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Sample records for cycle fatigue strength

  1. Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

    NASA Technical Reports Server (NTRS)

    Lerch, Brad; Draper, Sue; Pereira, J. Mike

    2002-01-01

    High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

  2. Fatigue of Austempered Ductile Iron with Two Strength Grades in Very High Cycle Regime

    NASA Astrophysics Data System (ADS)

    Zhang, Jiwang; Li, Wei; Song, Qingpeng; Zhang, Ning; Lu, Liantao

    2016-03-01

    In this study, Austempered ductile irons (ADIs) with two different strength grades were produced and the fatigue properties were measured at 109 cycles. The results show that the S-N curves give a typical step-wise shape and there is no fatigue limit in the very high cycle fatigue regime. The two grades ADI have the similar fracture behaviors and fatigue failure can initiate from defects at specimen surface and subsurface zone. On the fracture surfaces of some specimens, the `granular-bright-facet' area with rich carbon distribution is observed in the vicinity of the defect. The microstructure affects the crack behaviors at the early propagation stage. The ADI with upper and lower bainite shows higher fatigue strength compared with the ADI with coarse upper bainite.

  3. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, High-Cycle and Low-Cycle Mechanical Fatigue, Creep and Thermal Fatigue Effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    The development of methodology for a probabilistic material strength degradation is described. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing predictions of high-cycle mechanical fatigue and high temperature effects with experiments are presented. Results from this limited verification study strongly supported that material degradation can be represented by randomized multifactor interaction models.

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

    SciTech Connect

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

    1983-06-01

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

  5. Probabilistic material strength degradation model for Inconel 718 components subjected to high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    This report presents the results of both the fifth and sixth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA). The research included on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for five variables, namely, high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using an updated version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of high-cycle mechanical fatigue, creep and thermal fatigue was performed. Then using the current version of PROMISS, entitled PROMISS94, a second sensitivity study including the effect of low-cycle mechanical fatigue, as well as, the three previous effects was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of high-cycle mechanical

  6. Effects of Hydrogen Gas Environment on Fatigue Strength at 107 cycles in Plain Specimen of Type 316L Stainless Steel

    NASA Astrophysics Data System (ADS)

    Kawamoto, Kyohei; Ochi, Kazuhiko; Oda, Yasuji; Noguchi, Hiroshi

    In order to clarify the hydrogen effect on the fatigue strength at 107 cycles in a plain specimen of type 316L austenitic stainless steel, rotating bending fatigue tests in laboratory air and plane bending fatigue tests in 1.0 MPa dry hydrogen gas and in air at 313 K were carried out. The main results obtained are as follows. The observed fatigue behavior showed that the fatigue strength at 107 cycles in both environments is determined by the non-propagation of a fatigue crack of the order of the grain size. Also, the strength at 107 cycles in hydrogen gas is slightly higher than that in air. In the region of high-cycle fatigue, the fatigue life in hydrogen gas is longer than that in air, which is mainly caused by the longer crack initiation life in hydrogen gas. The crack propagation life in hydrogen gas is shorter than that in air but has only a small ratio to the fatigue life in this region.

  7. Analysis of methods for determining high cycle fatigue strength of a material with investigation of titanium-aluminum-vanadium gigacycle fatigue behavior

    NASA Astrophysics Data System (ADS)

    Pollak, Randall D.

    Today, aerospace engineers still grapple with the qualitative and quantitative understanding of fatigue behavior in the design and testing of turbine-driven jet engines. The Department of Defense has taken a very active role in addressing this problem with the formation of the National High Cycle Fatigue Science & Technology Program in 1994. The primary goal of this program is to further the understanding of high cycle fatigue (HCF) behavior and develop methods in order to mitigate the negative impact of HCF on aerospace operations. This research supports this program by addressing the fatigue strength testing guidance currently provided by the DoD to engine manufacturers, with the primary goal to investigate current methods and recommend a test strategy to characterize the fatigue strength of a material at a specified number of cycles, such as the 109 design goal specified by MIL-HDBK-1783B, or range of cycles. The research utilized the benefits of numerical simulation to initially investigate the staircase method for use in fatigue strength testing. The staircase method is a commonly used fatigue strength test, but its ability to characterize fatigue strength variability is extremely suspect. A modified staircase approach was developed and shown to significantly reduce bias and scatter in estimates for fatigue strength variance. Experimental validation of this proposed test strategy was accomplished using a dual-phase Ti-6Al-4V alloy. The HCF behavior of a second material with a very different microstructure (beta annealed Ti-6Al-4V) was also investigated. The random fatigue limit (RFL) model, a recently developed analysis tool, was investigated to characterize stress-life behavior but found to have difficulty representing fatigue life curves with sharp transitions. Two alternative models (bilinear and hyperbolic) were developed based on maximum likelihood methods to better characterize the Ti-6Al-4V fatigue life behavior. These models provided a good fit to the

  8. 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.

  9. 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.

  10. Influence of HVOF sprayed WC/Co coatings on the high-cycle fatigue strength of mild steel

    SciTech Connect

    Steffens, H.D.; Wilden, J.; Nassenstein, K.; Moebus, S.

    1995-12-31

    HVOF thermally sprayed WC/Co coatings are applied onto components which are exposed to wear caused by abrasion, erosion, fretting and sliding. Beside wear attacks and static stresses in lots of cases alternating mechanical stresses caused by dynamic loads occur additionally. Therefore, the fatigue resistance of WC/Co 88/12 and WC/Co 83/17 coated specimens was investigated by high-cycle fatigue tests (HCF). The results of the fatigue tests were documented in statistically ascertained Woehler-diagrams (S-N-curves). Furthermore, the mechanisms of failure are discussed.

  11. Strength gradient enhances fatigue resistance of steels.

    PubMed

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-01-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch's tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility. PMID:26907708

  12. Strength gradient enhances fatigue resistance of steels

    PubMed Central

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-01-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility. PMID:26907708

  13. Strength gradient enhances fatigue resistance of steels

    NASA Astrophysics Data System (ADS)

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-02-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility.

  14. Analytical and experimental investigation of aircraft metal structures reinforced with filamentary composites. Phase 2: Structural fatigue, thermal cycling, creep, and residual strength

    NASA Technical Reports Server (NTRS)

    Blichfeldt, B.; Mccarty, J. E.

    1972-01-01

    Specimens representative of metal aircraft structural components reinforced with boron filamentary composites were manufactured and tested under cyclic loading, cyclic temperature, or continuously applied loading to evaluate some of the factors that affect structural integrity under cyclic conditions. Bonded, stepped joints were used throughout to provide composite-to-metal transition regions at load introduction points. Honeycomb panels with titanium or aluminum faces reinforced with unidirectional boron composite were fatigue tested at constant amplitude under completely reversed loading. Results indicated that the matrix material was the most fatigue-sensitive part of the design, with debonding initiating in the stepped joints. However, comparisons with equal weight all-metal specimens show a 10 to 50 times improved fatigue life. Fatigue crack propagation and residual strength were studied for several different stiffened panel concepts, and were found to vary considerably depending on the configuration. Composite-reinforced metal specimens were also subjected to creep and thermal cycling tests. Thermal cycling of stepped joint tensile specimens resulted in a ten percent decrease in residual strength after 4000 cycles.

  15. Corrosion fatigue of high strength fastener materials in seawater

    NASA Astrophysics Data System (ADS)

    Tipton, D. G.

    1983-12-01

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

  16. Corrosion fatigue of high strength fastener materials in seawater

    NASA Technical Reports Server (NTRS)

    Tipton, D. G.

    1983-01-01

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

  17. Effects of conventional machining on the high cycle fatigue strength and crack initiation sites of the gamma titanium aluminide alloy Ti-47Al-2Nb-2Cr (at%) at 23 and 760 C

    SciTech Connect

    Jones, P.E.; Eylon, D.

    1999-07-01

    Effects of a deformed surface layer, created by conventional machining, on the high cycle fatigue strength (10e6 cycles) and fatigue initiation sites of Ti-48Al-2Nb-2Cr (at%) were examined above and below the ductile-to-brittle transition temperature. All samples were tested to failure under the same step loading profile. Comparisons were made between samples having the same load history. At room temperature, fatigue strength and initiation sites were equivalent for turned and electropolished surface conditions. At the anticipated service temperature, 760 C, the work hardened layer created by turning quickly recrystallized. This fine recrystallized surface enhanced the fatigue crack initiation resistance of turned specimens when compared to coarse grained electropolished samples which did not recrystallize during the test. The severe surface deformation resulting from conventional machining did not impair the high cycle fatigue behavior of this intermetallic alloy under the conditions evaluated.

  18. Low-cycle thermal fatigue

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1986-01-01

    A state-of-the-art review is presented of the field of thermal fatigue. Following a brief historical review, the concept is developed that thermal fatigue can be viewed as processes of unbalanced deformation and cracking. The unbalances refer to dissimilar mechanisms occurring in opposing halves of thermal fatigue loading and unloading cycles. Extensive data summaries are presented and results are interpreted in terms of the unbalanced processes involved. Both crack initiation and crack propagation results are summarized. Testing techniques are reviewed, and considerable discussion is given to a technique for thermal fatigue simulation, known as the bithermal fatigue test. Attention is given to the use of isothermal life prediction methods for the prediction of thermal fatigue lives. Shortcomings of isothermally-based life prediction methods are pointed out. Several examples of analyses and thermal fatigue life predictions of high technology structural components are presented. Finally, numerous dos and don'ts relative to design against thermal fatigue are presented.

  19. Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

    NASA Astrophysics Data System (ADS)

    Yao, Jun; Qu, Xuan-hui; He, Xin-bo; Zhang, Lin

    2012-07-01

    The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30 μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa·m1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

  20. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  1. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  2. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  3. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  4. 14 CFR 23.627 - Fatigue strength.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service....

  5. A description of spinal fatigue strength.

    PubMed

    Huber, Gerd; Nagel, Katrin; Skrzypiec, Daniel M; Klein, Anke; Püschel, Klaus; Morlock, Michael M

    2016-04-11

    Understanding fatigue failure of the spine is important to establish dynamic loading limits for occupational health and safety. In this study experimental data were combined with published data to develop a description of the predictive parameters for spinal fatigue failure. 41 lumbar functional spinal units (FSUs) from cadaveric spines (age 49.0±11.9yr) where cyclically loaded. Three different levels of sinusoidal axial compression (0-3kN, 0-2kN or 1-3kN) were applied for 300,000 cycles. Further, published data consisted of 70 thoracic and lumbar FSUs loaded in axial compression for 5000 cycles. Cyclic forces ranged from lower peaks (Fmin) of 0.7-1kN to upper peaks (Fmax) of 1.2-7.1kN. Based on Wöhler analysis, a fatigue model was developed accounting for three parameters: I) specimen-specific scaling based on the endplate area, II) specimen-specific strength dependency on age or bone mineral density, III) load-specific correction factors based on Fmax and Fmin. The most predictive model was achieved for a combination of Fmax, endplate area and bone mineral density; this model explained 61% of variation (p<0.001). A model including Fmax, endplate area and age explained only 28% of variation (p<0.001). Inclusion of a load-specific correction factor did not significantly improve model prediction of fatigue failure. This analysis presents the basis for the prediction of specimen-specific fatigue failure of the lumbar spine, provided the endplate area and bone mineral density can be derived. PMID:26948575

  6. Fatigue Strength of Airplane and Engine Materials

    NASA Technical Reports Server (NTRS)

    Matthaes, Kurt

    1934-01-01

    This report was undertaken to give a brief summary of the laws governing the fatigue stresses and of the most important strength coefficients necessary for the correct dimensioning of the structural members.

  7. Optical Fiber Strength/Fatigue Experiments

    NASA Astrophysics Data System (ADS)

    Quan, F.; Helfinstine, J. D.

    1982-01-01

    Optical communication via hair-thin silica waveguides has revolutionized the telecommunications industry. Because its uses are spreading beyond telephony, with its relatively benign environments, to more exotic undersea and space applications, a new emphasis is now placed on optical fiber strength and fatigue characteristics. This paper will trace the historical development of optical waveguides strength/fatigue experiments and a recent attempt to determine the material fatigue constant "n" of modern silica waveguides. Stressing practical application, detailed derivations have been purposely left out for the sake of brevity.

  8. Low cycle fatigue in turbines

    NASA Technical Reports Server (NTRS)

    Brun, M.

    1978-01-01

    Behavior of certain components at low-cycle fatigue is a parameter related to the conditions of use of turbines, to the technology of engine production and to the precision of its regulation. The laboratory takes this into account using data from sophisticated tests and rigorous analyses. The production plan includes careful examination of possible causes of premature rupture. This parameter has motivated the metallurgy industry to develop new materials and new technology.

  9. Multiaxial fatigue low cycle fatigue testing

    NASA Technical Reports Server (NTRS)

    Zamrik, S. Y.

    1985-01-01

    Multiaxial testing methods are reviewed. Advantages and disadvantages of each type test is discussed. Significant multiaxial data available in the literature is analyzed. The yield theories are compared for multiaxial fatigue analysis.

  10. Improving fatigue strength of welded joints

    NASA Astrophysics Data System (ADS)

    Takamori, Hiroyuki

    One series of fatigue tests was carried out on coverplated bridge girders with small fatigue cracks that had been treated in 1976. The treatment and preconditions were reported in NCHRP Report 206. The Category E' coverplated. beams that were removed from the Yellow Mill Pond Bridge in 1997 had been retrofitted in 1976 by either air hammer peening or GTA remelting the weld toe. Most of the details had small fatigue cracks at the time the retrofit was carried out. No detectable fatigue cracking was observed at the treated coverplate ends after 20 years of service on I-95 and an estimated 56 million truck passages. All beams were tested at a stress range of 69 MPa (10 ksi). Cracks eventually developed from the root of the transverse end welds and propagated through the weld throat and from there into the beam flange via the longitudinal welds. The fatigue resistance of the treated weld toe details was improved to Category C. The one GTA remelted detail that recracked at the weld toe exceeded Category D. The second series of tests was carried out on large scale HPS-485W steel plate girders with as-welded and ultrasonic impact treated (UIT) details. The UIT treatment was applied to the weld toe of transverse stiffeners welded to the web and flanges (Category C details) and to coverplated ends (Category E' details). The as-welded details cracked as expected at their corresponding fatigue resistance. All UIT treated details were improved. The treated transverse stiffeners achieved Category B fatigue resistance. The treated coverplated details achieved Category C. The third series of tests was conducted on large scale HPS-485W steel plate girders with undermatched groove welded details at flange transition. The objectives of using undermatched weld materials compared to the base material is to reduce the potentiality of hydrogen cracking at flange groove welds and to improve the fatigue strength of the welded joints. Fatigue strength of undermatched welded joints was

  11. Factors Influencing the Fatigue Strength of Materials

    NASA Technical Reports Server (NTRS)

    Bollenrath, F

    1941-01-01

    A number of factors are considered which influence the static and fatigue strength of materials under practical operating conditions as contrasted with the relations obtaining under conditions of the usual testing procedure. Such factors are interruptions in operation, periodically fluctuating stress limits and mean stresses with periodic succession of several groups and stress states, statistical changes and succession of stress limits and mean stresses, frictional corrosion at junctures, and notch effects.

  12. Probabilistic analysis for fatigue strength degradation of materials

    NASA Technical Reports Server (NTRS)

    Royce, Lola

    1989-01-01

    This report presents the results of the first year of a research program conducted for NASA-LeRC by the University of Texas at San Antonio. The research included development of methodology that provides a probabilistic treatment of lifetime prediction of structural components of aerospace propulsion systems subjected to fatigue. Material strength degradation models, based on primitive variables, include both a fatigue strength reduction model and a fatigue crack growth model. Linear elastic fracture mechanics is utilized in the latter model. Probabilistic analysis is based on simulation, and both maximum entropy and maximum penalized likelihood methods are used for the generation of probability density functions. The resulting constitutive relationships are included in several computer programs, RANDOM2, RANDOM3, and RANDOM4. These programs determine the random lifetime of an engine component, in mechanical load cycles, to reach a critical fatigue strength or crack size. The material considered was a cast nickel base superalloy, one typical of those used in the Space Shuttle Main Engine.

  13. High-cycle Fatigue Properties of Alloy718 Base Metal and Electron Beam Welded Joint

    NASA Astrophysics Data System (ADS)

    Ono, Yoshinori; Yuri, Tetsumi; Nagashima, Nobuo; Sumiyoshi, Hideshi; Ogata, Toshio; Nagao, Naoki

    High-cycle fatigue properties of Alloy 718 plate and its electron beam (EB) welded joint were investigated at 293 K and 77 K under uniaxial loading. At 293 K, the high-cycle fatigue strength of the EB welded joint with the post heat treatment exhibited somewhat lower values than that of the base metal. The fatigue strengths of both samples basically increased at 77 K. However, in longer life region, the EB welded joint fractured from a blow hole formed in the welded zone, resulting in almost the same fatigue strength at 107 cycles as that at 293 K.

  14. Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

    NASA Astrophysics Data System (ADS)

    Takahashi, Kyouhei; Ogawa, Takeshi

    Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

  15. New Powder Metallurgical Approach to Achieve High Fatigue Strength in Ti-6Al-4V Alloy

    NASA Astrophysics Data System (ADS)

    Cao, Fei; Ravi Chandran, K. S.; Kumar, Pankaj; Sun, Pei; Zak Fang, Z.; Koopman, Mark

    2016-05-01

    Recently, manufacturing of titanium by sintering and dehydrogenation of hydride powders has generated a great deal of interest. An overarching concern regarding powder metallurgy (PM) titanium is that critical mechanical properties, especially the high-cycle fatigue strength, are lower than those of wrought titanium alloys. It is demonstrated here that PM Ti-6Al-4V alloy with mechanical properties comparable (in fatigue strength) and exceeding (in tensile properties) those of wrought Ti-6Al-4V can be produced from titanium hydride powder, through the hydrogen sintering and phase transformation process. Tensile and fatigue behavior, as well as fatigue fracture mechanisms, have been investigated under three processing conditions. It is shown that a reduction in the size of extreme-sized pores by changing the hydride particle size distribution can lead to improved fatigue strength. Further densification by pneumatic isostatic forging leads to a fatigue strength of ~550 MPa, comparable to the best of PM Ti-6Al-4V alloys prepared by other methods and approaching the fatigue strengths of wrought Ti-6Al-4V alloys. The microstructural factors that limit fatigue strength in PM titanium have been investigated, and pathways to achieve greater fatigue strengths in PM Ti-6Al-4V alloys have been identified.

  16. Assessment of Bending Fatigue Strength of Crankshaft Sections with Consideration of Quenching Residual Stress

    NASA Astrophysics Data System (ADS)

    Qin, W. J.; Dong, C.; Li, X.

    2016-03-01

    High-cycle bending fatigue is the primary failure mode of crankshafts in engines. Compressive residual stresses are often introduced by induction quenching to improve the fatigue strength of crankshafts. The residual stresses, which are commonly obtained by numerical methods, such as the finite element method (FEM), should be included in fatigue failure analysis to predict the fatigue strength of crankshafts accurately. In this study, the simulation method and theory of quenching process are presented and applied to investigate the residual stresses of a diesel engine crankshaft. The coupling calculation of temperature, microstructure, and stress fields of the crankshaft section is conducted by FEM. Then, the fatigue strength of the crankshaft section is analytically assessed by Susmel and Lazzarin's criterion based on the critical plane approach that superimposes the residual stresses onto the bending stresses. The resonant bending fatigue tests of the crankshaft sections are conducted, and the tests and analytical assessments yield consistent results.

  17. [On fatigue bending strength of PMMA-specimen (author's transl)].

    PubMed

    Rojczyk, M; Rojczyk-Pflüger, J

    1980-01-01

    The fatigue response of PMMA-specimen was tested under cyclic bending of 1.5 Hz in a particularly designed testing device. Specimen were tested that a "Wöhler" curve and the corresponding fatigue strength could be evaluated. The fatigue strength was reached after a comparatively short time and ranged in the order of 33 per cent of static breaking strength. PMID:7447658

  18. The Development of Confidence Limits for Fatigue Strength Data

    SciTech Connect

    SUTHERLAND,HERBERT J.; VEERS,PAUL S.

    1999-11-09

    Over the past several years, extensive databases have been developed for the S-N behavior of various materials used in wind turbine blades, primarily fiberglass composites. These data are typically presented both in their raw form and curve fit to define their average properties. For design, confidence limits must be placed on these descriptions. In particular, most designs call for the 95/95 design values; namely, with a 95% level of confidence, the designer is assured that 95% of the material will meet or exceed the design value. For such material properties as the ultimate strength, the procedures for estimating its value at a particular confidence level is well defined if the measured values follow a normal or a log-normal distribution. Namely, based upon the number of sample points and their standard deviation, a commonly-found table may be used to determine the survival percentage at a particular confidence level with respect to its mean value. The same is true for fatigue data at a constant stress level (the number of cycles to failure N at stress level S{sub 1}). However, when the stress level is allowed to vary, as with a typical S-N fatigue curve, the procedures for determining confidence limits are not as well defined. This paper outlines techniques for determining confidence limits of fatigue data. Different approaches to estimating the 95/95 level are compared. Data from the MSU/DOE and the FACT fatigue databases are used to illustrate typical results.

  19. Fatigue strength of adhesive bonded section beams under torsion

    SciTech Connect

    Tomioka, Noboru; Kakiage, Masashi; Niisawa, Junetsu; Kitagawa, Hideo

    1995-11-01

    Fatigue strength of adhesive bonded box beams was investigated. From results of the fatigue tests, it was seen that the fatigue strength of bonded beams was higher than that of spot welded beams. Fatigue strength of bonded beams was independent of plate thickness and partition. The flexural rigidity of the box beams in the plane of partition can increase without decrease of torsional rigidity and torsional fatigue strength, if the partition is jointed by adhesive bonding instead of spot welding. Since the fatigue strength and rigidity of adhesive bonded joints can be higher than the spot welded joints in the weight saving structures, it is expected that the structural adhesive joints will be employed more in the automobile body structure. For assuring the introduction of this joint more into the automobile body structures, it is necessary that the fatigue tests on the model members of the actual members used in the automobile body structure are conducted, in addition to those of the simple joints such as tension shear and T-type tension, and the property of the fatigue strength on the adhesive bonded members is known. But, the authors now have little data on fatigue tests of the adhesive bonded members. In the present research to be reported, the fatigue tests on adhesive bonded box beams under torsion, which are typical members in automobile body structure, were carried out and the effects of the presence of longitudinal partition and plate thickness on fatigue strength were investigated. Comparing the results of fatigue tests on adhesive bonded box beams with those on spot welded box beams, the property of fatigue strength on these adhesive bonded box beams was cleared.

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

    NASA Astrophysics Data System (ADS)

    Pejkowski, Łukasz; Skibicki, Dariusz

    2016-08-01

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

  1. Porous Ti6Al4V alloys with enhanced normalized fatigue strength for biomedical applications.

    PubMed

    Li, Fuping; Li, Jinshan; Kou, Hongchao; Zhou, Lian

    2016-03-01

    In this paper, porous Ti6Al4V alloys for biomedical applications were fabricated by diffusion bonding of alloy meshes. The compression-compression fatigue behavior was studied. It results that porous Ti6Al4V alloys show enhanced normalized fatigue strength which is in the range of 0.5-0.55 at 10(6)cycles. The porosity has some effect on the absolute S-N curves but minor effect on the normalized S-N curves. The relationship between strain per cycle and number of cycles shows three distinct stages and the value of strain per cycle is constant in stage II. The reasons for the higher normalized fatigue strength of porous Ti6Al4V alloys are discussed based on the fatigue crack initiation and propagation. PMID:26706555

  2. Fracture strength of all-ceramic restorations after fatigue loading

    NASA Astrophysics Data System (ADS)

    Baladhandayutham, Balasudha

    Fracture strength of monolithic and bilayered LAVA and e. max lower molar crowns after load cycling was measured and compared. The study included three groups (n = 8) from LAVA zirconia and three groups from e. max lithium disilicate to compare influences of different layers, thicknesses and manufacturing techniques. Prefabricated anatomically designed crowns were cemented to dies made from Z 100 composite resin using Rely X Luting Plus resin modified glass ionomer cement. Cemented crowns were stored at 37° C for 24 hours then cyclic loaded to test fatigue properties. The crowns were loaded to 200,000 cycles at 25N at a rate of 40 cycles / minute to simulate oral function. Subsequently, fracture properties for each group were measured using an Instron Universal Testing machine. Microscopic evaluation of the surface of fatigued samples did not reveal micro-cracks at the end of 50,000 cycles but minor wear facets were observed at the site of contact from the steatite ball antagonist. Crowns from LAVA bilayered groups showed step by step fractures while crowns from all other groups fractured as a single event as observed by the high speed camera. Zirconia bilayered crowns showed the highest loads to fracture while lithium disilicate monolithic crowns showed the lowest, within the limitations of the study. The study also showed that monolithic zirconia crowns of 0.6mm thickness resulted in relatively high magnitude for forces at fracture.

  3. Fatigue strength of Ce-TZP/Al2O3 nanocomposite with different surfaces.

    PubMed

    Takano, T; Tasaka, A; Yoshinari, M; Sakurai, K

    2012-08-01

    Ce-TZP/Al(2)O(3) nanocomposite (NANOZR) has not only higher strength, but also higher fracture toughness than conventional Y-TZP, indicating its potential for use in dental implants. Surface treatment to obtain osseointegration, however, may alter its surface topography, thus affecting the cyclic fatigue strength that plays such an important role in the durability of this material. The aim of this study was to evaluate the influence of surface treatment on cyclic fatigue strength in NANOZR as compared with grit-blasted and acid-etched Y-TZP (125BE Y-TZP). Bi-axial flexure strength was measured in both static and cyclic fatigue tests, as recommended by ISO 6872. The cyclic fatigue test was performed by the staircase method in distilled water at 37°C, with a load of 10(6) cycles and 10 Hz. Bi-axial flexure strength of NANOZR was 1111-1237 MPa and 667-881 MPa in the static and cyclic fatigue tests, respectively. The bi-axial flexure strength of NANOZR under all conditions was greater than that of 125BE Y-TZP in the static and cyclic fatigue tests. The cyclic fatigue strength of NANOZR was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the promise of this material for use in dental implants. PMID:22736446

  4. The influence of tensile fatigue damage on residual compressive strength of woven composites

    SciTech Connect

    Mitrovic, M.; Carman, G.P.

    1995-12-31

    The long term mechanical fatigue of a Celion G30-500/PMR-15 woven composite system is investigated to study the interrelationship between thermo-mechanical properties, namely the thermal expansion coefficient (TEC) and the compressive strength. Residual compressive strength measurements (IITRI fixture) conducted on specimens subjected to tension-tension fatigue cycling indicate that this material property is sensitive to cracks and delaminations which form during mechanical cycling. Measured compressive strength degradation are as large as 49% for this material undergoing mechanical fatigue cycling with TEC degradation as large as 61%. Experimental results show that a correlation exists between TEC measurements and compressive strength. This correlation suggests that TEC measurements may be used as a damage evaluation technique.

  5. Fatigue behavior of high-strength concrete under marine conditions

    SciTech Connect

    Mor, A.

    1987-01-01

    In this study, 24 high-strength reinforced concrete beams were tested in fatigue under simulated marine conditions. Low-cycle, high-magnitude loading was imposed on beams, some of which were exposed to air, and others which were submerged in water. The beams were cycled at 1 Hz, to 80% of their yield capacity in negative and positive flexure. Four concrete mixes were compared. Half of the specimens were made with lightweight aggregate (LWA), and half were made with river gravel (NWA). Half of each group contained silica-fume as partial replacement of cement (13%). By manipulating the water/cement ratio, the 28-day compressive strength of all concretes was 9500 {plus minus} 300 psi. The previously reported phenomenon of water pumping through the cracks was observed, but did not appear to be directly related to the subsequent failure. When silica fume is added to the concrete mix, the adhesion is greatly improved. LWA concrete utilizes this additional adhesion effectively. NWA concrete with silica-fume, on the other hand, is not able to utilize the increased adhesion due to microcracking. Main findings of both the fatigue and pull-out bond tests are listed.

  6. Final report on low-cycle fatigue and creep-fatigue testing of salt-filled alloy 800 specimens

    SciTech Connect

    Kaae, J L

    1982-05-01

    Uniaxial low-cycle fatigue and creep-fatigue tests have been carried out on hollow alloy 800 specimens that were either filled with air or with a molten mixture of sodium nitrate, potassium nitrate and an oxidizer. Low-cycle fatigue tests were carried out at 1200/sup 0/F and 650/sup 0/F by cycling the strain continuously between equal mangitude of tensile and compressive values at a rate of 4 x 10/sup -3/sec/sup -1/ until failure. The creep-fatigue tests were carried out at 1200/sup 0/F. The loading cycle differed from that of low-cycle fatigue testing only in the imposition of a hold at the peak compressive strain in each cycle. Cracks always initiated on the inner surface of the hollow specimen, and therefore, corrosive effects on crack propagation and initiation were controlled by the environment within the specimen cavity. In common with tests carried out earlier on steam-filled alloy 800 specimens, at 1200/sup 0/F in the presence of molten salt the heat of alloy 800 with the lower carbon content had a higher fatigue strength than the heat with the higher carbon content even though different heats were used in the two testing programs. The fatigue strength of the two heats of material in the presence of molten salt at 650/sup 0/F were about the same. Tests with air-filled specimens indicated that the presence of the molten salt degraded the fatigue life at 1200/sup 0/F but did not affect the creep fatigue life, while the presence of steam enhanced both the fatigue life and the creep-fatigue life.

  7. Compressive Strength of Notched Poly(Phenylene Sulfide) Aerospace Composite: Influence of Fatigue and Environment

    NASA Astrophysics Data System (ADS)

    Niitsu, G. T.; Lopes, C. M. A.

    2013-08-01

    The purpose of this work is to evaluate the influences of fatigue and environmental conditions (-55 °C, 23 °C, and 82 °C/Wet) on the ultimate compression strength of notched carbon-fiber-reinforced poly(phenylene sulfide) composites by performing open-hole compression (OHC) tests. Analysis of the fatigue effect showed that at temperatures of -55 and 23 °C, the ultimate OHC strengths were higher for fatigued than for not-fatigued specimens; this could be attributed to fiber splitting and delamination during fatigue cycling, which reduces the stress concentration at the hole edge, thus increasing the composite strength. This effect of increasing strength for fatigued specimens was not observed under the 82 °C/Wet conditions, since the test temperature near the matrix glass transition temperature ( T g) together with moisture content resulted in matrix softening, suggesting a reduction in fiber splitting during cycling; similar OHC strengths were verified for fatigued and not-fatigued specimens tested at 82 °C/Wet. Analysis of the temperature effect showed that the ultimate OHC strengths decreased with increasing temperature. A high temperature together with moisture content (82 °C/Wet condition) reduced the composite compressive strengths, since a temperature close to the matrix T g resulted in matrix softening, which reduced the lateral support provided by the resin to the 0° fibers, leading to fiber instability failure at reduced applied loads. On the other hand, a low temperature (-55 °C) improved the compressive strength because of possible fiber-matrix interfacial strengthening, increasing the fiber contribution to compressive strength.

  8. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size

    PubMed Central

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-01-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 107 cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of “damage reduction” was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials. PMID:27264347

  9. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size.

    PubMed

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-01-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 10(7) cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of "damage reduction" was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials. PMID:27264347

  10. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size

    NASA Astrophysics Data System (ADS)

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-06-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 107 cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of “damage reduction” was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials.

  11. Low-cycle fatigue testing methods

    NASA Technical Reports Server (NTRS)

    Lieurade, H. P.

    1978-01-01

    The good design of highly stressed mechanical components requires accurate knowledge of the service behavior of materials. The main methods for solving the problems of designers are: determination of the mechanical properties of the material after cyclic stabilization; plotting of resistance to plastic deformation curves; effect of temperature on the life on low cycle fatigue; and simulation of notched parts behavior.

  12. Relationship among fatigue strength, mean grain size and compressive strength of a rock

    NASA Astrophysics Data System (ADS)

    Singh, S. K.

    1988-10-01

    Fatigue tests carried on three sets of samples having different mean grain sizes revealed that fatigue strength is a function of mean grain size of the rock. Samples having smaller grain size show higher value of fatigue strength. Graywacke samples from Flagstaff formation having mean grain sizes of 1.79 mm, 1.35 mm and 0.93 mm showed fatigue strengths of 87%, 88.25% and 89.1% respectively. Since the mean uniaxial compressive strength also varied with varying grain size, i. e. higher mean strength value for samples having finer grain size; the fatigue strength of a rock also shows a converse relation with mean uniaxial compressive strength.

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

    SciTech Connect

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

    1993-08-01

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

  14. Low cycle fatigue of Eurofer 97

    NASA Astrophysics Data System (ADS)

    Marmy, Pierre; Kruml, Tomas

    2008-06-01

    We have investigated the low cycle fatigue and creep-fatigue properties of Eurofer 97 and observed the associated microstructural changes. The as received structure is composed of equiaxed subgrains and a few martensite laths with a high dislocation density. Fatigue tests have been carried out in air or in high vacuum, from room temperature to 550 °C, under total strain control. It has been found that the influence of the test temperature on the fatigue endurance is not significant. The softening behaviour as a function of the imposed strain amplitude and temperature has been analysed in detail. The softening rate is independent of the imposed strain but strongly enhanced at the highest test temperature. Creep-fatigue tests were run, imposing a 500 s dwell at the maximum tensile strain of the loading cycle, at a total strain range of 0.5%, 0.8% and 1.4%, and at 150, 300 and 550 °C. The influence of the hold time is important only at the highest test temperature, under low applied strains. It was found that at the beginning of life, at the highest temperature, the softening rate with hold times is much stronger as compared to the softening rate without hold times. The amount of stress relaxed during the dwell is independent of the applied strain, at the end of life. The effect of fatigue with and without hold times up to medium temperatures on the microstructure was to lower the dislocation density and to decompose the laths and large grains into a homogeneous structure of submicron grains. At the highest test temperature, an increase of the subgrain size and carbide coarsening were observed.

  15. The fatigue strength of riveted joints and lugs

    NASA Technical Reports Server (NTRS)

    Schijve, J

    1956-01-01

    This report deals with a number of tests on riveted joints and lugs for the primary purpose of comparing the several types of riveted joints and to study the effect of various factors on the fatigue strength of lugs. A check was made to ascertain whether or not an estimate of the fatigue life at a certain loading could be made from the dimensions of the joint and the fatigue data of the unnotched materials. Recommendations are made on the proportioning of joints to obtain better fatigue behavior.

  16. 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.

  17. Al-Li alloy AA2198's very high cycle fatigue crack initiation mechanism and its fatigue thermal effect

    NASA Astrophysics Data System (ADS)

    Xu, Luopeng; Cao, Xiaojian; Chen, Yu; Wang, Qingyuan

    2015-10-01

    AA2198 alloy is one of the third generation Al-Li alloys which have low density, high elastic modulus, high specific strength and specific stiffness. Compared With the previous two generation Al-Li alloys, the third generation alloys have much improved in alloys strength, corrosion resistance and weldable characteristic. For these advantages, the third generation Al-Li alloys are used as aircraft structures, such as C919 aviation airplane manufactured by China and Russia next generation aviation airplane--MS-21. As we know, the aircraft structures are usually subjected to more than 108 cycles fatigue life during 20-30 years of service, however, there is few reported paper about the third generation Al-Li alloys' very high cycle fatigue(VHCF) which is more than 108 cycles fatigue. The VHCF experiment of AA2198 have been carried out. The two different initiation mechanisms of fatigue fracture have been found in VHCF. The cracks can initiate from the interior of the testing material with lower stress amplitude and more than 108 cycles fatigue life, or from the surface or subsurface of material which is the dominant reason of fatigue failures. During the experiment, the infrared technology is used to monitor the VHCF thermal effect. With the increase of the stress, the temperature of sample is also rising up, increasing about 15 °C for every 10Mpa. The theoretical thermal analysis is also carried out.

  18. Residual strength of five boron/aluminum laminates with crack-like notches after fatigue loading

    NASA Technical Reports Server (NTRS)

    Simonds, R. A.

    1984-01-01

    Boron/aluminum specimens were made with crack-like slits in the center and with various proportions of 0 and + or - 45 deg plies. They were fatigue loaded and then fractured to determine their residual strengths. The fatigue loads were generally in the range of 60 to 80 percent of the static tensile strength of the specimen as determined from a previous study, and the stress ratio was .05. For virtually all of the specimens the fatigue loading was continued for 100,000 cycles. The specimens were radiographed after the fatigue loading to determine the nature of the fatigue damage. A few specimens were sectioned and examined in a scanning electron microscope after being radiographed in order to verify the interpretation of the radiographs and also to get a better insight into the nature of the fatigue damage. The results indicate that the fatiguing does not significantly affect the strength of the specimens tested. The results of the radiography and of the scanning electron microscopy indicate that the 45 deg plies suffer extensive damage in the form of split and broken fibers and matrix cracking in the vicinity of the ends of the split. By contrast, the only significant damage to the 0 deg plies was a single 0 deg matric crack growing from the ends of the slit and between the 0 deg fibers.

  19. Residual strength of five boron/aluminum laminates with crack-like notches after fatigue loading

    NASA Technical Reports Server (NTRS)

    Simonds, R. A.

    1986-01-01

    Boron/aluminum specimens were made with crack-like slits in the center and with various proportions of 0 and + or - 45 deg plies. They were fatigue loaded and then fractured to determine their residual strengths. The fatigue loads were generally in the range of 60 to 80 percent of the static tensile strength of the specimen as determined from a previous study, and the stress ratio was .05. For virtually all of the specimens the fatigue loading was continued for 100,000 cycles. The specimens were radiographed after the fatigue loading to determine the nature of the fatigue damage. A few specimens were sectioned and examined in a scanning electron microscope after being radiographed in order to verify the interpretation of the radiographs and also to get a better insight into the nature of the fatigue damage. The results indicate that the fatiguing does not significantly affect the strength of the specimens tested. The results of the radiography and of the scanning electron microscopy indicate that the 45 deg plies suffer extensive damage in the form of split and broken fibers and matrix cracking in the vicinity of the ends of the split. By contrast, the only significant damage to the 0 deg plies was a single 0 deg matric crack growing from the ends of the slit and between the 0 deg fibers.

  20. Investigation of fatigue strength of multilayer advanced fiber composites

    NASA Technical Reports Server (NTRS)

    Thornton, H. R.; Kozik, T. J.

