

    Wong, F.M.G.

    1990-06-01

    An explosively-bonded copper/Inconel 718/copper laminate conductor was proposed to withstand the severe face compression stresses in the central core of the Alcator C-MOD tokamak toroidal field (TF) magnet. Due to the severe duty of the TF magnet, it is critical that an accurate estimate of useful life be determined. As part of the effort to formulate an appropriate life prediction, fatigue crack growth experiments were performed on the laminate as well as its components. Metallographic evaluation of the laminate interface revealed many shear bands in the Inconel 718. Shear bands and shear band cracks were produced in the Inconel 718 as a result of the explosion bonding process. These shear bands were shown to have a detrimental effect on the crack growth behavior of the laminate, by significantly reducing the load carrying capability of the reinforcement layer and providing for easy crack propagation paths. Fatigue crack growth rate was found not only to be dependent on temperature but also on orientation. Fatigue cracks grew faster in directions which contained shear bands in the plane of the propagating crack. Fractography showed crack advancement by fatigue cracking in the Inconel 718 and ductile tearing of the copper at the interface. However, further away from the interfaces, the copper exhibited fatigue striations indicating that cracks were now propagating by fatigue. Laminate life prediction results showed a strong dependence on shear band orientation, and exhibited little variation between room temperature and 77{degree}K. Predicted life of this laminate was lower when the crack propagation was along a shear band than when crack propagation was across the shear bands. Shear bands appear to have a dominating effect on crack growth behavior.

  18. Fatigue Life of Haynes 188 Superalloy in Direct Connect Combustor Durability Rig

    NASA Technical Reports Server (NTRS)

    Gabb, TIm; Gayda, John; Webster, Henry; Ribeiro, Greg

    2007-01-01

    The Direct Connect Combustor Durability Rig (DCR) will provide NASA a flexible and efficient test bed to demonstrate the durability of actively cooled scramjet engine structure, static and dynamic sealing technologies, and thermal management techniques. The DCR shall be hydrogen fueled and cooled, and test hydrogen coolded structural panels at Mach 5 and 7. Actively cooled Haynes 188 superalloy DCR structural panels exposed to the combustion environment shall have electrodischarge machined (EDM) internal cooling holes with flowing liquid hydrogen. Hydrogen combustion could therefore produce severe thermal conditions that could challenge low cycle fatigue durability of this material. The objective of this study was to assess low cycle fatigue capability of Haynes 188 for DCR application. Tests were performed at 25 and 650 C, in hydrogen and helium environments, using specimens with low stress ground (LSG) and electro-discharge machined (EDM) surface finish. Initial fatigue tests in helium and hydrogen indicate the low cycle fatigue life capability of Haynes 188 in hydrogen appears quite satisfactory for the DCR application. Fatigue capability did not decrease with increasing test temperature. Fatigue capability also did not decrease with EDM surface finish. Failure evaluations indicate retention of ductility in all conditions. Additional tests are planned to reconfirm these positive trends.

  19. A Statistical Simulation Approach to Safe Life Fatigue Analysis of Redundant Metallic Components

    NASA Technical Reports Server (NTRS)

    Matthews, William T.; Neal, Donald M.

    1997-01-01

    This paper introduces a dual active load path fail-safe fatigue design concept analyzed by Monte Carlo simulation. The concept utilizes the inherent fatigue life differences between selected pairs of components for an active dual path system, enhanced by a stress level bias in one component. The design is applied to a baseline design; a safe life fatigue problem studied in an American Helicopter Society (AHS) round robin. The dual active path design is compared with a two-element standby fail-safe system and the baseline design for life at specified reliability levels and weight. The sensitivity of life estimates for both the baseline and fail-safe designs was examined by considering normal and Weibull distribution laws and coefficient of variation levels. Results showed that the biased dual path system lifetimes, for both the first element failure and residual life, were much greater than for standby systems. The sensitivity of the residual life-weight relationship was not excessive at reliability levels up to R = 0.9999 and the weight penalty was small. The sensitivity of life estimates increases dramatically at higher reliability levels.

  20. Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C

    SciTech Connect

    Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A; ERDMAN III, DONALD L; Mo, Kun; Stubbins, James

    2014-01-01

    Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.

  1. SHM-Based Probabilistic Fatigue Life Prediction for Bridges Based on FE Model Updating.

    PubMed

    Lee, Young-Joo; Cho, Soojin

    2016-01-01

    Fatigue life prediction for a bridge should be based on the current condition of the bridge, and various sources of uncertainty, such as material properties, anticipated vehicle loads and environmental conditions, make the prediction very challenging. This paper presents a new approach for probabilistic fatigue life prediction for bridges using finite element (FE) model updating based on structural health monitoring (SHM) data. Recently, various types of SHM systems have been used to monitor and evaluate the long-term structural performance of bridges. For example, SHM data can be used to estimate the degradation of an in-service bridge, which makes it possible to update the initial FE model. The proposed method consists of three steps: (1) identifying the modal properties of a bridge, such as mode shapes and natural frequencies, based on the ambient vibration under passing vehicles; (2) updating the structural parameters of an initial FE model using the identified modal properties; and (3) predicting the probabilistic fatigue life using the updated FE model. The proposed method is demonstrated by application to a numerical model of a bridge, and the impact of FE model updating on the bridge fatigue life is discussed. PMID:26950125

  2. Effect of lubricant extreme-pressure additives on surface fatigue life of AISI 9310 spur gears

    NASA Technical Reports Server (NTRS)

    Scibbe, H. W.; Townsend, D. P.; Aron, P. R.

    1984-01-01

    Surface fatigue tests were conducted with AISI 9310 spur gears using a formulated synthetic tetraester oil (conforming to MIL-L-23699 specifications) as the lubricant containing either sulfur or phosphorus as the EP additive. Four groups of gears were tested. One group of gears tested without an additive in the lubricant acted as the reference oil. In the other three groups either a 0.1 wt % sulfur or phosphorus additive was added to the tetraester oil to enhance gear surface fatigue life. Test conditions included a gear temperature of 334 K (160 F), a maximum Hertz stress of 1.71 GPa (248 000 psi), and a speed of 10,000 rpm. The gears tested with a 0.1 wt % phosphorus additive showed pitting fatigue life 2.6 times the life of gears tested with the reference tetraester based oil. Although fatigue lives of two groups of gears tested with the sulfur additive in the oil showed improvement over the control group gear life, the results, unlike those obtained with the phosphorus oil, were not considered to be statistically significant.

  3. Quality of Life in Patients with Multiple Sclerosis: The Impact of Depression, Fatigue, and Disability

    ERIC Educational Resources Information Center

    Goksel Karatepe, Altlnay; Kaya, Taciser; Gunaydn, Rezzan; Demirhan, Aylin; Ce, Plnar; Gedizlioglu, Muhtesem

    2011-01-01

    Aim: The aim of this study was to assess the quality of life (QoL) in patients with multiple sclerosis (MS), and to evaluate its association with disability and psychosocial factors especially depression and fatigue. Methods: Demographic characteristics, education level, disease severity, and disease duration were documented for each patient. QoL,

  4. Compassion Fatigue, Compassion Satisfaction, and Burnout: Factors Impacting a Professional's Quality of Life

    ERIC Educational Resources Information Center

    Sprang, Ginny; Whitt-Woosley, Adrienne; Clark, James J.

    2007-01-01

    This study examined the relationship between three variables, compassion fatigue (CF), compassion satisfaction (CS), and burnout, and provider and setting characteristics in a sample of 1,121 mental health providers in a rural southern state. Respondents completed the Professional Quality of Life Scale as part of a larger survey of provider

  5. Surface pitting fatigue life of noninvolute, low-contact-ratio gears

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.

    1990-01-01

    Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of noninvolute gears with low numbers of teeth and low contact ratios for use in advanced applications. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 8.89 cm (3.50 in.) with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.49 GPa (216 ksi), and a speed of 10 000 rpm. The following results were obtained: the noninvolute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design; and the surface pitting fatigue life of the 3.43-pitch AISI 8620 noninvolute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load but at a considerably higher maximum Hertz stress.

  6. A method of calculating the safe fatigue life of compact, highly-stressed components

    NASA Technical Reports Server (NTRS)

    Cardick, Arthur W.; Pike, Vera J.

    1994-01-01

    This paper describes a method which has been developed for estimating the safe fatigue life of compact, highly-stressed and inaccessible components for aeroplanes and helicopters of the Royal Air Force. It is explained why the Design Requirements for British Military Aircraft do not favor the use of a damage-tolerance approach in these circumstances.

  7. Effects of High-Temperature Exposures on the Fatigue Life of Disk Superalloys Examined

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Kantzos, Pete T.; Smith, James W.

    2005-01-01

    Tests used to characterize the low-cycle-fatigue resistance of disk superalloys are usually performed at cyclic frequencies of 0.33 Hz or faster. However, service conditions for disks in some aerospace and land-based gas turbine engines can produce major cycle periods extending from minutes to hours and days. Over a service life, this can produce total service times near the maximum temperature that exceed 100 hr for aerospace applications and 100,000 hr for land-based applications. Such time-dependent effects of realistic mission cycles on fatigue resistance can be significant in superalloy disks, and need to be considered for accurate disk life prediction. The purpose of this study at the NASA Glenn Research Center was to examine the effects of extended exposures and extended cycle periods on the fatigue resistance of two disk superalloys. Current alloy Udimet 720 (Special Metals Corporation, Huntington, WV) disk material was provided by Solar Turbines/Caterpillar Co., and advanced alloy ME3 was provided by the NASA Ultra-Efficient Engine Technologies (UEET) Project, in powder-metallurgy-processed, supersolvus heat-treated form. Fatigue specimens were fully machined and exposed in air at temperatures of 650 to 704 C for extended times. Then, they were tested using conventional fatigue tests with a total strain range of 0.70 percent and a minimum-to-maximum strain ratio of zero to determine the effects of prior exposure on fatigue resistance. Subsequent tests with extended dwells at minimum strain in each fatigue cycle were performed to determine cyclic exposure effects.

  8. 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.

  9. Fatigue life prediction of circumferentially notched component based on elastic-plastic fracture mechanics

    NASA Astrophysics Data System (ADS)

    Hatanaka, K.; Fujimitsu, T.; Omori, J.

    The elastic-plastic fracture mechanics parameters for the 3D surface and circumferential cracks generated in the circumferentially grooved cylinder component were analyzed from the viewpoint of engineering. Then, fatigue life spent during crack growth was estimated for the bluntly and acutely notched cylindrical components. Consequently, it was found that the crack propagation life of the notched cylinder component was successfully predicted by analyzing the extension of the semielliptical surface crack and the circumferential crack based on the proposed method.

  10. Stress-life relation of the rolling-contact fatigue spin rig

    NASA Technical Reports Server (NTRS)

    Butler, Robert H; Carter, Thomas L

    1957-01-01

    The rolling-contact fatigue spin rig was used to test groups of SAE 52100 9.16-inch-diameter balls lubricated with a mineral oil at 600,000-, 675,000-, and 750,000-psi maximum Hertz stress. Cylinders of AISI M-1 vacuum and commercial melts and MV-1 (AISI M-50) were used as race specimens. Stress-life exponents produced agree closely with values accepted in industry. The type of failure obtained in the spin rig was similar to the subsurface fatigue spells found in bearings.

  11. 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.

  12. Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

    DOE PAGESBeta

    Wu, Wei; An, Ke

    2015-10-03

    The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

  13. Split mandrel versus split sleeve coldworking: Dual methods for extending the fatigue life of metal structures

    NASA Technical Reports Server (NTRS)

    Rodman, Geoffrey A.; Creager, Matthew

    1994-01-01

    It is common practice to use split sleeve coldworking of fastener holes as a means of extending the fatigue life of metal structures. In search of lower manufacturing costs, the aerospace industry is examining the split mandrel (sleeveless) coldworking process as an alternative method of coldworking fastener holes in metal structures. The split mandrel process (SpM) significantly extends the fatigue life of metal structures through the introduction of a residual compressive stress in a manner that is very similar to the split sleeve system (SpSl). Since the split mandrel process is significantly less expensive than the split sleeve process and more adaptable to robotic automation, it will have a notable influence upon other new manufacture of metal structures which require coldworking a significant number of holes, provided the aerospace community recognizes that the resulting residual stress distributions and fatigue life improvement are the same for both processes. Considerable testing has validated the correctness of that conclusion. The findings presented in this paper represent the results of an extensive research and development program, comprising data collected from over 400 specimens fabricated from 2024-T3 and 7075-T651 aluminum alloys in varied configurations, which quantify the benefits (fatigue enhancement and cost savings) of automating a sleeveless coldworking system.

  14. Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

    SciTech Connect

    Wu, Wei; An, Ke

    2015-10-03

    The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impacts on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.

  15. Profiled Roller Stress/Fatigue Life Analysis Methodology and Establishment of an Appropriate Stress/Life Exponent

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The objective of this work was to determine the three dimensional volumetric stress field, surface pressure distribution and actual contact area between a 0.50" square roller with different crown profiles and a flat raceway surface using Finite Element Analysis. The 3-dimensional stress field data was used in conjunction with several bearing fatigue life theories to extract appropriate values for stress-life exponents. Also, results of the FEA runs were used to evaluate the laminated roller model presently used for stress and life prediction.

  16. Changes in exercise capacity, quality of life and fatigue in cancer patients during an intervention.

    PubMed

    Banzer, W; Bernhrster, M; Schmidt, K; Niederer, D; Lungwitz, A; Thiel, C; Jger, E; Vogt, L

    2014-09-01

    The study explored the interdependence of changes in oxygen uptake, quality of life and cancer-related side-effect fatigue during a 4-month exercise intervention. Participants were during adjuvant (curative) or palliative therapy and post-adjuvant therapy (finished within the previous 12 months). Aerobic exercise capacity (VO2 peak), quality of life and fatigue symptom (EORTC QLQ-C30) were obtained in 101 cancer patients (30-77 years). After initial examination, patients participated in supervised and/or home-based training interventions. Patients were re-examined after 16-20 weeks and stratified into 3 subgroups (terciles) with respect to the absolute change in VO2 peak. The ANCOVA, with significant covariate effect for pretest fatigue score (F(5,101) = 8.150, P < 0.001), indicated significant differences between groups in outcome measures (P < 0.001). Based on the absolute change of VO2 peak (1.9 1.7; 1.8 0.8; 5.7 2.8?ml/kg/min) there were significant differences in the quality of life improvement (17.2 15.1 vs. 4.8 22.0 points, P < 0.05) and cancer-related fatigue reduction (-6.1 30.7; -11.5 20.9; -21.2 21.4 points) between upper and lower tercile. The findings point towards a relationship of exercise capacity enhancement, quality of life improvement and fatigue symptom reduction during and shortly after cancer treatment. PMID:24724813

  17. 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.

  18. Relation Between Residual and Hoop Stresses and Rolling Bearing Fatigue Life

    NASA Technical Reports Server (NTRS)

    Oswald, Fred B.; Zaretsky, Erwin V.; Poplawski, Joseph V.

    2015-01-01

    Rolling-element bearings operated at high speed or high vibration may require a tight interference fit between the bore of the bearing and shaft to prevent rotation of the bearing bore around the shaft and fretting damage at the interfaces. Previous work showed that the hoop stresses resulting from tight interference fits can reduce bearing lives by as much as 65 percent. Where tight interference fits are required, case-carburized steel such as AISI 9310 or M50 NiL is often used because the compressive residual stresses inhibit subsurface crack formation and the ductile core inhibits inner-ring fracture. The presence of compressive residual stress and its combination with hoop stress also modifies the Hertz stress-life relation. This paper analyzes the beneficial effect of residual stresses on rolling-element bearing fatigue life in the presence of high hoop stresses for three bearing steels. These additional stresses were superimposed on Hertzian principal stresses to calculate the inner-race maximum shearing stress and the resulting fatigue life of the bearing. The load-life exponent p and Hertz stress-life exponent n increase in the presence of compressive residual stress, which yields increased life, particularly at lower stress levels. The Zaretsky life equation is described and is shown to predict longer bearing lives and greater load- and stress-life exponents, which better predicts observed life of bearings made from vacuum-processed steel.

  19. Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

    NASA Technical Reports Server (NTRS)

    Hannum, N. P.; Kasper, H. J.; Pavli, A. J.

    1976-01-01

    During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The zirconium in this alloy was not evenly distributed in the chamber materials. The life that was achieved was nominally the same as would have been predicted from OFHC copper isothermal test data.

  20. Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps

    NASA Technical Reports Server (NTRS)

    Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.

    1972-01-01

    Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.

  1. 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.

  2. Fatigue, Sleep Quality, and Disability in Relation to Quality of Life in Multiple Sclerosis

    PubMed Central

    Radfar, Moloud

    2015-01-01

    Background: Quality of life (QOL) is impaired in multiple sclerosis (MS) in part due to physical disability. MS-associated fatigue and poor sleep are common and treatable features of MS that affect QOL. We assessed the association between fatigue, sleep quality, and QOL in people with MS. Methods: Cross-sectional data were collected from 217 patients with MS. Health-related QOL (MS Quality of Life-54), fatigue (Fatigue Severity Scale [FSS]), and sleep quality (Pittsburgh Sleep Quality Inventory [PSQI]) were assessed. Expanded Disability Status Scale scores were also provided by a qualified neurologist. Results: The mean SD age of the 217 patients was 32.6 8.6 years, and 79% were female. One hundred fifty-two patients (70.0%) were classified as poor sleepers based on PSQI scores; 122 (56.2%) had significant fatigue based on FSS results. The mean SE physical (PCS) and mental (MCS) health composite scores of the MSQOL-54 were 40.12 1.27 and 43.81 1.61, respectively. There was a strong statistically significant positive correlation between PCS scores and MCS (r = 0.58), FSS (r = 0.49), and PSQI (r = 0.52) scores. MCS scores were strongly correlated with FSS (r = 0.53) and PSQI (r = 0.35) scores. Age exhibited statistically significant negative correlations with PCS (r = ?0.21) and MCS (r = ?0.58) scores, and was statistically significantly correlated with FSS (r = 0.23) and PSQI (r = 0.21) scores. Expanded Disability Status Scale scores were strongly correlated with FSS scores. Conclusions: These findings support screening of fatigue severity and sleep quality and their effects on QOL. PMID:26664332

  3. Adaptive active vibration control to improve the fatigue life of a carbon-epoxy smart structure

    NASA Astrophysics Data System (ADS)

    Ripamonti, Francesco; Cazzulani, Gabriele; Cinquemani, Simone; Resta, Ferruccio; Torti, Alessandro

    2015-04-01

    Active vibration controls are helpful in improving fatigue life of structures through limitation of absolute displacements. However, control algorithms are usually designed without explicitly taking into account the fatigue phenomenon. In this paper, an adaptive vibration controller is proposed to increase the fatigue life of a smart structure made of composite material and actuated with piezoelectric patches. The main innovation with respect to the most common solutions is that the control laws are directly linked to a damage driving force, which is correlated to a fatigue damage model for the specific material. The control logic is different depending on the damage state of the structure. If no significant damage affects the structure, the controller decreases the crack nucleation probability by limiting the driving forces in the overall structure. On the contrary, if initiated cracks are present, their further propagation is prevented by controlling the damage driving forces in the already damaged areas. The structural diagnostics is performed through a vibration-based health monitoring technique, while periodical adaptation of the controller is adopted to consider damage-induced changes on the structure state-space model and to give emphasis to the most excited modes. The control algorithm has been numerically validated on the finite element model of a cantilever plate.

  4. 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

  5. Optimal Shot Peening Treatments to Maximize the Fatigue Life of Quenched and Tempered Steels

    NASA Astrophysics Data System (ADS)

    Llaneza, V.; Belzunce, F. J.

    2015-07-01

    The search for the optimal Almen intensity to use in shot peening treatments to maximize the fatigue life of industrial steel components involves many different variables and physical phenomena. In this paper, the optimal peening intensity of different steel grades obtained from an AISI 4340 steel through heat treatments has been determined. Six different steel grades were subjected to shot peening treatments, which were performed under full coverage, but employing diverse Almen intensities, shot sizes and air pressures. The role of the mechanical properties of the treated steel and the applied Almen intensity on the shot peening effects were studied to understand the results obtained by means of rotating bending fatigue tests. Each steel has a specific Almen intensity value able to optimize its fatigue life, thereby allowing an optimal balance between the positive and negative effects induced by shot peening. This value, or range of values, is dependent on the mechanical properties of the treated steel, increasing with increasing steel properties up to a certain point and then decreasing for stronger steels. In these cases, over peening treatments produce sufficiently large surface defects to induce relaxation of the surface residual stress and facilitate the initiation of surface fatigue cracks.

  6. Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure

    SciTech Connect

    Zhou, J; Huang, M; Niu, X; soboyejo, W

    2006-10-09

    In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).

  7. A crystal plasticity based methodology for modeling fatigue crack initiation and estimating material coefficients to predict fatigue crack initiation life at micro, nano and macro scales

    NASA Astrophysics Data System (ADS)

    Voothaluru, Rohit

    Fatigue failure is a dominant mechanism that governs the failure of components and structures in many engineering applications. In conventional engineering applications due to the design specifications, a significant proportion of the fatigue life is spent in the crack initiation phase. In spite of the large number of works addressing fatigue life modeling, the problem of modeling crack initiation life still remains a major challenge. In this work, a novel computational methodology based upon crystal plasticity formulations has been developed to predict crack initiation life at macro, micro and nano length scales. The crystal plasticity based constitutive model has been employed to model the micromechanical deformation and damage accumulation under cyclic loading in polycrystalline metals. This work provides a first of its kind, fundamental basis for employing crystal plasticity formulations for evaluating a quantifiable estimate of fatigue crack initiation life. A semi-empirical energy based fatigue crack initiation criterion s employed to allow for accurate modeling of the underlying microstructural phenomenon leading to the initiation of cracks at different material length scales. The results of the fatigue crack initiation life prediction in case of polycrystalline metals such as Copper and Nickel demonstrated that the crack initiation life prediction using the proposed methodology yielded an improvement of more than 30% in comparison to the existing continuum methodologies for fatigue crack initiation prediction and more than 80% improvement compared to the existing analytical models. The computational methodology developed in this work also provides a first of its kind technique to evaluate the fatigue crack initiation coefficient in the form of energy dissipation coefficient that can be used at varying length scales. The methodology and the computational framework proposed in this work, are developed such that experimental inputs are used to improve computational model performance and the closed loop feedback system enables the modeling of micro, macro and nano scale mechanisms very well. The computational models for the representative material microstructures were built by creating randomized Voronoi tessellations of the representative region that allows for reducing the need for extensive testing which is the major challenge in crack initiation predictions in engineering structures. In order to facilitate the use of the model for engineering applications, an analytical expression for fatigue crack initiation prediction using macro-scale loading conditions has been developed. The analytical model developed for fatigue crack initiation using macro-scale conditions has been validated using benchmark data in the literature to allow for the identification of the material co-efficients necessary to predict the fatigue crack initiation life while considering surface finish, grain size and crack size. The computational modeling and prediction of fatigue crack initiation life in nanostructured graphene reinforced materials is also studied by creating an effective interface method based computational model. The results of the model prediction showed good agreement with the trend of fatigue crack initiation life compared with the experimental results. This work lays the foundation for linking micromechanical plastic deformation to the nano-scale phenomenon while simultaneously providing a tool for engineers predicting crack initiation in macro-scale applications.

  8. Fatigue and quality of life in women treated for various types of gynaecological cancers: a cross-sectional study

    PubMed Central

    Sekse, Ragnhild Johanne Tveit; Hufthammer, Karl Ove; Vika, Margrethe Elin

    2015-01-01

    Aims and objectives To examine the prevalence of cancer-related fatigue in women treated for various types of gynaecological cancers and, for these cancers, to assess fatigue in relation to distress, health-related quality of life, demography and treatment characteristics. Background Advances in treatment of cancer have improved the likelihood of survival. Consequently, there are a growing number of patients who become survivors after cancer and who face side effects even years after treatment. One of the most frequently reported side effects across all types and stages of the disease is cancer-related fatigue. Design A descriptive cross-sectional study. Methods One hundred and twenty women treated for gynaecological cancers who were participants in an intervention study were included. Fatigue, psychological distress, health-related QoL and demographics were assessed by questionnaires. Disease and treatment characteristics were extracted from medical records. Results Cancer-related fatigue was reported in 53% of the women treated for gynaecological cancers, with a higher proportion in the group of cervical cancer, followed by ovarian cancer. Younger participants reported fatigue more frequently than older participants. When adjusting for age, the type of cancer a woman experiences was shown to have little impact on her risk of experiencing fatigue. The participants with fatigue reported higher levels of anxiety and depression than participants without fatigue. There was a relationship between fatigue and quality of life as measured by SF-36 domains. Conclusion The findings underscore the importance of screening for fatigue, patient education and symptom management. This should be included in a standard procedure during treatment and follow-up. Both somatic and psychological aspects of fatigue should be emphasised. Relevance to clinical practice The findings imply the need for health personnel to have focus on fatigue during the entire cancer trajectory of women after gynaecological cancers, as well as the need for screening, information, guidance and symptom management. PMID:25040957

  9. Experimental fatigue life investigation of cylindrical thrust chambers

    NASA Technical Reports Server (NTRS)

    Quentmeyer, R. J.

    1977-01-01

    Twenty-two cylindrical test sections of a cylindrical rocket thrust chamber were fabricated and 21 of them were cycled to failure to explore the failure mechanisms, determine the effects of wall temperature on cyclic life, and to rank the material life characteristics for comparison with results from isothermal tests of 12 alloys at 538 C. Cylinder liners were fabricated from OFHC copper, Amzirc, and NAR1loy-Z. Tests were conducted at a chamber pressure of 4.14 MW/sq m using hydrogen-oxygen propellants at an oxidant-fuel ratio of 6.0, which resulted in an average throat heat flux of 54 MW/sq m. The cylinders were cooled with liquid hydrogen at an average rate of 0.91 Kg/sec. All failures were characterized by a thinning of the cooling channel wall at the centerline and eventual failure by tensile rupture. Cyclic life rankings of the materials based on temperature do not agree with published rankings based on uniaxial, isothermal strain tests.

  10. 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.

  11. Effects of material and loading variables on fatigue life of carbon and low-alloy steels in LWR environments

    SciTech Connect

    Chopra, O.K.; Shack, W.J.

    1995-03-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Section III of the Code specifies fatigue design curves for structural materials. While effects of reactor coolant environments are not explicitly addressed by the design curves, test data suggest that the Code fatigue curves may not always be adequate in coolant environments. This paper reports the results of recent fatigue tests that examine the effects of steel type, strain rate, dissolved oxygen level, strain range, loading waveform, and surface morphology on the fatigue life of A106-Gr B carbon steel and A533-Gr B low-alloy steel in water.

  12. The Effect of Drive Signal Limiting on High Cycle Fatigue Life Analysis

    NASA Technical Reports Server (NTRS)

    Kihm, Frederic; Rizzi, Stephen A.

    2014-01-01

    It is common practice to assume a Gaussian distribution of both the input acceleration and the response when modeling random vibration tests. In the laboratory, however, shaker controllers often limit the drive signal to prevent high amplitude peaks. The high amplitudes may either be truncated at a given level (socalled brick wall limiting or abrupt clipping), or compressed (soft limiting), resulting in drive signals which are no longer Gaussian. The paper first introduces several methods for limiting a drive signal, including brick wall limiting and compression. The limited signal is then passed through a linear time-invariant system representing a device under test. High cycle fatigue life predictions are subsequently made using spectral fatigue and rainflow cycle counting schemes. The life predictions are compared with those obtained from unclipped input signals. Some guidelines are provided to help the test engineer decide how clipping should be applied under different test scenarios.

  13. Comparison of Fatigue Life Estimation Using Equivalent Linearization and Time Domain Simulation Methods

    NASA Technical Reports Server (NTRS)

    Mei, Chuh; Dhainaut, Jean-Michel

    2000-01-01

    The Monte Carlo simulation method in conjunction with the finite element large deflection modal formulation are used to estimate fatigue life of aircraft panels subjected to stationary Gaussian band-limited white-noise excitations. Ten loading cases varying from 106 dB to 160 dB OASPL with bandwidth 1024 Hz are considered. For each load case, response statistics are obtained from an ensemble of 10 response time histories. The finite element nonlinear modal procedure yields time histories, probability density functions (PDF), power spectral densities and higher statistical moments of the maximum deflection and stress/strain. The method of moments of PSD with Dirlik's approach is employed to estimate the panel fatigue life.

