Sample records for blade fatigue life

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

    Microsoft Academic Search

    Franck Gallerneau; Jean-Louis Chaboche

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    Wind turbines must withstand harsh environments that induce many stress cycles into their components. A numerical analysis package is used to illustrate the sobering variability in predicted fatigue life with relatively small changes in inputs. The variability of the input parameters is modeled to obtain estimates of the fatigue reliability of the turbine blades.

  3. 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.

  4. Blade fatigue life assessment with application to VAWTs

    NASA Astrophysics Data System (ADS)

    Veers, P. S.

    1982-05-01

    The possibility of satisfactory modeling of the vibratory stress level history of a vertical axis wind turbine (VAWT) is considered. Fatigue life prediction is expressed as a function of the vibratory stress level, the wind speed, and the wind speed distribution on-site. A statistical distribution of stress levels is asserted to more accurately simulate the stress level than determination of the stress levels at each wind speed. Miner's cumulative damage rule is examined as a tool to generate a vibratory stress level distribution in terms of peak vibrations in a narrow-band Gaussian process. Examples are given for 30-40 sec intervals on the 17 m VAWT at Sandia Laboratories. A threshold was set beneath which no vibrations were recorded, yielding a Rayleigh distribution at the 0.5 significance level. It is concluded that a Rayleigh distribution from test data produces a cycle to failure versus wind speed curve which is superior to constant amplitude fatigue life data such as appropriate to Miner's Rule.

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

    NASA Technical Reports Server (NTRS)

    Ingram, J.; Gross, L.

    1985-01-01

    The results of low cycle fatigue testing on turbine blades for use in hydrogen/oxygen rocket engines is presented. Cored blade and cored blades with circulation were tested in the MSFC thermal fatigue tester. Both blade configurations showed significant low cycle fatigue life improvements when compared to baseline solid blades.

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

    SciTech Connect

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

    1997-01-01

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

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

    Microsoft Academic Search

    Nobuhiro Isobe; Shuhei Nogami

    2009-01-01

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

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

    Microsoft Academic Search

    V. T. Troshchenko; A. V. Prokopenko

    1999-01-01

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

  9. 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).

  10. 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..

  11. 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.

  12. Fatigue strength of gas turbine compressor blades

    Microsoft Academic Search

    V. T. Troshchenko; A. V. Prokopenko

    2000-01-01

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

  13. 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.

  14. 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.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2002-01-01

    Fretting fatigue describes the formation and growth of cracks at the edge-of-contact of nominally clamped components subjected to cyclic loading. Components that are known to be subject to fretting fatigue include riveted lap joints and blade/disk contacts in launch vehicle turbomachinery. Recent efforts have shown that conventional mechanics tools, both fatigue and fracture based, can be used to model fretting fatigue experiments leading to successful life predictions. In particular, experiments involving contact load configurations similar to those that occur in the blade/disk connection of gas turbine engines have been performed extensively. Predictions of fretting fatigue life have been compared favorably to experimental observations [1]. Recent efforts are aimed at performing experiments at higher temperatures as shown in the photograph below along with a sample fracture surface. The talk will describe the status of these experiments as will as model developments relevant to the single crystal material properties.

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

    SciTech Connect

    Veers, P.S.

    1981-01-01

    A cursory analysis of the stress history of wind turbine blades indicates that a single stress level at each wind speed does not adequately describe the blade stress history. A statistical description is required. Blade stress data collected from the DOE/ALCOA Low Cost experimental turbines indicate that the Rayleigh probability density function adequately describes the distribution of vibratory stresses at each wind speed. The Rayleigh probability density function allows the distribution of vibratory stresses to be described by the RMS of the stress vs. time signal. With the RMS stress level described for all wind speeds, the complete stress history of the turbine blades is known. Miner's linear cumulative damage rule is used as a basis for summing the fatigue damage over all operating conditions. An analytical expression is derived to predict blade fatigue life.

  18. 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.

  19. 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.

  20. Selection of Wind Turbine Blade Materials for Fatigue Resistance

    E-print Network

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

  1. 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.

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

    Microsoft Academic Search

    Paul S. Prevéy; N. Jayaraman; Ravi Ravindranath

    Compressor blades of a military aircraft turbine engine made of 17 -4 PH stainless steel have been reported to have blade edge foreign object damage (FOD), corrosion pitting, and erosion damage that reduce fatigue life. This paper reports the findings of a comprehensive investigation of the effect of residual compressive stresses, imparted by various surface treatments, to improve leading edge

  3. 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

  4. Simulation of fatigue failure in composite axial compressor blades

    Microsoft Academic Search

    Qubo Li; Janusz Piechna; Norbert Müeller

    2011-01-01

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

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

    Microsoft Academic Search

    R. Rajasekaran; D. Nowell

    2006-01-01

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

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

    E-print Network

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

  7. Fatigue failure of a compressor blade

    Microsoft Academic Search

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

    2008-01-01

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

  8. 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.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    To improve the reliability and the thermal efficiency of LP (Low Pressure) end blades of steam turbine, new standard series of LP end blades have been developed. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. One of the probable failure modes of the ISB structure seems to be fretting fatigue, because the ISB utilizes friction damping between adjacent shrouds and stubs. Therefore, in order to design a blade with high reliability, the design procedure for evaluating the fretting fatigue strength was established by the model test and the nonlinear contact analysis. This paper presents the practical design method for predicting the fretting fatigue strength of the ISB structure, and the some applications are explained.

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

    Microsoft Academic Search

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

    2012-01-01

    This paper presents experimental results of several structural health monitoring (SHM) methods applied to a 9-meter CX-100 wind turbine blade that underwent fatigue loading. The blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. It underwent harmonic excitation at its first natural frequency using a hydraulically actuated resonant excitation system. The blade was initially excited

  12. 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.

  13. 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.

  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. 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.

  16. 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.

  17. 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.

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

    Microsoft Academic Search

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

    2002-01-01

    Fretting fatigue describes the formation and growth of cracks at the edge-of-contact of nominally clamped components subjected to cyclic loading. Components that are known to be subject to fretting fatigue include riveted lap joints and blade\\/disk contacts in launch vehicle turbomachinery. Recent efforts have shown that conventional mechanics tools, both fatigue and fracture based, can be used to model fretting

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

    SciTech Connect

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

    1995-06-01

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

  20. 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.

  1. 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

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

    PubMed Central

    Wito?, Miros?aw

    2013-01-01

    The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF) have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM), experimental modal analysis (EMA) and tip timing (TTM) methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy), have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed. PMID:24191135

  3. Constitutive and life modeling of single crystal blade alloys for root attachment analysis

    NASA Technical Reports Server (NTRS)

    Meyer, T. G.; Mccarthy, G. J.; Favrow, L. H.; Anton, D. L.; Bak, Joe

    1988-01-01

    Work to develop fatigue life prediction and constitutive models for uncoated attachment regions of single crystal gas turbine blades is described. At temperatures relevant to attachment regions, deformation is dominated by slip on crystallographic planes. However, fatigue crack initiation and early crack growth are not always observed to be crystallographic. The influence of natural occurring microporosity will be investigated by testing both hot isostatically pressed and conventionally cast PWA 1480 single crystal specimens. Several differnt specimen configurations and orientations relative to the natural crystal axes are being tested to investigate the influence of notch acuity and the material's anisotropy. Global and slip system stresses in the notched regions were determined from three dimensional stress analyses and will be used to develop fatigue life prediction models consistent with the observed lives and crack characteristics.

  4. 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.

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

    Microsoft Academic Search

    Darris L. White

    2003-01-01

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

  6. 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.

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

    SciTech Connect

    Mandell, John F. (Montana State University, Bozeman, MT); Ashwill, Thomas D.; Wilson, Timothy J. (Montana State University, Bozeman, MT); Sears, Aaron T. (Montana State University, Bozeman, MT); Agastra, Pancasatya (Montana State University, Bozeman, MT); Laird, Daniel L.; Samborsky, Daniel D. (Montana State University, Bozeman, MT)

    2010-12-01

    This report presents an analysis of trends in fatigue results from the Montana State University program on the fatigue of composite materials for wind turbine blades for the period 2005-2009. Test data can be found in the SNL/MSU/DOE Fatigue of Composite Materials Database which is updated annually. This is the fifth report in this series, which summarizes progress of the overall program since its inception in 1989. The primary thrust of this program has been research and testing of a broad range of structural laminate materials of interest to blade structures. The report is focused on current types of infused and prepreg blade materials, either processed in-house or by industry partners. Trends in static and fatigue performance are analyzed for a range of materials, geometries and loading conditions. Materials include: sixteen resins of three general types, five epoxy based paste adhesives, fifteen reinforcing fabrics including three fiber types, three prepregs, many laminate lay-ups and process variations. Significant differences in static and fatigue performance and delamination resistance are quantified for particular materials and process conditions. When blades do fail, the likely cause is fatigue in the structural detail areas or at major flaws. The program is focused strongly on these issues in addition to standard laminates. Structural detail tests allow evaluation of various blade materials options in the context of more realistic representations of blade structure than do the standard test methods. Types of structural details addressed in this report include ply drops used in thickness tapering, and adhesive joints, each tested over a range of fatigue loading conditions. Ply drop studies were in two areas: (1) a combined experimental and finite element study of basic ply drop delamination parameters for glass and carbon prepreg laminates, and (2) the development of a complex structured resin-infused coupon including ply drops, for comparison studies of various resins, fabrics and pry drop thicknesses. Adhesive joint tests using typical blade adhesives included both generic testing of materials parameters using a notched-lap-shear test geometry developed in this study, and also a series of simulated blade web joint geometries fabricated by an industry partner.

  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. [Los Alamos National Laboratory; Farinholt, Kevin M. [Los Alamos National Laboratory; Jeong, Hyomi [Chonbuk National University, Korea; Jang, JaeKyung [Chonbuk National University, Korea; Park, Gyu Hae [Los Alamos National Laboratory; Todd, Michael D. [Los Alamos National Laboratory; Farrar, Charles R. [Los Alamos National Laboratory; Ammerman, Curtt N. [Los Alamos National Laboratory

    2012-06-28

    This paper presents experimental results of several structural health monitoring (SHM) methods applied to a 9-meter CX-100 wind turbine blade that underwent fatigue loading. The blade was instrumented with piezoelectric transducers, accelerometers, acoustic emission sensors, and foil strain gauges. It underwent harmonic excitation at its first natural frequency using a hydraulically actuated resonant excitation system. The blade was initially excited at 25% of its design load, and then with steadily increasing loads until it failed. Various data were collected between and during fatigue loading sessions. The data were measured over multiple frequency ranges using a variety of acquisition equipment, including off-the-shelf systems and specially designed hardware developed by the authors. Modal response, diffuse wave-field transfer functions, and ultrasonic guided wave methods were applied to assess the condition of the wind turbine blade. The piezoelectric sensors themselves were also monitored using a sensor diagnostics procedure. This paper summarizes experimental procedures and results, focusing particularly on fatigue crack detection, and concludes with considerations for implementing such damage identification systems, which will be used as a guideline for future SHM system development for operating wind turbine blades.

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

    E-print Network

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

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

    NASA Astrophysics Data System (ADS)

    Birkbeck, Janine C.

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

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

    SciTech Connect

    Janetzke, D.C.

    1983-01-01

    The WEST-1 wind turbine simulator is an implementation of mathematical models for an aeroelastic horizontal-axis wind turbine rotor using current hybrid electronics technology. High-speed digital and analog circuitry enable the computation of complex dynamic characteristics and performance of a wind turbine in real time. To test the ability of WEST-1 to predict blade fatigue load distribution, actual wind signals were fed into the simulator and the response data were recorded and processed in the same manner as actual wind turbine data. The WEST-1 simulator was operated in a stable, unattended mode for six hours. The probability distribution of the cyclic flatwise bending moment for the blade was comparable to that for an actual wind turbine in winds with low turbulence. The input from a stationary anemometer was found to be inadequate for use in the prediction of fatigue load distribution for blade design purposes and modifications are necessary.

  13. Predicting the Fatigue life of Structures

    NASA Technical Reports Server (NTRS)

    Besuner, P. M.; Harris, D. O.; Thomas, J. M.; Allison, D. E.; Bannantine, J. M.; Brown, S. B.; Davis, C. S.; Derbalian, G. A.; Eischen, J. W.; Fowler, G. F.; Osteraas, J. D.; Robinson, J. N.; Sire, R. A.; Vroman, G. A.

    1985-01-01

    Report reviews fracture-mechanics technology for predicting life expectancy of structural components subjected to cyclic loads. Report covers analytical tools for modeling and forecasting subcritical fatigue-crack growth in structures. It emphasizes use of tools in practical, day-to-day problems of engineering design, development, and decisionmaking.

  14. Mechanical Bending Fatigue Life Prediction Analysis

    Microsoft Academic Search

    Erdogan Madenci; Ibrahim Guven; Bahattin Kilic

    \\u000a The fatigue life prediction of solder joints under cyclic bending requires a three-stage analysis: (1) a three-dimensional\\u000a finite element analysis with linear material properties for computing the assembly stiffness and imposed strain values, (2)\\u000a a one-dimensional combined creep and time-independent plastic deformation analysis under cyclic loading for computing the\\u000a inelastic strain energy, and (3) a life prediction analysis.

  15. Low-Cycle Fatigue Deformation Behavior and Evaluation of Fatigue Life on Extruded Magnesium Alloys

    Microsoft Academic Search

    K. Shiozawa; J. Kitajima; T. Kaminashi; T. Murai; T. Takahashi

    2011-01-01

    To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloy, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during total strain-controlled fatigue process and mean compressive strain during stress-controlled fatigue process appeared due to

  16. Deformation and fatigue behavior of SSME turbopump blade materials

    NASA Technical Reports Server (NTRS)

    Milligan, Walter W.; Antolovich, Stephen D.

    1987-01-01

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

  17. Effective strain–fatigue life data for variable amplitude fatigue

    Microsoft Academic Search

    T. H. Topper; T. S. Lam

    1997-01-01

    The usual analysis procedure for variable amplitude fatigue calculates fatigue damage based on constant amplitude strain controlled fatigue tests of smooth specimens. The resulting predictions are typically nonconservative due to a load interaction effect in variable amplitude fatigue. This paper reviews recent work which shows that large loads in a service load history decrease the crack opening stress and as

  18. Fatigue life prediction under conditions where cyclic creep–fatigue interaction occurs

    Microsoft Academic Search

    S. Kwofie; H. D. Chandler

    2007-01-01

    A stress-based model is proposed for correlating data and predicting fatigue life under conditions where cyclic creep–fatigue interaction occurs. This model is an extension of the Basquin’s stress–life relation and considers that both the fatigue strength coefficient ?f? and fatigue strength exponent b are sensitive to mean stress, both decreasing as an exponential function of the ratio of mean stress-to-stress

  19. 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.

  20. Upper and lower fatigue life limits model using energy-based fatigue properties

    Microsoft Academic Search

    H. Jahed; A. Varvani-Farahani

    2006-01-01

    Cyclic strain-life data and corresponding Coffin–Manson coefficients for both normal and shear strain-lives were first defined. Energy–fatigue life curves were then generated from strain-fatigue life properties. The upper and lower limits of life are estimated using the proposed life equations. The upper life limit is obtained by assuming that the dominant cracking mechanism is Case A and the lower life

  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. 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.

  3. Assessment of reliable fatigue life of orthotropic steel deck

    NASA Astrophysics Data System (ADS)

    Luka?evi?, Ivan; Androi?, Boris; Dujmovi?, Darko

    2011-09-01

    The fatigue life assessment of orthotropic steel decks of highway bridges still hasn't been sufficiently investigated. The inspection results of orthotropic steel decks have shown that their working life can be shorter than other members of steel highway bridges due to fatigue. This means that particular details of orthotropic decks can be critical regarding the service life of a bridge. The fatigue life of typical details of orthotropic steel decks for the real load models in Croatia and for the standardized load model of highway bridges in Eurocode has been analysed. The reliability indices have also been calculated for these details and they have been used to determine reliable fatigue life. The paper proposed the introduction of the reliable fatigue life concept which is not explicitly specified in the modern standards for structures. This concept has been offered as well as the guidelines for further probabilistic research on reliable fatigue life.

  4. Fatigue life and crack growth prediction methodology

    SciTech Connect

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

    1993-10-01

    The capabilities of a plasticity-induced crack-closure model and life-prediction code to predict fatigue crack growth and fatigue lives of metallic materials are reviewed. Crack-tip constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta(K[sub eff])) under constant-amplitude loading. Some modifications to the delta(K[sub eff])-rate relations were needed in the near threshold regime to fit small-crack growth rate behavior and endurance limits. The model was then used to calculate small- and large-crack growth rates, and in some cases total fatigue lives, for several aluminum and titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading. Fatigue lives were calculated using the crack growth relations and microstructural features like those that initiated cracks. Results from the tests and analyses agreed well.

  5. Fatigue life and crack growth prediction methodology

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    The capabilities of a plasticity-induced crack-closure model and life-prediction code to predict fatigue crack growth and fatigue lives of metallic materials are reviewed. Crack-tip constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta(K(sub eff))) under constant-amplitude loading. Some modifications to the delta(K(sub eff))-rate relations were needed in the near threshold regime to fit small-crack growth rate behavior and endurance limits. The model was then used to calculate small- and large-crack growth rates, and in some cases total fatigue lives, for several aluminum and titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading. Fatigue lives were calculated using the crack growth relations and microstructural features like those that initiated cracks. Results from the tests and analyses agreed well.

  6. ICAF Symposium Montral, 13 June 2011 FATIGUE LIFE ASSESSMENT

    E-print Network

    Texas at Arlington, University of

    assessment of useful life for composite aircraft fatigue-critical, flight-critical components and structure advances in the technologies which could enable accurate assessment of useful life for composite aircraft26th ICAF Symposium ­ Montréal, 1­3 June 2011 FATIGUE LIFE ASSESSMENT FOR COMPOSITE STRUCTURE

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

    Microsoft Academic Search

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

    1997-01-01

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

  8. Thermal fatigue life evaluation of CSP joints by mechanical fatigue testing

    Microsoft Academic Search

    Yoshihiko Kanda; Kunihiro Zama; Yoshiharu Kariya; Hironori Oota; Shunichi Kikuchi; Hideki Yamabe; Kazuhiko Nakamura

    2010-01-01

    The interrelation between a thermal cycle test and a mechanical shear fatigue test has been studied for CSP joints from the view point of fatigue life and the microstructural damage of solder joints. The fatigue lives in both methods are almost equivalent even though loading method is different. From the viewpoint of microstructure, the fact is attributed to that the

  9. 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.

  10. Weld detail fatigue life improvement techniques. Part 1: review

    Microsoft Academic Search

    K. J. Kirkhope; R. Bell; L. Caron; R. I. Basu; K.-T. Ma

    1999-01-01

    Fatigue cracks in fabricated steel structures often occur at welded joints where stress concentrations due to the joint geometry are relatively high. In many cases the fatigue performance can be improved by employing good detail design practices. However, when this is not practicable, or is not sufficient, fatigue life improvement techniques which rely on improving the stress field in and

  11. Predicting the fatigue life of asphalt concrete overlay systems 

    E-print Network

    Germann, Frederick P

    1979-01-01

    shed in this report, for quantitative analysis of overlay methods designed to reduce reflection cracking. From this testing procedure the overlay scheme that shows the most resistance to fatigue crack1ng can be chosen. The procedure uses fatigue...'s resistance to cracking can be easily seen. One way to determine the fatigue 11fe is to perform fatigue tests on over- lay samples using the overlay tester. These tests can be time consuming and costly. Another method to find the fatigue life is to use a...

  12. Fatigue life of automotive rubber jounce bumper

    NASA Astrophysics Data System (ADS)

    Sidhu, R. S.; Ali, Aidy

    2010-05-01

    It is evident that most rubber components in the automotive industry are subjected to repetitive loading. Vigorous research is needed towards improving the safety and reliability of the components. The study was done on an automotive rubber jounce bumper with a rubber hardness of 60 IRHD. The test was conducted in displacement-controlled environment under compressive load. The existing models by Kim, Harbour, Woo and Li were adopted to predict the fatigue life. The experimental results show strong similarities with the predicted models.

  13. A method for multiaxial fatigue life prediction using energy approaches

    Microsoft Academic Search

    1991-01-01

    Fatigue criteria based on the concept of damage energy have been proposed and evaluated with experimental fatigue data generated under uniaxial as well as biaxial loading conditions. Most of the energy-based methods utilize plastic energy of stress-strain hysteresis loops as a correlating parameter. Limited success has been made in predicting fatigue life in the low-cycle fatigue range where the plastic

  14. Impact of aerothermal modeling on the estimation of turbine blade life

    E-print Network

    Collin, Jean E., 1978-

    2004-01-01

    The impact of aerothermal modeling on estimates of turbine blade heat transfer and life was assessed for three high pressure turbine blades. The work was conducted as part of a project aimed at the evaluation of the effect ...

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

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

    The remarkable evolution of new generation wind turbines has led to a dramatic increase of wind turbine blade size. In turn, a reliable structural health monitoring (SHM) system will be a key factor for the successful implementation of such systems. Detection of damage at an early stage is a crucial issue as blade failure would be a catastrophic result for the entire wind turbine. In this study the SHM analysis will be based on experimental measurements of Frequency Response Functions (FRFs) extracted by using an input/output acquisition technique under a fatigue loading of a 9m CX-100 blade at the National Renewable Energy Laboratory (NREL) and National Wind Technology Center (NWTC) performed in the Los Alamos National Laboratory. The blade was harmonically excited at its first natural frequency using a Universal Resonant Excitation (UREX) system. For analysis, the Auto-Associative Neural Network (AANN) is a non-parametric method where a set of damage sensitive features gathered from the measured structure are used to train a network that acts as a novelty detector. This traditionally has a highly complex "bottleneck" structure with five layers in the AANN. In the current paper, a new attempt is also exploited based on an AANN with one hidden layer in order to reduce the theoretical and computational difficulties. Damage detection of composite bodies of blades is a "grand challenge" due to varying aerodynamic and gravitational loads and environmental conditions. A study of the noise tolerant capability of the AANN which is associated to its generalisation capacity is addressed. It will be shown that vibration response data combined with AANNs is a robust and powerful tool, offering novelty detection even when operational and environmental variations are present. The AANN is a method which has not yet been widely used in the structural health monitoring of composite blades.

  16. 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.

  17. 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.

  18. Rolling-element fatigue life of AMS 5900 balls

    NASA Technical Reports Server (NTRS)

    Parker, R. J.

    1983-01-01

    The rolling-element fatigue life of AMS 5900 12.7-mm (1/2-in.) dia was determined in five-ball fatigue testers. The 10% life with the warm headed AMS 5900 balls was equivalent to that of AMS 5749 and over eight times that of AISI M-50. The AMS balls fabricated by cold heading had small surface cracks which initiated fatigue spalls where these cracks were crossed by running tracks. The cold-headed AMS 5900 balls had a 10% fatigue life an order of magnitude less than that of the warm headed balls even when failures on the cold headed balls at visible surface cracks were omitted.

  19. Computer Prediction and Experimental Determination of Fatigue Life Probability Distributions

    Microsoft Academic Search

    Hoda Abdel-Kader Elmaraghy

    1976-01-01

    One of the central unsolved problems of engineering design is prediction of the probability distribution of fatigue life of structural members and machine components. Fatigue data scatter is a manifestation of the probabilistic nature of fatigue failure. A relationship is known to exist between the distributions of the number of cycles-to-failure and the applied stress through the probabilistic stress-life (S-N)

  20. 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.

  1. Fatigue life prediction based on variable amplitude tests—methodology

    Microsoft Academic Search

    Pär Johannesson; Thomas Svensson; Jacques de Maré

    2005-01-01

    The reliability of mechanical systems depends in part on the fatigue strength of the material, whose properties need to be determined by experiments. In a standard fatigue test a Wöhler curve is established, i.e. the relation between the life in the number of cycles and the load amplitude. Based on a damage accumulation rule, the life can be predicted for

  2. Fatigue life prediction under wide band random loading

    Microsoft Academic Search

    G. PETRUCCI; B. ZUCCARELLO

    2004-01-01

    In this paper, a method for the high-cycle fatigue life prediction of components subjected to gaussian, stationary, wide band random loading is presented. It allows the user to evaluate the fatigue life of components subjected to uniaxial stress states directly from the stress power spectral density (PSD), avoiding onerous simulations in time domain. The proposed method can be applied to

  3. Prediction of optimal inspection time for structural fatigue life

    Microsoft Academic Search

    Guangwei Meng; Feng Li; Lirong Sha; Zhenping Zhou

    2007-01-01

    An optimal inspection time model for structural fatigue life based on stochastic finite element method (SFEM) and first order reliability method (FORM) was presented. The uncertainties such as material parameters and loads which affect the fatigue life of the structure were regarded as random variables. Taylor expansion stochastic finite element method (TSFEM) was introduced to simulate the material behavior of

  4. A neural network approach to fatigue life prediction

    Microsoft Academic Search

    João Carlos Figueira Pujol; João Mário Andrade Pinto

    2011-01-01

    In this work, a novel approach to fatigue life prediction under step-stress conditions is introduced, where the cumulative distribution function for the failure of components was implemented by means of a neural network. The model was fit to experimental data on the fatigue life of steel under step-stress conditions. For comparison, a standard approach based on the lognormal distribution function

  5. Effect of corrosion pitting on fatigue crack initiation and fatigue life

    SciTech Connect

    Rokhlin, S.I.; Nagy, H.; Zoofan, B. [Ohio State Univ., Columbus, OH (United States). Dept. of Industrial, Welding and Systems Engineering

    1997-12-31

    Fatigue crack initiation and growth from artificial pits of different depths has been studied. The experimental results were analyzed using fracture-mechanical models including those for small cracks. The model shows very good agreement with experiment in describing the initiation and growth of a fatigue crack emanating from the pit and in predicting the dependence of reduction of fatigue life on pit size. Also an empirical relation between depth of the corrosion pit and fatigue life has been established. A microradiographic method for corrosion pitting depth determination has been described.