    1974-01-01

    The analytical characterization of a multilayer fiber composite plate (without hole) was accomplished for both static and dynamic loading conditions using the finite difference technique. Thornel 300/5208 composites with and without holes were subjected to static and tensile fatigue testing. Five (5) fiber orientations were submitted to test. Tensile fatigue testing also included three (3) loading conditions and two (2) frequencies. The low-cycle test specimens demonstrated a shorter tensile fatigue life than the high-cycle test specimens. Failure surfaces demonstrated effect of testing conditions. Secondary failure mechanisms, such as: delamination, fiber breakage, and edge fiber delamination were present. Longitudinal delamination between plies also occurred in these specimens.

  1. Loading frequencies up to 20Hz as an alternative to accelerate fatigue strength tests in a Y-TZP ceramic.

    PubMed

    Fraga, Sara; Pereira, Gabriel Kalil Rocha; Freitas, Mariana; Kleverlaan, Cornelis Johannes; Valandro, Luiz Felipe; May, Liliana Gressler

    2016-08-01

    Considering the interest of the research community in the fatigue behavior of all-ceramic restorations and the time consumed in low-frequency cyclic fatigue tests, this study aimed to investigate the influence of the loading frequency on the zirconia fatigue strength. The biaxial flexural fatigue strength of Y-TZP discs was determined by the staircase approach after 500,000 cycles. The investigated frequencies were 2Hz (control-simulation of the chewing activity; n=20), 10Hz (n=20), 20Hz (n=20), and 40Hz (n=21). The fatigue strength data were analyzed using one-way ANOVA and post-hoc Tukey׳s test (α=0.05). Pearson coefficient (r) was calculated to assess the existence of a correlation between fatigue strength and loading frequency. X-ray diffraction analysis was used to determine the relative amount of monoclinic phase under each fatigue test condition. The fatigue strength was significantly higher for 40Hz group (630.7±62.1MPa) and did not differ among the groups 2Hz (550.3±89.7MPa), 10Hz (574.0±47MPa) and 20Hz (605.1±30.7MPa). Pearson correlation coefficient indicated a significantly moderate correlation (r=0.57) between fatigue strength and loading frequency. The percentage of monoclinic phase was similar among the groups. Therefore, the use of loading frequencies up to 20Hz seems a good alternative to expedite the cycling strength fatigue tests in polycrystalline ceramics without significantly changing the fatigue behavior showed by zirconia in tests employing the frequency of the masticatory cycle. PMID:26849030

  2. Fracture resistance of Zr-Nb alloys under low-cycle fatigue tests

    NASA Astrophysics Data System (ADS)

    Nikulin, S. A.; Rozhnov, A. B.; Gusev, A. Yu.; Nechaykina, T. A.; Rogachev, S. O.; Zadorozhnyy, M. Yu.

    2014-03-01

    Comparative low-cycle fatigue tests of small-scale specimens cut from the cladding tubes of E110, E125, E110opt zirconium alloys at temperatures of 25 and 350 °C using a dynamic mechanical analyzer have been carried out. It is shown that the limited cycles fatigue stress for all alloys is 50% less at temperature of 350 °C comparing to 25 °C. Besides it has been revealed that the limited cycles fatigue stress increases with increasing the strength of zirconium alloy.

  3. Fatigue Properties of Automobile High-Strength Bolts

    NASA Astrophysics Data System (ADS)

    Zhou, Congling; Nishida, Shin-Ichi; Hattori, Nobusuke

    This study is focused on the fatigue properties of automobile high-strength bolts, including the effect of mean stress level, pre-processing schedule and the residual stresses. And the mean stress levels are 0.3, 0.5 and 0.7 times to the tensile strength (σB) of the material respectively. The main results obtained are as follows: 1) the fatigue strength increases under the mean stress loading, but the differences between the loading levels are not so evident; 2) most of the cases in this study are broken from the bottom of the screw thread, and the crack initiated from the impurities.

  4. Fatigue crack retardation of high strength steel in saltwater

    SciTech Connect

    Tokaji, K.; Ando, Z.; Imai, T.; Kojima, T.

    1983-04-01

    A high strength steel was studied in 3 percent saltwater to investigate the effects of a corrosive environment and sheer thickness on fatigue crack propagation behavior following the application of a single tensile overload. Experiments were carried out under sinusoidally varying loads at a load ratio of 0 and frequency of 10 H /SUB z/ . A single tensile overload was found to cause delayed retardation, and the crack propagation rate at first increased, followed by fairly rapid decrease to a minimum value and then increased gradually to its steady-state value, just as it did in air. The overload affected zone size and the retardation cycles increased with decreasing sheet thickness, just as they did in air. However, the zone size and the cycles were larger in 3 percent saltwater than in air. Since the crack propagation rates through the overload affected zone were not affected by the test environment, the longer retardation cycles in 3 percent saltwater were attributed to an enlargement of the overload affected zone size. The crack propagation behavior following the application of a single tensile overload in 3 percent saltwater was well explained by the crack closure concept.

  5. Notch Fatigue Strength of a PM Disk Superalloy

    NASA Technical Reports Server (NTRS)

    Gayda, John; Gabb, Timothy P.; Telesman, Jack

    2007-01-01

    New powder metallurgy (PM) disk superalloys, such as ME3, LSHR, and Alloy 10, have been developed in recent years which enable rim temperatures in turbine disk applications to approach 1300 F. Before these alloys can be utilized at 1300 F their long term durability must be ensured. One of the key requirements for disk rims is notch fatigue strength. This issue is extremely important and is a direct result of the blade attachment geometry employed at the disk rim. Further, the imposition of a dwell at maximum load, associated with take off and landing, can also affect notch fatigue strength. For these reasons a study has been undertaken to assess the notch dwell fatigue strength of a modern PM disk alloy through spin pit evaluation of a prototypical disk. The first element of this program involves screening potential heat treatments with respect to notch fatigue strength at 1300 F utilizing a conventional notch fatigue specimen with a stress concentration factor (K(sub t)) of 2 and a 90 sec dwell at peak load. The results of this effort are reported in this paper including the downselect of an optimal heat treatment, from a notch fatigue standpoint.

  6. Fatigue strength of Co-Cr-Mo alloy clasps prepared by selective laser melting.

    PubMed

    Kajima, Yuka; Takaichi, Atsushi; Nakamoto, Takayuki; Kimura, Takahiro; Yogo, Yoshiaki; Ashida, Maki; Doi, Hisashi; Nomura, Naoyuki; Takahashi, Hidekazu; Hanawa, Takao; Wakabayashi, Noriyuki

    2016-06-01

    We aimed to investigate the fatigue strength of Co-Cr-Mo clasps for removable partial dentures prepared by selective laser melting (SLM). The Co-Cr-Mo alloy specimens for tensile tests (dumbbell specimens) and fatigue tests (clasp specimens) were prepared by SLM with varying angles between the building and longitudinal directions (i.e., 0° (TL0, FL0), 45° (TL45, FL45), and 90° (TL90, FL90)). The clasp specimens were subjected to cyclic deformations of 0.25mm and 0.50mm for 10(6) cycles. The SLM specimens showed no obvious mechanical anisotropy in tensile tests and exhibited significantly higher yield strength and ultimate tensile strength than the cast specimens under all conditions. In contrast, a high degree of anisotropy in fatigue performance associated with the build orientation was found. For specimens under the 0.50mm deflection, FL90 exhibited significantly longer fatigue life (205,418 cycles) than the cast specimens (112,770 cycles). In contrast, the fatigue lives of FL0 (28,484 cycles) and FL45 (43,465 cycles) were significantly shorter. The surface roughnesses of FL0 and FL45 were considerably higher than those of the cast specimens, whereas there were no significant differences between FL90 and the cast specimens. Electron backscatter diffraction (EBSD) analysis indicated the grains of FL0 showed preferential close to <001> orientation of the γ phase along the normal direction to the fracture surface. In contrast, the FL45 and FL90 grains showed no significant preferential orientation. Fatigue strength may therefore be affected by a number of factors, including surface roughness and crystal orientation. The SLM process is a promising candidate for preparing tough removable partial denture frameworks, as long as the appropriate build direction is adopted. PMID:26974490

  7. Preliminary Study on Fatigue Strengths of Fretted Ti-48Al-2Cr-2Nb

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Lerch, Bradley A.; Draper, Susan L.

    2002-01-01

    The fatigue behavior (stress-life curve) of gamma titanium aluminide (Ti-48Al-2Cr-2Nb, atomic percent) was examined by conducting two tests: first, a fretting wear test with a fatigue specimen in contact with a typical nickel-based superalloy contact pad in air at temperatures of 296 and 823 K and second, a high-cycle fatigue test of the prefretted Ti-48Al-2Cr-2Nb fatigue specimen at 923 K. Reference high-cycle fatigue tests were also conducted with unfretted Ti-48Al-2Cr-2Nb specimens at 923 K. All Ti-48Al-2Cr-2Nb fatigue specimens were machined from cast slabs. The results indicate that the stress-life results for the fretted Ti-48Al-2Cr-2Nb specimens exhibited a behavior similar to those of the unfretted Ti-48Al-2Cr-2Nb specimens. The values of maximum stress and life for the fretted specimens were almost the same as those for the unfretted specimens. The resultant stress-life curve for the unfretted fatigue specimens was very flat. The flat appearance in the stress-life curve of the unfretted specimens is attributed to the presence of a high density of casting pores. The fatigue strengths of both the fretted and unfretted specimens can be significantly affected by the presence of this porosity, which can decrease the fatigue life of Ti-48Al-2Cr-2Nb. The presence of the porosity made discerning the effect of fretting damage on fatigue strength and life of the specimens difficult.

  8. Fatigue strength of woven kenaf fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Ismail, A. E.; Aziz, M. A. Che Abdul

    2015-12-01

    Nowadays, green composites provide alternative to synthetic fibers for non-bearing and load-bearing applications. According to literature review, lack of information is available on the fatigue performances especially when the woven fiber is used instead of randomly oriented fibers. In order to overcome this problem, this paper investigates the fatigue strength of different fiber orientations and number of layers of woven kenaf fiber reinforced composites. Four types of fiber orientations are used namely 0°, 15°, 30° and 45°. Additionally, two numbers of layers are also considered. It is revealed that the fatigue life has no strong relationship with the fiber orientations. For identical fiber orientations, the fatigue life can be predicted considerably using the normalized stress. However as expected, the fatigue life enhancement occur when the number of layer is increased.

  9. Dynamic fatigue and strength characterization of three ceramic materials.

    PubMed

    Teixeira, Erica C; Piascik, Jeffrey R; Stoner, Brian R; Thompson, Jeffrey Y

    2007-06-01

    Fracture strength and fatigue parameters of three ceramic materials submitted to dynamic fatigue were evaluated. A machinable leucite-reinforced dental ceramic, aluminum oxide, and yttria-stabilized zirconia (YSZ) were tested. The inert strength of the materials was determined in air (25 degrees C) at stressing rates of 70, 250, 400 MPa/s for Porcelain, Alumina and YSZ respectively. The data was analyzed using a two-parameter Weibull distribution. The Weibull modulus (m) and the characteristic of fracture (sigma0) parameters were determined for each material. Specimens were also tested in 3-point bending at different stressing rates in distilled/deionized water at 37 degrees C (dynamic fatigue) in order to calculate the fatigue parameters n and ln B. The strength for each material was characterized using Strength-Probability-Time (SPT) diagrams for 1 day, 1 year and 10 years. YSZ showed a high-fracture strength sigma0 (1,459 MPa) at a failure probability of 63.2% and high resistance to subcritical crack growth. YSZ and alumina showed better resistance to slow crack growth than porcelain, indicating less susceptibility to strength degradation by stress corrosion. Lifetime predictions after 10 years indicate a reduction of 50%, 36% and 29% in strength for porcelain, alumina and YSZ respectively. YSZ seems to be a very promising material for long-term dental and biomedical applications. PMID:17277977

  10. Factors that affect the fatigue strength of power transmission shafting

    NASA Technical Reports Server (NTRS)

    Loewenthal, S. H.

    1984-01-01

    A long standing objective in the design of power transmission shafting is to eliminate excess shaft material without compromising operational reliability. A shaft design method is presented which accounts for variable amplitude loading histories and their influence on limited life designs. The effects of combined bending and torsional loading are considered along with a number of application factors known to influence the fatigue strength of shafting materials. Among the factors examined are surface condition, size, stress concentration, residual stress and corrosion fatigue.

  11. Effect of microstructure on high-cycle fatigue properties of Alloy718 plates

    NASA Astrophysics Data System (ADS)

    Ono, Y.; Yuri, T.; Nagashima, N.; Ogata, T.; Nagao, N.

    2015-12-01

    Effect of microstructure on high-cycle fatigue properties of Alloy718 were investigated at 77 K by using samples with three different microstructures; fine-grained (FG), coarse-grained (CG) and bimodal-grained (BG) ones. The BG sample consisted of FG and CG microstructural regions and grain sizes of those regions were close to those of the FG and the CG samples, respectively. High-cycle fatigue strength of the FG sample was higher than that of the CG sample. High-cycle fatigue strength of the BG sample was clearly lower than that of the FG sample and almost the same as that of the CG one. Flat area (facet) was found at fatigue crack initiation site in all specimens. Facet size was similar to the grain size and found to be almost same in the CG and the BG samples. Observations of the microstructure beneath the fatigue crack initiation site of the BG sample revealed that the facet corresponds to transgranular cracking in the course grain, meaning that fatigue crack initiated at the coarse grain in the BG sample. It is deduced that the high-cycle fatigue strength of Alloy 718 with the BG microstructure is strongly affected by that of the CG region in that material.

  12. Weibull models of fracture strengths and fatigue behavior of dental resins in flexure and shear.

    PubMed

    Baran, G R; McCool, J I; Paul, D; Boberick, K; Wunder, S

    1998-01-01

    In estimating lifetimes of dental restorative materials, it is useful to have available data on the fatigue behavior of these materials. Current efforts at estimation include several untested assumptions related to the equivalence of flaw distributions sampled by shear, tensile, and compressive stresses. Environmental influences on material properties are not accounted for, and it is unclear if fatigue limits exist. In this study, the shear and flexural strengths of three resins used as matrices in dental restorative composite materials were characterized by Weibull parameters. It was found that shear strengths were lower than flexural strengths, liquid sorption had a profound effect on characteristic strengths, and the Weibull shape parameter obtained from shear data differed for some materials from that obtained in flexure. In shear and flexural fatigue, a power law relationship applied for up to 250,000 cycles; no fatigue limits were found, and the data thus imply only one flaw population is responsible for failure. Again, liquid sorption adversely affected strength levels in most materials (decreasing shear strengths and flexural strengths by factors of 2-3) and to a greater extent than did the degree of cure or material chemistry. PMID:9730059

  13. Human quadriceps strength and fatiguability in patients with post viral fatigue.

    PubMed Central

    Rutherford, O M; White, P D

    1991-01-01

    Quadriceps isometric strength, activation and fatiguability were measured in 11 patients with symptoms of fatigue three months after glandular fever or a glandular fever-like illness. Predicted normal and lower limits of normal muscle strength were calculated from height and age. These measures and the fatigue index were compared with a group of healthy students of similar age. Two of the patients were unable to activate fully their muscles. After allowing for this inhibition the group mean (SD) strength was 104 (22%) of predicted. Although there was no significant difference in the fatigue index between the patients and the control group, there was a trend for the patients to show less fatigue than controls. There was no difference in the muscle results for those patients who were found to have Epstein-Barr virus infections and those who did not. The feelings of weakness and fatigue experienced by the patients could not be explained by either physiological muscle fatigue or lack of effort. PMID:1800667

  14. Observation of fatigue in sandstone samples exposed to repeated freeze-thaw cycles

    NASA Astrophysics Data System (ADS)

    Hailiang, Jia; Wei, Xiang; Krautblatter, Michael

    2014-05-01

    The effect of rock fatigue is one of the key elements in the analysis and evaluation of rockfall preparation. We performed a series of laboratory freezing-thawing cycles experiments on an array of identical sandstone samples (cylinder samples with diameter of 5cm and length of 10cm). During each cycle we measured surface deformations and effective porosity for three samples, and after each thawing phase we removed two samples for destructive testing (uniaxial compressive and tensile strength). Our results indicate that: (1) frost action causes primarily reversible strain in samples with maximum magnitudes of ~1*10-4, we suggest low-cycle fatigue causes minor plastic deformation (2) with the increase of cycles, we observed a marked increase of effective porosity and a sharp decrease of uniaxial tensile strength. The decrease in uniaxial compressive strength was not as significant as that of the tensile strength in response to this frost action; (3) Curves describing effective porosity increases demonstrate a rapid increase during the first 3 - 4 freeze-thaw cycles, followed by a more linear increase, with steps in the porosity profile indicating discrete cycles with increased fatigue damage. Here we show how 17 freeze-thaw cycles cause progressive fatigue in sandstone samples and how this affects effective porosity and uniaxial compressive strength.

  15. High Cycle Thermal Fatigue in French PWR

    SciTech Connect

    Blondet, Eric; Faidy, Claude

    2002-07-01

    Different fatigue-related incidents which occurred in the world on the auxiliary lines of the reactor coolant system (SIS, RHR, CVC) have led EDF to search solutions in order to avoid or to limit consequences of thermodynamic phenomenal (Farley-Tihange, free convection loop and stratification, independent thermal cycling). Studies are performed on mock-up and compared with instrumentation on nuclear power stations. At the present time, studies allow EDF to carry out pipe modifications and to prepare specifications and recommendations for next generation of nuclear power plants. In 1998, a new phenomenal appeared on RHR system in Civaux. A crack was discovered in an area where hot and cold fluids (temperature difference of 140 deg. C) were mixed. Metallurgic studies concluded that this crack was caused by high cycle thermal fatigue. Since 1998, EDF is making an inventory of all mixing areas in French PWR on basis of criteria. For all identified areas, a method was developed to improve the first classifying and to keep back only potential damage pipes. Presently, studies are performing on the charging line nozzle connected to the reactor pressure vessel. In order to evaluate the load history, a mock-up has been developed and mechanical calculations are realised on this nozzle. The paper will make an overview of EDF conclusions on these different points: - dead legs and vortex in a no flow connected line; - stratification; - mixing tees with high {delta}T. (authors)

  16. Effect of Preloading on Fatigue Strength in Dynamic Fatigue Testing of Ceramic Materials at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Salem, Jonathan A.

    1995-01-01

    Previously derived solutions of fatigue strength as a function of preloading were verified by applying preloads to elevated temperature dynamic fatigue tests of 96 wt% alumina at 1000 C and NC 132 silicon nitride at 1100 C. The technique was found very useful in identification and control of the governing failure mechanism when multiple failure mechanisms, such as slow crack growth, creep and oxidation occurred simultaneously at elevated temperatures.

  17. High-Cycle Fatigue Properties at Cryogenic Temperatures in INCONEL 718

    NASA Astrophysics Data System (ADS)

    Ono, Y.; Yuri, T.; Sumiyoshi, H.; Takeuchi, E.; Matsuoka, S.; Ogata, T.

    2006-03-01

    High-cycle fatigue properties at 4 K, 20 K, 77 K and 293 K were investigated in forged-INCONEL 718 nickel-based superalloy with a mean gamma (γ) grain size of 25 μm. In the present material, plate-like delta phase precipitated at γ grain boundaries and niobium (Nb)-enriched MC type carbides precipitated coarsely throughout the specimens. The 0.2% proof stress and the tensile strength of this alloy increased with decreasing temperature, without decreasing elongation or reduction of area. High-cycle fatigue strengths also increased with decreasing temperature although the fatigue limit at each temperature didn't appear even around 107 cycles. Fatigue cracks initiated near the specimen surface and formed faceted structures around crack initiation sites. Fatigue cracks predominantly initiated from coarse Nb-enriched carbides and faceted structures mainly corresponded to these carbides. In lower stress amplitude tests, however, facets were formed through transgranular crack initiation and growth. These kinds of distinctive crack initiation behavior seem to lower the high-cycle fatigue strength below room temperature in the present material.

  18. High-Cycle Fatigue Properties at Cryogenic Temperatures in INCONEL 718

    SciTech Connect

    Ono, Y.; Yuri, T.; Sumiyoshi, H.; Takeuchi, E.; Ogata, T.; Matsuoka, S.

    2006-03-31

    High-cycle fatigue properties at 4 K, 20 K, 77 K and 293 K were investigated in forged-INCONEL 718 nickel-based superalloy with a mean gamma ({gamma}) grain size of 25 {mu}m. In the present material, plate-like delta phase precipitated at {gamma} grain boundaries and niobium (Nb)-enriched MC type carbides precipitated coarsely throughout the specimens. The 0.2% proof stress and the tensile strength of this alloy increased with decreasing temperature, without decreasing elongation or reduction of area. High-cycle fatigue strengths also increased with decreasing temperature although the fatigue limit at each temperature didn't appear even around 107 cycles. Fatigue cracks initiated near the specimen surface and formed faceted structures around crack initiation sites. Fatigue cracks predominantly initiated from coarse Nb-enriched carbides and faceted structures mainly corresponded to these carbides. In lower stress amplitude tests, however, facets were formed through transgranular crack initiation and growth. These kinds of distinctive crack initiation behavior seem to lower the high-cycle fatigue strength below room temperature in the present material.

  19. Low cycle dwell time fatigue in Ti-6242

    SciTech Connect

    Kassner, M.E.; Faber, R.; Li, X.; Ge, Y.; Kosaka, Y.; Bristow, B.; Reichman, S.H.; Hall, J.A.

    1999-07-01

    Ambient temperature low cycle dwell time and conventional low cycle fatigue tests were performed on Ti-6Al-2Sn-4Zr-2Mo (Ti-6242). Specimens were solution annealed at various temperatures below the beta transus to control the volume fraction of primary alpha. The influence of the changes in primary alpha phase on low cycle dwell time fatigue life (DLCF) were determined and compared to the conventional low cycle fatigue (LCF) properties of the alloy. A dwell significantly decreased the number of cycles to failure. Increasing primary alpha associated with lower solution temperatures significantly increased susceptibility to low cycle dwell time fatigue although this effect, and DLCF in general, diminished with decreasing stress. It is believed that the susceptibility to dwell fatigue may be associated with ambient temperature, time-dependent, cyclic (creep) plasticity.

  20. Damage formation, fatigue behavior and strength properties of ZrO2-based ceramics

    NASA Astrophysics Data System (ADS)

    Kozulin, A. A.; Narikovich, A. S.; Kulkov, S. N.; Leitsin, V. N.; Kulkov, S. S.

    2016-08-01

    It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO2-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91-0.98, 0.8-0.83, and 0.73-0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 105 stress cycles is in the range 33-34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.

  1. High-cycle fatigue behavior of Ti-5Al-2.5Sn ELI alloy forging at low temperatures

    SciTech Connect

    Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko; Matsuoka, Saburo; Sunakawa, Hideo

    2014-01-27

    High-cycle fatigue properties of Ti-5Al-2.5Sn Extra Low Interstitial (ELI) alloy forging were investigated at low temperatures. The high-cycle fatigue strength at low temperatures of this alloy was relatively low compared with that at ambient temperature. The crystallographic orientation of a facet formed at a fatigue crack initiation site was determined by electron backscatter diffraction (EBSD) method in scanning electron microscope (SEM) to understand the fatigue crack initiation mechanism and discuss on the low fatigue strength at low temperature. Furthermore, in terms of the practical use of this alloy, the effect of the stress ratio (or mean stress) on the high-cycle fatigue properties was evaluated using the modified Goodman diagram.

  2. High-cycle fatigue behavior of Ti-5Al-2.5Sn ELI alloy forging at low temperatures

    NASA Astrophysics Data System (ADS)

    Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko; Matsuoka, Saburo; Sunakawa, Hideo

    2014-01-01

    High-cycle fatigue properties of Ti-5Al-2.5Sn Extra Low Interstitial (ELI) alloy forging were investigated at low temperatures. The high-cycle fatigue strength at low temperatures of this alloy was relatively low compared with that at ambient temperature. The crystallographic orientation of a facet formed at a fatigue crack initiation site was determined by electron backscatter diffraction (EBSD) method in scanning electron microscope (SEM) to understand the fatigue crack initiation mechanism and discuss on the low fatigue strength at low temperature. Furthermore, in terms of the practical use of this alloy, the effect of the stress ratio (or mean stress) on the high-cycle fatigue properties was evaluated using the modified Goodman diagram.

  3. Fatigue strength of high-temperature alloys under conditions of cyclic temperature variation. Communication 1: Experimental procedure and results

    NASA Astrophysics Data System (ADS)

    Troshchenko, V. T.; Gryaznov, B. A.; Yamshanov, Yu. B.

    1994-03-01

    Determination of the serviceability of the material of gas-turbine engine blades, one of the most loaded elements of the engine, critical for the reliability of the turbine, is discussed. The NUM-3 setup, intended for studying fatigue strength of high-temperature alloys under conditions simulating service ones, is briefly described. The results of the investigation into the fatigue of alloys EP962 and EI698 under isothermal conditions and complex thermal-mechanical loading are presented. The analysis of the findings revealed a number of regularities in the effect of thermal cycling and resulting varying thermal stresses on the fatigue strength of the materials studied.

  4. Bending Fatigue Strength of Austempered Ductile Iron Spur Gears

    NASA Astrophysics Data System (ADS)

    Yamanaka, Masashi; Tamura, Ryo; Inoue, Katsumi; Narita, Yukihito

    This paper deals with an experimental evaluation of bending fatigue strength for austempered ductile iron (ADI) spur gears. The module is 2.5 and the number of teeth is 26 in the test gears. The material of the test gears corresponds to Japan Industrial Standard (JIS) FCAD1100-15. Some gears are processed by one of two types of fine particle bombarding (FPB). The surface roughness is slightly increased by FPB. The obtained strengths are 623 MPa for the as-austempered gears, and 1011 and 1085 MPa for the gears after FPB. The strength is expressed by the fillet stress level, which is calculated by FEM. The strength of a gear with the same dimensions made of carburized SCr420H alloy steel is 1205 MPa, and the strength of the ADI gear is approximately half that of the carburized steel gear. The FPB process has a significant effect on the ADI gear, improving its strength by 62-74%.

  5. Stochastic models for the tensile strength, fatigue

    NASA Technical Reports Server (NTRS)

    Phoenix, S. L.

    1976-01-01

    The time-to-failure of a single fiber is modeled as a functional of the fiber load history and reasonable forms for this functional are proposed. Earlier models by Daniels and Coleman are shown to be special cases of the proposed model and apparent disparities in their behavior are discussed. Techniques are presented for determining analytically the asymptotic distributions of the tensile strength and time-to-failure for bundles of a large number of fibers. For smaller bundles, exact results are far too cumbersome to be of use so that efficient Monte Carlo simulation procedures are proposed.

  6. A Very High-Cycle Fatigue Test and Fatigue Properties of TC17 Titanium Alloy

    NASA Astrophysics Data System (ADS)

    Jiao, Shengbo; Gao, Chao; Cheng, Li; Li, Xiaowei; Feng, Yu

    2016-03-01

    The present work studied the very high-cycle fatigue (VHCF) test and fatigue properties of TC17 titanium alloy. The specimens for bending vibration were designed using the finite element method and the VHCF tests were conducted by using the ultrasonic fatigue testing system. The results indicated that there is no the fatigue limit for TC17 titanium alloy, and the S-N curve shows a continuously descending trend. The fatigue crack initiates at the specimen surface within the range of VHCF and the VHCF lives follow the log-normal distribution more closely.

  7. Effect of Microstructure on Fatigue Strength of Bovine Compact Bones

    NASA Astrophysics Data System (ADS)

    Kim, Jong Heon; Niinomi, Mitsuo; Akahori, Toshikazu; Takeda, Junji; Toda, Hiroyuki

    Despite its clinical importance in developing artificial bone, limited information is available regarding the microstructure with respect to the fatigue characteristics of bones. In this study, the fatigue characteristics of the bovine humerus and femur were investigated with respect to microstructures. Fatigue tests were conducted on the bovine humerus and femur at a stress ratio of 0.1 and a frequency of 10Hz. The fatigue strength of the plexiform bone is slightly greater than that of the haversian bone. This is because the volume fraction of voids in the haversian bone, which is the site of stress concentration, is higher than that of voids in the plexiform bone. Several microcracks are observed on the fatigue fracture surface of the haversian bone. The microcracks are short and their propagation directions are random. However, the number of the microcracks in the plexiform bone is very small. The microcracks are relatively long and their propagation directions are parallel to the longitudinal direction of the lamellar bone. Therefore, the crack requires relatively more energy to propagate across the lamella in the plexiform bone.

  8. Fatigue strength of Inconel 625 plate and weldments used in the DIII-D configuration vacuum vessel

    SciTech Connect

    Trester, P.W.; Kaae, J.L.; Gallix, R.

    1984-12-01

    The Doublet III-D vacuum vessel will enable fusion experiments with large dee-configuration plasmas in the tokamak device at GA Technologies Inc. The vessel is a welded structure of Ni-Cr-Mo-Nb alloy Inconel 625, in the forms of mill-annealed plate and sheet. An emphasis was placed on spceifying material with small grain size to enhance fatigue resistance. Fatigue strength was determined by tension-compression axial strain cycling of specimens excised from stock plate 25 mm thick. In addition, tests were conducted on gas-tungsten-arc weldments. The strain ranges and the resulting alternating, which produced fatigue lives between 10/sup 3/ and 10/sup 6/ cycles, were determined in the test program. Comparisons are presented with published data obtained using the rotating-beam test method. A discussion is also presented on the effect of the grain size on fatigue strength.

  9. Low-cycle fatigue of thermal-barrier coatings at 982 deg C

    NASA Technical Reports Server (NTRS)

    Kaufman, A.; Liebert, C. H.; Nachtigall, A. J.

    1978-01-01

    The low-cycle fatigue lives of ZrO2-NiCrAlY and Al2O3-ZrO2-NiCrAlY thermal-barrier coatings in air at 982 C were determined from cyclic flexural tests of coated TAZ-8A strips. Strains were computed as a function of specimen displacements from a nonlinear, three-dimensional stress analysis program. Fatigue resistances of thermal-barrier coatings applied to the strips were compared with those of uncoated and NiCrAlY-coated strips. The results indicate that ZrO2 is about four times greater in fatigue life than TAZ-8A at 982 C, that ZrO2 would probably retain that fatigue strength up to 1316 C, and that adding an outer coat of Al2O3 to ZrO2 is neither beneficial nor detrimental to fatigue resistance.

  10. Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

    PubMed

    Iijima, Toshihiko; Homma, Shinya; Sekine, Hideshi; Sasaki, Hodaka; Yajima, Yasutomo; Yoshinari, Masao

    2013-01-01

    Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10(6) cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material. PMID:23538763

  11. Modeling the Tensile Strength of Carbon Fiber - Reinforced Ceramic - Matrix Composites Under Multiple Fatigue Loading

    NASA Astrophysics Data System (ADS)

    Li, Longbiao

    2016-06-01

    An analytical method has been developed to investigate the effect of interface wear on the tensile strength of carbon fiber - reinforced ceramic - matrix composites (CMCs) under multiple fatigue loading. The Budiansky - Hutchinson - Evans shear - lag model was used to describe the micro stress field of the damaged composite considering fibers failure and the difference existed in the new and original interface debonded region. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The interface shear stress degradation model and fibers strength degradation model have been adopted to analyze the interface wear effect on the tensile strength of the composite subjected to multiple fatigue loading. Under tensile loading, the fibers failure probabilities were determined by combining the interface wear model and fibers failure model based on the assumption that the fiber strength is subjected to two - parameter Weibull distribution and the loads carried by broken and intact fibers satisfy the Global Load Sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength corresponding to multiple fatigue peak stress levels and different cycle number have been analyzed.

  12. Modeling the Tensile Strength of Carbon Fiber - Reinforced Ceramic - Matrix Composites Under Multiple Fatigue Loading

    NASA Astrophysics Data System (ADS)

    Li, Longbiao

    2015-09-01

    An analytical method has been developed to investigate the effect of interface wear on the tensile strength of carbon fiber - reinforced ceramic - matrix composites (CMCs) under multiple fatigue loading. The Budiansky - Hutchinson - Evans shear - lag model was used to describe the micro stress field of the damaged composite considering fibers failure and the difference existed in the new and original interface debonded region. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The interface shear stress degradation model and fibers strength degradation model have been adopted to analyze the interface wear effect on the tensile strength of the composite subjected to multiple fatigue loading. Under tensile loading, the fibers failure probabilities were determined by combining the interface wear model and fibers failure model based on the assumption that the fiber strength is subjected to two - parameter Weibull distribution and the loads carried by broken and intact fibers satisfy the Global Load Sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength corresponding to multiple fatigue peak stress levels and different cycle number have been analyzed.

  13. Very high cycle fatigue behavior of SAE52100 bearing steel by ultrasonic nanocrystalline surface modification.

    PubMed

    Cho, In Shik; He, Yinsheng; Li, Kejian; Oh, Joo Yeon; Shin, Keesam; Lee, Chang Soon; Park, In Gyu

    2014-11-01

    In this paper, the SAE52100 bearing steel contained large quantities of cementite dispersed in ferrite matrix was subjected to the ultrasonic nanocrystalline surface modification (UNSM) treatment that aims for the extension of fatigue life. The microstructure and fatigue life of the untreated and treated specimens were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and a developed ultra-high cycle fatigue test (UFT). After UNSM treatment, the coarse ferrite grains (- 10 μm) were refined to nanosize (- 200 nm), therefore, nanostructured surface layers were fabricated. Meanwhile, in the deformed layer, the number density and area fraction of cementite were increased up to - 400% and - 550%, respectively, which increased with the decrease in depth from the topmost treated surface. The improvement of hardness (from 200 Hv to 280 Hv) and high cycles fatigue strength by - 10% were considered the contribution of the developed nanostructure in the UNSM treated specimen. PMID:25958512

  14. Anomolous Fatigue Crack Growth Phenomena in High-Strength Steel

    NASA Technical Reports Server (NTRS)

    Forth, Scott C.; James, Mark A.; Johnston, William M., Jr.; Newman, James C., Jr.

    2004-01-01

    The growth of a fatigue crack through a material is the result of a complex interaction between the applied loading, component geometry, three-dimensional constraint, load history, environment, material microstructure and several other factors. Previous studies have developed experimental and computational methods to relate the fatigue crack growth rate to many of the above conditions, with the intent of discovering some fundamental material response, i.e. crack growth rate as a function of something. Currently, the technical community uses the stress intensity factor solution as a simplistic means to relate fatigue crack growth rate to loading, geometry and all other variables. The stress intensity factor solution is a very simple linear-elastic representation of the continuum mechanics portion of crack growth. In this paper, the authors present fatigue crack growth rate data for two different high strength steel alloys generated using standard methods. The steels exhibit behaviour that appears unexplainable, compared to an aluminium alloy presented as a baseline for comparison, using the stress intensity factor solution.

  15. Fatigue strength of a single lap joint SPR-bonded

    SciTech Connect

    Di Franco, G.; Fratini, L.; Pasta, A.

    2011-05-04

    In the last years, hybrid joints, meaning with this the joints which consist in combining a traditional mechanical joint to a layer of adhesive, are gradually attracting the attention of various sectors of the construction of vehicles and transportation industries, for their better performance compared to just mechanical joints (self-piercing riveting SPR, riveting, and so on) or just to bonded joints.The paper investigates the fatigue behavior of a single lap joint self-piercing riveted (SPR) and bonded throughout fatigue tests. The considered geometric configuration allowed the use of two rivets placed longitudinally; an epoxy resin was used as adhesive. In the first part of the work static characterization of the joints was carried out through tensile tests. Then fatigue tests were made with the application of different levels of load. The fatigue curves were also obtained at the varying the distance between the two rivets in order to better assess the joint strength for a given length of overlap.

  16. Crack tip field and fatigue crack growth in general yielding and low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Minzhong, Z.; Liu, H. W.

    1984-01-01

    Fatigue life consists of crack nucleation and crack propagation periods. Fatigue crack nucleation period is shorter relative to the propagation period at higher stresses. Crack nucleation period of low cycle fatigue might even be shortened by material and fabrication defects and by environmental attack. In these cases, fatigue life is largely crack propagation period. The characteristic crack tip field was studied by the finite element method, and the crack tip field is related to the far field parameters: the deformation work density, and the product of applied stress and applied strain. The cyclic carck growth rates in specimens in general yielding as measured by Solomon are analyzed in terms of J-integral. A generalized crack behavior in terms of delta is developed. The relations between J and the far field parameters and the relation for the general cyclic crack growth behavior are used to analyze fatigue lives of specimens under general-yielding cyclic-load. Fatigue life is related to the applied stress and strain ranges, the deformation work density, crack nucleus size, fracture toughness, fatigue crack growth threshold, Young's modulus, and the cyclic yield stress and strain. The fatigue lives of two aluminum alloys correlate well with the deformation work density as depicted by the derived theory. The general relation is reduced to Coffin-Manson low cycle fatigue law in the high strain region.

  17. Low cycle fatigue behavior of aluminum/stainless steel composites

    NASA Technical Reports Server (NTRS)

    Bhagat, R. B.

    1983-01-01

    Composites consisting of an aluminum matrix reinforced with various volume fractions of stainless steel wire were fabricated by hot die pressing under various conditions of temperature, time, and pressure. The composites were tested in plane bending to complete fracture under cycle loading, and the results were analyzed on a computer to obtain a statistically valid mathematical relationship between the low-cycle fatigue life and the fiber volume fraction of the composite. The fractured surfaces of the composites were examined by scanning electron microscopy to identify the characteristic features of fatigue damage. Fatigue damage mechanisms are proposed and discussed.

  18. The effect of weld porosity on the cryogenic fatigue strength of ELI grade Ti-5Al-2.5Sn

    NASA Technical Reports Server (NTRS)

    Rogers, P. R.; Lambdin, R. C.; Fox, D. E.

    1992-01-01

    The effect of weld porosity on the fatigue strength of ELI grade Ti-5Al-2.5Sn at cryogenic temperature was determined. A series of high cycle fatigue (HCF) and tensile tests were performed at -320 F on specimens made from welded sheets of the material. All specimens were tested with weld beads intact and some amount of weld offset. Specimens containing porosity and control specimens containing no porosity were tested. Results indicate that for the weld configuration tested, the fatigue life of the material is not affected by the presence of spherical embedded pores.

  19. An Investigation of High-Cycle Fatigue Models for Metallic Structures Exhibiting Snap-Through Response

    NASA Technical Reports Server (NTRS)

    Przekop, Adam; Rizzi, Stephen A.; Sweitzer, Karl A.