  14. Finite element nonlinear flutter and fatigue life of 2-D panels with temperature effects

    NASA Technical Reports Server (NTRS)

    Mei, Chuh; Xue, David Y.

    1991-01-01

    A frequency domain method for two-dimensional nonlinear panel flutter with thermal effects obtained from a consistent finite element formulation is presented. The von Karman nonlinear strain-displacement relation is used to account for large deflections, and the quasi-steady first-order piston theory is employed for aerodynamic loading. The finite element frequency domain results are compared with analytical time domain solutions. In a limit-cycle motion, the panel frequency and stress can be determined, thus fatigue life can be predicted. The influence of temperature and dynamic pressure on panel fatigue life is presented. An endurance dynamic pressure can be established at a given temperature from the present method.

  15. The effects of ageing and environment on the fatigue life of adhesive joints

    NASA Astrophysics Data System (ADS)

    Su, Ning; Mackie, R. I.; Harvey, W. J.

    1992-04-01

    This paper presents the results of a durability program designed to study the effects of aging and environment on the fatigue life of adhesive joints. The adhesives were typical of those which might be used in civil engineering applications. Specimens were kept under a variety of loading and environmental conditions for eight years. It was observed that some adhesives showed excellent durability properties, and that the fatigue life of some specimens actually improved with age. Other adhesives were adversely affected by the environment, particularly high humidity or exposure to the natural environment. It was found that good performance in a laboratory high humidity environment does not guarantee good performance when exposed to the natural environment. The durability performance of the adhesives bore a close relation to the effects of moisture uptake in the adhesives.

  16. On the fatigue life of M50 NiL rolling bearings

    NASA Astrophysics Data System (ADS)

    Harris, T. A.; Skiller, John; Spitzer, Ronald F.

    1992-10-01

    The fatigue life of rolling bearings made of M50 NiL (a nickel-low carbon variant of M50 tool steel) was investigated using data from a battery of 15 R2 endurance test rigs specially modified to accommodate the aircraft application test conditions. Results indicate that bearings manufactured from case-hardened M50 NiL steel can provide significantly greater rolling contact fatigue life than bearings made from through-hardened M50 steel. In addition, it was found that M50 NiL bearings endurance-tested under conditions of heavy tensile hoop stresses showed no tendency toward raceway spalling or cracking through, unlike M50 bearings, which exhibited both tendencies.

  17. Strainrange partitioning life predictions of the long time Metal Properties Council creep-fatigue tests

    NASA Technical Reports Server (NTRS)

    Saltsman, J. F.; Halford, G. R.

    1979-01-01

    The method of Strainrange Partitioning is used to predict the cyclic lives of the Metal Properties Council's long time creep-fatigue interspersion tests of several steel alloys. Comparisons are made with predictions based upon the Time- and Cycle-Fraction approach. The method of Strainrange Partitioning is shown to give consistently more accurate predictions of cyclic life than is given by the Time- and Cycle-Fraction approach.

  18. Strainrange partitioning life predictions of the long time metal properties council creep-fatigue tests

    NASA Technical Reports Server (NTRS)

    Saltsman, J. F.; Halford, G. R.

    1979-01-01

    The method of strainrange partitioning is used to predict the cyclic lives of the Metal Properties Council's long time creep-fatigue interspersion tests of several steel alloys. Comparisons are made with predictions based upon the time- and cycle-fraction approach. The method of strainrange partitioning is shown to give consistently more accurate predictions of cyclic life than is given by the time- and cycle-fraction approach.

  19. Space Shuttle Rudder Speed Brake Actuator-A Case Study Probabilistic Fatigue Life and Reliability Analysis

    NASA Technical Reports Server (NTRS)

    Oswald, Fred B.; Savage, Michael; Zaretsky, Erwin V.

    2015-01-01

    The U.S. Space Shuttle fleet was originally intended to have a life of 100 flights for each vehicle, lasting over a 10-year period, with minimal scheduled maintenance or inspection. The first space shuttle flight was that of the Space Shuttle Columbia (OV-102), launched April 12, 1981. The disaster that destroyed Columbia occurred on its 28th flight, February 1, 2003, nearly 22 years after its first launch. In order to minimize risk of losing another Space Shuttle, a probabilistic life and reliability analysis was conducted for the Space Shuttle rudder/speed brake actuators to determine the number of flights the actuators could sustain. A life and reliability assessment of the actuator gears was performed in two stages: a contact stress fatigue model and a gear tooth bending fatigue model. For the contact stress analysis, the Lundberg-Palmgren bearing life theory was expanded to include gear-surface pitting for the actuator as a system. The mission spectrum of the Space Shuttle rudder/speed brake actuator was combined into equivalent effective hinge moment loads including an actuator input preload for the contact stress fatigue and tooth bending fatigue models. Gear system reliabilities are reported for both models and their combination. Reliability of the actuator bearings was analyzed separately, based on data provided by the actuator manufacturer. As a result of the analysis, the reliability of one half of a single actuator was calculated to be 98.6 percent for 12 flights. Accordingly, each actuator was subsequently limited to 12 flights before removal from service in the Space Shuttle.

  20. 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.

  1. The impact of disability, fatigue and sleep quality on the quality of life in multiple sclerosis

    PubMed Central

    Ghaem, Haleh; Haghighi, Afshin Borhani

    2008-01-01

    Background: Only few papers have investigated the impact of multiple sclerosis (MS), especially MS-related fatigue and the impact of the quality of sleep on the quality of life (QoL) in MS patients. Objective: The objective of this study was to measure the quality of life in MS patients and the impact of disability, fatigue and sleep quality, using statistical modeling. Materials and Methods: A cross-sectional study was conducted and data was collected from 141 MS patients, who were referred to the Mottahari Clinic, Shiraz, Iran, in 2005. Data on health-related quality of life (MSQoL-54), fatigue severity scale (FSS), and Pittsburgh sleep quality Index (PSQI) were obtained in the case of all the patients. Epidemiology data concerning MS type, MS functional system score, expanded disability status scale (EDSS) etc. were also provided by a qualified neurologist. Spearman ? coefficient, Mann-Whitney U test, and linear regression model were used to analyze the data. Results: The mean SD age of 141 MS patients was 32.69.6 year. Thirty five (24.8%) of them were male and the others were female. Eighty two (58.1%) of the patients had EDSS score of ? 2, 36 (25.5%) between 2.5 and 4.5, and 23 (16.3%) ? 5. As per PSQI scores, two (1.4%) of the patients had good sleep, 16 (11.3%) had moderate sleep and 123 (87.2%) had poor sleep. There was a significant high positive correlation between the quality of mental and physical health composite scores (r = 0.791, P<0.001). There was a significant negative correlation between the quality of physical score and age (r = -0.88, P<0.001), fatigue score (r = -0.640, P<0.001), EDSS score (r = -0.476, P<0.001) and PSQI (sleep quality r = -0.514, P<0.000). Linear regression analysis showed that PSQI score, EDSS, and fatigue score were predictors in the model between the quality of physical score and covariates (P<0.001). Linear regression model showed that fatigue score and PSQI were predictors in the model between the quality of mental score and covariates (P<0.001). Discussion and Conclusion: In conclusion, it may be said that MS patients had poor and moderate quality of mental and physical health. The quality of life was impaired as seen by PSQI, EDSS, and FSS. It is our suggestion that these patients require the attention of health care professionals, to be observed for the need of possible psychological support. PMID:19893680

  2. The Effects of Laser Marking and Symbol Etching on the Fatigue Life of Medical Devices

    PubMed Central

    Ogrodnik, P. J.; Moorcroft, C. I.; Wardle, P.

    2013-01-01

    This paper examines the question;“ does permanent laser marking affect the mechanical performance of a metallic medical component?” The literature review revealed the surprising fact that very little has been presented or studied even though intuition suggests that its effect could be detrimental to a component's fatigue life. A brief investigation of laser marking suggests that defects greater than 25 μm are possible. A theoretical investigation further suggests that this is unlikely to cause issues with relation to fast fracture but is highly likely to cause fatigue life issues. An experimental investigation confirmed that laser marking reduced the fatigue life of a component. This combination of lines of evidence suggests, strongly, that positioning of laser marking is highly critical and should not be left to chance. It is further suggested that medical device designers, especially those related to orthopaedic implants, should consider the position of laser marking in the design process. They should ensure that it is in an area of low stress amplitude. They should also ensure that they investigate worst-case scenarios when considering the stress environment; this, however, may not be straightforward.

  3. Effect of shot peening on surface fatigue life of carburized and hardened AISI 9310 spur gears

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Zaretsky, E. V.

    1982-01-01

    Surface fatigue tests were conducted on two groups of AISI 9310 spur gears. Both groups were manufactured with standard ground tooth surfaces, with the second group subjected to an additional shot peening process on the gear tooth flanks. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a gear temperature of 350 K (170 F), a maximum Hertz stress of 1.71 billion N/sq m (248,000 psi), and a speed of 10,000 rpm. The shot peened gears exhibited pitting fatigue lives 1.6 times the life of standard gears without shot peening. Residual stress measurements and analysis indicate that the longer fatigue life is the result of the higher compressive stress produced by the shot peening. The life for the shot peened gear was calculated to be 1.5 times that for the plain gear by using the measured residual stress difference for the standard and shot peened gears. The measured residual stress for the shot peened gears was much higher than that for the standard gears.

  4. A Probabilistic Approach to Predict Thermal Fatigue Life for Ball Grid Array Solder Joints

    NASA Astrophysics Data System (ADS)

    Wei, Helin; Wang, Kuisheng

    2011-11-01

    Numerous studies of the reliability of solder joints have been performed. Most life prediction models are limited to a deterministic approach. However, manufacturing induces uncertainty in the geometry parameters of solder joints, and the environmental temperature varies widely due to end-user diversity, creating uncertainties in the reliability of solder joints. In this study, a methodology for accounting for variation in the lifetime prediction for lead-free solder joints of ball grid array packages (PBGA) is demonstrated. The key aspects of the solder joint parameters and the cyclic temperature range related to reliability are involved. Probabilistic solutions of the inelastic strain range and thermal fatigue life based on the Engelmaier model are developed to determine the probability of solder joint failure. The results indicate that the standard deviation increases significantly when more random variations are involved. Using the probabilistic method, the influence of each variable on the thermal fatigue life is quantified. This information can be used to optimize product design and process validation acceptance criteria. The probabilistic approach creates the opportunity to identify the root causes of failed samples from product fatigue tests and field returns. The method can be applied to better understand how variation affects parameters of interest in an electronic package design with area array interconnections.

  5. Vibration-induced fatigue life estimation of ball grid array packaging

    NASA Astrophysics Data System (ADS)

    Wu, Mei-Ling

    2009-06-01

    Vibration loading has become very important in the reliability assessment of modern electronic systems. The objective of this paper is to develop a rapid assessment methodology that can determine the solder joint fatigue life of ball grid array (BGA) and chip scale packages (CSP) under vibration loading. The current challenge is how to execute the vibration fatigue life analysis rapidly and accurately. The approach in this paper will involve global (entire printed wiring board (PWB)) and local (particular component of interest) modeling approaches. In the global model approach, the vibration response of the PWB will be determined. This global model will give us the response of the PWB at specific component locations of interest. This response is then fed into a local stress analysis for accurate assessment of the critical stresses in the solder joints of interest. The stresses are then fed into a fatigue damage model to predict the life. The goal is to retain as much accuracy and physical insight as possible while retaining computation efficiency.

  6. Fatigue life analysis for traction drives with application to a toroidal type geometry

    NASA Technical Reports Server (NTRS)

    Coy, J. J.; Loewenthal, S. H.; Zaretsky, E. V.

    1976-01-01

    A contact fatigue life analysis for traction drives was developed which was based on a modified Lundberg-Palmgren theory. The analysis was used to predict life for a cone-roller toroidal traction drive. A 90-percent probability of survival was assumed for the calculated life. Parametric results were presented for life and Hertz contact stress as a function of load, drive ratio, and size. A design study was also performed. The results were compared to previously published work for the dual cavity toroidal drive as applied to a typical compact passenger vehicle drive train. For a representative duty cycle condition wherein the engine delivers 29 horsepower at 2000 rpm with the vehicle moving at 48.3 km/hr (30 mph) the drive life was calculated to be 19,200 km (11 900 miles).

  7. A work-life perspective on sleep and fatigue--looking beyond shift workers.

    PubMed

    Skinner, Natalie; Dorrian, Jill

    2015-01-01

    This study examines sleep and fatigue through a work-life lens. Whilst most often thought of as an issue for shift workers, this study observed that self-reported insufficient sleep and fatigue were prevalent for workers on standard daytime schedules. Using a representative sample of 573 daytime workers (51.3% men; 70.7% aged 25-54?yr) from one Australian state, it was observed that 26.4% of daytime workers never or rarely get the seven hours of sleep a night that is recommended for good health. Those with parenting responsibilites (29.4%) or working long (45+) hours (37.4%) were most likely to report insufficient sleep. Whereas mothers in full-time work were most likely to report frequent fatigue (42.5%). This study highlights the common experience of insufficient sleep and fatigue in a daytime workforce, with significant implications for health and safety at work and outside of work. Stronger and more effective legislation addressing safe and 'decent' working time is clearly needed, along with greater awareness and acceptance within workplace cultures of the need to support reasonable workloads and working hours. PMID:26027709

  8. Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

    NASA Technical Reports Server (NTRS)

    Hannum, N. P.; Kasper, H. J.; Pavli, A. J.

    1976-01-01

    During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The chamber liners were fabricated of copper or copper alloy and contained milled coolant channels. The chambers were completed by means of an electroformed nickel closeout. The oxidant/fuel ratio for the liquid oxygen and gaseous hydrogen propellants was 6.0. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The lives were much shorter than were predicted by an analytical structural analysis computer program used in conjunction with fatigue life data from isothermal test specimens, due to the uneven distribution of Zr in the chamber material.

  9. Cancer Related Fatigue and Quality of Life in Patients with Advanced Prostate Cancer Undergoing Chemotherapy

    PubMed Central

    Charalambous, Andreas; Kouta, Christiana

    2016-01-01

    Cancer related fatigue (CRF) is a common and debilitating symptom that can influence quality of life (QoL) in cancer patients. The increase in survival times stresses for a better understanding of how CRF affects patients' QoL. This was a cross-sectional descriptive study with 148 randomly recruited prostate cancer patients aiming to explore CRF and its impact on QoL. Assessments included the Cancer Fatigue Scale, EORTC QLQ-C30, and EORTC QLQ-PR25. Additionally, 15 in-depth structured interviews were performed. Quantitative data were analyzed with simple and multiple regression analysis and independent samples t-test. Qualitative data were analyzed with the use of thematic content analysis. The 66.9% of the patients experienced CRF with higher levels being recorded for the affective subscale. Statistically significant differences were found between the patients reporting CRF and lower levels of QoL (mean = 49.1) and those that did not report fatigue and had higher levels of QoL (mean = 72.1). The interviews emphasized CRF's profound impact on the patients' lives that was reflected on the following themes: “dependency on others,” “loss of power over decision making,” and “daily living disruption.” Cancer related fatigue is a significant problem for patients with advanced prostate cancer and one that affects their QoL in various ways. PMID:26981530

  10. Laser Peening and Shot Peening Effects on Fatigue Life and Surface Roughness of Friction Stir Welded 7075-T7351 Aluminum

    NASA Technical Reports Server (NTRS)

    Hatamleh, Omar; Lyons, Jed; Forman, Royce

    2006-01-01

    The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening conditions with different intensities, durations, and peening order were tested to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using laser peening compared to shot peened versus their native welded specimens.

  11. The impact of regular physical activity on fatigue, depression and quality of life in persons with multiple sclerosis

    PubMed Central

    Stroud, Nicole M; Minahan, Clare L

    2009-01-01

    Background The purpose of this study was to compare fatigue, depression and quality of life scores in persons with multiple sclerosis who do (Exercisers) and do not (Non-exercisers) regularly participate in physical activity. Methods A cross-sectional questionnaire study of 121 patients with MS (age 2565 yr) living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of life were assessed using the International Physical Activity Questionnaire, Health Status Questionnaire Short Form 36, Becks Depression Inventory and Modified Fatigue Impact Scale. Results 52 participants performed at least two 30-min exercise sessionswk-1 (Exercisers) and 69 did not participate in regular physical activity (Non-exercisers). Exercisers reported favourable fatigue, depression and quality of life scores when compared to Non-exercisers. Significant weak correlations were found between both leisure-time and overall reported physical activity levels and some subscales of the quality of life and fatigue questionnaires. Additionally, some quality of life subscale scores indicated that regular physical activity had a greater benefit in subjects with moderate MS. Conclusion Favourable fatigue, depression and quality of life scores were reported by persons with MS who regularly participated in physical activity, when compared to persons with MS who were classified as Non-exercisers. PMID:19619337

  12. 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.

  13. 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.

  14. A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

    NASA Astrophysics Data System (ADS)

    Sun, Chengqi; Liu, Xiaolong; Hong, Youshi

    2015-06-01

    In this paper, ultrasonic (20 kHz) fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue (VHCF) regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area (FGA) centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.

  15. Fatigue-Life Computational Analysis for the Self-Expanding Endovascular Nitinol Stents

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Pandurangan, B.; Arakere, A.; Snipes, J. S.

    2012-11-01

    Self-expanding endovascular stents made of Nitinol (a Ni-Ti intermetallic compound possessing superelastic and shape-memory properties) are being widely used to treat a common circulatory problem in which narrowed arteries, primarily due to fatty deposits, hamper blood flow to the extremities (the problem commonly referred to as "peripheral artery disease"). The stents of this type unfortunately occasionally fail structurally (and, in turn, functionally) rendering the stenting procedure ineffective. The failure is most often attributed to the fatigue-induced damage since over its expected ten-year life span, the stent will normally experience 370-400 million pulsating-blood flow-induced loading cycles. Redesign/redevelopment of the stents using the conventional make-and-test approaches is quite expensive and time consuming and therefore is being increasingly complemented by computational engineering methods and tools. In the present study, advanced structural and fluid-structure interaction finite element computational methods are combined with the advanced fatigue-based durability analysis techniques to further enhance the use of the computational engineering analysis tools in the development of vascular stents with improved high-cycle fatigue life.

  16. Fatigue life of high-speed ball bearings with silicon nitride balls

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Zaretsky, E. V.

    1974-01-01

    Hot-pressed silicon nitride was evaluated as a rolling-element bearing material. The five-ball fatigue tester was used to test 12.7-mm- diameter silicon nitride balls at maximum Hertz stresses ranging from 4.27 x 10 to the 9th power n/sq m to 6.21 x 10 to the 9th power n/sq m at a race temperature of 328K. The fatigue life of NC-132 hot-pressed silicon nitride was found to be equal to typical bearing steels and much greater than other ceramic or cermet materials at the same stress levels. A digital computer program was used to predict the fatigue life of 120-mm- bore angular-contact ball bearings containing either steel or silicon nitride balls. The analysis indicates that there is no improvement in the lives of bearings of the same geometry operating at DN values from 2 to 4 million where silicon nitride balls are used in place of steel balls.

  17. A generalized fitting technique for the LIFE2 fatigue analysis code

    SciTech Connect

    Sutherland, H.J.; Wilson, T.

    1996-08-01

    The analysis of component fatigue lifetime for a wind energy conversion system (WECS) requires that the component load spectrum be formulated in terms of stress cycles. Typically, these stress cycles are obtained from time series data using a cycle identification scheme. As discussed by many authors, the matrix or matrices of cycle counts that describe the stresses on a turbine are constructed from relatively short, representative samples of time series data. The ability to correctly represent the long-term behavior of the distribution of stress cycles from these representative samples is critical to the analysis of service lifetimes. Several techniques are currently used to convert representative samples to the lifetime cyclic loads on the turbine. There has been recently developed a set of fitting algorithms that is particularly useful for matching the body of the distribution of fatigue stress cycles on a turbine component. Fitting techniques are now incorporated into the LIFE2 fatigue/fracture analysis code for wind turbines. In this paper, the authors provide an overview of the fitting algorithms and describe the pre- and post-count algorithms developed to permit their use in the LIFE2 code. Typical case studies are used to illustrate the use of the technique.

  18. Deep surface rolling for fatigue life enhancement of laser clad aircraft aluminium alloy

    NASA Astrophysics Data System (ADS)

    Zhuang, W.; Liu, Q.; Djugum, R.; Sharp, P. K.; Paradowska, A.

    2014-11-01

    Deep surface rolling can introduce deep compressive residual stresses into the surface of aircraft metallic structure to extend its fatigue life. To develop cost-effective aircraft structural repair technologies such as laser cladding, deep surface rolling was considered as an advanced post-repair surface enhancement technology. In this study, aluminium alloy 7075-T651 specimens with a blend-out region were first repaired using laser cladding technology. The surface of the laser cladding region was then treated by deep surface rolling. Fatigue testing was subsequently conducted for the laser clad, deep surface rolled and post-heat treated laser clad specimens. It was found that deep surface rolling can significantly improve the fatigue life in comparison with the laser clad baseline repair. In addition, three dimensional residual stresses were measured using neutron diffraction techniques. The results demonstrate that beneficial compressive residual stresses induced by deep surface rolling can reach considerable depths (more than 1.0 mm) below the laser clad surface.

  19. The Surface Fatigue Life of Contour Induction Hardened AISI 1552 Gears

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.; Turza, Alan; Chaplin, Mike

    1995-01-01

    Two groups of spur gears manufactured from two different materials and heat treatments were endurance tested for surface fatigue life. One group was manufactured from AISI 1552 and was finished ground to a 0.4 micron (16 micro-in.) rms surface finish and then dual frequency contour induction hardened. The second group was manufactured from CEVM AISI 9310 and was carburized, hardened, and ground to a 0.4 micron (16 micro-in.) rms surface finish. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a maximum Hertz stress of 1.71 GPa (248 ksi), a bulk gear temperature of approximately 350 K (170 F) and a speed of 10,000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The test results showed that the 10 percent surface fatigue (pitting) life of the contour hardened AISI 1552 test gears was 1.7 times that of the carburized and hardened AISI 9310 test gears. Also there were two early failures of the AISI 1552 gears by bending fatigue.

  20. The surface fatigue life of contour induction hardened AISI 1552 gears

    NASA Astrophysics Data System (ADS)

    Townsend, Dennis P.; Turza, Alan; Chaplin, Mike

    1995-07-01

    Two groups of spur gears manufactured from two different materials and heat treatments were endurance tested for surface fatigue life. One group was manufactured from AISI 1552 and was finished ground to a 0.4 micron (16 micro-in.) rms surface finish and then dual frequency contour induction hardened. The second group was manufactured from CEVM AISI 9310 and was carburized, hardened, and ground to a 0.4 micron (16 micro-in.) rms surface finish. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a maximum Hertz stress of 1.71 GPa (248 ksi), a bulk gear temperature of approximately 350 K (170 F) and a speed of 10,000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The test results showed that the 10 percent surface fatigue (pitting) life of the contour hardened AISI 1552 test gears was 1.7 times that of the carburized and hardened AISI 9310 test gears. Also there were two early failures of the AISI 1552 gears by bending fatigue.

  1. Effects of High-Temperature Exposures on the Fatigue Life of Superalloy Udimet(Registered Trademark) 720

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Kantzos, Peter T.; Sweeney, Joseph W.; Browning, Paul F.

    2002-01-01

    The purpose of this study was to examine the effects of extended exposures on the near-surface fatigue resistance of a disk superalloy. Powder metallurgy processed, supersolvus heat-treated Udimet 720 (U720) fatigue specimens were exposed in air at temperatures from 650 to 705 C for 100 hr to over 1000 hr. They were then tested using conventional fatigue tests at 650 C to determine the effects of exposure on fatigue resistance. The exposures reduced life by up to 70% and increased the scatter in life, compared to unexposed levels. Fractographic evaluations indicated the failure mode was shifted by the exposures from internal to surface crack initiations. The increased scatter in life was related to the competition between internal crack initiations at inclusions or large grains producing longer lives, and surface crack initiations at an environmentally affected surface layer producing shorter lives.

  2. Effect of double vacuum melting and retained austenite on rolling-element fatigue life of AMS 5749 bearing steel

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Hodder, R. S.

    1977-01-01

    AMS 5749 steel combines the tempering, hot hardness, and hardness retention characteristics of AISI M-50 steel with the corrosion and oxidation resistance of AISI 440C stainless steel. The five-ball fatigue tester was used to evaluate the rolling-element fatigue life of AMS 5749. Double vacuum melting (vacuum induction melting plus vacuum arc remelting, VIM-VAR) produced AMS 5749 material with a rolling-element fatigue life at least 14 times that of vacuum induction melting alone. The VIM-VAR AMS 5749 steel balls gave lives from 6 to 12 times greater than VIM-VAR AISI M-50 steel balls. The highest level of retained austenite, 14.6 percent, was significantly detrimental to rolling-element fatigue life relative to the intermediate level of 11.1 percent.

  3. Discs low cycle fatigue life predictions for gas turbine engines in CSFR by using fractographic information

    NASA Astrophysics Data System (ADS)

    Statecny, Jiri; Drexler, Jan; Janak, Antonin

    Besides the conventional SL (Safe Life) philosophy for disk cyclic life predictions, the DT (Damage Tolerance) philosophy starts to be used in connection with the RFC (Retirement for Cause) strategy. The present paper is aimed especially at the certification demonstrations proofs. The use of advanced life prediction approaches is quite dependent on a reliable NDIT (Nondestructive Inspection Technique). Therefore the reliability of the information gained by NDI macrographic findings during the LCF (Low Cycle Fatigue) tests must be verified by micrographic analysis of the failed components. The approach used in ARTI and some experience from tests are presented. Several models have been developed in ARTI in recent years as a means for life prediction on a probabilistic basis. A new one is presented which may be useful for disks with critical circumferentially shaped concentrators.

  4. One-Year Longitudinal Study of Fatigue, Cognitive Functions, and Quality of Life After Adjuvant Radiotherapy for Breast Cancer

    SciTech Connect

    Noal, Sabine; Levy, Christelle; Hardouin, Agnes; Rieux, Chantal; Heutte, Natacha; Segura, Carine; Collet, Fabienne; Allouache, Djelila; Switsers, Odile; Delcambre, Corinne; Delozier, Thierry; Henry-Amar, Michel; Joly, Florence

    2011-11-01

    Purpose: Most patients with localized breast cancer (LBC) who take adjuvant chemotherapy (CT) complain of fatigue and a decrease in quality of life during or after radiotherapy (RT). The aim of this longitudinal study was to compare the impact of RT alone with that occurring after previous CT on quality of life. Methods and Materials: Fatigue (the main endpoint) and cognitive impairment were assessed in 161 CT-RT and 141 RT patients during RT and 1 year later. Fatigue was assessed with Functional Assessment of Cancer Therapy-General questionnaires, including breast and fatigue modules. Results: At baseline, 60% of the CT-RT patients expressed fatigue vs. 33% of the RT patients (p <0.001). Corresponding values at the end of RT were statistically similar (61% and 53%), and fatigue was still reported at 1 year by more than 40% of patients in both groups. Risk factors for long-term fatigue included depression (odds ratio [OR] = 6), which was less frequent in the RT group at baseline (16% vs. 28 %, respectively, p = 0.01) but reached a similar value at the end of RT (25% in both groups). Initial mild cognitive impairments were reported by RT (34 %) patients and CT-RT (24 %) patients and were persistent at 1 year for half of them. No biological disorders were associated with fatigue or cognitive impairment. Conclusions: Fatigue was the main symptom in LBC patients treated with RT, whether they received CT previously or not. The correlation of persistent fatigue with initial depressive status favors administering medical and psychological programs for LBC patients treated with CT and/or RT, to identify and manage this main quality-of-life-related symptom.

  5. 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.

  6. A combined approach to buffet response analyses and fatigue life prediction

    NASA Astrophysics Data System (ADS)

    Jacobs, J. H.; Perez, R.