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

    Microsoft Academic Search

    Yasutomo Kaneko; Masayuki Tomii; Hiroharu Ohyama; Takayuki Kurimura

    2008-01-01

    To improve the reliability and the thermal efficiency of LP (Low Pressure) end blades of steam turbine, new standard series of LP end blades have been developed. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate

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

    Microsoft Academic Search

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

    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.

  8. 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.

  9. 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

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

    SciTech Connect

    Kuo, C.G.; Sastry, S.M.L.; Jerina, K.L. [Washington Univ., St. Louis, MO (United States)

    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.

  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. Predicting the Effects of Lubricant Chemistry on Bearing Fatigue Life

    Microsoft Academic Search

    Richard E. Cantley

    1983-01-01

    A method for predicting the effects of lubricant chemistry on bearing fatigue life was evaluated. The method was based on a correlation that was developed from wear test data, obtained with a ring-on-black tester, and full-scale bearing life test data. The correlation revealed that the degree of wear was inversely proportional to bearing fatigue life. The relationship between wear and

  13. Fatigue properties of jointed wood composites Part I Statistical analysis, fatigue master curves and constant life diagrams

    Microsoft Academic Search

    I. P. Bond; M. P. Ansell

    1998-01-01

    The primary aim of this work was to assess the fatigue performance of scarf-jointed laminated wood composites used to manufacture wind turbine blades and establish simple fatigue design procedures. Laminates made from poplar (Populus canadensis\\/serotina), Khaya (Khaya ivorensis) and beech (Fagus sylvatica), incorporating typical scarf joints, were assessed under reversed loading (R =-1). Scarf joints were found to be great

  14. Fatigue Life Prediction of Pultruded E-glass\\/Polyurethane Composites

    Microsoft Academic Search

    Pizhong Qiao; Mijia Yang

    2006-01-01

    In this article, the tension–tension fatigue behavior of newly developed pultruded E-glass\\/polyurethane composites is characterized, and an improved model for fatigue life prediction including the effects of stress ratio, frequency, and mean stress as the testing parameters is proposed. The proposed non-dimensional analysis is in good agreement with the predictions of existing available fatigue data and present testing data. The

  15. 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.

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

    E-print Network

    Victoria, University of

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

  17. 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.

  18. 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.

  19. Fatigue tests and life estimation of Incoloy alloy 908

    SciTech Connect

    Feng, J.; Toma, L.S.; Jang, C.H.; Steeves, M.M. [Massachusetts Institute of Technology, Cambridge, MA (United States)

    1997-06-01

    Incoloy{reg_sign} alloy 908* is a candidate conduit material for Nb{sub 3}Sn cable-in-conduit superconductors. The conduit is expected to experience cyclic loads at 4 K. Fatigue fracture of the conduit is one possible failure mode. So far, fatigue life has been estimated from fatigue crack growth data, which provide conservative results. The more traditional practice of life estimation using S-N curves has not been done for alloy 908 due to a lack of data at room and cryogenic temperatures. This paper presents a series of fatigue test results in response to this need. Tests were performed in reversed bending, rotating bending, and uniaxial fatigue machines. The test matrix included different heat treatments, two load ratios (R=-1 and 0.1), two temperatures (298 and 77 K), and two orientations (longitudinal and transverse). As expected, there is a semi-log linear relation between the applied stress and fatigue life above an applied stress (e.g., 310 MPa for tests at 298 K and R=-1). Below this stress the curves show an endurance limit. The aged and cold-worked materials have longer fatigue lives and higher endurance limits than the others. Different orientations have no apparent effect on life. Cryogenic temperature results in a much high fatigue life than room temperature. A higher tensile mean stress gives shorter fatigue life. It was also found that the fatigue lives of the reversed bending specimens were of the same order as those of the uniaxial test specimens, but were only half the lives of the rotating bending specimens for given stresses. A sample application of the S-N data is discussed.

  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. 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.

  3. Probabilistic fatigue life prediction of metallic and composite materials

    NASA Astrophysics Data System (ADS)

    Xiang, Yibing

    Fatigue is one of the most common failure modes for engineering structures, such as aircrafts, rotorcrafts and aviation transports. Both metallic materials and composite materials are widely used and affected by fatigue damage. Huge uncertainties arise from material properties, measurement noise, imperfect models, future anticipated loads and environmental conditions. These uncertainties are critical issues for accurate remaining useful life (RUL) prediction for engineering structures in service. Probabilistic fatigue prognosis considering various uncertainties is of great importance for structural safety. The objective of this study is to develop probabilistic fatigue life prediction models for metallic materials and composite materials. A fatigue model based on crack growth analysis and equivalent initial flaw size concept is proposed for metallic materials. Following this, the developed model is extended to include structural geometry effects (notch effect), environmental effects (corroded specimens) and manufacturing effects (shot peening effects). Due to the inhomogeneity and anisotropy, the fatigue model suitable for metallic materials cannot be directly applied to composite materials. A composite fatigue model life prediction is proposed based on a mixed-mode delamination growth model and a stiffness degradation law. After the development of deterministic fatigue models of metallic and composite materials, a general probabilistic life prediction methodology is developed. The proposed methodology combines an efficient Inverse First-Order Reliability Method (IFORM) for the uncertainty propogation in fatigue life prediction. An equivalent stresstransformation has been developed to enhance the computational efficiency under realistic random amplitude loading. A systematical reliability-based maintenance optimization framework is proposed for fatigue risk management and mitigation of engineering structures.

  4. Prestraining and its influence on subsequent fatigue life

    SciTech Connect

    Kalluri, S. [NYMA, Inc., Cleveland, OH (United States). NASA Lewis Research Center; Halford, G.R.; McGaw, M.A. [NASA Lewis Research Center, Cleveland, OH (United States)

    1996-12-31

    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, 5, and 10% (engineering strains) in the tensile direction and to 2% (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 (LDR), (2) the linear strain and life fraction rule (LSLFR), and (3) the nonlinear damage curve approach (DCA). The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, the best remaining fatigue life predictions were obtained with the nonlinear damage curve approach.

  5. Prestraining and its influence on subsequent fatigue life

    SciTech Connect

    Halford, G.R.; Mcgaw, M.A.; Kalluri, S.

    1995-03-01

    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.

  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. 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.

  8. Fatigue life prediction of welded ship details

    Microsoft Academic Search

    Carole Erny; David Thevenet; Jean-Yves Cognard; Manuel Körner

    Ship structures are submitted to variable cyclic loading during navigation. The cyclic motion of waves induces variable and complex loadings in the structure, which could generate fatigue damage. Moreover, most of these metallic structures are welded assemblies. This technique generates local stress concentrations at the weld toe, which becomes a critical area regarding fatigue. In previous works, a methodology to

  9. 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

  10. 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.

  11. Contact fatigue : life prediction and palliatives

    E-print Network

    Conner, Brett P. (Brett Page), 1975-

    2002-01-01

    Fretting fatigue is defined as damage resulting from small magnitude (0.5-50 microns) displacement between contacting bodies where at least one of the bodies has an applied bulk stress. The applicability and limits of a ...

  12. Surface fatigue life of high temperature gear materials

    NASA Astrophysics Data System (ADS)

    Townsend, Dennis P.

    1994-04-01

    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. 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.

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

    SciTech Connect

    Brown, E. N. (Eric N.); Jones, A. S. (Alan S.); White, S. R. (Scott 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.

  15. 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

  16. 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.

  17. The Effect of Water in Lubricating Oil on Bearing Fatigue Life

    Microsoft Academic Search

    Richard E. Cantley

    1977-01-01

    The effect of water in an SAE 20 oil on tapered roller bearing fatigue life was evaluated. Full-scale bearing life tests were conducted with water concentrations of 25, 100, and 400 ppm. Good correlation was obtained between fatigue life and water content and the detrimental effects of water on fatigue life at these levels were clearly demonstrated. As a result

  18. Dependence of Bearing Fatigue Life on Film Thickness to Surface Roughness Ratio

    Microsoft Academic Search

    J. Y. Liu; T. E. Tallian; J. I. McCool

    1975-01-01

    A statistical expression, showing as a function of the film parameter (film thickness\\/surface roughness or h\\/?) the fractional reduction in fatigue life at “full film” conditions due to the competition between asperity induced fatigue and fatigue due to indigenous surface defects and subsurface inclusions, is presented.Several sources of endurance test data relating the fatigue life of a rolling bearing to

  19. 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.

  20. SOL-XX-XXXX, Samborsky,1 Comparison of Tensile Fatigue Resistance and Constant Life

    E-print Network

    for Several Potential Wind Turbine Blade Laminates Daniel D. Samborsky* , Timothy J. Wilson, and John F, USA Abstract New fatigue test results are presented for four multidirectional laminates of current and potential interest for wind turbine blades, representing three types of fibers: E-glass, WindStrandTM glass

  1. Evolution of creep-fatigue life prediction models

    Microsoft Academic Search

    Gary R. Halford

    1991-01-01

    The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940s. 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

  2. Thermomechanical fatigue life prediction for several solders

    Microsoft Academic Search

    Shengmin Wen

    2001-01-01

    Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage

  3. Study of the Fatigue Life of Steel Catenary Risers in Interaction with the Seabed 

    E-print Network

    Nakhaee, Ali

    2011-02-22

    The fatigue life of a Steel Catenary Riser (SCR) near its touch-down zone is substantially affected by its interaction with the seabed. Hence, accurate estimate of its fatigue life requires the understanding and realistic modeling of the interaction...

  4. 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.

  5. The effect of warm water surface treatments on the fatigue life in shear of aluminum joints

    Microsoft Academic Search

    P. R. Underhill; A. N. Rider; D. L. DuQuesnay

    2006-01-01

    The effect of warm water treatment on the fatigue life of 2024 T3 aluminum alloy adhesively bonded with FM73 epoxy adhesive was investigated. As expected, the fatigue life was shown to depend on the surface preparation of the bonds. Fatiguing the specimens in wet conditions led to a slightly shorter life than under dry conditions. There was a correlation between

  6. Effect of Interference Fits on Roller Bearing Fatigue Life

    Microsoft Academic Search

    Harold H. Coe; Erwin V. Zaretsky

    1987-01-01

    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

  7. A mesoscopic approach for fatigue life prediction under multiaxial loading

    Microsoft Academic Search

    Franck Morel; Narayanaswami Ranganathan; Jean Petit; André Bignonnet

    1999-01-01

    This paper deals with the presentation of a high cycle multiaxial fatigue life prediction method for metallic materials. By means of the mesoscopic approach introduced by Dang Van and developed by Papadopoulos, accumulated plastic strain due to external loading is estimated at a scale on the order of a grain or a few grains. Its evaluation requires the use of

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

    Microsoft Academic Search

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

    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

  9. Fatigue life extension by electroless nickel infiltration plating

    Microsoft Academic Search

    C. S Shin; Z. Z Chen

    2001-01-01

    Introducing artificial closure material into a fatigue crack has been shown to be able to retard the crack and give considerable life extension. Most of the previous work employed polymers as closure material which will disintegrate under a high service temperature. Moreover, infiltrations of these closure materials were made with the cyclic loading interrupted and the cracks held open at

  10. 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.

  11. 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.

  12. Simulation work of fatigue life prediction of rubber automotive components

    NASA Astrophysics Data System (ADS)

    Samad, M. S. A.; Ali, Aidy

    2010-05-01

    The usage of rubbers has always been so important, especially in automotive industries. Rubbers have a hyper elastic behaviour which is the ability to withstand very large strain without failure. The normal applications for rubbers are used for shock absorption, sound isolation and mounting. In this study, the predictions of fatigue life of an engine mount of rubber automotive components were presented. The finite element analysis was performed to predict the critical part and the strain output were incorporated into fatigue model for prediction. The predicted result shows agreement in term of failure location of rubber mount.

  13. 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.

  14. 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.

  15. 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).

  16. Fully Dynamic Numerical Simulation of the Hammer Peening Fatigue Life Improvement Technique

    Microsoft Academic Search

    R. Baptista; V. Infante; C. Branco

    2011-01-01

    This paper presents the results of the development process for a Finite Element Analysis of the Hammer Peening Fatigue Life Improvement Technique. The Fatigue Life of welded structures is still in need for improvement. The sheer number of Fatigue Live Improvement Techniques parameters leads to the need of simulating and predicting their results. For this study, two different materials were

  17. Fatigue life enhancement of aluminium joints through mechanical and thermal prestressing

    Microsoft Academic Search

    Bård Wathne Tveiten; Arne Fjeldstad; Gunnar Härkegård; Ole Runar Myhr; Børge Bjørneklett

    2006-01-01

    This paper presents some simple and flexible methods to enhance the fatigue life of welded aluminium components. Besides enhancing the fatigue life, the proposed methods can easily be implemented into manufacturing processes. The key element of the methods is to change residual stresses from tension to compression at locations vulnerable to fatigue. This is accomplished by mechanical prestressing using elastic

  18. Equivalent linearization for fatigue life estimates of a nonlinear structure

    NASA Technical Reports Server (NTRS)

    Miles, R. N.

    1989-01-01

    An analysis is presented of the suitability of the method of equivalent linearization for estimating the fatigue life of a nonlinear structure. Comparisons are made of the fatigue life of a nonlinear plate as predicted using conventional equivalent linearization and three other more accurate methods. The excitation of the plate is assumed to be Gaussian white noise and the plate response is modeled using a single resonant mode. The methods used for comparison consist of numerical simulation, a probabalistic formulation, and a modification of equivalent linearization which avoids the usual assumption that the response process is Gaussian. Remarkably close agreement is obtained between all four methods, even for cases where the response is significantly linear.

  19. 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.

  20. Storage tank design and fatigue life

    SciTech Connect

    Edwards, D.R.

    1982-05-01

    High-viscosity hydrocarbons sometimes require heating to 500 F to be discharged from storage tanks. To give minimum guidance for temperature ranges for certain grades of steels, American Petroleum Institute Standard 650, Appendix M, considers yield strength reduction to increase shell thicknesses and elastic modulus reduction to increase the effective maximum alternating stress amplitude and lower the cycle life. But guidelines are not given for high-strength steels in elevated-temperature service. This paper is concerned with the benefits derived from Appendix M and the effective strength reduction of heat-treated steels. A closed-form solution for the radial deflection of the shell is derived for hydrostatic and thermal conditions. This equation is then expanded to determine the hoop and bending stresses. This enables the maximum alternating stress amplitude to be determined both at the plate-shell junction and the nozzle-shell weldment, resulting in a minimum cycle life determination. Appendix M increased the cycle life by a maximum of 10 percent at 500 F and 2 percent at 300 F for A283-C material. Higher strength shell materials were considered at elevated temperatures via yield strength reduction per Section VIII, Division 2, of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. The reduction in thermal cycle life was very small for these heat-treated materials, even with the corresponding reduction in the elastic modulus.

  1. Bearing Fatigue Life Tests in a Synthetic Traction Lubricant

    Microsoft Academic Search

    D. V. Culp; J. D. Stover

    1976-01-01

    Two samples of 3.75-inch OD (95.3 mm) tapered roller bearings were tested under minimal film conditions using a synthetic (cycloaliphatic) hydrocarbon oil. These tests exhibited extended fatigue life when compared to two samples of the same bearings tested using equivalent viscosity petroleum oils. The apparent difference in pressure viscosity coefficients of these two oils only partially explained the difference in

  2. Effects of Low Speed on Roller Bearing Fatigue Life©

    Microsoft Academic Search

    John R. Miller; Yoshinobu Akamatsu

    1997-01-01

    Two test series were conducted to study the effect of low speed and high load on the rolling-element fatigue life of 30 mm and 40 mm bore cylindrical roller bearings at inner race speeds from 19 to 3725 rpm and lubricant film parameter Lambda (?) ratios from 0.03 to 1.2. Maximum Hertz stress ranged from 2.24 to 4.2 GPa (325

  3. Silicon MEMS components: a fatigue life assessment approach

    Microsoft Academic Search

    A. Varvani-Farahani

    2005-01-01

    A fatigue damage approach for life assessment of silicon micro-components is proposed. The components of this model have been developed based on the physics of crack initiation and damage progress on the most damaging planes. This approach may be of great importance in durability assessment of silicon-based MEMS components while the complexity of testing equipment, micro-sized specimen preparation, and the

  4. Fatigue Life Estimation of Structures Subjected to Vibratory Loading

    Microsoft Academic Search

    M. Fressinet; F. Fuchs; P. Madelpech

    \\u000a Fatigue life is commonly estimated by an analysis of the stress time history through a peak-valley counting method and the\\u000a damage is calculated thanks to a damage summation method. Unfortunately, vibratory loadings are often random and this kind\\u000a of calculation would be very time consuming. Such spectra require other methods and that’s why especially dedicated models\\u000a have been developed. Known

  5. Development of BGA solder joint vibration fatigue life prediction model

    Microsoft Academic Search

    T. E. Wong; B. A. Reed; H. M. Cohen; D. W. Chu

    1999-01-01

    The objective of the present study is to develop a vibration fatigue life prediction model for ball grid array (BGA) solder joint. In this study, 3D global\\/local finite element models were first constructed with MSC\\/PATRAN code. For the global model including BGA package soldered onto the printed wiring board (PWB), linear finite element dynamic analyses with an excitation normal to

  6. Plastic strain-controlled short crack growth and fatigue life

    Microsoft Academic Search

    Jaroslav Polák

    2005-01-01

    Constant plastic strain-controlled and constant stress-controlled tests were performed on smooth and lightly notched specimens machined from a massive forging of 42CrMo4 steel. Comparison of the fatigue life curves plotted as function of the plastic strain amplitude and stress amplitude shows a decisive role of plastic strain amplitude. Crack initiation and the kinetics of short crack growth were studied in

  7. 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.

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

    Microsoft Academic Search

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

    2011-01-01

    An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in service\\u000a gas turbine materials. The purpose of the life prediction framework is to account aging effect caused by cyclic loadings on\\u000a fatigue strength of gas turbine engines structural components which are usually designed for very long life. Previous studies\\u000a indicate the total

  9. Fatigue Life Prediction and Analysis of Wafer Level Packages with SnAgCu Solder Balls

    Microsoft Academic Search

    Rainer Dudek; S. Rzepka; S. Dobritz; R. Doring; K. Keyssig; S. Wiese; B. Michel

    2006-01-01

    Currently, various mainly tin-based lead free solders are in use or under evaluation. Many solder fatigue models have been developed to predict the fatigue life of solder joints under low-cycle fatigue conditions, however, because of the diversity of solders, more work is needed in this respect. The theoretical fatigue life prediction of solder joints, based upon non-linear finite element (FE-)

  10. Fatigue Life Prediction under Random Loading Conditions in 7475-T7351 Aluminum Alloy using the RMS Model

    Microsoft Academic Search

    Sang Tae Kim; Damir Tadjiev; Hyun Tae Yang

    2006-01-01

    This article is concerned with the fatigue life prediction in specimens of 7475-T7351 high strength aluminum alloy subjected to random fatigue loading. Fatigue life predictions are made using the root mean square model. This model is chosen because it has been defined as the most simple and effective one for fatigue life prediction in the components subjected to random loading

  11. 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.

  12. Effect of interference fits on roller bearing fatigue life

    NASA Technical Reports Server (NTRS)

    Coe, Harold H.; Zaretsky, Erwin V.

    1987-01-01

    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 reduction of 20 to 30 percent. The depth of the maximum shear stress remains virtually unchanged.

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

    Microsoft Academic Search

    Paul S. Prevéy; N. Jayaraman; Michael Shepard

    2007-01-01

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

  14. Prediction of the Fatigue Life of Cast Steel Containing Shrinkage Porosity

    E-print Network

    Beckermann, Christoph

    . A multiaxial strain-life simulation is then performed to deter- mine the fatigue life. An adaptive subgrid life of steel castings containing porosity. For ease of use in standard design practice, commonly used

  15. A review of the effects of coolant environments on the fatigue life of LWR structural materials.

    SciTech Connect

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

    2009-04-01

    The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code specifies design curves for the fatigue life of structural materials in nuclear power plants. However, the effects of light water reactor (LWR) coolant environments were not explicitly considered in the development of the design curves. The existing fatigue-strain-versus-life ({var_epsilon}-N) data indicate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives in water relative to those in air can be a factor of 15 lower for austenitic stainless steels and a factor of {approx}30 lower for carbon and low-alloy steels. This paper reviews the current technical basis for the understanding of the fatigue of piping and pressure vessel steels in LWR environments. The existing fatigue {var_epsilon}-N data have been evaluated to identify the various material, environmental, and loading parameters that influence fatigue crack initiation and to establish the effects of key parameters on the fatigue life of these steels. Statistical models are presented for estimating fatigue life as a function of material, loading, and environmental conditions. An environmental fatigue correction factor for incorporating the effects of LWR environments into ASME Code fatigue evaluations is described. This paper also presents a critical review of the ASME Code fatigue design margins of 2 on stress (or strain) and 20 on life and assesses the possible conservatism in the current choice of design margins.

  16. Effects of cyclic stress distribution models on fatigue life predictions

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.; Veers, P. S.

    1994-10-01

    The fatigue analysis of a wind turbine component typically uses representative samples of cyclic loads to determine lifetime loads. In this paper, several techniques currently in use are compared to one another based on fatigue life analyses. The generalized Weibull fitting technique is used to remove the artificial truncation of large-amplitude cycles that is inherent in relatively short data sets. Using data from the Sandia/DOE 34-m Test Bed, the generalized Weibull file technique is shown to be excellent for matching the body of the distribution of cyclic loads and for extrapolating the tail of the distribution. However, the data also illustrate that the fitting technique is not a substitute for an adequate data base.

  17. Effect of notch dimension on the fatigue life of V-notched structure

    Microsoft Academic Search

    Cheng Chang-zheng; Recho Naman; Niu Zhong-rong; Zhou Huan-lin

    2011-01-01

    The stress singularity degree associated to a V-notch has a great influence on the fatigue life of V-notched structure. The growth rate of the crack initiated at the tip of a V-notch depends on the stress singularity of the V-notch. The fatigue life accompanying with this small crack will represent a large amount of the total fatigue life. In this

  18. Fatigue Crack Initiation Life Prediction for a Flat Plate with a Central Hole

    Microsoft Academic Search

    Tso-Liang Teng; Peng-Hsiang Chang

    2003-01-01

    This work constructs an effective procedure that combines the finite element and strain-life methods in order to accurately predict fatigue crack initiation (FCI) life and then establish an estimated schedule of fatigue life. The proposed procedure is applied to a flat plate with a central hole to obtain predicted lives. The results from the proposed method are compared with those

  19. The experience of fatigue and quality of life in patients with advanced lung cancer

    Microsoft Academic Search

    Andrea Shaffer

    2009-01-01

    Fatigue is the most prevalent and distressing symptom experienced by patients with advanced lung cancer and especially among those patients undergoing therapy. Advanced lung cancer and its associated symptoms can significantly impact the quality of life (QOL) of those who have the disease. The primary purpose of this study was to measure fatigue levels, characterize the fatigue experience, and assess

  20. Fatigue life of a design subject to wide-band random loading

    Microsoft Academic Search

    Wendai Wang

    2010-01-01

    Metal fatigue is one of the most important failure modes to be considered in mechanical and structural design. The only satisfactory way to prevent fatigue failures in the service life span is by proper design; i.e., being able to predict the fatigue lifetime of a particular design through design analysis or testing. For engineering applications, designers need a simple and

  1. Fatigue life characterization of shape memory alloys undergoing thermomechanical cyclic loading

    E-print Network

    . The failure pattern observed provides information necessary to introduce a correction to the classical Wohler the earliest report on fatigue properties of NiTi specimens. Their work included results on mechanical fatigue%. Lagoudas et al. [7] reported a thermal fatigue life of nearly 20,000 cycles for a TiCuNi alloy annealed

  2. 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.