    2007-01-01

    A study is undertaken to develop a methodology for determining the suitability of various high-cycle fatigue models for metallic structures subjected to combined thermal-acoustic loadings. Two features of this problem differentiate it from the fatigue of structures subject to acoustic loading alone. Potentially large mean stresses associated with the thermally pre- and post-buckled states require models capable of handling those conditions. Snap-through motion between multiple post-buckled equilibrium positions introduces very high alternating stress. The thermal-acoustic time history response of a clamped aluminum beam structure with geometric and material nonlinearities is determined via numerical simulation. A cumulative damage model is employed using a rainflow cycle counting scheme and fatigue estimates are made for 2024-T3 aluminum using various non-zero mean fatigue models, including Walker, Morrow, Morrow with true fracture strength, and MMPDS. A baseline zero-mean model is additionally considered. It is shown that for this material, the Walker model produces the most conservative fatigue estimates when the stress response has a tensile mean introduced by geometric nonlinearity, but remains in the linear elastic range. However, when the loading level is sufficiently high to produce plasticity, the response becomes more fully reversed and the baseline, Morrow, and Morrow with true fracture strength models produce the most conservative fatigue estimates.

  20. High cycle fatigue behavior of implant Ti-6Al-4V in air and simulated body fluid.

    PubMed

    Liu, Yong-jie; Cui, Shi-ming; He, Chao; Li, Jiu-kai; Wang, Qing-yuan

    2014-01-01

    Ti-6Al-4V implants that function as artificial joints are usually subjected to long-term cyclic loading. To study long-term fatigue behaviors of implant Ti-6Al-4V in vitro and in vivo conditions exceeding 107 cycles, constant stress amplitude fatigue experiments were carried out at ultrasonic frequency (20 kHz) with two different surface conditions (ground and polished) in ambient air and in a simulated body fluid. The initiation mechanisms of fatigue cracks were investigated with scanning electron microscopy. Improvement of fatigue strength is pronounced for polished specimens below 106 cycles in ambient air since fatigue cracks are initiated from surfaces of specimens. While the cycles exceed 106, surface conditions have no effect on fatigue behaviors because the defects located within the specimens become favorable sites for crack initiation. The endurance limit at 108 cycles of polished Ti-6Al-4V specimens decreases by 7% if it is cycled in simulated body fluid instead of ambient air. Fracture surfaces show that fatigue failure is initiated from surfaces in simulated body fluid. Surface improvement has a beneficial effect on fatigue behaviors of Ti-6Al-4V at high stress amplitudes. The fatigue properties of Ti-6Al-4V deteriorate and the mean endurance limits decrease significantly in simulated body fluid. PMID:24211906

  1. Strength distribution of fatigue crack initiation sites in an Al-Li alloy

    NASA Astrophysics Data System (ADS)

    Zhai, T.

    2006-10-01

    The stress-number of cycles to failure (S-N) curves were measured along the short-transverse (S) and rolling (L) directions of a hot-cross-rolled AA 8090 Al-Li alloy plate (45-mm thick). The alloy was solution heat treated, quenched in water, strained by 6 pct, and peak aged. Fatigue tests were carried out in four-point bend at room temperature, 20 Hz, R=0.1, in air. It was found that the fatigue limits in the S and L directions were 147 and 197 MPa, respectively. The crack population on the surface of a sample at failure increased with the applied stress level and was found to be a Weibull function of the applied maximum stress in this alloy. The strength distribution of fatigue weakest links, where cracks were initiated, was derived from the Weibull function determined by the experimental data. The fatigue weakest-link density was defined as the crack population per unit area at a stress level close to the ultimate tensile stress and can be regarded as a materials property. The density and strength distribution of fatigue weakest links were found to be markedly different between the L and S directions, accounting for the difference in fatigue limit between the directions in this alloy. They were also found to be different between S-L and S-T samples, and between L-T and L-S samples of this alloy, which could not be revealed by the corresponding S-N curves measured. These differences were due to the anisotropy of the microstructures in different directions in this alloy.

  2. Fatigue crack growth and low cycle fatigue of two nickel base superalloys

    NASA Technical Reports Server (NTRS)

    Stoloff, N. S.; Duquette, D. J.; Choe, S. J.; Golwalkar, S.

    1983-01-01

    The fatigue crack growth and low cycle fatigue behavior of two P/M superalloys, Rene 95 and Astroloy, in the hot isostatically pressed (HIP) condition, was determined. Test variables included frequency, temperature, environment, and hold times at peak tensile loads (or strains). Crack initiation sites were identified in both alloys. Crack growth rates were shown to increase in argon with decreasing frequency or with the imposition of hold times. This behavior was attributed to the effect of oxygen in the argon. Auger analyses were performed on oxide films formed in argon. Low cycle fatigue lives also were degraded by tensile hold, contrary to previous reports in the literature. The role of environment in low cycle fatigue behavior is discussed.

  3. Fatigue strength of common tibial intramedullary nail distal locking screws

    PubMed Central

    Griffin, Lanny V; Harris, Robert M; Zubak, Joseph J

    2009-01-01

    Background Premature failure of either the nail and/or locking screws with unstable fracture patterns may lead to angulation, shortening, malunion, and IM nail migration. Up to thirty percent of all unreamed nail locking screws can break after initial weight bearing is allowed at 8–10 weeks if union has not occurred. The primary problem this presents is hardware removal during revision surgery. The purposes of our study was to evaluate the relative fatigue resistance of distal locking screws and bolts from representative manufacturers of tibial IM nail systems, and develop a relative risk assessment of screws and materials used. Evaluations included quantitative and qualitative measures of the relative performance of these screws. Methods Fatigue tests were conducted to simulate a comminuted fracture that was treated by IM nailing assuming that all load was carried by the screws. Each screw type was tested ten times in a single screw configuration. One screw type was tested an additional ten times in a two-screw parallel configuration. Fatigue tests were performed using a servohydraulic materials testing system and custom fixturing that simulated screws placed in the distal region of an appropriately sized tibial IM nail. Fatigue loads were estimated based on a seventy-five kilogram individual at full weight bearing. The test duration was one million cycles (roughly one year), or screw fracture, whichever occurred first. Failure analysis of a representative sample of titanium alloy and stainless steel screws included scanning electron microscopy (SEM) and quantitative metallography. Results The average fatigue life of a single screw with a diameter of 4.0 mm was 1200 cycles, which would correspond roughly to half a day of full weight bearing. Single screws with a diameter of 4.5 mm or larger have approximately a 50 percent probability of withstanding a week of weight bearing, whereas a single 5.0 mm diameter screw has greater than 90 percent probability of

  4. Low cycle dwell-time fatigue in Ti-6242

    SciTech Connect

    Kassner, M.E.; Kosaka, Y.; Hall, J.A.

    1999-09-01

    Ambient-temperature, low-cycle dwell-time and conventional low-cycle fatigue tests were performed on Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242). Specimens were solution annealed at various temperatures below the beta transus to control the volume fraction of primary alpha phase and were subsequently shot-peened. The influence of the changes in primary alpha phase on the low-cycle dwell-time fatigue life (LCDF) were determined and compared to the conventional low-cycle fatigue (LCF) properties of the alloy. A 120-second dwell significantly decreased the number of cycles to failure, although the factor decrease of LCF from a dwell, in general, diminished with decreasing stress. The Increasing primary alpha phase associated with lower solution temperatures appears to increase susceptibility to low-cycle dwell-time fatigue. It also appears that the susceptibility to dwell fatigue may be associated with ambient-temperature, time-dependent, cyclic (creep) plasticity.

  5. On high-cycle fatigue of 316L stents.

    PubMed

    Barrera, Olga; Makradi, Ahmed; Abbadi, Mohammed; Azaouzi, Mohamed; Belouettar, Salim

    2014-01-01

    This paper deals with fatigue life prediction of 316L stainless steel cardiac stents. Stents are biomedical devices used to reopen narrowed vessels. Fatigue life is dominated by the cyclic loading due to the systolic and diastolic pressure and the design against premature mechanical failure is of extreme importance. Here, a life assessment approach based on the Dang Van high cycle fatigue criterion and on finite element analysis is applied to explore the fatigue reliability of 316L stents subjected to multiaxial fatigue loading. A finite element analysis of the stent vessel subjected to cyclic pressure is performed to carry out fluctuating stresses and strain at some critical elements of the stent where cracks or complete fracture may occur. The obtained results show that the loading path of the analysed stent subjected to a pulsatile load pressure is located in the safe region concerning infinite lifetime. PMID:22587434

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

    NASA Technical Reports Server (NTRS)

    Yeh, H. Y.

    1973-01-01

    The cumulative damage of aluminium alloys with different yield strength and various ductility due to seismic loads was studied. The responses of an idealized beam with a centered mass at one end and fixed at the other end to El Centro's and Taft's earthquakes are computed by assuming that the alloys are perfectly elastoplastic materials and by using numerical technique. Consequently, the corresponding residual plastic strain can be obtained from the stress-strain relationship. The revised Palmgren-Miner cumulative damage theorem is utilized to calculate the fatigue damage. The numerical results show that in certain cases, the high ductility materials are more resistant to seismic loads than the high yield strength materials. The results also show that if a structure collapse during the earthquake, the collapse always occurs in the very early stage.

  7. NDE detectability of fatigue type cracks in high strength alloys

    NASA Technical Reports Server (NTRS)

    Christner, B. K.; Rummel, W. D.

    1983-01-01

    Specimens suitable for investigating the reliability of production nondestructive evaluation (NDE) to detect tightly closed fatigue cracks in high strength alloys representative of those materials used in spacecraft engine/booster construction were produced. Inconel 718 was selected as representative of nickel base alloys and Haynes 188 was selected as representative of cobalt base alloys used in this application. Cleaning procedures were developed to insure the reusability of the test specimens and a flaw detection reliability assessment of the fluorescent penetrant inspection method was performed using the test specimens produced to characterize their use for future reliability assessments and to provide additional NDE flaw detection reliability data for high strength alloys. The statistical analysis of the fluorescent penetrant inspection data was performed to determine the detection reliabilities for each inspection at a 90% probability/95% confidence level.

  8. ZERODUR®: new stress corrosion data improve strength fatigue prediction

    NASA Astrophysics Data System (ADS)

    Hartmann, Peter; Kleer, Günter; Rist, Tobias

    2015-09-01

    The extremely low thermal expansion glass ceramic ZERODUR® finds more and more applications as sophisticated light weight structures with thin ribs or as thin shells. Quite often they will be subject to higher mechanical loads such as rocket launches or modulating wobbling vibrations. Designing such structures requires calculation methods and data taking into account their long term fatigue. With brittle materials fatigue is not only given by the material itself but to a high extent also by its surface condition and the environmental media especially humidity. This work extends the latest data and information gathered on the bending strength of ZERODUR® with new results concerning its long term behavior under tensile stress. The parameter needed for prediction calculations which combines the influences of time and environmental media is the stress corrosion constant n. Results of the past differ significantly from each other. In order to obtain consistent data the stress corrosion constant has been measured with the method comparing the breakage statistical distributions at different stress increase rates. For better significance the stress increase rate was varied over four orders of magnitude from 0.004 MPa/s to 40 MPa/s. Experiments were performed under normal humidity for long term earth bound applications and under nitrogen atmosphere as equivalent to dry environment occurring for example with telescopes in deserts and also equivalent to vacuum for space applications. As shown earlier the bending strength of diamond ground surfaces of ZERODUR® can be represented with a three parameter Weibull distribution. Predictions on the long term strength change of ZERODUR® structures under tensile stress are possible with reduced uncertainty if Weibull threshold strength values are considered and more reliable stress corrosion constant data are applied.

  9. High Cycle Fatigue in the Transmission Electron Microscope.

    PubMed

    Bufford, Daniel C; Stauffer, Douglas; Mook, William M; Syed Asif, S A; Boyce, Brad L; Hattar, Khalid

    2016-08-10

    One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this study, the tension-tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were applied at frequencies from one to several hundred hertz, enabling accumulations of 10(6) cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ∼10(-12) m·cycle(-1). This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. These observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu. PMID:27351706

  10. A Decline in Solar Cycle Strength

    NASA Astrophysics Data System (ADS)

    Chapman, G. A.; de Toma, G.; Cookson, A.

    2013-12-01

    The strength of solar activity appears to be in decline over the past three solar cycles. The decline is seen in sunspot area, facular/network area and the sunspot number. In addition, cycle 24 has been unusual in that many, if not most, of the bipolar sunspot groups have had only a leader spot with no follower spot. This research was partially supported by grants from NSF and NASA. Corrected spot area from CFDT1 at the San Fernando Observatory

  11. The effects of out-of-phase biaxial-strain cycling on low-cycle fatigue.

    NASA Technical Reports Server (NTRS)

    Zamrik, S. Y.; Frishmuth, R. E.

    1973-01-01

    The effects of out-of-phase or nonsychronous straining on low-cycle fatigue was investigated. Biaxial strains were imposed on thin-walled tubular 7075-T6 aluminum specimens by tension-compression and torsion. Phase angles of 0, 30, 45, 60, and 90 deg were applied between two strains. It was found that out-of-phase cycling has an effect on the failure mode in the low-cycle-fatigue range. An analysis based on the maximum total strain in three-dimensional strain is proposed for treating 'out-of-phase' straining conditions in low-cycle fatigue.

  12. Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

    SciTech Connect

    Cabet, Celine; Carroll, Laura; Wright, Richard

    2013-10-01

    Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the Very High Temperature Nuclear Reactor (VHTR), expected to have an outlet temperature as high as 950 degrees C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanism/s and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 degrees C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens, although evidence of grain boundary cavitation was not observed. Despite the absence of grain boundary cavitation to accelerate crack propagation, the addition of a hold time at peak tensile strain was detrimental to cycle life. This suggests that creepfatigue interaction may occur by a different mechanism or that the environment may be partially responsible for accelerating failure.

  13. Strength, Fatigue, and Fracture Toughness of Ti-6Al-4V Liner from a Composite Over-Wrapped Pressure Vessel

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Lerch, Brad; Thesken, John C.; Sutter, Jim; Russell, Richard

    2008-01-01

    It was demonstrated by way of experiment that Composite Over-wrapped Pressure Vessel (COPV) Ti-6Al-4V liner material can sustain the expected service loads and cycles. The experiments were performed as part of investigations on the residual life of COPV tanks being used in Space Shuttle Orbiters. Measured properties included tensile strength, compressive strength, reversed loading cycles to simulate liner proof strains, and cyclic fatigue loading to demonstrate the ability to sustain 1000 cycles after liner buckling. The liner material came from a salvaged 40 in. Columbia (orbiter 102) tank (SN029), and tensile strength measurements were made on both boss-transition (thick) and membrane regions (thin). The average measured yield strength was 131 ksi in the boss-transition and membrane regions, in good agreement with measurements made on 1970 s vintage forged plate stock. However, Young s modulus was 17.4+/-0.3 Msi, somewhat higher than typical handbook values (approx.16 Msi). The fracture toughness, as estimated from a failed fatigue specimen, was 74 ksi/sq in, in reasonable agreement with standardized measurements made on 1970 s vintage forged plate stock. Low cycle fatigue of a buckled test specimen implied that as-imprinted liners can sustain over 4000 load cycles.

  14. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, Mechanical Fatigue, Creep and Thermal Fatigue Effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie Corinne Scheidt

    1994-01-01

    This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, creep, and thermal fatigue was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

  15. Corrosion Fatigue of High-Strength Titanium Alloys Under Different Stress Gradients

    NASA Astrophysics Data System (ADS)

    Baragetti, Sergio; Villa, Francesco

    2015-05-01

    Ti-6Al-4V is the most widely used high strength-to-mass ratio titanium alloy for advanced engineering components. Its adoption in the aerospace, maritime, automotive, and biomedical sectors is encouraged when highly stressed components with severe fatigue loading are designed. The extents of its applications expose the alloy to several aggressive environments, which can compromise its brilliant mechanical characteristics, leading to potentially catastrophic failures. Ti-6Al-4V stress-corrosion cracking and corrosion-fatigue sensitivity has been known since the material testing for pressurized tanks for Apollo missions, although detailed investigations on the effects of harsh environment in terms of maximum stress reduction have been not carried out until recent times. In the current work, recent experimental results from the authors' research group are presented, quantifying the effects of aggressive environments on Ti-6Al-4V under fatigue loading in terms of maximum stress reduction. R = 0.1 axial fatigue results in laboratory air, 3.5 wt.% NaCl solution, and CH3OH methanol solution at different concentrations are obtained for mild notched specimens ( K t = 1.18) at 2e5 cycles. R = 0.1 tests are also conducted in laboratory air, inert environment, 3.5 wt.% NaCl solution for smooth, mild and sharp notched specimens, with K t ranging from 1 to 18.65, highlighting the environmental effects for the different load conditions induced by the specimen geometry.

  16. High cycle fatigue in the transmission electron microscope

    DOE PAGESBeta

    Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.; Syed Asif, S. A.; Boyce, Brad L.; Hattar, Khalid

    2016-06-28

    One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 106 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10–12 m·cycle–1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

  17. Fatigue strength reduction factors for welds based on nondestructive examination

    SciTech Connect

    Hechmer, J.L.; Kuhn, E.J. III

    1999-02-01

    Based on the author`s hypothesis that nondestructive examination (NDE) has a major role in predicting the fatigue life of pressure vessels, a project was initiated to develop a defined relationship between NDE and fatigue strength reduction factors (FSRF). Even though a relationship should apply to both base metal and weld metal, the project was limited to weld metal because NDE for base metal is reasonably well established, whereas NDE for weld metal is more variable, depending on application. A matrix of FSRF was developed based on weld type (full penetration, partial penetration, and fillet weld) versus the NDE that is applied. The NDE methods that are included are radiographic testing (RT), ultrasonic testing (UT), magnetic particle testing (MT), dye penetrant testing (PT), and visual testing (VT). The first two methods (RT and UT) are volumetric examinations, and the remaining three are surface examinations. Seven combinations of volumetric and surface examinations were defined; thus, seven levels of FSRF are defined. Following the initial development of the project, a PVRC (Pressure Vessel Research Council) grant was obtained for the purpose of having a broad review. The report (Hechmer, 1998) has been accepted by PVRC. This paper presents the final matrix, the basis for the FSRF, and key definitions for accurate application of the FSRF matrix. A substantial amount of additional information is presented in the PVRC report (Hechmer, 1998).

  18. Effects of stress concentration on the fatigue strength of 7003-T5 aluminum alloy butt joints with weld reinforcement

    NASA Astrophysics Data System (ADS)

    Zhu, Zongtao; Li, Yuanxing; Zhang, Mingyue; Hui, Chen

    2015-03-01

    7003-T5 Aluminum (Al) alloy plates with a thickness of 5 mm are welded by gas metal arc welding (GMAW) method in this work. In order to investigate the influence of stress concentration introduced by weld reinforcement on fatigue strength, the stress concentration factor of the butt joint is calculated. Microscopic and X-ray techniques were utilized to make sure there are no weld defects with large size in butt weld, which can induce extra stress concentration. The cyclic stress - number of cycles to failure (S-N) curves of the joints with and without the welder were obtained by fatigue testing, and the results show that the fatigue strength of 7003-T5 Al alloy butt joints with the weld reinforcement is 50 MPa, which is only 45% of the joints without the weld reinforcement. Fracture surface observation indicated that the fatigue source and propagation are dissimilar for the specimens with and without the welder due to the stress concentration at the weld root. The stress concentration with a factor of 1.7 has great effect on the fatigue strength, but little influence on the tensile strength.

  19. Effects of thermal fatigue on shear punch strength of tooth-colored restoratives

    PubMed Central

    Melody, Fam Mei Shi; U-Jin, Yap Adrian; Natalie, Tan Wei Min; Elizabeth, Tay Wan Ling; Chien, Jessica Yeo Siu

    2016-01-01

    Aims: This study investigated the effect of thermal fatigue on the shear strength of a range of tooth-colored restorative materials including giomers, zirconia-reinforced glass ionomer cement (GIC), nano-particle resin-modified GIC, highly viscous GICs, and composite resin. Materials and Methods: Twenty specimens of each material were fabricated in standardized washers (17 mm outer diameter, 9 mm internal diameter, 1 mm thick). The specimens were cured, stored in 100% humidity at 37.5°C for 24 h, and randomly divided into two groups of 10. Group A specimens were nonthermocycled (NT) and stored in distilled water at 37°C for 168 h. Group B specimens were thermocycled (TC) for 10,000 cycles (168 h) with baths X, Y, and Z adjusted to 35°C, 15°C, and 45°C, respectively. Each cycle had dwell times of 28 s in X, and 2s in Y/Z in the order XYXZ. Specimens then underwent shear punch testing at a crosshead speed of 0.5 mm/min with a 2 kN load cell. Statistical analysis of shear strength was done using t-test and two-way ANOVA/Scheffe's post hoc test at significance level P < 0.05. Results: The effect of thermal fatigue on shear strength was material dependent. Except for the “sculptable” giomer (Beautifil II) and a highly viscous GIC (Fuji IX GP Fast), no significant differences in shear strength were generally observed between the NT and TC groups. For both groups, the composite resin (Filtek Z250XT) had the highest shear strength while the zirconia-reinforced (zirconomer) and a highly viscous GIC (Ketac Molar Quick) had the lowest. Conclusions: The effect of thermocycling on shear strength was material dependent. Thermal fatigue, however, did not significantly influence the shear strength of most materials assessed. The “sculptable” composite and giomer were significantly stronger than the other materials evaluated. Shear strength of the “flowable” injectable hybrid giomer was intermediate between the composite and GICs. PMID:27563182

  20. The effect of low cycle fatigue cracks and loading history on high cycle fatigue threshold

    NASA Astrophysics Data System (ADS)

    Moshier, Monty Allen

    High cycle fatigue (HCF) has been of great concern of late in light of the many HCF gas turbine engine failures experienced by the U.S. Air Force. Due to the high frequency, failures occur rapidly when components sustain damage from other sources. Low cycle fatigue (LCF) can initiate cracks that produce such damage. This study investigates the HCF threshold of Ti-6A1-4V when naturally initiated small surface cracks (2a = 25 mum--600 mum) are present. Small surface cracks are initiated in notched specimens using two different LCF loading histories at room temperature and 10 Hz. Direct current potential difference (DCPD) is used to detect crack initiation. Surface crack measurements are made using a scanning electron microscope prior to HCF testing. Heat tinting prior to HCF testing is used to mark the crack front to allow for post fracture crack measurements. HCF thresholds at R = 0.1 and R = 0.5 are determined for each specimen using step loading at room temperature and 600 Hz. Additionally, the HCF threshold is measured at R = 0.1 for specimens with small cracks that have been stress relief annealed to eliminate residual stresses and load history. Long crack thresholds are determined using a similar step loading procedure at R = 0.1 and R = 0.5 for specimens which have been precracked using a range of Kmax. Long crack threshold measurements are also determined for specimens which have been precracked using a range of Kmax, but stress relief annealed prior to testing. Comparisons show that HCF threshold measurements, when naturally initiated small cracks are present, are dependent on the load histories that are used to initiate the cracks. Further comparisons show that the measured small crack thresholds follow similar trends for load history effects which occur in the long crack threshold data. Additionally, it is found that thresholds can be measured free of load history effects by using a stress relief annealing process after the precracking and prior to the

  1. Low- cycle fatigue behavior of polycrystalline nial at 1000 k

    NASA Astrophysics Data System (ADS)

    Lerch, B. A.; Noebe, R. D.

    1994-02-01

    The low-cycle fatigue behavior of polycrystalline NiAl was determined at 1000 K, a temperature above the monotonic brittle-to-ductile transition temperature (BDTT). Fully reversed, plastic strain-controlled fatigue tests were conducted on B2 intermetallic samples prepared by two fab-rication techniques: hot isostatic pressing (HIP) of prealloyed powders and extrusion of vacuum induction-melted [cast plus extruded (C+E)] castings. At 1000 K, in an air environment both the hot-isostatically pressed (“hipped”) and C + E samples cyclically softened throughout most of their fatigue lives, though the absolute change in stress was no greater than about 35 MPa. At this temperature, samples were insensitive to processing defects, which were a source of failure initiation in room-temperature tests. The processing method had a small effect on fatigue life; the lives of the hipped samples were about a factor of 3 shorter than the fatigue lives of the C+E NiAl. The C+E material also underwent dynamic grain growth during testing, while the hipped NiAl maintained a constant grain size. Stable fatigue-crack growth in both materials was intergranular in nature, while final fracture by tensile overload occurred by transgranular cleavage. However, at plastic strain ranges below 0.3 pct, the fatigue lives of the hipped NiAl were controlled by intergranular cavitation and creep processes such that the fatigue lives were shorter than anticipated. Finally, hipped samples tested in vacuum had a factor of 3 longer life than specimens tested in air. A comparison of NiAl to typical superalloys (which it may replace) showed that NiAl exhibited a superior fatigue life on a plastic strain basis but was inferior to most superalloys on a stress basis.

  2. Probabilistic Simulation for Combined Cycle Fatigue in Composites

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2010-01-01

    A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multifactor interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  3. The influence of cycle time on shoulder fatigue responses for a fixed total overhead workload.

    PubMed

    Dickerson, Clark R; Meszaros, Kimberly A; Cudlip, Alan C; Chopp-Hurley, Jaclyn N; Langenderfer, Joseph E

    2015-08-20

    The relationship between overhead work and musculoskeletal health depends on multiple task and individual factors. Knowledge gaps persist, despite examination of many of these factors individually and in combination. This investigation targeted task variation, as parameterized by cycle time within a fixed overall workload. Participants performed an intermittent overhead pressing task with four different cycle time conditions while overall workload and duty cycle was held constant. Several manifestations of fatigue were monitored during task performance. Endurance time was influenced by cycle time with shorter cycle times having endurance times up to 25% higher than longer cycle times. Surface electromyography (sEMG) results were mixed, with two muscles demonstrating amplitude increases (middle deltoid and upper trapezius) that varied with cycle time. sEMG frequency was not influenced by cycle time for any muscle monitored, despite decreases for several cycle times. Trends existed for the influence of cycle time on time-varying reported discomfort (p=0.056) and static strength (p=0.055); large effect sizes were present (ηp(2)=0.31 and 0.27, respectively). The equivocal association of fatigue indicators and cycle time is analogous to the influence of other factors implicated in overhead work musculoskeletal risk, and probabilistic modeling offers a compelling avenue for integration of the known variation in the many factors that combine to inform this risk. PMID:26117074

  4. Microstructural Influences on Very-High-Cycle Fatigue-Crack Initiation in Ti-6246

    NASA Astrophysics Data System (ADS)

    Szczepanski, C. J.; Jha, S. K.; Larsen, J. M.; Jones, J. W.

    2008-12-01

    The fatigue behavior of an alpha + beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, has been characterized in the very-high-cycle fatigue (VHCF) regime using ultrasonic-fatigue (20 kHz) techniques. Stress levels ( σ max) of 40 to 60 pct of the yield strength of this alloy have been examined. Fatigue lifetimes in the range of 106 to 109 cycles are observed, and fatigue cracks initiate from both surface and subsurface sites. This study examines the mechanisms of fatigue-crack formation by quantifying critical microstructural features observed in the fatigue-crack initiation region. The fracture surface near the fatigue-crack-initiation site was crystallographic in nature. Facets, which result from the fracture of primary alpha ( α p ) grains, are associated with the crack-initiation process. The α p grains that form facets are typically larger in size than average. The spatial distribution of α p grains relative to each other observed near the initiation site did not correlate with fatigue life. Furthermore, the spatial distribution of α p grains did not provide a suitable means for discerning crack-initiation sites from randomly selected nominal areas. Stereofractography measurements have shown that the facets observed at or near the initiation sites are oriented for high shear stress; i.e., they are oriented close to 45 deg with respect to the loading axis. Furthermore, a large majority of the grains and laths near the site of crack initiation are preferentially oriented for either basal or prism slip, suggesting that regions where α p grains and α laths have similar crystallographic orientations favor crack initiation. Microtextured regions with favorable and similar orientations of α p grains and the lath α are believed to promote cyclic-strain accumulation by basal and prism slip. Orientation imaging microscopy (OIM) indicates that these facets form on the basal plane of α p grains. The absence of a significant role of spatial clustering of α p grains

  5. PO2 Cycling Reduces Diaphragm Fatigue by Attenuating ROS Formation

    PubMed Central

    Zuo, Li; Diaz, Philip T.; Chien, Michael T.; Roberts, William J.; Kishek, Juliana; Best, Thomas M.; Wagner, Peter D.

    2014-01-01

    Prolonged muscle exposure to low PO2 conditions may cause oxidative stress resulting in severe muscular injuries. We hypothesize that PO2 cycling preconditioning, which involves brief cycles of diaphragmatic muscle exposure to a low oxygen level (40 Torr) followed by a high oxygen level (550 Torr), can reduce intracellular reactive oxygen species (ROS) as well as attenuate muscle fatigue in mouse diaphragm under low PO2. Accordingly, dihydrofluorescein (a fluorescent probe) was used to monitor muscular ROS production in real time with confocal microscopy during a lower PO2 condition. In the control group with no PO2 cycling, intracellular ROS formation did not appear during the first 15 min of the low PO2 period. However, after 20 min of low PO2, ROS levels increased significantly by ∼30% compared to baseline, and this increase continued until the end of the 30 min low PO2 condition. Conversely, muscles treated with PO2 cycling showed a complete absence of enhanced fluorescence emission throughout the entire low PO2 period. Furthermore, PO2 cycling-treated diaphragm exhibited increased fatigue resistance during prolonged low PO2 period compared to control. Thus, our data suggest that PO2 cycling mitigates diaphragm fatigue during prolonged low PO2. Although the exact mechanism for this protection remains to be elucidated, it is likely that through limiting excessive ROS levels, PO2 cycling initiates ROS-related antioxidant defenses. PMID:25299212

  6. Fatigue Performance of Powder Metallurgy (PM) Ti-6Al-4V Alloy: A Critical Analysis of Current Fatigue Data and Metallurgical Approaches for Improving Fatigue Strength

    NASA Astrophysics Data System (ADS)

    Cao, Fei; Ravi Chandran, K. S.

    2016-03-01

    A comprehensive assessment of fatigue performance of powder metallurgy (PM) Ti-6Al-4V alloy, manufactured using various powder-based processing approaches to-date, is performed in this work. The focus is on PM processes that use either blended element (BE) or pre-alloyed (PA) powder as feedstock. Porosity and the microstructure condition have been found to be the two most dominant material variables that control the fatigue strength. The evaluation reveals that the fatigue performance of PM Ti-6Al-4V, in the as-sintered state, is far lower than that in the wrought condition. This is largely caused by residual porosity, even if it is present in small amounts, or, by the coarse lamellar colony microstructure. The fatigue strength is significantly improved by the closure of pores, and it approaches the levels of wrought Ti-6Al-4V alloys, after hot-isostatic-pressing (HIPing). Further thermo-mechanical and heat treatments lead to additional increases in fatigue strength-in one case, a high fatigue strength level, exceeding that of the mill-annealed condition, was achieved. The work identifies the powder, process and microstructure improvements that are necessary for achieving high fatigue strength in powder metallurgical Ti-6Al-4V alloys in order for them to effectively compete with wrought forms. The present findings, gathered from the traditional titanium powder metallurgy, are also directly applicable to additively manufactured titanium, because of the similarities in pores, defects, and microstructures between the two manufacturing processes.

  7. Cyclic fatigue analysis of rocket thrust chambers. Volume 1: OFHC copper chamber low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Miller, R. W.

    1974-01-01

    A three-dimensional finite element elasto-plastic strain analysis was performed for the throat section of a regeneratively cooled rocket combustion chamber. The analysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the chamber operating cycle. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen combustion chamber which was fatigue tested to failure. The computed strain range at typical chamber operating conditions was used in conjunction with oxygen-free, high-conductivity (OHFC) copper isothermal fatigue test data to predict chamber low-cycle fatigue life.

  8. Isometric quadriceps strength determines sailing performance and neuromuscular fatigue during an upwind sailing emulation.

    PubMed

    Bourgois, Jan G; Callewaert, Margot; Celie, Bert; De Clercq, Dirk; Boone, Jan

    2016-01-01

    This study investigates the physiological responses to upwind sailing on a laser emulation ergometer and analyses the components of the physical profile that determine the physiological responses related to sailing level. Ten male high-level laser sailors performed an upwind sailing test, incremental cycling test and quadriceps strength test. During the upwind sailing test, heart rate (HR), oxygen uptake, ventilation, respiratory exchange ratio, rating of perceived exertion (RPE) and lactate concentration were measured, combined with near-infrared spectroscopy (NIRS) and electromyography (EMG) registration of the M. Vastus lateralis. Repeated measures ANOVA showed for the cardio-respiratory, metabolic and muscles responses (mean power frequency [MPF], root mean square [RMS], deoxy[Hb+Mb]) during the upwind sailing test an initial significant increase followed by a stabilisation, despite a constant increase in RPE. Stepwise regression analysis showed that better sailing level was for 46.5% predicted by lower MPF decrease. Lower MPF decrease was for 57.8% predicted by a higher maximal isometric quadriceps strength. In conclusion, this study indicates that higher sailing level was mainly determined by a lower rate of neuromuscular fatigue during the upwind sailing test (as indicated by MPF decrease). Additionally, the level of neuromuscular fatigue was mainly determined by higher maximal isometric quadriceps strength stressing the importance of resistance training in the planning of training. PMID:26323461

  9. Surface-finish effects on the high-cycle fatigue of Alloy 718

    SciTech Connect

    Korth, G.E.

    1981-06-01

    Alloy 718 us a precipitation-hardening nickel-base superalloy that is being specified for various components for liquid-meal fast breeder reactors (LMFBRs). This alloy maintains high strength at elevated temperatures making it a desirable structural material. But the property that justifies most LMFBR applications is the alloy's resistance to thermal striping damage due to its high fatigue endurance strength. Thermal striping is a high-cycle fatigue phenomenon caused by thermal stresses from the fluctuating mixing action of sodium streams of differing temperatures impinging on the metal surfaces. Most of the design data is generated from laboratory fatigue specimens with carefully controlled surface finishes prepared with a low-stress grind and buffed to a surface finish 8--12 in. Since Alloy 718 has been shown to be quite notch sensitive under cyclic loading, the detrimental effect on the high-cycle fatigue properties caused by shop surface finishes of actual components has been questioned. This report examines some of the surface finishes that could be produced in a commercial shop on an actual component.

  10. High and low-cycle fatigue behavior of prestressed concrete in offshore structures

    SciTech Connect

    Gerwick, B.C.; Venuti, W.J.

    1980-03-01

    Although concrete does suffer progressive loss of strength with increasing number of cycles, a comparison of the Woehler curves with the probable distribution of compressive stresses during a service life in an environment such as the North Sea shows extremely low cumulative usage at the high-cycle end of the spectrum. However, significant damage can occur at the low-cycle, high-amplitude end. Repeated excursions of submerged concrete into the crack opening range leads to pumping of water in and out of the crack and hydraulic wedging, leading to splitting of the concrete. Cracking subcects the reinforcing and prestressing steel to cyclic tension. Loss of bond ensues and may lead to eventual fatigue failure. Adequate endurance can be ensured by prestressing, so as to avoid a large number of cycles extending into the crack opening range, and by the provision of adequate percentages of steel across the section plus transverse and confining steel. For the typical concrete sea structure, high-cycle, low-amplitude, cumulative fatigue is not a significant problem. However low-cycle, high-amplitude fatigue requires consideration.

  11. Muscle Fiber Type Composition and Knee Extension Isometric Strength Fatigue Patterns in Power- and Endurance-Trained Males.

    ERIC Educational Resources Information Center

    Kroll, Walter; And Others

    1980-01-01

    There is a degree of uniqueness in fatigue patterns, particularly between different levels of absolute maximum strength. Caution should be used when analyzing fatigue curves among subjects with unspecified strength levels. (CJ)

  12. Thermal Cycling on Fatigue Failure of the Plutonium Vitrification Melter

    SciTech Connect

    Jordan, Jeffrey; Gorczyca, Jennifer

    2009-02-11

    One method for disposition of excess plutonium is vitrification into cylindrical wasteforms. Due to the hazards of working with plutonium, the vitrification process must be carried out remotely in a shielded environment. Thus, the equipment must be easily maintained. With their simple design, induction melters satisfy this criterion, making them ideal candidates for plutonium vitrification. However, due to repeated heating and cooling cycles and differences in coefficients of thermal expansion of contacting materials fatigue failure of the induction melter is of concern. Due to the cost of the melter, the number of cycles to failure is critical. This paper presents a method for determining the cycles to failure for an induction melter by using the results from thermal and structural analyses as input to a fatigue failure model.

  13. Microstructure, Mechanical, and Fatigue Strength of Ti-54M Processed by Rotary Swaging

    NASA Astrophysics Data System (ADS)

    Al-Khazraji, Hasan; El-Danaf, Ehab; Wollmann, Manfred; Wagner, Lothar

    2015-05-01

    TIMETAL 54M is a newly developed (α + β) titanium alloy with nominal composition Ti-5Al-4V-0.6Mo-0.4Fe. The alloy can provide a cost benefit over Ti-6Al-4V due to improved machinability and formability. In the present work, evolution of mechanical properties in terms of tensile and hardness values is investigated as a function of deformation degrees imposed via rotary swaging (RS). Microstructure, mechanical properties, and fatigue performance of Ti-54M are investigated after severe plastic deformation by RS conducted at 850 °C and after being subjected to two different post-swaging annealing conditions. Optical microscopy and scanning electron microscopy using electron back scatter diffraction were utilized to document the evolution of the microstructure. Tensile tests were conducted to characterize mechanical properties. RS, to a true strain of 3.0, is found to lead to a marked ultrafine-grained structure of about 1 μm grain size with low content of high angle grain boundaries (HAGBs). Post-swaging heat treatment at 800 °C followed by air cooling did not change the grain size but exhibited high content of HAGBs. Post-swaging heat treatment at 940 °C followed by furnace cooling resulted in a grain size of about 5 μm and enhanced work-hardening capability and ductility, which resulted in less fatigue notch sensitivity, but at the same time lower fatigue strength at 107 cycles.

  14. A New Perspective on Fatigue Performance of Advanced High- Strength Steels (AHSS) GMAW Joints

    SciTech Connect

    Feng, Zhili; Chiang, Dr. John; Kuo, Dr. Min; Jiang, Cindy; Sang, Yan

    2008-01-01

    Weld fatigue performance is a critical aspect for application of advanced high-strength steels (AHSS) in automotive body structures. A comparative study has been conducted to evaluate the fatigue life of AHSS welds. The material studied included seven AHSS of various strength levels - DP 600, DP 780, DP 980, M130, M220, solution annealed boron and fully hardened boron steels. Two conventional steels, HSLA 590 and DR 210, were also included for baseline comparison. Lap fillet welds were made on 2-mm nominal thick sheets by the gas metal arc welding process (GMAW). Fatigue test was conducted under a number of stress levels to obtain the S/N curves of the weld joints. It was found that, unlike in the static and impact loading conditions, the fatigue performance of AHSS is not influenced by the HAZ softening in AHSS. There are appreciable differences in the fatigue lives among different AHSS. Changes in weld parameters can influence the fatigue life of the weld joints, particularly of these of higher strength AHSS. A model is developed to predict the fatigue performance of AHSS welds. The validity of the model is benchmarked with the experimental results. This model is capable to capture the effects of weld geometry and weld microstructure and strength on the fatigue performance experimentally observed. The theoretical basis and application of the newly developed fatigue modeling methodology will be discussed.