    1994-03-01

    Experimental measurement and neural network based prediction of wind tunnel model empennage random pressures are discussed. Artificially generated neural network power spectral densities of surface pressures are used to augment existing data and then load an elastic finite element model to obtain response spectra. Details on the use of actual response spectra from flight test data are also discussed. A random spectra fatigue method is described which effectively combines buffet and maneuver loads into a time series based on aircraft usage data. A peak-valley damage analysis procedure is employed to compute the aggregate fatigue life of the structure based on five combined load time series information. Applications of the method as a continual learning tool for buffet response spectra is elaborated.

  7. Fatigue life of silumin irradiated by high intensity pulsed electron beam

    NASA Astrophysics Data System (ADS)

    Konovalov, S. V.; Alsaraeva, K. V.; Gromov, V. E.; Ivanov, Yu F.

    2015-09-01

    The electron-beam processing of silumin, leading to the evolution of structure-phase state of its surface is carried out. It has been shown that this alloy is a multiphase material and contains, except an aluminum-based phase, the particles of intermetallic compounds of Al-Si- Fe-Mn. It is shown that electron beam treatment of the eutectic silumin surface increases the fatigue service life more than in 3.5 times. The analysis of structure-phase states modification of silumin subjected to electron beam treatment with the following fatigue loading up to the failure is carried out by methods of optical and scanning electron diffraction microscopy. Analysis of the surface layer structure revealed the sources of nucleation of submicrocracks. It is revealed that the large silicon plates located on the surface and in the subsurface layer are the most dangerous stress concentrators.

  8. 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.

  9. 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.

  10. Empirical modeling of environment-enhanced fatigue crack propagation in structural alloys for component life prediction. Final report

    SciTech Connect

    Richey, E. III

    1995-10-01

    This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The approach couples empirical modeling of environmental FCP with corrosion fatigue experiments. Three different computer models have been developed and incorporated in the DOS executable program. UVAFAS. A multiple power law model is available, and can fit a set of fatigue data to a multiple power law equation. A model has also been developed which implements the Wei and Landes linear superposition model, as well as an interpolative model which can be utilized to interpolate trends in fatigue behavior based on changes in loading characteristics (stress ratio, frequency, and hold times).

  11. Slow Crack Growth and Fatigue Life Prediction of Ceramic Components Subjected to Variable Load History

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama

    2001-01-01

    Present capabilities of the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in slow crack growth (SCG) type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, while for cyclic fatigue applications various types of repetitive constant amplitude loads can be accounted for. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as, for example, engine start up, shut down, and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that takes into account the change in material response with time. In this paper, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code, which has also been modified to have the ability of interfacing with commercially available FEA codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.

  12. Corrosion fatigue of high strength fastener materials in seawater. Final report

    SciTech Connect

    Tipton, D.G.

    1983-12-01

    Environmental effects can significantly reduce the fatigue life of metals. As such, corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L40 high strength steel blade-to-hub attachment bolt at the MOD-0A 200 kW wind turbine generator in Oahu, Hawaii prompted the current test program. Tests were undertaken to confirm the dramatic reduction of fatigue strength of AISI 41L40 in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials. AISI 41L40, 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 were fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.

  13. Dynamic Capacity and Surface Fatigue Life for Spur and Helical Gears

    NASA Technical Reports Server (NTRS)

    Coy, J. J.; Townsend, D. P.; Zaretsky, E. V.

    1975-01-01

    A mathematical model for surface fatigue life of gear, pinion, or entire meshing gear train is given. The theory is based on a previous statistical approach for rolling-element bearings. Equations are presented which give the dynamic capacity of the gear set. The dynamic capacity is the transmitted tangential load which gives a 90 percent probability of survival of the gear set for one million pinion revolutions. The analytical results are compared with test data for a set of AISI 9310 spur gears operating at a maximum Hertz stress of 1.71 billion N/sq m and 10,000 rpm. The theoretical life predictions are shown to be good when material constants obtained from rolling-element bearing tests were used in the gear life model.

  14. Dynamic capacity and surface fatigue life for spur and helical gears

    NASA Technical Reports Server (NTRS)

    Coy, J. J.; Townsend, D. P.; Zaretsky, E. V.

    1975-01-01

    A mathematical model for surface fatigue life of gear, pinion, or entire meshing gear train is given. The theory is based on the statistical approach used by Lundberg and Palmgren for rolling-element bearings. Also equations are presented which give the dynamic capacity of the gear set. The dynamic capacity is the transmitted tangential load which gives a 90 percent probability of survival of the gear set for one million pinion revolutions. The analytical results were compared with test data for a set of AISI 9310 spur gears operating at a maximum Hertz stress of 1.71 billion N per sq m (248,000 psi) and 10,000 rpm. The theoretical life predictions were very good when material constants obtained from rolling-element bearing tests were used in the gear life model.

  15. CARES/Life Ceramics Durability Evaluation Software Enhanced for Cyclic Fatigue

    NASA Technical Reports Server (NTRS)

    Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.

    1999-01-01

    The CARES/Life computer program predicts the probability of a monolithic ceramic component's failure as a function of time in service. The program has many features and options for materials evaluation and component design. It couples commercial finite element programs--which resolve a component's temperature and stress distribution--to reliability evaluation and fracture mechanics routines for modeling strength-limiting defects. The capability, flexibility, and uniqueness of CARES/Life have attracted many users representing a broad range of interests and has resulted in numerous awards for technological achievements and technology transfer. Recent work with CARES/Life was directed at enhancing the program s capabilities with regards to cyclic fatigue. Only in the last few years have ceramics been recognized to be susceptible to enhanced degradation from cyclic loading. To account for cyclic loads, researchers at the NASA Lewis Research Center developed a crack growth model that combines the Power Law (time-dependent) and the Walker Law (cycle-dependent) crack growth models. This combined model has the characteristics of Power Law behavior (decreased damage) at high R ratios (minimum load/maximum load) and of Walker law behavior (increased damage) at low R ratios. In addition, a parameter estimation methodology for constant-amplitude, steady-state cyclic fatigue experiments was developed using nonlinear least squares and a modified Levenberg-Marquardt algorithm. This methodology is used to give best estimates of parameter values from cyclic fatigue specimen rupture data (usually tensile or flexure bar specimens) for a relatively small number of specimens. Methodology to account for runout data (unfailed specimens over the duration of the experiment) was also included.

  16. Fatiguing exercise initiated later in life reduces incidence of fibrillation and improves sleep quality in Drosophila.

    PubMed

    Zheng, Lan; Feng, Yue; Wen, Deng Tai; Wang, Hui; Wu, Xiu Shan

    2015-08-01

    As the human body ages, the risk of heart disease and stroke greatly increases. While there is evidence that lifelong exercise is beneficial to the heart's health, the effects of beginning exercise later in life remain unclear. This study aimed to investigate whether exercise training started later in life is beneficial to cardiac aging in Drosophila. We examined 4-week-old wild-type virgin female flies that were exposed to exercise periods of either 1.5, 2.0, or 2.5 h per day, 5 days a week for 2 weeks. Using M-mode traces to analyze cardiac function by looking at parameters including heart rate, rhythmicity, systolic and diastolic diameter, and interval and fractional shortening, we found that cardiac function declined with age, shown by an increase in the number of fibrillation events and a decrease in fractional shortening. About 2.0 and 2.5 h of exercise per day displayed a reduced incidence of fibrillation events, and only physical exercise lasting 2.5-h period increased fractional shortening and total sleep time in Drosophila. These data suggested that training exercise needs to be performed for longer duration to exert physiological benefits for the aging heart. Additionally, climbing ability to assess the exercise-induced muscle fatigue was also measured. We found that 2.0 and 2.5 h of exercise caused exercise-induced fatigue, and fatiguing exercise is beneficial for cardiac and healthy aging overall. This study provides a basis for further study in humans on the impact of beginning an exercise regimen later in life on cardiac health. PMID:26206392

  17. Effect of Environmental Exposures on Fatigue Life of P/M Disk Superalloys

    NASA Technical Reports Server (NTRS)

    Draper, Susan

    2011-01-01

    As the temperature capability of Ni-base superalloy powder metallurgy disks is steadily increased, environmental resistance and protection of advanced nickel-based turbine disk components are becoming increasingly important. Localized surface hot corrosion attack and damage from oxidation have been shown to impair disk fatigue life and may eventually limit disk operating temperatures. NASA Research Announcement (NRA) contracts have been awarded to GE Aviation and Honeywell Aerospace to separately develop fatigue resistant metallic and ceramic coatings for corrosion resistance and the corrosion/fatigue results of selected coatings will be presented. The microstructural response of a bare ME3 disk superalloy has been evaluated for moderate (704 C) and aggressive (760-816 C) oxidizing exposures up to 2,020 hours. Cross section analysis reveals sub-surface damage (significant for aggressive exposures) that consists of Al2O3 "fingers", interfacial voids, a recrystallized precipitate-free layer and GB carbide dissolution. The effects of a Nichrome corrosion coating on this microstructural response will also be presented.

  18. Strength and fatigue life evaluation of composite laminate with embedded sensors

    NASA Astrophysics Data System (ADS)

    Rathod, Vivek T.; Hiremath, S. R.; Roy Mahapatra, D.

    2014-04-01

    Prognosis regarding durability of composite structures using various Structural Health Monitoring (SHM) techniques is an important and challenging topic of research. Ultrasonic SHM systems with embedded transducers have potential application here due to their instant monitoring capability, compact packaging potential toward unobtrusiveness and noninvasiveness as compared to non-contact ultrasonic and eddy current techniques which require disassembly of the structure. However, embedded sensors pose a risk to the structure by acting as a flaw thereby reducing life. The present paper focuses on the determination of strength and fatigue life of the composite laminate with embedded film sensors like CNT nanocomposite, PVDF thin films and piezoceramic films. First, the techniques of embedding these sensors in composite laminates is described followed by the determination of static strength and fatigue life at coupon level testing in Universal Testing Machine (UTM). Failure mechanisms of the composite laminate with embedded sensors are studied for static and dynamic loading cases. The coupons are monitored for loading and failure using the embedded sensors. A comparison of the performance of these three types of embedded sensors is made to study their suitability in various applications. These three types of embedded sensors cover a wide variety of applications, and prove to be viable in embedded sensor based SHM of composite structures.

  19. Fatigue life prediction of liquid rocket engine combustor with subscale test verification

    NASA Astrophysics Data System (ADS)

    Sung, In-Kyung

    Reusable rocket systems such as the Space Shuttle introduced a new era in propulsion system design for economic feasibility. Practical reusable systems require an order of magnitude increase in life. To achieve this improved methods are needed to assess failure mechanisms and to predict life cycles of rocket combustor. A general goal of the research was to demonstrate the use of subscale rocket combustor prototype in a cost-effective test program. Life limiting factors and metal behaviors under repeated loads were surveyed and reviewed. The life prediction theories are presented, with an emphasis on studies that used subscale test hardware for model validation. From this review, low cycle fatigue (LCF) and creep-fatigue interaction (ratcheting) were identified as the main life limiting factors of the combustor. Several life prediction methods such as conventional and advanced viscoplastic models were used to predict life cycle due to low cycle thermal stress, transient effects, and creep rupture damage. Creep-fatigue interaction and cyclic hardening were also investigated. A prediction method based on 2D beam theory was modified using 3D plate deformation theory to provide an extended prediction method. For experimental validation two small scale annular plug nozzle thrusters were designed, built and tested. The test article was composed of a water-cooled liner, plug annular nozzle and 200 psia precombustor that used decomposed hydrogen peroxide as the oxidizer and JP-8 as the fuel. The first combustor was tested cyclically at the Advanced Propellants and Combustion Laboratory at Purdue University. Testing was stopped after 140 cycles due to an unpredicted failure mechanism due to an increasing hot spot in the location where failure was predicted. A second combustor was designed to avoid the previous failure, however, it was over pressurized and deformed beyond repair during cold-flow test. The test results are discussed and compared to the analytical and numerical predictions. A detailed comparison was not performed, however, due to the lack of test data resulting from a failure of the test article. Some theoretical and experimental aspects such as fin effect and round corner were found to reduce the discrepancy between prediction and test results.

  20. Multifrequency Eddy Current Inspection of Corrosion in Clad Aluminum Riveted Lap Joints and Its Effect on Fatigue Life

    NASA Astrophysics Data System (ADS)

    Okafor, A. C.; Natarajan, S.

    2007-03-01

    Aging aircraft are prone to corrosion damage and fatigue cracks in riveted lap joints of fuselage skin panels. This can cause catastrophic failure if not detected and repaired. Hence detection of corrosion damage and monitoring its effect on structural integrity are essential. This paper presents multifrequency eddy current (EC) inspection of corrosion damage and machined material loss defect in clad A1 2024-T3 riveted lap joints and its effect on fatigue life. Results of eddy current inspection, corrosion product removal and fatigue testing are presented.

  1. Machine for use in monitoring fatigue life for a plurality of elastomeric specimens

    NASA Technical Reports Server (NTRS)

    Fitzer, G. E. (inventor)

    1977-01-01

    An improved machine is described for use in determining the fatigue life for elastomeric specimens. The machine is characterized by a plurality of juxtaposed test stations, specimen support means located at each of the test stations for supporting a plurality of specimens of elastomeric material, and means for subjecting the specimens at each of said stations to sinusoidal strain at a strain rate unique with respect to the strain rate at which the specimens at each of the other stations is subjected to sinusoidal strain.

  2. Fatigue Life Prediction Based on Local Strain Energy for Healed Copper Film by Laser Irradiation

    NASA Astrophysics Data System (ADS)

    Liu, Feng-Zhu; Shang, De-Guang; Ren, Chong-Gang; Sun, Yu-Juan

    2016-02-01

    Changes of total cyclic strain energy at the notch for copper film specimen were analyzed before and after laser irradiation treatment. The results showed that laser irradiation can increase total cyclic strain energy and the effect of increase is more evident for the damaged copper specimen. Based on the damage-healing mechanism, an enhancement parameter and a healing parameter were defined by the local cyclic strain energy. A new model based on local strain energy was proposed to predict residual fatigue life for the damaged copper film specimen after laser irradiation. The predicted results by the proposed model agree well with the experimental lives.

  3. Advanced Failure Determination Measurement Techniques Used in Thermal Fatigue Life Testing of Electronic Packaging

    NASA Technical Reports Server (NTRS)

    Wallace, A. P.; Cornford, S. L.; Gross, M. A.

    1996-01-01

    Thermal fatigue life testing of various electronic packaging technologies is being performed by the Reliability Technology Group at the Jet Propulsion Laboratory. These testing efforts are in progress to improve uderstanding of the reliability issues associated with low volume packaging technologies for space applications and to develop qualification and acceptance approaches for these technologies. The work described here outlines the electrical failure detection techniques used during testing by documenting the circuits and components used to make these measurements, the sensitivity of the measurements, and the applicability of each specific measurement.

  4. Creep fatigue life prediction for engine hot section materials (isotropic): Fourth year progress review

    NASA Technical Reports Server (NTRS)

    Nelson, Richard S.; Schoendorf, John F.

    1986-01-01

    As gas turbine technology continues to advance, the need for advanced life prediction methods for hot section components is becoming more and more evident. The complex local strain and temperature histories at critical locations must be accurately interpreted to account for the effects of various damage mechanisms (such as fatigue, creep, and oxidation) and their possible interactions. As part of the overall NASA HOST effort, this program is designed to investigate these fundamental damage processes, identify modeling strategies, and develop practical models which can be used to guide the early design and development of new engines and to increase the durability of existing engines.

  5. Ion bombardment effects on the fatigue life of stainless steel under simulated fusion first wall conditions

    SciTech Connect

    Kohse, G.; Harling, O.K.

    1983-01-01

    Pressurized tube specimens have been exposed to simultaneous multi-energy surface ion bombardment, fast neutron irradiation and stress and temperature cycling, in a simulation of a possible fusion reactor first wall environment. After ion bombardments equivalent to months-years of reactor operation and up to 30,000 cycles, no detrimental effects on post-irradiation fatigue life were found. The ion damage is found to enhance surface cracking, but this effect is limited to the several micron surface layer in which the ions are implanted.

  6. Effect of speed and press fit on fatigue life of roller-bearing inner-race contact

    NASA Technical Reports Server (NTRS)

    Coe, H. H.; Zaretsky, E. V.

    1985-01-01

    An analysis was performed to determine the effects of inner ring speed and press fit on the rolling element fatigue life of a roller bearing inner race contact. The effects of the resultant hoop and radial stresses on the principal stresses were considered. The maximum shear stresses below the Hertzian contact were determined for different conditions of inner ring speed, load, and geometry and were applied to a conventional ring life analysis. The race contact fatigue life was reduced by more than 90 percent for some conditions when speed and press fit were considered. The depth of the maximum shear stress remained virtually unchanged.

  7. 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.

  8. 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.

  9. Surface fatigue life and failure characteristics of EX-53, CBS 1000M, and AISI 9310 gear materials

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.

    1985-01-01

    Spur gear endurance tests and rolling-element surface fatigue tests are conducted to investigate EX-53 and CBS 1000M steels for use as advanced application gear materials, to determine their endurance characteristics, and to compare the results with the standard AISI 9310 gear material. The gear pitch diameter is 8.89 cm (3.50 in). Gear test conditions are an oil inlet temperature of 320 K (116 F), an oil outlet temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. Bench-type rolling-element fatigue tests are conducted at ambient temperature with a bar specimen speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa (700 ksi). The EX-53 test gears have a surface fatigue life of twice that of the AISI 9310 spur gears. The CBS 1000M test gears have a surface fatigue life of more than twice that of the AISI 9310 spur gears. However, the CBS 1000M gears experience a 30-percent tooth fracture failure which limits its use as a gear material. The rolling-contact fatigue lines of RC bar specimens of EX-53 and ASISI 9310 are approximately equal. However, the CBS 1000M RC specimens have a surface fatigue life of about 50 percent that of the AISI 9310.

  10. Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part II: Fatigue Life and Fracture Behavior

    NASA Astrophysics Data System (ADS)

    Prasad Reddy, G. V.; Sandhya, R.; Sankaran, S.; Mathew, M. D.

    2014-10-01

    Influence of nitrogen content on low cycle fatigue life and fracture behavior of 316LN stainless steel (SS) alloyed with 0.07 to 0.22 wt pct nitrogen is presented in this paper over a range of total strain amplitudes ( 0.25 to 1.0 pct) in the temperature range from 773 K to 873 K (500 C to 600 C). The combined effect of nitrogen and strain amplitude on fatigue life is observed to be complex i.e., fatigue life either decreases/increases with increase in nitrogen content or saturates/peaks at 0.14 wt pct N depending on strain amplitude and temperature. Coffin-Manson plots (CMPs) revealed both single-slope and dual-slope strain-life curves depending on the test temperature and nitrogen content. 316LN SS containing 0.07 and 0.22 wt pct N showed nearly single-slope CMP at all test temperatures, while 316LN SS with 0.11 and 0.14 wt pct N exhibited marked dual-slope behavior at 773 K (500 C) that changes to single-slope behavior at 873 K (600 C). The changes in slope of CMP are found to be in good correlation with deformation substructural changes.

  11. The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

    NASA Astrophysics Data System (ADS)

    Winter, L.; Morgenstern, R.; Hockauf, K.; Lampke, T.

    2016-03-01

    In this work the mean stress influence on the high cycle fatigue behavior of the plasma electrolytic oxidized (PEO) 6082 aluminum alloy (AlSi1MgMn) is investigated. The present study is focused on the fatigue life time and the susceptibility of fatigue-induced cracking of the oxide coating and their dependence on the applied mean stress. Systematic work is done comparing conditions with and without PEO treatment, which have been tested using three different load ratios. For the uncoated substrate the cycles to failure show a significant dependence on the mean stress, which is typical for aluminum alloys. With increased load ratio and therefore increased mean stress, the fatigue strength decreases. The investigation confirms the well-known effect of PEO treatment on the fatigue life: The fatigue strength is significantly reduced by the PEO process, compared to the uncoated substrate. However, also the mean stress sensitivity of the fatigue performance is reduced. The fatigue limit is not influenced by an increasing mean stress for the PEO treated conditions. This effect is firstly shown in these findings and no explanation for this effect can be found in literature. Supposedly the internal compressive stresses and the micro-cracks in the oxide film have a direct influence on the crack initiation and growth from the oxide film through the interface and in the substrate. Contrary to these findings, the susceptibility of fatigue-induced cracking of the oxide coating is influenced by the load ratio. At tension-tension loading a large number of cracks, which grow partially just in the aluminum substrate, are present. With decreasing load ratio to alternating tension-compression stresses, the crack number and length increases and shattering of the oxide film is more pronounced due to the additional effective compressive part of the load cycle.

  12. Oxidation and the Effects of High Temperature Exposures on Notched Fatigue Life of an Advanced Powder Metallurgy Disk Superalloy

    NASA Technical Reports Server (NTRS)

    Sudbrack, Chantal K.; Draper, Susan L.; Gorman, Timothy T.; Telesman, Jack; Gab, Timothy P.; Hull, David R.

    2012-01-01

    Oxidation and the effects of high temperature exposures on notched fatigue life were considered for a powder metallurgy processed supersolvus heat-treated ME3 disk superalloy. The isothermal static oxidation response at 704 C, 760 C, and 815 C was consistent with other chromia forming nickel-based superalloys: a TiO2-Cr2O3 external oxide formed with a branched Al2O3 internal subscale that extended into a recrystallized - dissolution layer. These surface changes can potentially impact disk durability, making layer growth rates important. Growth of the external scales and dissolution layers followed a cubic rate law, while Al2O3 subscales followed a parabolic rate law. Cr- rich M23C6 carbides at the grain boundaries dissolved to help sustain Cr2O3 growth to depths about 12 times thicker than the scale. The effect of prior exposures was examined through notched low cycle fatigue tests performed to failure in air at 704 C. Prior exposures led to pronounced debits of up to 99 % in fatigue life, where fatigue life decreased inversely with exposure time. Exposures that produced roughly equivalent 1 m thick external scales at the various isotherms showed statistically equivalent fatigue lives, establishing that surface damage drives fatigue debit, not exposure temperature. Fractographic evaluation indicated the failure mode for the pre-exposed specimens involved surface crack initiations that shifted with exposure from predominately single intergranular initiations with transgranular propagation to multi-initiations from the cracked external oxide with intergranular propagation. Weakened grain boundaries at the surface resulting from the M23C6 carbide dissolution are partially responsible for the intergranular cracking. Removing the scale and subscale while leaving a layer where M23C6 carbides were dissolved did not lead to a significant fatigue life improvement, however, also removing the M23C6 carbide dissolution layer led to nearly full recovery of life, with a transgranular initiation typical to that observed in unexposed specimens.

  13. Life prediction of thermomechanical fatigue using total strain version of strainrange partitioning (SRP): A proposal

    NASA Technical Reports Server (NTRS)

    Saltsman, James F.; Halford, Gary R.

    1988-01-01

    A method is proposed (without experimental verification) for extending the total strain version of Strainrange Partitioning (TS-SRP) to predict the lives of thermomechanical fatigue (TMF) cycles. The principal feature of TS SRP is the determination of the time-temperature-waveshape dependent elastic strainrange versus life lines that are added subsequently to the classical inelastic strainrange versus life lines to form the total strainrange versus life relations. The procedure is based on a derived relation between failure and flow behavior. Failure behavior is represented by conventional SRP inelastic strainrange versus cyclic life relations, while flow behavior is captured in terms of the cyclic stress-strain response characteristics. Stress-strain response is calculated from simple equations developed from approximations to more complex cyclic constitutive models. For applications to TMF life prediction, a new testing technique, bithermal cycling, is proposed as a means for generating the inelastic strainrange versus life relations. Flow relations for use in predicting TMF lives would normally be obtained from approximations to complex thermomechanical constitutive models. Bithermal flow testing is also proposed as an alternative to thermomechanical flow testing at low strainranges where the hysteresis loop is difficult to analyze.

  14. Overview of the fatigue/fracture/life working group program at the Lewis Research Center

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1989-01-01

    Constitutive and life prediction models are developed and verified for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operating environments. The efforts were centered on the development of crack initiation life prediction methods, while the efforts of a counterpart group were centered on the development of cyclic crack propagation life prediction methods. The complexion of the active tasks are presented. A significant new task started this year will incorporate the various material constitutive and life prediction models developed in this program into a comprehensive creep-fatigue damage analysis and life assessment computer code. The program will function as a postprocessor to general structural analysis programs (such as finite element or boundary element codes) using the output of such analyses (stress, strain, and temperature fields as functions of time) as the input to the damage analysis and life assessment code. The code will be designed to execute on engineering/scientific workstations and will feature a windowing, mouse-driven user interface. Current plans call for the code to be finished and made available for use in mid 1991.

  15. Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop

    PubMed Central

    Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo

    2013-01-01

    Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

  16. Fatigue and life prediction for cobalt-chromium stents: A fracture mechanics analysis.

    PubMed

    Marrey, Ramesh V; Burgermeister, Robert; Grishaber, Randy B; Ritchie, R O

    2006-03-01

    To design against premature mechanical failure, most implant devices such as coronary and endovascular stents are assessed on the basis of survival, i.e., if a fatigue life of 10(8) cycles is required, testing is performed to ascertain whether the device will survive 10(8) cycles under accelerated in vitro loading conditions. This is a far from satisfactory approach as the safety factors, which essentially tell you how close you are to failure, remain unknown; rather, the probability of fatigue failure should instead be assessed on the basis of testing to failure. In this work, a new damage-tolerant analysis of a cardiovascular stent is presented, where the design life is conservatively evaluated using a fracture mechanics methodology. In addition to enabling estimates of safe in vivo lifetimes to be made, this approach serves to quantify the effect of flaws in terms of their potential effect on device failure, and as such provides a rational basis for quality control. PMID:16260033

  17. Fatigue Life of Lead Free Solder BGA Joints Against Vibration Stress under High Temperature Circumstance

    NASA Astrophysics Data System (ADS)

    Matsushima, Michiya; Furusawa, Takeshi; Fukuda, Kyohei; Egusa, Minoru; Yasuda, Kiyokazu; Fujimoto, Kozo

    Recently, the wave of car computerizing is surging such as electronic control unit, car navigation system, electronic toll collection system, car to car communication system, etc. The use environment of in-car devices is under combined environmental stresses such as thermal stress, vibration, and humidity. In general, the reliability of the joints of the devices is individually tested by the evaluation methods for each stress. Our main purpose of this study is to construct the evaluation method for the damages of solder joints under multiple environmental stresses. We investigated the relationship between the plastic strain caused by one cycle vibration stress calculated with FEM analysis considering the temperature dependency of the elasto-plasticity and the fatigue life obtained by the vibration experiment. We indicated the adequacy of the analysis by the correspondence of the resonance frequency of the BGA package mounting board with the experimental result. We also showed that the plastic strain concentrating position corresponded to the crack position. We clarified that the creep strain rate in the total strain was less than 1 percent. We demonstrated that we could apply the power-law equation to predict the fatigue life of the vibration stress from plastic strain rate under 80C and 125C as well as the room temperature.

  18. 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.

  19. Fatigue Life Assessment of Structures Using Electro-Mechanical Impedance Technique

    NASA Astrophysics Data System (ADS)

    Bhalla, S.

    2012-05-01

    This paper describes a new experimental approach for fatigue life assessment of structures based on the equivalent stiffness determined by surface bonded piezo-impedance transducers through the electro-mechanical impedance (EMI) technique. The remaining life of the component (in terms of the cycles of loading that can be sustained) is non-dimensionally correlated with the equivalent identified stiffness. The proposed approach circumvents the determination of the absolute stiffness of the joint and employs the admittance signature of the surface-bonded piezo-transducers directly. The second part of the paper briefly describes the recent advances made in the field of impedance based structural health monitoring (SHM) in terms of low-cost hardware system and improved damage diagnosis through the integration of global dynamic and EMI techniques using the same set of piezo-sensors. Other recent applications such as bio-sensors and traffic sensors pioneered at the Smart Structures and Dynamics Laboratory (SSDL) are also briefly covered.

  20. Fatigue mechanics - An assessment of a unified approach to life prediction

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Phillips, E. P.; Swain, M. H.; Everett, R. A., Jr.