  3. 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.

  4. Fracture toughness and fatigue life of MWCNT\\/epoxy composites

    Microsoft Academic Search

    N. Yu; Z. H. Zhang; S. Y. He

    2008-01-01

    The present work experimentally characterizes the mode-I fracture toughness and stress–life curve of multi-walled carbon nanotube-(MWCNT-)reinforced epoxy-matrix composites. The effects of carbon nanotube weight fraction and voids on the composite fracture toughness are studied. The average fracture toughness of 1wt%- and 3wt%-MWCNT\\/epoxy composites is 1.29 and 1.62 times of that of pure epoxy, respectively. The 0.5wt%-MWCNT\\/epoxy composites’ fatigue lives are

  5. Rolling-element fatigue life of AMS 5749 corrosion resistant, high temperature bearing steel

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    The rolling element fatigue lives of AMS 5749 and AISI M-50 were compared in tests run in the five ball fatigue tester and the rolling contact fatigue tester. The effects of double vacuum melting and retained austenite on the life of AMS 5749 were determined in five ball fatigue tests. The double vacuum melting process consisted of induction vacuum melting followed by vacuum arc remelting (VIM-VAR). In the five ball tests, VIM-VAR AMS 5749 gave lives at least six times that of VIM-VAR AISI M-50. Similar tests in the rolling contact fatigue tester showed no significant difference in the lives of the two materials. The rolling element fatigue life of VIM-VAR AMS 5749 was at least 14 times that of vacuum induction melted AMS 5749. A trend toward increased rolling element fatigue life with decreased retained austenite is apparent, but the confidence that all experimental differences are significant is not great.

  6. 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.

  7. A General Methodology to Predict Fatigue Life in Lead-Free Solder Alloy Interconnects

    Microsoft Academic Search

    David M. Pierce; Sheri D. Sheppard; Paul T. Vianco

    2009-01-01

    The ubiquitous eutectic tin-lead (Sn-Pb) solder alloys are soon to be replaced with lead-free alternatives. In light of this transition, new computational tools for predicting the fatigue life of lead-free solders are required. A fatigue life prediction methodology was developed, based upon stress-strain, creep and isothermal fatigue data; the later generated using a double lap-shear (DLS) test assembly. The proposed

  8. Fretting fatigue of laser shock peened Ti–6Al–4V

    Microsoft Academic Search

    S. Srinivasan; D. B. Garcia; M. C. Gean; H. Murthy; T. N. Farris

    2009-01-01

    The objective of this paper is to examine fretting fatigue of laser shock peened (LSP) titanium to quantify the influence of LSP on fretting fatigue life. Contact conditions such as loads and pad geometry are chosen to generate fretting fatigue stresses similar to those occurring in blade\\/disk contacts in gas turbine engines. LSP treated specimens attained 5-, 10- and 25-fold

  9. The Effect of Aircraft Gas Turbine Oils on Roller Bearing Fatigue Life

    Microsoft Academic Search

    Mark E. Otterbein

    1958-01-01

    A series of fatigue life tests on aircraft gear box size (45 mm bore) roller bearings were conducted with various aircraft gas turbine lubricants and with specific reference to Mil-L-7808 and variations thereof. It is shown that the 7808 lubricants generally cause a marked reduction in fatigue life as compared to that obtained with a medium viscosity mineral oil. It

  10. Fatigue Life Improvement Factors Obtained by Weld Reinforcement and Toe Grinding

    Microsoft Academic Search

    Christopher Mullen; John Merwin

    1982-01-01

    The potential of weld reinforcement and toe grinding techniques for improving the fatigue life of welded joints protected from seawater corrosion is quantified based on tests performed in air on welded plate specimens. Results are presented in terms of median fatigue life improvement factors and prediction intervals obtained by linear regression analysis. The significant improvements possible with weld reinforcement are

  11. Fatigue life prediction of flip-chips in terms of nonlinear behavior of solder and underfill

    Microsoft Academic Search

    Zhengfang Qian; Minfu Lu; Sheng Liu

    1999-01-01

    The nonlinear properties of eutectic solder and underfill FP4526 have been reported and incorporated into ABAQUS material model library for the fatigue life prediction of advanced electronic packages. The methods of unified constitutive modeling, separated constitutive modeling, and fatigue life prediction have been described and compared in detail. The nonlinear constitutive modeling of solder alloys and underfills plays an important

  12. Fatigue Life Properties and Availability of Proof Testing in Ceramics-Coated Glass

    NASA Astrophysics Data System (ADS)

    Hoshide, Toshihiko; Shimizu, Shohei; Tanaka, Motoki

    2014-03-01

    The long-term durability of high-performance ceramics-coated glass should be appropriately evaluated prior to their practical applications. Fatigue properties of such materials should be clarified to ensure the long-term durability. In this work, a borosilicate glass was coated with alumina or silicon carbide thin films by sputtering method. Fatigue tests of coated glass were conducted under three-point bending. It was clarified that the fatigue life was elongated by coating ceramic thin films on glass and the fatigue life distribution in glass coated with thicker films shifted toward longer life region. Proof testing was carried out for coated glass specimens to remove specimens having lower fatigue lives. It was suggested that proof testing for fatigue of ceramics-coated glass was effective as a screening procedure which can remove weaker specimens by static pre-loading before fatigue tests. In correlating average fatigue lives, fatigue resistance strength was introduced as the average bending strength divided by the applied maximum stress. It was revealed that the average fatigue lives of every coated glass, including average lives after proof testing, were well correlated by a power function of the fatigue resistance strength and its modified parameter, irrespective of film material and thickness and also applied stress level.

  13. 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.

  14. Heat-Aging Effects on the Material Properties and Fatigue Life Prediction of Vulcanized Natural Rubber

    NASA Astrophysics Data System (ADS)

    Woo, Chang Su; Kim, Wan Doo

    The fatigue analysis and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Heat-aging process affects not only the material properties but also the fatigue life of vulcanized natural rubber. In this paper, the heat-aging effects on the material properties and fatigue life prediction of natural rubber were experimentally investigated. The stress-strain curves were obtained from the results of tensile test. The rubber specimens were heat-aged in an oven at the temperature ranging from 50°C to 100°C for a period ranging from 1 day to 90 days. Fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Fatigue life tests were performed using the 3-dimensional dumbbell specimen, which were aged in different amounts. The Green-Lagrange strain at the critical location determined from the finite element method used for evaluating the fatigue damage parameter. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain.

  15. An energy-based fatigue life assessment model for various metallic materials under proportional and non-proportional loading conditions

    Microsoft Academic Search

    H. Jahed; A. Varvani-Farahani; M. Noban; I. Khalaji

    2007-01-01

    The present study examines the capability of a lately developed energy-based fatigue damage parameter [Jahed H, Varvani-Farahani A. Upper and lower fatigue life limits model using energy-based fatigue properties. Int J Fatigue 2006;28:467–73] to assess fatigue life of various metallic materials subjected to proportional and non-proportional loading conditions. The proposed damage is defined based on (i) shear and axial stress

  16. 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.

  17. Effects of laser shock processing on the fatigue life of 2024-T62 aluminium alloy

    SciTech Connect

    Zhang Hong; Lu Boliang; Zhang Shuren [Changchun Inst. of Optics and Fine Mechanics (China). Dept. of Mechanical Engineering; Tang Yaxin; Yu Chengye [Nanjing Univ. of Aeronautics and Astronautics (China). Dept. of Mechanical Engineering

    1996-12-31

    Laser shock processing (LSP) is a new technology for strengthening the materials. The feasibility of using a high energy, pulsed laser beam to shock-harden the localized stress concentration zone, i.e., small holes in 2024-T62 aluminum alloy was investigated in this paper. Confining plasma technique was used in the study. In order to generate the pressure which is required to exceed the dynamic yield strength of 2024-T62 aluminum alloy, laser parameters were optimized. The fatigue life of specimens was studied before and after laser shocking. The fatigue tests showed that the fatigue life of 2024-T62 aluminum alloy treated by LSP had been improved significantly. With 95% confidence, the median fatigue life of shocked specimens was 1.9 to 2.5 times than that of unshocked ones. It is expected that LSP will be used as a good treatment for improving the fatigue life of aviation structures.

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

    SciTech Connect

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

    1996-12-31

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

  19. Influence of Asymmetrical Waveform on Low-Cycle Fatigue Life of Micro Solder Joint

    NASA Astrophysics Data System (ADS)

    Kanda, Yoshihiko; Kariya, Yoshiharu

    2010-02-01

    The effects of waveform symmetry on the low-cycle fatigue life of the Sn-3.0Ag-0.5Cu alloy have been investigated, using micro solder joint specimens with approximately the same volume of solder as is used in actual products. Focusing on crack initiation life, fatigue tests on Sn-Ag-Cu micro solder joints using asymmetrical triangular waveforms revealed no significant reduction in fatigue life. A slight reduction in fatigue life at low strain ranges caused by an increase in the fatigue ductility exponent, which is the result of a weakening microstructure due to loads applied at high temperature for long testing time, was observed. This was due to the fact that grain boundary damage, which has been reported in large-size specimens subjected to asymmetrical triangular waveforms, does not occur in Sn-Ag-Cu micro size solder joints with only a small number of crystal grain boundaries.

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

    Microsoft Academic Search

    J. Xu; S. Reuter; W. Rothkegel

    2008-01-01

    This paper briefly describes thermo-mechanical fatigue tests performed on cylindrical and flat specimens of the single crystal material CMSX-4 in ?001?, ?011? and ?111?-orientation. The test matrix was defined based on the thermo-mechanical loading identified at different positions of actual turbine rotor blades. It included tensile strain-controlled TMF-test conditions on the cylindrical plain specimens and tensile load-controlled TMF-test conditions on

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

    Microsoft Academic Search

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

    1997-01-01

    We analyze the experimental procedures aimed at testing specimens which simulate contact pairs and full-scale lock joints\\u000a of blades of compressors of gas-turbine engines with grooved disks for fretting fatigue. The experimental results corroborate\\u000a the efficiency of these procedures and enable one to choose coatings and procedures of treatment of contacting surfaces which\\u000a guarantee the attainment of higher values of

  2. 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.

  3. 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.

  4. Application of artificial neural network for predicting strain-life fatigue properties of steels on the basis of tensile tests

    Microsoft Academic Search

    K Genel

    2004-01-01

    The applicability of artificial neural networks (ANN) in predicting the strain-life fatigue properties using tensile material data for 73 steels was investigated by conducting four separate neural networks for individual fatigue properties. The fatigue data of these steels extracted from available literatures were used in the formation of training set of ANN. Results of neural network modelling indicated that fatigue

  5. Crack growth-based fatigue-life prediction using an equivalent initial flaw model. Part II: Multiaxial loading

    Microsoft Academic Search

    Zizi Lu; Yibing Xiang; Yongming Liu

    2010-01-01

    A general methodology is proposed in this paper for fatigue-life prediction using crack growth analysis. This is the part II of the paper and focuses on the fatigue-life prediction under proportional and nonproportional multiaxial loading. The proposed multiaxial fatigue-life prediction is based on a critical plane-based multiaxial fatigue damage model and the Equivalent Initial Flaw Size (EIFS) concept. An equivalent

  6. Fatigue life prediction in AlMgSi1 lap joint weldments

    Microsoft Academic Search

    J. A. M Pinho da Cruz; J. D. M Costa; L. F. P Borrego; J. A. M Ferreira

    2000-01-01

    The fatigue behaviour of an AlMgSi1 alloy lap welded joint and the improvement in fatigue strength due to post-weld heat treatment were investigated. Two series of fatigue tests were performed: one in as-welded specimens and another in heat-treated specimens. The prediction of crack initiation life under a plane strain condition was made based on the local strain approach using Morrow's

  7. 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.

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

    Microsoft Academic Search

    Raghu V. Prakash; R. Sunder

    1993-01-01

    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

  9. The effects of testing methods on the flexural fatigue life of human cortical bone

    Microsoft Academic Search

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

    1999-01-01

    A flexural model of four-point bending fatigue that has been experimentally validated for human cortical bone under load control was used to determine how load and displacement control testing affects the fatigue behavior of human cortical bone in three-point and symmetric four-point bending. Under load control, it was predicted that three-point bending produced no significant differences in fatigue life when

  10. 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.

  11. 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 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400?kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406

  12. 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.

  13. 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.

  14. Fatigue life improvement of drill collars through control of bore eccentricity

    Microsoft Academic Search

    M. J. Knight; F. P. Brennan

    1999-01-01

    The majority of drillstem failures are attributed to fatigue, particularly in BHA connections where there is a high level of stress concentration in the thread roots. Any stress concentration combined with a modest amount of bore eccentricity in the drill collar may result in a notable reduction in the fatigue life of the component under bending loads. This paper examines

  15. Fatigue life prediction of welded cruciform joints using strain energy density factor approach

    Microsoft Academic Search

    V Balasubramanian; B Guha

    2000-01-01

    The influences of two welding processes, namely, shielded metal arc welding (SMAW) and flux cored arc welding (FCAW), on fatigue life of cruciform joints containing lack of penetration (LOP) defects have been analyzed by using the strain energy density factor (SEDF) approach. Load carrying cruciform joints were fabricated from ASTM 517 ‘F’ grade steel. Fatigue crack growth experiments were carried

  16. A fracture mechanics based fatigue life prediction for welded joints of square tubes

    Microsoft Academic Search

    J. M. Ferreira; A. H. Pereira; C. M. Branco

    1995-01-01

    Square tubes of mild and low alloy steels are extensively used in vehicle structures and offshore platforms. Despite this fact the fatigue behaviour of welded nodes of these tubes is not sufficiently known, especially in thin sections.The paper presents the results of fatigue life predictions based on fracture mechanics, in non-load carrying T and also load carrying cruciform joints. The

  17. Assessment of the fatigue life of aluminium spot-welded and weld-bonded joints

    Microsoft Academic Search

    A. M. Pereira; J. A. M. Ferreira; F. V. Antunes; P. J. Bártolo

    2012-01-01

    In modern machinery and automobile structures weight reduction and increased durability are the main issues in design. In these applications, lap welded and\\/or bonded joints are widely used; therefore, tools are needed to accurately predict their fatigue life. This paper is concerned with the fatigue strength of single lap joints formed with thin plates of 6082-T6 aluminium alloy using a

  18. Cyclic plastic response and fatigue life in superduplex 2507 stainless steel

    Microsoft Academic Search

    Jaroslav Polák; Martin Petrenec; Tomáš Kruml

    2010-01-01

    Superduplex 2507 type steel has been subjected to symmetric cyclic loading with constant strain rate and constant plastic strain amplitude or sinusoidal cyclic loading with constant stress amplitude at room temperature in a wide interval of stress and plastic strain amplitudes. Fatigue hardening\\/softening curves were recorded and compared for both types of loading. Cyclic stress–strain curves and fatigue life curves

  19. Effects of carburization on expected fatigue life of alloys steel shafts

    Microsoft Academic Search

    T. M. Loganathan; J. Purbolaksono; J. I. Inayat-Hussain; N. Wahab

    2011-01-01

    The motivation of this work is to improve fatigue life of the alloys steel power transmission shafts of the palm oil screw press machines in a Malaysia palm oil company. In order to improve daily productions of the palm oil, a high extraction efficiency of the machine with bigger crushing forces are required. Consequently, the failures due to torsional fatigue

  20. Reinforcing effect of coverlayers on the fatigue life of copper-Kapton flex cables

    Microsoft Academic Search

    Alan T. Zehnder; Anthony R. Ingraffea

    1995-01-01

    Flex cables constructed of copper sandwiched between Kapton (polyimide) fail under repeated bending due to the formation and propagation of fatigue cracks in the copper. It is observed that fatigue life of rolled-annealed copper cables with a coverlayer of Kapton is significantly higher than cables without a coverlayer. This result is explained using a fracture mechanics analysis where the Kapton

  1. ElastoPlastic Fatigue Life Improvement of Bolted Joints and Introducing FBI Method

    Microsoft Academic Search

    Peyman Honarmandi; Jean W. Zu; Kamran Behdinan

    2005-01-01

    The failures of bolted joints, which are the basic and popular fasteners in industry, are mostly due to fatigue. This paper presents an effective method to improve the elasto-plastic fatigue life of a bolt. A complete bolted joint is considered and modeled with the finite element approach to calculate stress and strain. The code based on crack initiation theory is

  2. MODELING OF THE FATIGUE LIFE OF ADHESIVELY-BONDED FRP JOINTS WITH GENETIC

    E-print Network

    Fernandez, Thomas

    investigation. Keywords: Fatigue, genetic programming, life prediction, adhesive joints, temperature INTRODUCTION The effect of the environment on the fatigue behavior of adhesively-bonded joints has formed mode changed to substrate failure for ambient temperature, while very rapid propagation was observed

  3. Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications

    Microsoft Academic Search

    Paul S. Prevéy; Ravi A. Ravindranath; Michael Shepard; Timothy Gabb

    2006-01-01

    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

  4. 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.

  5. The significance of weld imperfections and surface peening on fatigue crack propagation life of butt-welded joints

    Microsoft Academic Search

    M. A. Wahab; M. S. Alam

    2004-01-01

    This study describes the influence of various weld imperfections (solidification crack, undercut and porosity) on fatigue crack propagation life due to combined axial and torsional fatigue loading. The stress intensity factors for different weld imperfections have been calculated by finite element method. The fatigue crack propagation life has been calculated using fracture mechanics approaches. It has been found that the

  6. A numerical method for predicting the bending fatigue life of NiTi and stainless steel root canal

    E-print Network

    Zheng, Yufeng

    A numerical method for predicting the bending fatigue life of NiTi and stainless steel root canal. A numerical method for predicting the bending fatigue life of NiTi and stainless steel root canal instruments of endodontic files. Keywords: bending fatigue, finite element analysis, nickel­titanium, root canal instruments

  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. 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.

  9. Microcomputer system for measurements and analysis of signals for fatigue life calculations under biaxial random stress state

    NASA Astrophysics Data System (ADS)

    Macha, Ewald; Stezala, Henryk

    1992-07-01

    The algorithm of calculations, hardware and software for the Microcomputer Fatigue Damage Cumulator (MFDC) are presented. MFDC is used for direct determination fatigue life under biaxial random stress state. The equivalent stress history is described by the known methods of cycle counting. Damages are cumulated by linear hypotheses. Owing to the modular structure of software it is possible to calculate fatigue life according to different variants of the algorithm. Some selected examples of application of the discussed computer system to determine fatigue life under biaxial random stress state are presented. Good agreement is obtained by comparing experimental and calculated fatigue life results.

  10. Laser moiré interferometry for fatigue life prediction of lead-free solders

    Microsoft Academic Search

    Krishna Tunga; Suresh K. Sitaraman

    2010-01-01

    A laser moiré interferometry based technique to predict the fatigue life of Sn4.0Ag0.5Cu solder joints in a plastic ball grid array (PBGA) package when subjected to a typical accelerated thermal cycling (ATC) loading has been presented in this paper. The fatigue life is estimated by measuring the in-plane strains in the solder joints at various temperatures. The methodology can be

  11. 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.

  12. Effect of mean stress and ratcheting strain on fatigue life of steel

    Microsoft Academic Search

    Z. Xia; D. Kujawski; F. Ellyin

    1996-01-01

    Detailed results of stress-controlled fatigue tests with tensile mean stress on ASTM A-516 Gr. 70 steel are presented. By using different preloading procedures, the ratcheting effect on the fatigue life of materials was separated from the mean stress effect. A previously proposed energy-based life prediction criterion is extended to include the effects of both mean stress and ratcheting. A comparison

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

    Microsoft Academic Search

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

    1989-01-01

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

  14. A new fracture mechanics method to predict the fatigue life of welded cruciform joints

    Microsoft Academic Search

    Bimalendu Guha

    1995-01-01

    The fatigue life of MIG welded cruciform joint failing from root (LOP) region was successfully predicted using new fracture mechanics equations. These equations were developed by combining Paris' law and ?Ki-endurance equation and incorporating an integral factor (Ip) obtained by integrating Paris' equation. In the numerical formulation of the equation, the initiation life (Ni) and propagation life (Np) of the

  15. Sickle blade life-history and the transition to agriculture: an early Neolithic case study from Southwest Asia

    E-print Network

    Kohler, Tim A.

    Sickle blade life-history and the transition to agriculture: an early Neolithic case study from September 2009 Received in revised form 7 December 2009 Accepted 9 December 2009 Keywords: Neolithic Lithics-life histories during the early Neolithic in the Southern Levant. Ó 2009 Elsevier Ltd. All rights reserved. 1

  16. 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.

  17. Physical training and fatigue, fitness, and quality of life in Guillain-Barré syndrome and CIDP.

    PubMed

    Garssen, M P J; Bussmann, J B J; Schmitz, P I M; Zandbergen, A; Welter, T G; Merkies, I S J; Stam, H J; van Doorn, P A

    2004-12-28

    Many patients with Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP) experience excessive fatigue, which may persist for years and reduce quality of life. The authors performed a 12-week study of bicycle exercise training in 20 patients with severe fatigue, 16 with relatively good recovery from GBS, and 4 with stable CIDP. Training seemed well tolerated, and self-reported fatigue scores decreased 20% (p = 0.001). Physical fitness, functional outcome, and quality of life were improved. PMID:15623709

  18. The effects of testing methods on the flexural fatigue life of human cortical bone.

    PubMed

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

    1999-01-01

    A flexural model of four-point bending fatigue that has been experimentally validated for human cortical bone under load control was used to determine how load and displacement control testing affects the fatigue behavior of human cortical bone in three-point and symmetric four-point bending. Under load control, it was predicted that three-point bending produced no significant differences in fatigue life when compared to four-point bending. However, three-point bending produced less stiffness loss with increasing cycles than four-point bending. In four-point bending, displacement control was predicted to produce about one and a half orders of magnitude greater fatigue life when compared to load control. This prediction agrees with experimental observations of equine cannon bone tested in load and displacement control (Gibson et al., 1998). Displacement controlled three-point bending was found to produce approximately a 25% greater fatigue life when compared to load control. The prediction of longer fatigue life under displacement control may have clinical relevance for the repair of damaged bone. The model can also be adapted to other geometric configurations, including modeling of whole long bones, and with appropriate fatigue data, other cortical bone types. PMID:10050958

  19. Multiaxial fatigue models for short glass fiber reinforced polyamide. Part II: Fatigue life estimation.

    E-print Network

    Paris-Sud XI, Université de

    -as-moulded (DAM). Post-processing the cyclic response in steady-state allows the comparison of several fatigue to design those components against fatigue failure has become a serious issue during the last years, when giving the best correlation with the number of cycles to failure. The relationship

  20. 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.

  1. Fatigue in children with juvenile idiopathic arthritis: reliability of the "Pediatric Quality of Life Inventory-Multidimensional Fatigue Scale".

    PubMed

    Paulo, Luciana Tudech S P; Len, Claudio A; Hilario, Maria Odete E; Pedroso, Soraya A; Vitalle, Maria Sylvia S; Terreri, Maria Teresa

    2015-01-01

    The aim of the study was (1) to translate the "Pediatric Quality of Life Inventory-Multidimensional Fatigue Scale" (PedsQL-Fatigue) into Brazilian Portuguese language and culture and evaluate its reliability and (2) to measure fatigue among patients with juvenile idiopathic arthritis (JIA): (1) Translation of the PedsQL-Fatigue by two bilingual researchers; (2) Backtranslation into English assessed by the authors of the original version; (3) Pilot study with five patients followed in the Pediatric Rheumatology Outpatient Clinic and their parents; and (4) Field study and assessment of measurement properties (internal consistency, reproducibility, and construct validity). In this stage, the scale was administered to 67 patients with JIA and 63 healthy individuals, aged from 2 to 18 years old, matched by age (from 2 to 4, 5 to 7, 8 to 12, and from 13 to 18 years old). Cronbach's alpha coefficient ranged from 0.6 to 0.8 for children and parents, indicating the instrument's good internal consistency. The scale's construct validity was confirmed by a satisfactory Spearman's coefficient between the PedsQL-Fatigue and the generic PedsQL 4.0 (0.840 for the children and 0.742 for the parents). Reproducibility was also adequate (0.764 for the children and 0.938 for the parents). No differences were found between the scores obtained by the JIA group and control group, though lower scores were observed among patients with clinically active JIA when compared to those without clinical activity. The PedsQL-Fatigue is a valid and reliable tool, and that can be used to measure fatigue among patients with JIA. PMID:24941921

  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. 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.