  15. Indoor mobility-related fatigue and muscle strength in nonagenarians: a prospective longitudinal study

    PubMed Central

    Ekmann, Anette; Thinggaard, Mikael; Christensen, Kaare; Avlund, Kirsten

    2014-01-01

    Background and aims Mobility-related fatigue is an important indicator of functional decline in old age, however, very little is known about fatigue in the oldest old population segment. The aim of this study was to examine the association between indoor mobility-related fatigue and muscle strength decline in nonagenarians. Methods The study is based on a prospective longitudinal study of all Danes born in 1905 and assessed in 1998, 2000 and 2003, and includes 92- to 93-year-old persons who were independent of help in basic indoor mobility at baseline (n = 1,353). Fatigue was assessed at baseline and defined as a subjective feeling of fatigue when transferring or walking indoors. The outcome measure, maximum grip strength, was measured at each measurement point. Results Grip strength declined throughout the study in participants with and without fatigue, but those reporting fatigue had significantly (P < .001) lower muscle strength during the entire study period. Longitudinal analyses indicated slightly slower decline in muscle strength among participants with fatigue compared to those without; however, observed selective dropout of participants with fatigue and poor performance at baseline needs to be considered when interpreting the results. Accordingly, participants without fatigue had significantly higher chances of being alive and having muscle strength above gender-specific median at first (RR 1.32, 95 % CI 1.07–1.58), second (RR 1.51, 1.06–1.96) and third (RR 1.39, 1.01–1.97) measurement points. Conclusions Indoor mobility-related fatigue in advanced later life should not merely be considered as an unpleasant symptom, but rather an indicator of physical impairment, and consequently declined physiological reserve. PMID:24297217

  16. Improving the High-Cycle Fatigue Lives of Fe-30Mn-0.9C Twinning-Induced Plasticity Steel Through Pre-straining

    NASA Astrophysics Data System (ADS)

    Wang, B.; Zhang, Z. J.; Shao, C. W.; Duan, Q. Q.; Pang, J. C.; Yang, H. J.; Li, X. W.; Zhang, Zhe-Feng

    2015-08-01

    The tensile properties, high-cycle fatigue properties, and microstructure evolutions during fatigue process of as-received and pre-strained Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel were investigated. It is found that the fatigue lives of the TWIP steel can be effectively improved through pre-straining, since the deformation twins induced by pre-straining could effectively lead to the improved yield strength and the homogenized deformation. This study may provide possible ways for improving the high-cycle fatigue properties of TWIP steels.

  17. High cycle fatigue behavior of Incoloy 800H in a simulated high-temperature gas-cooled reactor helium environment

    SciTech Connect

    Soo, P.; Sabatini, R.L.; Epel, L.G.; Hare, J.R. Sr.

    1980-01-01

    The current study was an attempt to evaluate the high cycle fatigue strength of Incoloy 800H in a High-Temperature Gas-Cooled Reactor helium environment containing significant quantities of moisture. As-heat-treated and thermally-aged materials were tested to determine the effects of long term corrosion in the helium test gas. Results from in-helium tests were compared to those from a standard air environment. It was found that the mechanisms of fatigue failure were very complex and involved recovery/recrystallization of the surface ground layer on the specimens, sensitization, hardness changes, oxide scale integrity, and oxidation at the tips of propagation cracks. For certain situations a corrosion-fatigue process seems to be controlling. However, for the helium environment studied, there was usually no aging or test condition for which air gave a higher fatigue strength.

  18. Muscle strength, endurance and recovery in the post-infection fatigue syndrome.

    PubMed Central

    Lloyd, A R; Hales, J P; Gandevia, S C

    1988-01-01

    A test of muscle strength and "fatiguability" was administered to 20 normal subjects and 20 patients suffering from post-infection fatigue syndrome. Maximal isometric torque for the elbow flexors was measured before, during and after an endurance sequence of 18 maximal static contractions (10 s duration, 10 s rest interval). The maximal isometric strength was not significantly different between the patient and control groups. The relative torque produced at the end of the series of 18 static contractions did not differ significantly between patients and normal subjects. In the patients with post-infection fatigue syndrome there was impairment of the recovery of peak torque at 10 minutes after the endurance sequence (p less than 0.02). The prominent subjective complaint of muscle fatigue in patients with post-infection fatigue syndrome contrasts with the relatively normal behaviour of their muscles during a controlled test of fatigue. The syndrome may include a disordered perception of achieved force and exertion. PMID:2852211

  19. Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

    SciTech Connect

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

    2013-01-01

    Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weaker regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.

  20. High Cycle Fatigue (HCF) Science and Technology Program

    NASA Astrophysics Data System (ADS)

    Bartsch, Thomas M.

    2002-05-01

    This fifth annual report of the National Turbine Engine High Cycle Fatigue (HCF) Program is a brief review of work completed, work in progress, and technical accomplishments. This program is a coordinated effort with participation by the Air Force, the Navy, and NASA. The technical efforts are organized under seven action teams Materials Damage Tolerance Research, Forced Response Prediction, Component Analysis, Instrumentation, Passive Damping Technology, Component Surface Treatments, and Engine Demonstration and two Programs Test and Evaluation, and Transitions (ENSIP).

  1. Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480

    NASA Technical Reports Server (NTRS)

    Majumdar, S.; Antolovich, S. D.; Milligan, W. W.

    1985-01-01

    PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

  2. The Rehbinder effect in iron during giga-cycle fatigue loading

    NASA Astrophysics Data System (ADS)

    Bannikov, M. V.; Naimark, O. B.

    2015-10-01

    The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.

  3. The Rehbinder effect in iron during giga-cycle fatigue loading

    SciTech Connect

    Bannikov, M. V. Naimark, O. B.

    2015-10-27

    The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.

  4. Fatigue failure of hydrogen embrittled high strength steels

    NASA Technical Reports Server (NTRS)

    Kim, Y. G.; Aleszka, J.

    1975-01-01

    Results of an experimental investigation are presented concerning the fracture behavior of cathodically charged, quenched and tempered martensitic steels under cyclic load conditions. Introduction of H2 by cathodic charging reduced fatigue life by as much as 60%. It is proposed that subsurface transverse fatigue cracks nucleate simultaneously at multiple sites, such as at microcracks, voids, or inclusions. Fatigue crack growth then occurs on planes perpendicular to the major applied stress axis in the presence of the critical combination of applied external stress and hydrogen.

  5. Low cycle fatigue behavior of polycrystalline NiAl at 300 and 1000 K

    NASA Technical Reports Server (NTRS)

    Lerch, Bradley A.; Noebe, Ronald D.

    1993-01-01

    The low cycle fatigue behavior of polycrystalline NiAl was determined at 300 and 1000 K - temperatures below and above the brittle- to-ductile transition temperature (BDTT). Fully reversed, plastic strain-controlled fatigue tests were conducted on two differently fabricated alloy samples: hot isostatically pressed (HIP'ed) prealloyed powder and hot extruded castings. HIP'ed powder (HP) samples were tested only at 1000 K, whereas the more ductile cast-and-extruded (C+E) NiAl samples were tested at both 1000 and 300 K. Plastic strain ranges of 0.06 to 0.2 percent were used. The C+E NiAl cyclically hardened until fracture, reaching stress levels approximately 60 percent greater than the ultimate tensile strength of the alloy. Compared on a strain basis, NiAl had a much longer fatigue life than other B2 ordered compounds in which fracture initiated at processing-related defects. These defects controlled fatigue life at 300 K, with fracture occurring rapidly once a critical stress level was reached. At 1000 K, above the BDTT, both the C+E and HP samples cyclically softened during most of the fatigue tests in air and were insensitive to processing defects. The processing method did not have a major effect on fatigue life; the lives of the HP samples were about a factor of three shorter than the C+E NiAl, but this was attributed to the lower stress response of the C+E material. The C+E NiAl underwent dynamic grain growth, whereas the HP material maintained a constant grain size during testing. In both materials, fatigue life was controlled by intergranular cavitation and creep processes, which led to fatigue crack growth that was primarily intergranular in nature. Final fracture by overload was transgranular in nature. Also, HP samples tested in vacuum had a life three times longer than their counterparts tested in air and, in contrast to those tested in air, hardened continuously over half of the sample life, thereby indicating an environmentally assisted fatigue damage

  6. Effects of Laser Peening Treatment on High Cycle Fatigue and Crack Propagation Behaviors in Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Masaki, Kiyotaka; Ochi, Yasuo; Matsumura, Takashi; Ikarashi, Takaaki; Sano, Yuji

    Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about 1mm from the surface. High cycle fatigue tests with four-points rotating bending loading were carried out to confirm the effects of the LPwC treatment on fatigue strength and surface fatigue crack propagation behaviors. The fatigue strength was remarkably improved by the LPwC treatment over the whole regime of fatigue life up to 108 cycles. Specimens with a pre-crack from a small artificial hole due to fatigue loading were used for the quantitative study on the effect of the LPwC treatment. The fracture mechanics investigation on the pre-cracked specimens showed that the LPwC treatment restrained the further propagation of the pre-crack if the stress intensity factor range ΔK on the crack tip was less than 7.6 MPa√m. Surface cracks preferentially propagated into the depth direction as predicted through ΔK analysis on the crack by taking account of the compressive residual stresses due to the LPwC treatment.

  7. A Comparative Evaluation of the Effect of Low Cycle Fatigue and Creep-Fatigue Interaction on Surface Morphology and Tensile Properties of 316L(N) Stainless Steel

    NASA Astrophysics Data System (ADS)

    Mariappan, K.; Shankar, Vani; Sandhya, R.; Bhaduri, A. K.; Laha, Kinkar

    2016-04-01

    In the present work, the deformation and damage evolution in 316L(N) stainless steel during low cycle fatigue (LCF) and creep-fatigue interaction (CFI) loadings have been compared by evaluating the residual tensile properties. Towards this, LCF and CFI experiments were carried out at constant strain amplitude of ±0.6 pct, strain rate of 3 × 10-3 s-1 and temperature of 873 K (600 °C). During CFI tests, 30 minutes hold period was introduced at peak tensile strain. Experiments were interrupted up to various levels of fatigue life viz. 5, 10, 30, 50, and 60 pct of the total fatigue life ( N f) under both LCF and CFI conditions. The specimens subjected to interrupted fatigue loadings were subsequently monotonically strained at the same strain rate and temperature up to fracture. Optical and scanning electron microscopy and profilometry were conducted on the untested and tested samples to elucidate the damage evolution during the fatigue cycling under both LCF and CFI conditions. The yield strength (YS) increased sharply with the progress of fatigue damage and attained saturation within 10 pct of N f under LCF condition. On the contrary, under CFI loading condition, the YS continuously increased up to 50 pct of N f, with a sharp increase of YS up to 5 pct of N f followed by a more gradual increase up to 50 pct of N f. The difference in the evolution of remnant tensile properties was correlated with the synergistic effects of the underlying deformation and damage processes such as cyclic hardening/softening, oxidation, and creep. The evolution of tensile properties with prior fatigue damage has been correlated with the change in surface roughness and other surface features estimated by surface replica technique and fractography.

  8. High-Cycle Fatigue Behavior of a Nicalon(tm)/Si-N-C Composite

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Kalluri, Sreeramesh; Kantzos, Peter T.

    1999-01-01

    Elevated temperature, high-cycle fatigue behavior of a woven SiC/Si-N-C ceramic matrix composite system was investigated at 910 C. High frequency (100 Hz) fatigue tests were conducted in air on specimens machined from the composite system, A power-law type fatigue life relationship adequately characterized the high-cycle fatigue data generated in the study. Post failure fractographic and metallographic studies were performed to document the fatigue crack initiation regions and damage mechanisms in the composite system. Fatigue cracks initiated primarily from the corners of the specimens and propagated along the 90 degree fiber tows.

  9. Carbohydrate Mouth Rinse Counters Fatigue Related Strength Reduction.

    PubMed

    Jensen, Matt; Stellingwerff, Trent; Klimstra, Marc

    2015-06-01

    The purpose was to determine the effect of carbohydrate (CHO) mouth rinse on maximal voluntary contraction (MVC) and neuromuscular output in a fatigued state. It was hypothesized that CHO mouth rinse would potentiate torque output in a fatigued state. In a double-blind, cross-over design, 12 competitive male athletes (9 rowers, 1 cyclist, 1 runner and 1 volleyball player) initially performed 3 × 5 s MVC isometric knee extensions followed by a 50% MVC contraction until volitional exhaustion, with quadriceps muscle activity measured via electromyography (EMG). Immediately after, either an 8% CHO maltodextrin (WASH), or noncaloric artificial sweetener (PLA) was mouth rinsed for 10sec, before 3 × 5 s final MVCs. Fatigue caused a significant decline in post fatigue MVC trial 1 for 3 s average torque (p = .03) and peak torque (p = .02) for PLA. This fatigue related decline in torque was not noticed for WASH, with a 2.5% and 3.5% less attenuation in peak and average torque, respectively in post fatigue MVC1 compared with PLA. The effect size for MVC trial 1 between WASH/PLA was seen to be small positive (ES = 0.22; 55% likelihood of positive). Overall for EMG RMS, there were no significant differences between PLA and WASH among all muscles. EMG median frequency showed comparable results between conditions with significant reductions due to fatigue. Taken together, this evidence suggests that the attenuation of torque post fatigue was less for CHO mouth rinse than a placebo. Even though the gains were marginal, these discoveries may play an important role in sport performance, as small performance effects can have significant outcomes in real-world competitions. PMID:25203506

  10. Thin-metal lined PRD 49-III composite vessels. [evaluation of pressure vessels for burst strength and fatigue performance

    NASA Technical Reports Server (NTRS)

    Hoggatt, J. T.

    1974-01-01

    Filament wound pressure vessels of various configurations were evaluated for burst strength and fatigue performance. The dimensions and characteristics of the vessels are described. The types of tests conducted are explained. It was determined that all vessels leaked in a relatively few cycles (20 to 60 cycles) with failure occurring in all cases in the metallic liner. The thin liner would de-bond from the composite and buckling took place during depressurization. No composite failures or indications of impeding composite failures were obtained in the metal-lined vessels.

  11. Low cycle fatigue behavior of Zircaloy-2 at room temperature

    NASA Astrophysics Data System (ADS)

    Sudhakar Rao, G.; Chakravartty, J. K.; Nudurupati, Saibaba; Mahobia, G. S.; Chattopadhyay, Kausik; Santhi Srinivas, N. C.; Singh, Vakil

    2013-10-01

    Fuel cladding and pressure tubes of Zircaloy-2 in pressurized light and heavy water nuclear reactors experience plastic strain cycles due to power fluctuations in the reactor, such strain cycles cause low cycle fatigue (LCF) and could be life limiting factor for them. Factors like strain rate, strain amplitude and temperature are known to have marked influence on LCF behavior. The effect of strain rate from 10-2 to 10-4 s-1 on LCF behavior of Zircaloy-2 was studied, at different strain amplitudes between ±0.50% and ±1.25% at room temperature. Fatigue life was decreased with lowering of strain rate from 10-2 to 10-4 s-1 at all the strain amplitudes studied. While there was cyclic softening at lower strain amplitudes (Δεt/2 ⩽ ±0.60%) cyclic hardening was exhibited at higher strain amplitudes (Δεt/2 ⩾ ±1.00%) at all the strain rates. Further, there was secondary cyclic hardening during the later stage of cycling at all the strain amplitudes and the strain rates. Cyclic stress-strain hysteresis loops at the lowest strain rate of 10-4 s-1 were found to be heavily serrated, resulting from dynamic strain aging (DSA). There was significant effect of strain rate on dislocation substructure. The results are discussed in terms of high concentration of point defects generated during cyclic straining and their role in enhancing interaction between solutes and dislocations.

  12. Low Cycle Fatigue Behavior and Life Prediction of a Cast Cobalt-Based Superalloy

    NASA Astrophysics Data System (ADS)

    Yang, Ho-Young; Kim, Jae-Hoon; Yoo, Keun-Bong

    Co-base superalloys have been applied in the stationary components of gas turbine owing to their excellent high temperature properties. Low cycle fatigue data on ECY-768 reported in a companion paper were used to evaluate fatigue life prediction models. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are examined in order to predict the low cycle fatigue life of Cobalt-based super alloy at different temperatures. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

  13. Isometric Arm Strength and Subjective Rating of Upper Limb Fatigue in Two-Handed Carrying Tasks

    PubMed Central

    Li, Kai Way; Chiu, Wen-Sheng

    2015-01-01

    Sustained carrying could result in muscular fatigue of the upper limb. Ten male and ten female subjects were recruited for measurements of isometric arm strength before and during carrying a load for a period of 4 minutes. Two levels of load of carrying were tested for each of the male and female subjects. Exponential function based predictive equations for the isometric arm strength were established. The mean absolute deviations of these models in predicting the isometric arm strength were in the range of 3.24 to 17.34 N. Regression analyses between the subjective ratings of upper limb fatigue and force change index (FCI) for the carrying were also performed. The results indicated that the subjective rating of muscular fatigue may be estimated by multiplying the FCI with a constant. The FCI may, therefore, be adopted as an index to assess muscular fatigue for two-handed carrying tasks. PMID:25794159

  14. Effect of polymer coatings on fatigue strength of aluminum alloy 2024 box beams

    NASA Technical Reports Server (NTRS)

    Nordmark, G. E.; Kelsey, R. A.

    1972-01-01

    Previous investigators have shown that polymer coatings raise the fatigue strength of metals tested in air to about the same level as that of uncoated specimens tested in vacuum. The results are given of tests to determine if a polymer coating would improve the fatigue strength of built-up aluminum alloy members simulating aircraft construction. Aluminum alloy 2024-T4 riveted box beams were subjected to constant amplitude fatigue tests in air as well as in salt water fog. The coating did not improve the fatigue strength of beams tested in either environment. This is believed to result from the fact that most failures originated at rivet holes, which were isolated from both the coating and the environment.

  15. Influence of Cyclic Straining on Fatigue, Deformation, and Fracture Behavior of High-Strength Alloy Steel

    NASA Astrophysics Data System (ADS)

    Manigandan, K.; Srivatsan, T. S.; Vasudevan, V. K.; Tammana, D.; Poorganji, B.

    2016-01-01

    In this paper, the results of a study on microstructural influences on mechanical behavior of the high-strength alloy steel Tenax™ 310 are presented and discussed. Under the influence of fully reversed strain cycling, the stress response of this alloy steel revealed softening from the onset of deformation. Cyclic strain resistance exhibited a linear trend for the variation of both elastic strain amplitude with reversals-to-failure, and plastic strain amplitude with reversals-to-failure. Fracture morphology was essentially the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, this high-strength alloy steel revealed fracture to be mixed-mode with features reminiscent of "locally" ductile and brittle mechanisms. The macroscopic mechanisms governing stress response at the fine microscopic level, resultant fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

  16. Microstructure and Low-Cycle Fatigue of a Friction-Stir-Welded 6061 Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Feng, A. H.; Chen, D. L.; Ma, Z. Y.

    2010-10-01

    Strain-controlled low-cycle fatigue (LCF) tests and microstructural evaluation were performed on a friction-stir-welded 6061Al-T651 alloy with varying welding parameters. Friction stir welding (FSW) resulted in fine recrystallized grains with uniformly distributed dispersoids and dissolution of primary strengthening precipitates β″ in the nugget zone (NZ). Two low-hardness zones (LHZs) appeared in the heat-affected zone (HAZ) adjacent to the border between the thermomechanically-affected zone (TMAZ) and HAZ, with the width decreasing with increasing welding speed. No obvious effect of the rotational rate on the LHZs was observed. Cyclic hardening of the friction-stir-welded joints was appreciably stronger than that of base metal (BM), and it also exhibited a two-stage character where cyclic hardening of the friction-stir-welded 6061Al-T651 alloy at higher strain amplitudes was initially stronger followed by an almost linear increase of cyclic stress amplitudes on the semilog scale. Fatigue life, cyclic yield strength, cyclic strain hardening exponent, and cyclic strength coefficient all increased with increasing welding speed, but were nearly independent of the rotational rate. Most friction-stir-welded joints failed along the LHZs and exhibited a shear fracture mode. Fatigue crack initiation was observed to occur from the specimen surface, and crack propagation was mainly characterized by the characteristic fatigue striations. Some distinctive tiremark patterns arising from the interaction between the hard dispersoids/inclusions and the relatively soft matrix in the LHZ under cyclic loading were observed to be present in-between the fatigue striations.

  17. Effects of weld defects at root on rotating bending fatigue strength of small diameter socket welded pipe joints

    SciTech Connect

    Higuchi, Makoto; Nakagawa, Akira; Chujo, Noriyuki; Iida, Kunihiro; Matsuda, Fukuhisa; Sato, Masanobu

    1996-12-01

    Rotating bending fatigue tests were conducted on socket welded joints of a nominal diameter 20 mm, and effects of root defect and other various factors, including post-weld heat treatment (PWHT), pipe wall thickness, and socket wall thickness, were investigated. The socket joints exhibited, in the rotating bending fatigue mode, fatigue strengths that were markedly lower than the same 20 mm diameter joints in four-point bending fatigue. Also, where the latter specimens failed always at the toe, root-failures occurred in rotating bending fatigue. When PWHT`d, however, the fatigue strength showed a remarkable improvement, while the failure site reverted to toe. Thicker pipe walls and socket walls gave rise to higher fatigue strength. A formula relating the size of root defects to the fatigue strength reduction has been proposed.

  18. Effects of Hot Rolling on Low-Cycle Fatigue Properties of Zn-22 wt.% Al Alloy at Room Temperature

    NASA Astrophysics Data System (ADS)

    Dong, X. H.; Cao, Q. D.; Ma, S. J.; Han, S. H.; Tang, W.; Zhang, X. P.

    2016-06-01

    The effects of the reduction ratio (RR) on the low-cycle fatigue (LCF) properties of the Zn-22 wt.% Al (Zn-22Al) alloy were investigated. Various grain sizes from 0.68 to 1.13 μm were obtained by controlled RRs. Tensile and LCF tests were carried out at room temperature. Superplasticity and cyclic softening were observed. Strength and ductility of the rolled Zn-22Al alloy increased with the RR, owing to the decrease in its grain size. The RR did not affect the cyclic softening behavior of the alloy. The fatigue life of the alloy decreased with increasing strain amplitude, while the fatigue life first decreased and then increased with increasing RR. The longest fatigue life was observed for the alloy rolled at a RR of 60%. A bilinear Coffin-Manson relationship was observed to hold true for this alloy.

  19. Fatigue detection in strength training using three-dimensional accelerometry and principal component analysis.

    PubMed

    Brown, Niklas; Bichler, Sebastian; Fiedler, Meike; Alt, Wilfried

    2016-06-01

    Detection of neuro-muscular fatigue in strength training is difficult, due to missing criterion measures and the complexity of fatigue. Thus, a variety of methods are used to determine fatigue. The aim of this study was to use a principal component analysis (PCA) on a multifactorial data-set based on kinematic measurements to determine fatigue. Twenty participants (strength training experienced, 60% male) executed 3 sets of 3 exercises with 50 (12 repetitions), 75 (12 repetitions) and 100%-12 RM (RM). Data were collected with a 3D accelerometer and analysed by a newly developed algorithm to evaluate parameters for each repetition. A PCA with six variables was carried out on the results. A fatigue factor was computed based on the loadings on the first component. One-way ANOVA with Bonferroni post hoc analysis was calculated to test for differences between the intensity levels. All six input variables had high loadings on the first component. The ANOVA showed a significant difference between intensities (p < 0.001). Post-hoc analysis revealed a difference between 100% and the lower intensities (p < 0.05) and no difference between 50 and 75%-12RM. Based on these results, it is possible to distinguish between fatigued and non-fatigued sets of strength training. PMID:27111008

  20. Degradation in the Fatigue Strength of Dentin by Cutting, Etching and Adhesive Bonding

    PubMed Central

    Lee, H.-H.; Majd, H.; Orrego, S.; Majd, B.; Romberg, E.; Mutluay, M.M.; Arola, D.

    2014-01-01

    The processes involved in placing resin composite restorations may degrade the fatigue strength of dentin and increase the likelihood of fractures in restored teeth. Objective The objective of this study was to evaluate the relative changes in strength and fatigue behavior of dentin caused by bur preparation, etching and resin bonding procedures using a 3-step system. Methods Specimens of dentin were prepared from the crowns of unrestored 3rd molars and subjected to either quasi-static or cyclic flexural loading to failure. Four treated groups were prepared including dentin beams subjected to a burr treatment only with a conventional straight-sided bur, or etching treatment only. An additional treated group received both bur and etching treatments, and the last was treated by bur treatment and etching, followed by application of a commercial resin adhesive. The control group consisted of “as sectioned” dentin specimens. Results Under quasi-static loading to failure there was no significant difference between the strength of the control group and treated groups. Dentin beams receiving only etching or bur cutting treatments exhibited fatigue strengths that were significantly lower (p≤0.0001) than the control; there was no significant difference in the fatigue resistance of these two groups. Similarly, the dentin receiving bur and etching treatments exhibited significantly lower (p≤0.0001) fatigue strength than that of the control, regardless of whether an adhesive was applied. Significance The individual steps involved in the placement of bonded resin composite restorations significantly decrease the fatigue strength of dentin, and application of a bonding agent does not increase the fatigue strength of dentin. PMID:24985539

  1. Degradation of residual strength in SCS-6/Ti-15-3 Due to fully reversed fatigue

    NASA Astrophysics Data System (ADS)

    Calcaterra, J. R.; Mall, S.; Coghlan, S. C.

    1999-02-01

    Little attention has been given to residual strength degradation in titanium matrix composites (TMCs) after exposure to fatigue loading. To address this problem, fatigue tests on SCS-6/Ti-15-3 were performed to investigate the fatigue life and residual strength behavior of TMCs with different fiber volume fractions. Results indicate that fiber volume fraction seems to have an effect on both of these quantities. Lower fiber percentages result in a material where the characteristics of the matrix, such as hardening or cracking, play a much larger role in the composite response. Fatigue lives were not affected by fiber volume fraction at higher strain ranges, but lower fiber volume fractions resulted in shorter fatigue lives at lower strain values. Also, a slight increase in residual strength occurred up to 75 pct of fatigue life, for the lower-fiber volume fraction material. Despite these distinctions between specimens with different fiber contents, all specimens tested retained the majority of their strength prior to failure.

  2. Low cycle fatigue and strengthening mechanism of cold extruded large diameter internal thread of Q460 steel

    NASA Astrophysics Data System (ADS)

    Miao, Hong; Mei, Qing; Yuan, Jingyun; Zheng, Zaixiang; Jin, Yifu; Zuo, Dunwen

    2016-04-01

    large diameter internal thread of high-strength steel(LDITHSS) manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion process is an effective means to realize higher accuracy and longer life. The low-cycle fatigue properties of LDITHSS are obtained by experiments, and the initiation and propagation of fatigue cracks are observed by scanning electron microscope(SEM). Based on the mechanical properties, surface microstructure and residual stress, the strengthening mechanism of cold extruded large diameter internal thread(LDIT) is discussed. The results show that new grains or sub-grains can be formed on the surface of LDIT due to grain segmentation and grain refinement during cold extrusion. The fibrous structures appear as elongated and streamlined along the normal direction of the tooth surface which leads to residual compressive stress on the extruded surface. The maximum tension stress of LDIT after cold extrusion is found to be 192.55 kN. Under low stress cycling, the yield stress on thread increases, the propagation rate of crack reduces, the fatigue life is thus improved significantly with decreasing surface grain diameter and the average fatigue life increases to 45.539×103 cycle when the maximum applied load decreases to 120 kN. The low cycle fatigue and strengthening mechanism of cold extruded LDIT revealed by this research has significant importance to promote application of internal thread by cold extrusion processing.

  3. Low cycle fatigue and strengthening mechanism of cold extruded large diameter internal thread of Q460 steel

    NASA Astrophysics Data System (ADS)

    Miao, Hong; Mei, Qing; Yuan, Jingyun; Zheng, Zaixiang; Jin, Yifu; Zuo, Dunwen

    2016-05-01

    large diameter internal thread of high-strength steel(LDITHSS) manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion process is an effective means to realize higher accuracy and longer life. The low-cycle fatigue properties of LDITHSS are obtained by experiments, and the initiation and propagation of fatigue cracks are observed by scanning electron microscope(SEM). Based on the mechanical properties, surface microstructure and residual stress, the strengthening mechanism of cold extruded large diameter internal thread(LDIT) is discussed. The results show that new grains or sub-grains can be formed on the surface of LDIT due to grain segmentation and grain refinement during cold extrusion. The fibrous structures appear as elongated and streamlined along the normal direction of the tooth surface which leads to residual compressive stress on the extruded surface. The maximum tension stress of LDIT after cold extrusion is found to be 192.55 kN. Under low stress cycling, the yield stress on thread increases, the propagation rate of crack reduces, the fatigue life is thus improved significantly with decreasing surface grain diameter and the average fatigue life increases to 45.539×103 cycle when the maximum applied load decreases to 120 kN. The low cycle fatigue and strengthening mechanism of cold extruded LDIT revealed by this research has significant importance to promote application of internal thread by cold extrusion processing.

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

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  5. Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    1998-01-01

    Thick thermal barrier coating systems in a diesel engine experience severe thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) during engine operation. In this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO2-8wt% Y2O3 thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO2 laser. Experiments showed that the combined LCF-HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damage at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, was observed especially for the combined LCF-HCF tests. It is found that the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence.

  6. Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    1998-01-01

    Thick thermal barrier coating systems in a diesel engine experience severe thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) during engine operation. In this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO2-8wt.% Y2O3 thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO2 laser. Experiments showed that the combined LCF/HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damages at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, were observed especially for the combined LCF/HCF tests. It is found that the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (<0.74J) whereas Hertzian crack length (impact side damage) was the best predictor for higher energy impacts. The impacted gamma - TiAl samples displayed a classical mean stress dependence on the fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.

  8. Factors that affect the fatigue strength of power transmission shafting and their impact on design

    NASA Technical Reports Server (NTRS)

    Leowenthal, S. H.

    1986-01-01

    A long standing objective in the design of power transmission shafting is to eliminate excess shaft material without compromising operational reliability. A shaft design method is presented which accounts for variable amplitude loading histories and their influence on limited life designs. The effects of combined bending and torsional loading are considered along with a number of application factors known to influence the fatigue strength of shafting materials. Among the factors examined are surface condition, size, stress concentration, residual stress and corrosion fatigue.

  9. The role of cyclic plastic zone size on fatigue crack growth behavior in high strength steels

    NASA Astrophysics Data System (ADS)

    Korda, Akhmad A.; Miyashita, Y.; Mutoh, Y.

    2015-09-01

    The role of cyclic plastic zone in front of the crack tip was studied in high strength steels. Estimated plastic zone size would be compared with actual observation. Strain controlled fatigue tests of the steels were carried out to obtain cyclic stress-strain curves for plastic zone estimation. Observations of plastic zone were carried out using in situ SEM fatigue crack growth tests under a constant-ΔK. Hard microstructures in structural steels showed to inhibit the extent of plastic deformation around the crack tip. The rate of crack growth can be correlated with the size of plastic zone. The smaller the plastic zone size, the slower the fatigue crack growth.

  10. Fatigue strength improvement of MIG-welded joint by shot peening

    NASA Astrophysics Data System (ADS)

    Azida Che Lah, Nur; Ali, Aidy

    2011-02-01

    In this study, the effect of controlled shot peening (CSP) treatment on the fatigue strength of an ASTM A516 grade 70 carbon steel MIG-welded joint has been studied quantitatively. Metallurgical modifications, hardness, elemental compositions, and internal discontinuities, such as porosity and inclusions found in treated and untreated fusion welded joints, were characterized. The fatigue results of as-welded and peened skimmed joints were compared. It was observed that the effect of the CSP and skimming processes improved the fatigue life of the fusion weld by 63% on MIG-welded samples.

  11. Fatigue reliability based on residual strength model with hybrid uncertain parameters

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Qiu, Zhi-Ping

    2012-02-01

    The aim of this paper is to evaluate the fatigue reliability with hybrid uncertain parameters based on a residual strength model. By solving the non-probabilistic set-based reliability problem and analyzing the reliability with randomness, the fatigue reliability with hybrid parameters can be obtained. The presented hybrid model can adequately consider all uncertainties affecting the fatigue reliability with hybrid uncertain parameters. A comparison among the presented hybrid model, non-probabilistic set-theoretic model and the conventional random model is made through two typical numerical examples. The results show that the presented hybrid model, which can ensure structural security, is effective and practical.

  12. Cyclic fatigue analysis of rocket thrust chambers. Volume 2: Attitude control thruster high cycle fatigue

    NASA Technical Reports Server (NTRS)

    Miller, R. W.

    1974-01-01

    A finite element stress analysis was performed for the film cooled throat section of an attitude control thruster. The anlaysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the thruster operating cycle. The configuration and operating conditions considered, correspond to a flightweight integrated thruster assembly which was thrust pulse tested. The computed strain range was used in conjuction with Haynes 188 Universal Slopes minimum life data to predict throat section fatigue life. The computed number of cycles to failure was greater than the number of pulses to which the thruster was experimentally subjected without failure.

  13. Fatigue performance of laser additive manufactured Ti-6Al-4V in very high cycle fatigue (VHCF) regime up to 109 cycles

    NASA Astrophysics Data System (ADS)

    Wycisk, Eric; Siddique, Shafaqat; Herzog, Dirk; Walther, Frank; Emmelmann, Claus

    2015-12-01

    Additive manufacturing technologies are in the process of establishing themselves as an alternative production technology to conventional manufacturing such as casting or milling. Especially laser additive manufacturing (LAM) enables the production of metallic parts with mechanical properties comparable to conventionally manufactured components. Due to the high geometrical freedom in LAM the technology enables the production of ultra-light weight designs and therefore gains increasing importance in aircraft and space industry. The high quality standards of these industries demand predictability of material properties for static and dynamic load cases. However, fatigue properties especially in the very high cycle fatigue regime until 109 cycles have not been sufficiently determined yet. Therefore this paper presents an analysis of fatigue properties of laser additive manufactured Ti-6Al-4V under cyclic tension-tension until 107 cycles and tension-compression load until 109 cycles. For the analysis of laser additive manufactured titanium alloy Ti-6Al-4V Woehler fatigue tests under tension-tension and tension-compression were carried out in the high cycle and very high cycle fatigue regime. Specimens in stress-relieved as well as hot-isostatic-pressed conditions were analyzed regarding crack initiation site, mean stress sensitivity and overall fatigue performance. The determined fatigue properties show values in the range of conventionally manufactured Ti-6Al-4V with particularly good performance for hot-isostatic-pressed additive-manufactured material. For all conditions the results show no conventional fatigue limit but a constant increase in fatigue life with decreasing loads. No effects of test frequency on life span could be determined. However, independently of testing principle, a shift of crack initiation from surface to internal initiation could be observed with increasing cycles to failure.

  14. Residual strength of composite laminates subjected to tensile-compressive fatigue loading

    NASA Technical Reports Server (NTRS)

    Rotem, Assa; Nelson, H. G.

    1990-01-01

    Results are presented on the measurements of the residual strengths of T300/934 graphite epoxy laminates, in tension and in compression, after the samples were exposed to tension-compression fatigue loading (R = -1). Four laminate ocnfigurations were tested: unidirectional, cross-ply, angle-ply, and quasi-isotropic. It was found that the fatigue behavior of laminates was dependent on the quasi-static strengths and the specific structure of the laminate. No direct correlation was found between remaining residual strengths and the percentage of average fatigue life. However, a correlation scheme was developed for the individual specimen under test, based on a cumulative damage model and a stiffness change of the material.

  15. Fatigue strength reduction model: RANDOM3 and RANDOM4 user manual. Appendix 2: Development of advanced methodologies for probabilistic constitutive relationships of material strength models

    NASA Technical Reports Server (NTRS)

    Boyce, Lola; Lovelace, Thomas B.

    1989-01-01

    FORTRAN programs RANDOM3 and RANDOM4 are documented in the form of a user's manual. Both programs are based on fatigue strength reduction, using a probabilistic constitutive model. The programs predict the random lifetime of an engine component to reach a given fatigue strength. The theoretical backgrounds, input data instructions, and sample problems illustrating the use of the programs are included.

  16. Ultrasonic Spot Welding of Aluminum to High-Strength Low-Alloy Steel: Microstructure, Tensile and Fatigue Properties

    NASA Astrophysics Data System (ADS)

    Patel, V. K.; Bhole, S. D.; Chen, D. L.

    2014-04-01

    The structural applications of lightweight aluminum alloys inevitably involve dissimilar welding with steels and the related durability issues. This study was aimed at evaluating the microstructural change, lap shear tensile load, and fatigue resistance of dissimilar ultrasonic spot-welded joints of aluminum-to-galvanized high-strength low-alloy (HSLA) steel. Two non-uniform layers were identified in between Al and HSLA steel via SEM/EDS and XRD. One was an Al-Zn eutectic layer and the other was a thin (<2 μm) layer of intermetallic compound (IMC) of Al and Fe in the nugget zone. The lap shear tensile testing gave a maximum load of 3.7 kN and the sample failed initially in between the Al-Zn eutectic film and Al-Fe IMC, and afterward from the region containing Al on both matching fracture surfaces. The fatigue test results showed a fatigue limit of about 0.5 kN (at 1 × 107 cycles). The maximum cyclic stress at which transition of the fatigue fracture from transverse through-thickness crack growth mode to the interfacial failure mode occurs increases with increasing energy input.

  17. Fatigue strength of Al7075 notched plates based on the local SED averaged over a control volume

    NASA Astrophysics Data System (ADS)

    Berto, Filippo; Lazzarin, Paolo

    2014-01-01

    When pointed V-notches weaken structural components, local stresses are singular and their intensities are expressed in terms of the notch stress intensity factors (NSIFs). These parameters have been widely used for fatigue assessments of welded structures under high cycle fatigue and sharp notches in plates made of brittle materials subjected to static loading. Fine meshes are required to capture the asymptotic stress distributions ahead of the notch tip and evaluate the relevant NSIFs. On the other hand, when the aim is to determine the local Strain Energy Density (SED) averaged in a control volume embracing the point of stress singularity, refined meshes are, not at all, necessary. The SED can be evaluated from nodal displacements and regular coarse meshes provide accurate values for the averaged local SED. In the present contribution, the link between the SED and the NSIFs is discussed by considering some typical welded joints and sharp V-notches. The procedure based on the SED has been also proofed to be useful for determining theoretical stress concentration factors of blunt notches and holes. In the second part of this work an application of the strain energy density to the fatigue assessment of Al7075 notched plates is presented. The experimental data are taken from the recent literature and refer to notched specimens subjected to different shot peening treatments aimed to increase the notch fatigue strength with respect to the parent material.