    1992-01-01

    Consideration is given to the development of a total-life prediction methodology for aerospace structures based solely on crack propagation from a microstructural defect at stress concentrations. Crack-growth lives were calculated for a given loading condition by integrating the crack-growth-rate-against-delta K relationships for crack growth from a microstructural defect size to failure. Both small- and large-crack growth rate data were used. The assessment was based on data on 2024-T3 aluminum alloy, 2090-T8E41 aluminum-lithium alloy, annealed Ti-6Al-4V titanium alloy, and high-strength 4340 steel under either constant-amplitude or spectrum loading. Good agreement was found between fatigue lives measured on notched specimens with those computed from the total-life analysis.

  1. 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.

  2. Uniaxial and Multiaxial Fatigue Life Prediction of the Trabecular Bone Based on Physiological Loading: A Comparative Study.

    PubMed

    Fatihhi, S J; Harun, M N; Abdul Kadir, Mohammed Rafiq; Abdullah, Jaafar; Kamarul, T; Öchsner, Andreas; Syahrom, Ardiyansyah

    2015-10-01

    Fatigue assessment of the trabecular bone has been developed to give a better understanding of bone properties. While most fatigue studies are relying on uniaxial compressive load as the method of assessment, in various cases details are missing, or the uniaxial results are not very realistic. In this paper, the effect of three different load histories from physiological loading applied on the trabecular bone were studied in order to predict the first failure surface and the fatigue lifetime. The fatigue behaviour of the trabecular bone under uniaxial load was compared to that of multiaxial load using a finite element simulation. The plastic strain was found localized at the trabecular structure under multiaxial load. On average, applying multiaxial loads reduced more than five times the fatigue life of the trabecular bone. The results provide evidence that multiaxial loading is dominated in the low cycle fatigue in contrast to the uniaxial one. Both bone volume fraction and structural model index were best predictors of failure (p < 0.05) in fatigue for both types of loading, whilst uniaxial loading has indicated better values in most cases. PMID:25828397

  3. Cable connected active tuned mass dampers for control of in-plane vibrations of wind turbine blades

    NASA Astrophysics Data System (ADS)

    Fitzgerald, B.; Basu, B.

    2014-11-01

    In-plane vibrations of wind turbine blades are of concern in modern multi-megawatt wind turbines. Today's turbines with capacities of up to 7.5 MW have very large, flexible blades. As blades have grown longer the increasing flexibility has led to vibration problems. Vibration of blades can reduce the power produced by the turbine and decrease the fatigue life of the turbine. In this paper a new active control strategy is designed and implemented to control the in-plane vibration of large wind turbine blades which in general is not aerodynamically damped. A cable connected active tuned mass damper (CCATMD) system is proposed for the mitigation of in-plane blade vibration. An Euler-Lagrangian wind turbine model based on energy formulation has been developed for this purpose which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations and also the interaction between the blades and the tower including the CCATMDs. The CCATMDs are located inside the blades and are controlled by an LQR controller. The turbine is subject to turbulent aerodynamic loading simulated using a modification to the classic Blade Element Momentum (BEM) theory with turbulence generated from rotationally sampled spectra. The turbine is also subject to gravity loading. The effect of centrifugal stiffening of the rotating blades has also been considered. Results show that the use of the proposed new active control scheme significantly reduces the in-plane vibration of large, flexible wind turbine blades.

  4. Low strain, long life creep fatigue of AF2-1DA and INCO 718

    SciTech Connect

    Thakker, A.B.; Cowles, B.A.

    1983-04-01

    Two aircraft turbine disk alloys, GATORIZED AF2-DA and INCO 718 were evaluated for their low strain long life creep-fatigue behavior. Static (tensile and creep rupture) and cyclic properties of both alloys were characterized. The cntrolled strain LCF tests were conducted at 760 C (1400 F) and 649 C (1200 F) for AF2-1DA and INCO 718, respectively. Hold times were varied for tensile, compressive and tensile/compressive strain dwell (relaxation) tests. Stress (creep) hold behavior of AF2-1DA was also evaluated. Generally, INCO 718 exhibited more pronounced reduction in cyclic life due to hold than AF2-1DA. The percent reduction in life for both alloys for strain dwell tests was greater at low strain ranges (longer life regime). Changing hold time from 0 to 0.5, 2.0 and 15.0 min. resulted in corresponding reductions in life. The continuous cycle and cyclic/dwell initiation failure mechanism was predominantly transgranular for AF2-1DA and intergranular for INCO 718.

  5. Low strain, long life creep fatigue of AF2-1DA and INCO 718

    NASA Technical Reports Server (NTRS)

    Thakker, A. B.; Cowles, B. A.

    1983-01-01

    Two aircraft turbine disk alloys, GATORIZED AF2-DA and INCO 718 were evaluated for their low strain long life creep-fatigue behavior. Static (tensile and creep rupture) and cyclic properties of both alloys were characterized. The cntrolled strain LCF tests were conducted at 760 C (1400 F) and 649 C (1200 F) for AF2-1DA and INCO 718, respectively. Hold times were varied for tensile, compressive and tensile/compressive strain dwell (relaxation) tests. Stress (creep) hold behavior of AF2-1DA was also evaluated. Generally, INCO 718 exhibited more pronounced reduction in cyclic life due to hold than AF2-1DA. The percent reduction in life for both alloys for strain dwell tests was greater at low strain ranges (longer life regime). Changing hold time from 0 to 0.5, 2.0 and 15.0 min. resulted in corresponding reductions in life. The continuous cycle and cyclic/dwell initiation failure mechanism was predominantly transgranular for AF2-1DA and intergranular for INCO 718.

  6. Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components

    NASA Technical Reports Server (NTRS)

    Ko, W. L.; Carter, A. L.; Totton, W. W.; Ficke, J. M.

    1989-01-01

    Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels.

  7. A high temperature fatigue life prediction computer code based on the total strain version of StrainRange Partitioning (SRP)

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.; Saltsman, James F.

    1993-01-01

    A recently developed high-temperature fatigue life prediction computer code is presented and an example of its usage given. The code discussed is based on the Total Strain version of Strainrange Partitioning (TS-SRP). Included in this code are procedures for characterizing the creep-fatigue durability behavior of an alloy according to TS-SRP guidelines and predicting cyclic life for complex cycle types for both isothermal and thermomechanical conditions. A reasonably extensive materials properties database is included with the code.

  8. Microstructural Influence on Deformation and Fatigue Life of Composites Using the Generalized Method of Cells

    NASA Technical Reports Server (NTRS)

    Arnold, S. M.; Murthy, P.; Bednarcyk, B. A.; Pineda, E. J.

    2015-01-01

    A fully coupled deformation and damage approach to modeling the response of composite materials and composite laminates is presented. It is based on the semi-­-analytical generalized method of cells (GMC) micromechanics model as well as its higher fidelity counterpart, HFGMC, both of which provide closed-form constitutive equations for composite materials as well as the micro scale stress and strain fields in the composite phases. The provided constitutive equations allow GMC and HFGMC to function within a higher scale structural analysis (e.g., finite element analysis or lamination theory) to represent a composite material point, while the availability of the micro fields allow the incorporation of lower scale sub­-models to represent local phenomena in the fiber and matrix. Further, GMC's formulation performs averaging when applying certain governing equations such that some degree of microscale field accuracy is surrendered in favor of extreme computational efficiency, rendering the method quite attractive as the centerpiece in a integrated computational material engineering (ICME) structural analysis; whereas HFGMC retains this microscale field accuracy, but at the price of significantly slower computational speed. Herein, the sensitivity of deformation and the fatigue life of graphite/epoxy PMC composites, with both ordered and disordered microstructures, has been investigated using this coupled deformation and damage micromechanics based approach. The local effects of fiber breakage and fatigue damage are included as sub-models that operate on the microscale for the individual composite phases. For analysis of laminates, classical lamination theory is employed as the global or structural scale model, while GMC/HFGMC is embedded to operate on the microscale to simulate the behavior of the composite material within each laminate layer. A key outcome of this study is the statistical influence of microstructure and micromechanics idealization (GMC or HFGMC) on the overall accuracy of unidirectional and laminated composite deformation and fatigue response.

  9. Evaluation of effects of LWR coolant environments on fatigue life of carbon and low-alloy steels

    SciTech Connect

    Chopra, O.K.; Shack, W.J.

    1996-02-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figure I-90 of Appendix I to Section III of the Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Recent test data indicate a significant decrease in fatigue life of carbon and low-alloy steels in LWR environments when five conditions are satisfied simultaneously, viz., applied strain range, temperature, dissolved oxygen in the water, and sulfur content of the steel are above a minimum threshold level, and the loading strain rate is below a threshold value. Only a moderate decrease in fatigue life is observed when any one of these conditions is not satisfied. This paper summarizes available data on the effects of various material and loading variables such as steel type, dissolved oxygen level, strain range, strain rate, and sulfur content on the fatigue life of carbon and low-alloy steels. The data have been analyzed to define the threshold values of the five critical parameters. Methods for estimating fatigue lives under actual loading histories are discussed.

  10. Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

    NASA Technical Reports Server (NTRS)

    Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

    1998-01-01

    The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

  11. Pre-crack fatigue life assessment of relevant aircraft materials using fractal analysis of eddy current test data

    NASA Astrophysics Data System (ADS)

    Schreiber, Jrgen; Cikalova, Ulana; Hillmann, Susanne; Meyendorf, Norbert; Hoffmann, Jochen

    2013-01-01

    Successful determination of residual fatigue life requires a comprehensive understanding of the fatigue related material deformation mechanism. Neither macroscopic continuum mechanics nor micromechanic observations provide sufficient data to explain subsequent deformation structures occurring during the fatigue life of a metallic structure. Instead mesomechanic deformation on different scaling levels can be studied by applying fractal analysis of various means of nondestructive inspection measurements. The resulting fractal dimension data can be correlated to the actual material damage states, providing an estimation of the remaining residual fatigue life before macroscopic fracture develops. Recent efforts were aimed to apply the fractal concept to aerospace relevant materials AA7075-T6 and Ti-6Al-4V. Proven and newly developed fractal analysis methods were applied to eddy current (EC) measurements of fatigued specimens, with the potential to transition this approach to an aircraft for an in-situ nondestructive inspection. The occurrence of mesomechanic deformation at the material surface of both AA7075-T6 and Ti-6Al-4V specimens could be established via topography images using confocal microscopy (CM). Furthermore, a pulsed eddy current (PEC) approach was developed, combined with a sophisticated new fractal analysis algorithm based on short pulse excitation and evaluation of EC relaxation behavior. This paper presents concept, experimental realization, fractal analysis procedures, and results of this effort.

  12. Fatigue Life Prediction of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures. Part I: Experimental Analysis

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-05-01

    This paper presents an experimental analysis on the fatigue behavior in C/SiC ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply and 2.5D woven, at room and elevated temperatures in air atmosphere. The experimental fatigue life S - N curves of C/SiC composites corresponding to different stress levels and test conditions have been obtained. The damage evolution processes under fatigue loading have been analyzed using fatigue hysteresis modulus and fatigue hysteresis loss energy. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the interface shear stress corresponding to different peak stress, fiber preforms and test conditions have been estimated. It was found that the degradation of interface shear stress and fibres strength caused by oxidation markedly decreases the fatigue life of C/SiC composites at elevated temperature.

  13. Independent effect of fatigue on health-related quality of life in patients with idiopathic Parkinson's disease.

    PubMed

    Dogan, Vasfiye Burcu; Koksal, Ayhan; Dirican, Ayten; Baybas, Sevim; Dirican, Ahmet; Dogan, Gulsum Buse

    2015-12-01

    Nonmotor symptoms (NMS) of idiopathic Parkinson's disease (IPD), specifically fatigue, depression and sleep disturbances, are important contributors for worse quality of life and poor patient outcomes. The aim of this research is to determine the relationship between fatigue and other NMS and the independent effect of fatigue on health-related quality of life (HRQoL) in patients with IPD. 86 IPD patients and 85 healthy individuals were included in our study. Participants were evaluated by their answers to the Beck Depression Inventory, Fatigue Severity Scale, Epworth Sleepiness Scale and Parkinson's Disease Questionnaire-39. Hoehn-Yahr stage, disease duration, medications and demographical characteristics were also noted. ROC analysis was used to determine the cutoff point for HRQoL. Nonparametric Spearman correlation analysis was used for determining the relationship between variables. Independent factors which affect HRQoL were detected by multiple forward stepwise logistic regression analysis. NMS were associated with each other and with HRQoL when they act concomitantly (p<0.001). Of these three frequent NMS, depression (p<0.05) and fatigue (p<0.001) had independent worsening effect on HRQoL, whereas sleep disturbances did not (p>0.05). The stage of IPD and levodopa-entacapone treatment had independent effects on HRQoL too (p<0.05). Fatigue was found as the most important factor which affects HRQoL among all investigated NMS. So, it is important to ask about fatigue in routine controls of IPD patients and try to treat it for improving life quality. PMID:26198763

  14. 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.

  15. Effects of strain rate change on fatigue life of carbon steel in high-temperature water

    SciTech Connect

    Higuchi, Makoto; Iida, Kunihiro; Asada, Yasuhide

    1997-12-01

    In high temperature waters that contain dissolved oxygen (DO) to certain content, the fatigue life of carbon steel is strongly affected by strain rate. A formula has been advanced to quantify this effect when the strain rate is held constant. However, the strain rate changes continuously in most of transients of actual plant operation. There is no way currently to assess the effects of strain rate is varied as in the actual plant transients. To find a solution to this problem, a series of strain controlled fatigue tests have been conducted wit the strain rate changed stepwise or continuously. It is shown that a method, in which the product of the environmental effect and the strain increment within a unit time interval in a transient period is integrated from the minimum strain to the maximum, evaluates the environmental effect with satisfactorily high accuracy. This method is called the modified rate approach method. It is shown also that the procedure of taking the strain rate as averaged over the minimum to peak of the strain change as giving rise to more conservative evaluations than the ones the modified rate approach method produces.

  16. Fatigue life calculation of desuperheater for solving pipe cracking issue using finite element method (FEM) software

    NASA Astrophysics Data System (ADS)

    Kumar, Aravinda; Singh, Jeetendra Kumar; Mohan, K.

    2012-06-01

    Desuperheater assembly experiences thermal cycling in operation by design. During power plant's start up, load change and shut down, thermal gradient is highest. Desuperheater should be able to handle rapid ramp up or ramp down of temperature in these operations. With "hump style" two nozzle desuperheater, cracks were appearing in the pipe after only few cycles of operation. From the field data, it was clear that desuperheater is not able to handle disproportionate thermal expansion happening in the assembly during temperature ramp up and ramp down in operation and leading to cracks appearing in the piping. Growth of thermal fatigue crack is influenced by several factors including geometry, severity of thermal stress and applied mechanical load. This paper seeks to determine cause of failure of two nozzle "hump style" desuperheater using Finite Element Method (FEM) simulation technique. Thermal stress simulation and fatigue life calculation were performed using commercial FEA software "ANSYS" [from Ansys Inc, USA]. Simulation result showed that very high thermal stress is developing in the region where cracks are seen in the field. From simulation results, it is also clear that variable thermal expansion of two nozzle studs is creating high stress at the water manifold junction. A simple and viable solution is suggested by increasing the length of the manifold which solved the cracking issues in the pipe.

  17. Improvement in surface fatigue life of hardened gears by high-intensity shot peening

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.

    1992-01-01

    Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

  18. The Effect of Weld Profile and Geometries of Butt Weld Joints on Fatigue Life Under Cyclic Tensile Loading

    NASA Astrophysics Data System (ADS)

    Al-Mukhtar, A. M.; Biermann, H.; Hbner, P.; Henkel, S.

    2011-11-01

    The fatigue life of welded joint was calculated based on numerical integration of simple Paris' law and a reliable solution of the stress intensity factor (SIF). The initial crack length ( a i) was assumed to be equal to 0.1 mm in case of weld toe. This length was satisfactory for different butt joints geometries. The comparisons with the available data from standards and literature were demonstrated. It was shown numerically that the machining of weld reinforcements will increase the fatigue life. The increase of plate thickness decreases the fatigue strength (FAT) and the number of cycles to failure when using the proportional scaling of crack length. The validation processes of the current calculations have been shown. Therefore, it can be concluded that it will prevent the unnecessary waste of time consumed to carry out the experiments.

  19. Creep-Fatigue Life Prediction and Reliability Analysis of P91 Steel Based on Applied Mechanical Work Density

    NASA Astrophysics Data System (ADS)

    Ji, D. M.; Shen, M.-H. H.; Wang, D. X.; Ren, J. X.

    2015-01-01

    A creep-fatigue (CF) life prediction model and its simplified expression were developed based on the applied mechanical work density (AMWD). The foundation of this model was an integration of N- S curve. Comparisons of the model predicted fatigue lifetimes with the experimental data of load-controlled CF tests on P91 base metal and welded metal at 848 K from the reference were made and apparently illustrated that the model predictions were in a good agreement with the experimental fatigue lifetimes. In addition, the curve of the numbers of cycles to failure versus AMWD at the associated probability was deduced. A reliability model was constructed by combining the curve and the simplified life prediction model.

  20. Initial Assessment of the Effects of Nonmetallic Inclusions on Fatigue Life of Powder-Metallurgy-Processed Udimet(TM) 720

    NASA Technical Reports Server (NTRS)

    Gabb, T. P.; Telesman, J.; Kantzos, P. T.; Bonacuse, P. J.; Barrie, R. L.

    2002-01-01

    The fatigue lives of modern powder metallurgy (PM) disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary due to the different steps of materials/component processing and machining. One of these variables, the presence of nonmetallic inclusions, has been shown to significantly degrade low-cycle fatigue (LCF) life. Nonmetallic inclusions are inherent defects in powder alloys that are a by-product of powder-processing techniques. Contamination of the powder can occur in the melt, during powder atomization, or during any of the various handling processes through consolidation. In modern nickel disk powder processing facilities, the levels of inclusion contamination have been reduced to less than 1 part per million by weight. Despite the efforts of manufacturers to ensure the cleanliness of their powder production processes, the presence of inclusions remains a source of great concern for the designer. the objective of this study was to investigate the effects on fatigue life of these inclusions. Since natural inclusions occur so infrequently, elevated levels of inclusions were carefully introduced in a nickel-based disk superalloy, Udimet 720 (registered trademark of Special Metals Corporation), produced using PM processing. Multiple strain-controlled fatigue tests were then performed on this material at 650 C. Analyses were performed to compare the LCF lives and failure initiation sites as functions of inclusion content and fatigue conditions. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface. The inclusions could reduce fatigue life by up to 100 times. These effects were found to be dependent on strain range and strain ratio. Tests at lower strain ranges and higher strain ratios produced larger effects of inclusions on life.

  1. The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

    NASA Technical Reports Server (NTRS)

    Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.

    2001-01-01

    Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

  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. Fatigue life prediction for 6261-T6 aluminium alloy I-beams with welded cover plates

    NASA Astrophysics Data System (ADS)

    James, M. Neil; Lambrecht, H. O.; Paterson, A. E.

    1992-07-01

    The fatigue strength data were acquired in bend from some 50 extruded 6261 aluminum alloy I-beams with cover plates welded to them. The cover plates were rectangular, oval or rhomboid in shape with either welded or unwelded transverse ends. The data from stress range versus number of cycles diagrams (S-N diagrams) were compared with design curves from British Standard (BS) CP 118 : 1969 and BS 8118 Part 1 : 1991. An S-N diagram element analysis of a model cover plate/I beam geometry was linked with other growth rate data, to provide a life prediction S-N curve a Paris law integration. Good agreement was found between the results from the model and the experimental data.

  4. Fatigue life of anti-friction bearings subjected to cyclic loading

    SciTech Connect

    Dominik, W.K.

    1986-01-01

    Cyclic loading is defined as external loading that varies within the revolution of a bearing and is repeated for every revolution. The cyclicly varying loads may consist of a series of discrete loads that occur in a repeating pattern or a continuously varying force or a combination of these. A simple example of cyclic loading is a single cylinder, double acting piston pump in which the force on the bearings reverse every 180/sup 0/ of a revolution; as a result, the same half of the rotating bearing race passes under the load twice in a single revolution. More complex patterns of cyclic loads occur in rotary engines, fuel injection pumps, nutating engines, etc. The paper presents the theoretical relationships and methods that predict the effect of cyclic loading on the fatigue life of anti-friction bearings. An example problem solved with the aid of a special analysis program illustrates the results from these methods.

  5. Reliability approach to rotating-component design. [fatigue life and stress concentration

    NASA Technical Reports Server (NTRS)

    Kececioglu, D. B.; Lalli, V. R.

    1975-01-01

    A probabilistic methodology for designing rotating mechanical components using reliability to relate stress to strength is explained. The experimental test machines and data obtained for steel to verify this methodology are described. A sample mechanical rotating component design problem is solved by comparing a deterministic design method with the new design-by reliability approach. The new method shows that a smaller size and weight can be obtained for specified rotating shaft life and reliability, and uses the statistical distortion-energy theory with statistical fatigue diagrams for optimum shaft design. Statistical methods are presented for (1) determining strength distributions for steel experimentally, (2) determining a failure theory for stress variations in a rotating shaft subjected to reversed bending and steady torque, and (3) relating strength to stress by reliability.

  6. Surface fatigue life of CBN and vitreous ground carburized and hardened AISI 9310 spur gears

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.; Patel, P. R.

    1988-01-01

    Spur gear surface endurance tests were conducted to investigate CBN ground AISI 9310 spur gears for use in aircraft applications, to determine their endurance characteristics and to compare the results with the endurance of standard vitreous ground AISI 9310 spur gears. Tests were conducted with VIM-VAR AISI 9310 carburized and hardened gears that were finish ground with either CBN or vitreous grinding methods. Test conditions were an inlet oil temeprature of 320 K (116 F), an outlet oil temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. The CBN ground gears exhibited a surface fatigue life that was slightly better than the vitreous ground gears. The subsurface residual stress of the CBN ground gears was approximately the same as that for the standard vitreous ground gears for the CBN grinding method used.

  7. User`s guide for the frequency domain algorithms in the LIFE2 fatigue analysis code

    SciTech Connect

    Sutherland, H.J.; Linker, R.L.

    1993-10-01

    The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.

  8. 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.

  9. User's guide for the frequency domain algorithms in the LIFE2 fatigue analysis code

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.; Linker, R. L.

    1993-10-01

    The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.

  10. Fatigue life estimation program for Part 23 airplanes, `AFS.FOR`

    SciTech Connect

    Kaul, S.K.

    1993-12-31

    The purpose of this paper is to introduce to the general aviation industry a computer program which estimates the safe fatigue life of any Federal Aviation Regulation (FAR) Part 23 airplane. The algorithm uses the methodology (Miner`s Linear Cumulative Damage Theory) and the various data presented in the Federal Aviation Administration (FAA) Report No. AFS-120-73-2, dated May 1973. The program is written in FORTRAN 77 language and is executable on a desk top personal computer. The program prompts the user for the input data needed and provides a variety of options for its intended use. The program is envisaged to be released through issuance of a FAA report, which will contain the appropriate comments, instructions, warnings and limitations.

  11. Life prediction of expulsion bladders through fatigue test and fold strain analysis.

    NASA Technical Reports Server (NTRS)

    Chu, H. N.; Unterberg, W.

    1972-01-01

    Consideration of the problem of reducing the probability of mechanical failure of bladder systems used for the expulsion of propellants into liquid rocket engines. It is shown that individual local folds in collapsing bladders can be classified into single and double folds, specifiable by nondimensional geometrical parameters which directly define the maximum strains at these folds. From these maximum strains the number of collapse/inflation cycles to failure can be obtained from low-cycle fatigue data experimentally determined for the bladder material of interest. Cycle life data are presented in terms of true maximum strain for four metals, two plastics, and two elastomers. It is found that double folds give rise to much more severe folding strains than do simple folds.

  12. Artificial neural networks and the effects of loading conditions on fatigue life of carbon and low-alloy steels

    SciTech Connect

    Pleune, T.T. |; Chopra, O.K.

    1996-11-01

    The ASME Boiler and Pressure Vessel Code contains rules for the construction of nuclear power plant components. Figure 1-90 of Appendix I to Section III of the Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Recent test data indicate significant decreases in the fatigue lives of carbon and low-alloy steels in LWR environments when five conditions are satisfied simultaneously. When applied strain range, temperature, dissolved oxygen in the water, and sulfur content of the steel are above a minimum threshold level, and the loading strain rate is below a threshold value, environmentally assisted fatigue occurs. For this study, a data base of 1036 fatigue tests was used to train an artificial neural network (ANN). Once the optimal ANN was designed, ANN were trained and used to predict fatigue life for specified sets of loading and environmental conditions. By finding patterns and trends in the data, the ANN can find the fatigue lifetime for any set of conditions. Artificial neural networks show great potential for predicting environmentally assisted corrosion. Their main benefits are that the fit of the data is based purely on data and not on preconceptions and that the network can interpolate effects by learning trends and patterns when data are not available.

  13. Effect of sulfur on rolling contact fatigue life of high-manganese precipitation-hardening austenitic steel

    SciTech Connect

    Haruna, Y.; Yamamoto, A.; Tsubakino, H.

    1998-10-05

    For mechanical components used in high magnetic flux such as bearings and shafts that undergo cyclic stress, materials require low permeability with high strength, hardness, appropriate machinability, and good fatigue properties. Although it is implied that low permeability and machinability will be achieved by a selection of sulfurized austenitic ({gamma}) steel grades, effect of manganese sulfide (MnS) on fatigue properties of such grades especially for bearing applications is not clarified. For high-carbon chromium bearing steels, the effect of MnS on rolling contact fatigue life of the steels containing sulfur less than 0.03% are discussed. In these studies, the effect of MnS is not clearly determined whether it is beneficial or harmful to contact fatigue lives of the steels. However, effect of MnS under higher sulfur content, i.e., 0.10%, on the fatigue properties of {gamma} steel has not been studied. In this paper, the effect of sulfur on rolling contact fatigue properties of vanadium added {gamma} steel, 10Cr-6Ni-8Mn-1.6V-0.6C, was investigated focusing on microstructural change in connection with MnS particles.

  14. A creep cavity growth model for creep-fatigue life prediction of a unidirectional W/Cu composite

    NASA Technical Reports Server (NTRS)

    Kim, Young-Suk; Verrilli, Michael J.; Halford, Gary R.

    1992-01-01

    A microstructural model was developed to predict creep-fatigue life in a (0)(sub 4), 9 volume percent tungsten fiber-reinforced copper matrix composite at the temperature of 833 K. The mechanism of failure of the composite is assumed to be governed by the growth of quasi-equilibrium cavities in the copper matrix of the composite, based on the microscopically observed failure mechanisms. The methodology uses a cavity growth model developed for prediction of creep fracture. Instantaneous values of strain rate and stress in the copper matrix during fatigue cycles were calculated and incorporated in the model to predict cyclic life. The stress in the copper matrix was determined by use of a simple two-bar model for the fiber and matrix during cyclic loading. The model successfully predicted the composite creep-fatigue life under tension-tension cyclic loading through the use of this instantaneous matrix stress level. Inclusion of additional mechanisms such as cavity nucleation, grain boundary sliding, and the effect of fibers on matrix-stress level would result in more generalized predictions of creep-fatigue life.

  15. The relationship between cough-specific quality of life and abdominal muscle endurance, fatigue, and depression in patients with COPD

    PubMed Central

    Arikan, Hulya; Savci, Sema; Calik-Kutukcu, Ebru; Vardar-Yagli, Naciye; Saglam, Melda; Inal-Ince, Deniz; Coplu, Lutfi

    2015-01-01

    Background Cough is a prevalent symptom that impacts quality of life in COPD. The aim of this study was to assess the relationship between cough-specific quality of life, abdominal muscle endurance, fatigue, and depression in stable patients with COPD. Methods Twenty-eight patients with COPD (mean age 60.68.7 years) referred for pulmonary rehabilitation participated in this cross-sectional study. Sit-ups test was used for assessing abdominal muscle endurance. Leicester Cough Questionnare (LCQ) was used to evaluate symptom-specific quality of life. Fatigue perception was evaluated with Fatigue Impact Scale (FIS). Beck Depression Inventory (BDI) was used for assessing depression level. Results The LCQ total score was significantly associated with number of sit-ups; BDI score; FIS total; physical, cognitive, and psychosocial scores (P<0.05). Scores of the LCQ physical, social, and psychological domains were also significantly related with number of sit-ups, FIS total score, and BDI score (P<0.05). FIS total score and number of sit-ups explained 58% of the variance in LCQ total score (r=0.76, r2=0.577, F(220)=12.296, P<0.001). Conclusion Chronic cough may adversely affect performance in daily life due to its negative effect on fatigue and decrease abdominal muscle endurance in patients with COPD. Decreased cough-related quality of life is related with increased level of depression in COPD patients. Effects of increased abdominal muscle endurance and decreased fatigue in COPD patients with chronic cough need further investigation. PMID:26379433

  16. Surface fatigue life of M50NiL and AISI 9310 spur gears and R C bars

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.; Bamberger, Eric N.