  4. American Institute of Aeronautics and Astronautics Comparison of Tensile Fatigue Resistance and Constant

    E-print Network

    and Constant Life Diagrams for Several Potential Wind Turbine Blade Laminates Daniel D. Samborsky, Timothy J, Bozeman, MT, 59717, USA Abstract New fatigue test results are presented for four multidirectional laminates of current and potential interest for wind turbine blades, representing three types of fibers: E

  5. Smart structure for small wind turbine blade

    NASA Astrophysics Data System (ADS)

    Supeni, E. E.; Epaarachchi, J. A.; Islam, M. M.; Lau, K. T.

    2013-08-01

    Wind energy is seen as a viable alternative energy option for future energy demand. The blades of wind turbines are generally regarded as the most critical component of the wind turbine system. Ultimately, the blades act as the prime mover of the whole system which interacts with the wind flow during the production of energy. During wind turbine operation the wind loading cause the deflection of the wind turbine blade which can be significant and affect the turbine efficiency. Such a deflection in wind blade not only will result in lower performance in electrical power generation but also increase of material degradation due high fatigue life and can significantly shorten the longevity for the wind turbine material. In harnessing stiffness of the blade will contribute massive weight factor and consequently excessive bending moment. To overcome this excessive deflection due to wind loading on the blade, it is feasible to use shape memory alloy (SMA) wires which has ability take the blade back to its optimal operational shape. This paper details analytical and experimental work being carried out to minimize blade flapping deflection using SMA.

  6. 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

  7. 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.

  8. Strain Range Approximation for Estimating Fatigue Life of Lead-free Solder Interconnects Under Temperature Cycle Loading

    Microsoft Academic Search

    Michael Osterman

    2006-01-01

    The ability to estimate the fatigue life of solder interconnects under life-cycle loading conditions is critical for ensuring the reliability of electronic hardware. While multiple models have been published and successfully demonstrated to estimate the fatigue life of solder interconnects, a strain range model based on the work of Engelmaier remains one of the most widely used. In estimating the

  9. Reliability and fatigue life evaluation of railway axles

    Microsoft Academic Search

    Meral Bayraktar; Necati Tahrali; Rahmi Guclu

    2010-01-01

    The axle is one of the most important components of a rail vehicle which transmits the weight of the vehicle to the wheels,\\u000a meets the vertical and horizontal loads formed during static and dynamic moving, and carries the driving moment and braking\\u000a moment. The prediction of fatigue failure of axles plays an important role in preventing fatigue fractures. Varying loads

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

    Microsoft Academic Search

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

    1995-01-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 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.

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

    Microsoft Academic Search

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

    1995-01-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due\\u000a to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are incorporated into eutectic tin-lead alloy by rapid solidification processes to formin situ composite solders. In this study, thein situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic

  12. Strain-controlled fatigue life and modeling of conduit polymers

    Microsoft Academic Search

    Pei Chen; Shing-Chung Wong

    2011-01-01

    Strain-controlled fatigue lives of conduit polymers, viz., nylon 6, polypropylene (PP) and calcium carbonate filled black\\u000a colored polypropylene (PP-blk) were studied. Thermal and mechanical analyses were conducted before fatigue tests. Thermal\\u000a characteristics, such as the degree of molecular degradation, glass transition temperatures, and melting points were determined.\\u000a Tensile strength, elastic modulus, and Poisson’s ratio were obtained from tests under quasi-static

  13. Fatigue life prediction of gas metal arc welded crucifrom joints of AA7075 aluminium alloy failing from root region

    Microsoft Academic Search

    B. RAVINDRA; T. SENTHIL KUMAR; V. BALASUBRAMANIAN

    2011-01-01

    Empirical relationship was developed to predict the fatigue life of gas metal arc welded (GMAW) cruciform joints failing from root region. High strength, age hardenable aluminium alloy of AA7075-T6 grade was used as the base material. The design of experiments concept was used to optimize the required number of fatigue testing experiments. Fatigue experiment was conducted in a servo hydraulic

  14. Fatigue life assessment of load-carrying fillet-welded cruciform joints inclined to uniaxial cyclic loading

    Microsoft Academic Search

    In-Tae Kim; Shigenobu Kainuma

    2005-01-01

    This study examines, the relationship between the direction of an applied stress cycle and the fatigue behaviour of load-carrying fillet-welded cruciform joints with weld root cracks, and presents the fatigue life assessment of the joints. Fatigue tests were performed on four sets of cruciform joints inclined at an angle of 0, 15, 30, or 45° to the normal direction of

  15. Effect of weld geometry on the fatigue life of non-load-carrying fillet welded cruciform joints

    Microsoft Academic Search

    Chin-Hyung Lee; Kyong-Ho Chang; Gab-Chul Jang; Chan-Young Lee

    2009-01-01

    In the present study, the effect of weld geometry on the fatigue life of non-load-carrying fillet welded cruciform joints was experimentally investigated. The weld geometry of the cruciform specimens was intentionally varied, and fatigue tests were carried out on various weld geometry configurations. The configurations included weld flank angle, weld toe radius and weld throat thickness. Constant amplitude fatigue tests

  16. An evaluation of shot peening, residual stress and stress relaxation on the fatigue life of AISI 4340 steel

    Microsoft Academic Search

    M. A. S. Torres; H. J. C. Voorwald

    2002-01-01

    Shot peening is a method widely used to improve the fatigue strength of materials, through the creation of a compressive residual stress field (CRSF) in their surface layers. In the present research the gain in fatigue life of AISI 4340 steel, used in landing gear, is evaluated under four shot peening conditions. Rotating bending fatigue tests were conducted and the

  17. The Effect of Three Mineral Base Oils on Roller Bearing Fatigue Life

    Microsoft Academic Search

    Irwin Koved

    1966-01-01

    The effect of three mineral base oils on roller bearing fatigue life has been studied. Life performance tests were conducted, using a specially controlled group of 45-mm bore cylindrical roller bearings. The results indicate that base oil stock affects bearing performance. Of the highly naphthenic, naphthenic, and paraffinic mineral oils studied, bearings lubricated with the latter achieved superior lives. The

  18. Finite element mesh generation and analysis of solder joints for fatigue life predictions

    Microsoft Academic Search

    Nasser H. Paydar; Yihong Tong; Hasan U. Akay; William Boehmer

    1993-01-01

    Tools for fatigue life prediction of solder joints are developed. This report consists of two parts. In part One, the creep and plastic deformations stored in a solder joint are calculated by implementing appropriate plastic and creep constitutive models in a nonlinear finite element program. The calculated damage in each cycle is then related to the life of the material

  19. 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.

  20. Fatigue Life and Crack Growth Behavior in Annealed and Normalized 0.83% Carbon Steel

    NASA Astrophysics Data System (ADS)

    Makabe, Chobin; Yamazaki, Shinya; Miyazaki, Tatsujiro; Fujikawa, Masaki

    2015-09-01

    The variations of fatigue limit and fatigue life of a plain specimen of annealed and normalized 0.83% carbon steel were investigated. This material is used for cutting tools and the original microstructure includes a spherical microstructure. After heat treatment under some conditions, the microstructure changed to a lamellar microstructure. However, the fatigue lives of the plain specimens of this material showed almost the same tendency even after heat treatment under some conditions. In those cases, the initial crack length in the fatigue process is related to the size of the crystal structure and related to the distribution of ferrite. In the present study, the relationship between the distribution of hardness and the fatigue limit was investigated. Also, it was discussed that the fatigue limit of heat-treated 0.83% carbon steel could be evaluated by a relationship in which the parameters are the hardness and initial crack length. Finally, the tendencies of fatigue life of heat-treated 0.83% carbon steel were discussed based on the observations of crack growth behavior.

  1. 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.

  2. Evaluation of the EHL film thickness and extreme pressure additives on gear surface fatigue life

    NASA Astrophysics Data System (ADS)

    Townsend, Dennis P.; Shimski, John

    1994-07-01

    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.

  3. Fatigue and quality of life of women undergoing chemotherapy or radiotherapy for breast cancer

    Microsoft Academic Search

    Winnie K. W. So; Gene Marsh; W. M. Ling; F. Y. Leung; Joe C. K. Lo; Maggie Yeung; George K. H. Li

    2009-01-01

    Objective  To examine fatigue and quality of life (QOL) in breast cancer patients undergoing chemotherapy or radiotherapy.\\u000a \\u000a \\u000a \\u000a Methods  A self-report survey derived from the Chinese version of Brief Fatigue Inventory, the Functional Assessment of Chronic Illness\\u000a Therapy for Breast Cancer, and the Medical Outcomes Study Social Support Survey. Descriptive statistics was used to examine\\u000a the intensity of fatigue and the prevalence of

  4. Effect of extreme-pressure additives on rolling bearing fatigue life

    Microsoft Academic Search

    G. T. Y. Wan; E. V. Amerongen; H. Lankamp

    1992-01-01

    Rolling-bearing fatigue tests showed that under marginal film lubrication conditions (lambda, lambda = 1.2), a commercially available sulphur-phosphorus extreme-pressure (EP) additive package used in blended lubricating oil reduced the bearing fatigue life by at least a factor of 4.5 compared with the base oil alone. The Weibull slope was found to be significantly higher than normally observed for material tests

  5. Temperature dependence of stress–fatigue life data of FRP composites

    Microsoft Academic Search

    H. Mivehchi; A. Varvani-Farahani

    2011-01-01

    Polymer-matrix composites are viscoelastic materials, and their mechanical properties are significantly influenced by temperature.\\u000a The present study develops a power-law stress–fatigue life relation which takes into account the effect of temperature on\\u000a the fatigue strength of fibre-reinforced polymer (FRP) composites. The validity of the relation is evaluated on the basis\\u000a of various sets of experimental data found in the literature,

  6. Erratum to: Temperature dependence of stress–fatigue life data of FRP composites

    Microsoft Academic Search

    H. Mivehchi; A. Varvani-Farahani

    2011-01-01

    Polymer-matrix composites are viscoelastic materials, and their mechanical properties are significantly influenced by temperature.\\u000a The present study develops a power-law stress–fatigue life relation which takes into account the effect of temperature on\\u000a the fatigue strength of fibre-reinforced polymer (FRP) composites. The validity of the relation is evaluated on the basis\\u000a of various sets of experimental data found in the literature,

  7. Fracture-mechanics concept offers models to help calculate fatigue life in drillpipe

    SciTech Connect

    Kral, E.; Newlin, L.; Quan, S.S.; Sengupta, P.K.

    1984-08-13

    This paper is the second of two articles on drillpipe fatigue analysis, and discusses the use of concepts set forth in part 1 to address the problem of calculating fatigue life of drillpipe under known operating conditions. The study tacitly accepts the presence of crack-like defects of various types in the pipe even in the as-received condition. The paper attempts to characterize the most severe surface cracks in terms of their dimensions and location by non-destructive examination.

  8. Fatigue life improvements of the AISI 304 stainless steel ground surfaces by wire brushing

    Microsoft Academic Search

    Nabil Ben Fredj; Mohamed Ben Nasr; Amir Ben Rhouma; Habib Sidhom; Chedly Braham

    2004-01-01

    The surface and subsurface integrity of metallic ground components is usually characterized by an induced tensile residual\\u000a stress, which has a detrimental effect on the fatigue life of these components. In particular, it tends to accelerate the\\u000a initiation and growth of the fatigue cracks. In this investigation, to deliberately generate compressive residual stresses\\u000a into the ground surfaces of the AISI

  9. High-temperature fatigue life of type 316 stainless steel containing irradiation induced helium

    Microsoft Academic Search

    M. L. Grossbeck; K. C. Liu

    1981-01-01

    Specimens of 20%-cold-worked AISI type 316 stainless steel were irradiated in the High Flux Isotope Reactor (HFIR) at 550°C to a maximum damage level of 15 dpa and a transmutation produced helium level of 820 at. ppM. Fully reversed strain controlled fatigue tests were performed in a vacuum at 550°C. No significant effect of the irradiation on low-cycle fatigue life

  10. Fatigue life and mechanical behaviors of bearing steel by nitrogen plasma immersion ion implantation

    Microsoft Academic Search

    Hongxi Liu; Baoyin Tang; Langping Wang; Xiaofeng Wang; Bo Jiang

    2007-01-01

    Rolling contact fatigue (RCF) performance and mechanical characteristics of nitrogen plasma immersion ion implantation (PIII) on AISI52100 bearing steel surface has been investigated using a conventional three ball-on-rod rig. Testing investigations include optical microscopy (OM), friction and wear behavior, rolling contact fatigue life, and nano-indentation measurements. Results indicate that the rolling elements failed at the surface or near-surface layer. Moreover,

  11. IMPACT OF POST-POLIO-RELATED FATIGUE ON QUALITY OF LIFE

    Microsoft Academic Search

    Arzu Yagiz On; Julide Oncu; Funda Atamaz; Berrin Durmaz

    2006-01-01

    Objective: To assess the impact of post-polio-related fatigue on quality of life. Design: Cross-sectional case control study. Subjects: Patients without additional health problems that may induce fatigue were selected from among 82 polio survivors. Twenty-six patients with post-polio syndrome and 10 without post-polio syndrome were included. Control group consisted of 30 healthy volunteers. Methods: We assessed presence and severity of

  12. 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

  13. Dynamic loads in Francis runners and their impact on fatigue life

    NASA Astrophysics Data System (ADS)

    Seidel, U.; Mende, C.; Hübner, B.; Weber, W.; Otto, A.

    2014-03-01

    Reliable fatigue life assessment of Francis runners combines two parts: At first, the load universe describing how the plant will be operated. And secondly, for all essential operating conditions, component stresses due to static and dynamic loading have to be predicted and considered in the design process by the manufacturer. Therefore, dynamic loading conditions and the resulting impact on the fatigue life of hydroelectric components are an integral part of research activities. Especially off-design conditions and transient operations have been addressed in the last years. Based on strain gauge measurements in prototype runners, model test experiences, and advanced numerical simulations, the understanding of dynamic loads has been highly improved. From correlations of measurement and simulation, standard procedures have been developed to enhance the fatigue life. The present paper summarizes findings of recent investigations enabling Francis runners which combine high efficiency and a robust mechanical design.

  14. Surface Crack Growth Path and Fatigue Life Prediction Due to Repeated Rolling/Sliding Contact

    NASA Astrophysics Data System (ADS)

    Goshima, Takahito; Ishihara, Sotomi; Shimizu, Masayoshi; Yoshida, Hirokazu; Tsuchida, Yuji

    This paper deals with the surface crack growth path description and the fatigue life prediction due to repeated rolling/sliding contact on the elastic half-space, accompanied by frictional heat generation and crack-face pressure. The stress intensity factors are analyzed for the surface crack which is kinked in multiple times from the inclined initial main crack. The rolling/sliding contact is simulated as a Hertzian contact pressure and a frictional load with heat generation, moving with constant velocity over the surface of the half-space. Applying the maximum energy release rate criterion to each kinked angle, the crack growth path can be described, and employing a mixed mode fatigue crack growth law, the associated fatigue life also can be predicted. The effects of frictional coefficient, slide/roll ratio and crack-face pressure on the crack growth path and associated life are considered for a high carbon-chromium bearing steel (AISI52100).

  15. Fatigue

    MedlinePLUS

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

  16. A CHARACTERISTIC PLANE METHOD FOR MULTIAXIAL FATIGUE LIFE PREDICTION

    Microsoft Academic Search

    Y. Liu; S. Mahadevan

    This paper proposes a new multiaxial fatigue damage model based on a characteristic plane approach. The characteristic plane in the proposed model is defined as the material plane on which the damage caused by the cyclic hydrostatic strain amplitude is minimized to zero. The characteristic plane in the proposed model depends not only on the stress state but also on

  17. The effect of hot isostatic pressing (HIP) on the fatigue life of A206-T71 aluminum castings

    Microsoft Academic Search

    James T. Staley; Murat Tiryakio?lu; John Campbell

    2007-01-01

    The effect of hot isostatic pressing (HIP) on fatigue properties of A206-T71 castings was investigated. Castings were (i) non-HIPed, or HIPed at (ii) typical HIP temperature, (iii) solution heat-treat temperature and (iv) eutectic melting temperature. HIP conditions were found to increase average and maximum fatigue life. However, the range in fatigue life also increased after HIP, which is attributed to

  18. 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.

  19. Shape optimization of a pressure vessel under plastic flow, plastic instability, weight and fatigue life criteria

    SciTech Connect

    El Abdi, R.; Touratier, M.; Convert, P.; Lalanne, B. [Lab Genie de Production, Tarbes (France)] [Lab Genie de Production, Tarbes (France)

    1994-06-01

    The structural shape optimization of a complex shell under complex criteria is presented. The shell is one of various cases of a turboshaft, and optimization criteria are associated with the cost, the technology, and above all the working conditions for the turboshaft. Optimization criteria involved are of course the weight of the structure, but also the plastic flow, plastic instability and fatigue life. The fatigue life criterion is an extension to the three-dimensional state of the one-dimensional Lemaitre-Chaboche rule, taking into account the elasto-plastic Neuber correction. All computations have been made with the ANSYS finite element program in which an optimization module exists. 20 refs.

  20. Shape optimization of a pressure vessel under plastic flow, plastic instability, weight and fatigue life criteria

    NASA Astrophysics Data System (ADS)

    El Abdi, R.; Touratier, M.; Convert, P.; Lalanne, B.

    1994-06-01

    The structural shape optimization of a complex shell under complex criteria is presented. The shell is one of various cases of a turboshaft, and optimization criteria are associated with the cost, the technology, and above all the working conditions for the turboshaft. Optimization criteria involved are of course the weight of the structure, but also the plastic flow, plastic instability and fatigue life. The fatigue life criterion is an extension to the three-dimensional state of the one-dimensional Lemaitre-Chaboche rule, taking into account the elasto-plastic Neuber correction. All computations have been made with the ANSYS finite element program in which an optimization module exists.

  1. 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.

  2. Analysing the influences of weld size on fatigue life prediction of FCAW cruciform joints by strain energy concept

    Microsoft Academic Search

    V Balasubramanian; B Guha

    1999-01-01

    The effect of weld size on fatigue life of flux cored arc welded (FCAW) cruciform joints containing lack of penetration (LOP) defect has been analysed by using the strain energy density factor (SEDF) concept. Moreover, new fracture mechanics equations have been developed to predict the fatigue life of the cruciform joints. Load carrying cruciform joints were fabricated from ASTM 517

  3. New thermal fatigue life prediction method for BGA\\/FBGA solder joints with basic crack propagation study

    Microsoft Academic Search

    Yasumi Uegai; Akinobu Kawazu; Qiang Wu; Hironori Matsushima; Masatoshi Yasunaga; Haruo Shimamoto

    2002-01-01

    Evaluation of the thermal fatigue life of the solder joints that connect the BGA package to the system board electrically and mechanically, and the improvement of precision are important issues in the development of BGA\\/FBGA packages. The fatigue life of the BGA solder joint consists of a process of micro-crack initiation followed by its propagation. This results in the increase

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

    Microsoft Academic Search

    Soo Woo Nam

    2002-01-01

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

  5. Effects of stress concentrations on the fatigue life of a gamma based titanium aluminide

    SciTech Connect

    Trail, S.J.; Bowen, P. [Univ. of Birmingham (United Kingdom)

    1995-12-31

    S-N curves for a gamma based titanium aluminide alloy of composition Ti-47.2Al-2.1Mn-1.9Nb(at.%)+2TiB{sub 2}(wt.%) have been used to define fatigue life. Effects of residual stress, stressed volume, loading ratio, loading mode, elevated temperature and surface roughness have been considered. Residual tensile stresses and micro-cracking are introduced by Electro Discharge Machining and the fatigue life is reduced slightly compared with polished samples. Notched fatigue tests show a significant notch strengthening effect which increases with increasing stress concentration factor. The fracture surfaces of specimens tested at room temperature reveal fully brittle failure mechanisms and no evidence of stable crack growth is observed. The fatigue life appears, therefore, to be determined predominantly by the number of cycles to crack initiation. At the elevated temperature of 830 C, evidence for some stable fatigue crack growth has been found. Probable sites for crack initiation are addressed.

  6. 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 (? = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (? = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy ( p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.

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

    Microsoft Academic Search

    L. Frýba

    1980-01-01

    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

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

    SciTech Connect

    Cheney, M. C. (PS Enterprises, Glastonbury, Connecticut); Olsen, T.; Quandt, G.; Archidiacono, P.

    1999-07-19

    PS Enterprises, Inc. investigated a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades. A rotor was designed, manufactured and tested in the field. A preliminary design study and proof of concept test were conducted to assess the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study and a scaled 80 kW rotor was fabricated and field tested as a demonstration of the concept. The design studies continued to support the premise that pultruded blades offer the potential for significant reductions in rotor weight and cost. The field test provided experimental performance and loads data that compared well with predictions using the FLEXDYNE aeroelastic analysis. The field test also demonstrated stable yaw behavior and the absence of stall flutter over the wind conditions tested. During the final year of the contract, several studies were conducted by a number of independent consultants to address specific technical issues related to pultruded blades that could impact the commercial viability of turbines using this technology. The issues included performance, tower strikes, yaw stability, stall flutter, fatigue, and costs. While the performance of straight pultruded blades was projected to suffer a penalty of about 13% over fully twisted and tapered blades, the study showed that an aerodynamic fairing over the inner 40% could recover 85% of that loss while still keeping the blade cost well below that of conventional blades. Other results of the study showed that with proper design, rotors using pultruded blades could operate without aeroelastic problems, have acceptable fatigue life, and cost less than half that of rotors employing conventionally manufactured blades.

  9. 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

  10. 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.

  11. 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.

  12. Bearing Fatigue Life Tests in Advanced Base Oil and Grease for Space Applications

    Microsoft Academic Search

    Nobuyoshi Ohno; Hidekazu Komiya; Sobahan Mia; Shigeki Morita; Naoki Satoh; Shingo Obara

    2008-01-01

    Two synthetic base oils (815Z and 2001A) and two greases (601EF and R2000) used for space applications have been studied at ground level. Rheological tests were performed in order to characterize the behavior of each of the base oils versus the pressure and the temperature. Next, the effect of base oils and greases on ball bearing fatigue life was carried

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

    Microsoft Academic Search

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

    2005-01-01

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

  14. High-cycle fatigue life prediction for Pb-free BGA under random vibration loading

    Microsoft Academic Search

    Da Yu; Abdullah Al-Yafawi; Tung T. Nguyen; Soonwan Chung

    2011-01-01

    This paper develops an assessment methodology based on vibration tests and finite element analysis (FEA) to predict the fatigue life of electronic components under random vibration loading. A specially designed PCB with ball grid array (BGA) packages attached was mounted to the electro-dynamic shaker and was subjected to different vibration excitations at the supports. An event detector monitored the resistance

  15. Finite element based fatigue life prediction for electronic components under random vibration loading

    Microsoft Academic Search

    Da Yu; Abdullah Al-Yafawi; Soonwan Chung

    2010-01-01

    This work develops an assessment methodology based on experiments and finite element analysis (FEA) to determine the solder joint fatigue life of electronic components under random vibration loading. Specially designed PCB with Ball Grid Array (BGA) packages attached was mounted to the Electro dynamic shaker and was applied to different random vibration excitations at the supports. Meanwhile, an event detector

  16. Fatigue life prediction of load carrying cruciform joints of pressure vessel steel by statistical tools

    Microsoft Academic Search

    V. Balasubramanian; B. Guha

    2004-01-01

    Mathematical models have been developed to predict the fatigue life of shielded metal arc welded (SMAW) and flux cored arc welded (FCAW) cruciform joints failing from root and toe regions. High strength, quenched and tempered steel (ASTM 517 `F' grade) has been used as the base material throughout the investigation. The design of experiments (DoE) concept has been used to

  17. The effect of residual stresses and weld geometry on the improvement of fatigue life

    Microsoft Academic Search

    Nguyen T. Ninh; M. A. Wahab

    1995-01-01

    In this paper, the effect of residual stresses and weld geometry on the fatigue life of butt welded joints was studied by developing an analytical model using Linear Elastic Fracture Mechanics (LEFM), superposition and finite element approaches. Various configurations of residual stresses and weld geometry in butt welded joints were considered and corresponding effective stress intensity factors were calculated by

  18. GUIDE FOR APPLICATION OF ULTRASONIC IMPACT TREATMENT IMPROVING FATIGUE LIFE OF WELDED STRUCTURES

    Microsoft Academic Search

    S. Statnikov; RUSSIAN DELEGATION

    In recent years, in the context of fatigue life improvement methods, Ultrasonic Impact Treatment (UIT) has attracted a particular attention . Independent expert assessments of this method provide indications of its effectiveness, workability, compatibility with welding fabrication and repair processes, controllability, simplicity in use and in quality control, high stability and reproducibility of results. The last feature (reproducibility) is largely

  19. Comparison of fatigue life for T and cruciform welded joints with different combinations of geometrical parameters

    Microsoft Academic Search

    A. Khodadad Motarjemi; A. H Kokabi; F. M Burdekin

    2000-01-01

    The fatigue life for T and cruciform welded joints containing different extents of lack of root penetration was calculated for different combinations of geometrical parameters, including thicknesses up to 45 mm, by integration of the Paris law and use of stress intensity factor solutions calculated previously. The effect of attachment and main plate thickness, weld leg length and initial lack

  20. Creep-Fatigue Life Evaluation for Materials Subjected to Nonproportionally Combined Tension and Torsion

    Microsoft Academic Search

    Katsuyuki Tokimasa

    2011-01-01

    The author and his colleagues have proposed in their recent works the creep-fatigue life prediction method based on the strain range partitioning concept for nonproportionally combined tension and torsion using new inelastic strain range parameters and have been studying their applicability to the materials subjected to nonproportional axial-torsional loading at elevated temperatures. In the present paper are summarized the results

  1. Life prediction techniques for variable amplitude multiaxial fatigue. Part 2: Comparison with experimental results

    Microsoft Academic Search

    C. H. Wang; M. W. Brown

    1996-01-01

    An extensive multiaxial random fatigue test program was conducted at room temperature using tubular specimens. Experiments were performed under combined tension\\/torsion and triaxial loading, covering proportional and nonproportional variable amplitude loading cases. The two proposed life prediction methods discussed in Part 1 are evaluated using the experimental results, demonstrating that these two methods provide satisfactory predictions.