  18. High temperature, low-cycle fatigue of copper-base alloys for rocket nozzles. Part 2: Strainrange partitioning and low-cycle fatigue results at 538 deg C

    NASA Technical Reports Server (NTRS)

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1976-01-01

    Low-cycle fatigue tests of 1/2 Hard AMZIRC Copper and NARloy Z were performed in argon at 538 C to determine partitioned strain range versus life relationships. Strain-controlled low-cycle fatigue tests of a Zr-Cr-Mg copper-base alloy were also performed. Strain ranges, lower than those employed in previous tests, were imposed in order to extend the fatigue life curve out to approximately 400,000 cycles. An experimental copper alloy and an experimental silver alloy were also studied. Tensile tests were performed in air at room temperature and in argon at 538 C. Strain-controlled low-cycle fatigue tests were performed at 538 C in argon to define the fatigue life over the regime from 300 to 3,000 cycles. For the silver alloy, three additional heat treatments were introduced, and a limited evaluation of the short-term tensile and low-cycle fatigue behavior at 538 C was performed.

  19. The Effect of Boron on the Low Cycle Fatigue Behavior of Disk Alloy KM4

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy; Gayda, John; Sweeney, Joseph

    2000-01-01

    The durability of powder metallurgy nickel base superalloys employed as compressor and turbine disks is often limited by low cycle fatigue (LCF) crack initiation and crack growth from highly stressed surface locations (corners, holes, etc.). Crack growth induced by dwells at high stresses during aerospace engine operation can be particularly severe. Supersolvus solution heat treatments can be used to produce coarse grain sizes approaching ASTM 6 for improved resistance to dwell fatigue crack growth. However, the coarse grain sizes reduce yield strength, which can lower LCF initiation life. These high temperature heat treatments also can encourage pores to form. In the advanced General Electric disk superalloy KM4, such pores can initiate fatigue cracks that limit LCF initiation life. Hot isostatic pressing (HIP) during the supersolvus solution heat treatment has been shown to improve LCF initiation life in KM4, as the HIP pressure minimizes formation of the pores. Reduction of boron levels in KM4 has also been shown to increase LCF initiation life after a conventional supersolvus heat treatment, again possibly due to effects on the formation tendencies of these pores. However, the effects of reduced boron levels on microstructure, pore characteristics, and LCF failure modes in KM4 still need to be fully quantified. The objective of this study was to determine the effect of boron level on the microstructure, porosity, LCF behavior, and failure modes of supersolvus heat treated KM4.

  20. Gigacycle Fatigue Properties of High-Strength Steels According to Inclusion and ODA Sizes

    NASA Astrophysics Data System (ADS)

    Furuya, Y.; Hirukawa, H.; Kimura, T.; Hayaishi, M.

    2007-08-01

    Gigacycle fatigue tests were conducted for several versions of JIS-SCM440 low-alloy and JIS-SUJ2 bearing steels using 20-kHz ultrasonic fatigue testing to elucidate the relationship of the inclusion size and type to fish-eye fracture properties. The total number of tested specimens was over 200. Most of the specimens revealed Al2O3 or (Cr, Fe)3C inclusion-originating types of fish-eye fractures, while TiN inclusions and the matrix also caused fish-eye fractures in some specimens. Based on these fatigue test results, 109-cycle fatigue limits were estimated according to inclusion size by resorting the obtained data points according to their inclusion sizes at the fish-eye fracture origin. The estimated fatigue limits revealed saturation when the inclusion sizes were smaller than 15 μm, while those fatigue limits depended on the inclusion sizes to the -1/6th power in the case of inclusions above 15 μm in size. The saturation of the 109-cycle fatigue limits was considered to be caused by the effects of the optically dark areas (ODAs). Moreover, the fatigue limits also depended on inclusion type. In comparing the Al2O3 and (Cr, Fe)3C inclusions, the key features causing the difference in the fatigue limits were likely to be bonding between the inclusion and the matrix, i.e., the (Cr, Fe)3C inclusions were tightly bonded to the matrix, unlike the Al2O3 inclusions, although both inclusions were of the hard type.

  1. Nonsteady thermal stress analysis and thermal fatigue strength of metal-CFRP bonded joints

    NASA Astrophysics Data System (ADS)

    Yu, Qiang; Shiratori, Masaki; Mori, Takao

    1993-01-01

    In this paper, a finite-element method (FEM) system of nonsteady thermal stress analysis has been developed to analyze the problem of metal-fiber-reinforced plastic (FRP) bonded joints. The authors have presented a new algorithm for the system, which can provide an effective thermal stress analysis for metal-carbon-FRP (CFRP) bonded joints. The effectiveness, in terms of the accuracy and central processing unit (CPU) time, has been discussed by analyzing some typical problems. The thermal fatigue strength of Al-CFRP bonded joints has been studied through a series of thermal cyclic fatigue tests. It has been shown that the thermal fatigue strength of the joints can be well described by the maximum equivalent stress at the adhesive layer, which can be calculated by the developed FEM system.

  2. Effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates

    NASA Technical Reports Server (NTRS)

    Roberts, Gary D.; Ho, Barry Ping Hsiao; Wallace, John F.

    1993-01-01

    The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientation of (0(2),90(2))2S and (90(2),0(2))2S are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0 deg ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the 'apparent' strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to +85 C, 500 cycles). Mechanical cycling (0 to 50 percent of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue.

  3. The application of probabilistic design theory to high temperature low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Wirsching, P. H.

    1981-01-01

    Metal fatigue under stress and thermal cycling is a principal mode of failure in gas turbine engine hot section components such as turbine blades and disks and combustor liners. Designing for fatigue is subject to considerable uncertainty, e.g., scatter in cycles to failure, available fatigue test data and operating environment data, uncertainties in the models used to predict stresses, etc. Methods of analyzing fatigue test data for probabilistic design purposes are summarized. The general strain life as well as homo- and hetero-scedastic models are considered. Modern probabilistic design theory is reviewed and examples are presented which illustrate application to reliability analysis of gas turbine engine components.

  4. Residual Static Strength of ALuminum-Alloy Beams Containing Fatigue Cracks in the Tension Covers

    NASA Technical Reports Server (NTRS)

    Leybold, Herbert A.

    1961-01-01

    Static tests were performed on 31 box beams containing fatigue cracks in order to determine their residual static strengths. The beams were constructed of 7075 and 2024 aluminum alloy according to several designs and employed stringers that were either bonded, riveted, or an integral part of the skin. skin (both aaterials) had the highest residual static strengths, whereas 7075 beams with integrally stiffened covers had the lowest residual static strengths. Except for the integrally stiffened beams, the skin material did not contribute to the residual static strength of the beams because the crack propagated across the skin before maximum load was reached. For the integrally stiffened beams, crack propagation and failure were synonymous. The test results are compared with predictions of the residual static strength. Fair agreement between predicted strength and actual strength was obtained for all beams tested.

  5. Time-dependent strength and fatigue resistance of dental direct restorative materials.

    PubMed

    Lohbauer, Ulrich; Frankenberger, Roland; Krämer, Norbert; Petschelt, Anselm

    2003-12-01

    Elastic modulus (EM), initial fracture strength (FS) and flexural fatigue limit (FFL) of dental restorative materials were measured in a simulated oral environment to correlate mechanical response under the influence of water with the chemical nature of the test materials under investigation. One resin composite (RC; Tetric Ceram, Ivoclar-Vivadent Corp., Liechtenstein), an ion-leaching resin composite (ILRC; Ariston pHc, Ivoclar-Vivadent Corp., Liechtenstein) a compomer (CO; Dyract AP, Dentsply Corp., USA) and a glass-ionomer cement (GIC; Ketac Molar, 3MEspe Corp., Germany) were tested. Static EM, FS and dynamic FFL experiments were performed. The FFL was determined under cyclic loading for 10(5) cycles in terms of a staircase approach. The materials were stored for 1, 8, 30, 90 and 180 days in 37 degrees C distilled water, respectively. The RC degraded over time due to water adsorption followed by failure within the resin matrix. The ILRC suffered from a pronounced decrease in FS as well as in FFL due to a constant ion-leaching and macroscopic crack growth. CO failed over time due to resin-filler interface cracking. The GIC exhibited improved mechanical performance over time due to a post-hardening mechanism. The results reveal the necessity for substantial preclinical evaluation of direct restorative materials. The material parameters under investigation are capable of predicting clinical performance over time. PMID:15348497

  6. Notch effects on high-cycle fatigue properties of Ti 6Al 4V ELI alloy at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Yuri, T.; Ono, Y.; Ogata, T.

    2006-01-01

    Notch effects on the high-cycle fatigue properties of the forged Ti-6Al-4V ELI alloy at cryogenic temperatures were investigated. Also, the high-cycle fatigue data were compared with the rolled Ti-5Al-2.5Sn ELI alloy. The one million cycles fatigue strength (FS) of the smooth specimen for the forged Ti-6Al-4V ELI alloy increased with a decrease of test temperature. However, the FS of each notched specimen at 4 K were lower than those at 77 K. On the other hand, the FS of the smooth and the notched specimens for the forged Ti-6Al-4V ELI alloy at 4 K were lower than those for the rolled Ti-5Al-2.5Sn ELI alloy. This is considered to be the early initiation of the fatigue crack in the forged Ti-6Al-4V ELI alloy compares with the forged Ti-5Al-2.5Sn ELI.

  7. Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Miller, Robert A.

    1998-01-01

    Ceramic thermal barrier coatings have attracted increased attention for diesel engine applications. The advantages of using the ceramic coatings include a potential increase in efficiency and power density and a decrease in maintenance cost. Zirconia-based ceramics are the most important coating materials for such applications because of their low thermal conductivity, relatively high thermal expansivity and excellent mechanical properties. However, durability of thick thermal barrier coatings (TBCS) under severe temperature cycling encountered in engine conditions, remains a major question. The thermal transients associated with the start/stop and no-load/full-load engine cycle, and with the in-cylinder combustion process, generate thermal low cycle fatigue (LCF) and thermal high cycle fatigue (HCF) in the coating system. Therefore, the failure mechanisms of thick TBCs are expected to be quite different from those of thin TBCs under these temperature transients. The coating failure is related not only to thermal expansion mismatch and oxidation of the bond coats and substrates, but also to the steep thermal stress gradients induced in the coating systems. Although it has been reported that stresses generated by thermal transients can initiate surface and interface cracks in a coating system, the mechanisms of the crack propagation and of coating failure under the complex LCF and HCF conditions are still not understood. In this paper, the thermal fatigue behavior of an yttria partially stabilized zirconia coating system under simulated LCF and HCF engine conditions is investigated. The effects of LCF and HCF on surface crack initiation and propagation are also discussed.

  8. Quadriceps and Respiratory Muscle Fatigue Following High-Intensity Cycling in COPD Patients

    PubMed Central

    Bachasson, Damien; Wuyam, Bernard; Pepin, Jean-Louis; Tamisier, Renaud; Levy, Patrick; Verges, Samuel

    2013-01-01

    Exercise intolerance in COPD seems to combine abnormal ventilatory mechanics, impaired O2 transport and skeletal muscle dysfunction. However their relatie contribution and their influence on symptoms reported by patients remain to be clarified. In order to clarify the complex interaction between ventilatory and neuromuscular exercise limiting factors and symptoms, we evaluated respiratory muscles and quadriceps contractile fatigue, dynamic hyperinflation and symptoms induced by exhaustive high-intensity cycling in COPD patients. Fifteen gold II-III COPD patients (age = 67±6 yr; BMI = 26.6±4.2 kg.m-2) performed constant-load cycling test at 80% of their peak workload until exhaustion (9.3±2.4 min). Before exercise and at exhaustion, potentiated twitch quadriceps strength (Qtw), transdiaphragmatic (Pdi,tw) and gastric (Pga,tw) pressures were evoked by femoral nerve, cervical and thoracic magnetic stimulation, respectively. Changes in operational lung volumes during exercise were assessed via repetitive inspiratory capacity (IC) measurements. Dyspnoea and leg discomfort were measured on visual analog scale. At exhaustion, Qtw (-33±15%, >15% reduction observed in all patients but two) and Pdi,tw (-20±15%, >15% reduction in 6 patients) were significantly reduced (P<0.05) but not Pga,tw (-6±10%, >15% reduction in 3 patients). Percentage reduction in Qtw correlated with the percentage reduction in Pdi,tw (r=0.66; P<0.05). Percentage reductions in Pdi,tw and Pga,tw negatively correlated with the reduction in IC at exhaustion (r=-0.56 and r=-0.62, respectively; P<0.05). Neither dyspnea nor leg discomfort correlated with the amount of muscle fatigue. In conclusion, high-intensity exercise induces quadriceps, diaphragm and less frequently abdominal contractile fatigue in this group of COPD patients. In addition, the rise in end-expiratory lung volume and diaphragm flattening associated with dynamic hyperinflation in COPD might limit the development of abdominal and

  9. Quadriceps and respiratory muscle fatigue following high-intensity cycling in COPD patients.

    PubMed

    Bachasson, Damien; Wuyam, Bernard; Pepin, Jean-Louis; Tamisier, Renaud; Levy, Patrick; Verges, Samuel

    2013-01-01

    Exercise intolerance in COPD seems to combine abnormal ventilatory mechanics, impaired O2 transport and skeletal muscle dysfunction. However their relative contribution and their influence on symptoms reported by patients remain to be clarified. In order to clarify the complex interaction between ventilatory and neuromuscular exercise limiting factors and symptoms, we evaluated respiratory muscles and quadriceps contractile fatigue, dynamic hyperinflation and symptoms induced by exhaustive high-intensity cycling in COPD patients. Fifteen gold II-III COPD patients (age = 67 ± 6 yr; BMI = 26.6 ± 4.2 kg.m(-2)) performed constant-load cycling test at 80% of their peak workload until exhaustion (9.3 ± 2.4 min). Before exercise and at exhaustion, potentiated twitch quadriceps strength (Q(tw)), transdiaphragmatic (P(di,tw)) and gastric (P(ga,tw)) pressures were evoked by femoral nerve, cervical and thoracic magnetic stimulation, respectively. Changes in operational lung volumes during exercise were assessed via repetitive inspiratory capacity (IC) measurements. Dyspnoea and leg discomfort were measured on visual analog scale. At exhaustion, Q(tw) (-33 ± 15%, >15% reduction observed in all patients but two) and Pdi,tw (-20 ± 15%, >15% reduction in 6 patients) were significantly reduced (P<0.05) but not Pga,tw (-6 ± 10%, >15% reduction in 3 patients). Percentage reduction in Q(tw) correlated with the percentage reduction in P(di,tw) (r = 0.66; P<0.05). Percentage reductions in P(di,tw) and P(ga,tw) negatively correlated with the reduction in IC at exhaustion (r = -0.56 and r = -0.62, respectively; P<0.05). Neither dyspnea nor leg discomfort correlated with the amount of muscle fatigue. In conclusion, high-intensity exercise induces quadriceps, diaphragm and less frequently abdominal contractile fatigue in this group of COPD patients. In addition, the rise in end-expiratory lung volume and diaphragm flattening associated with dynamic hyperinflation in COPD might limit

  10. Effect of notch location on fatigue crack growth behavior of strength-mismatched high-strength low-alloy steel weldments

    NASA Astrophysics Data System (ADS)

    Ravi, S.; Balasubramanian, V.; Nasser, S. Nemat

    2004-12-01

    Welding of high-strength low-alloy (HSLA) steels involves the use of low-strength, equal-strength, and high-strength filler materials (electrodes) compared with the parent material, depending on the application of the welded structures and the availability of filler material. In the present investigation, the fatigue crack growth behavior of weld metal (WM) and the heat-affected zone (HAZ) of undermatched (UM), equally matched (EM), and overmatched (OM) joints has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded metal arc welding (SMAW) has been used to fabricate the butt joints. A center-cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behavior of welded joints, utilizing a servo-hydraulic-controlled fatigue-testing machine at constant amplitude loading (R=0). The effect of notch location on the fatigue crack growth behavior of strength mismatched HSLA steel weldments also has been analyzed.

  11. On massive carbide precipitation during high temperature low cycle fatigue in alloy 800H

    SciTech Connect

    Bhanu Sankara Rao, K.; Halford, G.R. . Lewis Research Center); Schuster, H. . Inst. for Reactor Materials)

    1994-08-15

    Alloys engineered for high-temperature application are frequently put into use in a thermodynamically unstable condition. Subsequent exposure to service temperatures may promote many thermally-assisted reactions such as formation, coarsening, and/or coalescence of precipitates. Superposition of cyclic straining may accelerate the kinetics of these reactions but also may cause reaction products having specific features not observed under simple thermal exposure. The influence of cyclic strain-induced microstructural changes on the fatigue behavior has to be considered in terms of their effects on both cyclic strength and life. The occurrence of massive (cellular) precipitation of M[sub 23]C[sub 6] on grain boundaries during elevated temperature low cycle fatigue testing has been reported in Type 304 stainless steel, Type 316 stainless steel, and Inconel 617 superalloy, and its presence has already been linked with reduction in high temperature ductility, an important engineering property on which low cycle fatigue (LCF) life depends to a large extent. Massive precipitation may render the austenitic engineering alloys susceptible to corrosion, which would have important bearing on the performance of these alloys in the oxidizing environments. Furthermore, the long term stability of massive M[sub 23]C[sub 6] particles is particularly important since the transformation of such a large structure into a brittle intermetallic phase (such as sigma) could produce a detrimental effect on the mechanical properties. The conditions and the mechanisms responsible for the occurrence of massive precipitation during LCF have not yet been established. This investigation is specifically aimed at understanding the influence of strain rate on massive precipitation and the mechanism responsible for the occurrence of massive M[sub 23]C[sub 6] precipitation in Alloy 800H during elevated temperature LCF testing.

  12. Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

  13. Mechanical surface treatments of lightweight materials -- effects on fatigue strength and near-surface microstructures

    SciTech Connect

    Zinn, W.; Scholtes, B.

    1999-04-01

    Mechanical surface treatments such as shot peening or deep rolling are well-known processes to improve the fatigue strength of metallic components. This is due to favorable microstructural alterations in relatively thin surface layers as a consequence of near-surface inhomogeneous plastic deformations. Typical examples demonstrate the fatigue-strength increase for mechanically surface-treated specimens. Existing possibilities to improve the fatigue strength of welded joints by mechanical surface treatments are also included. In the case of lightweight materials (e.g., magnesium- or aluminum-base alloys), process parameters must be well adapted in individual cases to achieve optimum near-surface material states, taking into account the wide range of mechanical properties attainable as a result of their specific material microstructure. The effects of process parameters and microstructures on near-surface materials properties resulting from mechanical surface treatments are demonstrated with examples. Depth distributions of macroresidual and microresidual stresses are analyzed together with microstructural observations. An important point for the effectiveness of mechanical surface treatments is the stability of the near-surface material states during loading history. This aspect is treated for the case of fatigue loading.

  14. On the Use of Equivalent Linearization for High-Cycle Fatigue Analysis of Geometrically Nonlinear Structures

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A.

    2003-01-01

    The use of stress predictions from equivalent linearization analyses in the computation of high-cycle fatigue life is examined. Stresses so obtained differ in behavior from the fully nonlinear analysis in both spectral shape and amplitude. Consequently, fatigue life predictions made using this data will be affected. Comparisons of fatigue life predictions based upon the stress response obtained from equivalent linear and numerical simulation analyses are made to determine the range over which the equivalent linear analysis is applicable.

  15. Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep, and thermal fatigue

    NASA Technical Reports Server (NTRS)

    Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

    1992-01-01

    The results of a fourth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA) are presented. The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subjected to a number of effects or primitive variables. These primitive variables may include high temperature, fatigue, or creep. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation was randomized and is included in the computer program, PROMISC. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 was analyzed using the developed methodology.

  16. Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep and thermal fatigue

    NASA Technical Reports Server (NTRS)

    Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

    1992-01-01

    This report presents the results of a fourth year effort of a research program, conducted for NASA-LeRC by the University of Texas at San Antonio (UTSA). The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subject to a number of effects or primitive variables. These primitive variables may include high temperature, fatigue or creep. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation has been randomized and is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 has been analyzed using the developed methodology.

  17. High cycle fatigue of AA6082 and AA6063 aluminum extrusions

    NASA Astrophysics Data System (ADS)

    Nanninga, Nicholas E.

    The high cycle fatigue behavior of hollow extruded AA6082 and AA6063 aluminum extrusions has been studied. Hollow extruded aluminum profiles can be processed into intricate shapes, and may be suitable replacements for fatigue critical automotive applications requiring reduced weight. There are several features inherent in hollow aluminum extrusions, such as seam welds, charge welds, microstructural variations and die lines. The effects of such extrusion variables on high cycle fatigue properties were studied by taking specimens from an actual car bumper extrusion. It appears that extrusion die lines create large anisotropy differences in fatigue properties, while welds themselves have little effect on fatigue lives. Removal of die lines greatly increased fatigue properties of AA6082 specimens taken transverse to the extrusion direction. Without die lines, anisotropy in fatigue properties between AA6082 specimens taken longitudinal and transverse to the extrusion direction, was significantly reduced, and properties associated with the orientation of the microstructure appears to be isotropic. A fibrous microstructure for AA6082 specimens showed great improvements in fatigue behavior. The effects of elevated temperatures and exposure of specimens to NaCl solutions was also studied. Exposure to the salt solution greatly reduced the fatigue lives of specimens, while elevated temperatures showed more moderate reductions in fatigue lives.

  18. Low-cycle fatigue behavior of oxygen-free high-conductivity copper at 300/sup 0/C in high vacuum

    SciTech Connect

    Liu, K.C.; Loring, C.M. Jr.

    1983-01-01

    In-vacuum fatigue tests were performed on commercially-pure OFHC copper and 35% Au-65% Cu brazing filler metal at 300/sup 0/C. Excessive recrystallization due to exposure in the 1025/sup 0/C brazing temperature cycle was detrimental to the fatigue life of the base metal; cold work was beneficial to the fatigue resistance. Triple-point cracking and grain boundary sliding were the prevailing modes of fatigue failure observed in the full-size specimens. However, a mixed morphology of ductile and cleavage-like fracture was observed on the fracture surface of the subsize specimen in which the grain structure appeared to have undergone a change because of the presence of surface cold work. The braze has superior fatigue resistance, but to exploit the maximum strength, the brazed joint must be devoid of defects such as cavities and cracks.

  19. Static and Fatigue Strength Evaluations for Bolted Composite/Steel Joints for Heavy Vehicle Chassis Components

    SciTech Connect

    Sun, Xin; Stephens, Elizabeth V.; Herling, Darrell R.

    2004-09-14

    In May 2003, ORNL and PNNL began collaboration on a four year research effort focused on developing joining techniques to overcome the technical issues associated with joining lightweight materials in heavy vehicles. The initial focus of research is the development and validation of joint designs for a composite structural member attached to a metal member that satisfy the structural requirements both economically and reliably. Huck-bolting is a common joining method currently used in heavy truck chassis structures. The initial round of testing was conducted to establish a performance benchmark by evaluating the static and fatigue behavior of an existing steel/steel chassis joint at the single huck-bolt level. Both tension and shear loading conditions were considered, and the resulting static and fatigue strengths will be used to guide the joint design for a replacement composite/steel joint. A commercially available, pultruded composite material was chosen to study the generic issues related to composite/steel joints. Extren is produced by STRONGWELL, and it is a combination of fiberglass reinforcement and thermosetting polyester or vinyl ester resin systems. Extren sheets of 3.2 mm thick were joined to 1.4 mm SAE1008 steel sheets with a standard grade 5 bolt with 6.35 mm diameter. Both tension and shear loading modes were considered for the single hybrid joint under static and fatigue loading conditions. Since fiberglass reinforced thermoset polymer composites are a non-homogenous material, their strengths and behavior are dependent upon the design of the composite and reinforcement. The Extren sheet stock was cut along the longitudinal direction to achieve maximum net-section strength. The effects of various manufacturing factors and operational conditions on the static and fatigue strength of the hybrid joint were modeled and experimentally verified. It was found that loading mode and washer size have significant influence on the static and fatigue strength of

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  1. Influence of Prior Fatigue Cycling on Creep Behavior of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Sarkar, Aritra; Vijayanand, V. D.; Parameswaran, P.; Shankar, Vani; Sandhya, R.; Laha, K.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

    2014-06-01

    Creep tests were carried out at 823 K (550 °C) and 210 MPa on Reduced Activation Ferritic-Martensitic (RAFM) steel which was subjected to different extents of prior fatigue exposure at 823 K at a strain amplitude of ±0.6 pct to assess the effect of prior fatigue exposure on creep behavior. Extensive cyclic softening that characterized the fatigue damage was found to be immensely deleterious for creep strength of the tempered martensitic steel. Creep rupture life was reduced to 60 pct of that of the virgin steel when the steel was exposed to as low as 1 pct of fatigue life. However, creep life saturated after fatigue exposure of 40 pct. Increase in minimum creep rate and decrease in creep rupture ductility with a saturating trend were observed with prior fatigue exposures. To substantiate these findings, detailed transmission electron microscopy studies were carried out on the steel. With fatigue exposures, extensive recovery of martensitic-lath structure was distinctly observed which supported the cyclic softening behavior that was introduced due to prior fatigue. Consequently, prior fatigue exposures were considered responsible for decrease in creep ductility and associated reduction in the creep rupture strength.

  2. Strength, fracture, and fatigue behavior of advanced high-temperature intermetallics reinforced with ductile phases

    NASA Astrophysics Data System (ADS)

    Soboyejo, W. O.; Rao, K. T. Venkateswara; Sastry, S. M. L.; Ritchie, R. O.

    1993-03-01

    The results of recent studies on the fatigue and fracture behavior of extruded Ti-48A1 + 20 vol pct TiNb and hot-isostatically pressed (“hipped”) MoSi2 + 20 vol pct Nb are presented (compositions in atomic percent unless stated otherwise). The effects of ductile phase reinforcement of Ti-48A1 and MoSi2 on the micromechanisms of fracture under monotonie and cyclic loading are elucidated. Micromechanics models are applied to the prediction of crack-tip shielding components, and the effects of temperature on tensile/compressive/flexure strengths are discussed. Ductile phase toughening under monotonie loading conditions is shown to be associated with lower fatigue crack growth resistance. The lower fatigue resistance is attributed to the absence of crack-tip shielding, higher crack opening displacements, and the effects of inelastic strains that are developed in ductile phase-reinforced composites under cyclic loading conditions.

  3. Effective Fatigue Stress and Criterion for High-Cycle Multi-axial Fatigue

    NASA Astrophysics Data System (ADS)

    Cai, Xiaojing; Xu, Jinquan

    2015-01-01

    Multi-axial fatigue criterion corresponding to the limiting condition of complicated multi-axial stress state is very important in application. Stresses and deformations are usually elastic if cyclic loadings are near to the limiting condition. A definition of effective fatigue stress has been proposed. Adopting the effective fatigue stress, a multi-axial fatigue criterion has been proposed by considering the equivalence of multi-axial stresses to a uni-axial problem. To clarify the fatigue criterion for a uni-axial problem with arbitrary mean stress, a quantitative relationship between fatigue limit and mean stress has also been proposed and examined. To verify the multi-axial fatigue criterion, examinations have been carried out for the cases of pure shear, shear and axial, and two-axial fatigue by experimental results. It is found that the criterion agrees well with experimental results, even for the cases with various multi-axial mean stresses and phase differences. It is also found that the shear fatigue limit is not an independent material property in common metals.

  4. Fracture morphologies of carbon-black-loaded SBR (styrene-butadiene rubber) subjected to low-cycle, high-stress fatigue. [Styrene-butadiene rubber

    SciTech Connect

    Goldberg, A.; Lesuer, D.R.; Patt, J.

    1988-02-01

    Experimental results, together with an analytical model, related to the loss in tensile strength of styrene-butadiene rubber (SBR) loaded with carbon black (CB) that had been subjected to low-cycle, high-stress fatigue tests were presented in a prior paper. The drop in tensile strength relative to that of a virgin sample was considered to be a measure of damage induced during the fatigue test. The present paper is a continuation of this study dealing with the morphological interpretations of the fractured surfaces, whereby the cyclic-tearing behavior, resulting in the damage, is related to the test and material parameters. It was found that failure is almost always initiated in the bulk of a sample at a material flaw. The size and definition of a flaw increase with an increase in carbon-black loading. Initiation flaw sites are enveloped by fan-shaped or penny-shaped regions which develop during cycling. The size and morphology of a fatigue-tear region appears to be independent of the fatigue load or the extent of the damage (strength loss). By contrast, either an increase in cycling load or an increase in damage at constant load increases the definition of the fatigue-region morphology for all formulations of carbon-black. On the finest scale, the morphology can be described in terms of tearing of individual groups of rubber strands, collapsing to form a cell-like structure. 18 refs., 13 figs.

  5. Topology optimization in damage governed low cycle fatigue

    NASA Astrophysics Data System (ADS)

    Desmorat, Boris; Desmorat, Rodrigue

    2008-05-01

    Topology optimization is applied here to discuss an optimization problem of fatigue resistance. Fatigue lifetime is maximized by optimizing the shape of a structure in cyclic plasticity combined with Lemaitre damage law. The topology optimization algorithm is detailed. A 3D numerical example is given. To cite this article: B. Desmorat, R. Desmorat, C. R. Mecanique 336 (2008).

  6. The effects of strength training and disuse on the mechanisms of fatigue.

    PubMed

    Behm, D G; St-Pierre, D M

    1998-03-01

    Increases in force, electromyography, reflex potentiation, muscle action potential amplitude and protein synthesis occur with strength training. Training-induced increases in the efficiency of the neuromuscular system and capacity of the muscle to generate force result in an improved ability to cope with a submaximal load. There is also some evidence of improved fatigue resistance with maximal contractions which could be attributed to a prolongation of membrane excitation or decreased antagonist activity with training. On the other hand, although a variety of factors including strength are diminished with disuse, a number of studies have demonstrated no significant difference in the rate of fatigue with maximal contractions (fatigue index) between trained, untrained and disused muscle. Equivalent control and disuse fatigue indexes in some studies might be attributed to decreased muscle activation resulting in a comparison of maximal (control) and submaximal (disuse) efforts. Furthermore, increases in the duration of muscle membrane electrical propagation with disuse may increase the quantity of Ca++ released, augmenting force production. In addition, the smaller volume of disused muscle may allow a more efficient diffusion of oxygen and energy substrates in comparison with a hypertrophied muscle. PMID:9554028

  7. Real-time monitoring of acoustic linear and nonlinear behavior of titanium alloys during low-cycle fatigue and high-cycle fatigue

    NASA Astrophysics Data System (ADS)

    Frouin, Jerome; Sathish, Shamachary; Na, Jeong K.

    2000-05-01

    An in-situ technique to measure sound velocity, ultrasonic attenuation and acoustic nonlinear property has been developed for characterization and early detection of fatigue damage in aerospace materials. For this purpose we have developed a computer software and measurement technique including hardware for the automation of the measurement. New transducer holder and special grips are designed. The automation has allowed us to test the long-term stability of the electronics over a period of time and so proof of the linearity of the system. Real-time monitoring of the material nonlinearity has been performed on dog-bone specimens from zero fatigue all the way to the final fracture under low-cycle fatigue test condition (LCF) and high-cycle test condition (HCF). Real-time health monitoring of the material can greatly contribute to the understanding of material behavior under cyclic loading. Interpretation of the results show that correlation exist between the slope of the curve described by the material nonlinearity and the life of the component. This new methodology was developed with an objective to predict the initiation of fatigue microcracks, and to detect, in-situ fatigue crack initiation as well as to quantify early stages of fatigue damage.

  8. Low cycle thermal fatigue testing of beryllium grades for ITER plasma facing components

    SciTech Connect

    Watson, R.D.; Youchison, D.L.; Dombrowski, D.E.; Guiniatouline, R.N.; Kupriynov, I.B.

    1996-02-01

    A novel technique has been used to test the relative low cycle thermal fatigue resistance of different grades of US and Russian beryllium, which is proposed as plasma facing armor for fusion reactor first wall, limiter, and divertor components. The 30 kW electron beam test system at Sandia National Laboratories was used to sweep the beam spot along one direction at 1 Hz. This produces a localized temperature ``spike`` of 750{degree}C for each pass of the beam. Large thermal stresses in excess of the yield strength are generated due to very high spot heat flux, 250 MW/m{sup 2}. Cyclic plastic strains on the order of 0.6% produced visible cracking on the heated surface in less than 3000 cycles. An in-vacuo fiber optic borescope was used to visually inspect the beryllium surfaces for crack initiation. Grades of US beryllium tested included: S-65C, S- 65H, S-200F, S-200F-H, SR-200, I-400, extruded high purity, HIP`d spherical powder, porous beryllium (94% and 98% dense), Be/30% BeO, Be/60% BeO, and TiBe{sub 12}. Russian grades included: TGP-56, TShGT, DShG-200, and TShG-56. Both the number of cycles to crack initiation, and the depth of crack propagation, were measured. The most fatigue resistant grades were S-65C, DShG-200, TShGT, and TShG-56. Rolled sheet Be (SR-200) showed excellent crack propagation resistance in the plane of rolling, despite early formation of delamination cracks. Only one sample showed no evidence of surface melting, Extruded (T). Metallographic and chemical analyses are provided. Good agreement was found between the measured depth of cracks and a 2-D elastic-plastic finite element stress analysis.

  9. Fatigue strength reduction model: RANDOM3 and RANDOM4 user manual, appendix 2

    NASA Technical Reports Server (NTRS)

    Boyce, Lola; Lovelace, Thomas B.

    1989-01-01

    The FORTRAN programs RANDOM3 and RANDOM4 are documented. They are based on fatigue strength reduction, using a probabilistic constitutive model. They predict the random lifetime of an engine component to reach a given fatigue strength. Included in this user manual are details regarding the theoretical backgrounds of RANDOM3 and RANDOM4. Appendix A gives information on the physical quantities, their symbols, FORTRAN names, and both SI and U.S. Customary units. Appendix B and C include photocopies of the actual computer printout corresponding to the sample problems. Appendices D and E detail the IMSL, Version 10(1), subroutines and functions called by RANDOM3 and RANDOM4 and SAS/GRAPH(2) programs that can be used to plot both the probability density functions (p.d.f.) and the cumulative distribution functions (c.d.f.).

  10. Sensitivity Variation on Low Cycle Fatigue Cracks Using Level 4/Method B Penetrant

    SciTech Connect

    FULWOOD,HARRY; MOORE,DAVID G.

    1999-09-02

    The Federal Aviation Administration's Airworthiness Assurance NDI Validation Center (AANC) is currently conducting experiments with Level 4, Method B penetrant on low cycle fatigue specimens. The main focus of these experiments is to document the affect on penetrant brightness readings by varying inspection parameters. This paper discusses the results of changing drying temperature, drying time, and dwell time of both penetrant and emulsifier on low cycle fatigue specimens.

  11. Acoustic emission characteristics of copper alloys under low-cycle fatigue conditions

    NASA Technical Reports Server (NTRS)

    Krampfner, Y.; Kawamoto, A.; Ono, K.; Green, A.

    1975-01-01

    The acoustic emission (AE) characteristics of pure copper, zirconium-copper, and several copper alloys were determined to develop nondestructive evaluation schemes of thrust chambers through AE techniques. The AE counts rms voltages, frequency spectrum, and amplitude distribution analysis evaluated AE behavior under fatigue loading conditions. The results were interpreted with the evaluation of wave forms, crack propagation characteristics, as well as scanning electron fractographs of fatigue-tested samples. AE signals at the beginning of a fatigue test were produced by a sample of annealed alloys. A sample of zirconium-containing alloys annealed repeatedly after each fatigue loading cycle showed numerous surface cracks during the subsequent fatigue cycle, emitting strong-burst AE signals. Amplitude distribution analysis exhibits responses that are characteristic of certain types of AE signals.

  12. Predicting Strength and Fatigue for Suited and Unsuited Conditions from Empirical Data

    NASA Technical Reports Server (NTRS)

    Maida, James C.; Gonzalez, L. J.; Rajulu, S.; Russo, Dane M. (Technical Monitor)

    2001-01-01

    The need for longer and more labor-intensive extra-vehicular activities (EVA) is required for construction and maintenance of the International Space Station (ISS). Issues pertaining to human performance while wearing a space suit (EMU) for prolonged periods have become more important. This project was conducted to investigate how a pressurized Extra-vehicular Mobility Unit (EMU) affects human upper body joint strength and fatigue and how to predict it from computer models based on the data collected.

  13. Ultrahigh vacuum, high temperature, low cycle fatigue of coated and uncoated Rene 80

    NASA Technical Reports Server (NTRS)

    Kortovich, C. S.

    1976-01-01

    A study was conducted on the ultrahigh vacuum strain controlled by low cycle fatigue behavior of uncoated and CODEP B-1 aluminide coated Rene' 80 nickel-base superalloy at 1000 C (1832 F) and 871 C (1600 F). The results indicated little effect of coating or temperature on the fatigue properties. There was, however, a significant effect on fatigue life when creep was introduced into the strain cycles. The effect of this creep component was analyzed in terms of the method of strainrange partitioning.

  14. Low-cycle fatigue analysis of a cooled copper combustion chamber

    NASA Technical Reports Server (NTRS)

    Miller, R. W.

    1974-01-01

    A three-dimensional finite element elastoplastic strain analysis was performed for the throat section of regeneratively cooled rocket engine combustion chamber. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the engine operating cycle. The strain range was used in conjunction with OFHC copper isothermal fatigue test data to predict engine low-cycle fatigue life. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen chamber which was fatigue tested to failure at the NASA Lewis Research Center.

  15. Effects of temperature and humidity cycling on the strengths of textile reinforced carbon/epoxy composite materials

    NASA Technical Reports Server (NTRS)

    Cano, Roberto J.; Furrow, Keith W.