    1991-01-01

    Spur gear endurance tests and rolling element surface fatigue tests were conducted to study vacuum induction melted, vacuum arc remelted (VIM-VAR) M50NiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance characteristics, and to compare the results with those for standard VAR and VIM-VAR AISI 9310 gear material. Tests were conducted with spur gears and rolling contact bars manufactured from VIM-VAR M50NiL and VAR and VIM-VAR AISI 9310. The gear pitch diameter was 8.9 cm. Gear test conditions were an inlet oil temperature of 320 K, and outlet oil temperature of 350 K, a maximum Hertz stress of 1.71 GPa, and a speed of 10000 rpm. Bench rolling element fatigue tests were conducted at ambient temperatures with a bar speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa. The VIM-VAR M50NiL gears had a surface fatigue life that was 4.5 and 11.5 times that for VIM-VAR and VAR AISI 9310 gears, respectively. The surface fatigue life of the VIM-VAR M50NiL rolling contact bars was 13.2 and 21.6 times that for the VIM-VAR and VAR AISI 9310, respectively. The VIM-VAR M50NiL material was shown to have good resistance to fracture through a fatigue spall and superior fatigue life to both other gears.

  17. Specimen Design for Fatigue Testing at Very High Frequencies

    NASA Astrophysics Data System (ADS)

    MATIKAS, T. E.

    2001-11-01

    Components in rotational machinery such as turbine blades used in military aircraft engines are subjected to low-amplitude, high-frequency loads in the kHz range. Under high cycle fatigue (HCF), the initiation state of a crack consumes most of the life of the component. Vibratory stresses may therefore result in unexpected failures of the material. Hence, there is a need for HCF studies to address HCF-related failures of turbine engines and to develop a life prediction methodology. Ultrasonic fatigue provides accelerated HCF testing enabling the simulation of realistic loading conditions for testing materials used in structural components subjected to vibratory stresses. Specimen design is critical for optimum ultrasonic fatigue testing. The objective of this study is therefore to develop analytical modelling necessary for the design of test coupons to be fatigue tested at ultrasonic frequencies.

  18. 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.

    1996-11-01

    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 upwind and 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 vertical shear and a 15 percent superimposed spectrum of turbulence; and occasional exposure to 62 m/s hurricanes. Accounted for herein is the effect of flatwise bending flexibility on the loads spectra of root flatwise bending moment, thrust, and torque (both open loop and closed loop). Using Miner`s rule, the moments are converted to fatigue lives. With aerodynamic control, RMS flatwise 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 feather controlled in the high wind so that its life is dominated by turbulent loads. Simplified fatigue analysis permits weight reductions to be estimated which yield controlled blades capable of 30 years` operation with a safety factor of 11. The resulting weights are about 400 kg for the aileron-controlled blade, and 230 kg for the all-movable blade. However, such light-weight rotors require attention to other design considerations, such as start-stop cycles. Apart from limit loads, the methods of analysis are linearized (locally for aerodynamic loads). It follows that the results are likely to be meaningful in terms of comparative, rather than absolute, values of fatigue life and weight.

  19. Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 ?m is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

  20. 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.

  1. Influence of Solid-State Diffusion during Equilibration on Microstructure and Fatigue Life of Superalloy Wide-Gap Brazements

    NASA Astrophysics Data System (ADS)

    Osoba, L. O.; Ojo, O. A.

    2013-09-01

    The influence of solid-state diffusion-controlled solute-loss into additive powder particles (APPs), as determined by particles size, during the equilibration stage of wide-gap brazing, on microstructure and fatigue behavior of a brazed aerospace superalloy was studied. The results, which experimentally confirm previously reported numerical model simulation results, show that, in order to avoid degradation of fatigue life of wide-gap brazement, adequate solute-loss into the APPs, which is necessary to prevent their complete melting, but has not been generally considered, is imperative.

  2. 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.

  3. Improvement of Fatigue Life of a Holed Specimen of Aluminum-Alloy 2024-T3 by Indentation and Hole Expansion

    NASA Astrophysics Data System (ADS)

    Shafiul Ferdous, Md.; Makabe, Chobin; Miyazaki, Tatsujiro; Hattori, Nobusuke

    A method of improving the fatigue life and crack growth behavior of a center holed specimen was investigated. Local plastic deformation was applied around the hole by indentation to achieve the purpose. A series of fatigue tests was conducted on aluminum-alloy 2024-T3. Push-pull tests were performed under a stress ratio of R= -1 and a frequency of 10Hz. The observations of the crack initiation and growth were performed with a microscope, and hardness around the hole was measured by Vickers hardness testing machine. In the present study, the longest fatigue life was observed in the case of an indentation specimen with the highest load. The indentation was performed on both sides of the hole edges. The crack growth rate was decreased by indentation or expansion of the material around the hole. From the experimental results, it is found that the fatigue life and crack growth behavior of a holed or notched specimen can be improved by a simple technical method that is related to the local plastic working.

  4. Grain boundary oxidation and an analysis of the effects of pre-oxidation on subsequent fatigue life

    NASA Technical Reports Server (NTRS)

    Oshida, Y.; Liu, H. W.

    1986-01-01

    The effects of preoxidation on subsequent fatigue life were studied. Surface oxidation and grain boundary oxidation of a nickel-base superalloy (TAZ-8A) were studied at 600 to 1000 C for 10 to 1000 hours in air. Surface oxides were identified and the kinetics of surface oxidation was discussed. Grain boundary oxide penetration and morphology were studied. Pancake type grain boundary oxide penetrates deeper and its size is larger, therefore, it is more detrimental to fatigue life than cone-type grain boundary oxide. Oxide penetration depth, a (sub m), is related to oxidation temperature, T, and exposure time, t, by an empirical relation of the Arrhenius type. Effects of T and t on statistical variation of a (sub m) were analyzed according to the Weibull distribution function. Once the oxide is cracked, it serves as a fatigue crack nucleus. Statistical variation of the remaining fatigue life, after the formation of an oxide crack of a critical length, is related directly to the statistical variation of grain boundary oxide penetration depth.

  5. Fatigue modeling for small wind systems: basic theory

    SciTech Connect

    Waldon, C.A.; Hansen, A.C.

    1983-06-01

    This report discusses the theory of fatigue as applied to horizontal-axis wind systems and reviews current techniques for predicting fatigue loads and fatigue life. Wind systems are subjected to a complex and diverse variety of loads, ranging from simple gravity and centrifugal loads to complex and random wind loads. The categories of loads described here include transient, periodic, and control-induced loads, as well as loads induced by severe aeroelastic instabilities. Within these categories, load types include centrifugal, aerodynamic thrust and torque, parked rotor survival loads, gravity loads, gyroscopic loads, and aerodynamic loads induced by crossflow or yaw motion. Control systems can impose loads whenever they are activated. Catastrophic failure can result from severe aeroelastically-induced loads caused by flutter. Techniques available for predicting fatigue loads include various aerodynamic performance codes (such as PROP) and simplified methods for calculating the convection of the vortex wake. MOSTAB, an aeroelasticity computer code, treats all major load sources. Results using this code are shown to be fairly comparable to experimental data in the case of a rigid-bladed wind system. Fatigue life of a machine component can be predicted during design by several techniques, including the strength-of-materials method, the fatigue curve method, and the fatigue event method. The theories of Miner, Manson, and Corten-Dolan can be used to predict fatigue life based on test data and operational experience. A fatigue research project to be performed at Rocky Flats will attempt to resolve whether any of these theories or a combination of theories can be used with an acceptable degree of accuracy in predicting fatigue loads and life for wind systems. An appendix to the report provides sample calculations of fatigue load magnitudes made using available methods.

  6. Alendronate in bone cement: fatigue life degraded by liquid, not by powder.

    PubMed

    Lewis, Gladius; Janna, Si

    2006-04-01

    Bisphosphonates have the potential to reduce osteolysis, a phenomenon that has been postulated to play a key role in aseptic loosening of total joint replacements. Bisphosphonates may contribute to the in vivo longevity of total joint replacements. Some authors have suggested there are decreases in flexural strength and flexural modulus of the cured cement when a liquid form of disodium pamidronate is added to a commercially available acrylic bone cement (Palacos R). We proposed that it is comparatively easier to blend a bisphosphonate in powder form into an acrylic bone cement than it is when the drug is in liquid form; and that the cement's fatigue life is decreased when the bisphosphonate is added in liquid rather than in solid form. The bisphosphonate and bone cement used were alendronate sodium and Cemex XL, respectively. The fatigue tests were done using phosphate buffered saline solution at 37 degrees +/- 1 degrees C. The data supported both hypotheses. Our findings should guide orthopaedic surgeons when using bisphosphonate-impregnated acrylic bone cements in total joint replacements. Bisphosphonates are endogenous pyrophosphate analogs in which a carbon atom replaces the central oxygen atom. These therapeutic agents may be classified into nitrogen and non-nitrogen containing types. Some examples are alendronate, pamidronate, ibandronate, risedronate, etidronate, clodronate, and zoledronate. There are many targets and mechanisms of action of this family of drugs, therefore making them efficacious against diverse clinical conditions such as osteoporosis, periprosthetic bone loss subsequent to total joint replacement, tumor cell proliferation, apoptosis and angiogenesis, Charcot neuroarthropathy, rheumatoid arthritis, ankylosing spondylitis and spondyloarthropathies, and arterial calcification. It has been proposed that some bisphosphonates are effective against the mechanisms that have been suggested as being implicated in aseptic loosening of total joint replacements, these being osteoclast-mediated bone resorption and wear particle-induced osteolysis. A meta-analysis of randomized controlled trials showed that alendronate and pamidronate had beneficial effects maintaining periprosthetic bone for as much as 1 year after a total joint replacement. PMID:16446596

  7. Neural network fatigue life prediction in steel i-beams using mathematically modeled acoustic emission data

    NASA Astrophysics Data System (ADS)

    Selvadorai, Prathikshen N.

    The purpose of this research is to predict fatigue cracking in metal beams using mathematically modeled acoustic emission (AE) data. The AE data was collected from nine samples of steel Ibeam that were subjected to three-point bending caused by cyclic loading. The data gathered during these tests were filtered in order to remove long duration hits, multiple hit data, and obvious outliers. Based on the duration, energy, amplitude, and average frequency of the AE hits, the filtered data were classified into the various failure mechanisms of metals using NeuralWorksRTM Professional II/Plus software based self-organizing map (SOM) neural network. The parameters from mathematically modeled AE failure mechanism data were used to predict plastic deformation data. Amplitude data from classified plastic deformation data is mathematically modeled herein using bounded Johnson distributions and Weibull distribution. A backpropagation neural network (BPNN) is generated using MATLABRTM. This BPNN is able to predict the number of cycles that ultimately cause the steel I-beams to fail via five different models of plastic deformation data. These five models are data without any mathematical modeling and four which are mathematically modeled using three methods of bounded Johnson distribution (Slifker and Shapiro, Mage and Linearization) and Weibull distribution. Currently, the best method is the Linearization method that has prediction error not more than 17%. Multiple linear regression (MLR) analysis is also performed on the four sets of mathematically modeled plastic deformation data as named above using the bounded Johnson and Weibull shape parameters. The MLR gives the best prediction for the Linearized method which has a prediction error not more than 2%. The final conclusion made is that both BPNN and MLR are excellent tools for accurate fatigue life cycle prediction.

  8. Finite element analysis of sucker rod couplings with guidelines for improving fatigue life

    SciTech Connect

    Hoffman, E.L.

    1997-09-01

    The response of a variety of sucker rod couplings to an applied axial load was simulated using axisymmetric finite element models. The calculations investigated three sucker rod sizes and various combinations of the slimhole, Spiralock, and Flexbar modifications to the coupling. In addition, the effect of various make-ups (assembly tightness) on the performance of coupling was investigated. An axial load was applied to the sucker rod ranging from {minus}5 ksi to 40 ksi, encompassing three load cycles identified on a modified Goodman diagram as acceptable for indefinite service life of the sucker rods. The simulations of the various coupling geometries and make-ups were evaluated with respect to how well they accomplish the two primary objectives of preloading threaded couplings: (1) to lock the threaded coupling together so that it will not loosen and eventually uncouple, and (2) to improve the fatigue resistance of the threaded connection by reducing the stress amplitude in the coupling when subjected to cyclic loading. Perhaps the most significant finding in this study was the characterization of the coupling parameters which affect two stress measures. The mean hydrostatic stress, which determines the permissible effective alternating stress, is a function of the coupling make-up. Whereas, the alternating effective stress is a function of the relative stiffnesses of the pin and box sections of the coupling and, as long as the coupling does not separate, is unaffected by the amount of circumferential displacement applied during make-up. The results of this study suggest approaches for improving the fatigue resistance of sucker rod couplings.

  9. Fatigue Life Prediction in Rapid Die Casting - Preliminary Work in View of Current Research

    SciTech Connect

    Chuan Huat Ng; Grote, Karl-Heinrich; Baehr, Ruediger

    2007-05-17

    Numerical simulation technique as a prediction tool is slowly adopted in metal casting industry for predicting design modelling solidification analysis. The reasons for this activity is found in the need to further enhance the geometrical design and mechanical properties of the tool design and the correct prediction methodology to fulfil industrial needs. The present state of numerical simulation capabilities in rapid die casting technologies is reviewed and the failure mode mechanisms of thermal fatigue, aimed at developing a numerical simulation with a systematic design guidance for predicting the thermal cyclic loading analysis and improvement is presented along with several other methods. The economic benefits of a numerical simulation technique in die casting are limited to tool life time, mechanical properties and design guidance. The extensive computer capabilities of a numerical simulation with a systematic design guidance methodology are exploited to provide a solution for flexible design, mechanical properties and mould life time. Related research carried out worldwide by different organisations and academic institutions are discussed.

  10. NASALife-Component Fatigue and Creep Life Prediction Program and Illustrative Examples

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.; Mital, Subodh K.; Gyekenyesi, John Z.

    2005-01-01

    NASALife is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although, the primary focus was for CMC components the underlying methodologies are equally applicable to other material systems as well. The program references data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method. Lastly, damage due to cyclic loading (Miner s rule) and creep are combined to determine the total damage per mission and the number of missions the component can survive before failure are calculated. Illustration of code usage is provided through example problem of a CMC turbine stator vane made of melt-infiltrated, silicon carbide fiber-reinforced, silicon carbide matrix composite (MI SiC/SiC)

  11. Displacement measurement on specimens subjected to non-Gaussian random vibrations in fatigue life tests

    NASA Astrophysics Data System (ADS)

    Troncossi, M.; Di Sante, R.; Rivola, A.

    2014-05-01

    High-cycle fatigue life tests conducted using controlled random vibrations are commonly used to evaluate failure in components and structures. In most cases, a Gaussian distribution of both the input vibration and the stress response is assumed, while real-life loads may be non-Gaussian causing the response to be non-Gaussian as well. Generating non-Gaussian drive signals with high kurtosis and a given power spectral density, however, does not always guarantee that the stress response will actually be non-Gaussian, because this depends on the adherence of the tested system to the Central Limit Theorem. On the other side, suitable measurement methods need to be developed in order to estimate the stress amplitude response at critical failure locations, and therefore to evaluate and select input loads. In this paper, a simple test rig with a notched cantilevered specimen was developed to measure the response and examine the kurtosis values in the case of stationary Gaussian, stationary non-Gaussian, and non-stationary non-Gaussian excitation signals. The Laser Doppler Vibrometry (LDV) technique was used for the first time in this type of test, to estimate the specimen stress amplitude response in terms of differential displacement at the notch section ends. A method based on the use of accelerometers to correct for the occasional signal drops occurring during the experiment is described and the results are discussed with respect to the ability of the test procedure to evaluate the output signal.

  12. Review of time-dependent fatigue behavior and life prediction for 2 1/4 Cr-1 Mo steel. [LMFBR

    SciTech Connect

    Booker, M.K.; Majumdar, S.

    1982-01-01

    Available data on creep-fatigue life and fracture behavior of 2 1/4 Cr-1 Mo steel are reviewed. Whereas creep-fatigue interaction is important for Type 304 stainless steel, oxidation effects appear to dominate the time-dependent fatigue behavior of 2 1/4 Cr-1 Mo steel. Four of the currently available predictive methods - the Linear Damage Rule, Frequency Separation Equation, Strain Range Partitioning Equation, and Damage Rate Equation - are evaluated for their predictive capability. Variations in the parameters for the various predictive methods with temperature, heat of material, heat treatment, and environment are investigated. Relative trends in the lives predicted by the various methods as functions of test duration, waveshape, etc., are discussed. The predictive methods will need modification in order to account for oxidation and aging effects in the 2 1/4 Cr-1 Mo steel. Future tests that will emphasize the difference between the various predictive methods are proposed.

  13. Rolling-element fatigue life of silicon nitride balls. [as compared to that of steel, ceramic, and cermet materials

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Zaretsky, E. V.

    1974-01-01

    The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of bearing quality steel running against steel at stress levels typical rolling-element bearing application. The fatigue life of hot-pressed silicon nitride is considerably greater than that of any ceramic or cermet tested. Computer analysis indicates that there is no improvement in the lives of 120-mm-bore angular--contact ball bearings of the same geometry operating at DN values from 2 to 4 million where hot-pressed silicon nitride balls are used in place of steel balls.

  14. An estimation of fatigue life for a carbon fibre/poly ether ether ketone hip joint prosthesis.

    PubMed

    Akay, M; Aslan, N

    1995-01-01

    A fracture mechanics approach was applied to estimate the life of a prosthesis injection moulded from short carbon fibre reinforced poly ether ether ketone. Flexural modulus and strength, fracture toughness, fatigue endurance limit, fatigue crack growth rate and threshold stress intensity factor were determined. The dimensions of the test pieces were selected to yield fibre orientation and fibre length distributions similar to those obtained in the prosthesis. Stress levels generated in the prosthesis under different activities were estimated by conducting three-dimensional finite element analysis. It was shown by a fracture mechanics approach that a fatigue failure due to the propagation of an embedded elliptical slit, under these stresses, would be unlikely for a crack length smaller than 1.85 mm. However, the cement would fail under the same conditions, irrespective of the type of the prosthesis employed. PMID:7495431

  15. 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

  16. Application of two creep fatigue life models for the prediction of elevated temperature crack initiation of a nickel base alloy

    NASA Technical Reports Server (NTRS)

    Moreno, V.; Nissley, D. M.; Halford, G. R.; Saltsman, J. F.

    1985-01-01

    Cyclic Damage Accumulation (CDA) and Total Strain-Strain Range Partitioning (TS-SRP) models for predicting the creep-fatigue crack initiation life of high temperature alloys are presented. The models differ in their fundamental assumptions regarding the controlling parameters for fatigue crack initiation and in the amount of data required to determine model constants. The CDA model represents a ductility exhaustion approach and uses stress quantities to calculate the cyclic fatigue damage. The TS-SRP model is based on the use of total mechanical strain and earlier concepts of the Strain Range Partitioning Method. Both models were applied to a well controlled fatigue data set at a high temperature nickel base alloy, B1900 + Hf, tested at 1600 F and 1800 F. The tests were divided into a baseline data set required to determine model constants and a verification data set for evaluation of the predictive capability of the models. Both models correlated the baseline data set to within factors of two in life, and predicted the verification data set to within a factor of three or better. In addition, sample calculations to demonstrate the application of each model and discusions of the predictive capabilities and areas requiring further development are presented.

  17. Test Method for the Fatigue Life of Layered TiB/Ti Functionally Graded Beams Subjected to Fully Reversed Bending

    NASA Astrophysics Data System (ADS)

    Byrd, Larry; Rickerd, Greg; Wyen, Travis; Cooley, Glenn; Quast, Jeff

    2008-02-01

    Sonic fatigue of aircraft is characterized by fully reversed bending of components subjected to acoustic excitation. This problem is compounded in high temperature environments because solutions for acoustics which tend to result in stiff structures make thermal problems worse. Conversely solutions to the thermal problem which allow expansion often fail in the presence of high acoustic levels. Errors in fatigue life prediction in the combined environment often range from a factor of 4 to 10. This results in either heavy, overly stiff structure or premature failure. This work will test the hypothesis that the fatigue life of a layered functionally graded material (FGM) will be dominated by the failure of the stiffest outer layer. This is based on the observation that for isotropic materials the life is approximately 90% crack initiation and only 10% crack growth before failure. Four sets of cantilever specimens will be tested using an electro-mechanical shaker for base excitation. The excitation will be narrow band random around the fundamental frequency. Two sets of specimens are of uniform composition consisting of 85%TiB/Ti and two are graded specimens consisting of layers that vary from commercially pure titanium to 85%TiB/Ti. Strain vs number of cycles to failure curves will be generated with both constant amplitude sine and narrow band random around the fundamental frequency excitation. The results will be examined to compare life of the uniform material to the functionally graded material. Also to be studied will be the use of Miner's rule to predict the fatigue life of the randomly excited specimens.

  18. FLAPS (Fatigue Life Analysis Programs): Computer Programs to Predict Cyclic Life Using the Total Strain Version of Strainrange Partitioning and Other Life Prediction Methods. Users' Manual and Example Problems, Version 1.0

    NASA Technical Reports Server (NTRS)

    Arya, Vinod K.; Halford, Gary R. (Technical Monitor)

    2003-01-01

    This manual presents computer programs FLAPS for characterizing and predicting fatigue and creep-fatigue resistance of metallic materials in the high-temperature, long-life regime for isothermal and nonisothermal fatigue. The programs use the Total Strain version of Strainrange Partitioning (TS-SRP), and several other life prediction methods described in this manual. The user should be thoroughly familiar with the TS-SRP and these life prediction methods before attempting to use any of these programs. Improper understanding can lead to incorrect use of the method and erroneous life predictions. An extensive database has also been developed in a parallel effort. The database is probably the largest source of high-temperature, creep-fatigue test data available in the public domain and can be used with other life-prediction methods as well. This users' manual, software, and database are all in the public domain and can be obtained by contacting the author. The Compact Disk (CD) accompanying this manual contains an executable file for the FLAPS program, two datasets required for the example problems in the manual, and the creep-fatigue data in a format compatible with these programs.

  19. Deformation, Failure, and Fatigue Life of SiC/Ti-15-3 Laminates Accurately Predicted by MAC/GMC

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Arnold, Steven M.

    2002-01-01

    NASA Glenn Research Center's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) (ref.1) has been extended to enable fully coupled macro-micro deformation, failure, and fatigue life predictions for advanced metal matrix, ceramic matrix, and polymer matrix composites. Because of the multiaxial nature of the code's underlying micromechanics model, GMC--which allows the incorporation of complex local inelastic constitutive models--MAC/GMC finds its most important application in metal matrix composites, like the SiC/Ti-15-3 composite examined here. Furthermore, since GMC predicts the microscale fields within each constituent of the composite material, submodels for local effects such as fiber breakage, interfacial debonding, and matrix fatigue damage can and have been built into MAC/GMC. The present application of MAC/GMC highlights the combination of these features, which has enabled the accurate modeling of the deformation, failure, and life of titanium matrix composites.

  20. Multidisciplinary Design Optimization for Glass-Fiber Epoxy-Matrix Composite 5 MW Horizontal-Axis Wind-Turbine Blades

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Arakere, G.; Pandurangan, B.; Sellappan, V.; Vallejo, A.; Ozen, M.

    2010-11-01

    A multi-disciplinary design-optimization procedure has been introduced and used for the development of cost-effective glass-fiber reinforced epoxy-matrix composite 5 MW horizontal-axis wind-turbine (HAWT) blades. The turbine-blade cost-effectiveness has been defined using the cost of energy (CoE), i.e., a ratio of the three-blade HAWT rotor development/fabrication cost and the associated annual energy production. To assess the annual energy production as a function of the blade design and operating conditions, an aerodynamics-based computational analysis had to be employed. As far as the turbine blade cost is concerned, it is assessed for a given aerodynamic design by separately computing the blade mass and the associated blade-mass/size-dependent production cost. For each aerodynamic design analyzed, a structural finite element-based and a post-processing life-cycle assessment analyses were employed in order to determine a minimal blade mass which ensures that the functional requirements pertaining to the quasi-static strength of the blade, fatigue-controlled blade durability and blade stiffness are satisfied. To determine the turbine-blade production cost (for the currently prevailing fabrication process, the wet lay-up) available data regarding the industry manufacturing experience were combined with the attendant blade mass, surface area, and the duration of the assumed production run. The work clearly revealed the challenges associated with simultaneously satisfying the strength, durability and stiffness requirements while maintaining a high level of wind-energy capture efficiency and a lower production cost.

  1. Variations in gear fatigue life for different wind turbine braking strategies

    SciTech Connect

    McNiff, B.P. ); Musial, W.D. ); Errichello, R. )

    1991-06-01

    A large number of gearbox failures have occurred in the wind industry in a relatively short period, many because service loads were underestimated. High-torque transients that occur during starting and stopping are difficult to predict and may be overlooked in specifying gearbox design. Although these events comprise a small portion of total load cycles, they can be the most damaging. The severity of these loads varies dramatically with the specific configuration of the wind turbine. The large number of failures in Danish-designed Micon 65 wind turbines prompted this investigation. The high-speed and low-speed shaft torques were measured on a two-stage helical gearbox of a single Micon 65 turbine. Transient events and normal running loads were combined statistically to obtain a typical annual load spectrum. The pitting and bending fatigue lives of the gear teeth were calculated by using Miner's rule for four different high-speed shaft brake configurations. Each breaking scenario was run for both a high- and a low-turbulence normal operating load spectrum. The analysis showed increases in gear life by up to a factor of 25 when the standard high-speed shaft brake is replaced with a dynamic brake or modified with a damper. 9 refs., 9 figs., 3 tabs.

  2. Combining Turbine Blade-Strike and Life Cycle Models to Assess Mitigation Strategies for Fish Passing Dams

    SciTech Connect

    Ferguson, John W.; Ploskey, Gene R.; Leonardsson, Kjell; Zabel, Richard W.; Lundqvist, Hans

    2008-08-01

    Combining the two models produced a rapid, cost effective tool for assessing dam passage impacts to fish populations and prioritizing among mitigation strategies for conserving fish stocks in regulated rivers. Estimated mortality of juvenile and adult Atlantic salmon (Salmo salar) and sea trout (S. trutta) passing turbines at two dams in northern Sweden was significantly higher for Kaplan turbines compared to Francis turbines, and for adult fish compared to juveniles based on blade strike models. Mean probability of mortality ranged from 6.7% for salmon smolts passing Francis turbines to >100% for adult salmon passing Kaplan turbines. Life cycle modeling allowed benefits to be assessed for three alternatives that mitigated this mortality. Salmon population responses varied considerably among alternatives and rivers: growth rates improved as much as 17.9%, female escapements increased up to 669%, and more than 1,300 additional female salmon were produced in one case. Protecting both smolts and adults provided benefits, and in one river, mitigating turbine mortality alone was estimated to have met the production capacity of the available habitat.