  2. An Analytical Solution of Equivalent Stress for Structure Fatigue Life Prediction under Broad Band Random Loading

    Microsoft Academic Search

    Xiaoyun Liu; Pengmin Lü

    1997-01-01

    An analytical solution of an equivalent stress-range calculation, based on the power-spectral density of stress in critical points of structures, and a statistical theory for the peak distribution of a stationary Gaussian random process are presented in this paper for fatigue life assessment under broad-band random loading. This model has more advantages than similar existing models.

  3. Effect of the loading spectrum and history length on fatigue life distribution under random loading

    Microsoft Academic Search

    J. Dominguez; J. Zapatero

    1992-01-01

    One major source of error commonly encountered in determining the fatigue life of a given element arises from the loads involved, which are usually of random nature. As a rule, resistance analyses, carried out by simulation or tests, are done by using a loading history accounting for the real loads involved that is repeated indefinitely until failure is encountered. The

  4. Fatigue life prediction based on natural frequency changes for spot welds under random loading

    Microsoft Academic Search

    Rui-Jie Wang; De-Guang Shang

    2009-01-01

    Fatigue tests were carried out on tensile-shear spot-welded specimens under random loading; at the same time, natural frequencies at different life stages were measured. Test results were compared with that under constant amplitude loading. The relationship between damage and natural frequency change ratio established under constant amplitude loading is here modified. The nonlinear damage evolution equation was established using the

  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. Modeling cyclic ratcheting based fatigue life of HSLA steels using crystal plasticity FEM simulations and experiments

    Microsoft Academic Search

    Shashwat Sinha; Somnath Ghosh

    2006-01-01

    This paper develops a plastic ratcheting based fatigue failure model for HSLA steels from a combination of results from experiments and finite element simulations using crystal plasticity constitutive relations. It predicts the nucleation of major cracks in the microstructure in ratcheting. Subsequently, the total life is limited by the growth of ductile fracture in the microstructure, which is factored in

  7. Effect of combined shot-peening and PEO treatment on fatigue life of 2024 Al alloy

    Microsoft Academic Search

    D. T. Asquith; A. L. Yerokhin; J. R. Yates; A. Matthews

    2006-01-01

    One of the most important objectives in the surface engineering of light-weight alloys is to enhance their fatigue properties, allowing both increased performance and an extended service life. This can be achieved by forming a hard surface layer while incorporating a favourable stress state. Single surface treatments, for example, Plasma Electrolytic Oxidation (PEO), are not always capable of creating optimal

  8. Osteonal effects on elastic modulus and fatigue life in equine bone

    Microsoft Academic Search

    V. A. Gibson; S. M. Stover; J. C. Gibeling; S. J. Hazelwood; R. B. Martin

    2006-01-01

    We hypothesized that recently formed, incompletely mineralized, and thus, relatively deformable osteons in the equine third metacarpus enhance in vitro load-controlled fatigue life in two ways. Macroscopically, there is a compliance effect, because reduced tissue elastic modulus diminishes the stress required to reach a given strain. Microscopically, there is a cement line effect, in which new osteons and their cement

  9. 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.

  10. 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,…

  11. Life extension of self-healing polymers with rapidly growing fatigue cracks

    E-print Network

    Sottos, Nancy R.

    Life extension of self-healing polymers with rapidly growing fatigue cracks A. S. Jones1,*, J. D 61801, USA Self-healing polymers, based on microencapsulated dicyclopentadiene and Grubbs' catalyst periods, effectively training the self-healing polymeric material to achieve higher endurance limits

  12. Finite element mesh generation and analysis of solder joints for fatigue life predictions

    NASA Astrophysics Data System (ADS)

    Paydar, Nasser H.; Tong, Yihong; Akay, Hasan U.; Boehmer, William

    1993-08-01

    Tools for fatigue life prediction of solder joints are developed. This report consists of two parts. In part One, the creep and plastic deformations stored in a solder joint are calculated by implementing appropriate plastic and creep constitutive models in a nonlinear finite element program. The calculated damage in each cycle is then related to the life of the material using two failure criteria: strain-life and energy-partitioning. The importance of parameters affecting the fatigue life of solders are evaluated. In part Two, the finite element analysis is combined with x-ray and laser imaging systems, from which real solder joint geometries can be constructed. The approaches presented herein provides a useful tool in the design and manufacturing of surface-mount assemblies.

  13. 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.

  14. 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.

  15. Scatter in fatigue life due to effects of porosity in cast A356-T6 aluminum-silicon alloys

    NASA Astrophysics Data System (ADS)

    Yi, J. Z.; Gao, Y. X.; Lee, P. D.; Flower, H. M.; Lindley, T. C.

    2003-09-01

    Porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed scatter in fatigue life of a cast A356-T6 aluminum-silicon alloy due to the presence of porosity. Specimens containing a controlled amount of porosity were prepared by employing a wedge-shaped casting mold and adjusting the degassing process during casting. High-cycle fatigue tests were conducted under fixed stress conditions on a series of specimens with controlled microstructures (especially, the secondary dendrite-arm spacing), and the degree of scatter in the results was assessed. Stochastically, such scatter was found to be adequately characterized by a three-parameter Weibull distribution function. Large pores at or close to the specimen surface were found to be responsible for crack initiation in all fatigue-test specimens, and the resultant fatigue life was related to the initiating pore size through a relationship based on the rate of small-fatigue-crack propagation. With respect to the probabilities for the pores of various sizes and locations to initiate a fatigue crack, a statistical model was developed to establish the relationship between the porosity population and the resultant scatter in fatigue life. The modeling predictions are in agreement with the experimental results. Moreover, Monte-Carlo simulation based on this model demonstrated that the average pore size, pore density, and standard deviation of the pore sizes, together with the specimen size and geometry, are all of consequence regarding scatter in fatigue life.

  16. 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.

  17. 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.

  18. Microstructure-based fatigue life prediction for cast A356-T6 aluminum-silicon alloys

    NASA Astrophysics Data System (ADS)

    Yi, J. Z.; Gao, Y. X.; Lee, P. D.; Lindley, T. C.

    2006-04-01

    Fatigue life prediction and optimization is becoming a critical issue affecting the structural applications of cast aluminum-silicon alloys in the aerospace and automobile industries. In this study, a range of microstructure and porosity populations in A356 alloy was created by controlling the casting conditions and by applying a subsequent hot isostatic pressing (“hipping”) treatment. The microstructure and defects introduced during the processing were then quantitatively characterized, and their effects on the fatigue performance were examined through both experiment and modeling. The results indicated that whenever a pore is present at or near the surface, it initiates fatigue failure. In the absence of large pores, a microcell consisting of ?-Al dendrites and associated Si particles was found to be responsible for crack initiation. Crack initiation life was quantitatively assessed using a local plastic strain accumulation model. Moreover, the subsequent crack growth from either a pore or a microcell was found to follow a small-crack propagation law. Based on experimental observation and finite-element analysis, a unified model incorporating both the initiation and small crack growth stages was developed to quantitatively predict the dependency of fatigue life on the microstructure and porosity. Good agreement was obtained between the model and experiment.

  19. Substrate creep on the fatigue life of a model dental multilayer structure.

    PubMed

    Zhou, J; Huang, M; Niu, X; Soboyejo, W O

    2007-08-01

    In this article, we investigated the effects of substrate creep on the fatigue life 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 or 600 grit sand papers before bonding to create different subsurface 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 subsurfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels, i.e. P(m) < 60 N (P(m) is the maximum magnitude of cyclic load). But at relatively high load levels, i.e. P(m) > 65 N, slow crack growth was the major failure mechanism. 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. PMID:17245742

  20. 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.

  1. Effects of weld profile and undercut on fatigue crack propagation life of thin-walled cruciform joint

    Microsoft Academic Search

    F. R. Mashiri; X. L. Zhao; P. Grundy

    2001-01-01

    Fatigue may occur in undercarriages and support systems of trailers, haymakers, graders and swing-ploughs made up of thin-walled tubular sections with wall thicknesses less than 4 mm. Little research has been done on the fatigue of thin-walled tubular sections below 4 mm thickness. The weld profile and weld undercut may affect the fatigue crack propagation life of welded joints especially

  2. 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.

  3. Inclusions Size-based Fatigue Life Prediction Model of NiTi Alloy for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Urbano, Marco Fabrizio; Cadelli, Andrea; Sczerzenie, Frank; Luccarelli, Pietro; Beretta, Stefano; Coda, Alberto

    2015-06-01

    Current standards consider the size and distribution of inclusions in semi-finished material, but do not place requirements on final biomedical devices made of NiTi shape memory alloys. In this paper, we analyze this by comparing the fatigue performances of NiTi superelastic wires obtained by different processes through a simple bilinear model of fatigue response in terms of strain life. The fracture surfaces of failed wires are analyzed through SEM microscopy and data regarding the presence of particles, and their morphology is recorded and analyzed using Type-I extreme value distribution. The results show a strong correlation between the fatigue limit of wires (in terms of strain) and the predicted extreme values of inclusions at fracture origin. Then, following the concept of treating the inclusions as `small cracks,' a simple relationship between fatigue limit strain range and inclusion size is proposed based on ?Kth data from the literature. The model is compared with the fatigue data obtained from the tested wires.

  4. Natalizumab Treatment Reduces Fatigue in Multiple Sclerosis. Results from the TYNERGY Trial; A Study in the Real Life Setting

    PubMed Central

    Svenningsson, Anders; Falk, Eva; Celius, Elisabeth G.; Fuchs, Siegrid; Schreiber, Karen; Berkö, Sara; Sun, Jennifer; Penner, Iris-Katharina; for the TYNERGY trial investigators

    2013-01-01

    Fatigue is a significant symptom in multiple sclerosis (MS) patients. First-generation disease modifying therapies (DMTs) are at best moderately effective to improve fatigue. Observations from small cohorts have indicated that natalizumab, an antibody targeting VLA-4, may reduce MS-related fatigue. The TYNERGY study aimed to further evaluate the effects of natalizumab treatment on MS-related fatigue. In this one-armed clinical trial including 195 MS patients, natalizumab was prescribed in a real-life setting, and a validated questionnaire, the Fatigue Scale for Motor and Cognitive functions (FSMC), was used both before and after 12 months of treatment to evaluate a possible change in the fatigue experienced by the patients. In the treated cohort all measured variables, that is, fatigue score, quality of life, sleepiness, depression, cognition, and disability progression were improved from baseline (all p values<0.0001). Walking speed as measured by the six-minute walk-test also increased at month 12 (p?=?0.0016). All patients were aware of the nature of the treatment agent, and of the study outcomes. Conclusion Natalizumab, as used in a real-life setting, might improve MS-related fatigue based on the results from this one-armed un-controlled stud. Also other parameters related to patients' quality of life seemed to improve with natalizumab treatment. Trial Registration ClinicalTrials.gov NCT00884481 PMID:23555589

  5. Influences of welding processes on fatigue life of cruciform joints of pressure vessel grade steels containing LOP defects

    Microsoft Academic Search

    V Balasubramanian; B Guha

    2000-01-01

    The influences of two welding processes, namely, shielded metal arc welding (SMAW) and flux cored arc welding (FCAW), on fatigue life of cruciform joints, containing lack of penetration (LOP) defects, have been studied. Load carrying cruciform joints were fabricated from high strength, quenched and tempered steels of pressure vessel (ASTM 517 ‘F’) grade. Fatigue crack growth experiments were carried out

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Llaneza, V.; Belzunce, F. J.

    2015-05-01

    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.

  8. 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

  9. Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results

    Microsoft Academic Search

    D. T. Rusk; W. Hoppe; W. Braisted; N. Powar

    2009-01-01

    The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that

  10. 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.

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

    SciTech Connect

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

    1984-09-01

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

  12. Expert system for remnant life prediction of defected components under fatigue and creep-fatigue loadings

    Microsoft Academic Search

    Xiao Liu; Fu-zhen Xuan; Jun Si; Shan-tung Tu

    2008-01-01

    Life prediction and management of cracked high temperature structures is a matter of great importance for both economical and safe reasons. To implement such a task, many fields such as material science, structure engineering and mechanics science etc. are involved and expertise is generally required. In terms of the methodology of advanced time-dependent fracture mechanics, this paper developed an expert

  13. Shot peening for Ti-6Al-4V alloy compressor blades

    NASA Technical Reports Server (NTRS)

    Carek, Gerald A.

    1987-01-01

    A text program was conducted to determine the effects of certain shot-peening parameters on the fatigue life of the Ti-6Al-4V alloys as well as the effect of a demarcation line on a test specimen. This demarcation line, caused by an abrupt change from untreated surface to shot-peened surface, was thought to have caused the failure of several blades in a multistage compressor at the NASA Lewis Research Center. The demarcation line had no detrimental effect upon bending fatigue specimens tested at room temperature. Procedures for shot peening Ti-6Al-4V compressor blades are recommended for future applications.

  14. Shot peening for Ti-6Al-4V alloy compressor blades

    SciTech Connect

    Carek, G.A.

    1987-04-01

    A text program was conducted to determine the effects of certain shot-peening parameters on the fatigue life of the Ti-6Al-4V alloys as well as the effect of a demarcation line on a test specimen. This demarcation line, caused by an abrupt change from untreated surface to shot-peened surface, was thought to have caused the failure of several blades in a multistage compressor at the NASA Lewis Research Center. The demarcation line had no detrimental effect upon bending fatigue specimens tested at room temperature. Procedures for shot peening Ti-6Al-4V compressor blades are recommended for future applications.

  15. Enhancement of Fatigue Life Performance of Holed Specimen of Aluminum Alloy 2024-T3 by Local Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Rana, Muhammed Sohel; Yamanaka, Taisuke; Makabe, Chobin

    The effect of local plastic deformation on the fatigue life in a holed specimen was investigated. The local plastic deformation was applied around the hole by inserting a pin into the hole, and the pin was removed before the testing. The material used was aluminum alloy 2024-T3. After removing the pin, there was a circular hole or elliptical hole in the center of the flat section of the specimen. Due to the application of local deformation, the fatigue life of holed specimens became longer. In particular, in specimens where the hole shape was made elliptical, the fatigue life was clearly improved. Hardness distribution around the hole was measured to understand the effect of the local plastic deformation on the fatigue life expansion. Consequently, it is concluded that the local plastic hardening and compression residual stress in the vicinity of the hole are the cause of the strengthening of the holed specimen.

  16. 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.

  17. Effects of weld metal profile on the fatigue life of integrally reinforced weldon fittings

    Microsoft Academic Search

    G. E. Woods; E. C. Rodabaugh

    1994-01-01

    The cyclic fatigue life of fabricated tee intersections, including integrally reinforced weld-on fittings, has been a topic of discussion in the recent past. The discussion has centered around questions concerning the accuracy of the ASME B31.3 Code equations in calculating the stress intensification factors, (SIFs), for these types of intersection geometries. The SIF of an intersection is an indicator of

  18. A neural network approach to elevated temperature creep–fatigue life prediction

    Microsoft Academic Search

    Vasisht Venkatesh; H. J Rack

    1999-01-01

    A new approach using a back-propagation neural network for life prediction was developed and demonstrated for predicting the elevated temperature (0.7–0.8Tm) creep–fatigue behavior of Ni-base alloy INCONEL 690. The neural network was trained with five extrinsic parameters, characterized via a 25–1 fractional factorial design methodology, and an intrinsic parameter (final grain size). The back-propagation network training error, prediction error and

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

    Microsoft Academic Search

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

    2003-01-01

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

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

    Microsoft Academic Search

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

    2010-01-01

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

  1. 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.

  2. 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.

  3. Surface Crack Growth Path and Fatigue Life Prediction Due to Repeated Rolling\\/Sliding Contact

    Microsoft Academic Search

    Takahito Goshima; Sotomi Ishihara; Masayoshi Shimizu; Hirokazu Yoshida; Yuji Tsuchida

    2003-01-01

    This paper deals with the surface crack growth path description and the fatigue life prediction due to repeated rolling\\/sliding contact on the elastic half-space, accompanied by frictional heat generation and crack-face pressure. The stress intensity factors are analyzed for the surface crack which is kinked in multiple times from the inclined initial main crack. The rolling\\/sliding contact is simulated as

  4. Improvement of Rolling Bearing Fatigue Life Under Debris-Contaminated Lubrication by Decreasing the Crack Sensitivity of the Material

    Microsoft Academic Search

    Ikuo Sugiura; Osamu Kato; Noriyuki Tsushima; Hiroshi Muro

    1982-01-01

    Rolling contact fatigue life under debris- (or foreign particle-) contaminated lubrication is less than one-tenth the life under non-contaminated lubrication when the contaminating debris is hard, large particles (0.1 mm). A small “crevasse-type” crack initiates at the forward or backward side of a debris Particle indentation and grows into fatigue flaking. The size of the initial crack can be described

  5. An investigation of the reduction in tensile strength and fatigue life of pre-corroded 7075-T6 aluminum alloy

    Microsoft Academic Search

    B. Obert; K. Ngo; J. Hashemi; S. Ekwaro-Osire; T. P. Sivam

    2000-01-01

    In aging aircraft, the synergetic interaction between corrosion and fatigue has been shown to reduce the life expectancy of\\u000a aluminum alloys. The objective of this study was to quantify the effects of corrosion, in terms of mass loss per unit area,\\u000a on the static strength and fatigue life of 7075-T6 aluminum alloy. This was an experimental study in which test

  6. 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.

  7. 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).

  8. Effect of L\\/ T p ratio on fatigue life prediction of SMAW cruciform joints of ASTM 517 ‘F’ Grade steels

    Microsoft Academic Search

    V. Balasubramanian; B. Guha

    1998-01-01

    New fracture mechanics equations have been developed to predict the fatigue life of shielded metal arc welded (SMAW) cruciform joints of ASTM 517 ‘F’ Grade steels, containing lack of penetration (LOP) defects. These equations have been developed by combining the Paris law with the ?Ki-endurance equation The initiation life (Ni) and the propagation life (Np) of the joints were accounted

  9. 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.

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

    NASA Technical Reports Server (NTRS)

    Schijve, J.

    1994-01-01

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

  11. Life improvement and repair of fatigue cracks in welded joints by hammer peening

    SciTech Connect

    Haagensen, P.J. [Norwegian Inst. of Technology, Trondheim (Norway). Dept. of Civil Engineering

    1995-12-31

    Hammer peening is an effective method for extending the life of welded joints by the introduction of a deep compressive stress field which delays crack growth. In this paper hammer peening is examined as a repair method for cracks in welded T-joints. Fatigue cracks were grown is as-welded joints to depths from approximately 0.5 mm to 2 mm. The crack line was then hammer peened following typical peening procedures. The remaining fatigue life of components with untreated cracks of these sizes would constitute from a few hundred cycles to a few percent of the told life. The fatigue strength of the repaired specimens was compared with data from earlier tests on as-welded specimens and specimens that had been improved by weld toe grinding followed by hammer peening. All tests were carried out at constant amplitude loading in air. The material was a low carbon micro alloyed steel of 360 MPa yield strength. The specimens were T-joints with non-load carrying welds loaded in four point bending.

  12. Prediction of Contact Fatigue Life of Alloy Cast Steel Rolls Using Back-Propagation Neural Network

    NASA Astrophysics Data System (ADS)

    Jin, Huijin; Wu, Sujun; Peng, Yuncheng

    2013-12-01

    In this study, an artificial neural network (ANN) was employed to predict the contact fatigue life of alloy cast steel rolls (ACSRs) as a function of alloy composition, heat treatment parameters, and contact stress by utilizing the back-propagation algorithm. The ANN was trained and tested using experimental data and a very good performance of the neural network was achieved. The well-trained neural network was then adopted to predict the contact fatigue life of chromium alloyed cast steel rolls with different alloy compositions and heat treatment processes. The prediction results showed that the maximum value of contact fatigue life was obtained with quenching at 960 °C, tempering at 520 °C, and under the contact stress of 2355 MPa. The optimal alloy composition was C-0.54, Si-0.66, Mn-0.67, Cr-4.74, Mo-0.46, V-0.13, Ni-0.34, and Fe-balance (wt.%). Some explanations of the predicted results from the metallurgical viewpoints are given. A convenient and powerful method of optimizing alloy composition and heat treatment parameters of ACSRs has been developed.

  13. 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.

  14. 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.

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

    Microsoft Academic Search

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

    1984-01-01

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

  16. ANALYSIS OF THE MATERIAL STRESS STATE IN THE FRETTING ZONE FOR PREDICTING LIFE UNDER CYCLIC LOADING

    Microsoft Academic Search

    G. Tsyban; P. Kurash

    Fatigue damage is frequent in the site of contact between the blade root and disk in high -performance gas-turbine engines, which leads to premature fracture of a blade. The presence of contact pressure and slight relative slip on the contacting surfaces initiates the damaging processes known as fretting. This study evaluates how well some of the strain-life parameters predict fretting

  17. 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.

  18. Osteonal effects on elastic modulus and fatigue life in equine bone.

    PubMed

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

    2006-01-01

    We hypothesized that recently formed, incompletely mineralized, and thus, relatively deformable osteons in the equine third metacarpus enhance in vitro load-controlled fatigue life in two ways. Macroscopically, there is a compliance effect, because reduced tissue elastic modulus diminishes the stress required to reach a given strain. Microscopically, there is a cement line effect, in which new osteons and their cement lines more effectively serve as barriers to crack propagation. We studied 18 4 x 10 x 100 mm beams from the medial, lateral, and dorsal cortices of metacarpal bones from 6 thoroughbred racehorses. Following load-controlled fatigue testing to fracture in 4 point bending, a transverse, 100 microm thick, basic fuchsin-stained cross-section was taken from the load-bearing region. The number and diameter of all intact (and thus recently formed/compliant) secondary osteons in a 3.8 x 3.8 mm region in the center of the section were determined. The associated area fraction and cement line length of intact osteons were calculated, and the relationships between these variables, elastic modulus (E), and the logarithm of fatigue life (logN(F)) were analyzed. As expected, logN(F) was negatively correlated with E, which was in turn negatively correlated with intact osteon area fraction and density. (LogN(F))/E increased in proportion to intact osteon density and nonlinearly with cement line density (mm/mm(2)). These results support the hypothesis that remodeling extends load-controlled fatigue life both through the creation of osteonal barriers to microdamage propagation and modulus reduction. PMID:16321623

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1995-04-01

    Severe fretting damage has been observed on the pressure surfaces of fan and compressor blade dovetails/disks in an aerospace gas turbine engine. A study has been carried out to evaluate the effect of an ion implantation technique in combination with the presently used surface treatments, such as shot peening and coating, on the fretting fatigue life of titanium alloy gas turbine engine components. The results from fretting fatigue tests, residual stress measurements, and nanoindentation tests were used to quantitatively evaluate the effect of various surface treatments on the fretting fatigue life of the fan blade and disk materials. Results from microstructural characterization and analyses of elemental and phase distributions within the implanted region are used to understand the effect of ion implantation on the surface properties of the alloys. Finally, an attempt has been made to evaluate the potential for improving the fretting fatigue life of the engine components using various surface modification techniques.

  2. 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.

  3. 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.

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

    SciTech Connect

    Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States). Wind Energy Research Dept.; Wilson, T. [Univ. of New Mexico, Albuquerque, NM (United States). New Mexico Engineering Research Inst.

    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.