    1993-01-01

    Results are presented from an experimental evaluation of the combined effects of temperature and humidity cycling on AS4/3501-6 composites (unstitched, Kevlar 29 stitched, and S-2 glass stitched uniweave fabric) and AS4/E905L composites (2-D, S-2 glass stitched 2-D, and 3-D braided fabric). The AS4/3501-6 uniweave material had a quasi-isotropic layup, whereas the AS4/E905L materials were braided in a (+/-30 deg/0 deg)(sub s) orientation. Data presented include compression strengths and compression-compression fatigue results for uncycled composites and cycled composites (160, 480, 720, and 1280 cycles from 140 deg F at 95 percent relative humidity to -67 deg F). To observe the presence of microcracking within the laminates, photomicrographs were taken of each material type at the end of each cycling period. Microcracks were found to be more prevalent within stitched laminates, predominantly around individual stitches. The glass stitched laminates showed significant microcracking even before cycling. Less microcracking was evident in the Kevlar stitched materials, whereas the unstitched uniweave material developed microcracks only after cycling. The 3-D braid did not develop microcracks. The static compression strengths of the unstitched and Kevlar stitched uniweave materials were degraded by about 10 percent after 1280 temperature/humidity cycles, whereas the reduction in compression strength for the glass stitched uniweave was less than 3 percent. The reduction in compression strength for the glass stitched 2-D braid was less than 8 percent. The unstitched 2-D and 3-D braids did not lose strength from temperature/humidity cycling. The compression-compression fatigue properties of all six material types were not affected by temperature/humidity cycling.

  16. High temperature, low-cycle fatigue of copper-base alloys in argon. Part 2: Zirconium-copper at 482, 538 and 593 C

    NASA Technical Reports Server (NTRS)

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1973-01-01

    Zirconium-copper (1/2 hard) was tested in argon over the temperature range from 482 to 593 C in an evaluation of short-term tensile and low-cycle fatigue behavior. The effect of strain rate on the tensile properties was evaluated at 538 C and in general it was found that the yield and ultimate strengths increased as the strain rate was increased from 0.0004 to 0.01/sec. Ductility was essentially insensitive to strain rate in the case of the zirconium-copper alloy. Strain-rate and hold-time effects on the low cycle fatigue behavior of zirconium-copper were evaluated in argon at 538 C. These effects were as expected in that decreased fatigue life was noted as the strain rate decreased and when hold times were introduced into the tension portion of the strain-cycle. Hold times in compression were much less detrimental than hold times in tension.

  17. In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance

    PubMed Central

    Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

    2015-01-01

    Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding. PMID:26067176

  18. In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance.

    PubMed

    Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

    2015-01-01

    Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding. PMID:26067176

  19. High cycle fatigue and fracture behaviour of a hot isostatically pressed nickel-based superalloy

    NASA Astrophysics Data System (ADS)

    Qiu, Chunlei; Wu, Xinhua

    2014-01-01

    Powder of a nickel-based superalloy, RR1000, has been hot isostatically pressed (HIPped) at a supersolvus temperature and post-HIP heat treated to produce different microstructures. Microstructures were investigated using a scanning electron microscope together with an energy dispersive X-ray spectrometer and a wave-length dispersive X-ray spectrometer. High cycle four-point bending fatigue and tension-tension fatigue tests have been performed on the fabricated samples. It was found that HIPped and aged samples showed the best four-point bending fatigue limit while HIPped and solution-treated and aged samples had the lowest fatigue limit. The four-point bending fatigue crack initiations all occurred from the sample surfaces either at the sites of inclusion clusters or by cleavage through large grains on the surfaces. The tension-tension fatigue crack initiation occurred mainly due to large hafnia inclusion clusters, with lower fatigue lives for samples where inclusions were closer to the surface. Crack initiation at the compact Al2O3 inclusion cluster led to a much higher fatigue life than found when cracks were initiated by large hafnia inclusion clusters. The tension-tension fatigue limits were shown to decrease with increased testing temperature (from room temperature to 700 °C).

  20. High-temperature low cycle fatigue behavior of a gray cast iron

    SciTech Connect

    Fan, K.L. He, G.Q.; She, M.; Liu, X.S.; Lu, Q.; Yang, Y.; Tian, D.D.; Shen, Y.

    2014-12-15

    The strain controlled low cycle fatigue properties of the studied gray cast iron for engine cylinder blocks were investigated. At the same total strain amplitude, the low cycle fatigue life of the studied material at 523 K was higher than that at 423 K. The fatigue behavior of the studied material was characterized as cyclic softening at any given total strain amplitude (0.12%–0.24%), which was attributed to fatigue crack initiation and propagation. Moreover, this material exhibited asymmetric hysteresis loops due to the presence of the graphite lamellas. Transmission electron microscopy analysis suggested that cyclic softening was also caused by the interactions of dislocations at 423 K, such as cell structure in ferrite, whereas cyclic softening was related to subgrain boundaries and dislocation climbing at 523 K. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain amplitudes. It showed that the higher the temperature, the rougher the crack face of the examined gray cast iron at the same total strain amplitude. Additionally, the microcracks were readily blunted during growth inside the pearlite matrix at 423 K, whereas the microcracks could easily pass through pearlite matrix along with deflection at 523 K. The results of fatigue experiments consistently showed that fatigue damage for the studied material at 423 K was lower than that at 523 K under any given total strain amplitude. - Highlights: • The low cycle fatigue behavior of the HT250 for engine cylinder blocks was investigated. • TEM investigations were conducted to explain the cyclic deformation response. • The low cycle fatigue cracks of HT250 GCI were studied by SEM. • The fatigue life of the examined material at 523 K is higher than that at 423 K.

  1. Low-Cycle Fatigue Behavior of Die-Cast Mg Alloys AZ91 and AM60

    NASA Astrophysics Data System (ADS)

    Rettberg, Luke H.; Jordon, J. Brian; Horstemeyer, Mark F.; Jones, J. Wayne

    2012-07-01

    The influence of microstructure and artificial aging response (T6) on the low-cycle fatigue behavior of super vacuum die-cast (SVDC) AZ91 and AM60 has been investigated. Fatigue lifetimes were determined from the total strain-controlled fatigue tests for strain amplitudes of 0.2 pct, 0.4 pct, 0.6 pct, 0.8 pct, and 1.0 pct under fully reversed loading at a frequency of 5 Hz. Cyclic stress-strain behavior was determined using an incremental step test (IST) and compared with the more traditional constant amplitude test. Two locations in a prototype casting were investigated to examine the role of microstructure and porosity on fatigue behavior. At all total strain amplitudes microstructure refinement had a negligible impact on fatigue life because of significant levels of porosity. AM60 showed an improvement in fatigue life at higher strain amplitudes when compared with AZ91 because of higher ductility. T6 heat treatment had no impact on fatigue life. Cyclic stress-strain behavior obtained via the incremental step test varied from constant amplitude test results due to load history effects. The constant amplitude test is believed to be the more accurate test method. In general, larger initiation pores led to shorter fatigue life. The fatigue life of AZ91 was more sensitive to initiation pore size and pore location than AM60 at the lowest tested strain amplitude of 0.2 pct. Fatigue crack paths did not favor any specific phase, interdentritic structure or eutectic structure. A multistage fatigue (MSF) model showed good correlation to the experimental strain-life results. The MSF model reinforced the dominant role of inclusion (pore) size on the scatter in fatigue life.

  2. Strength and fatigue of zirconia-induced weak spots in optical fiber

    NASA Astrophysics Data System (ADS)

    Breuls, Anton H. E.; Svenson, T.

    1994-03-01

    The reliability of long lengths of fibers in optical cables is determined by the presence of weak spots which are infrequently produced by normal fiber production methods. It is important to investigate the influence on strength of fiber from different kinds of weak spots. The present study is confined to weak spots resulting from melted-in zirconia particles. Tensile testing of optical fiber, in which strength degrading particles of a roughly dual-size distribution have been introduced on purpose, was done At a wide range of stress rates. The Weibull plots of tensile strength of the fiber were compared with a theoretical distribution, based on a simple relation between particle size and fiber strength. In this way, failure modes could be identified and related to the size of particles. From the comparison it was concluded that the size of zirconia particles has no significant influence on the fatigue of fiber, within the applied stress rates. A significant retardment of the fatigue of weak spots was also observed at low stress rates.

  3. Fatigue

    MedlinePlus

    ... sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of not caring ... fatigue symptoms, and your lifestyle, habits, and feelings. Tests that may be ordered include the following: Blood ...

  4. Bithermal Low-Cycle Fatigue Evaluation of Automotive Exhaust System Alloy SS409

    NASA Technical Reports Server (NTRS)

    Lu, Gui-Ying; Behling, Mike B.; Halford, Gary R.

    2000-01-01

    This investigation provides, for the first time, cyclic strainrange-controlled, thermomechanical fatigue results for the ferritic stainless steel alloy SS409. The alloy has seen extensive application for automotive exhaust system components. The data were generated to calibrate the Total Strain Version of the Strainrange Partitioning (TS-SRP) method for eventual application to the design and durability assessment of automotive exhaust systems. The thermomechanical cyclic lifetime and cyclic stress-strain constitutive behavior for alloy SS409 were measured using bithermal tests cycling between isothermal extremes of 400 and 800 C. Lives ranged up to 10,000 cycles to failure with hold-times of 0.33 to 2.0 minutes. The bithermal fatigue behavior is compared to isothermal, strain-controlled fatigue behavior at both 400 and 800 C. Thermomechanical cycling was found to have a profound detrimental influence on the fatigue failure resistance of SS409 compared to isothermal cycling. Supplementary bithermal cyclic stress-strain constitutive tests with hold-times ranging from 40 seconds up to 1.5 hours were conducted to calibrate the TS-SRP equation for extrapolation to longer lifetime predictions. Observed thermomechanical (bithermal) fatigue lives correlated well with lives calculated using the calibrated TS-SRP equations: 70% of the bithermal fatigue data fall within a factor of 1.2 of calculated life; 85% within a factor of 1.4; and 100% within a factor of 1.8.

  5. Low-Cycle Fatigue Properties of P92 Ferritic-Martensitic Steel at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Hu, ZhengFei; Schmauder, Siegfried; Mlikota, Marijo; Fan, KangLe

    2016-04-01

    The low-cycle fatigue behavior of P92 ferritic-martensitic steel and the corresponding microstructure evolution at 873 K has been extensively studied. The test results of fatigue lifetime are consistent with the Coffin-Manson relationship over a range of controlled total strain amplitudes from 0.15 to 0.6%. The influence of strain amplitude on the fatigue crack initiation and growth has been observed using optical microscopy and scanning electron microscopy. The formation mechanism of secondary cracks is established according to the observation of fracture after fatigue process and there is an intrinsic relationship between striation spacing, current crack length, and strain amplitude. Transmission electron microscopy has been employed to investigate the microstructure evolution after fatigue process. It indicates the interaction between carbides and dislocations together with the formation of cell structure inhibits the cyclic softening. The low-angle sub-boundary elimination in the martensite is mainly caused by the cyclic stress.

  6. 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.

  7. Low-cycle fatigue/high-cycle fatigue (LCF/HCF) interaction studies using a 10- to 40-kHz HCF loading device

    NASA Astrophysics Data System (ADS)

    Matikas, Theodore E.

    1999-02-01

    To simulate the testing conditions experienced by aircraft engine turbine blades, a new experimental facility was developed capable of providing interactive low cycle fatigue (LCF)/high cycle fatigue (HCF) loading. The new facility is based on a HCF cell that can operate in the 10-40 kHz frequency range. This HCF testing cell can also be interfaced to a servo-hydraulic load frame, which provides a second fatigue cycle. Sample geometry is critical for the HCF cell to produce the desired applied load on the specimen. The objective of this research is to develop analytical modeling necessary for the design of test coupons to be used in the new HCF testing cell operating at ultrasonic frequencies, and also to demonstrate the capabilities of the new device by performing LCF/HCF interaction studies in Ti-6Al-4V. The results of these studies clearly showed the effect of the HCF component of the load in spite the fact that the HCF component was only 15-19 percent of the overall load. It was also found that the HCF component of the load was the major cause of observed damage with the LCF component having much less effect. Eliminating the HCF component completely resulted in increasing the fatigue life at least an order of magnitude.

  8. Cryogenic Tensile Strength and Fatigue Life of Carbon Nanotube Multi-Yarn.

    PubMed

    Misak, H E; Mall, S

    2016-03-01

    Carbon nanotube (CNT) multi-yarns, consisting of 30 yarns, were tested under monotonic tensile load and fatigue at the room temperature (298 K) and two cryogenic temperatures (232 and 123 K). Tensile stiffness increased with the decrease of temperature. The average ultimate tensile strength was higher at 123 K when compared to the higher temperatures (232 and 298 K). Failure mechanism changed from a combination of classical variant and independent fiber breakage at the two higher temperatures to mostly classical variant failure mechanism at the lower temperature. The CNT-yarn's fatigue life also increased with decreasing temperature. CNT-yarns have been shown to function well at lower temperatures making them usable for applications requiring operation at cryogenic temperatures, such as in satellites and high altitude aircraft. PMID:27455753

  9. Effects of fatigue and environment on residual strengths of center-cracked graphite/epoxy buffer strip panels

    NASA Technical Reports Server (NTRS)

    Bigelow, Catherine A.

    1989-01-01

    The effects of fatigue, moisture conditioning, and heating on the residual tension strengths of center-cracked graphite/epoxy buffer strip panels were evaluated using specimens made with T300/5208 graphite epoxy in a 16-ply quasi-isotropic layup, with two different buffer strip materials, Kevlar-49 or S-glass. It was found that, for panels subjected to fatigue loading, the residual strengths were not significantly affected by the fatigue loading, the number of repetitions of the loading spectrum, or the maximum strain level. The moisture conditioning reduced the residual strengths of the S-glass buffer strip panels by 10 to 15 percent below the ambient results, but increased the residual strengths of the Kevlar-49 buffer strip panels slightly. For both buffer strip materials, the heat increased the residual strengths of the buffer strip panels slightly over the ambient results.

  10. Low-cycle fatigue resistance of AD1 aluminum and AMg5 aluminum alloy

    SciTech Connect

    Kholodilo, A.A.; Balyuk, L.M.; Modestova, R.V.

    1985-02-01

    This paper reports on investigations carried out by the Severodonetsk branch of the Ukranian Scientific-Research Institute of Chemical Engineering into the low-cycle fatigue resistance of aluminum AD1 and AMg/sup 5/ aluminum alloy. The cylindrical specimens were tested in an UME-1oTM machine with recording of the cyclic deformation diagram. It is concluded that the Landger equation can be used to construct the calculation curves of low-cycle fatigue of the aluminum alloys; the quality of the welded joints plays the controlling role in the resistance of the vessels and plant to low-cycle fracture.

  11. Low-cycle fatigue of a VZh175 high-temperature alloy under elastoplastic deformation conditions

    NASA Astrophysics Data System (ADS)

    Belyaev, M. S.; Terent'ev, V. F.; Bakradze, M. M.; Gorbovets, M. A.; Gol'dberg, M. A.

    2015-04-01

    The low-cycle fatigue of a VZh175 nickel superalloy is studied under conditions of complete deformation per loading cycle at an initial cycle asymmetry R = 0, a deformation amplitude ɛa = 0.4-0.6%, and a temperature of 20 and 650°C. The specific features of cyclic hardening/softening of the alloy under these conditions are detected. The mechanisms of fatigue crack nucleation and growth are analyzed as functions of the deformation amplitude and the test temperature.

  12. Accommodating and cracking mechanisms in low-cycle fatigue

    NASA Technical Reports Server (NTRS)

    Pineau, A.

    1978-01-01

    The three main stages of fatigue life (accommodation, crack initiation and crack growth) are briefly reviewed. The cyclic behavior of annealed or predeformed face-centered cubic metals is described. Moreover, two types of alloys (Al-4-Cu and WASPALOY) are examined regarding the influence of the interactions between the precipitates and the dislocations on the cyclic behavior. Data on the percent of life to crack initiation (for a microcrack smaller than about 100 microns) are also given. Finally, experimental and theoretical results on crack growth rates in lowcycle fatigue are described.

  13. Tensile and low-cycle fatigue measurements on cross-rolled tungsten

    SciTech Connect

    Schmunk, R.E.; Korth, G.E.

    1981-08-01

    Low-cycle fatigue and tensile tests were performed on specimens fabricated from 14-mm (0.55-in.) cross-rolled tungsten plate which was prepared by a powder metallurgy process. Tests included measurements on both as-received and recrystallized specimens. Data have been obtained at 1088 K (1500/sup 0/F) in vacuum, and at room temperature. Low-cycle fatigue data at both 1088 K and room temperature are in fair agreement with predictions based on the universal slopes equation for the as-received material condition. In contrast, fatigue data for recrystallized specimens at 1088 K fall considerably below prediction, except in the high cycles-to-fail (10/sup 5/ cycles) regime. Details of the test procedure as well as modification of the specimen configuration which was required for room temperature testing are reported.

  14. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    DOE PAGESBeta

    Wang, Hong; Lee, Sung Min; Wang, James L.; Lin, Hua-Tay

    2014-12-19

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10^8 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and themore » fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications such as piezoelectric fuel injectors in heavy-duty diesel engines.« less

  15. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    SciTech Connect

    Wang, Hong; Lee, Sung Min; Wang, James L.; Lin, Hua-Tay

    2014-12-19

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10^8 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications such as piezoelectric fuel injectors in heavy-duty diesel engines.

  16. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    SciTech Connect

    Wang, Hong Lee, Sung-Min; Wang, James L.; Lin, Hua-Tay

    2014-12-21

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10{sup 8} cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines.

  17. Influence of Fatigue Loading and Bone Turnover on Bone Strength and Pattern of Experimental Fractures of the Tibia in Mice.

    PubMed

    Bonnet, Nicolas; Gerbaix, Maude; Ominsky, Michael; Ammann, Patrick; Kostenuik, Paul J; Ferrari, Serge L

    2016-07-01

    Bone fragility depends on bone mass, structure, and material properties, including damage. The relationship between bone turnover, fatigue damage, and the pattern and location of fractures, however, remains poorly understood. We examined these factors and their integrated effects on fracture strength and patterns in tibia. Adult male mice received RANKL (2 mg/kg/day), OPG-Fc (5 mg/kg 2×/week), or vehicle (Veh) 2 days prior to fatigue loading of one tibia by in vivo axial compression, with treatments continuing up to 28 more days. One day post fatigue, crack density was similarly increased in fatigued tibiae from all treatment groups. After 28 days, the RANKL group exhibited reduced bone mass and increased crack density, resulting in reduced bone strength, while the OPG-Fc group had greater bone mass and bone strength. Injury repair altered the pattern and location of fractures created by ex vivo destructive testing, with fractures occurring more proximally and obliquely relative to non-fatigued tibia. A similar pattern was observed in both non-fatigued and fatigued tibia of RANKL. In contrast, OPG-Fc prevented this fatigue-related shift in fracture pattern by maintaining fractures more distal and transverse. Correlation analysis showed that bone strength was predominantly determined by aBMD with minor contributions from structure and intrinsic strength as measured by nanoindentation and cracks density. In contrast, fracture location was predicted equally by aBMD, crack density and intrinsic modulus. The data suggest that not only bone strength but also the fracture pattern depends on previous damage and the effects of bone turnover on bone mass and structure. These observations may be relevant to further understand the mechanisms contributing to fracture pattern in long bone with different levels of bone remodeling, including atypical femur fracture. PMID:26945756

  18. High-cycle fatigue characterization of titanium 5Al-2.5Sn alloy

    NASA Technical Reports Server (NTRS)

    Mahfuz, H.; Xin, Yu T.; Jeelani, S.

    1993-01-01

    High-cycle fatigue behavior of titanium 5Al 2.5Sn alloy at room temperature has been studied. S-N curve characterization is performed at different stress ratios ranging from 0 to 0.9 on a subsized fatigue specimen. Both two-stress and three-stress level tests are conducted at different stress ratios to study the cumulative fatigue damage. Life prediction techniques of linear damage rule, double linear damage rule and damage curve approaches are applied, and results are compared with the experimental data. The agreement between prediction and experiment is found to be excellent.

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

    SciTech Connect

    Zhang, Jianfeng; Xuan, Fu-Zhen

    2014-05-28

    The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A “mountain shape” correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The “mountain shape” correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.

  20. Effect of cyclic high loading rates on the fatigue strength of aluminum-based composites

    NASA Astrophysics Data System (ADS)

    Calderon Arteaga, Hermes Eskander

    The study of fatigue under high loading rates is of great interest in the complete characterization of a new series of composites with Al-Cu-Mg matrix reinforced with AlB2 dispersoids. Homogeneous and functionally graded composites were prepared via gravity and centrifugal casting, respectively. Through centrifugal casting a gradual variation of the volume fraction of reinforcing particles along the cross section was obtained. In specific fabrication conditions, even complete segregation of the reinforcement particles was achieved. Charpy impact tests as well as hardness tests were conducted to assess the composite strength as a function of the weight percent of boron. The tensile properties of gravity cast samples were obtained. Then for both casting conditions, simple edge-notched bend SE(B) specimens were tested under fatigue conditions (three-point bending). The results from impact and hardness tests allowed identifying an interaction between the Mg dissolved in the matrix and the diborides. This interaction, which has never been reported before, was responsible for the strength reduction observed. It was assumed that a substitutional diffusion of Al by Mg atoms in the hp3 structure of diboride was causing the strength reduction, and three approaches were developed to estimate the amount of Mg depleted from the matrix by the diborides during the composite processing. Gravity cast samples were more sensitive to monotonic damage due to fatigue loads where compared with functionally-graded composites. Contrary to the centrifugal cast samples, gravity samples were also affected by the loading rate. The Mg-AlB2 interaction was also responsible for the reduction in the fatigue resistance as the weight percent of boron increased in both types of composites; regression models were obtained to predict the crack growth curve slope change as function of the boron level. The particle distribution showed to affect the crack growth behavior of the FGMs, decreasing the

  1. On massive carbide precipitation during high temperature low cycle fatigue in alloy 800H

    NASA Technical Reports Server (NTRS)

    Sankararao, K. Bhanu; Schuster, H.; Halford, G. R.

    1994-01-01

    The effect of strain rate on massive precipitation and the mechanism for the occurrence of massive precipitation of M23C6 in alloy 800H is investigated during elevated temperature low cycle fatigue testing. It was observed that large M23C6 platelets were in the vicinity of grain and incoherent twin boundaries. The strain controlled fatigue testing at higher strain rates that promoted cyclic hardening enabled massive precipitation to occur more easily.

  2. The influence of hold times on LCF and FCG behavior in a P/M Ni-base superalloy. [Low Cycle Fatigue/Fatigue Crack Growth

    NASA Technical Reports Server (NTRS)

    Choe, S. J.; Golwalker, S. V.; Duquette, D. J.; Stoloff, N. S.

    1984-01-01

    The relative importance of creep and environmental interactions in high temperature fatigue behavior has been investigated for as-HIP Rene 95. Strain-controlled low cycle fatigue and load-controlled fatigue crack growth tests were performed at elevated temperatures in argon, followed by fractographic analyses of the fracture surfaces by scanning electron microscopy. Fatigue lives were drastically reduced and crack growth rates increased one hundred fold as a result of superposition of hold times on continuous cycling. A change in fracture mode with hold time also was noted. Chromium oxide was detected on the fracture surface by Auger electron spectroscopy. The drastic changes in fatigue resistance due to hold times were attributed primarily to environmental interactions with fatigue processes.

  3. Tensile and fatigue strength properties of Kevlar 29 aramid/epoxy unidirectional composites

    SciTech Connect

    Zweben, C.

    1981-07-22

    Static and fatigue tensile strength properties of filament wound undirectional Kevlar 29/epoxy, typical of filament wound material used in flywheel rotors, were studied. Machining techniques were developed to minimize fiber fuzzing on edges. The static modulus, normalized to 70% fiber volume fraction is 8.87 x 10/sup 6/ psi. The major Poisson's ratio is 0.37. The static composite tensile strength, normalized to 70% fiber volume fraction is 200 x 10/sup 3/ psi, corresponding to a fiber stress at failure of 286 x 10/sup 3/ psi, which is good for materials having a very high fiber volume fraction. The S-N curve for R = 0.7 was found to be quite flat. Although the techniques used in this program had previously been employed successfully to study the fatigue behavior of Kevlar 29/epoxy and Kevlar 49/epoxy unidirectional materials, we were unable to overcome the persistent problem of cohesive material failure in the tab regions. The apparent reason for this is the very low interlaminar shear strength of the filament wound material. 16 figures.

  4. Surface Studies of Ultra Strength Drilling Steel after Corrosion Fatigue in Simulated Sour Environment

    SciTech Connect

    M. Ziomek-Moroz; J.A. Hawk; R. Thodla; F. Gui

    2012-05-06

    The Unites States predicted 60% growth in energy demand by 2030 makes oil and natural gas primary target fuels for energy generation. The fact that the peak of oil production from shallow wells (< 5000 m) is about to be reached, thereby pushing the oil and natural gas industry into deeper wells. However, drilling to depths greater than 5000 m requires increasing the strength-to weight ratio of the drill pipe materials. Grade UD-165 is one of the ultra- high yield strength carbon steels developed for ultra deep drilling (UDD) activities. Drilling UDD wells exposes the drill pipes to Cl{sup -}, HCO{sub 3}{sup -}/CO{sub 3}{sup 2-}, and H{sub 2}S-containig corrosive environments (i.e., sour environments) at higher pressures and temperatures compared to those found in conventional wells. Because of the lack of synergism within the service environment, operational stresses can result in catastrophic brittle failures characteristic for environmentally assisted cracking (EAC). Approximately 75% of all drill string failures are caused by fatigue or corrosion fatigue. Since there is no literature data on the corrosion fatigue performance of UD-165 in sour environments, research was initiated to better clarify the fatigue crack growth (FCGR) behavior of this alloy in UDD environments. The FCGR behavior of ultra-strength carbon steel, grade UD-165, was investigated by monitoring crack growth rate in deaerated 5%NaCl solution buffered with NaHCO{sub 3}/Na{sub 2}CO{sub 3} and in contact with H{sub 2}S. The partial pressure of H{sub 2}S (p{sub H2S}) was 0.83 kPa and pH of the solution was adjusted by NaOH to 12. The fatigue experiments were performed at 20 and 85 C in an autoclave with surface investigations augmented by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy. In this study, research focused on surface analyses supported by the fatigue crack growth rate measurements. Fig. 1 shows an SEM micrograph of the crack that propagated from the

  5. Effect of Solder-Joint Geometry on the Low-Cycle Fatigue Behavior of Sn-xAg-0.7Cu

    NASA Astrophysics Data System (ADS)

    Lee, Hwa-Teng; Huang, Kuo-Chen

    2016-07-01

    Low-cycle fatigue tests of Sn-Ag-Cu (SAC) Pb-free solder joints under fixed displacement were performed to evaluate the influence of Ag content (0-3 wt.%) and solder-joint geometry (barrel and hourglass types) on solder-joint fatigue behavior and reliability. The solder joints were composed of fine particles of Ag3Sn and Cu6Sn5, which aggregated as an eutectic constituent at grain boundaries of the primary β-Sn phase and formed a dense network structure. A decrease in the Ag content resulted in coarsening of the β-Sn and eutectic phases, which, in turn, decreased the strength of the joint and caused earlier failure. Solder joints in the hourglass form exhibited better fatigue performance with longer life than barrel-type joints. The sharp contact angle formed between the solder and the Cu substrate by the barrel-type joints concentrated stress, which compromised fatigue reliability. The addition of Ag to the solder, however, enhanced fatigue performance because of strengthening caused by Ag3Sn formation. The cracks of the barrel-type SAC solder joints originated mostly at the contact corner and propagated along the interfacial layer between the interfacial intermetallic compound (IMC) and solder matrix. Hourglass-type solder joints, however, demonstrated both crack initiation and propagation in the solder matrix (solder mode). The addition of 1.5-2.0 wt.% Ag to SAC solder appears to enhance the fatigue performance of solder joints while maintaining sufficient strength.

  6. Mechanistic dissimilarities between environmentally-influenced fatigue-crack propagation at near-threshold and higher growth rates in lower-strength steels

    SciTech Connect

    Suresh, S.; Ritchie, R. O.

    1981-11-01

    The role of hydrogen gas in influencing fatigue crack propagation is examined for several classes of lower strength pressure vessel and piping steels. Based on measurements over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, crack propagation rates are found to be significantly higher in dehumidified gaseous hydrogen compared to moist air in two distinct regimes of crack growth, namely (i) at the intermediate range of growth typically above approx. 10/sup -5/ mm/cycle, and (ii) at the near-threshold region below approx. 10/sup -6/ mm/cycle approaching lattice dimensions per cycle. Both effects are seen at maximum stress intensities (K/sub max/) far below the sustained-load threshold stress intensity for hydrogen-assisted cracking (K/sub Iscc/). Characteristics of environmentally influenced fatigue crack growth in each regime are shown to be markedly different with regard to fractography and the effect of such variables as load ratio and frequency. It is concluded that the primary mechanisms responsible for the influence of the environment in each regime are distinctly different. Whereas corrosion fatigue behavior at intermediate growth rates can be attributed to hydrogen embrittlement processes, the primary role of moist environments at near-threshold levels is shown to involve a contribution from enhanced crack closure due to the formation of crack surface corrosion deposits at low load ratios.

  7. A New Multiaxial High-Cycle Fatigue Criterion Based on the Critical Plane for Ductile and Brittle Materials

    NASA Astrophysics Data System (ADS)

    Wang, Cong; Shang, De-Guang; Wang, Xiao-Wei

    2015-02-01

    An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.

  8. Evaluation of the Effect of Surface Finish on High-Cycle Fatigue of SLM-IN718

    NASA Technical Reports Server (NTRS)

    Lambert, D. M.

    2016-01-01

    The surface finish of parts produced by additive manufacturing processes is much rougher than the surface finish generated by machining processes, and a rougher surface can reduce the fatigue strength of a part. This paper discusses an effort to quantify that reduction of strength in high-cycle fatigue for selective laser melt (SLM) coupons. A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the SLM process. This factor is the percentage reduction from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition at the same fatigue life. Specimens were provided by a number of vendors, free to use their "best practice"; only one heat treat condition was considered; and several test temperatures were characterized, including room temperature, 800F, 1000F, and 1200F. The 1000F data had a large variance, and was omitted from consideration in this document. A first method used linear approximations extracted from the graphs, and only where data was available for both. A recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness no more than 4 micro-inches/inch) was established at approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce a similar life in the as-built surface condition. In this first evaluation, the knockdown factor did not appear to be a function of temperature. A second approach, the "KP method", incorporated the surface finish measure into a new parameter termed the pseudo-stress intensity factor, Kp, which was formulated to be similar to the fracture mechanics stress intensity factor. Using Kp, the variance seemed to be reduced across all sources, and knockdown factors were estimated using Kp over the range where data occurred. A

  9. Low Cycle and Ratchetting Fatigue Behavior of High UTS/YS Ratio Reinforcing Steel Bars

    NASA Astrophysics Data System (ADS)

    Bar, H. N.; Sivaprasad, S.; Narasaiah, N.; Paul, Surajit K.; Sen, B. N.; Chandra, Sanjay

    2013-06-01

    Cyclic deformation behavior of high UTS/YS rebars has been studied employing both symmetric strain-controlled and asymmetric stress-controlled cycles in an attempt to understand the influence of UTS/YS ratio on fatigue life. While strain-controlled cyclic deformation did not exhibit a pronounced influence of UTS/YS ratio, a substantial life enhancement is noted for the asymmetric stress-controlled cycle. Reasons for life enhancement were found to be due to the ratchetting strain development and the associated hardening behavior. An equivalent stress-based model has been used to predict both the symmetric and asymmetric fatigue lives of rebars.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  11. Remote laser cutting of CFRP: influence of the edge quality on fatigue strength

    NASA Astrophysics Data System (ADS)

    Stock, Johannes W.; Zaeh, Michael F.; Spaeth, Justinian P.

    2014-02-01

    The additional weight of the batteries in electric cars can be compensated by using carbon fiber reinforced plastics (CFRP) for structural parts of the passenger cell. Various machining processes for CFRP are currently subject to investigations. Milling and abrasive waterjet cutting implicate fiber pull out or delamination and, thus, do not thoroughly meet the requirements for mass production. Despite this, laser beam cutting has a great potential in large scale cutting of CFRP and is a predominant research topic. Remote laser beam cutting especially provides a good cut surface quality. Currently, the correlation between cutting parameters and edge quality is not sufficiently known. In particular, studies on the dynamic strength of remote laser cut parts are missing. Therefore, fatigue testing was performed with specimens cut by laser radiation and the results were compared with others made by milling and abrasive waterjet cutting. With these experiments, a comparable study of the different methods of CFRP cutting was achieved. The influence of both the heat affected zone (HAZ) and of defects like micro-fissures on the fatigue strength were evaluated.

  12. Effects of foreign object damage from small hard particles on the high-cycle fatigue life of titanium-(6)aluminum-(4)vanadium

    NASA Astrophysics Data System (ADS)

    Hamrick, Joseph L., II

    Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: (1) impact with 2 mm. and 5 mm diameter glass spheres at 305 m/s, (2) impact with 2 mm and 4 mm diameter steel spheres at 305 m/s, (3) quasi-static displacement controlled indentation using steel chisels with 1 mm, 2 nun and 5 mm diameter tips and (4) shearing notches with a 2 mm. diameter chisel point under a quasi-static loading condition. Finite element analysis was used to study the relationship between the stress state created by the plastic damage and the fatigue strength. A new method of quantifying the amount of plastic damage from multiple methods was developed. The fatigue strength required for crack initiation at 10E7 cycles was found to be a function of the total depth from the edge of the undeformed specimen up to the end of the plastically deformed zone. For damage depths less than 1750 mum, the reduction in fatigue strength is proportional to the depth of total damage. For depths > 1750 mum, there appears to be a threshold value of fatigue strength.

  13. Development of India-specific RAFM steel through optimization of tungsten and tantalum contents for better combination of impact, tensile, low cycle fatigue and creep properties

    NASA Astrophysics Data System (ADS)

    Laha, K.; Saroja, S.; Moitra, A.; Sandhya, R.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

    2013-08-01

    Effects of tungsten and tantalum contents on impact, tensile, low cycle fatigue and creep properties of Reduced Activation Ferritic-Martensitic (RAFM) steel were studied to develop India-specific RAFM steel. Four heats of the steel have been melted with tungsten and tantalum contents in the ranges 1-2 wt.% and 0.06-0.14 wt.% respectively. Increase in tungsten content increased the ductile-to-brittle transition temperature (DBTT), low cycle fatigue and creep strength of the steel, whereas the tensile strength was not changed significantly. Increase in tantalum content increased the DBTT and low cycle fatigue strength of the steel whereas the tensile and creep strength decreased. Detailed TEM investigations revealed enhanced microstructural stability of the steel against creep exposure on tungsten addition. The RAFM steel having 1.4 wt.% tungsten with 0.06 wt.% tantalum was found to possess optimum combination of impact, tensile, low cycle fatigue and creep properties and is considered for Indian-specific RAFM steel. Low temperature impact energy of the RAFM steel is quite sensitive to the contents of tungsten and tantalum. The DBTT increased with both the tungsten and tantalum contents. Tungsten and tantalum contents in the investigated ranges had no appreciable effect on the tensile properties of the RAFM steel. Low cycle fatigue life of the RAFM steel increased with the increase in tungsten and tantalum contents. The softening rate with cyclic exposure was lowest for tungsten content of 1.4 wt.%, further increase in tungsten led to an increase in softening rate. Creep deformation and rupture strength of the RAFM steel were found to be quite sensitive to the tungsten and tantalum contents. Creep strength of the steel increased with increase in tungsten content and decreased with increase in tantalum content. Based on the study, the chemical composition of India-specific RAFM steel has been established as 9Cr-1.4W-0.06Ta-V, having optimum combination of strength and

  14. Cycle time influences the development of muscle fatigue at low to moderate levels of intermittent muscle contraction.

    PubMed

    Rashedi, Ehsan; Nussbaum, Maury A

    2016-06-01

    Localized muscle fatigue (LMF) during a repetitive task can be influenced by several aspects such as the level and duration of exertions. Among these aspects, though, the influence of cycle time remains unclear. Here, the effect of cycle time on LMF and performance was examined for a simple biomechanical system during repetitive static efforts. Participants performed 1-h trials of intermittent isometric index finger abduction with a duty cycle of 50% in all combinations of two cycle times (30 and 60s) and two exertion levels (15% and 25% of maximum voluntary capacity). Measures of discomfort, performance (force fluctuations), and muscle capacity (voluntary strength and low-frequency twitch responses) were obtained, all of which demonstrated a beneficial effect of the 30s cycle time. Specifically, the shorter cycle time led to lower rates of increase in perceived discomfort, lower rates of increase in force fluctuations, lower rates of decrease in voluntary capacity, and smaller changes in twitch responses. These benefits, reflecting less LMF development in the shorter cycle time, were quite consistent between genders and the two levels of effort. Results of this study can be used to modify current models predicting work-rest allowance and/or LMF, helping to enhance performance and reduce the risk of adverse musculoskeletal outcomes. PMID:26995711

  15. Ratcheting Assessment of GFRP Composites in Low-Cycle Fatigue Domain

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    The present study intends to examine ratcheting response of Glass Fiber Reinforced Polymer (GFRP) composites over fatigue cycles by means of parametric variables. Stages of ratcheting deformation were related to stress cycles, lifespan, mechanical properties and cyclic stress levels by means of linear and non-linear functions. The coefficients B and C in the proposed ratcheting formulation calibrated ratcheting equation by means of material properties over ratcheting stages. Coefficients A and C calibrated the stages I and II of ratcheting strain curve over stress cycles. The ratcheting curve over initial and final stages was affected as composite modulus of elasticity ( E c ) increased. An increase in E c -dependent coefficients A and B increased the magnitude of ratcheting strains over stress cycles. Ratcheting data for continuous and short fiber GFRP composites with various volume fractions were employed to evaluate the proposed ratcheting formulation. Interaction of ratcheting and fatigue phenomena was further assumed when the proposed parametric ratcheting equation was coupled with a fatigue damage model developed earlier by present authors. Overall damage is achieved from accumulation of ratcheting and fatigue over stress cycles.

  16. Low cycle fatigue behavior of a ferritic reactor pressure vessel steel

    NASA Astrophysics Data System (ADS)

    Sarkar, Apu; Kumawat, Bhupendra K.; Chakravartty, J. K.

    2015-07-01

    The cyclic stress-strain response and the low cycle fatigue (LCF) behavior of 20MnMoNi55 pressure vessel steel were studied. Tensile strength and LCF properties were examined at room temperature (RT) using specimens cut from rolling direction of a rolled block. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The cyclic strain-stress relationships and the strain-life relationships were obtained through the test results, and related LCF parameters of the steel were calculated. The studied steel exhibits cyclic softening behavior. Furthermore, analysis of stabilized hysteresis loops showed that the steel exhibits non-Masing behavior. Complementary scanning electron microscopy examinations were also carried out on fracture surfaces to reveal dominant damage mechanisms during crack initiation, propagation and fracture. Multiple crack initiation sites were observed on the fracture surface. The investigated LCF behavior can provide reference for pressure vessel life assessment and fracture mechanisms analysis.