  3. Assessment of Cancer-Related Fatigue, Pain, and Quality of Life in Cancer Patients at Palliative Care Team Referral: A Multicenter Observational Study (JORTC PAL-09)

    PubMed Central

    Iwase, Satoru; Kawaguchi, Takashi; Tokoro, Akihiro; Yamada, Kimito; Kanai, Yoshiaki; Matsuda, Yoshinobu; Kashiwaya, Yuko; Okuma, Kae; Inada, Shuji; Ariyoshi, Keisuke; Miyaji, Tempei; Azuma, Kanako; Ishiki, Hiroto; Unezaki, Sakae; Yamaguchi, Takuhiro

    2015-01-01

    Introduction Cancer-related fatigue greatly influences quality of life in cancer patients; however, no specific treatments have been established for cancer-related fatigue, and at present, no medication has been approved in Japan. Systematic research using patient-reported outcome to examine symptoms, particularly fatigue, has not been conducted in palliative care settings in Japan. The objective was to evaluate fatigue, pain, and quality of life in cancer patients at the point of intervention by palliative care teams. Materials and Methods Patients who were referred to palliative care teams at three institutions and met the inclusion criteria were invited to complete the Brief Fatigue Inventory, Brief Pain Inventory, and European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 15-Palliative. Results Of 183 patients recruited, the majority (85.8%) were diagnosed with recurrence or metastasis. The largest group (42.6%) comprised lung cancer patients, of whom 67.2% had an Eastern Cooperative Oncology Group Performance Status of 0–1. The mean value for global health status/quality of life was 41.4, and the highest mean European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 15-Palliative symptom item score was for pain (51.0). The mean global fatigue score was 4.1, and 9.8%, 30.6%, 38.7%, and 20.8% of patients’ fatigue severity was classified as none (score 0), mild (1–3), moderate (4–6), and severe (7–10), respectively. Discussion Cancer-related fatigue, considered to occur more frequently in cancer patients, was successfully assessed using patient-reported outcomes with the Brief Fatigue Inventory for the first time in Japan. Results suggested that fatigue is potentially as problematic as pain, which is the main reason for palliative care. PMID:26244975

  4. 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.

  5. Demonstrating the Effect of Particle Impact Dampers on the Random Vibration Response and Fatigue Life of Printed Wiring Assemblies

    NASA Technical Reports Server (NTRS)

    Knight, Brent; Montgomery, Randall; Geist, David; Hunt, Ron; LaVerde, Bruce; Towner, Robert

    2013-01-01

    In a recent experimental study, small Particle Impact Dampers (PID) were bonded directly to the surface of printed circuit board (PCB) or printed wiring assemblies (PWA), reducing the random vibration response and increasing the fatigue life. This study provides data verifying practicality of this approach. The measured peak strain and acceleration response of the fundamental out of plane bending mode was significantly attenuated by adding a PID device. Attenuation of this mode is most relevant to the fatigue life of a PWA because the local relative displacements between the board and the supported components, which ultimately cause fatigue failures of the electrical leads of the board-mounted components are dominated by this mode. Applying PID damping at the board-level of assembly provides mitigation with a very small mass impact, especially as compared to isolation at an avionics box or shelf level of assembly. When compared with other mitigation techniques at the PWA level (board thickness, stiffeners, constrained layer damping), a compact PID device has the additional advantage of not needing to be an integral part of the design. A PID can simply be bonded to heritage or commercial off the shelf (COTS) hardware to facilitate its use in environments beyond which it was originally qualified. Finite element analysis and test results show that the beneficial effect is not localized and that the attenuation is not due to the simple addition of mass. No significant, detrimental reduction in frequency was observed. Side-by-side life testing of damped and un-damped boards at two different thicknesses (0.070" and 0.090") has shown that the addition of a PID was much more significant to the fatigue life than increasing the thickness. High speed video, accelerometer, and strain measurements have been collected to correlate with analytical results.

  6. Strainrange partitioning - A total strain range version. [for creep fatigue life prediction by summing inelastic and elastic strain-range-life relations for two Ni base superalloys

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Saltsman, J. F.

    1983-01-01

    Procedures are presented for expressing the Strainrange Partitioning (SRP) method for creep fatigue life prediction in terms of total strain range. Inelastic and elastic strain-range - life relations are summed to give total strain-range - life relations. The life components due to inelastic strains are dealt with using conventional SRP procedures while the life components due to elastic strains are expressed as families of time-dependent terms for each type of SRP cycle. Cyclic constitutive material behavior plays an important role in establishing the elastic strain-range life relations as well as the partitioning of the inelastic strains. To apply the approach, however, it is not necessary to have to determine the magnitude of the inelastic strain range. The total strain SRP approach is evaluated and verified using two nickel base superalloys, AF2-1DA and Rene 95. Excellent agreement is demonstrated between observed and predicted cyclic lifetimes with 70 to 80 percent of the predicted lives falling within factors of two of the observed lives. The total strain-range SRP approach should be of considerable practical value to designers who are faced with creep-fatigue problems for which the inelastic strains cannot be calculated with sufficient accuracy to make reliable life predictions by the conventional inelastic strain range SRP approach.

  7. Axial-thrust responses due to a gas turbine's rotor blade distortions

    NASA Astrophysics Data System (ADS)

    Lebele-Alawa, B. T.

    2010-11-01

    The axial thrust imposed on the shaft of a gas turbine depends upon its rotor blade inlet inclination to the turbine's axial direction: this inclination can change due to the distortions resulting from fouling, aging, tip rubbing, erosion, thermal-fatigue cracks, and corrosion. Relevant influential parameters for an operational gas turbine were measured. Theoretical predictions for the behavior of the same turbine were obtained from computer simulations. The results of both measurements and theoretical predictions were compared and showed qualitative correspondence. The rotor blade profile distortions result in significant increases in the axial thrust on the compressor, which adversely affects the gas turbine's thermodynamic performance, reliability, and operational life.

  8. Fatigue handbook: Offshore steel structures

    SciTech Connect

    Almarnaess, A.

    1985-01-01

    The contents of this book are: Overview of Offshore Steel Structures; Loads on Ocean Structures; Fracture Mechanics As a Tool in Fatigue Analysis; Basic Fatigue Properties of Welded Joints; Significance of Defects; Improving the Fatigue Strength of Welded Joints; Effects of Marine Environment and Cathodic Protection on Fatigue of Structural Steels Fatigue of Tubular Joints; Unstable Fracture; Fatigue Life Calculations; and Fatigue in Building Codes Background and Applications.

  9. 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...

  10. 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...

  11. 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...

  12. 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...

  13. 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...

  14. 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.

  15. High-temperature fatigue in metals - A brief review of life prediction methods developed at the Lewis Research Center of NASA

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1983-01-01

    The presentation focuses primarily on the progress we at NASA Lewis Research Center have made. The understanding of the phenomenological processes of high temperature fatigue of metals for the purpose of calculating lives of turbine engine hot section components is discussed. Improved understanding resulted in the development of accurate and physically correct life prediction methods such as Strain-Range partitioning for calculating creep fatigue interactions and the Double Linear Damage Rule for predicting potentially severe interactions between high and low cycle fatigue. Examples of other life prediction methods are also discussed. Previously announced in STAR as A83-12159

  16. Effects of a 4-Week Multimodal Rehabilitation Program on Quality of Life, Cardiopulmonary Function, and Fatigue in Breast Cancer Patients

    PubMed Central

    Do, Junghwa; Cho, Youngki

    2015-01-01

    Purpose This study examines the effects of a rehabilitation program on quality of life (QoL), cardiopulmonary function, and fatigue in breast cancer patients. The program included aerobic exercises as well as stretching and strengthening exercises. Methods Breast cancer patients (n=62) who had completed chemotherapy were randomly assigned to an early exercise group (EEG; n=32) or a delayed exercise group (DEG; n=30). The EEG underwent 4 weeks of a multimodal rehabilitation program for 80 min/day, 5 times/wk for 4 weeks. The DEG completed the same program during the next 4 weeks. The European Organization for Research and Treatment of Cancer-Core Quality of Life Questionnaire (EORTC QLQ-C30), EORTC Breast Cancer-Specific Quality of Life Questionnaire (EORTC QLQ-BR23), predicted maximal volume of oxygen consumption (VO2max), and fatigue severity scale (FSS) were used for assessment at baseline, and at 2, 4, 6, and 8 weeks. Results After 8 weeks, statistically significant differences were apparent in global health, physical, role, and emotional functions, and cancer-related symptoms such as fatigue and pain, nausea, and dyspnea on the EORTC QLQ-C30; cancer-related symptoms involving the arm and breast on the EORTC QLQ-BR23; the predicted VO2max; muscular strength; and FSS (p<0.050), according to time, between the two groups. Conclusion The results of our study suggest that a supervised multimodal rehabilitation program may improve the physical symptoms, QoL, and fatigue in patients with breast cancer. PMID:25834616

  17. Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    1993-01-01

    The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element analyses, advanced constitutive stress-strain-temperature-time relations, and creep-fatigue-environmental models for crack initiation and propagation. The high-temperature durability methods that have evolved for calculating high-temperature fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design. Recently, two of the methods were transcribed into computer software for use with personal computers.

  18. Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation

    NASA Astrophysics Data System (ADS)

    Halford, Gary R.

    1993-10-01

    The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element analyses, advanced constitutive stress-strain-temperature-time relations, and creep-fatigue-environmental models for crack initiation and propagation. The high-temperature durability methods that have evolved for calculating high-temperature fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design.

  19. Analytical study of thermal barrier coated first-stage blades in an F100 engine

    NASA Technical Reports Server (NTRS)

    Andress, D. E.

    1978-01-01

    Heat transfer and stress analyses were performed on two sections of a thermal barrier coated (TBC) F100 1st-stage turbine blade. Results of the analyses indicate that the TBC on the leading edges of both sections experience the highest elastic strain ranges and these occur during transient engine operation. Further study is recommended to determine the effects of plastic deformation (creep) and creep-fatigue interaction on coating life.

  20. Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation

    SciTech Connect

    Halford, G.R.

    1993-10-01

    The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940`s. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material`s crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the `build-em and bust-em` approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed.

  1. Rolling Contact Fatigue Life of Steel Rollers Treated by Cavitation Peening and Shot Peening

    NASA Astrophysics Data System (ADS)

    Seki, Masanori; Soyama, Hitoshi; Kobayashi, Yuji; Gowa, Daisuke; Fujii, Masahiro

    The purpose of this study is to investigate the influence of peening on the rolling contact fatigue (RCF) life of steel rollers. First, steel rollers were treated by three types of peenings to ensure the same surface roughness of peened rollers. One is the cavitation peening (CP) used a cavitating jet in water with an injection pressure of 30 MPa, and the others are the fine particle peening (FPP) with a shot diameter of 0.1 mm and the normal shot peening (NSP) with a shot diameter of 0.3 mm. The surface hardness and the surface compressive residual stress of the steel rollers were increased by all the peenings. In particular, they were most increased by the FPP. On the other hand, the work-hardened depth due to the CP and the NSP was larger than that due to the FPP. As a result of the RCF tests, the RCF lives of the steel rollers were improved by all the peenings, and they were most improved by the NSP. Judging from the pmax - N curves and the [A(?y/?3 HV)]max - N curves, the improvement in RCF lives due to the FPP depended heavily on the increase in surface hardness due to that, and the effects of the CP and the NSP on the RCF were equivalent under the same surface roughness and the same surface hardness. It follows from these that the surface treatment condition should be selected according to the rolling contact conditions and the failure modes of machine elements.

  2. Effectiveness of grinding and peening techniques for fatigue life extension of welded joints

    SciTech Connect

    Haagensen, P.J.

    1994-12-31

    Weld improvement methods can be used to upgrade existing structures and to repair weldments containing fatigue cracks. Some methods are suitable for use underwater to repair damaged structures. The fatigue strength properties of as-welded specimens and specimens improved by weld toe grinding, and toe grinding combined with hammer peening were investigated in constant amplitude tests in air. The material was a low carbon microalloyed steel of 360 MPa yield strength. The specimens were non-load carrying T-joints that were loaded in four point bending. The effectiveness of weld toe grinding and grinding combined with hammer peening to repair fatigue cracks was examined in tests on specimens with simulated fatigue cracks repaired by grinding followed by hammer peening.

  3. 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.

  4. Fatigue Life Prediction of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures. Part II: Experimental Comparisons

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    This paper follows on from the earlier study (Part I) which investigated the fatigue behavior of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures. In this paper, a micromechanics approach to predict the fatigue life S-N curves of fiber-reinforced CMCs has been developed considering the fatigue damage mechanism of interface wear or interface oxidation. Upon first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. The two-parameter Weibull model is used to describe fibers strength distribution. The stress carried by broken and intact fibres on the matrix crack plane under fatigue loading is determined based on the Global Load Sharing (GLS) criterion. The fibres failure probabilities under fatigue loading considering the degradation of interface shear stress and fibres strength have been obtained. When the broken fibres fraction approaches critical value, the composite would fatigue fail. The fatigue life S-N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures have been predicted. The predicted results agreed with experimental data.

  5. Cyclic Strain Resistance, Stress Response, Fatigue Life, and Fracture Behavior of High Strength Low Alloy Steel 300 M

    NASA Astrophysics Data System (ADS)

    Manigandan, K.; Srivatsan, T. S.; Tammana, Deepthi; Poorgangi, Behrang; Vasudevan, Vijay K.

    2014-05-01

    The focus of this technical manuscript is a record of the specific role of microstructure and test specimen orientation on cyclic stress response, cyclic strain resistance, and cyclic stress versus strain response, deformation and fracture behavior of alloy steel 300 M. The cyclic strain amplitude-controlled fatigue properties of this ultra-high strength alloy steel revealed a linear trend for the variation of log elastic strain amplitude with log reversals-to-failure, and log plastic strain amplitude with log reversals-to-failure for both longitudinal and transverse orientations. Test specimens of the longitudinal orientation showed only a marginal improvement over the transverse orientation at equivalent values of plastic strain amplitude. Cyclic stress response revealed a combination of initial hardening for the first few cycles followed by gradual softening for a large portion of fatigue life before culminating in rapid softening prior to catastrophic failure by fracture. Fracture characteristics of test specimens of this alloy steel were different at both the macroscopic and fine microscopic levels over the entire range of cyclic strain amplitudes examined. Both macroscopic and fine microscopic observations revealed fracture to be a combination of both brittle and ductile mechanisms. The underlying mechanisms governing stress response, deformation characteristics, fatigue life, and final fracture behavior are presented and discussed in light of the competing and mutually interactive influences of test specimen orientation, intrinsic microstructural effects, deformation characteristics of the microstructural constituents, cyclic strain amplitude, and response stress.

  6. Inversion of the strain-life and strain-stress relationships for use in metal fatigue analysis

    NASA Technical Reports Server (NTRS)

    Manson, S. S.

    1979-01-01

    The paper presents closed-form solutions (collocation method and spline-function method) for the constants of the cyclic fatigue life equation so that they can be easily incorporated into cumulative damage analysis. The collocation method involves conformity with the experimental curve at specific life values. The spline-function method is such that the basic life relation is expressed as a two-part function, one applicable at strains above the transition strain (strain at intersection of elastic and plastic lines), the other below. An illustrative example is treated by both methods. It is shown that while the collocation representation has the advantage of simplicity of form, the spline-function representation can be made more accurate over a wider life range, and is simpler to use.

  7. A zero torsional stiffness twist morphing blade as a wind turbine load alleviation device

    NASA Astrophysics Data System (ADS)

    Lachenal, X.; Daynes, S.; Weaver, P. M.

    2013-06-01

    This paper presents the design, analysis and realization of a zero stiffness twist morphing wind turbine blade. The morphing blade is designed to actively twist as a means of alleviating the gust loads which reduce the fatigue life of wind turbine blades. The morphing structure exploits an elastic strain energy balance within the blade to enable large twisting deformations with modest actuation requirements. While twist is introduced using the warping of the blade skin, internal pre-stressed members ensure that a constant strain energy balance is achieved throughout the deformation, resulting in a zero torsional stiffness structure. The torsional stability of the morphing blade is characterized by analysing the elastic strain energy in the device. Analytical models of the skin, the pre-stressed components and the complete blade are compared to their respective finite element models as well as experimental results. The load alleviation potential of the adaptive structure is quantified using a two-dimensional steady flow aerodynamic model which is experimentally validated with wind tunnel measurements.

  8. 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.

  9. 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.

  10. 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.

  11. The Relationships Between Microstructure, Tensile Properties and Fatigue Life in Ti-5Al-5V-5Mo-3Cr-0.4Fe (Ti-5553)

    NASA Astrophysics Data System (ADS)

    Foltz, John W., IV

    beta-titanium alloys are being increasingly used in airframes as a way to decrease the weight of the aircraft. As a result of this movement, Ti-5Al-5V-5Mo-3Cr-0.4Fe (Timetal 555), a high-strength beta titanium alloy, is being used on the current generation of landing gear. This alloy features good combinations of strength, ductility, toughness and fatigue life in alpha+beta processed conditions, but little is known about beta-processed conditions. Recent work by the Center for the Accelerated Maturation of Materials (CAMM) research group at The Ohio State University has improved the tensile property knowledge base for beta-processed conditions in this alloy, and this thesis augments the aforementioned development with description of how microstructure affects fatigue life. In this work, beta-processed microstructures have been produced in a Gleeble(TM) thermomechanical simulator and subsequently characterized with a combination of electron and optical microscopy techniques. Four-point bending fatigue tests have been carried out on the material to characterize fatigue life. All the microstructural conditions have been fatigue tested with the maximum test stress equal to 90% of the measured yield strength. The subsequent results from tensile tests, fatigue tests, and microstructural quantification have been analyzed using Bayesian neural networks in an attempt to predict fatigue life using microstructural and tensile inputs. Good correlation has been developed between lifetime predictions and experimental results using microstructure and tensile inputs. Trained Bayesian neural networks have also been used in a predictive fashion to explore functional dependencies between these inputs and fatigue life. In this work, one section discusses the thermal treatments that led to the observed microstructures, and the possible sequence of precipitation that led to these microstructures. The thesis then describes the implications of microstructure on fatigue life and implications of tensile properties on fatigue life. Several additional experiments are then described that highlight possible causes for the observed dependence of microstructure on fatigue life, including fractographic evidence to provide support of microstructural dependencies.

  12. Influence of test specimen fabrication method and cross-section configuration on tension-tension fatigue life of PMMA bone cement.

    PubMed

    Sheafi, E M; Tanner, K E

    2015-11-01

    Different cyclic loading modes have been used in in vitro fatigue studies of PMMA bone cement. It is unclear which loading mode is most appropriate from the perspective of the in vivo loading experienced by the cement in a cemented arthroplasty. Also, in different in vitro fatigue studies, different test specimen configurations have been used. The present work considers the influence of test specimen fabrication method (direct moulding vs moulding followed by machining) and cross-section shape (rectangular vs circular) on the tension-tension fatigue performance of two bone cement brands (SmartSet GHV and CMW1), under force control conditions. Two trends were consistent: 1) for each of the cements, for moulded specimens, a longer fatigue life was obtained with circular cross-sectioned specimens and, 2) for either rectangular or circular CMW1 specimens, a longer fatigue life was obtained using machined specimens. A comparison of the present results to those reported in our previous work on fully-reversed tension-compression loading under force control showed that, regardless of the test specimen fabrication method or cross-section configuration used, the fatigue life was considerably shorter under tension-compression than tension-tension loading. This finding highlights the fact that the presence of the compression portion in the loading cycle accelerates fatigue failure. PMID:26295451

  13. 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.

  14. Low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Solomon, H. D. (editor); Kaisand, L. R. (editor); Halford, G. R. (editor); Leis, B. N. (editor)

    1988-01-01

    The papers contained in this volume focus on various aspects of low cycle fatigue, including cyclic deformation, crack propagation, high-temperature low cycle fatigue, microstructural defects, multiaxial and variable amplitude loading, and life prediction. Papers are presented on the low cycle fatigue of some aluminum alloys, prediction of crack growth under creep-fatigue loading conditions, high-temperature low cycle fatigue behavior and lifetime prediction of a nickel-base ODS alloy, and an integrated approach to creep-fatigue life prediction. Other topics discussed include thermal fatigue testing of coated monocrystalline superalloys, low cycle fatigue of Al-Mg-Si alloys, and the effect of superimposed stresses at high frequency on low cycle fatigue.

  15. 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.

  16. Vibration of axial turbomachinery blades: Measurement and fluid-structure interactions

    NASA Astrophysics Data System (ADS)

    Mikrut, Paul Louis

    The focus of this dissertation is on turbomachinery blade vibration measurements and unsteady fluid-structure interactions. Vibration of turbomachinery blades are critical to jet engine durability and performance. The combined high natural frequency of the vibrations and long service life of modern jet engines can result in high cycle fatigue. There are two main topics discussed in this dissertation. The first topic of this dissertation is the investigation of unsteady fluid-structure interactions an isolated compressor blade in transonic flow. This was preferred as a simpler alternative to a cascade of blades. Note that the boundary conditions of an single vibrating blade are much simpler than those for a vibrating cascade, and so a more clear understanding of the fundamental interactions are provided with the simple setup. New insights were obtained regarding aerodynamic damping and "quasi-steady" blade vibrations in transonic flow. The second topic of this dissertation discusses the development and application of a novel blade vibration measurement technique. Accurate blade vibration measurements are critical in product aero-mechanical design validation and can be difficult to obtain. This measurement technique, termed Blade Image Velocimetry, provides an alternative to the current measurement methods which is both easy to implement and can have the potential to exceed the current accuracy of Blade Tip Timing. The theory of measurement and uncertainty analysis and benchtop validation measurements will be presented. This will be followed by the application of the measurement technique to a high speed axial compressor rotor. Tip deflections as low as 8mum were resolved by the measurement technique at a rotor tip speed of 350 m/s.

  17. Fatigue behavior of a single-crystal superalloy

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Mcgaw, Michael A.

    1989-01-01

    A single-crystal superalloy, PWA 1480 is under consideration as a replacement material for the turbine blades of the high pressure fuel turbopump (HPFTP) of the space shuttle main engine (SSME). Three separate experimental programs were conducted to characterize the fatigue behavior of this alloy. Fatigue tests were conducted at room temperature (in air) and at 1000 F (in vacuum) on smooth specimens machined from both cast bars and slabs. The data from all of these programs are consolidated to provide a broader characterization of the fatigue behavior of the single crystal PWA 1480. The zero-mean-stress fatigue relationships are expressed in terms of stress range versus cyclic life lines on log-log plots. Characterization of the fatigue behavior of (001) oriented PWA 1480 single crystal under conditions of tensile mean stress was performed by using the unified approach proposed by Heidmann. In this approach the fatigue life is modified by a mean stress parameter so that a single life relationship can be used to represent both zero and tensile mean stress data.

  18. PREDICTION OF LOW-CYCLE FATIGUE-LIFE BY ACOUSTIC EMISSION. PART 1: 2024-T3 ALUMINUM ALLOY PART 2: ALCLAD 7075-T6/ ALUMINUM ALLOY

    SciTech Connect

    Baram, J.; Rosen, M.

    1980-05-01

    Low-cycle fatigue tests were conducted by tension-compression until rupture, on a 2024-T3 aluminum alloy sheet. Initial crack sizes and orientations in the fatigue specimens were found to be randomly distributed. Acoustic emission was continuously monitored during the tests. Every few hundred cycles, the acoustic signal having the highest peak-amplitude, was recorded as an extremal event for the elapsed period. This high peak-amplitude is related to a fast crack propagation rate through a phenomenological relationship. The extremal peakamplitudes are shown by an ordered statistics treatment, to be extremally distributed. The statistical treatment enables the prediction of the number of cycles left until failure. Predictions performed a-posteriori based on results gained early in each fatigue test are in good agreement with actual fatigue lives. The amplitude distribution analysis of the acoustic signals emitted during cyclic stress appears to be a promising nondestructive method of predicting fatigue life.

  19. Surface modification of polyurethane heart valves: effects on fatigue life and calcification.

    PubMed

    Bernacca, G M; Wheatley, D J

    1998-12-01

    Polyurethane heart valves can be functionally durable with minimal calcification, in vitro. In vivo, these characteristics will depend on the resistance of the polyurethane to thrombogenesis and biodegradation. Surface modification may improve the polyurethane in these respects, but may adversely affect calcification and durability. This study investigates the effects of surface modifications of two polyurethane heart valves (PEU and PEUE) on their in vitro fatigue and calcification behaviour. Modifications included heparin, taurine, 3-aminopropyltriethoxysilane and polyethylene oxide (PEO). Neither hydrodynamic function nor leaflet thickness distribution was significantly altered by surface modification. PEO-modification was detrimental to valve fatigue durability and calcification. Heparin, taurine or aminosilane modifications of PEU valves increased durability. Aminosilane modification of PEUE valves increased durability compared with PEO modification. Appropriate surface modification may be useful to improve blood compatibility of implantable polyurethanes, and may also be advantageous as regards fatigue durability of flexing materials in longterm applications. PMID:9988359

  20. Effect of simultaneous B sup + and N sup + sub 2 implantation on microhardness, fatigue life, and microstructure in Fe-13Cr-15Ni base alloys

    SciTech Connect

    Lee, E.H.; Mansur, L.K. )

    1989-11-01

    Microhardness and cantilever beam fatigue measurements were conducted on Fe-13Cr-15Ni base austenitic alloys that were implanted with boron and nitrogen ions either singly or simultaneously. The microstructure of the modified surface layer and dislocation slip modes after fatigue tests were investigated by optical and transmission electron microscopy. Both hardness and fatigue life were improved by ion implantation, but the greatest improvement was achieved when boron and nitrogen were implanted simultaneously. The degree of fatigue life improvement also varied with minor changes in the base alloying compositions: nitrogen was detrimental or ineffective on the presence of titanium, and boron was much more effective in the presence of molybdenum. Comparison of slip band morphology between the compression and tension cycles indicated that implantation improved the reversibility of surface slip and delayed crack initiation.

  1. 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.

  2. Impact of Medical Qigong on quality of life, fatigue, mood and inflammation in cancer patients: a randomized controlled trial

    PubMed Central

    Oh, B.; Butow, P.; Mullan, B.; Clarke, S.; Beale, P.; Pavlakis, N.; Kothe, E.; Lam, L.; Rosenthal, D.

    2010-01-01

    Background: Substantial numbers of cancer patients use complementary medicine therapies, even without a supportive evidence base. This study aimed to evaluate in a randomized controlled trial, the use of Medical Qigong (MQ) compared with usual care to improve the quality of life (QOL) of cancer patients. Patients and methods: One hundred and sixty-two patients with a range of cancers were recruited. QOL and fatigue were measured by Functional Assessment of Cancer TherapyGeneral and Functional Assessment of Cancer TherapyFatigue, respectively, and mood status by Profile of Mood State. The inflammatory marker serum C-reactive protein (CRP) was monitored serially. Results: Regression analysis indicated that the MQ group significantly improved overall QOL (t144?=??5.761, P?fatigue (t153?=??5.621, P?

  3. Effect of Application of Short and Long Holds on Fatigue Life of Modified 9Cr-1Mo Steel Weld Joint

    NASA Astrophysics Data System (ADS)

    Shankar, Vani; Mariappan, K.; Sandhya, R.; Mathew, M. D.; Jayakumar, T.

    2013-11-01

    Modified 9Cr-1Mo steel is a heat-treatable steel and hence the microstructure is temperature sensitive. During welding, the weld joint (WJ) is exposed to various temperatures resulting in a complex heterogeneous microstructure across the weld joint, such as the weld metal, heat-affected zone (HAZ) (consisting of coarse-grained HAZ, fine-grained HAZ, and intercritical HAZ), and the unaffected base metal of varying mechanical properties. The overall creep-fatigue interaction (CFI) response of the WJ is hence due to a complex interplay between various factors such as surface oxides and stress relaxation (SR) occurring in each microstructural zone. It has been demonstrated that SR occurring during application of hold in a CFI cycle is an important parameter that controls fatigue life. Creep-fatigue damage in a cavitation-resistant material such as modified 9Cr-1Mo steel base metal is accommodated in the form of microstructural degradation. However, due to the complex heterogeneous microstructure across the weld joint, SR will be different in different microstructural zones. Hence, the damage is accommodated in the form of preferential coarsening of the substructure, cavity formation around the coarsened carbides, and new surface formation such as cracks in the soft heat-affected zone.

  4. 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.

  5. Improvements to the materials characterization and fatigue life prediction methods of the Texas rigid pavement overlay design procedure

    NASA Astrophysics Data System (ADS)

    Taute, A.; McCullough, B. F.; Hudon, W. R.

    1981-11-01

    Certain improvements to the Texas Rigid Pavement Overlay Procedure (RPOD2) with regard to materials characterization and fatigue life predictions are presented. Suggestions are made for characterizing rigid pavement layers from Dynaflect deflections and material tests, and some guidelines for selecting design sections along the length of a road are presented. Finite element analysis is used to quantify the effect of pavement discontinuities on the tresses obtained from layered theory. Further finite element analysis is used in an attempt to relate the critical reflection stresses in an ac overlay to deflection measurements obtained before overlaying.