  5. An investigation of cyclic transient behavior and implications on fatigue life estimates

    SciTech Connect

    Jiang, Y. [Univ. of Nevada, Reno, NV (United States). Dept. of Mechanical Engineering; Kurath, P. [Univ. of Illinois, Urbana, IL (United States)

    1997-04-01

    Current research focuses on proportional cyclic hardening and non-Massing behaviors. The interaction of these two hardenings can result in the traditionally observed overall softening, hardening or mixed behavior exhibited for fully reversed strain controlled fatigue tests. Proportional experiments were conducted with five materials 304 stainless steel, normalized 1070 and 1045 steels, and 7075-T6 and 6061-T6 aluminum alloys. All the materials display similar trends, but the 304 stainless steel shows the most pronounced transient behavior and will be discussed in detail. Existing algorithms for this behavior are evaluated in light of the recent experiments, and refinements to the Armstrong-Frederick class of incremental plasticity models are proposed. Modifications implemented are more extensive than the traditional variation of yield stress, and a traditional strain based memory surface is utilized to track deformation history. Implications of the deformation characteristics with regard to fatigue life estimation, especially variable amplitude loading, will be examined. The high-low step loading is utilized to illustrate the effect of transient deformation on fatigue life estimation procedures, and their relationship to the observed and modeled deformation.

  6. 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.

  7. 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.

  8. Effect of residual stresses induced by prestressing on rolling element fatigue life

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    A mechanical prestress cycle suitable to induce compressive stress beneath the surface of the inner race of radially loaded 207-size bearings was determined. Compressive residual stress in excess 0.69 x 10 to the 9th power N/sq m (100,000 psi), as measured by X-ray diffraction, were induced at the depth of maximum shearing stress. The prestress cycle consisted of running the bearings for 25 hours at 2750 rpm at a radial load which produced a maximum Hertz stress of 3.3 x 10 to the 9th power N/sq m (480,000 psi) at the contact of the inner race and the heaviest loaded ball. Bearings subjected to this prestress cycle and subsequently fatigue tested gave a 10 percent fatigue life greater than twice that of a group of baseline bearings.

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

    SciTech Connect

    Syrett, B.C.; Viswanathan, R.

    1982-02-01

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

  10. Fatigue life prediction of gas tungsten arc welded AISI 304L cruciform joints with different LOP sizes

    Microsoft Academic Search

    P. Johan Singh; D. R. G Achar; B Guha; Hans Nordberg

    2003-01-01

    Fatigue life evaluations have been carried out on gas tungsten arc welded (GTAW) load-carrying cruciform joints of AISI 304L stainless steel with lack of penetration (LOP) using conventional S-N and crack initiation-propagation (I-P) methods. The crack process normally comprises two major phases: (1) the crack initiation life (Ni): and (2) the crack propagation life (Np). The local stress-life approach is

  11. 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.

  12. Fatigue Crack Initiation Life Prediction of Rails Using Theory of Critical Distance and Critical Plane Approach

    NASA Astrophysics Data System (ADS)

    Akama, Makoto; Matsuda, Hiroyuki; Doi, Hisayo; Tsujie, Masahiro

    The procedure for the head check initiation life prediction of railway rails has been developed. It is mainly performed by three-dimensional finite element (FE) analyses that account for the local material response generated by the contact load between wheel and rail. Both wheel and rail are modeled by FE mesh, and the wheels are loaded then rotated to the rolling direction on the rails repeatedly. The Chaboche and Lemaitre model is used to simulate the material response that is important in rolling contact situations. The results obtained from FE analyses are combined with the theory of critical distance and the critical plane approach to predict fatigue crack initiation life in the railhead. Parametric studies are performed to investigate the influence of several factors on the crack initiation life. Finally, the predictions are compared with the data obtained from the investigation in the field.

  13. Reliability analysis for low cycle fatigue life of the aeronautical engine turbine disc structure under random environment

    Microsoft Academic Search

    C. L. Liu; Z. Z. Lu; Y. L. Xu; Z. F. Yue

    2005-01-01

    The low cycle fatigue life (LCFL) of the aeronautical engine turbine disc structure is related to the stress–strain level of the disc applied by cyclic load and the life characteristic of the material. The randomness of the basic variables, such as applied load, working temperature, geometrical dimensions and material properties, has significant effect on the statistical properties of the stress

  14. The Effect of War Stressors and Life Events on Gulf War Veterans With Chronic Fatigue Syndrome Symptoms

    Microsoft Academic Search

    Kieran Dhillon; Kendal C. Boyd

    2010-01-01

    This study examines the association of life stressors and the period when they occur, with the development of chronic fatigue syndrome (CFS) symptoms in Gulf War veterans. Of data collected from Gulf War Health Registry veterans, 113 met CFS criteria and 441were controls. After hierarchical multiple regression, several negative life stressors were associated with CFS group membership: being wounded, experiencing

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

    SciTech Connect

    Okafor, A. C.; Natarajan, S. [Nondestructive Evaluation and Structural Health Monitoring Laboratory, Department of Mechanical and Aerospace Engineering, University of Missouri - Rolla, 1870 Miner Circle, Rolla, MO 65409-0050 (United States)

    2007-03-21

    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.

  16. Influence of flux cored arc welded cruciform joint dimensions on fatigue life of ASTM 517 `F' grade steels

    Microsoft Academic Search

    V Balasubramanian; B Guha

    1998-01-01

    A mathematical model has been developed to predict the fatigue life of flux-cored arc-welded (FCAW) cruciform joints containing lack of penetration (LOP) defects. High strength, quenched and tempered steel (ASTM 517 `F' grade) has been used as the base material throughout the investigation. The design of experiments (DoE) concept has been used to optimize the required number of experiments. Fatigue

  17. The effects of ultrasonic peening treatment on the ultra-long life fatigue behavior of welded joints

    Microsoft Academic Search

    Danqing Yin; Dongpo Wang; Hongyang Jing; Lixing Huo

    2010-01-01

    The conventional fatigue design codes was formulated based on the data from test stress cycles less than 1×107. Most of them could not be applied for welded structures serviced in the ultra-long life region so the new recommendations were discussed. The method of ultrasonic peening treatment (UPT) was introduced in this thesis as a post-weld treatment to improve the fatigue

  18. Effect of stress ratio on long life fatigue behavior of Ti-Al alloy under flexural loading

    Microsoft Academic Search

    Hong-qian XUE; Hua TAO; Ren-ping SHAO; B. CLAUDE

    2008-01-01

    A new ultrasonic three-point bending fatigue test device was introduced to investigate fatigue life ranging up to 1010 cycles and associated fracture behavior of Ti-Al alloy. Tests were performed at a frequency of 20 kHz with stress ratio R=0.5 and R=0.7 at ambient temperature in air. Three groups of specimens with different surface roughness were applied to investigate the effect

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

    Microsoft Academic Search

    Nicole M Stroud; Clare L Minahan

    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 25–65 yr) living in Queensland, Australia was conducted. Physical activity level, depression, fatigue and quality of

  20. 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.

  1. An investigation of the reduction in tensile strength and fatigue life of pre-corroded 7075-T6 aluminum alloy

    NASA Astrophysics Data System (ADS)

    Obert, B.; Ngo, K.; Hashemi, J.; Ekwaro-Osire, S.; Sivam, T. P.

    2000-08-01

    In aging aircraft, the synergetic interaction between corrosion and fatigue has been shown to reduce the life expectancy of aluminum alloys. The objective of this study was to quantify the effects of corrosion, in terms of mass loss per unit area, on the static strength and fatigue life of 7075-T6 aluminum alloy. This was an experimental study in which test specimens were corroded in a laboratory environment. The corrosion process was accelerated by use of a corrosion cell. Test specimens were cut from flat sheets of aluminum and covered with masking material to restrict corrosion to a confined area. After testing, the fatigue life, ultimate tensile strength (UTS), and hardness of the specimens were observed to drop significantly with small amounts of corrosion. After the initial decrease, the UTS was observed to decrease linearly with increasing corrosion levels. The fatigue life of the specimens decreased in an inverse exponential fashion as mass loss per unit area increased. The hardness values of the corroded surfaces were also observed to drop. The topology of the pits and the related subsurface damage produced areas of high stress concentration resulting in the immediate reduction of UTS and fatigue life of the specimens. Subsurface corrosion damage was responsible for the reduction in hardness.

  2. 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.

  3. Interference fits and stress-corrosion failure. [aircraft parts fatigue life analysis

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Carter, A. E.

    1976-01-01

    It is pointed out that any proper design of interference fit fastener, interference fit bushings, or stress coining processes should consider both the stress-corrosion susceptibility and fatigue-life improvement together. Investigations leading to such a methodology are discussed. A service failure analysis of actual aircraft parts is considered along with the stress-corrosion susceptibility of cold-working interference fit bushings. The optimum design of the amount of interference is considered, giving attention to stress formulas and aspects of design methodology.

  4. 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.

  5. A review of the Workshop on Fatigue Life Methodologies for Wind Turbines

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.; Butterfield, C. P.

    From March 31 - April 1, 1993, Sandia National Laboratories (SNL) and the National Renewable Energy Laboratory (NREL) hosted a workshop entitled 'Fatigue Life Methodologies.' The purpose of this workshop was to bring together a representative panel of experts to discuss the prediction and measurement of infrequent events that contribute significantly to the damage of wind turbine components. The diverse backgrounds of the participants yielded discussions that covered a wide range of research and design activities from many varying viewpoints. Consensus was not reached on most of the questions raised at the workshop; however, the workshop laid the foundation for a program that now knows what questions must be answered.

  6. 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.

  7. Fatigue life estimation of a 1D aluminum beam under mode-I loading using the electromechanical impedance technique

    NASA Astrophysics Data System (ADS)

    Lim, Yee Yan; Kiong Soh, Chee

    2011-12-01

    Structures in service are often subjected to fatigue loads. Cracks would develop and lead to failure if left unnoticed after a large number of cyclic loadings. Monitoring the process of fatigue crack propagation as well as estimating the remaining useful life of a structure is thus essential to prevent catastrophe while minimizing earlier-than-required replacement. The advent of smart materials such as piezo-impedance transducers (lead zirconate titanate, PZT) has ushered in a new era of structural health monitoring (SHM) based on non-destructive evaluation (NDE). This paper presents a series of investigative studies to evaluate the feasibility of fatigue crack monitoring and estimation of remaining useful life using the electromechanical impedance (EMI) technique employing a PZT transducer. Experimental tests were conducted to study the ability of the EMI technique in monitoring fatigue crack in 1D lab-sized aluminum beams. The experimental results prove that the EMI technique is very sensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model for fatigue life estimation has been developed by incorporating the linear elastic fracture mechanics (LEFM) theory into the finite element (FE) model. The prediction of the model matches closely with the experiment, suggesting the possibility of replacing costly experiments in future.

  8. Effect of casting imperfections on the fatigue life of 319-F and A356-T6 Al–Si casting alloys

    Microsoft Academic Search

    H. R. Ammar; A. M. Samuel; F. H. Samuel

    2008-01-01

    Casting imperfections, such as porosity, in cast aluminum components greatly influence their fatigue properties. The effect of porosity on the fatigue life of 319-F and A356-T6 aluminum alloys was studied, where the porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The results show that porosity has the greatest detrimental effect on fatigue

  9. 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

  10. Dynamic stall on wind turbine blades

    SciTech Connect

    Butterfield, C.P.; Simms, D.; Scott, G. (National Renewable Energy Lab., Golden, CO (United States)); Hansen, A.C. (Utah Univ., Salt Lake City, UT (United States))

    1991-12-01

    Dynamic loads must be predicted accurately in order to estimate the fatigue life of wind turbines operating in turbulent environments. Dynamic stall contributes to increased dynamic loads during normal operation of all types of horizontal-axis wind turbine (HAWTs). This report illustrates how dynamic stall varies throughout the blade span of a 10 m HAWT during yawed and unyawed operating conditions. Lift, drag, and pitching moment coefficients during dynamics stall are discussed. Resulting dynamic loads are presented, and the effects of dynamic stall on yaw loads are demonstrated using a yaw loads dynamic analysis (YAWDYN). 12 refs., 22 figs., 1 tab.

  11. 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.

  12. 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.

  13. Fatigue life prediction of GTA welded AISI 304L cruciform joints with lack of penetration using local-stress approach

    Microsoft Academic Search

    P Johan Singh; B Guha; D. R. G Achar

    2003-01-01

    The influence of welding procedure on fatigue properties of gas tungsten arc welded (GTAW) AISI 304L load carrying cruciform joints, containing lack of penetration (LOP) has been studied using a crack initiation–propagation (I-P) method. The crack process normally comprises two major phases: (1) the crack initiation life (NI): and (2) the crack propagation life (Np). The local stress-life approach is

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

    Microsoft Academic Search

    Gary R. Halford

    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

  15. Effects of weld metal profile on the fatigue life of integrally reinforced weld-on fittings

    SciTech Connect

    Woods, G.E. (M.W. Kellogg Co., Houston, TX (United States)); Rodabaugh, E.C. (Rodabaugh (E.C.), Dublin, OH (United States))

    1994-06-01

    The cyclic fatigue life of fabricated tee intersections, including integrally reinforced weld-on fittings, has been a topic of discussion in the recent past. The discussion has centered around questions concerning the accuracy of the ASME B31.3 Code equations in calculating the stress intensification factors, (SIFs), for these types of intersection geometries. The SIF of an intersection is an indicator of the fatigue life of the intersection when it is subjected to bending moments caused by thermal, flow, or mechanically induced cyclical displacements. Schneider, Rodabaugh, and Woods concur that inaccuracies in the Code SIF equations do exist and that these equations should be revised. This report presents new Markl type SIF data on the B.W.Pipet (BWP), an integrally reinforced weld-on branch fitting, manufactured by WFI International, Inc., in Houston, Texas. The scope of this research project was to determine the influence of the installation weld metal profile of the Pipet to the run pipe on the SIF. The SIF data were then compared to calculated SIF values using equations from the American Society of Mechanical engineers (ASME) B31.1, ASME B31.3, and ASME Section 3, Subsection NC, for the purpose of determining which Code equation may be the most appropriate for calculating the SIF for these particular fittings.

  16. Thermal Fatigue Life of Glidcop Al-15 High-Heat-Load Components

    SciTech Connect

    Jin, J. F.; Xiao, W. L.; Chen, H. B. [CAS Key Laboratory Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2010-05-21

    Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation of synchrotron radiation light source and is presently under construction as a large scale national scientific project in China. Depending on the outstanding thermal and mechanical performance, Glidcop Al-15, a dispersion strengthened copper alloy, is chosen to serve for the high-heat-load components at beam line front end in SSRF. Present study is to investigate the thermal fatigue lives of critical SSRF components. A nonlinear finite element method (FEM) is used to simulate the nonlinear three dimensional stress-strain fields of the critical component-Mask2 at SSRF beam line. The method consists of transient temperature analyses followed by elastic-plastic stress analyses. Then, a critical plane approach is used to predict the thermal fatigue life of mask2. The critical plane approach is appropriate for estimating service life of critical SSRF components since the results are in good consistent with the experimental ones taken at the Advanced Photon Source (APS).

  17. 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.

  18. Investigation of the fatigue behaviour of butt-welded joints treated by ultrasonic peening process and compared with fatigue life assessment standards

    Microsoft Academic Search

    G. R. Jinu; P. Sathiya; G. Ravichandran; A. Rathinam

    2009-01-01

    Ultrasonic peening is a technique to be used for improving the fatigue life of welded structures. The technique makes use\\u000a of an ultrasonically vibrated pin which is pressed against the toe regions of the weld. The beneficial effect is mainly due\\u000a to the introduction of favourable compressive stresses on weld toe regions, causing local plastic deformation and reducing\\u000a stress concentration

  19. Fatigue as a Driver of Overall Quality of Life in Cancer Patients

    PubMed Central

    McCabe, Ryan M.; Grutsch, James F.; Braun, Donald P.; Nutakki, Swetha B.

    2015-01-01

    Background This manuscript describes an approach for analyzing large amounts of disparate clinical data to elucidate the most impactful factor(s) that relate to a meaningful clinical outcome, in this case, the quality of life of cancer patients. The relationships between clinical and quality of life variables were evaluated using the EORTC QLQ-C30 global health domain—a validated surrogate variable for overall cancer patient well-being. Methods A cross-sectional study design was used to evaluate the determinants of global health in cancer patients who initiated treatment at two regional medical centers between January 2001 and December 2009. Variables analyzed included 15 EORTC QLQ-C30 scales, age at diagnosis, gender, newly diagnosed/ recurrent disease status, and stage. The decision tree algorithm, perhaps unfamiliar to practicing clinicians, evaluates the relative contribution of individual parameters in classifying a clinically meaningful functional endpoint, such as the global health of a patient. Findings Multiple patient characteristics were identified as important contributors. Fatigue, in particular, emerged as the most prevalent indicator of cancer patients’ quality of life in 16/23 clinically relevant subsets. This analysis allowed results to be stated in a clinically-intuitive, rule set format using the language and quantities of the Quality of Life (QoL) tool itself. Interpretation By applying the classification algorithms to a large data set, identification of fatigue as a root factor in driving global health and overall QoL was revealed. The ability to practice mining of clinical data sets to uncover critical clinical insights that are immediately applicable to patient care practices is illustrated. PMID:26070133

  20. 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.

  1. 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.

  2. The mediating effect of coping on the association between fatigue and quality of life in patients with multiple sclerosis.

    PubMed

    Mikula, Pavol; Nagyova, Iveta; Krokavcova, Martina; Vitkova, Marianna; Rosenberger, Jaroslav; Szilasiova, Jarmila; Gdovinova, Zuzana; Groothoff, Johan W; van Dijk, Jitse P

    2015-09-01

    Fatigue, as one of the most frequent symptoms in patients with multiple sclerosis (MS), has various adverse effects on the physical and mental health-related quality of life (PCS, MCS) of patients. The aim of this study was to explore whether coping mediates the relationship between fatigue and PCS and MCS. We collected data from 154 consecutive MS patients (76.0% women; mean age 40.0 ± 9.9). Patients completed the Short-Form Health Survey (SF-36), the multidimensional fatigue inventory (MFI-20) and the coping self-efficacy scale. The mediating effect of coping was analysed using linear regressions and the Sobel z-test. In PCS significant mediation was found in some of the fatigue dimensions (general, physical and reduced Motivation), while in MCS, it was significant in all dimensions. These results can be implemented into educational programmes for patients, their caregivers or physicians, and can also be helpful in the treatment process. PMID:25879302

  3. 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.

  4. 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.

  5. 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.

  6. 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. [RANN, Inc., Palo Alto, CA (United States)

    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.

  7. 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.

  8. Enhancement of Fatigue Life Performance of Holed Specimen of Aluminum Alloy 2024-T3 by Local Plastic Deformation

    Microsoft Academic Search

    Muhammed Sohel Rana; Taisuke Yamanaka; Chobin Makabe

    2009-01-01

    The effect of local plastic deformation on the fatigue life in a holed specimen was investigated. The local plastic deformation was applied around the hole by inserting a pin into the hole, and the pin was removed before the testing. The material used was aluminum alloy 2024-T3. After removing the pin, there was a circular hole or elliptical hole in

  9. Fatigue life prediction of shielded metal arc welded cruciform joints containing LOP defects by a mathematical model

    Microsoft Academic Search

    V. Balasubramanian; B. Guha

    1999-01-01

    A new mathematical model is developed to predict the fatigue life of Shielded Metal Arc Welded (SMAW) cruciform joints containing Lack of Penetration (LOP) defect. High strength, quenched and tempered steel (ASTM 517 ‘F’ Grade) is used as the base material throughout the investigation. Four factors, five level, central composite, rotatable design matrix is used to optimise the required number

  10. Application of new damage indicator-based sequential law for remaining fatigue life estimation of railway bridges

    Microsoft Academic Search

    Sudath Siriwardane; Mitao Ohga; Ranjith Dissanayake; Kazuhiro Taniwaki

    2008-01-01

    Miner’s rule is generally accepted as the fatigue criteria for life estimation of railway bridges. Similarly, it has always been acknowledged as a simplification that is easy to use in design where detailed loading history is unknown. But in the case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of

  11. The influence of material build up around artificial defects on rolling contact fatigue life and failure mechanism

    Microsoft Academic Search

    R. C. Dommarco; P. C. Bastias; C. A. Rubin; G. T. Hahn

    2006-01-01

    This paper reports the results obtained in tests conducted to evaluate the evolution of wear tracks and artificial defects under rolling contact fatigue (RCF) loading and its effect on RCF life. The experiments were conducted on specimens of different materials commonly used in rolling bearings and gears. The artificial defects were introduced with the rounded tip of a Rockwell-C type

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

    SciTech Connect

    Pleune, T.T. [Argonne National Lab., IL (United States)]|[Massachusetts Institute of Technology, Cambridge, MA (United States). Nuclear Engineering Dept.; Chopra, O.K. [Argonne National Lab., IL (United States)

    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. 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.

  14. Random Vibration Tests for Prediction of Fatigue Life of Diffuser Structure for Gas Dynamic Laser

    NASA Astrophysics Data System (ADS)

    Maurer, O. F.; Banaszak, D. L.

    1980-01-01

    Static and dynamic strain measurements which were taken during test stand operations of the gas dynamic laser (GDL) for the AF Airborne Laser Laboratory indicated that higher than expected vibrational stress levels may possibly limit the fatigue life of the laser structure. Particularly the diffuser sidewall structure exhibited large amplitude random vibrations which were excited by the internal gas flow. The diffuser structure consists of two layers of brazed stainless steel, AISI-347, panels. Cooling ducts were milled into the outer face sheet. These in turn are backed by the inner face sheet. So called T-rail stiffeners silver-brazed to the outer face sheets add the required stiffness and divide the sidewall into smaller rectangular plate sections.

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

    SciTech Connect

    Sutherland, H.J. [Sandia National Labs., Albuquerque, NM (United States); Linker, R.L. [New Mexico Engineering Research Inst., Albuquerque, NM (United States)

    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.

  16. Frequency-domain stress prediction algorithm for the LIFE2 fatigue analysis code

    SciTech Connect

    Sutherland, H.J.

    1992-01-01

    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 mount 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 module has been added to the code. The module transforms the frequency 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 uses experimental data to illustrate their use. 10 refs., 11 figs.

  17. Experimental evaluation of fatigue life and fatigue crack growth in a tension bolt–nut threaded connection

    Microsoft Academic Search

    I. Korin; J. Perez Ipiña

    2011-01-01

    Threaded components are structural elements that play an important role in the integrity of an efficient engineering design. The assessment of their fatigue and fracture behaviors under real load conditions becomes many times extremely complex. This is because of the experimental difficulties involved in the laboratory simulation of the “nut–bolt” interaction. As a consequence, crack initiation and crack growth data

  18. Influence of antibiotic impregnation on the fatigue life of Simplex P and Palacos R acrylic bone cements, with and without centrifugation.

    PubMed

    Davies, J P; O'Connor, D O; Burke, D W; Harris, W H

    1989-04-01

    The fatigue properties of Simplex P and Palacos R bone cements were compared to their antibiotic impregnated counterparts AKZ* and Palacos R with gentamycin. The effect of porosity reduction by centrifugation of all four cement types was also assessed. Fifteen specimens of each cement type were prepared according to manufacturer's instructions and 15 additional specimens of each cement type were prepared by mixing the powder with chilled monomer (0 degrees C) and then centrifuging the cement immediately after mixing. Fifteen fully reversed tension-compression fatigue tests were performed at 15 MPa in stress control for each cement preparation in vitro while simulating the in vivo state (37 degrees C and 100% humidity). The number of cycles to failure were recorded. There was no significant difference in the fatigue life of Palacos R and Simplex P when both cements were prepared in the standard fashion. The addition of 1/2 g of gentamycin to Palacos R did not significantly alter its fatigue properties. The addition of 0.5 g of erythromycin and 0.24 g of colistin did not decrease the fatigue life of Simplex P. Centrifugation significantly improved the fatigue properties of Simplex P and AKZ. The fatigue lives of Palacos R and Palacos R with gentamycin were not improved by centrifugation. The fatigue life of centrifuged Simplex P was significantly greater than the fatigue life of Palacos R and of Palacos R with gentamycin, whether the Palacos R based cements were centrifuged or not. PMID:2708414

  19. Detect, troubleshoot gas-turbine blade failures

    SciTech Connect

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

    1995-12-01

    Approximately 40% of all gas-turbine failures stem from blading problems. This article describes state-of-the-art condition monitoring technologies that can help avoid or minimize the damage, and troubleshoot failures when they occur. In today`s gas-turbine (GT) fleet, predominant blade-failure mechanism and commonly affected components include: low-cycle fatigue--compressor and turbine disks; high-cycle fatigue--compressor and turbine blades and disks, compressor stator vanes; thermal fatigue--nozzles, combustors; environmental attack, such as oxidation, sulfidation, hot corrosion, and standby corrosion--hot-section blades and stators, transition pieces, and combustors; creep damage--hot-section nozzles and blades; erosion and wear; impact overload damage; thermal aging; combined failure mechanisms, such as creep/fatigue corrosion/fatigue, oxidation/erosion, and so on. Avoiding GT blade problems requires that two conditions be met: first, and most important, the basic design has to be sound, with adequate safety factors incorporates. Second, the proper operating regime must be maintained. Properly applied, condition monitoring can help maintain the operating regime and minimize blade distress. Should blade failures occur, data captured in a monitoring program may provide valuable clues to help identify the root causes. Reviewed here are the latest GT condition monitoring techniques, as well as several case histories that illustrate their importance.