  17. Influence of cubic boron nitride grinding on the fatigue strengths of carbon steels and a nickel-base superalloy

    SciTech Connect

    Kawagoishi, N.; Chen, Q.; Kondo, E.; Goto, M.; Nisitani, H.

    1999-04-01

    The influence of cubic boron nitride (CBN) grinding on fatigue strength was investigated on an annealed carbon steel, a quenched and tempered carbon steel at room temperature, and a nickel-base superalloy, Inconel 718, at room temperature and 500 C. The results were discussed from several viewpoints, including surface roughness, residual stress, and work hardening or softening due to CBN grinding. The fatigue strength increased upon CBN grinding at room temperature, primarily because of the generation of compressive residual stress in the surface region. However, in the case of Inconel 718, this marked increase in the fatigue strength tended to disappear at the elevated temperature due to the release of compressive residual stress and the decrease of crack growth resistance at an elevated temperature.

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

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  19. Effects of temperature and hold times on low cycle fatigue of Astroloy

    NASA Technical Reports Server (NTRS)

    Choe, S. J.; Stoloff, N. S.; Duquette, D. J.

    1986-01-01

    Low cycle fatigue (LCF) and creep-fatigue-environment interactions of HIP Astroloy were studied at 650 C and 725 C. The results showed that the model proposed by Kaisand and Mowbray (1979) was successful in predicting the magnitude and trend of the fatigue crack growth rate from LCF data. Raising the temperature from 650 C to 725 C did not change the fracture mode, while employing tensile hold caused a change in fracture mode and was more damaging than raising the temperature by 75 C. All samples displayed multiple fracture origins, which is initiated transgranularly in continuous cycling tests and intergranularly in hold time tests. An examination of the secondary crack showed no apparent creep damage. Oxidation in high purity argon appeared to be the major factor in LCF life degradation due to hold time.

  20. Probabilistic high cycle fatigue failure analysis with application to liquid propellant rocket engines

    NASA Technical Reports Server (NTRS)

    Sutharshana, S.; Newlin, L.; Ebbeler, D.; Moore, N.; O'Hara, K.

    1990-01-01

    A probabilistic high cycle fatigue (HCF) failure analysis of a welded duct in a rocket engine of the Space Shuttle main engine class is described. A state-of-the-art HCF failure prediction method was used in a Monte Carlo simulation to generate a distribution of failure lives. A stochastic stress/life model is used for material characterization, and a composite stress history is generated for accurately deriving the stress cycles for the fatigue-damage calculations. The HCF failure model expresses fatigue life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A series of HCF failure life analyses were performed to study the impact of a fixed parameter and to assess the importance of each stochastic input parameter through marginal analyses.

  1. Effect of the Machining Processes on Low Cycle Fatigue Behavior of a Powder Metallurgy Disk

    NASA Technical Reports Server (NTRS)

    Telesman, J.; Kantzos, P.; Gabb, T. P.; Ghosn, L. J.

    2010-01-01

    A study has been performed to investigate the effect of various machining processes on fatigue life of configured low cycle fatigue specimens machined out of a NASA developed LSHR P/M nickel based disk alloy. Two types of configured specimen geometries were employed in the study. To evaluate a broach machining processes a double notch geometry was used with both notches machined using broach tooling. EDM machined notched specimens of the same configuration were tested for comparison purposes. Honing finishing process was evaluated by using a center hole specimen geometry. Comparison testing was again done using EDM machined specimens of the same geometry. The effect of these machining processes on the resulting surface roughness, residual stress distribution and microstructural damage were characterized and used in attempt to explain the low cycle fatigue results.

  2. Microstructure-sensitive weighted probability approach for modeling surface to bulk transition of high cycle fatigue failures dominated by primary inclusions

    NASA Astrophysics Data System (ADS)

    Salajegheh, Nima

    The mechanical alloying and casting processes used to make polycrystalline metallic materials often introduce undesirable non-metallic inclusions and pores. These are often the dominant sites of fatigue failure origination at the low stress amplitudes that correspond to the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regimes, in which the number of cycles to crack initiation is more than 106. HCF and VHCF experiments on some advanced metallic alloys, such as powder metallurgy Ni-base superalloys, titanium alloys, and high-strength steels have shown that the critical inclusions and pores can appear on the surface as well as in the bulk of the specimen. Fatigue lives have been much higher for specimens that fail from a bulk site. The relative number of bulk initiations increases as the stress amplitude decreases such that just below the traditional HCF limit, fatigue life data appears to be evenly scattered between two datasets corresponding to surface and bulk initiations. This is often referred to as surface to bulk transition in the VHCF regime. Below this transition stress, the likelihood of surface versus bulk initiation significantly impacts the low failure probability estimate of fatigue life. Under these circumstances, a large number of very costly experiments need to be conducted to obtain a statistically representative distribution of fatigue life and to predict the surface versus bulk initiation probability. In this thesis, we pursue a simulation-based approach whereby microstructure-sensitive finite element simulations are performed within a statistical construct to examine the VHCF life variability and assess the surface initiation probability. The methodology introduced in this thesis lends itself as a cost-effective platform for development of microstructure-property relations to support design of new or modified alloys, or to more efficiently predict the properties of existing alloys.

  3. Muscle Fatigue Increases Metabolic Costs of Ergometer Cycling without Changing VO2 Slow Component

    PubMed Central

    Ratkevicius, Aivaras; Stasiulis, Arvydas; Dubininkaite, Loreta; Skurvydas, Albertas

    2006-01-01

    The aim of the present study was to investigate effects of muscle fatigue on oxygen costs of ergometer cycling and slow component of pulmonary oxygen uptake (VO2) kinetics. Seven young men performed 100 drop jumps (drop height of 40 cm) with 20 s of rest after each jump. After the subsequent hour of rest, they cycled at 70, 105, 140 and 175 W, which corresponded to 29.6 ± 5.4, 39.4 ± 7.0, 50.8 ± 8.4 and 65.8 ± 11.8 % of VO2peak, respectively, for 6 min at each intensity with 4-min intervals of rest in between the exercise bouts. The VO2 response to cycling after the exercise (fatigue condition) was compared to ergometer cycling without prior exercise (control condition). From 3rd to 6th min of cycling at 105, 140 and 175 W, VO2 was higher (p < 0.05-0.01) when cycling in the fatigue compared to the control condition. Slow component of VO2 kinetics was observed when cycling at 175 W in the control condition (0.17 ± 0.09, l·min-1, mean ± SD), but tended to decrease in the fatigue condition (0.13 ± 0.15 l·min-1). In summary, results of the study are in agreement with the hypothesis that muscle fatigue increases oxygen costs of cycling exercise, but does not affect significantly the slow component of pulmonary oxygen uptake (VO2) kinetics. Key Points Repetitive fatiguing exercise induce an increase in metabolic costs of ergometer cycling exercise. It is argued that muscle pain, muscle temperature, elevated pulmonary ventilation and heart rate, shift towards from carbohydrate to fat metabolism are of minor importance in this phenomenon. Increased recruitment of type II fibres and impaired force transmission between muscle fibres due to damage of structural proteins appear to play the major role in reducing efficiency of ergometer cycling. PMID:24353462

  4. Exploring the optimal pre-sintering temperature on compressive strength and anti-fatigue property of graded zirconia-based glass/zirconia structure.

    PubMed

    Qian, Haixin; Cui, Chang; Su, Tingshu; Zhang, Fuqiang; Sun, Jian

    2016-01-01

    To explore the optimal pre-sintering temperature for graded glass/zirconia material, glass/zirconia specimens were prepared and pre-sintered at 900, 1,000 and 1,100°C respectively, glass infiltration and densification at 1,450°C. Monolith Y-TZP specimens were sintered at 1,450°C. Nanoindentation was used to test Young's modulus and Hardness. Compressive strength test and cycling fatigue test were conducted. Nanoindentation test showed graded change of Young's modulus in glass/zirconia structure. The compressive strength and the number of cycles to failure of specimens pre-sintered at 1,000°C were significantly higher than those of Y-TZP and the specimens pre-sintered at 900 and 1,000°C (p<0.05). It is concluded that when the pre-sintering temperature is set at 1,000°C, the graded glass/zirconia structure exhibits the most optimal compressive strength and anti-fatigue property. PMID:27251987

  5. 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.

  6. Fatigue

    MedlinePlus

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

  7. Low-cycle fatigue behavior of polycrystalline NiAl at 1000 K

    SciTech Connect

    Lerch, B.A.; Noebe, R.D. )

    1994-02-01

    The low-cycle fatigue behavior of polycrystalline NiAl was determined at 1000 K, a temperature above the monotonic brittle-to-ductile transition temperature (BDTT). Fully reversed, plastic strain-controlled fatigue tests were conducted on B2 intermetallic samples prepared by two fabrication techniques: hot isostatic pressing (HIP) of prealloyed powders and extrusion of vacuum induction-melted [cast plus extruded (C + E)] castings. At 1,000 K, in an air environment both the hot-isostatically pressed ( hipped') and C + E samples cyclically softened throughout most of their fatigue lives, though the absolute change in stress was no greater than about 35 MPa. At this temperature, samples were insensitive to processing defects, which were a source of failure initiation in room-temperature tests. The processing method had a small effect on fatigue life; the lives of the hipped samples were about a factor of 3 shorter than the fatigue lives of the C + E NiAl. The C + E material also underwent dynamic grain growth during testing, while the hipped NiAl maintained a constant grain size. Stable fatigue-crack growth in both materials was intergranular in nature, while final fracture by tensile overload occurred by transgranular cleavage. However, at plastic strain ranges below 0.3 pct, the fatigue lives of the hipped NiAl were controlled by intergranular cavitation and creep processes such that the fatigue lives were shorter than anticipated. Finally, hipped samples tested in vacuum had a factor of 3 longer life than specimens tested in air.

  8. High fatigue strength and enhanced biocompatibility of UFG CP Ti for medical innovative applications

    NASA Astrophysics Data System (ADS)

    Polyakov, A. V.; Semenova, I. P.; Valiev, R. Z.

    2014-08-01

    This study is focused on the fatigue properties of the UFG Ti Grade 4 and its biocompatibility. The UFG titanium was produced by ECAP-Conform in combination with subsequent drawing, which allows fabricating rods of up to 3 mm suitable for industrial applications. The endurance limit of smooth and notched samples of UFG Ti is considerably higher than in conventional Ti. The UFG Ti also demonstrates an increased capacity of human osteoblast-like U2OS cells to colonize and, therefore, better osseointegration. Torsional strength of standard Ti-6Al-7Nb products and UFG Ti Grade 4 products was evaluated. An advantage of the UFG titanium over the conventional coarse-grained material was shown.

  9. Effect of alternately high and low repeated stresses upon the fatigue strength of 25S-T aluminum alloy

    NASA Technical Reports Server (NTRS)

    Stickley, G W

    1941-01-01

    Fatigue tests were made on one lot of 3/4 inch diameter rolled-and-drawn 25S-T aluminum-alloy rod normal in composition and tensile properties. The specimens were tested at 3500 cycles per second in a rotating-beam fatigue test machine. Tests were made for three ratios (20:1, 50:1, and 200:1) of the number of cycles applied at low stress to the number applied at high stress. In general, failure occurred when the number of cycles at either the low or the high stress approached the ordinary fatigue curve for the material, regardless of the sequence in which the stresses were applied.

  10. Low cycle fatigue of FeAl(42 at. % Al) at room temperature

    SciTech Connect

    Hanes, D.B.; Gibala, R.

    1997-12-31

    The monotonic mechanical behavior in tension and compression of FeAl has been well documented. However, very little work has been done on the cyclic deformation behavior of this material. In this work, the behavior of FeAl (42 at. % Al) under low cycle fatigue was studied, including the effects of test environments and surface coatings. It was found that the fatigue life of this alloy is limited by environmental embrittlement. This embrittlement process can be equally well prevented by deformation in an oxygen environment or by coating the alloy with a protective film. The type of film applied appears to have little effect. Similar results were seen in monotonic testing.

  11. On the Specific Role of Microstructure in Governing Cyclic Fatigue, Deformation, and Fracture Behavior of a High-Strength Alloy Steel

    NASA Astrophysics Data System (ADS)

    Manigandan, K.; Srivatsan, T. S.

    2015-06-01

    In this paper, the results of an experimental study that focused on evaluating the conjoint influence of microstructure and test specimen orientation on fully reversed strain-controlled fatigue behavior of the high alloy steel X2M are presented and discussed. The cyclic stress response of this high-strength alloy steel revealed initial hardening during the first few cycles followed by gradual softening for most of fatigue life. Cyclic strain resistance exhibited a linear trend for the variation of elastic strain amplitude with reversals to failure, and plastic strain amplitude with reversals to failure. Fracture morphology was the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, the alloy steel revealed fracture to be essentially ductile with features reminiscent of predominantly "locally" ductile and isolated brittle mechanisms. The mechanisms governing stress response at the fine microscopic level, fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

  12. Low-cycle impact fatigue of SiC{sub W}/7475Al composite

    SciTech Connect

    Yang, P.; Liu, Y.; Xu, F.

    1998-10-01

    Important uses in the future for metal-matrix composites are in aerospace, weaponry, and high-speed power plants in which the inertial force produced by great acceleration is a load of high strain rate. Therefore close attention is given to the mechanical behavior of a composite at high strain rates. This paper reports a study of the behavior and mechanisms of a SiC{sub w}/7475 composite in low-cycle impact fatigue (LCIF). The LCIF and impact tension tests were conducted by using the push-pull impact fatigue apparatus developed by the authors, in which the loading assembly was actually a combination of a Hopkinson`s pressure bar and an extension bar. In the apparatus the trapezoidal stress wave loads were produced. The strain rates in specimens may reach 400 s{sup {minus}1}. The results show that for a SiC{sub w}/7475 composite, the strain-rate effects on yield stress, ductility, cyclic hardening and softening, {Delta}{epsilon}{sub e}/2 {minus} N{sub f} relation, and transition life were slight. In low-cycle impact fatigue the cracks often initiated within or near the SiC particles, which mingled in the composite. The SiC{sub w}/7475 composite was found to be less ductile than its alloy matrix; in low-cycle fatigue brittleness appears. Therefore great attention must be given to the behavior of the composite when it is used as a structural material.

  13. An in vitro investigation into retention strength and fatigue resistance of various designs of tooth/implant supported overdentures.

    PubMed

    Fatalla, Abdalbseet A; Song, Ke; Du, Tianfeng; Cao, Yingguang

    2012-02-01

    Previously, the choice of prosthetic implant-retained overdentures has depended on data from previous studies about the retention-fatigue strength of the attachment system selected. Little or no data have been available on the correlation between the attachment system selected and the overdenture support configuration. The purpose of the present study was to evaluate the retention force and fatigue resistance of three attachment systems and four support designs of overdenture prosthesis. Four lower edentulous acrylic models were prepared and eight combinations of attachments groups were investigated in the study. These included: O-Rings with mini-dental implants (MDIs), Dalbo elliptic with Dalbo Rotex and fabricated flexible acrylic attachments with both MDI and Dalbo Rotex. The study was divided into four test groups: groups A and B, controls, and groups C and D, experimental groups. Control group A contained three overdenture supports: two free standing MDIs in the canine region and at the midline, and one simulated tooth root with Dalbo Rotex screwed in. Control group B contained four overdenture support foundations: two free standing MDIs in the right canine region and the first premolar region, and two simulated tooth roots with Dalbo Rotex screwed in at the same MDI position, but on the left side of the model. Experimental group C contained three overdenture support foundations: two free standing MDIs in the canine region and at the midline, and one simulated tooth root with MDI screwed in. Experimental group D contained four overdenture support foundations: two free standing MDIs in the right canine region and the first premolar region, and two simulated tooth roots with MDIs screwed in at the same MDI position, but on the left side of the model. Each group was further divided into two subgroups according to attachment type used. Five samples were prepared for each group. Retention force (N) values were recorded initially (0 cycles) and after 360, 720, 1440

  14. Influence of creep damage on the low cycle thermal-mechanical fatigue behavior of two tantalum base alloys

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.; Doble, G. S.

    1972-01-01

    Low cycle fatigue tests have been performed on the tantalum base alloys T-111 and ASTAR 811C with synchronized, independently programmed temperature and strain cycling. The thermal-mechanical cycles applied fell into three basic categories: these were isothermal cycling, in-phase thermal cycling, and out-of-phase thermal cycling. In-phase cycling was defined as tensile deformation associated with high temperature and compressive deformation with low temperature, while out-of-phase thermal cycling was defined as the reverse case. The in-phase thermal cycling had a pronounced detrimental influence on the fatigue life of both alloys, with the life reduction being greater in the solid solution strengthened T-111 alloy than in the carbide strengthened ASTAR 811C alloy. The out-of-phase tests also showed pronounced effects on the fatigue life of both alloys, although not as dramatic.

  15. Energy Approach-Based Simulation of Structural Materials High-Cycle Fatigue

    NASA Astrophysics Data System (ADS)

    Balayev, A. F.; Korolev, A. V.; Kochetkov, A. V.; Sklyarova, A. I.; Zakharov, O. V.

    2016-02-01

    The paper describes the mechanism of micro-cracks development in solid structural materials based on the theory of brittle fracture. A probability function of material cracks energy distribution is obtained using a probabilistic approach. The paper states energy conditions for cracks growth at material high-cycle loading. A formula allowing to calculate the amount of energy absorbed during the cracks growth is given. The paper proposes a high- cycle fatigue evaluation criterion allowing to determine the maximum permissible number of solid body loading cycles, at which micro-cracks start growing rapidly up to destruction.

  16. Influence of subsolvus thermomechanical processing on the low-cycle fatigue properties of haynes 230 alloy

    NASA Astrophysics Data System (ADS)

    Vecchio, Kenneth S.; Fitzpatrick, Michael D.; Klarstrom, Dwaine

    1995-03-01

    Strain-controlled low-cycle fatigue tests have been conducted in air at elevated temperature to determine the influence of subsolvus thermomechanical processing on the low-cycle fatigue (LCF) behavior of HAYNES 230 alloy. A series of tests at various strain ranges was conducted on material experimentally processed at 1121 °C, which is below the M23C6 carbide solvus temperature, and on material fully solution annealed at 1232 °C. A comparative strain-life analysis was performed on the LCF results, and the cyclic hardening/softening characteristics were examined. At 760 °C and 871 °C, the fatigue life of the experimental 230/1121 material was improved relative to the standard 230/1232 material up to a factor of 3. The fatigue life advantage of the experimental material was related primarily to a lower plastic (inelastic) strain amplitude response for a given imposed total strain range. It appears the increase in monotonic flow stress exhibited by the finer grain size experimental material has been translated into an increase in cyclic flow stress at the 760 °C and 871 °C test temperatures. Both materials exhibited entirely transgranular fatigue crack initiation and propagation modes at these temperatures. The LCF performance of the experimental material in tests performed at 982 °C was improved relative to the standard material up to a factor as high as 2. The life advantage of the 230/1121 material occurred despite having a larger plastic strain amplitude than the standard 230/1232 material for a given total strain range. Though not fully understood at present, it is suspected that this behavior is related to the deleterious influence of grain boundaries in the fatigue crack initiations of the standard processed material relative to the experimental material, and ultimately to differences in carbide morphology as a result of thermomechanical processing.

  17. Advanced Finite Element Modeling of Low Cycle Fatigue Crack Growth

    NASA Technical Reports Server (NTRS)

    Gregg, Wayne; McGill, Preston; Swanson, Greg; Wells, Doug; Throckmorton, D. A. (Technical Monitor)

    2001-01-01

    This document (a viewgraph presentation) assumes a crack-like defect of a size which may be missed in inspection will exist in most critical location of any critical structure or component. Flaw existence assumption is usually, but not always, conservative based on past experiences in NASA and knowledge of manufacturing processes. Cyclic, environmental, and sustained loads used to generate stresses on models. Fracture Mechanics analysis used to predict crack growth and residual strength. Must show that defective structure will still provide four times required mission lifetime. Special exemptions cover redundant structures, low risk parts, etc. Assessments require specialized software tools, experienced analysts, and reliable material crack growth rate test database.

  18. A New High-Speed, High-Cycle, Gear-Tooth Bending Fatigue Test Capability

    NASA Technical Reports Server (NTRS)

    Stringer, David B.; Dykas, Brian D.; LaBerge, Kelsen E.; Zakrajsek, Andrew J.; Handschuh, Robert F.

    2011-01-01

    A new high-speed test capability for determining the high cycle bending-fatigue characteristics of gear teeth has been developed. Experiments were performed in the test facility using a standard spur gear test specimens designed for use in NASA Glenn s drive system test facilities. These tests varied in load condition and cycle-rate. The cycle-rate varied from 50 to 1000 Hz. The loads varied from high-stress, low-cycle loads to near infinite life conditions. Over 100 tests were conducted using AISI 9310 steel spur gear specimen. These results were then compared to previous data in the literature for correlation. Additionally, a cycle-rate sensitivity analysis was conducted by grouping the results according to cycle-rate and comparing the data sets. Methods used to study and verify load-path and facility dynamics are also discussed.

  19. Low ponderal index is associated with decreased muscle strength and fatigue resistance in college-aged women

    PubMed Central

    Brutsaert, Tom D.; Tamvada, Kelli H.; Kiyamu, Melisa; White, Daniel D.; Gage, Timothy B

    2011-01-01

    Poor fetal growth is associated with decrements in muscle strength likely due to changes during myogenesis. We investigated the association of poor fetal growth with muscle strength, fatigue resistance, and the response to training in the isolated quadriceps femoris. Females (20.6 yrs) born to term but below the 10th percentile of ponderal index (PI)-for-gestational-age (LOWPI, n=14) were compared to controls (HIGHPI, n=14), before and after an 8-week training. Muscle strength was assessed as grip-strength and as the maximal isometric voluntary contraction (MVC) of the quadriceps femoris. Muscle fatigue was assessed during knee extension eercise. Body composition and the maximal oxygen consumption (VO2max) were also measured. Controlling for fat free mass (FFM), LOWPI versus HIGHPI women had ~11% lower grip-strength (P=0.023), 9–24% lower MVC values (P=0.042 pre-trained; P=0.020 post-trained), a higher rate of fatigue (pre- and post-training), and a diminished training response (P=0.016). Statistical control for FFM increased rather than decreased strength differences between PI groups. The PI was not associated with VO2max or measures of body composition. Strength and fatigue decrements strongly suggest that poor fetal growth affects the pathway of muscle force generation. This could be due to neuromotor and/or muscle morphologic changes during development e.g., fiber number, fiber type, etc. Muscle from LOWPI women may also be less responsive to training. Indirectly, results also implicate muscle as a potential mediator between poor fetal growth and adult chronic disease, given muscle’s direct role in determining insulin resistance, type II diabetes, physical activity, and so forth. PMID:21641734

  20. Prediction of low-cycle fatigue-life by acoustic emission—2: 7075-T6 aluminum alloy

    SciTech Connect

    Baram, J.; Rosen, M.

    1981-01-01

    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.

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

    SciTech Connect

    Wu, Wei; An, Ke

    2015-10-03

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

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

    DOE PAGESBeta

    Wu, Wei; An, Ke

    2015-10-03

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

  3. Integrating water flow, locomotor performance and respiration of Chinese sturgeon during multiple fatigue-recovery cycles.

    PubMed

    Cai, Lu; Chen, Lei; Johnson, David; Gao, Yong; Mandal, Prashant; Fang, Min; Tu, Zhiying; Huang, Yingping

    2014-01-01

    The objective of this study is to provide information on metabolic changes occurring in Chinese sturgeon (an ecologically important endangered fish) subjected to repeated cycles of fatigue and recovery and the effect on swimming capability. Fatigue-recovery cycles likely occur when fish are moving through the fishways of large dams and the results of this investigation are important for fishway design and conservation of wild Chinese sturgeon populations. A series of four stepped velocity tests were carried out successively in a Steffensen-type swimming respirometer and the effects of repeated fatigue-recovery on swimming capability and metabolism were measured. Significant results include: (1) critical swimming speed decreased from 4.34 bl/s to 2.98 bl/s; (2) active oxygen consumption (i.e. the difference between total oxygen consumption and routine oxygen consumption) decreased from 1175 mgO2/kg to 341 mgO2/kg and was the primary reason for the decrease in Ucrit; (3) excess post-exercise oxygen consumption decreased from 36 mgO2/kg to 22 mgO2/kg; (4) with repeated step tests, white muscle (anaerobic metabolism) began contributing to propulsion at lower swimming speeds. Therefore, Chinese sturgeon conserve energy by swimming efficiently and have high fatigue recovery capability. These results contribute to our understanding of the physiology of the Chinese sturgeon and support the conservation efforts of wild populations of this important species. PMID:24714585

  4. Fatigue Response of a PZT Multilayer Actuator under High-Field Electric Cycling with Mechanical Preload

    SciTech Connect

    Wang, Hong; Wereszczak, Andrew A; Lin, Hua-Tay

    2009-01-01

    An electric fatigue test system has been developed for piezoelectric actuator with a mechanical loading capability. Fatigue responses of a lead zirconate titanate (PZT) multilayer actuator (MLA) with a plate-through electrode configuration have been studied under an electric field (1.7 times that of a coercive field of PZT material) and a concurrent mechanical preload (30.0 MPa). A total of 1.0x10^9 cycles were carried out. Variations in charge density and mechanical strain under a high electric field and constant mechanical loads were observed during the fatigue test. The dc and the first harmonic (at 10 Hz) dielectric and piezoelectric coefficients were subsequently characterized by using FFT (Fast Fourier Transformation). It has been observed that both the dielectric and the piezoelectric coefficients underwent a monotonic decrease prior to 2.86x10^8 cycles under the relevant preload, and then fluctuated to a certain extent. Both the dielectric loss tangent and the piezoelectric loss tangent also exhibited the fluctuations after a certain amount of drop but at different levels relative to the pre-fatigue. And finally, the results were discussed with respect to domain wall mobility, microcracking, and other pre-existing anomalies.

  5. Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Krantz, Timothy L.; Lerch, Bradley A.; Burke, Christopher S.

    2007-01-01

    An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semilogarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

  6. Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Krantz, Timothy L.; Lerch, Bradley A.; Burke, Christopher S.

    2007-01-01

    An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semi-logarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

  7. High-temperature, low-cycle fatigue of advanced copper-base alloys for rocket nozzles. Part 1: Narloy Z

    NASA Technical Reports Server (NTRS)

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1974-01-01

    Short-term tensile and low-cycle fatigue data are reported for Narloy Z, a centrifugally cast, copper-base alloy. Tensile tests were performed at room temperature in air and in argon at 482, 538 and 593 C using an axial strain rate of .002/sec to the -1 power. In addition tensile tests were performed at 538 C in an evaluation of tensile properties at strain rates of .004 and .01/sec to the -1 power. Ultimate and yield strength values of about 315 and 200 MN/sq m respectively were recorded at room temperature and these decreased to about 120 and 105 respectively as the temperature was increased to 593 C. Reduction in area values were recorded in the range from 40 to 50% with some indication of a minimum ductility point at 538 C.

  8. Fatigue

    MedlinePlus

    ... Fatigue can be a symptom of anemia, particularly iron-deficiency anemia . Your body needs iron to make hemoglobin, the substance in red blood ... tissues and to your baby. Your need for iron increases during pregnancy because of the needs of ...

  9. A study of microstructure, quasi-static response, fatigue, deformation and fracture behavior of high strength alloy steels

    NASA Astrophysics Data System (ADS)

    Kannan, Manigandan

    The history of steel dates back to the 17th century and has been instrumental in the betterment of every aspect of our lives ever since, from the pin that holds the paper together to the Automobile that takes us to our destination steel touches everyone every day. Path breaking improvements in manufacturing techniques, access to advanced machinery and understanding of factors like heat treatment, corrosion resistance have aided in the advancement in the properties of steel in the last few years. In this dissertation document, the results of a study aimed at the influence of alloy chemistry, processing and influence of the quasi static and fatigue behavior of seven alloy steels is discussed. The microstructure of the as-received steel was examined and characterized for the nature and morphology of the grains and the presence of other intrinsic features in the microstructure. The tensile, cyclic fatigue and bending fatigue tests were done on a fully automated closed-loop servo-hydraulic test machine at room temperature. The failed samples of high strength steels were examined in a scanning electron microscope for understanding the fracture behavior, especially the nature of loading be it quasi static, cyclic fatigue or bending fatigue . The quasi static and cyclic fatigue fracture behavior of the steels examined coupled with various factors contributing to failure are briefly discussed in light of the conjoint and mutually interactive influences of intrinsic microstructural effects, nature of loading, and stress (load)-deformation-microstructural interactions.

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

    NASA Technical Reports Server (NTRS)

    Kihm, Frederic; Rizzi, Stephen A.

    2014-01-01

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

  11. MECHANICAL STRAIN AND PIEZOELECTRIC PROPERTIES OF PZT STACKS RELATED TO SEMI-BIPOLAR ELECTRIC CYCLING FATIGUE

    SciTech Connect

    Wang, Hong; Lin, Hua-Tay; Wereszczak, Andrew A; Cooper, Thomas A

    2009-01-01

    PZT stacks that had an inter-digital internal electrode configuration and consisted of a specific number of multilayer actuators were tested to more than 108 cycles by using a 100-Hz semi-bipolar sine wave with a field range of +4.5/-0.9 kV/mm and a 20-MPa mechanical preload. Significant reductions in mechanical strain and piezoelectric coefficients were observed during the fatigue cycling, depending on the measuring condition. Extensive surface discharges and arcs were also observed. These surface events as well as related dielectric breakdown resulted in the erosion of external electrode and outcrop of internal electrode, and that partially accounts for the reduction observed above. The data obtained in this study demonstrated the feasibility of using a semi-bipolar mode to drive a PZT stack with a designed mechanical preload applied and illustrated the potential fatigue of stack~{!/~}s performance during its service.

  12. Ductile and Compacted Graphite Iron Casting Skin -- Evaluation, Effect on Fatigue Strength and Elimination

    NASA Astrophysics Data System (ADS)

    Boonmee, Sarum

    Compacted graphite (CG) iron features a good combination of tensile strength, impact resistance, thermal conductivity and damping capacity. This combination makes CG iron a material of choice for various applications, especially for the automobile industry. The mechanical properties of CG iron listed in the standards (i.e. ASTM) are for machined specimens. However, since most iron castings retain the original casting surface (a.k.a. casting skin), the actual performance of the part could be significantly different from that of the machined specimens. Recent studies have shown the negative effect of the casting skin, but little quantification of its effect on mechanical properties is available. Further, the understanding of its mechanism of formation is at best incomplete. In this research, the effect of the casting skin on mechanical properties in CG and ductile irons (DI) is explored. The differences in tensile and fatigue properties between as-cast and machined samples were quantified and correlated to the casting skin features. It was found that the presence of the casting skin was accountable for 9% reduction of tensile strength and up to 32% reduction of fatigue strength (for CG iron with 40% nodularity). Several mechanisms of the casting skin formation are proposed in this research. The formation of ferritic and pearlitic rims is explained by decarburizing/carburizing reactions at the mold/metal interface. Mg depletion and solidification kinetics effect were identified as the formation mechanisms of the graphite degradation. A 2-D thermal diffusion model was formulated based on Mg depletion theory. The model can be used to predict the casting skin thickness when Mg depletion is the dominant mechanism. Furthermore, using the asymmetric Fe-Gr phase diagram, some instances of casting skin formation were explained based on solidification kinetics theory. The experimental microstructural evidence and the theoretical progress were conducive to the development of

  13. Thermal High- and Low-Cycle Fatigue Behavior of Thick Thermal Barrier Coating Systems

    NASA Technical Reports Server (NTRS)

    Miller, Robert A.

    1998-01-01

    Ceramic thermal barrier coatings have received increasing attention for advanced gas turbine and diesel engine applications because of their ability to provide thermal insulation to engine components. However, the durability of these coatings under the severe thermal cycling conditions encountered in a diesel engine (ref. 1) still remains a major issue. In this research at the NASA Lewis Research Center, a high-power laser was used to investigate the thermal fatigue behavior of a yttria-stabilized zirconia coating system under simulated diesel engine conditions. The mechanisms of fatigue crack initiation and propagation, and of coating failure under complex thermal low-cycle fatigue (LCF, representing stop/start cycles) and thermal high-cycle fatigue (HCF, representing operation at 1300 rpm) are described. Continuous wave and pulse laser modes were used to simulate pure LCF and combined LCF/HCF, respectively (ref. 2). The LCF mechanism was found to be closely related to the coating sintering and creep at high temperatures. These creep strains in the ceramic coating led to a tensile stress state during cooling, thus providing the major driving force for crack growth under LCF conditions. The combined LCF/HCF tests induced more severe coating surface cracking, microspallation, and accelerated crack growth than did the pure LCF test. HCF thermal loads also facilitated lateral crack branching and ceramic/bond coat interface delaminations. HCF is associated with the cyclic stresses originating from the high-frequency temperature fluctuation at the ceramic coating surface. The HCF thermal loads act on the crack by a wedging mechanism (ref. 1), resulting in continuous crack growth at temperature. The HCF stress intensity factor amplitude increases with the interaction depth and temperature swing, and decreases with the crack depth. HCF damage also increases with the thermal expansion coefficient and the Young's modulus of the ceramic coating (refs. 1 and 3).

  14. Enhancing the mechanical integrity of the implant-bone interface with BoneWelding technology: determination of quasi-static interfacial strength and fatigue resistance.

    PubMed

    Ferguson, Stephen J; Weber, Urs; von Rechenberg, Brigitte; Mayer, Joerg

    2006-04-01

    The BoneWelding technology is an innovative bonding method, which offers new alternatives in the treatment of fractures and other degenerative disorders of the musculoskeletal system. The BoneWelding process employs ultrasonic energy to liquefy a polymeric interface between orthopaedic implants and the host bone. Polymer penetrates the pores of the surrounding bone and, following a rapid solidification, forms a strong and uniform bond between implant and bone. Biomechanical testing was performed to determine the quasi-static push-out strength and fatigue performance of 3.5-mm-diameter polymeric dowels bonded to a bone surrogate material (Sawbones solid and cellular polyurethane foam) using the BoneWelding process. Fatigue tests were conducted over 100,000 cycles of 20-100 N loading. Mechanical test results were compared with those obtained with a comparably-sized, commercial metallic fracture fixation screw. Tests in surrogate bone material of varying density demonstrated significantly superior mechanical performance of the bonded dowels in comparison to conventional bone screws (p < 0.01), with holding strengths approaching 700 N. Even in extremely porous host material, the performance of the bonded dowels was equivalent to that of the bone screws. For both cellular and solid bone analog materials, failure always occurred within the bone analog material surrounding and distant to the implant; the infiltrated interface was stronger than the surrounding bone analog material. No significant decrease in interfacial strength was observed following conditioning in a physiological saline solution for a period of 1 month prior to testing. Ultrasonically inserted implants migrated, on average, less than 20 microm over, and interfacial stiffness remained constant the full duration of fatigue testing. With further refinement, the BoneWelding technology may offer a quicker, simpler, and more effective method for achieving strong fixation and primary stability for fracture

  15. Influence of subsolvus thermomechanical processing on the low-cycle fatigue properties of HAYNES 230 alloy

    SciTech Connect

    Vecchio, K.S.; Fitzpatrick, M.D.; Klarstrom, D.

    1995-03-01

    Strain-controlled low-cycle fatigue tests have been conducted in air at elevated temperature to determine the influence of subsolvus thermomechanial processing on the low-cycle fatigue (LCF) behavior of HAYNES 230 alloy. A series of tests at various strain ranges was conducted on material experimentally processed at 1,121 C, which is below the M{sub 23}C{sub 6} carbide solvus temperature, and on material fully solution annealed at 1,232 C. A comparative strain-life analyses was performed on the LCF results, and the cyclic hardening/softening characteristics were examined. At 760 C and 871 C, the fatigue life of the experimental 230/1121 material was improved relative to the standard 230/1232 material up to a factor of 3. The fatigue life advantage of the experimental material was related primarily to a lower plastic (inelastic) strain amplitude response for a given imposed total strain range. It appears the increase in monotonic flow stress exhibited by the finer grain size experimental material has been translated into an increase in cyclic flow stress at the 760 C and 871 C test temperature. Both materials exhibited entirely transgranular fatigue crack initiation and propagation modes at these temperature. The LCF performance of the experimental material in tests performed at 982 C was improved relative to the standard material up to a factor as high as 2. The life advantage of the 230/1121 material occurred despite having a larger plastic strain amplitude than the sandbar 230/1232 material for a given total strain range.

  16. On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550?C

    SciTech Connect

    Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

    2012-04-01

    The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed) condition. Although the fatigue resistance of the Ti-6Al-4V alloy declined with increasing test temperature regardless of surface condition, deep-rolling and laser-shock peening surface treatments were found to extend the fatigue lives by factors of more than 30 and 5-10, respectively, in the high-cycle and low-cycle fatigue regimes at temperatures as high as 550?C. At these temperatures, compressive residual stresses are essentially relaxed; however, it is the presence of near-surface work hardened layers, with a nanocystalline structure in the case of deep-rolling and dense dislocation tangles in the case of laser-shock peening, which remain fairly stable even after cycling at 450?-550?C, that provide the basis for the beneficial role of mechanical surface treatments on the fatigue strength of Ti-6Al-4V at elevated temperatures.