  6. Rolling-element fatigue life with traction fluids and automatic transmission fluid in a high-speed rolling-contact rig

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Nahm, A. H.; Loewenthal, S. H.

    1982-01-01

    Rolling-element fatigue tests were run in standard and high-speed rolling-contact rigs at bar speeds from 5000 to 50,000 rpm to determine the effects of speed and lubricant film parameter on rolling-element fatigue life. AISI 52100 test bars were tested at a maximum Hertz stress of 4.83 GPa (700,000 psi) with three traction fluids and an automatic transmission fluid. Rolling-element fatigue life increased with speed, with the greatest increases occurring from 10,000 to 50,000 rpm. The life data tended to follow published life-versus-lubricant-film-parameter data up to a film parameter of approximately 3.

  7. Adhesive and Protective Characteristics of Ceramic Coating A-417 and Its Effect on Engine Life of Forged Refractaloy-26 (AMS 5760) and Cast Stellite 21 (AMS 5385) Turbine Blades

    NASA Technical Reports Server (NTRS)

    Garrett, Floyd B; Gyorgak, Charles A

    1953-01-01

    The adhesive and protective characteristics of National Bureau of Standards Coating A-417 were investigated, as well as the effect of the coating on the life of forged Refractaloy 26 and cast Stellite 21 turbine blades. Coated and uncoated blades were run in a full-scale J33-9 engine and were subjected to simulated service operations consisting of consecutive 20-minute cycles (15 min at rated speed and approximately 5 min at idle). The ceramic coating adhered well to Refractaloy 26 and Stellite 21 turbine blades operated at 1500 degrees F. The coating also prevented corrosion of the Refractaloy 26, a corrosion-sensitive nickel-base alloy, and of the Stellite 21, a relatively corrosion-resistant cobalt-base alloy. Although the coating prevented corrosion of both alloys, it had no apparent effect on blade life.

  8. Fatigue design considerations for deepwater fixed platforms

    SciTech Connect

    Hanna, S.Y.; Chang, N.H.; Nair, V.V.D.; Wang, W.J.

    1984-05-01

    Fatigue is an important consideration in the design of deepwater platforms. In this study, fatigue design strategies for deepwater fixed platforms are presented. Parameters influencing the fatigue design as well as areas susceptible to fatigue failure are identified. Recommended design solutions and resizing charts to improve the fatigue life are presented. Relevant results from fatigue analyses of typical deepwater platforms are presented. Uncertainties in various parameters contributing to fatigue and research needed to improve the reliability of fatigue predictions are discussed.

  9. Fatigue strain-life behavior of carbon and low-alloy steels, austenitic stainless steels, and Alloy 600 in LWR environments

    SciTech Connect

    Keisler, J.; Chopra, O.K.; Shack, W.J.

    1995-08-01

    The existing fatigue strain vs. life (S-N) data, foreign and domestic, for carbon and low-alloy steels, austenitic stainless steels, and Alloy 600 used in the construction of nuclear power plant components have been compiled and categorized according to material, loading, and environmental conditions. Statistical models have been developed for estimating the effects of the various service conditions on the fatigue life of these materials. The results of a rigorous statistical analysis have been used to estimate the probability of initiating a fatigue crack. Data in the literature were reviewed to evaluate the effects of size, geometry, and surface finish of a component on its fatigue life. The fatigue S-N curves for components have been determined by adjusting the probability distribution curves for smooth test specimens for the effect of mean stress and applying design margins to account for the uncertainties due to component size/geometry and surface finish. The significance of the effect of environment on the current Code design curve and on the proposed interim design curves published in NUREG/CR-5999 is discussed. Estimations of the probability of fatigue cracking in sample components from BWRs and PWRs are presented.

  10. Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

    This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

  11. Turbofan blade stresses induced by the flow distortion of a VTOL inlet at high angles of attack

    NASA Technical Reports Server (NTRS)

    Williams, R. C.; Diedrich, J. H.; Shaw, R. J.

    1983-01-01

    A 51-cm-diameter turbofan with a tilt-nacelle VTOL inlet was tested in the Lewis Research Center's 9- by 15-Ft Low Speed Wind Tunnel at velocities up to 72 m/s and angles of attack up to 120 deg. Fan-blade vibratory stress levels were investigated over a full aircraft operating range. These stresses were due to inlet air flow distortion resulting from (1) internal flow separation in the inlet, and (2) ingestion of the exterior nacelle wake. Stress levels are presented, along with an estimated safe operating envelope, based on infinite blade fatigue life.

  12. Creep-fatigue interaction in aircraft gas turbine components by simulation and testing at scaled temperatures

    NASA Astrophysics Data System (ADS)

    Sabour, Mohammad Hossein

    Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional creep model, using ANSYS has been formulated in order to predict the creep life of a gas turbine engine blade. Innovative mathematical models for the prediction of the operating life of aircraft components, specifically gas turbine blades, which are subjected to creep-fatigue at high temperatures, are proposed. The components are modeled by FEM, mathematically, and using similitude principles. Three models have been suggested and evaluated numerically and experimentally. Using FEM method for natural frequencies causes phenomena such as curve veering which is studied in more detail. The simulation studies on the life-limiting modes of failure, as well as estimating the expected lifetime of the blade, using the proposed models have been carried out. Although the scale model approach has been used for quite some time, the thermal scaling has been used in this study for the first time. The only thermal studies in literature using scaling for structures is by NASA in which materials of both the prototype and the model are the same, but in the present study materials also are different. The finite element method is employed to model the structure. Because of stress redistribution due to the creep process, it is necessary to include a full inelastic creep step in the finite element formulation. Otherwise over-conservative creep life predictions will be estimated if only the initial elastic stresses are considered. The experimental investigations are carried out in order to validate the models. The main contributions in the thesis are: (1) Using similitude theory for life prediction of components in general, and specifically using thermal scaling for the first time for prototype and model with two different materials. (2) Developing 1-D creep ANSYS macro to study creep effects to get meaningful results for industrial applications of gas turbine blade. (3) Analyzing the curve veering and flattening phenomena in rotating blade at thermal environment, using Lagrange-Bhat method. (4) Simple constitutive models in creep-fatigue interaction are proposed that can predict the lifetime in complicated situations of creep-fatigue, using the pure creep and pure fatigue test data.

  13. Casting dimensional control and fatigue life prediction for permanent mold casting dies. Technical report, September 29, 1993--May 31, 1997

    SciTech Connect

    1997-06-01

    Efforts as part of a three year program to address metal casting dimensional control and fatigue life prediction for permanent mold casting dies are described. Procedures have been developed and implemented to collect dimensional variability data from production steel casting. The influence of process variation and casting geometry variables on dimensional tolerances have been investigated. Also efforts leading to the developments and validation of a CAD/CAE model to predict the thermal fatigue life of permanent molds for aluminum castings are described. An appropriate thermomechanical property database for metal, mold and coating materials has been constructed. A finite element model has been developed to simulate the mold temperature distribution during repeated casting cycles. Validation trials using a permanent mold casting machine have indicated the success of the temperature distribution model developed. A combination of experimental and modeling techniques have been employed to extend their knowledge of permanent mold casting. The influence of coatings on casting solidification and mold temperatures has been determined. The computer model has been extended to predict thermally induced stresses and strains in the mold and to predict the number of cycles required to crack the mold. Experimental results have been used to validate the extended model.

  14. Structural health monitoring of wind turbine blades : SE 265 Final Project.

    SciTech Connect

    Barkley, W. C.; Jacobs, Laura D.; Rutherford, A. C.; Puckett, Anthony

    2006-03-23

    ACME Wind Turbine Corporation has contacted our dynamic analysis firm regarding structural health monitoring of their wind turbine blades. ACME has had several failures in previous years. Examples are shown in Figure 1. These failures have resulted in economic loss for the company due to down time of the turbines (lost revenue) and repair costs. Blade failures can occur in several modes, which may depend on the type of construction and load history. Cracking and delamination are some typical modes of blade failure. ACME warranties its turbines and wishes to decrease the number of blade failures they have to repair and replace. The company wishes to implement a real time structural health monitoring system in order to better understand when blade replacement is necessary. Because of warranty costs incurred to date, ACME is interested in either changing the warranty period for the blades in question or predicting imminent failure before it occurs. ACME's current practice is to increase the number of physical inspections when blades are approaching the end of their fatigue lives. Implementation of an in situ monitoring system would eliminate or greatly reduce the need for such physical inspections. Another benefit of such a monitoring system is that the life of any given component could be extended since real conditions would be monitored. The SHM system designed for ACME must be able to operate while the wind turbine is in service. This means that wireless communication options will likely be implemented. Because blade failures occur due to cyclic stresses in the blade material, the sensing system will focus on monitoring strain at various points.

  15. QL-20PROGNOSTIC IMPORTANCE OF HEALTH-RELATED QUALITY OF LIFE AND FATIGUE IN NEWLY DIAGNOSED GLIOBLASTOMA

    PubMed Central

    Peters, Katherine; Randazzo, Dina; Affronti, Mary; Lipp, Eric; McSherry, Frances; Herndon, James; Flahiff, Charlene; Miller, Elizabeth; Woodring, Sarah; Freeman, Maria; Healy, Patrick; Minchew, Janet; Boulton, Susan; Desjardins, Annick; Ranjan, Tulika; Vlahovic, Gordana; Jones, Lee; Friedman, Henry

    2014-01-01

    After diagnosis, glioblastoma (GBM) patients quickly experience the neurological, physical, and emotional impact of their disease. Even before chemoradiation treatment, health-related quality of life (HRQoL) can be impaired and fatigue can be present due to neurological dysfunction, co-morbidities (e.g. seizures, depression), and medications (e.g. corticosteroids, anti-epileptics). We evaluated the impact of HRQoL and fatigue on survival in newly diagnosed GBM. Data collected within the Preston Robert Tisch Brain Tumor Center at Duke as part of the PRoGREss registry between 11/21/2011 and 10/10/2013 were queried retrospectively. In addition to demographic and clinical information, data were obtained from patient-reported outcome questionnaires including Functional Assessment of Cancer Therapy-Brain Cancer (FACT-Br) and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F). Cox proportional hazard models were utilized to evaluate the effect of HRQoL and fatigue on overall survival. For this study, 322 subjects were identified. Mean age was 59 (SD = 13) years. KPS ranged from 40-100 with KPS ≥90 for 36.7%, KPS = 80 for 34.5%, KPS ≤ 70 for 21.4% and unknown for 7.5%. In univariate Cox analyses, the FACT-Br Total (HR = 0.986 (CI 95%: 0.98, 0.992) and FACIT-F (HR = 0.969 (CI 95%: 0.955, 0.982)) were both significant predictors of overall survival. Both the FACT-Br Total and FACIT-F added prognostic information beyond that provided by KPS alone (Likelihood ratio (LR) p = 0.003 and p = 0.004, respectively), but did not provide additional prognostic information when KPS, age, gender, and extent of resection were added to the multivariate model (LR p = 0.17 and p = 0.19, respectively). In fact, the strongest predictor of overall survival in this population was extent of resection (gross total resection vs biopsy, (HR = 3.11 (CI 95%: 2.12, 4.57))). Based on these findings, HRQoL and fatigue in newly diagnosed GBM are independent predictors of survival that provide incremental prognostic value to KPS but not to other prognostic factors such as extent of resection.

  16. 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.

  17. Development of an integral damping treatment for NASA's next-generation hollow fan blades

    NASA Astrophysics Data System (ADS)

    Kosmatka, John B.; Mehmed, Oral

    2002-06-01

    A NASA research program is underway to develop fan blades that have significantly greater propulsive efficiency, lower acoustic noise, and lower weight. These blades have a large internal manifold and open trailing edge that is used to blow air in the downwash. The blades are composed of a titanium root and composite internal manifold with an outer graphite/epoxy shell. Due to the complex internal structure and open-cell design, these blades have low natural frequencies and bending-torsion coupled mode shapes that could potentially lead to aeroelastic instabilities. Increasing the damping levels in these blades will improve the fatigue life and reduce aeroelastic instability concerns. The vibratory modes of interest include the first and second bending modes as well as first torsion mode. Due to the geometric constraints of the outer blade shape and large internal manifold very little room is available for damping treatment placement. Results from the analysis study reveal that (1) significantly more damping can be obtained by embedding the material in the outer shells than within the manifold vanes, (2) carefully designing a patch that fills approximately 29% of the surface area and is only 0.005' thick will produce a loss factor of at least 0.01 for the first three structural modes, and (3) a patch that fills approximately 45% of the surface area will produce a loss factor of at least 0.02 for the first three structural modes.

  18. The effects of decellularization and cross-linking techniques on the fatigue life and calcification of mitral valve chordae tendineae.

    PubMed

    Gunning, Gillian M; Murphy, Bruce P

    2016-04-01

    In cases of severely diseased mitral valves (MV), the required treatment is often valve replacement. Bioprosthetic and stentless replacement valves are usually either fully or partially composed of animal derived tissue treated with a decellularization process, a cross-linking process, or both. In this study, we analysed the effects of these treatments on the fatigue properties of porcine MV chordae tendineae (CT), as well as on the calcification of the CT using an in vitro technique. CT were tested in 4 groups; (1) native, (2) decellularized (DC), (3) decellularized and cross-linked with glutaraldehyde (DC-GTH), and (4) decellularized and cross-linked with 1-ehtyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)(DC-EDC). CT were tested in both uniaxial tension, and in fatigue at 10MPa peak stress (1Hz). The cycles to failure (mean±SD) for the four groups are as follows; Native- 53,397±55,798, DC- 28,013±30,634, DC-GTH- 97,665±133,556, DC-EDC- 318,601±322,358. DC-EDC CT were found to have a slightly longer fatigue life than the native and DC groups. The DC-EDC group also had a marginally lower dynamic creep rate, meaning those CT elongate more slowly. After in vitro calcification, X-ray microtomography was used to determine relative levels of calcification. The DC-EDC and DC-GTH groups had the lowest volume of calcific deposits. Under uniaxial testing, the ultimate tensile strength (UTS) of the DC-GTH CT was statistically significantly reduced after calcification, while the UTS was relatively unchanged for the DC-EDC group. Overall, these results indicate that a treatment of decellularization plus cross-linking with EDC may improve the fatigue life of porcine CT, reduce the rate of elongation, and help the CT resist the negative effects of calcification. This may be a preferable treatment in the preparation of porcine MVs for the replacement of diseased MVs. PMID:26875146

  19. 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).

  20. Turbine blade tip durability analysis

    NASA Technical Reports Server (NTRS)

    Mcknight, R. L.; Laflen, J. H.; Spamer, G. T.

    1981-01-01

    An air-cooled turbine blade from an aircraft gas turbine engine chosen for its history of cracking was subjected to advanced analytical and life-prediction techniques. The utility of advanced structural analysis techniques and advanced life-prediction techniques in the life assessment of hot section components are verified. Three dimensional heat transfer and stress analyses were applied to the turbine blade mission cycle and the results were input into advanced life-prediction theories. Shortcut analytical techniques were developed. The proposed life-prediction theories are evaluated.

  1. Effect of grinding on the fatigue life of titanium alloy (5 Al-2.5 Sn) under dry and wet conditions

    NASA Technical Reports Server (NTRS)

    Rangaswamy, Partha; Terutung, Hendra; Jeelani, Shaik

    1989-01-01

    The principal factors in the performance of aerospace materials are strength-to-weight ratio, fatigue life, fracture toughness, survivability and, of course, reliability. Machining processes and, in particular, grinding under adverse conditions have been found to cause damage to surface integrity and affect the residual stress distribution in the surface and subsurface region. These effects have a direct bearing on the fatigue life. In this investigation the effects of grinding conditions on the fatigue life of Titanium 5 Al-2.5Sn were studied. This alloy is used in ground form in the manufacturing of some critical components in the space shuttle's main engine. It is essential that materials for such applications be properly characterized for use in severe service conditions. Flat sub-size specimens 0.1 inch thick were ground on a surface grinding machine equipped with a variable speed motor at speeds of 2000 to 6000 rpm using SiC wheels of grit sizes 60 and 120. The grinding parameters used in this investigation were chosen from a separate study. The ground specimens were then fatigued at a selected stress and the resulting lives were compared with that of the virgin material. The surfaces of the specimens were examined under a scanning electron microscope, and the roughness and hardness were measured using a standard profilometer and microhardness tester, respectively. The fatigue life of the ground specimens was found to decrease with the increase in speed for both dry and wet conditions. The fatigue life of specimens ground under wet conditions showed a significant increase at the wheel speed of 2000 rpm for both the grit sizes and thereafter decreased with increase profilometry, microhardness measurements and scanning electron microscopic examination.

  2. The effect of group mindfulness - based stress reduction program and conscious yoga on the fatigue severity and global and specific life quality in women with breast cancer

    PubMed Central

    Rahmani, Soheila; Talepasand, Siavash

    2015-01-01

    Background: Cancer is not merely an event with a certain end, but it is a permanent and vague situation that is determined by delayed effects due to the disease, its treatment and its related psychological issues. The aim of this study was to examine the effectiveness of the mindfulness-based stress reduction program and conscious yoga on the mental fatigue severity and life quality of women with breast cancer. Methods: This was a quasi-experimental study with a pre-test, post-test and control group. In this study, 24 patients with the diagnosis of breast cancer were selected among the patients who referred to the Division of Oncology and Radiotherapy of Imam Hossein hospital in Tehran using available sampling method, and were randomly assigned into the experimental and control groups. All the participants completed the Fatigue Severity Scale, Global Life Quality of Cancer Patient and Specific Life Quality of Cancer Patient questionnaires. Data were analyzed by multivariate repeated measurement variance analysis model. Results: Findings revealed that the mindfulness-based stress reduction treatment significantly improved the overall quality of life, role, cognitive, emotion, social functions and pain and fatigue symptoms in global life quality in the experimental group. It also significantly improved the body image, future functions and therapy side effects in specific life quality of the experimental group compared to the control group. In addition, fatigue severity caused by cancer was reduced significantly. Conclusion: The results showed that the mindfulness - based stress reduction treatment can be effective in improving global and specific life quality and fatigue severity in women with breast cancer. PMID:26034728

  3. Fatigue life prediction for a carbon fiber reinforced resin composite subjected to reversed cycle loading

    SciTech Connect

    Adam, T.; Gathercole, N.; Harris, B.; Reiter, H.

    1993-12-31

    A study has been made of the fatigue behavior of an intermediate modulus Toray T800 carbon fiber/resin laminate with a [({+-}45,O{sub 2}){sub 2}]{sub s} lay-up. While in sequences of all-tension blocks, a linear damage law was found to be appropriate, in all compression or mixed tension-compression modes a linear law was no longer valid. An analysis of data from 2-block loading tests shows the potential of a power law of cumulative damage for describing behavior in reversed loading.

  4. Fatigue Criterion for System Design

    NASA Technical Reports Server (NTRS)

    Zeretsky, E. V.

    1986-01-01

    Report discusses principles of structural-life prediction. Generalized methodology developed for structural life prediction, design, and reliability, based upon fatigue criterion. Approach incorporates computed life of elemental stress volumes of complex machine elements to predict system life. Results of coupon fatigue testing incorporated into analysis, allowing for life prediction and component or structural renewal rates, with reasonable statistical certainty.

  5. Life prediction technologies for aeronautical propulsion systems

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1990-01-01

    Fatigue and fracture problems continue to occur in aeronautical gas turbine engines. Components whose useful life is limited by these failure modes include turbine hot-section blades, vanes, and disks. Safety considerations dictate that catastrophic failures be avoided, while economic considerations dictate that catastrophic failures be avoided, while economic considerations dictate that noncatastrophic failures occur as infrequently as possible. Therefore, the decision in design is making the tradeoff between engine performance and durability. LeRC has contributed to the aeropropulsion industry in the area of life prediction technology for over 30 years, developing creep and fatigue life prediction methodologies for hot-section materials. At the present time, emphasis is being placed on the development of methods capable of handling both thermal and mechanical fatigue under severe environments. Recent accomplishments include the development of more accurate creep-fatigue life prediction methods such as the total strain version of LeRC's strain-range partitioning (SRP) and the HOST-developed cyclic damage accumulation (CDA) model. Other examples include the development of a more accurate cumulative fatigue damage rule - the double damage curve approach (DDCA), which provides greatly improved accuracy in comparison with usual cumulative fatigue design rules. Other accomplishments in the area of high-temperature fatigue crack growth may also be mentioned. Finally, we are looking to the future and are beginning to do research on the advanced methods which will be required for development of advanced materials and propulsion systems over the next 10-20 years.

  6. 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.

  7. Influence of process parameters on rolling-contact-fatigue life of ion plated nickel-copper-silver lubrication

    SciTech Connect

    Danyluk, Mike; Dhingra, Anoop

    2012-05-15

    In this paper, we present a connection between argon ion flux, element-mixing, and rolling contact fatigue (RCF) life of a thin film nickel-copper-silver lubricant on ball bearings. The film is deposited on the balls using an ion plating process and tested for RCF in high vacuum. The ion flux is measured using a Langmuir probe and the plane stress within the film during deposition is calculated using a thin film model. Experiments reveal that there is an inverse relationship between ion flux and RCF life for most deposition voltage and pressure combinations tested, specifically, 15.5-18.5 mTorr and 1.5-3.5 kV. For voltages up to 2.5 kV, RCF life decreases as ion flux increases due to increased compressive stress within the film, reaching as high as 2.6 GPa. For voltages between 2.5 and 3.5 kV, interlayer mixing of nickel and copper with the silver layer reduces RCF life due to contamination, even as ion flux and corresponding film compressive stress are reduced. A Monte Carlo-based simulation tool, SRIM is used to track collision cascades of the argon ions and metal atoms within the coating layers. At process voltages above 2.5 kV we observe elemental mixing of copper and nickel with the silver layer using Auger electron spectroscopy of coated steel and Si{sub 3}N{sub 4} balls. The authors conclude that an ion flux greater than 5.0 x 10{sup 14} cm{sup -2} s{sup -1} leads to reduced RCF life due to high film stress. In addition, process voltages greater than 2.5 kV also reduce RCF life due to contamination and interlayer mixing of nickel and copper within the silver layer.

  8. 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.

  9. Comparison of pitting fatigue life of ausforged and standard forged AISI M-50 and AISI 9310 spur gears

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Bamberger, E. N.; Zaretsky, E. V.

    1975-01-01

    Standard forged and ausforged spur gears made of vacuum-induction-melted, consumable-electrode, vacuum-arc-remelted AISI M-50 steel were tested under conditions that produced fatigue pitting. The gears were 8.89 cm (3.5 in.) in pitch diameter and had tip relief. The M-50 standard forged and ausforged test results were compared with each other. They were then compared with results for machined vacuum-arc-remelted AISI 9310 gears tested under identical conditions. Both types of M-50 gears had lives approximately five times that of the 9310 gears. The life at which 10 percent of the M-50 ausforged gears failed was slightly less than that at which the M-50 standard forged gears failed. The ausforged gears had a slightly greater tendency to fail by tooth fracture than did the standard forged gears, most likely because of the better forging and grain flow pattern of standard forged gears.

  10. Case histories involving fatigue and fracture mechanics; Proceedings of the Symposium, Charleston, SC, Mar. 21, 22, 1985

    NASA Technical Reports Server (NTRS)

    Hudson, C. Michael (editor); Rich, Thomas P. (editor)

    1986-01-01

    Papers are presented on cracking at nozzle corners in the nuclear pressure vessel industry, applied fracture mechanics for assessing defect significance in a crude oil pipeline, failure analysis of a large wind-tunnel compressor blade, analysis of a compressor-wheel failure, and preventing fracture by inspection and analysis. Consideration is also given to the fatigue crack growth predictions of welded aircraft structures containing flaws in the residual stress field, the fatigue and fracture mechanics analysis of a compression loaded aircraft structure, fracture of an aircraft horizontal stabilizer, fatigue life analysis of fuel tank skins under combined loads, and aircraft structural maintenance recommendations based on fracture mechanics analysis. Additional papers discuss an analysis of two metal-forming die failures, an analysis of a failed saw arbor, and the role of fracture mechanics in assessing the effect on fatigue life of design changes in welded fabrications.

  11. Mitigation of edgewise vibrations in wind turbine blades by means of roller dampers

    NASA Astrophysics Data System (ADS)

    Zhang, Zili; Li, Jie; Nielsen, Søren R. K.; Basu, Biswajit

    2014-10-01

    Edgewise vibrations in wind turbine blades are lightly damped, and large amplitude vibrations induced by the turbulence may significantly shorten the fatigue life of the blade. This paper investigates the performance of roller dampers for mitigation of edgewise vibrations in rotating wind turbine blades. Normally, the centrifugal acceleration of the rotating blade can reach to a magnitude of 7-8g, which makes it possible to use this kind of damper with a relatively small mass ratio for suppressing edgewise vibrations effectively. The parameters of the damper to be optimized are the mass ratio, the frequency ratio, the coefficient of rolling friction and the position of the damper in the blade. The optimization of these parameters has been carried out on a reduced 2-DOF nonlinear model of the rotating wind turbine blade equipped with a roller damper in terms of a ball or a cylinder, ignoring the coupling with other degrees of freedom of the wind turbine. The edgewise modal loading on the blade has been calculated from a more sophisticated 13-DOF aeroelastic wind turbine model with due consideration to the indicated couplings, the turbulence and the aerodynamic damping. Various turbulence intensities and mean wind speeds have been considered to evaluate the effectiveness of the roller damper in reducing edgewise vibrations when the working conditions of the wind turbine are changed. Further, the optimized roller damper is incorporated into the 13-DOF wind turbine model to verify the application of the decoupled optimization. The results indicate that the proposed damper can effectively improve the structural response of wind turbine blades.

  12. 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

  13. Improved stud configurations for attaching laminated wood wind turbine blades

    SciTech Connect

    Faddoul, J.R.

    1985-09-01

    In order to improve joint strength for bonded studs in laminated wood structures (wind turbine blades) a series of designs was developed and tested. Each design systematically varied a parameter which was expected to have a significant effect on performance. The structural capability of each design was established based on tension-tension fatigue tests, and it was found that a stud with a concave tapered carrot design, bonded in place with an epoxy thickened with chopped carbon fiber, was the most effective design. Further improvements in joint performance could be made by augmenting the laminated wood with thin plies of carbon cloth (10 percent thickness buildup) in the area of the stud. Two designs were selected for further testing, which demonstrated that joint strengths approaching the membrane wood strength could be achieved. For a 3- by 3-inch wood block, an ultimate load exceeding 100,000 lbs could be introduced through a single bonded stud. For the same type of specimen in cyclic tension at an R-ratio of 0.1, the bonded studs were projected to have a fatigue life of 4 x 10/sup 8/ cycles at maximum loads of 30,000 lbs. For reversed axial fatigue, a reduction of 25 percent from these numbers was shown to be appropriate. These values represent an improvement of 100 percent over the stud designs used previously for laminated wood wind turbine blades. However, temperatures of 100/sup 0/F with humidity at 100 percent in certain cases caused a loss of ultimate load capability approaching 35 percent and a loss of fatigue capacity approaching 50 percent. While this result may have been specimen-related, additional testing or a change in the epoxy resin system should be considered before using the bonded stud designs in hot, humid environments.

  14. Developments in new aircraft tire tread materials. [fatigue life of elastomeric materials

    NASA Technical Reports Server (NTRS)

    Yager, T. J.; Mccarty, J. L.; Riccitiello, S. R.; Golub, M. A.

    1976-01-01

    Comparative laboratory and field tests were conducted on experimental and state-of-the-art aircraft tire tread materials in a program aimed at seeking new elastomeric materials which would provide improved aircraft tire tread wear, traction, and blowout resistance in the interests of operational safety and economy. The experimental stock was formulated of natural rubber and amorphous vinyl polybutadiene to provide high thermal-oxidative resistance, a characteristic pursued on the premise that thermal oxidation is involved both in the normal abrasion or wear of tire treads and probably in the chain of events leading to blowout failures. Results from the tests demonstrate that the experimental stock provided better heat buildup (hysteresis) and fatigue properties, at least equal wet and dry traction, and greater wear resistance than the state-of-the-art stock.