  20. Self-regulatory Fatigue in Hematologic Malignancies: Impact on Quality of Life, Coping, and Adherence to Medical Recommendations

    PubMed Central

    Ehlers, Shawna L.; Patten, Christi A.; Gastineau, Dennis A.

    2015-01-01

    Background Hematopoietic stem cell transplantation (HSCT) is an intensive cancer therapy entailing numerous physical, emotional, cognitive, and practical challenges. Patients' ability to adjust and cope with such challenges may depend on their ability to exert control over cognitive, emotional, and behavioral processes, that is, ability to self-regulate. Self-regulatory capacity is a limited resource that can be depleted or fatigued (i.e., “self-regulatory fatigue”), particularly in the context of stressful life events such as cancer diagnosis and treatment. Purpose This is one of the first studies to examine self-regulatory fatigue in a cancer population. The current study aimed to (1) extract items for a specific scale of self-regulatory capacity and (2) examine the impact of such capacity on adaptation in patients with hematologic malignancies preparing for HSCT. Methods Factor analysis of four existing scales gauging psychological adjustment and well-being in 314 patients preparing for HSCT (63% male and 89% Caucasian) identified 23 items (?=0.85) related to self-regulatory control or fatigue. This measure was then examined using existing clinical data obtained from 178 patients (57% male and 91% Caucasian) undergoing treatment for hematologic malignancies in relationship to quality of life, coping, and self-reported adherence to physicians' recommendations. Results Controlling for pain severity, physical fatigue, and depression, self-regulatory fatigue scores were incrementally associated with decreased quality of life, use of avoidance coping strategies, and decreased adherence to physicians' recommendations. Conclusion These results emphasize the potential role of self-regulatory capacity in coping with and adjusting to hematologic cancers and future research is warranted. PMID:21928059

  1. A Study on Fretting Fatigue Life in Elevated Temperature for Incoloy 800

    NASA Astrophysics Data System (ADS)

    Kwon, Jae Do; Woo, Seung Wan; Chung, Il Sup; Yoon, Dong Hwan; Park, Dae Kyu

    Incoloy 800, which is used within steam generator tubes, is a heat resistant material since it is an iron-nickel-chromium alloy. However, construction of a systematic database is needed to receive integrity data defecting insurance of specific data about room and elevated temperature fretting fatigue behavior for Incoloy 800. Accordingly, this study investigates the specific change in fatigue limitations under the condition of the fretting fatigue as compared to that under the condition of the plain fatigue by performing plain and fretting fatigue tests on Incoloy 800 at 320°C, real operating temperature and at room-temperature, respectively. The change in the frictional force is measured during the fretting fatigue testing against the repeated cycle, and the mechanism of fretting fatigue is investigated through the observation of the fatigue-fracture surface.

  2. 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.

  3. A method of fatigue life prediction in notched and un-notched components

    Microsoft Academic Search

    A. Varvani-Farahani; T. Kodric; A. Ghahramani

    2005-01-01

    The present study intends to assess the fatigue damage of un-notched and notched components using a newly developed energy-based critical plane fatigue damage parameter. The parameter integrates the normal and shear energies calculated on the critical plane on which the stress and strain Mohr's circles are the largest during the loading and unloading parts of a cycle. For notched fatigue

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

    Microsoft Academic Search

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

    2006-01-01

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

  5. Multiaxial high-cycle fatigue criterion and life prediction for metals

    Microsoft Academic Search

    Yongming Liu; Sankaran Mahadevan

    2005-01-01

    A new high-cycle fatigue criterion based on the critical plane approach is proposed in this paper. Unlike most of the other multiaxial fatigue criteria based on the critical plane approach, the critical plane is directly correlated with the fatigue fracture plane. The proposed criterion has a wide range of applicability from very ductile metals to extremely brittle metals. Mean stress

  6. 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.

  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. 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

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

    SciTech Connect

    Hoffman, E.L. [Sandia National Labs., Albuquerque, NM (United States). Engineering and Structural Mechanics Div.

    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.

  10. Application of bi-linear loglog SN model to strain-controlled fatigue data of aluminum alloys and its effect on life predictions

    E-print Network

    Fatemi, Ali

    is mainly elastic. Endo and Morrow [3] observed that for 2024-T4 and 7075-T6 aluminum alloysApplication of bi-linear log­log S­N model to strain-controlled fatigue data of aluminum alloys­log model is applied to stress amplitude versus fatigue life data of 14 aluminum alloys. It is shown

  11. Prediction of high-cycle fatigue life reliability of aluminum cast alloy from statistical characteristics of defects at meso-scale

    Microsoft Academic Search

    Tatsujiro Miyazaki; Hyogyoung Kang; Hiroshi Noguchi; Keisaku Ogi

    2008-01-01

    In this paper, a growth rate law of a small fatigue crack of an arbitrary metal and a method for predicting a size distribution of spheroidal defects cut by a specimen are proposed. And then, by combining the crack growth rate law and the prediction method for the surface defect size distribution, a method for predicting a high-cycle fatigue life

  12. 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.

  13. Thermomechanical fatigue behavior of coated and bare nickel-based superalloy single crystals

    SciTech Connect

    Chataigner, E.; Remy, L.

    1996-12-31

    The thermal-mechanical fatigue behavior of chromium-aluminum coated [001] single crystals of AM1, a nickel-base superalloy for turbine blades, is studied using a diamond shape cycle from 600 to 1,100 C. Comparison with bare specimens does not show any significant difference in thermal-mechanical fatigue nor in isothermal low cycle fatigue at high temperature. Metallographic observations on fracture surfaces and longitudinal sections of specimens tested to fatigue life or to a definite fraction of expected life have shown that the major crack tends to initiate from casting micropores in the sub-surface area very early in bare and coated specimens, under low cycle fatigue or thermal-mechanical fatigue. But the interaction between oxidation and fatigue cracking seems to play a major role. A simple model proposed by Reuchet and Remy has been identified for this single crystal superalloy. Its application to the life prediction under low cycle fatigue and thermal-mechanical fatigue for bare and coated single crystals with different orientations is shown.

  14. 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.

  15. Effect of UIT on Fatigue Life in Web-Gusset Welded Joints

    Microsoft Academic Search

    Yu Togasaki; Hirokazu Tsuji; Takashi Honda; Tetsuya Sasaki; Atsushi Yamaguchi

    2010-01-01

    Ultrasonic impact treatment (UIT), which is a peening method, is usually used as a post-weld treatment in order to improve the fatigue strength of welded joints. In this study, fatigue tests were carried out on web-gusset welded joints treated by UIT and the results were compared with the fatigue lives of as-welded joints in order to examine the effects of

  16. Comparison of crack initiation life estimation procedures under creep-fatigue conditions

    Microsoft Academic Search

    M. P. O’Donnell

    2005-01-01

    This paper describes the application of “high temperature structural integrity assessment procedures” developed in the UK and Japan to creep-fatigue crack initiation in welded Type 316 features tests. The components were subjected to both fatigue and creep-fatigue loading at 630°C. The loadings are representative of those on the upper seal gimbal joint in an advanced gas cooled reactor (AGR), except

  17. Improvement of the fatigue life of titanium alloys for biomedical devices through microstructural control.

    PubMed

    Niinomi, Mitsuo; Akahori, Toshikazu

    2010-07-01

    A limited number of reports exist regarding the systematic investigation or comparison of the fatigue strength of titanium alloys for medical devices, including plain, fretting and notch fatigue, for improvement through various treatments and processes, with respect to related microstructures. This article focuses on the changes and improvements in fatigue strength of newly developed beta-type and practically used alpha + beta-titanium alloys for medical devices through heat treatments, thermomechanical treatments and surface modifications. PMID:20583885

  18. High-temperature corrosion-fatigue (circumferential) cracking life evaluation procedure for low alloy (Cr-Mo) boiler tube steels

    SciTech Connect

    Smith, B.J.; Erskine, C.P.; Hartranft, R.J.; Marder, A.R. [Lehigh Univ., Bethlehem, PA (United States)] [Lehigh Univ., Bethlehem, PA (United States)

    1995-03-01

    A laboratory simulation procedure for reproducing high-temperature cracks found in coal-fired boiler tubes was developed. The procedure design was based on an intergranular corrosion/thermal stress interactive initiation mechanism and an environmentally assisted fatigue crack propagation mechanism. Simulation results show the potential of this procedure as both an evaluation tool for material solutions to the problem and a life estimation procedure for new boiler tube surface modifications.

  19. A new model to predict the fatigue life of flux cored arc welded cruciform joints containing LOP defects

    Microsoft Academic Search

    V. Balasubramanian; B. Guha

    1998-01-01

    A mathematical model has been developed to predict the fatigue life of Flux Cored Arc Welded (FCAW) cruciform joints containing\\u000a Lack of Penetration (LOP) defect. High strength, Quenched and Tempered steel ASTM 517 ‘F’ Grade has been used as the base\\u000a material throughout the investigation. Two level, full factorial technique has been applied to design the experiments. The\\u000a model has

  20. Method for the evaluation of the service life under random loading based on the energy criterion of fatigue fracture

    Microsoft Academic Search

    P. A. Fomichev

    2008-01-01

    We propose a method aimed at the assessment of the service life of structural elements under random loads based on the energy\\u000a criterion of fatigue fracture and the model of cyclic deformation of materials after overloading. The possibility of determination\\u000a of the maximum amplitude of stresses according to the number of loading cycles prior to fracture is substantiated. The results

  1. Metastable effects on martensitic transformation in SMA part V. fatigue-life and detailed hysteresis behavior in NiTi and Cu-based alloys

    Microsoft Academic Search

    G. Carreras; A. Isalgue; V. Torra; F. C. Lovey; H. Soul

    2008-01-01

    The fatigue-life (traction-traction only) is experimentally studied mainly for pseudoelastic NiTi wire of 2.46 mm of diameter\\u000a for eventual application in damping of structures under wind or rain. Thermal effects are highly relevant in determining the\\u000a fatigue-life. The results shows that the fracture level overcomes 130000 cycles when the moving air is used for cooling. When\\u000a the number of working

  2. Fatigue life estimation of a bed-of-nails ultra-fine-pitch wafer level package using the macro-micro modelling approach

    Microsoft Academic Search

    A. C. Cling; A. A. Tay; K. M. Lim

    2003-01-01

    This paper presents package warpage and interconnect fatigue life estimates of bed-of-nails (BON) interconnect in a 20 mm by 20 mm package with 100 ?m pitch. The modelling was carried out in two stages using the macro-micro modelling approach. The effect of BON orientation, as well as chip thickness and substrate CTE (coefficient of thermal expansion) on fatigue life is

  3. 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.

  4. 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.

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

    SciTech Connect

    McNiff, B.P. (Second Wind, Inc., Somerville, MA (USA)); Musial, W.D. (Solar Energy Research Inst., Golden, CO (USA)); Errichello, R. (GEARTECH, Albany, CA (USA))

    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.

  6. 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.

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

    Microsoft Academic Search

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

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

  8. 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.

  9. Fatigue Life Prediction Criterion for Micro–Nanoscale Single-Crystal Silicon Structures

    Microsoft Academic Search

    Takahiro Namazu; Yoshitada Isono

    2009-01-01

    This paper describes fatigue damage evaluation for micro-nanoscale single-crystal silicon (SCS) structures toward the reliable design of microelectromechanical systems subjected to fluctuating stresses. The fatigue tests, by using atomic force microscope (AFM), nanoindentation tester, and specially developed uniaxial tensile tester, have been conducted under tensile and bending deformation modes for investigating the effects of specimen size, frequency, temperature, and deformation

  10. Probabilistic fatigue life prediction using an equivalent initial flaw size distribution

    Microsoft Academic Search

    Yongming Liu; Sankaran Mahadevan

    2009-01-01

    A new methodology is proposed in this paper to calculate the equivalent initial flaw size (EIFS) distribution. The proposed methodology is based on the Kitagawa–Takahashi diagram. Unlike the commonly used back-extrapolation method for EIFS calculation, the proposed methodology is independent of applied load level and only uses fatigue limit and fatigue crack threshold stress intensity factor. The advantage of the

  11. Fatigue Life Prediction of a Railway Bogie under Dynamic Loads through Simulation

    Microsoft Academic Search

    STEFAN DIETZ; HELMUTH NETTER; DELF SACHAU

    1998-01-01

    For dynamically loaded lightweight structures fatigue strength is an important design criteria. In this paper a new method to predict fatigue lifetime is shown. This is based on the combination of frequency domain and time domain calculations, which allows lifetime prediction with reduced computational effort. The method is implemented to work in a concurrent engineering software environment together with a

  12. Investigating the Effects of Corrosion on the Fatigue Life of Welded Steel Attachments 

    E-print Network

    Soape, Jack

    2012-07-16

    Diagram of Crack Growth and Corrosion Rate vs. Time .............. 20? Figure 8. Typical Weld Toe ............................................................................................. 23? Figure 9. Fatigue Specimen Geometry... for All Corrosion-Fatigue Specimens ........................................... 41? Figure 24. Thru Crack in Specimen 2.5-1 ?3.5 Day? (front) ............................................ 42? Figure 25. Thru Crack in Specimen 2.5-1 ?3.5 Day? (back...

  13. Fatigue life improvement of AISI 304L cruciform welded joints by cryogenic treatment

    Microsoft Academic Search

    P Johan Singh; B Guha; D. R. G Achar

    2003-01-01

    Existing theories and reported practical experience show that cryogenic processing greatly increases abrasion resistance and contact fatigue resistance of some metals and alloys. In the present work, an attempt has been made to investigate the effect of cryogenic treatment on the axial fatigue performance of fillet welded cruciform joints of AISI 304L stainless steel, which failed in the weld metal.

  14. Improving Fatigue Life for Aluminum Cruciform Joints by Weld Toe Grinding

    Microsoft Academic Search

    Naiquan Ye; Torgeir Moan

    Fatigue improvement by weld toe grinding for aluminum welded joints has been investigated in this paper. Fatigue tests were performed for a number of as- welded and toe-ground non-load carrying cruciform joints. Finite element analyses were carried out to further study the influence of the variation of the main weld parameters such as the weld toe angle, weld toe radius

  15. Estimation of the fatigue life according to lap joint weld profiles for ferritic stainless steel

    Microsoft Academic Search

    Jaesong Kim; Kyungmin Lee; Boyoung Lee

    2011-01-01

    Steel structures such as ships, ocean structures, automobile, aircraft and bridges should be designed and manufactured to be able to endure under various environmental conditions such as static load, impact, fatigue and torsion etc. Especially, many researches about improvement of fatigue strength have been performed in relation towelding to be used for connection of steel structures. In case that welded

  16. Fatigue Life Improvement for Cruciform Welded Joint by Mechanical Surface Treatment using Hammer Peening and UNSM

    Microsoft Academic Search

    Seung-Ho Han; Jeong-Woo Han; Yong-Yun Nam; In-Ho Cho

    2009-01-01

    For the improvement of fatigue strength of welded structures, mechanical post treatments have been applied in various industrial fields and have in most cases been founded to give substantial increases in their fatigue lives. These methods, generally, consist of the modification of weld toe geometry and the introduction of compressive residual stresses. In mechanical surface treatments, e.g. PHP (pneumatic hammer

  17. Investigation of the solder joint fatigue life in combined vibration and thermal cycling tests

    Microsoft Academic Search

    Tilman Eckert; Michael Kruger; Wolfgang H. Muller; Nils F. Nissen; Herbert Reichl

    2010-01-01

    In this paper, we discuss lifetime prediction for flip chips under temperature and vibration loading in terms of the failure mechanisms related to solder joint fatigue. Our approach does not need additional data from the experiment but can be used in the design stage. For lifetime prediction solder fatigue coefficients from the literature and results from Finite Element Analysis (FEA)

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

    NASA Astrophysics Data System (ADS)

    Bashir, S.; Thomas, M. C.

    1993-08-01

    Alloy 720 is a high-strength cast and wrought turbine disc alloy currently in use for temperatures up to about 650 °C in Allison’s T800, T406, GMA 2100, and GMA 3007 engines. In the original composition in-tended for use as turbine blades, large carbide and boride stringers formed and acted as preferred crack initiators. Stringering was attributed to relatively higher boron and carbon levels. These interstitials are known to affect creep and ductility of superalloys, but the effects on low-cycle fatigue and fatigue crack propagation have not been studied. Recent emphasis on the total life approach in the design of turbine discs necessitates better understanding of the interactive fatigue crack propagation and low-cycle fatigue behavior at high temperatures. The objective of this study was to improve the damage tolerance of Alloy 720 by systematically modifying boron and carbon levels in the master melt, without altering the low-cy-cle fatigue and strength characteristics of the original composition. Improvement in strain-controlled low-cycle fatigue life was achieved by fragmenting the continuous stringers via composition modifica-tion. The fatigue crack propagation rate was reduced by a concurrent reduction of both carbon and bo-ron levels to optimally low levels at which the frequency of brittle second phases was minimal. The changes in composition have been incorporated for production disc forgings.

  19. Relationship between creep-fatigue interaction and fracture life of Ni[sub 3]Al(B) alloy

    SciTech Connect

    Li, G.; Wang, Z.G.; Guo, J.T. (Academia Sinica, Shenyang (China). State Key Lab. of Fatigue and Fracture for Materials)

    1994-09-01

    The interest in the intermetallic compound Ni[sub 3]Al as a potential candidate for high temperature structural applications has been renewed, since the ductility of this material at room temperature rather than elevated temperature can be dramatically improved by a small boron addition and hypostoichiometric deviation. It is believed that the combination of the damage resulting from both cyclic stress and creep at elevated temperatures could affect the materials life. Therefore, the creep-fatigue interaction at a high temperature is another crucial factor for engineering applications, and may determine whether Ni[sub 3]Al can be put into practical service or not. Recently, the creep-fatigue behavior of directionally solidified and single crystal castings of Ni[sub 3]Al (B,Hf) was studied at 450 C and 760 C under load-control. However, the creep-fatigue behavior of polycrystalline Ni[sub 3]Al+B alloys, which is brittle at a high temperature, has never been reported. Therefore, the Ni[sub 3]Al+B alloy was selected for investigation object in this paper where the interest was focused on the influence of the cyclic stress range and the mean stress on creep-fatigue resistance.

  20. 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.

  1. 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.

  2. 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

    2015-05-01

    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.

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

    SciTech Connect

    Galib Abumeri; Frank Abdi (PhD)

    2012-02-16

    The objective of the program was to demonstrate and verify Certification-by-Analysis (CBA) capability for wind turbine blades made from advanced lightweight composite materials. The approach integrated durability and damage tolerance analysis with robust design and virtual testing capabilities to deliver superior, durable, low weight, low cost, long life, and reliable wind blade design. The GENOA durability and life prediction software suite was be used as the primary simulation tool. First, a micromechanics-based computational approach was used to assess the durability of composite laminates with ply drop features commonly used in wind turbine applications. Ply drops occur in composite joints and closures of wind turbine blades to reduce skin thicknesses along the blade span. They increase localized stress concentration, which may cause premature delamination failure in composite and reduced fatigue service life. Durability and damage tolerance (D&DT) were evaluated utilizing a multi-scale micro-macro progressive failure analysis (PFA) technique. PFA is finite element based and is capable of detecting all stages of material damage including initiation and propagation of delamination. It assesses multiple failure criteria and includes the effects of manufacturing anomalies (i.e., void, fiber waviness). Two different approaches have been used within PFA. The first approach is Virtual Crack Closure Technique (VCCT) PFA while the second one is strength-based. Constituent stiffness and strength properties for glass and carbon based material systems were reverse engineered for use in D&DT evaluation of coupons with ply drops under static loading. Lamina and laminate properties calculated using manufacturing and composite architecture details matched closely published test data. Similarly, resin properties were determined for fatigue life calculation. The simulation not only reproduced static strength and fatigue life as observed in the test, it also showed composite damage and fracture modes that resemble those reported in the tests. The results show that computational simulation can be relied on to enhance the design of tapered composite structures such as the ones used in turbine wind blades. A computational simulation for durability, damage tolerance (D&DT) and reliability of composite wind turbine blade structures in presence of uncertainties in material properties was performed. A composite turbine blade was first assessed with finite element based multi-scale progressive failure analysis to determine failure modes and locations as well as the fracture load. D&DT analyses were then validated with static test performed at Sandia National Laboratories. The work was followed by detailed weight analysis to identify contribution of various materials to the overall weight of the blade. The methodology ensured that certain types of failure modes, such as delamination progression, are contained to reduce risk to the structure. Probabilistic analysis indicated that composite shear strength has a great influence on the blade ultimate load under static loading. Weight was reduced by 12% with robust design without loss in reliability or D&DT. Structural benefits obtained with the use of enhanced matrix properties through nanoparticles infusion were also assessed. Thin unidirectional fiberglass layers enriched with silica nanoparticles were applied to the outer surfaces of a wind blade to improve its overall structural performance and durability. The wind blade was a 9-meter prototype structure manufactured and tested subject to three saddle static loading at Sandia National Laboratory (SNL). The blade manufacturing did not include the use of any nano-material. With silica nanoparticles in glass composite applied to the exterior surfaces of the blade, the durability and damage tolerance (D&DT) results from multi-scale PFA showed an increase in ultimate load of the blade by 9.2% as compared to baseline structural performance (without nano). The use of nanoparticles lead to a delay in the onset of delamination. Load-displacement relati

  4. Fatigue behavior and life prediction of a SiC/Ti-24Al-11Nb composite under isothermal conditions

    SciTech Connect

    Barolotta, P.A.

    1991-01-01

    Metal Matrix Composites (MMC) and Intermetallic Matrix Composites (IMC) are potential material candidates for advanced aerospace application. As part of this study, a series of strain- and load-controlled fatigue tests were conducted on unidirectional SiC/Ti-24Al-11Nb (atomic%) composite at 425 and 815[degree]C. Several damage mechanism regimes were identified by using a strain-based representation of the data. Results from these tests were then used to address issues of test control modes, definition of failure, and testing techniques. Factors such as fiber volume ratio, number of plys, and temperature dependence are implicitly incorporated into a model. The model parameters were determined by using fatigue data at temperatures of 425 and 815[degree]C. Fatigue-life data from two independent sources were used to verify the model at temperatures of 650 and 760[degree]C. Cross-ply life data from specimens with ply lay-ups of [0/90][sub 2s] and [0/[plus minus]45/90][sub 2s] at 760[degree]C were also predicted. Correlation between experimental and predicted livers was found to be vary reasonable.

  5. The Effect of Intravenous Vitamin C on Cancer- and Chemotherapy-Related Fatigue and Quality of Life

    PubMed Central

    Carr, Anitra C.; Vissers, Margreet C. M.; Cook, John S.

    2014-01-01

    Cancer patients commonly experience a number of symptoms of disease progression and the side-effects of radiation therapy and adjuvant chemotherapy, which adversely impact on their quality of life (QOL). Fatigue is one of the most common and debilitating symptom reported by cancer patients and can affect QOL more than pain. Several recent studies have indicated that intravenous (IV) vitamin C alleviates a number of cancer- and chemotherapy-related symptoms, such as fatigue, insomnia, loss of appetite, nausea, and pain. Improvements in physical, role, cognitive, emotional, and social functioning, as well as an improvement in overall health, were also observed. In this mini review, we briefly cover the methods commonly used to assess health-related QOL in cancer patients, and describe the few recent studies examining the effects of IV vitamin C on cancer- and chemotherapy-related QOL. We discuss potential mechanisms that might explain an improvement in QOL and also considerations for future studies. PMID:25360419

  6. Study on the turbine vane and blade for a 1,500 C class industrial gas turbine

    SciTech Connect

    Amagasa, S.; Shimomura, K.; Kadowaki, M. (Tohoku Electric Power Co., Inc., Sendai (Japan)); Takeishi, K.; Kawai, H.; Aoki, S.; Aoyama, K. (Mitsubishi Heavy Industries, Ltd., Takasago (Japan))

    1994-07-01

    This paper describes the summary of a three year development program for the first stage stationary vane and rotating blade for the next generation, 1,500 C class, high efficiency gas turbine. In such a high temperature gas turbine, the first turbine vane and blade are the most important hot parts. Full-coverage film cooling (FCFC) is adopted for the cooling scheme, and directionally solidified (DS) nickel base superalloy and thermal barrier coating (TBC) will be used to prolong the creep and thermal fatigue life. The concept of the cooling configuration, fundamental cascade test results, and material test results will be presented.