  15. Determination of Rolling-Element Fatigue Life From Computer Generated Bearing Tests

    NASA Technical Reports Server (NTRS)

    Vlcek, Brian L.; Hendricks, Robert C.; Zaretsky, Erwin V.

    2003-01-01

    Two types of rolling-element bearings representing radial loaded and thrust loaded bearings were used for this study. Three hundred forty (340) virtual bearing sets totaling 31400 bearings were randomly assembled and tested by Monte Carlo (random) number generation. The Monte Carlo results were compared with endurance data from 51 bearing sets comprising 5321 bearings. A simple algebraic relation was established for the upper and lower L(sub 10) life limits as function of number of bearings failed for any bearing geometry. There is a fifty percent (50 percent) probability that the resultant bearing life will be less than that calculated. The maximum and minimum variation between the bearing resultant life and the calculated life correlate with the 90-percent confidence limits for a Weibull slope of 1.5. The calculated lives for bearings using a load-life exponent p of 4 for ball bearings and 5 for roller bearings correlated with the Monte Carlo generated bearing lives and the bearing data. STLE life factors for bearing steel and processing provide a reasonable accounting for differences between bearing life data and calculated life. Variations in Weibull slope from the Monte Carlo testing and bearing data correlated. There was excellent agreement between percent of individual components failed from Monte Carlo simulation and that predicted.

  16. Influence of electroless nickel-phosphorus deposits on the corrosion-fatigue life of notched and unnotched samples of an AISI 1045 steel

    SciTech Connect

    Chitty, J.A.; Pertuz, A.; Puchi, E.S.; Hintermann, H.

    1999-02-01

    Electroless nickel-phosphorus deposits of approximately 10% phosphorus and about 20 {micro}m thickness are shown either to have no effect or sometimes to increase the corrosion-fatigue properties of a quenched and tempered AISI 1045 steel in the stress amplitude range of 481 to 687 MPa, in the presence of an aqueous solution of 3% sodium chloride. Such an increase is produced when the stress amplitude is below 516 MPa. For the notched specimens, no substantial differences are found between the fatigue life of the coated and uncoated specimens.

  17. Effects of voids on delamination behavior under static and fatigue mode I and mode II

    NASA Astrophysics Data System (ADS)

    Abdelal, Nisrin Rizek

    Composite materials have become materials of choice for wind turbine blade manufacturing due to their high specific stiffness, strength and fatigue life. Glass fiber composites are used extensively in light-weight structural components for wind turbines, aircrafts, marine craft and high performance automobile because glass fiber is inexpensive and usually provides high strength to weight ratio and good in-plane mechanical properties. The high cycle fatigue resistance of composite materials used in wind turbine blades has been recognized as a major uncertainty in predicting the reliability of wind turbines over their design lifetime. Blades are expected to experience 108 to 109 fatigue cycles over a 20 to 30 year lifetime. Delamination or interlaminar failure is a serious failure mode observed in composite structures. Even partial delamination will lead to a loss of local stiffness, which can preclude buckling failure. Manufacturing process defects such as voids and fiber waviness degrade the fatigue life and delamination resistance of the blade's composite. This research describes the effect of voids on static and fatigue interlaminar fracture behavior under mode I and mode II loading of wind turbine glass fiber composites. Samples with different void volume fractions in the 0.5%-7% range were successfully obtained by varying the vacuum in the hand layup vacuum bagging manufacturing process. Void content was characterized using four different methods; ultrasonic scanning, epoxy burn off, serial sectioning and X-Ray computed tomography. The effect of voids on both mode I and mode II interlaminar fracture toughness under static and fatigue loading was investigated. Finally, fractographic analysis (using optical and scanning electron microscopy) was conducted. The results showed that voids leads to slight reduction in static modes I and II interlaminar fracture toughness. In addition, voids lead to a decrease in modes I and II maximum cyclic strain energy release rates and fatigue life. Fractographic features allowed relations to be drawn between fracture surfaces and mechanical properties of the composite, and to investigate the differences in the fractographic features between panels fabricated at different vacuum levels, and between static and fatigue modes I and II.

  18. Fatigue in neuroimmunological diseases.

    PubMed

    Greim, Brigitte; Engel, Claudia; Apel, Annett; Zettl, Uwe K

    2007-05-01

    Fatigue is a widespread symptom in numerous neuroimmunological diseases like multiple sclerosis (MS), myasthenia gravis, morbus Behcet, neurosarcoidosis, neuroborreliosis or immune vasculitis. This phenomenon is best investigated in MS. The complex mechanisms underlying fatigue in MS are still poorly understood; alterations in immune system activation, central nervous system dysregulation, impaired nerve conduction, and neuroendocrine dysregulation have to be considered. These immune and neural mechanisms may cause the initial symptoms of fatigue; however, the fatigue symptom may be exacerbated by secondary overlapping factors (e. g. depressive mood, sleep disturbances, unhealthy life style) which are likely associated with the feeling of fatigue. Wessely conceptualised four components of fatigue: behaviour (effects of fatigue), feeling (subjective experience), mechanisms, and context (e. g. environment, attitudes). So far most examinations have dealt with the first or the second component of the multidimensional construct fatigue, either concentrating on the behavioural aspect in the physical or in the cognitive sphere or on the subjective aspect. The Rostock Fatigue Study investigated two of the components: objective performance and subjective fatigue estimation in the cognitive and in the physical sphere. MS patients showed a reversed relationship between below-average objective performance in the cognitive and in the physical sphere and high subjective feeling of tiredness when compared to healthy individuals. The clinical management of fatigue should include an assessment of the various factors that can cause fatigue as well as a step-wise treatment approach that encompasses nonpharmacological approaches and pharmacological interventions. PMID:17503116

  19. Creep fatigue life prediction for engine hot section materials (isotropic): Two year update

    NASA Technical Reports Server (NTRS)

    Moreno, V.

    1984-01-01

    Requirements for increased durability of gas turbine hot section components have placed a greater degree of importance on accurate structural analysis and life prediction. Various life prediction approaches for high temperature applications were investigated. Basic models were selected and developed for simple-cycle, isothermal loading conditions. Models will be developed which address thermomechanical cycling, multiaxial conditions, cumulative loading, environmental effects, and cyclic mean stress. Verification tests of models will be conducted on an alternate material and coating system.

  20. Induction of engineered residual stresses fields and enhancement of fatigue life of high reliability metallic components by laser shock processing

    NASA Astrophysics Data System (ADS)

    Ocaa, J. L.; Porro, J. A.; Daz, M.; Ruiz de Lara, L.; Correa, C.; Gil-Santos, A.; Peral, D.

    2013-02-01

    Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials mechanical and surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys characteristic of high reliability components in the aerospace, nuclear and biomedical sectors) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies. Additional remarks on the improved character of the LSP technique over the traditional "shot peening" technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.

  1. Optimization of rotor blades for combined structural, dynamic, and aerodynamic properties

    NASA Technical Reports Server (NTRS)

    He, Cheng-Jian; Peters, David A.

    1990-01-01

    Optimal helicopter blade design with computer-based mathematical programming has received more and more attention in recent years. Most of the research has focused on optimum dynamic characteristics of rotor blades to reduce vehicle vibration. There is also work on optimization of aerodynamic performance and on composite structural design. This research has greatly increased our understanding of helicopter optimum design in each of these aspects. Helicopter design is an inherently multidisciplinary process involving strong interactions among various disciplines which can appropriately include aerodynamics; dynamics, both flight dynamics and structural dynamics; aeroelasticity: vibrations and stability; and even acoustics. Therefore, the helicopter design process must satisfy manifold requirements related to the aforementioned diverse disciplines. In our present work, we attempt to combine several of these important effects in a unified manner. First, we design a blade with optimum aerodynamic performance by proper layout of blade planform and spanwise twist. Second, the blade is designed to have natural frequencies that are placed away from integer multiples of the rotor speed for a good dynamic characteristics. Third, the structure is made as light as possible with sufficient rotational inertia to allow for autorotational landing, with safe stress margins and flight fatigue life at each cross-section, and with aeroelastical stability and low vibrations. Finally, a unified optimization refines the solution.

  2. Relation of Engine Turbine-blade Life to Stress-rupture Properties of the Alloys, Stellite 21, Hastelloy B, Cast S-816, Forged S-816, X-40, Nimonic 80, Refractaloy 26, N-155, and Inconel X

    NASA Technical Reports Server (NTRS)

    Garrett, F B; Yaker, C

    1951-01-01

    An investigation was conducted to relate the engine performance of the heat-resistant alloys, Stellite 21, Hastelloy B, cast S-816, forged S-816, X-40, Nimonic 80, Refractory 26, N-155, and Iconel X to their stress-rupture properties. The engine test consisted of the repetition of a 20-minute cycle, 15 minutes at rated speed and approximately 5 minutes at idle. The results of the investigation indicated a direct correlation between stress-rupture life and blade life for the relatively low-strength alloys. The stress-rupture life and blade life for the relatively high-strength alloys did not correlate because of the effects of the vibratory stresses and the corrosive-gas atmosphere.

  3. Quality of life in multiple sclerosis (MS) and role of fatigue, depression, anxiety, and stress: A bicenter study from north of Iran

    PubMed Central

    Salehpoor, Ghasem; Rezaei, Sajjad; Hosseininezhad, Mozaffar

    2014-01-01

    Background: Although studies have demonstrated significant negative relationships between quality of life (QOL), fatigue, and the most common psychological symptoms (depression, anxiety, stress), the main ambiguity of previous studies on QOL is in the relative importance of these predictors. Also, there is lack of adequate knowledge about the actual contribution of each of them in the prediction of QOL dimensions. Thus, the main objective of this study is to assess the role of fatigue, depression, anxiety, and stress in relation to QOL of multiple sclerosis (MS) patients. Materials and Methods: One hundred and sixty-two MS patients completed the questionnaire on demographic variables, and then they were evaluated by the Persian versions of Short-Form Health Survey Questionnaire (SF-36), Fatigue Survey Scale (FSS), and Depression, Anxiety, Stress Scale-21 (DASS-21). Data were analyzed by Pearson correlation coefficient and hierarchical regression. Results: Correlation analysis showed a significant relationship between QOL elements in SF-36 (physical component summary and mental component summary) and depression, fatigue, stress, and anxiety (P < 0.01). Hierarchical regression analysis indicated that among the predictor variables in the final step, fatigue, depression, and anxiety were identified as the physical component summary predictor variables. Anxiety was found to be the most powerful predictor variable amongst all (? = ?0.46, P < 0.001). Furthermore, results have shown depression as the only significant mental component summary predictor variable (? = ?0.39, P < 0.001). Conclusions: This study has highlighted the role of anxiety, fatigue, and depression in physical dimensions and the role of depression in psychological dimensions of the lives of MS patients. In addition, the findings of this study indirectly suggest that psychological interventions for reducing fatigue, depression, and anxiety can lead to improved QOL of MS patients. PMID:25558256

  4. Work capacity and health-related quality of life among individuals with multiple sclerosis reduced by fatigue: a cross-sectional study

    PubMed Central

    2013-01-01

    Background Among individuals diagnosed with the chronic neurologic disease, multiple sclerosis (MS), a majority suffers from fatigue, which strongly influences their every-day-life. The aim of this study was to investigate work capacity and health-related quality of life (HRQoL) in a group of MS patients and also to investigate if work capacity and HRQoL could be predicted by background factors, fatigue, heat sensitivity, cognitive dysfunction, emotional distress or degree of disability. Methods A descriptive, cross-sectional, designed survey was undertaken A questionnaire was sent to 323 individuals diagnosed with MS, aged between 20 and 65years, with physical disability on the expanded disability status score (EDSS) in the interval 0???EDSS???6.5, living in stergtland county in eastern Sweden. Questions on background factors, occupation and work, together with the health-related quality of life short form instrument (SF-36), the fatigue severity scale (FSS), the perceived deficit questionnaire (PDQ) and the hospital anxiety depression scale (HAD) were posed. Associations between variables were analyzed using Pearsons and Spearmans correlations. Differences between groups were tested using the Chi-square test, the Mann Whitney U-test, and the Students t-test. Predictive factors were analyzed using multiple linear and multiple logistic regression analysis. Results Of those who completed the questionnaire (n?=?257, 79.6%), 59.8% were working. Work capacity was found significantly more among men (p?fatigue (p?fatigue, higher level of education, male sex and lower age. Those with work capacity showed significantly higher HRQoL than those who had no work capacity (p?fatigue, cognition and emotional distress were found to be major contributing factors for HRQoL. Conclusions Work capacity and HRQoL among individuals diagnosed with MS are highly influenced by fatigue which can be considered as a key symptom. Work capacity was influenced by heat-sensitivity, cognitive difficulties and emotional distress and significant predictive factors besides fatigue, were physical disability (EDSS), age, sex, and level of education. Remaining at work also gives a better HRQoL. PMID:23497281

  5. Delayed-release prednisone improves fatigue and health-related quality of life: findings from the CAPRA-2 double-blind randomised study in rheumatoid arthritis

    PubMed Central

    Alten, Rieke; Grahn, Amy; Holt, Robert J; Rice, Patricia; Buttgereit, Frank

    2015-01-01

    Objectives Like morning stiffness, fatigue is a common, debilitating symptom of rheumatoid arthritis (RA). Delayed-release (DR) prednisone is designed for evening administration (approximately 22:00) and releases 4 h later to coincide with the rise of nocturnal inflammatory cytokines associated with development of morning stiffness. The impact of DR prednisone on fatigue and other related patient-reported outcomes was analysed with data obtained from the Circadian Administration of Prednisone in Rheumatoid Arthritis (CAPRA) 2 study. Methods Patients with symptomatic RA (n=350) despite treatment with a disease-modifying antirheumatic drug (DMARD) were randomised 2:1 to receive additional therapy with DR prednisone 5 mg or placebo once daily for 12 weeks. Fatigue was assessed using validated instruments: the fatigue scale of the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) and the vitality domain of the Short Form-36 (SF-36). General quality of life was assessed using the general score and individual domains of Functional Assessment of Cancer Therapy-General (FACT-G) and SF-36. Results The change from baseline to week 12 in FACIT-F score was statistically significantly different with DR prednisone/DMARD (3.8) versus placebo/DMARD (1.6; difference 2.2, p=0.0032). Improvement in FACIT-F score correlated positively with clinical response. Compared with placebo/DMARD, DR prednisone/DMARD showed a significantly greater improvement in SF-36 vitality score (5.6, p=0.001), physical component of SF-36 (2.3, p=0.0003) and general score with FACT-G (2.6, p=0.0233). Conclusions DR prednisone in addition to a DMARD significantly improves fatigue and other aspects of health-related quality of life in patients with symptomatic RA compared with DMARD treatment alone. Trial registration number ClinicalTrials.gov NCT00650078. PMID:26535146

  6. Prediction of stochastic blade responses using measured wind-speed data as input to the FLAP code

    NASA Astrophysics Data System (ADS)

    Wright, A. D.; Thresher, R. W.

    1988-11-01

    Accurately predicting wind turbine blade loads and response is important in predicting the fatigue life of wind turbines. The necessity of including turbulent wind effects in structural dynamics models has long been recognized. At SERI, the structural dynamics model, or FLAP (Force and Loads Analysis Program), is being modified to include turbulent wind fluctuations in predicting rotor blade forces and moments. The objective of this paper is to show FLAP code predictions compared to measured blade loads, using actual anemometer array data and a curve-fitting routine to form series expansion coefficients as the turbulence input to FLAP. The predictions are performed for a three-blade upwind field test turbine. An array of nine anemometers was located 0.8 rotor diameters (D) upwind of the turbine, and data from each anemometer are used in a least-squares curve-fitting routine to obtain a series expansion of the turbulence field over the rotor disk. Three 10-min data cases are used to compare FLAP predictions to measured results. Each case represents a different mean wind speed and turbulence intensity. The time series of coefficients in the expansion of the turbulent velocity field are input to the FLAP code. Time series of predicted flap-bending, moments at two blade radial stations are obtained, and power spectra of the predictions are then compared to power spectra of the measured blade bending moments.

  7. Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition

    NASA Technical Reports Server (NTRS)

    Phillips, E. P.

    1974-01-01

    Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.

  8. Diagnostic methods of a bladed disc mode shape evaluation used for shrouded blades in steam turbines

    NASA Astrophysics Data System (ADS)

    Strnad, Jaromir; Liska, Jindrich

    2015-11-01

    This paper deals with advanced methods for the evaluation of a bladed disc behavior in terms of the wheel vibration and blade service time consumption. These methods are developed as parts of the noncontact vibration monitoring system of the steam turbine shrouded blades. The proposed methods utilize the time-frequency processing (cross spectra) and the method using least squares to analyse the data from the optical and magnetoresistive sensors, which are mounted in the stator radially above the rotor blades. Fundamentally, the blade vibrations are detected during the blade passages under the sensors and the following signal processing, which covers also the proposed methods, leads to the estimation of the blade residual service life. The prototype system implementing above mentioned techniques was installed into the last stage of the new steam turbine (LP part). The methods for bladed disc mode shape evaluation were successfully verified on the signals, which were obtained during the commission operation of the turbine.

  9. Low-cycle thermal fatigue

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1986-01-01

    A state-of-the-art review is presented of the field of thermal fatigue. Following a brief historical review, the concept is developed that thermal fatigue can be viewed as processes of unbalanced deformation and cracking. The unbalances refer to dissimilar mechanisms occurring in opposing halves of thermal fatigue loading and unloading cycles. Extensive data summaries are presented and results are interpreted in terms of the unbalanced processes involved. Both crack initiation and crack propagation results are summarized. Testing techniques are reviewed, and considerable discussion is given to a technique for thermal fatigue simulation, known as the bithermal fatigue test. Attention is given to the use of isothermal life prediction methods for the prediction of thermal fatigue lives. Shortcomings of isothermally-based life prediction methods are pointed out. Several examples of analyses and thermal fatigue life predictions of high technology structural components are presented. Finally, numerous dos and don'ts relative to design against thermal fatigue are presented.

  10. Influence of Ply Waviness on Fatigue Life of Tapered Composite Flexbeam Laminates

    NASA Technical Reports Server (NTRS)

    Murri, Gretchen B.

    1999-01-01

    Nonlinear tapered flexbeam laminates, with significant ply waviness, were cut from a full-size composite rotor hub flexbeam. The specimens were tested under combined axial tension and cyclic bending loads. All of the specimens had wavy plies through the center and near the surfaces (termed marcelled areas), although for some of the specimens the surface marcels were very obvious, and for others they were much smaller. The specimens failed by first developing cracks through the marcels at the surfaces, and then delaminations grew from those cracks, in both directions. Delamination failure occurred in these specimens at significantly shorter fatigue lives than similar specimens without waviness, tested in ref. 2. A 2D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. In addition, the FE model duplicated the waviness observed in one of the test specimens. The model was analyzed using a geometrically nonlinear FE code. Modifications were made to the original model to reduce the amplitude of the marcels near the surfaces. The analysis was repeated for each modification. Comparisons of the interlaminar normal stresses, sigma(sub n), in the various models showed that under combined axial-tension and cyclic-bending loading, for marcels of the same aspect ratio, sigma(sub n) stresses increased as the distance along the taper, from thick to thin end, increased. For marcels of the same aspect ratio and at the same X-location along the taper, sigma(sub n) stresses decreased as the distance from the surface into the flexbeam interior increased. A technique was presented for determining the smallest acceptable marcel aspect ratio at various locations in the flexbeam.

  11. Quality of life, depression and fatigue among persons co-infected with HIV and hepatitis C: outcomes from a population-based cohort.

    PubMed

    Braitstein, P; Montessori, V; Chan, K; Montaner, J S G; Schechter, M T; O'Shaughnessy, M V; Hogg, R S

    2005-05-01

    The objective of the study was to describe the additional burden generated by hepatitis C (HCV) infection among HIV-infected individuals as measured by self-reported quality of life, depression and fatigue. The provincial HIV/AIDS Drug Treatment Program (DTP) distributes all antiretroviral medication in the province of British Columbia. Eligibility for accessing antiretrovirals is based on published guidelines commensurate with the International AIDS Society. Each participant is asked to complete a self-administered mailed questionnaire that includes patient sociodemographic information, quality of life measures (Medical Outcomes Study-Short Form (MOS-SF), mental health issues (Centre for Epidemiological Studies Depression scale (CESD) and fatigue information. HIV-HCV co-infected individuals were compared to HIV mono-infected individuals using parametric and nonparametric methods. Multivariate logistic regression was used to examine the impact of hepatitis C on quality of life, depression and fatigue, after controlling for sociodemographics and HIV-specific clinical characteristics. Of the 4,134 individuals who were sent a HIV/AIDS DTP survey in 1999, 2000 or 2001, 484 participants both returned one and had an HCV-antibody test result on file. Of the 484 participants eligible for this analysis, 105 (22%) were HCV-positive. In comparison to the 379 (78%) patients testing negative for HCV, a larger proportion of co-infected patients were female (18% versus 3%, p<0.001), aboriginal (20% versus 3%, p<0.001), had ever injected drugs (79% versus 5%, p<0.001), were unemployed (91% versus 49%, p<0.001) and lived in unstable housing (19% versus 1%, p<0.001) at the time they completed the survey. Co-infected patients reported more symptoms consistent with depression, increased fatigue and poorer quality of life. However, using multivariate modeling, it was determined that the impact of HCV on quality of life, depression and fatigue was better explained by the sociodemographic factors related to poverty and injection drug use, than by HCV itself. In conclusion, individuals co-infected with HIV and HCV represent a patient population with significant physical and mental health challenges. Although these patients experience poorer quality of life, increased depression and fatigue, this experience appears to be primarily related to socio-economic issues rather than HCV infection. PMID:16036236

  12. 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.

  13. Surface fatigue life of carburized and hardened M50NiL and AISI 9310 spur gears and rolling-contact test bars

    NASA Technical Reports Server (NTRS)

    Townsend, Dennis P.; Bamberger, Eric N.

    1989-01-01

    Spur gear endurance tests and rolling-element surface tests were conducted to investigate vacuum-induction-melted, vacuum-arc-melted (VIM-VAR) M50NiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance characteristics, and to compare the results with those for standard VAR and VIM-VAR AISI 9310 gear material. Tests were conducted with spur gears and rolling-contact bars manufactured from VIM-VAR M50NiL and VAR and VIM-VAR AISI 9310. The gear pitch diameter was 8.9 cm (3.5 in.). Gear test conditions were an inlet oil temperature of 320 K (116 F), and outlet oil temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. Bench rolling-element fatigue tests were conducted at ambient temperatures with a bar speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPA (700 ksi). The VIM-VAR M50NiL gears had a surface fatigue life that was 4.5 and 11.5 times that for VIM-VAR and VAR AISI 9310 gears, respectively. The surface fatigue life of the VIM-VAR M50NiL rolling-contact bars was 13.2 and 21.6 times that for the VIM-VAR and VAR AISI 9310, respectively. The VIM-VAR M50NiL material was shown to have good resistance to fracture through a fatigue spall and to have fatigue life far superior to that of both VIM-VAR and VAR AISI 9310 gears and rolling-contact bars.

  14. Application of Single Crystal Failure Criteria: Theory and Turbine Blade Case Study

    NASA Technical Reports Server (NTRS)

    Sayyah, Tarek; Swanson, Gregory R.; Schonberg, W. P.

    1999-01-01

    The orientation of the single crystal material within a structural component is known to affect the strength and life of the part. The first stage blade of the High Pressure Fuel Turbopump (HPFTP)/ Alternative Turbopump Development (ATD), of the Space Shuttle Main Engine (SSME) was used to study the effects of secondary axis'orientation angles on the failure rate of the blade. A new failure criterion was developed based on normal and shear strains on the primary crystallographic planes. The criterion was verified using low cycle fatigue (LCF) specimen data and a finite element model of the test specimens. The criterion was then used to study ATD/HPFTP first stage blade failure events. A detailed ANSYS finite element model of the blade was used to calculate the failure parameter for the different crystallographic orientations. A total of 297 cases were run to cover a wide range of acceptable orientations within the blade. Those orientations are related to the base crystallographic coordinate system that was created in the ANSYS finite element model. Contour plots of the criterion as a function of orientation for the blade tip and attachment were obtained. Results of the analysis revealed a 40% increase in the failure parameter due to changing of the primary and secondary axes of material orientations. A comparison between failure criterion predictions and actual engine test data was then conducted. The engine test data comes from two ATD/HPFTP builds (units F3- 4B and F6-5D), which were ground tested on the SSME at the Stennis Space Center in Mississippi. Both units experienced cracking of the airfoil tips in multiple blades, but only a few cracks grew all the way across the wall of the hollow core airfoil.

  15. 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.

  16. Difference in quality of life, fatigue and societal participation between living and deceased donor kidney transplant recipients.

    PubMed

    de Groot, Ingrid B; Veen, J Iraida E; van der Boog, Paul J M; van Dijk, Sandra; Stiggelbout, Anne M; Marang-van de Mheen, Perla J

    2013-01-01

    Purpose of this study was to assess whether living (LD) and deceased donor (DD) kidney transplant recipients differ in health-related quality of life (HRQoL), fatigue and societal participation, depending on time since transplantation and after adjustment for clinical and demographic variables. A questionnaire study was performed among 309 LD and 226 DD recipients (response rate 74% and 61%) transplanted between 1997 and 2009. After adjustment for age, sex, and education, LD recipients transplanted less than or equal to five yr ago experienced better HRQoL than DD recipients on the domains' role limitations due to physical problems, general health perception, and on the physical component summary score (all p < 0.05) and a better societal participation (all subscales, p < 0.05). No differences were found in the mental health domains. The LD recipients also had better renal clearance than DD recipients (62.1 vs. 55.9 mL/min, p = 0.01). After additional adjustment for renal clearance, the differences in HRQoL and societal participation between LD and DD recipients remained. No differences were found in recipients transplanted more than five yr ago. We conclude that LD recipients on average have better HRQoL and societal participation than DD recipients, in the first years after transplantation. PMID:23808752

  17. Low cycle fatigue behaviour of a plasma-sprayed coating material

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  18. The low cycle fatigue behavior of a plasma-sprayed coating material

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V., Jr.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  19. Low cycle fatigue behavior of a plasma-sprayed coating material

    SciTech Connect

    Gayda, J.; Gabb, T.P.; Miner, R.V. Jr.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  20. Effects of resistance exercise on fatigue and quality of life in breast cancer patients undergoing adjuvant chemotherapy: A randomized controlled trial.

    PubMed

    Schmidt, Martina E; Wiskemann, Joachim; Armbrust, Petra; Schneeweiss, Andreas; Ulrich, Cornelia M; Steindorf, Karen

    2015-07-15

    Multiple exercise interventions have shown beneficial effects on fatigue and quality of life (QoL) in cancer patients, but various psychosocial interventions as well. It is unclear to what extent the observed effects of exercise interventions are based on physical adaptations or rather on psychosocial factors associated with supervised, group-based programs. It needs to be determined which aspects of exercise programs are truly effective. Therefore, we aimed to investigate whether resistance exercise during chemotherapy provides benefits on fatigue and QoL beyond potential psychosocial effects of group-based interventions. One-hundred-one breast cancer patients starting chemotherapy were randomly assigned to resistance exercise (EX) or a relaxation control (RC) group. Both interventions were supervised, group-based, 2/week over 12 weeks. The primary endpoint fatigue was assessed with a 20-item multidimensional questionnaire, QoL with the EORTC QLQ-C30/BR23. Analyses of covariance for individual changes from baseline to Week 13 were calculated. In RC, total and physical fatigue worsened during chemotherapy, whereas EX showed no such impairments (between-group p?=?0.098 and 0.052 overall, and p?=?0.038 and 0.034 among patients without severe baseline depression). Differences regarding affective or cognitive fatigue were not significant. Benefits of EX were also seen to affect role and social function. Effect sizes were between 0.43 and 0.48. Explorative analyses indicated significant effect modification by thyroxin use (p-interaction?=?0.044). In conclusion, resistance exercise appeared to mitigate physical fatigue and maintain QoL during chemotherapy beyond psychosocial effects inherent to supervised group-based settings. Thus, resistance exercise could be an integral part of supportive care for breast cancer patients undergoing chemotherapy. PMID:25484317