  7. 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.

  8. A design-centered approach in developing Al-Si-based light-weight alloys with enhanced fatigue life and strength

    NASA Astrophysics Data System (ADS)

    Fan, Jinghong; Hao, Su

    2004-01-01

    Material heterogeneities and discontinuities such as porosity, second phase particles, and other defects at meso/micro/nano scales, determine fatigue life, strength, and fracture behavior of aluminum castings. In order to achieve better performance of these alloys, a design-centered computer-aided renovative approach is proposed. Here, the term “design-centered” is used to distinguish the new approach from the traditional trial-and-error design approach by formulating a clear objective, offering a scientific foundation, and developing a computer-aided effective tool for the alloy development. A criterion for tailoring “child” microstructure, obtained by “parent” microstructure through statistical correlation, is proposed for the fatigue design at the initial stage. A dislocations pileup model has been developed. This dislocation model, combined with an optimization analysis, provides an analytical-based solution on a small scale for silicon particles and dendrite cells to enhance both fatigue performance and strength for pore-controlled castings. It can also be used to further tailor microstructures. In addition, a conceptual damage sensitivity map for fatigue life design is proposed. In this map there are critical pore sizes, above which fatigue life is controlled by pores; otherwise it is controlled by other mechanisms such as silicon particles and dendrite cells. In the latter case, the proposed criteria and the dislocation model are the foundations of a guideline in the design-centered approach to maximize both the fatigue life and strength of Al-Si-based light-weight alloy.

  9. 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.

  10. Computational Mechanics of Fatigue and Life Predictions for Composite Materials and Structures

    E-print Network

    Fish, Jacob

    Jacob Fish and Qing Yu Department of Civil Engineering, Mechanical and Aerospace Engineering Rensselaer, especially for high-cycle fatigue, is usually as high as tens of mil- lions or more, and therefore

  11. In vitro fatigue behavior of human dentin with implications for life prediction

    E-print Network

    Ritchie, Robert

    of California, Berkeley, California 94720 2 Department of Preventive and Restorative Dental Sciences, University events induced by very high occlusal stresses or, more plausibly, by cy- clic fatigue-induced subcritical

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

    SciTech Connect

    Haagensen, P.J. [Univ. of Trondheim (Norway)

    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.

  13. Fatigue-life prediction by an order statistics treatment of acoustic-emission signals

    Microsoft Academic Search

    Joseph Baram

    1993-01-01

    In fatigue, both the crack-propagation rates and the cumulative acoustic-emission activity are known to be related to the\\u000a applied stress-intensity range. By considering the energy balance during crack propagation and the relation of strain energy\\u000a release to the acoustic-emission characteristics, a formal relation between acoustic emission amplitudes and initial fatigue-crack-propagation\\u000a rates has been derived. Continuous monitoring of acoustic emission during

  14. Effect of hydrogen on low-cycle-fatigue life and subcritical crack growth in pipeline steels

    Microsoft Academic Search

    J. H. Holbrook; H. J. Cialone; M. E. Mayfield; P. M. Scott

    1982-01-01

    The present research, which has included experiments on both fracture-mechanics specimens and actual pipe sections, has shown that hydrogen gas can dramatically increase fatigue-crack-growth rates in steels that are typical of those used in pipelines. The specific materials used in the present work were ASTM A516, ASTM A106B, and API 5L-X42 steels. Battelle's observation of hydrogen-accelerated fatigue-crack growth confirms Sandia's

  15. Continuous electrical resistance monitoring, pull strength, and fatigue life of isotropically conductive adhesive joints

    Microsoft Academic Search

    J. H. Constable; T. Kache; H. Teichmann; S. Muhle; M. A. Gaynes

    1998-01-01

    Four isotropically conducting adhesives were used to form lap joints between copper fingers which had been prepared with four surface metallizations (Cu, Au, Pd, and PdNi). A micromechanical tester was used to perform pull and fatigue tests on the 16 adhesive\\/finish combinations. The micro-ohm resistance change was measured during both the pull and fatigue tests. The similarities and differences between

  16. Continuous electrical resistance monitoring, pull strength, and fatigue life of isotropically conductive adhesive joints

    Microsoft Academic Search

    James H. Constable; Thomas Kache; Heiko Teichmann; S. Muhle; M. A. Gaynes

    1999-01-01

    Four isotropically conducting adhesives were used to form lap joints between copper fingers which had been prepared with four surface metallizations (Cu, Au, Pd, and PdNi). A micromechanical tester was used to perform pull and fatigue tests on the 16 adhesive\\/finish combinations. The micro-ohm resistance change was measured during both the pull and fatigue tests. The similarities and differences between

  17. Thermomechanical fatigue behavior and life prediction of a cast nickel-based superalloy

    Microsoft Academic Search

    Z. W. Huang; Z. G. Wang; S. J. Zhu; F. H. Yuan; F. G. Wang

    2006-01-01

    The cyclic deformation and lifetime behavior of a cast nickel-based superalloy M963 was investigated under both thermomechanical fatigue (TMF) and isothermal fatigue (IF) conditions. Two types of TMF tests, i.e. in-phase (IP) and out-of-phase (OP), were performed in temperature range of 450–900°C, and IF tests were conducted at a temperature of 900°C. All tests were carried out under mechanical strain

  18. Sensitivity analysis of fatigue life prediction for deepwater steel lazy wave catenary risers

    Microsoft Academic Search

    HeZhen Yang; HuaJun Li

    2011-01-01

    Steel lazy wave catenary riser (SLWR) has been an attractive choice for deepwater oil field developments. However, fatigue\\u000a is a critical issue in assessing the feasibility of applying SLWR to large motion vessels such as floating production storage\\u000a and offloading (FPSO) or semi-submersibles. In this work, the time-domain fatigue analysis of SLWR was adopted for better\\u000a representing the structural nonlinearity,

  19. An investigation into the effect of various surface treatments on fatigue life of a tool steel

    Microsoft Academic Search

    G. H. Farrahi; H. Ghadbeigi

    2006-01-01

    The effects of nitriding, nitrocarburizing and shot peening on fatigue behavior of AISI D3 cold work tool steel were investigated. Five batches of fatigue specimens were manufactured according to the ASTM E466-96 standard. All specimens were quenched and tempered to a hardness of 50HRC. One group of specimens was shot peened with an Almen intensity of 16 A, one group

  20. PSN\\/PFL Curve Approach Using Three-Parameter Weibull Distribution for Life and Fatigue Analysis of Structural and Rolling Contact Components

    Microsoft Academic Search

    SHIGEO SHIMIZU

    2005-01-01

    In almost all cases of the estimation of fatigue limit for structural materials and bearing steels, the practice of using S-N curves obtained by plotting the applied stress against the number of stress cycles has been continuing to date. It usually takes into account the probabilistic approach of dealing with the stress or force life for only median life. Therefore,

  1. Structural health monitoring of wind turbine blades : SE 265 Final Project.

    SciTech Connect

    Barkley, W. C. (Walter C.); Jacobs, Laura D.; Rutherford, A. C. (Amanda 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.

  2. On the functional degradation of binary titanium-tantalum high-temperature shape memory alloys — A new concept for fatigue life extension

    NASA Astrophysics Data System (ADS)

    Niendorf, T.; Krooß, P.; Batyrsina, E.; Paulsen, A.; Frenzel, J.; Eggeler, G.; Maier, H. J.

    2014-05-01

    High-temperature shape memory alloys are promising candidates for actuator applications at elevated temperatures. Ternary nickel-titanium-based alloys either contain noble metals which are very expensive, or suffer from poor workability. Titanium-tantalum shape memory alloys represent a promising alternative if one can avoid the cyclic degradation due to the formation of the omega phase. The current study investigates the functional fatigue behavior of Ti-Ta and introduces a new concept providing for pronounced fatigue life extension.

  3. 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.

  4. 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.

  5. 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.

  6. Quality of life, fatigue and local response of patients with unstable spinal bone metastases under radiation therapy - a prospective trial

    PubMed Central

    2014-01-01

    Background To evaluate the local response according to stability after radiotherapy (RT) with a special focus on quality-of-life (QoL), fatigue, pain and emotional distress in patients with unstable spinal bone metastases. Methods In this prospective trial, 30 patients were treated from September 2011 until March 2013. The stability of osteolytic metastases in the thoracic and lumbar spine was evaluated on the basis of the Taneichi-score after three and six months. EORTC QLQ-BM22, EORTC QLQ-FA13, and QSC-R10 were assessed at baseline, and three months after RT. Results After 3 months, 25% (n?=?6) and after 6 months 33.3% (n?=?8) were classified as stable. QoL, fatigue, and emotional distress showed no difference over the course. The pain response 3 months after RT showed a significant difference (p?fatigue, and emotional distress. Trial registration Clinical trial identifier NCT01409720. PMID:24917420

  7. Young survivors of malignant bone tumours in the extremities: a comparative study of quality of life, fatigue and mental distress

    Microsoft Academic Search

    Liv Hege Aksnes; Kirsten Sundby Hall; Nina Jebsen; Sophie D. Fosså; Alv A. Dahl

    2007-01-01

    Purpose  The purpose of the study was to compare the quality of life (QoL), fatigue and mental distress in survivors of malignant extremity\\u000a bone tumours (EBT survivors) with age and gender-matched survivors of Hodgkin’s disease (HD survivors) and testicular cancer\\u000a (TC survivors) as well as normative samples from the general population.\\u000a \\u000a \\u000a \\u000a Patients and methods  Five years or more after end of treatment,

  8. Compassion fatigue in nurses

    Microsoft Academic Search

    Elizabeth A. Yoder

    2010-01-01

    Compassion fatigue, trigger situations, and coping strategies were investigated in hospital and home care nurses. The Professional Quality of Life Scale measured compassion fatigue, compassion satisfaction, and burnout. Narrative questions elicited trigger situations and coping strategies. Compassion fatigue scores were significantly different between nurses who worked 8- or 12-hour shifts. Fifteen percent of the participants had scores indicating risk of

  9. The fatigue life improvement of high strength steel welded joints using hammer peening techniques

    SciTech Connect

    Bell, R.; Militaru, D.V. [Carleton Univ., Ottawa, Ontario (Canada). Dept. of Mechanical and Aerospace Engineering; Braid, J.E.M. [Canada Centre for Materials and Metals Technology, Ottawa, Ontario (Canada). Metals Technology Labs.

    1995-12-31

    The fatigue strength of welded joints can be substantially improved by a number of methods. This paper will investigate the high cycle fatigue strength that is attainable in joints of high strength steels in the as-welded and hammer peened condition. A T-joint with a longitudinal fillet weld representing a stiffener or bracket end structural detail was selected for testing. These details are typical of joints found in ships, bridges and decks of offshore platforms. The specimens were fabricated from 350 MPa and 550 MPa yield strength grade steels and were loaded through the vertical member. During fatigue testing at several load levels the crack growth and crack shape development were monitored using potential drop and benchmarking techniques.

  10. Multiaxial fatigue life prediction for various metallic materials based on the critical plane approach

    Microsoft Academic Search

    Jing Li; Zhong-ping Zhang; Qiang Sun; Chun-wang Li

    2011-01-01

    This paper summarizes an attempt to devise a simple method suitable for assessing fatigue lives of metallic materials subjected to both proportional and non-proportional loading conditions. This proposed approach consists of the maximum shear strain range, the normal strain range and the maximum normal stress on the maximum shear strain range plane. In order to correctly account for the presence

  11. Effect of material, heat treatment, grinding and shot peening on contact fatigue life of carburised steels

    Microsoft Academic Search

    Mattias Widmark; Arne Melander

    1999-01-01

    Contact fatigue resistance has been tested in a roller to roller rig. The test simulates the conditions in a gearbox with finite slip and with impurities in the lubricant. Two case hardened alloys were included in the study, different sequences of carburising and grinding and finally additional shot peening. The tested samples were characterised with respect to residual stress, microstructure,

  12. An Investigation of PWB Layout by Genetic Algorithms to Maximize Fatigue Life

    Microsoft Academic Search

    Andrew J. Scholand; Robert E. Fulton; Bert Bras

    1999-01-01

    Thermal considerations in Printed Wiring Board (PWB) assemblies are becoming increasingly important as packaging constraints shrink and power use escalates. In this paper, we provide a study on the potential for a Genetic Algorithm-driven PWB layout design tool to improve the thermal performance of such assemblies. As a case study, the thermo-mechanical fatigue of surface mounted leadless chip carriers on

  13. FATIGUE LIFE EVALUATION OF WELDED JOINTS BASED ON NOMINAL STRESS AND FINITE ELEMENT ANALYSIS

    Microsoft Academic Search

    B. C. GOO; S. Y. YANG; J. W. SEO

    In the first part, experimental study on the fatigue behavior of a material, SM 490 A was carried out on double V-grooved butt welded plates such as reinforcement removed, as-welded and weld toe ground. In addition, welded plates with transverse fillet welded web, load carrying cruciform fillet welded plates, non- load carrying cruciform fillet welded plate and longitudinal butt welded

  14. Fatigue Life Improvement for Cruciform Welded Joint by Mechanical Surface Treatment using Hammer Peening and UNSM

    NASA Astrophysics Data System (ADS)

    Han, Seung-Ho; Han, Jeong-Woo; Nam, Yong-Yun; Cho, In-Ho

    For the improvement of fatigue strength of welded structures, mechanical post treatments have been applied in various industrial fields and have in most cases been founded to give substantial increases in their fatigue lives. These methods, generally, consist of the modification of weld toe geometry and the introduction of compressive residual stresses. In mechanical surface treatments, e.g. PHP (pneumatic hammer peening) and UNSM (ultrasonic nano-crystal surface modification), the weld profile is modified due to remove or reduce minute crack-like flaws, and compressive residual stresses are also induced. In this study, a pneumatic hammer peening procedure and a UNSM device were introduced, and a quantitative measure of fatigue strength improvement was performed. The fatigue strength at 2 × 106 cycles of hammer-peened and UNSM treated on a non-load carrying cruciform welded joint shows 220 and 260MPa, respectively, which are more than two times higher than that of as-welded specimen. Especially, the surface layer in the vicinity weld toe treated by the UNSM provides nano-crystal structure created by an ultrasonic cold forging and introduces very high welding residual stress in compression.

  15. Fatigue life prediction for the development of ship board exposed equipment

    Microsoft Academic Search

    S. Kery

    2005-01-01

    A mechanically scanned array type radar antenna was developed for several classes of US NAVY vessels. A light weight requirement as well as the RF properties required that substantial parts of the equipment be composed of aluminum alloys. The combined stress corrosion behavior of aluminum alloys exposed to cyclic loading in the ocean environment suggests that fatigue aggravated by corrosion

  16. FATIGUE PERFORMANCE COMPARISON AND LIFE PREDICTION OF FORGED STEEL AND DUCTILE CAST IRON CRANKSHAFTS

    Microsoft Academic Search

    JONATHAN WILLIAMS; FARZIN MONTAZERSADGH; ALI FATEMI

    2007-01-01

    The objective of this study was to compare the durability of crankshafts from two competing manufacturing processes, as well as to perform dynamic load and stress analysis, and optimization. The crankshafts used in the study were forged steel and ductile cast iron from a one-cylinder gasoline engine. Strain-controlled monotonic and fatigue tests as well as impact tests were performed on

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

    Microsoft Academic Search

    Julie Colin

    2010-01-01

    Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless

  18. STRUCTURAL INTEGRITY EVALUATION OF WIND TURBINE BLADES USING PATTERN RECOGNITION ANALYSIS ON ACOUSTIC EMISSION DATA

    Microsoft Academic Search

    A. A. Anastassopoulos; D. A. Kouroussis; V. N. Nikolaidis; A. Proust; A. G. Dutton; M. J. Blanch; L. E. Jones; P. Vionis; D. J. Lekou; D R V van Delft; P. A. Joosse

    2002-01-01

    Current Wind Turbine (W\\/T) Blade certification practices require the conduction of static and fatigue tests on new blades, in order to assess whether the blade can sustain the applied loads. Within the scopes of a current EC-funded research project, Acoustic Emission (AE) monitoring has been extensively applied during testing of various W\\/T Blades of similar design. All blades were loaded

  19. 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.

  20. 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.

  1. Improved Method of Roller Bearing Fatigue Life Prediction under Edge Loading Conditions

    Microsoft Academic Search

    Haruo Nagatani

    2010-01-01

    It has been deemed to be proper to use subsurface stress distributions in life predictions of roller bearings under edge loading conditions. But by using this method the decreased life caused by edge stresses is normalized in the process of relating them to the lives of other parts, and therefore life prediction accuracy is lessened. The life calculation method by

  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.

  3. An experimental study of heat transfer in the rectangular coolant passages of a gas turbine rotor blade 

    E-print Network

    Uddin, Mohammed Jalal

    2000-01-01

    Modern gas turbines have high inlet temperatures to harness maximum power output, which causes different components to experience severe thermal stresses and fatigue. To achieve turbine blade durability goals, the blades are cooled with air...

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

    SciTech Connect

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

    1996-12-31

    Concern about the reliability of the 1,300 mw Cumberland steam turbine units after an unexpected blade tip failure in the fall of 1995 caused TVA to conduct an investigation into the current reliability of the L-O blades. A probabilistic model based on the measured frequencies, damping and material fatigue data was generated. The influence of significant erosion damage on the blade natural frequencies and on the local stresses was estimated. A probabilistic model of the local fatigue limit was generated based on test data. Monte Carlo simulation was employed to estimate the probability of blade failure by comparing the dynamic stress with the fatigue limit. Risk assessment of the blade failure is presented.

  5. Multiaxial fatigue — An overview

    Microsoft Academic Search

    V M Radhakrishnan

    1995-01-01

    Many engineering components are subjected to multiaxial type of fatigue loading and the fatigue life relation based on uniaxial\\u000a testing needs modifications before it could be used for multiaxial condition. In this paper a brief review of the different\\u000a approaches based on stress and strain is presented for the correlation of bulk parameters with the fatigue life and the merits

  6. An energy method for predicting fatigue life, crack orientation, and crack growth under multiaxial loading conditions

    Microsoft Academic Search

    K. C. Liu; J. A. Wang

    2001-01-01

    A method based on a virtual strain-energy (VSE) concept has been shown to be effective for use in predicting multiaxial fatigue lives of two widely-used commercial alloys subjected to in-phase and out-of-phase biaxial loading conditions ASTM STP 1191 (1993) 67; J Eng Mater Tech 117 (1995) 285. This paper is intended to reaffirm the effectiveness of the VSE method for

  7. Method of improving fatigue life of cast nickel based superalloys and composition

    Microsoft Academic Search

    Allen F. Denzine; Thomas A. Kolakowski; John F. Wallace

    1978-01-01

    The invention consists of a method of producing a fine equiaxed grain structure (ASTM 2-4) in cast nickel-base superalloys which increases low cycle fatigue lives without detrimental effects on stress rupture properties to temperatures as high as 1800.degree. F. These superalloys are variations of the basic nickel-chromium matrix, hardened by gamma prime [Ni.sub.3 (Al, Ti)] but with optional additions of

  8. Fatigue crack growth and life prediction of foam core sandwich composites under flexural loading

    Microsoft Academic Search

    Nitin Kulkarni; Hassan Mahfuz; Shaik Jeelani; Leif A. Carlsson

    2003-01-01

    Fatigue crack growth of foam core sandwich beams loaded in flexure has been investigated. Sandwich panels were manufactured using an innovative co-injection resin transfer molding process. S2-glass fiber with epoxy resins was used as face sheets over a PVC foam core. Testing was performed in a three-point flexure mode utilizing a newly designed fixture such that the localized indentation damage

  9. An investigation of cyclic transient behavior and implications on fatigue life estimates

    Microsoft Academic Search

    Yanyao Jiang; Peter Kurath

    1997-01-01

    Current research focuses on proportional cyclic hardening and non-Massing behaviors. The interaction of these two hardenings can result in the traditionally observed overall softening, hardening or mixed behavior exhibited for fully reversed strain controlled fatigue tests. Proportional experiments were conducted with five materials 304 stainless steel, normalized 1070 and 1045 steels, and 7075-T6 and 6061-T6 aluminum alloys. All the materials

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

    Microsoft Academic Search

    Xue Fei; Yu Wei-Wei; Wang Zhao-Xi; Ti Wen-Xin; Lin Lei; Men Xin-Ming

    2010-01-01

    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

  11. 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.

  12. Fatigue life of a Nd:YAG laser-welded metal ceramic alloy.

    PubMed

    Lee, W V; Nicholls, J I; Butson, T J; Daly, C H

    1997-01-01

    Fifteen laser-welded Olympia alloy samples were divided into three groups of five samples each, with different gap distances between the welded halves. The first group was welded with a 0.0-mm gap distance. The second and third groups had Olympia shims placed in 0.3- and 1.0-mm gaps, respectively, prior to laser welding. Each of the samples was tested to failure in load fatigue at 30 Hz in a fatigue testing device using an applied stress of 35,000 psi (241.4 MPa). The means and standard deviations for the number of cycles required to produce fatigue failure for each group was 494,618 +/- 118,311 cycles for the group welded with 0.0-mm gap distance, and 242,741 +/- 44,623 and 232,021 +/- 55,877 cycles for the 0.3- and 1.0-mm specimens, respectively. A one-way analysis of variance showed that the 0.0-mm gap specimens had the greatest number of cycles to failure (P < or = 0.05). There was no significant difference between the other two groups. With the exception of two specimens that failed at the weld center, all failures occurred at the edge of the weld. PMID:9495162

  13. 75 FR 34390 - Airworthiness Directives; McCauley Propeller Systems Five-Blade Propeller Assemblies

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-17

    ...reduced life limits and eddy current inspections (ECIs) of...blade separation, and loss of control of the airplane...blade separation, and loss of control of the airplane...blade separation, and loss of control of the...

  14. Drill pipe fracture. Part 2. Fracture-mechanics concept offers models to help calculate fatigue life in drill pipe

    SciTech Connect

    Kral, E.; Sengupta, P.K.; Newlin, L.; Quan, S.S.

    1984-08-13

    This second of 2 articles on drill pipe fatigue analysis discusses the problem of calculating fatigue life of drill pipe under known operating conditions. Focusing attention on surface cracks, an attempt is made to characterize the most severe of these in terms of their dimensions and location by non-destructive examination. Keeping in mind the current threshold levels for crack detectability in routine nondestructive techniques like ultrasonic testing, it is assumed that a surface crack ca 0.03 to 0.04 in. deep may remain undetected in a length of unused pipe that has passed pre-service inspection. The stress intensity factors at the front of a surface crack and the attendant crack propagation rates into the wall of the cylinder are calculated on the basis of the behavior of the crack in the corresponding flat plate under the same uniform tensile stress at that experienced by the cylinder. The tensile stresses acting on the plate are calculated from the combined action of the axial load and the bending loads imposed on the pipe.

  15. Influence of process parameters on rolling-contact-fatigue life of ion plated nickel-copper-silver lubrication

    SciTech Connect

    Danyluk, Mike; Dhingra, Anoop [Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211-3029 (United States)

    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.

  16. LIM, CHEMIN. Low Cycle Fatigue Life Prediction of Four Bolt Extended Unstiffened End Plate Moment Connections. (Under the direction of Emmett A Sumner.)

    E-print Network

    ABSTRACT LIM, CHEMIN. Low Cycle Fatigue Life Prediction of Four Bolt Extended Unstiffened End Plate of connection. The parametric study identified the end plate thickness, the beam flange thickness, and the bolt Bolt Extended Unstiffened End Plate Moment Connections by Chemin Lim A dissertation submitted

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

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1991-01-01

    The objective is to develop and verify constitutive and life prediction models for materials typically used in hot gas path components of reusable space propulsion systems over the range of relevant operative environments. The efforts were concentrated on the development of crack initiation life prediction methods and on the development of cyclic crack propagation and fracture life prediction methods.

  19. Gas turbine disk-blade attachment crack

    Microsoft Academic Search

    David L. Davidson

    2005-01-01

    Evaluation of a gas turbine disk revealed a crack in the blade attachment area. The subsequent effort to understand the origin\\u000a of this crack led to a series of analyses that included computing the stresses on the attachment, characterization of fatigue\\u000a crack growth, and a model for fretting fatigue crack growth. These elements were brought together to simulate the conditions

  20. An assessment of the role of near-threshold crack growth in high-cycle-fatigue life prediction of aerospace titanium alloys under turbine engine spectra

    Microsoft Academic Search

    J. M. Larsen; B. D. Worth; C. G. Annis; F. K. Haake

    1989-01-01

    Increasingly accurate life prediction models are required to utilize the full capability of current and future advanced materials\\u000a in gas turbine engines. Of particular recent interest are predictions of the lifetimes of engine airfoil materials that experience\\u000a significant intervals of high-frequency, high-cycle fatigue (HCF). Conventional life management practices for HCF in the turbine\\u000a engine industry have been based principally on