  17. Effect of environment on low-cycle fatigue of a nickel-titanium instrument.

    PubMed

    Cheung, Gary S P; Shen, Ya; Darvell, Brian W

    2007-12-01

    This study examined the low-cycle fatigue (LCF) behavior of a nickel-titanium (NiTi) engine-file under various environmental conditions. One brand of NiTi instrument was subjected to rotational-bending fatigue in air, deionized water, sodium hypochlorite, or silicone oil. The curvature of each instrument, diameter of the fracture cross-section, and the number of rotations to failure were determined. The strain-life relationship in the LCF region was examined by using one-way analysis of variance, and the number of crack origins with chi2, for differences between groups. The results showed a linear relationship, on logarithmic scales, between the LCF life and the surface strain amplitude; regression line slopes were significantly different between noncorrosive (air, silicone oil) and corrosive (water, hypochlorite) environments (P < .05), as well as number of crack origins (P < .05). Hypochlorite was more detrimental to fatigue life than water. In conclusion, environmental conditions significantly affect the LCF behavior of NiTi rotary instruments. Fatigue testing of NiTi engine-files should be in a service-like environment. PMID:18037053

  18. The effect of a carbohydrate mouth-rinse on neuromuscular fatigue following cycling exercise.

    PubMed

    Jeffers, Robert; Shave, Robert; Ross, Emma; Stevenson, Emma J; Goodall, Stuart

    2015-06-01

    Carbohydrate (CHO) mouth-rinsing, rather than ingestion, is known to improve performance of high-intensity (>75% maximal oxygen uptake) short-duration (≤1 h) cycling exercise. Mechanisms responsible for this improvement, however, are unclear. The present study aimed to investigate the effect of a CHO mouth-rinse on cycling time-trial (TT) performance and mechanisms of fatigue. On 2 separate occasions, 9 male cyclists (mean ± SD; maximal oxygen uptake, 61 ± 5 mL·kg(-1)·min(-1)) completed 45 min at 70% maximum power output (preload) followed by a 15-min TT. At 7.5-min intervals during the preload and TT, participants were given either a tasteless 6.4% maltodextrin mouth-rinse (CHO) or water (placebo (PLA)) in a double-blind, counterbalanced fashion. Isometric knee-extension force and electromyographic responses to percutaneous electrical stimulation and transcranial magnetic stimulation were measured before, after the preload, and after the TT. There were greater decreases in maximal voluntary contraction after the TT in PLA (20% ± 10%) compared with the CHO (12% ± 8%; P = 0.019). Voluntary activation was reduced following exercise in both trials, but did not differ between conditions (PLA -10% ± 8% vs. CHO -5% ± 4%; P = 0.150). The attenuation in the manifestation of global fatigue did not translate into a TT improvement (248 ± 23 vs. 248 ± 39 W for CHO and PLA, respectively). Furthermore, no differences in heart rate or ratings of perceived exertion were found between the 2 conditions. These data suggest that CHO mouth-rinsing attenuates neuromuscular fatigue following endurance cycling. Although these changes did not translate into a performance improvement, further investigation is required into the role of CHO mouth-rinse in alleviating neuromuscular fatigue. PMID:25923580

  19. 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.

  20. High-temperature reverse-bend fatigue strength of Inconel Alloy 625

    SciTech Connect

    Purohit, A.; Greenfield, I.G.; Park, K.B.

    1983-06-01

    Inconel 625 has been selected as the clad material for Upgraded Transient Reactor Test Facility (TREAT Upgrade or TU) fuel assemblies. The range of temperatures investigated is 900 to 1100/sup 0/C. A reverse-bend fatigue test program was selected as the most-effective method of determining the fatigue characteristics of Inconel alloy 625 sheet metal. The paper describes the reverse bend fatigue experiments, the results obtained, and the analysis of data.

  1. An active control logic to improve the fatigue strength of smart flexible structures

    NASA Astrophysics Data System (ADS)

    Ambrosio, Pasquale; Braghin, Francesco; Resta, Ferruccio; Ripamonti, Francesco

    2013-04-01

    In general active vibration control intrinsically implies a fatigue damage reduction. Anyway, this assumption is not always verified. In these cases it is possible to deeper investigate the fatigue phenomena on smart flexible structures and their reduction from a control point of view. In this article, to identify the problem main parameters, a simplified interpretation of fatigue damage is given using the frequency analysis framework. Then, the active control logic is defined as an optimization problem with a quadratic functional taking into account the previously cited parameters. Finally, because of non-linearity of fatigue phenomenon, an adaptive approach is applied and a numerical/experimental validation is carried out.

  2. Dwell Notch Low Cycle Fatigue Behavior of a Powder Metallurgy Nickel Disk Alloy

    NASA Technical Reports Server (NTRS)

    Telesman, J.; Gabb, T. P.; Yamada, Y.; Ghosn, L. J.; Jayaraman, N.

    2012-01-01

    A study was conducted to determine the processes which govern dwell notch low cycle fatigue (NLCF) behavior of a powder metallurgy (P/M) ME3 disk superalloy. The emphasis was placed on the environmentally driven mechanisms which may embrittle the highly stressed notch surface regions and reduce NLCF life. In conjunction with the environmentally driven notch surface degradation processes, the visco-plastic driven mechanisms which can significantly change the notch root stresses were also considered. Dwell notch low cycle fatigue testing was performed in air and vacuum on a ME3 P/M disk alloy specimens heat treated using either a fast or a slow cooling rate from the solutioning treatment. It was shown that dwells at the minimum stress typically produced a greater life debit than the dwells applied at the maximum stress, especially for the slow cooled heat treatment. Two different environmentally driven failure mechanisms were identified as the root cause of early crack initiation in the min dwell tests. Both of these failure mechanisms produced mostly a transgranular crack initiation failure mode and yet still resulted in low NLCF fatigue lives. The lack of stress relaxation during the min dwell tests produced higher notch root stresses which caused early crack initiation and premature failure when combined with the environmentally driven surface degradation mechanisms. The importance of environmental degradation mechanisms was further highlighted by vacuum dwell NLCF tests which resulted in considerably longer NLCF lives, especially for the min dwell tests.

  3. Probabilistic low cycle fatigue failure analysis with application to liquid propellant rocket engines

    NASA Technical Reports Server (NTRS)

    Newlin, L.; Sutharshana, S.; Ebbeler, D.; Moore, N.; Fox, E.

    1990-01-01

    A probabilistic Low Cycle Fatigue (LCF) failure analysis of a candidate turbine disk for use in a turbopump of a rocket engine of the Space Shuttle Main Engine class is described. A state-of-the-art LCF failure prediction method was used in a Monte Carlo simulation to generate a distribution of failure lives. A stochastic Stress/Life (S/N) model was used for materials characterization. The LCF failure model expresses fatigue life as a function of stochastic parameters including environmental parameters, loads, material properties, structural parameters, and model specification errors. The rationale for the particular characterization of each stochastic input parameter is described. The results and interpretation of the failure analysis are given.

  4. Influence of High Cycle Thermal Loads on Thermal Fatigue Behavior of Thick Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    1997-01-01

    Thick thermal barrier coating systems in a diesel engine experience severe thermal Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF) during engine operation. In the present study, the mechanisms of fatigue crack initiation and propagation, as well as of coating failure, under thermal loads which simulate engine conditions, are investigated using a high power CO2 laser. In general, surface vertical cracks initiate early and grow continuously under LCF and HCF cyclic stresses. It is found that in the absence of interfacial oxidation, the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. Experiments show that the HCF cycles are very damaging to the coating systems. The combined LCF and HCF tests produced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. It is suggested that the HCF component cannot only accelerate the surface crack initiation, but also interact with the LCF by contributing to the crack growth at high temperatures. The increased LCF stress intensity at the crack tip due to the HCF component enhances the subsequent LCF crack growth. Conversely, since a faster HCF crack growth rate will be expected with lower effective compressive stresses in the coating, the LCF cycles also facilitate the HCF crack growth at high temperatures by stress relaxation process. A surface wedging model has been proposed to account for the HCF crack growth in the coating system. This mechanism predicts that HCF damage effect increases with increasing temperature swing, the thermal expansion coefficient and the elastic modulus of the ceramic coating, as well as the HCF interacting depth. A good agreement has been found between the analysis and experimental evidence.

  5. Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; Timmerman, R.; Boyce, B. L.; Stach, E. A.; De Hosson, J. Th. M.; Ritchie, R. O.

    2007-01-01

    Fatigue failure in micron-scale polycrystalline silicon structural films, a phenomenon that is not observed in bulk silicon, can severely impact the durability and reliability of microelectromechanical system devices. Despite several studies on the very high-cycle fatigue behavior of these films (up to 1012cycles), there is still an on-going debate on the precise mechanisms involved. We show here that for devices fabricated in the multiuser microelectromechanical system process (MUMPs) foundry and Sandia Ultra-planar, Multi-level MEMS Technology (SUMMiT V™) process and tested under equi-tension/compression loading at ˜40kHz in different environments, stress-lifetime data exhibit similar trends in fatigue behavior in ambient room air, shorter lifetimes in higher relative humidity environments, and no fatigue failure at all in high vacuum. The transmission electron microscopy of the surface oxides in the test samples shows a four- to sixfold thickening of the surface oxide at stress concentrations after fatigue failure, but no thickening after overload fracture in air or after fatigue cycling in vacuo. We find that such oxide thickening and premature fatigue failure (in air) occur in devices with initial oxide thicknesses of ˜4nm (SUMMiT V™) as well as in devices with much thicker initial oxides ˜20nm (MUMPs). Such results are interpreted and explained by a reaction-layer fatigue mechanism. Specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure of the entire device. The entirety of the evidence presented here strongly indicates that the reaction-layer fatigue mechanism is the governing mechanism for fatigue failure in micron-scale polycrystalline silicon thin films.

  6. AISI/DOE Technology Roadmap Program: Characterization of Fatigue and Crash Performance of New Generation High Strength Steels for Automotive Applications

    SciTech Connect

    Brenda Yan; Dennis Urban

    2003-04-21

    A 2-year project (2001-2002) to generate fatigue and high strain data for a new generation of high strength steels (HSS) has been completed in December 2002. The project tested eleven steel grades, including Dual Phase (DP) steels, Transformation-Induced Plasticity (TRIP) steels, Bake Hardenable (BH) steels, and conventional High Strength Low Alloy (HSLA) steels. All of these steels are of great interest in automotive industry due to the potential benefit in weight reduction, improved fuel economy, enhanced crash energy management and total system cost savings. Fatigue behavior includes strain controlled fatigue data notch sensitivity for high strength steels. High strain rate behavior includes stress-strain data for strain rates from 0.001/s to 1000/s, which are considered the important strain rate ranges for crash event. The steels were tested in two phases, seven were tested in Phase 1 and the remaining steels were tested in Phase. In a addition to the fatigue data and high st rain rate data generated for the steels studied in the project, analyses of the testing results revealed that Advanced High Strength Steels (AHSS) exhibit significantly higher fatigue strength and crash energy absorption capability than conventional HSS. TRIP steels exhibit exceptionally better fatigue strength than steels of similar tensile strength but different microstructure, for conditions both with or without notches present

  7. A transient plasticity study and low cycle fatigue analysis of the Space Station Freedom photovoltaic solar array blanket

    NASA Technical Reports Server (NTRS)

    Armand, Sasan C.; Liao, Mei-Hwa; Morris, Ronald W.

    1990-01-01

    The Space Station Freedom photovoltaic solar array blanket assembly is comprised of several layers of materials having dissimilar elastic, thermal, and mechanical properties. The operating temperature of the solar array, which ranges from -75 to +60 C, along with the material incompatibility of the blanket assembly components combine to cause an elastic-plastic stress in the weld points of the assembly. The weld points are secondary structures in nature, merely serving as electrical junctions for gathering the current. The thermal mechanical loading of the blanket assembly operating in low earth orbit continually changes throughout each 90 min orbit, which raises the possibility of fatigue induced failure. A series of structural analyses were performed in an attempt to predict the fatigue life of the solar cell in the Space Station Freedom photovoltaic array blanket. A nonlinear elastic-plastic MSC/NASTRAN analysis followed by a fatigue calculation indicated a fatigue life of 92,000 to 160,000 cycles for the solar cell weld tabs. Additional analyses predict a permanent buckling phenomenon in the copper interconnect after the first loading cycle. This should reduce or eliminate the pulling of the copper interconnect on the joint where it is welded to the silicon solar cell. It is concluded that the actual fatigue life of the solar array blanket assembly should be significantly higher than the calculated 92,000 cycles, and thus the program requirement of 87,500 cycles (orbits) will be met. Another important conclusion that can be drawn from the overall analysis is that, the strain results obtained from the MSC/NASTRAN nonlinear module are accurate to use for low-cycle fatigue analysis, since both thermal cycle testing of solar cells and analysis have shown higher fatigue life than the minimum program requirement of 87,500 cycles.

  8. Investigation of thermal fatigue in fiber composite materials. [(thermal cycling tests)

    NASA Technical Reports Server (NTRS)

    Fahmy, A. A.; Cunningham, T. G.

    1976-01-01

    Graphite-epoxy laminates were thermally cycled to determine the effects of thermal cycles on tensile properties and thermal expansion coefficients of the laminates. Three 12-ply laminate configurations were subjected to up to 5,000 thermal cycles. The cumulative effect of the thermal cycles was determined by destructive inspection (electron micrographs and tensile tests) of samples after progressively larger numbers of cycles. After thermal cycling, the materials' tensile strengths, moduli, and thermal expansion coefficients were significantly lower than for the materials as fabricated. Most of the degradation of properties occurred after only a few cycles. The property degradation was attributed primarily to the progressive development of matrix cracks whose locations depended upon the layup orientation of the laminate.

  9. Associations of fatigue from mid to late life with physical performance and strength in early old age: Results from a British prospective cohort study

    PubMed Central

    Mänty, Minna; Kuh, Diana; Cooper, Rachel

    2015-01-01

    OBJECTIVE To examine associations of fatigue in mid and later life with physical performance and strength in early old age. METHODS Data on approximately 1800 men and women from the UK Medical Research Council National Survey of Health and Development with data on fatigue at ages 43 and 60-64 years were used. Fatigue was defined as perceived tiredness and was assessed prospectively at ages 43 and 60-64. At both ages, participants were categorized as having no, occasional or frequent fatigue. Physical performance and strength were measured at age 60-64 using four objective measures: grip strength, standing balance, chair rising, and timed get-up-and-go (TUG) tests. RESULTS There were associations between reports of frequent fatigue at both ages and poorer grip strength, chair rise and TUG performance at 60-64 years. Furthermore, individuals reporting frequent fatigue at both ages had weaker grip strength (β -4.09 kg, 95% CI -6.71, -1.48), and slower chair rise (β -4.65 rep./min, 95% CI -6.65, -2.64) and TUG (β -4.22 cm/s, 95% CI -12.16, -2.28) speeds when compared to those who reported no fatigue at both time points. These associations were robust and were maintained after adjustment for a range of covariates including physical activity and health status. CONCLUSIONS Reports of frequent fatigue were associated with poorer physical performance in early old age, especially if sustained from mid to later life. These findings indicate that it is not just fatigue but fatigue sustained across adulthood that has implications for later life functioning. PMID:26176776

  10. Effects of two neuromuscular fatigue protocols on landing performance.

    PubMed

    James, C Roger; Scheuermann, Barry W; Smith, Michael P

    2010-08-01

    The purpose of the study was to investigate the effects of two fatigue protocols on landing performance. A repeated measures design was used to examine the effects of fatigue and fatigue protocol on neuromuscular and biomechanical performance variables. Ten volunteers performed non-fatigued and fatigued landings on two days using different fatigue protocols. Repeated maximum isometric squats were used to induce fatigue on day one. Sub-maximum cycling was used to induce fatigue on day two. Isometric squat maximum voluntary contraction (MVC) was measured before and after fatigued landings on each day. During the landings, ground reaction force (GRF), knee kinematics, and electromyographic (EMG) data were recorded. Isometric MVC, GRF peaks, loading rates, impulse, knee flexion at contact, range of motion, max angular velocity, and EMG root mean square (RMS) values were compared pre- and post-fatiguing exercise and between fatigue protocols using repeated ANOVA. Fatigue decreased MVC strength (p0.05), GRF second peak, and initial impulse (p0.01), but increased quadriceps medium latency stretch reflex EMG activity (p0.012). Knee flexion at contact was 5.2 degrees greater (p0.05) during fatigued landings following the squat exercise compared to cycling. Several variables exhibited non-significant but large effect sizes when comparing the effects of fatigue and fatigue protocol. In conclusion, fatigue alters landing performance and different fatigue protocols result in different performance changes. PMID:20006522

  11. The role of high cycle fatigue (HCF) onset in Francis runner reliability

    NASA Astrophysics Data System (ADS)

    Gagnon, M.; Tahan, S. A.; Bocher, P.; Thibault, D.

    2012-11-01

    High Cycle Fatigue (HCF) plays an important role in Francis runner reliability. This paper presents a model in which reliability is defined as the probability of not exceeding a threshold above which HCF contributes to crack propagation. In the context of combined Low Cycle Fatigue (LCF) and HCF loading, the Kitagawa diagram is used as the limit state threshold for reliability. The reliability problem is solved using First-Order Reliability Methods (FORM). A study case is proposed using in situ measured strains and operational data. All the parameters of the reliability problem are based either on observed data or on typical design specifications. From the results obtained, we observed that the uncertainty around the defect size and the HCF stress range play an important role in reliability. At the same time, we observed that expected values for the LCF stress range and the number of LCF cycles have a significant influence on life assessment, but the uncertainty around these values could be neglected in the reliability assessment.

  12. Elevation of Continuous Low-Cycle Fatigue Behaviour of High Temperature P122 Boiler Material

    SciTech Connect

    Pumwa, John; Soo Woo Nam

    2002-07-01

    The complex thermal-mechanical loading of power-generating plant components usually comprises of creep, high-cycle and low-cycle fatigue which are thermally induced by start-ups, load changes and shut-downs, producing in-stationary temperature gradients and hence creating strain as well as stress fields. In order to select the correct materials for these hostile environmental conditions, it is vitally important to understand the behaviour of mechanical properties of these materials. This paper reports the results of Low-cycle fatigue tests of P122 (HCM12A or 12Cr-1.8W-1.5Cu) high temperature boiler material, which is one of the latest developed materials for high temperature environments. The tests were conducted at temperatures ranging from 550 deg. C to 700 deg. C at 50 deg. C intervals with strain ranges of {+-}1.5 to {+-}3.0% at 0.5% intervals using a closed-loop hydraulic Instron material testing machine with a servo hydraulic controller. The results confirm that P122 is comparable to conventional high temperature steels. Moreover, the fracture mode assessments strongly revealed a ductile transgranular fracture mode. (authors)

  13. Fatigue responses of PZT stacks under semi-bipolar electric cycling with mechanical preload

    SciTech Connect

    Wang, Hong; Cooper, Thomas A; Lin, Hua-Tay; Wereszczak, Andrew A

    2010-01-01

    PZT stacks that had an inter-digital internal electrode configuration were tested to more than 10^8 cycles. A 100-Hz semi-bipolar sine wave with a field range of +4.5/-0.9 kV/mm was used in cycling with a concurrently-applied 20 MPa preload. Significant reductions in piezoelectric and dielectric responses were observed during the cycling depending on the measuring condition. Extensive surface discharges were also observed. These surface events resulted in the erosion of external electrode and the outcrop of internal electrode. Sections prepared by sequential polishing technique revealed a variety of damage mechanisms including delaminations, pores, and etch grooves. The scale of damage was correlated to the degree of fatigue-induced reduction in piezoelectric and dielectric responses. The results from this study demonstrate the feasibility of using a semi-bipolar mode to drive a PZT stack under a mechanical preload and illustrate the potential fatigue and damages of the stack in service.

  14. High temperature, low cycle fatigue of copper-base alloys in argon. Part 3: Zirconium-copper; thermal-mechanical strain cycling, hold-time and notch fatigue results

    NASA Technical Reports Server (NTRS)

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1973-01-01

    The low-cycle fatigue characteristics of smooth bar and notched bar specimens (hourglass shape) of zirconium-copper, 1/2 Hard, material (R-2 Series) were evaluated at room temperature in axial strain control. Over the fatigue life range from about 300 to 3000 cycles the ratio of fatigue life for smooth bar to fatigue life for notched bar remained constant at a value of about 6.0. Some additional hold-time data for the R-2 alloy tested in argon at 538 C are reported. An analysis of the relaxation data obtained in these hold-time tests is also reported and it is shown that these data yield a fairly consistent correlation in terms of instantaneous stress rate divided by instantaneous stress. Two thermal-mechanical strain cycling tests were also performed using a cyclic frequency of 4.5 cycles per hour and a temperature cycling interval from 260 to 538 C. The fatigue life values in these tests were noticeably lower than that observed in isothermal tests at 538 C.

  15. On bilinearity of Manson-Coffin low-cycle-fatigue relationship

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, V. M.

    1992-01-01

    Some alloy systems, such as aluminum-lithium alloys and dual-phase steels, have been found to show a bilinear Manson-Coffin low-cycle-fatigue relationship. This paper shows that such bilinear behavior is related to the cyclic stress-strain curve. A bilinear cyclic stress-strain curve is a likely indication of a bilinear Manson-Coffin relationship. It is shown that materials other than aluminum-lithium alloys and dual-phase steels also may exhibit bilinear Manson-Coffin behavior. Implications for design are discussed.

  16. Simulation of Delamination Under High Cycle Fatigue in Composite Materials Using Cohesive Models

    NASA Technical Reports Server (NTRS)

    Camanho, Pedro P.; Turon, Albert; Costa, Josep; Davila, Carlos G.

    2006-01-01

    A new thermodynamically consistent damage model is proposed for the simulation of high-cycle fatigue crack growth. The basis for the formulation is an interfacial degradation law that links Fracture Mechanics and Damage Mechanics to relate the evolution of the damage variable, d, with the crack growth rate da/dN. The damage state is a function of the loading conditions (R and (Delta)G) as well as the experimentally-determined crack growth rates for the material. The formulation ensures that the experimental results can be reproduced by the analysis without the need of additional adjustment parameters.

  17. Fatigue Strength Prediction for Titanium Alloy TiAl6V4 Manufactured by Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Leuders, Stefan; Vollmer, Malte; Brenne, Florian; Tröster, Thomas; Niendorf, Thomas

    2015-09-01

    Selective laser melting (SLM), as a metalworking additive manufacturing technique, received considerable attention from industry and academia due to unprecedented design freedom and overall balanced material properties. However, the fatigue behavior of SLM-processed materials often suffers from local imperfections such as micron-sized pores. In order to enable robust designs of SLM components used in an industrial environment, further research regarding process-induced porosity and its impact on the fatigue behavior is required. Hence, this study aims at a transfer of fatigue prediction models, established for conventional process-routes, to the field of SLM materials. By using high-resolution computed tomography, load increase tests, and electron microscopy, it is shown that pore-based fatigue strength predictions for a titanium alloy TiAl6V4 have become feasible. However, the obtained accuracies are subjected to scatter, which is probably caused by the high defect density even present in SLM materials manufactured following optimized processing routes. Based on thorough examination of crack surfaces and crack initiation sites, respectively, implications for optimization of prediction accuracy of the models in focus are deduced.

  18. Temperature-Dependent Fatigue Strength of Diamond Coating-Substrate Interface Quantified via the Shear Failure Stress

    NASA Astrophysics Data System (ADS)

    Skordaris, G.

    2015-09-01

    A dynamic 3D-finite element method (FEM) thermomechanical model is employed for quantifying the temperature-dependent fatigue strength of nanocrystalline diamond (NCD) coating-substrate interface. This model simulates dynamically the inclined impact test on NCD-coated cemented carbide inserts considering the temperature-dependent residual stresses in the NCD coating structure. A fatigue damage of the NCD coating-substrate interface develops after a certain number of repetitive impacts depending on the applied impact load and temperature. After the interface fatigue failure, the high compressive residual stresses of the NCD coating structure are released, and the detached coating hikes up at a certain maximum height (bulge formation). The critical impact forces for avoiding the fatigue failure of the NCD coating-substrate interface, and the subsequent film detachment after 106 impacts at various temperatures were determined by conducting inclined impact tests up to 400 °C. Considering the critical impact forces, using the mentioned FEM model, the related shear failure stresses in the NCD coating-substrate interface at various temperatures were predicted.

  19. Environmental degradation of 316 stainless steel in high temperature low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Manson, S. Stanford; Halford, Gary R.

    1987-01-01

    Procedures based on modification of the conventional Strainrange Partitioning method are proposed to characterize the time-dependent degradation of engineering alloys in high-temperature, low-cycle fatigue. Creep-fatigue experiments were conducted in air using different waveforms of loading on 316 stainless steel at 816 C (1500 F) to determine the effect of exposure time on cyclic life. Reductions in the partitioned cyclic lives were observed with an increase in the time of exposure (or with the corresponding decrease in the steady-state creep rate) for all the waveforms involving creep strain. Excellent correlations of the experimental data were obtained by modifying the Conventional Strainrange Partitioning life relationships involving creep strain using a power-law term of either: (1) time of exposure, or (2) steady-state creep rate of the creep-fatigue test. Environmental degradation due to oxidation, material degradation due to the precipitation of carbides along the grain boundaries and detrimental deformation modes associated with the prolonged periods of creep were observed to be the main mechanisms responsible for life reductions at long exposure times.

  20. A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys

    NASA Astrophysics Data System (ADS)

    Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

    2011-06-01

    Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

  1. Can the Lamberts and Lambert Submaximal Cycle Test Indicate Fatigue and Recovery in Trained Cyclists?

    PubMed

    Hammes, Daniel; Skorski, Sabrina; Schwindling, Sascha; Ferrauti, Alexander; Pfeiffer, Mark; Kellmann, Michael; Meyer, Tim

    2016-04-01

    The Lamberts and Lambert Submaximal Cycle Test (LSCT) is a novel test designed to monitor performance and fatigue/recovery in cyclists. Studies have shown the ability to predict performance; however, there is a lack of studies concerning monitoring of fatigue/recovery. In this study, 23 trained male cyclists (age 29 ± 8 y, VO2max 59.4 ± 7.4 mL · min-1 · kg-1) completed a training camp. The LSCT was conducted on days 1, 8, and 11. After day 1, an intensive 6-day training period was performed. Between days 8 and 11, a recovery period was realized. The LSCT consists of 3 stages with fixed heart rates of 6 min at 60% and 80% and 3 min at 90% of maximum heart rate. During the stages, power output and rating of perceived exertion (RPE) were determined. Heart-rate recovery was measured after stage 3. Power output almost certainly (standardized mean difference: 1.0) and RPE very likely (1.7) increased from day 1 to day 8 at stage 2. Power output likely (0.4) and RPE almost certainly (2.6) increased at stage 3. From day 8 to day 11, power output possibly (-0.4) and RPE likely (-1.5) decreased at stage 2 and possibly (-0.1) and almost certainly (-1.9) at stage 3. Heart-rate recovery was likely (0.7) accelerated from day 1 to day 8. Changes from day 8 to day 11 were unclear (-0.1). The LSCT can be used for monitoring fatigue and recovery, since parameters were responsive to a fatiguing training and a following recovery period. However, consideration of multiple LSCT variables is required to interpret the results correctly. PMID:26263163

  2. Fatigue of fiberglass beam substructures

    SciTech Connect

    Mandell, J.F.; Combs, D.W.; Samborsky, D.D.

    1995-09-01

    Composite material beams representative of wind turbine blade substructure have been designed, fabricated, and tested under constant amplitude flexural fatigue loading. Beam stiffness, strength, and fatigue life are predicted based on detailed finite element analysis and the materials fatigue database developed using standard test coupons and special high frequency minicoupons.Beam results are in good agreement with predictions when premature adhesive and delamination failures are avoided in the load transfer areas. The results show that fiberglass substructures can be designed and fabricated to withstand maximum strain levels on the order of 8,000 microstrain for about 10{sup 6} cycles with proper structural detail design and the use of fatigue resistant laminate constructions. The study also demonstrates that the materials fatigue database and accurate analysis can be used to predict the fatigue life of composite substructures typical of blades.

  3. Effect of Fatigue Crack on Static Strength: 2014-T6, 2024-T4, 6061-T6, 7075-T6 Open-Hole Monobloc Specimens

    NASA Technical Reports Server (NTRS)

    Nordmark, Glenn E.; Eaton, Ian D.

    1957-01-01

    Static tensile test results are presented for specimens of 2014-T6, 2024-T4, 6061-T6, and 7075-T6 aluminum alloy containing fatigue cracks. The results are found to be in good agreement with the results reported for similar tests from other sources. The results indicate that the presence of a fatigue crack reduced the static strength, in all cases, by an amount larger than the corresponding reduction in net area; the 6061-T6 alloy specimens were least susceptible to the crack and the 7075-T6 alloy specimens were most susceptible. It is indicated that a 7075-T6 specimen may develop as little as one-third of the expected static tensile strength when the fatigue crack was consumed only one-fourth of the original area. It was found that the static strength was substantially higher for specimens which had stop holes drilled at the end of the fatigue crack.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  5. Fatigue and failure responses of lead zirconate titanate multilayer actuator under unipolar high-field electric cycling

    SciTech Connect

    Zeng, Fan W; Wang, Hong; Lin, Hua-Tay

    2013-01-01

    Lead zirconate titanate (PZT) multilayer actuators with an interdigital electrode design were studied under high electric fields (3 and 6 kV/mm) in a unipolar cycling mode. A 100 Hz sine wave was used in cycling. Five specimens tested under 6 kV/mm failed from 3.8 10^5 to 7 10^5 cycles, whereas three other specimens tested under 3 kV/mm were found to be still functional after 10^8 cycles. Variations in piezoelectric and dielectric responses of the tested specimens were observed during the fatigue test, depending on the measuring and cycling conditions. Selected fatigued and damaged actuators were characterized using an impedance analyzer or small signal measurement. A scanning acoustic microscope also was employed as a nondestructive tool to detect the presence of defects. Failed plates were subsequently sectioned, and the extensive cracks and porous regions were observed to be across the PZT layers. The results from this study have demonstrated that the high-field cycling can accelerate the fatigue of PZT stacks as long as the partial discharge is controlled. The small signal measurement can also be integrated into the large signal measurement to characterize the fatigue response of PZT stacks in a more comprehensive basis. The former can further serve as an experimental method to monitor the behavior of PZT stacks.

  6. Laser High-Cycle Thermal Fatigue of Pulse Detonation Engine Combustor Materials Tested

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Fox, Dennis S.; Miller, Robert A.

    2001-01-01

    Pulse detonation engines (PDE's) have received increasing attention for future aerospace propulsion applications. Because the PDE is designed for a high-frequency, intermittent detonation combustion process, extremely high gas temperatures and pressures can be realized under the nearly constant-volume combustion environment. The PDE's can potentially achieve higher thermodynamic cycle efficiency and thrust density in comparison to traditional constant-pressure combustion gas turbine engines (ref. 1). However, the development of these engines requires robust design of the engine components that must endure harsh detonation environments. In particular, the detonation combustor chamber, which is designed to sustain and confine the detonation combustion process, will experience high pressure and temperature pulses with very short durations (refs. 2 and 3). Therefore, it is of great importance to evaluate PDE combustor materials and components under simulated engine temperatures and stress conditions in the laboratory. In this study, a high-cycle thermal fatigue test rig was established at the NASA Glenn Research Center using a 1.5-kW CO2 laser. The high-power laser, operating in the pulsed mode, can be controlled at various pulse energy levels and waveform distributions. The enhanced laser pulses can be used to mimic the time-dependent temperature and pressure waves encountered in a pulsed detonation engine. Under the enhanced laser pulse condition, a maximum 7.5-kW peak power with a duration of approximately 0.1 to 0.2 msec (a spike) can be achieved, followed by a plateau region that has about one-fifth of the maximum power level with several milliseconds duration. The laser thermal fatigue rig has also been developed to adopt flat and rotating tubular specimen configurations for the simulated engine tests. More sophisticated laser optic systems can be used to simulate the spatial distributions of the temperature and shock waves in the engine. Pulse laser high-cycle

  7. Effect of fiber length on static and fatigue strengths of short fiber reinforced thermoplastics with polypropylene matrix

    SciTech Connect

    Watanabe, T.; Fujii, T.; Tanaka, T.

    1996-10-01

    Changes in the damage mechanism as a function of fiber length were examined in a quasi-isotropically reinforced random chopped glass/polypropylene composite during uniaxial tensile testing (at various temperatures) and fatigue testing (at room temperature). Three types of specimens, which have the different fiber length in a pellet, were used. As a result, the effect of fiber length on mechanical properties was revealed. Moreover, the outline of the percolation theory was given, which estimates the strength and other important mechanical properties on the basis of the probabilistic microcrack initiation and bonding of microcracks.

  8. Effects of environmental variables on the crack initiation stages of corrosion fatigue of high strength aluminum alloys

    NASA Technical Reports Server (NTRS)

    Poteat, L. E.

    1981-01-01

    Fatigue initiation in six aluminum alloys used in the aircraft industry was investigated. Cyclic loading superimposed on a constant stress was alternated with atmospheric corrosion. Tests made at different stress levels revealed that a residual stress as low as 39% of the yield strength caused stress corrosion cracking in some of the alloys. An atmospheric corrosion rate meter developed to measure the corrosivity of the atmosphere is described. An easily duplicated hole in the square test specimen with a self-induced residual stress was developed.

  9. Some observations on loss of static strength due to fatigue cracks

    NASA Technical Reports Server (NTRS)

    Illg, Walter; Hardrath, Herbert F

    1955-01-01

    Static tensile tests were performed on simple notched specimens containing fatigue cracks. Four types of aluminum alloys were investigated: 2024-T3(formerly 24S-T3) and 7075-T6(formerly 75S-T6) in sheet form, and 2024-T4(formerly 24S-T4) and 7075-T6(formerly 75S-T6) in extruded form. The cracked specimens were tested statically under four conditions: unmodified and with reduced eccentricity of loading by three methods. Results of static tests on C-46 wings containing fatigue cracks are also reported.

  10. Neuromuscular function and fatigue resistance of the plantar flexors following short-term cycling endurance training

    PubMed Central

    Behrens, Martin; Weippert, Matthias; Wassermann, Franziska; Bader, Rainer; Bruhn, Sven; Mau-Moeller, Anett

    2015-01-01

    Previously published studies on the effect of short-term endurance training on neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC) and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after 8 weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100, 100–200 ms) and iMVC of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave), peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that cycling endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue resistance. PMID:26029114

  11. High temperature low-cycle fatigue mechanisms in single crystals of nickel-based superalloy Mar-M 200

    NASA Technical Reports Server (NTRS)

    Milligan, W. W.; Jayaraman, N.

    1984-01-01

    Twenty three high temperature low-cycle fatigue tests were conducted on single crystals of the nickel-based superalloy Mar-M 200. Tests were conducted at 760 and 870 C. SEM fractography and transmission electron microscopy were used to determine mechanisms responsible for the observed orientation dependent fatigue behavior. It has been concluded that the plastic characteristics of the alloy lead to orientation-dependent strain hardening and fatigue lives at 760 C. At 870 C, the elastic characteristics of the alloy dominated the behavior, even though the plastic strain ranges were about the same as they were at 760 C. This led to orientation-dependent fatigue lives, but the trends were not the same as they were at 760 C.

  12. 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.

  13. Problems of the high-cycle fatigue of the materials intended for the parts of modern gas-turbine engines and power plants

    NASA Astrophysics Data System (ADS)

    Petukhov, A. N.

    2010-10-01

    The problems related to the determination of the life of the structural materials applied for important parts in gas-turbine engines and power plants from the results of high-cycle fatigue tests are discussed. Methods for increasing the reliability of the high-cycle fatigue characteristics and the factors affecting the operational reliability are considered.

  14. Effect of Threaded and Serrated Holes on the Limited Time and Fatigue Strength of Flat Light-alloy Strips

    NASA Technical Reports Server (NTRS)

    Burnheim, H

    1941-01-01

    The investigation was made for the purpose of ascertaining the notch sensitivity of flat strips of light alloy with cylindrical holes under initial tension stress, with special attention to the change in notch-effect factors with the number of load cycles. Then the studies were extended to similar flat strips with pin-loaded holes (tension lugs). This report deals with fatigue tests under initial tension load on flat test specimens of 3116.5 duralumin and AZM 3510.1 electron with plain unloaded and pin-loaded holes (tension lugs) of different forms.

  15. High-Cycle Fatigue Resistance of Si-Mo Ductile Cast Iron as Affected by Temperature and Strain Rate

    NASA Astrophysics Data System (ADS)

    Matteis, Paolo; Scavino, Giorgio; Castello, Alessandro; Firrao, Donato

    2015-09-01

    Silicon-molybdenum ductile cast irons are used to fabricate exhaust manifolds of internal combustion engines of large series cars, where the maximum pointwise temperature at full engine load may be higher than 973 K (700 °C). In this application, high-temperature oxidation and thermo-mechanical fatigue (the latter being caused by the engine start and stop and by the variation of its power output) have been the subject of several studies and are well known, whereas little attention has been devoted to the high-cycle fatigue, arising from the engine vibration. Therefore, the mechanical behavior of Si-Mo cast iron is studied here by means of stress-life fatigue tests up to 10 million cycles, at temperatures gradually increasing up to 973 K (700 °C). The mechanical characterization is completed by tensile and compressive tests and ensuing fractographic examinations; the mechanical test results are correlated with the cast iron microstructure and heat treatment.

  16. Low cycle fatigue of MAR-M 200 single crystals at 760 and 870 deg C

    NASA Technical Reports Server (NTRS)

    Milligan, W. W.; Jayaraman, N.; Bill, R. C.

    1984-01-01

    Fully reversed low cycle fatigue tests were conducted on single crystals of the nickel-base superalloys Mar-M 200 at 760 C and 870 C. At 760 C, planar slip (octahedral) lead to orientation-dependent strain hardening and cyclic lives. Multiple slip crystals strain hardened the most, resulting in relatively high stress ranges and low lives. Single slip crystals strain hardened the least, resulting in relatively low stress ranges and higher lives. A preferential crack initiation site which was related to slip plane geometry was observed in single slip orientated crystals. At 870 C, the trends were quite different, and the slip character was much more homogeneous. As the tensile axis orientation deviated from 001 , the stress ranges increased and the cyclic lives decreased. Two possible mechanisms were proposed to explain the behavior: one is based on Takeuchi and Kuramoto's cube cross-slip model, and the other is based on orientation-dependent creep rates.

  17. Effect of temperature, microstructure, and stress state on the low cycle fatigue behavior of Waspaloy

    NASA Technical Reports Server (NTRS)

    Stahl, D. R.; Antolovich, S. D.; Mirdamadi, M.; Zamrik, S. Y.

    1988-01-01

    Specimens of Waspaloy of two different microstructures were tested in uniaxial and torsional low-cycle fatigue at 24 and 649 C. For all specimens, deformation and failure mechanisms are found to be independent of stress state at 24 C; in both microstructures, failure is associated with the formation of shear cracks. At 649 C, deformation and failure mechanisms for the fine-grain large gamma-prime specimens are independent of stress state, and the mechanisms are similar to those observed at 24 C. For the coarse-grain small gamma-prime specimens, however, failure occurs on principal planes in torsion and on shear plane in uniaxial tension. The results are interpreted in terms of deformation mode and microstructural instability.

  18. Mean stress effects on high-cycle fatigue of Alloy 718

    SciTech Connect

    Korth, G E

    1980-07-01

    This report covers an investigation of the effects of tensile mean stress on the high-cycle fatigue properties of Alloy 718. Three test temperatures (24, 427, and 649{degree}C) were employed, and there were tests in both strain and load control. Results were compared with three different models: linear Modified-Goodman, Peterson cubic, and stress-strain parameter. The linear Modified-Goodman model gave good correlation with actual test data for low and moderate mean stress values, but the stress-strain parameter showed excellent correlation over the entire range of possible mean stresses and therefore is recommended for predicting mean stress effects of Alloy 718. 13 refs., 12 figs.

  19. Temperature and Strain-Rate Effects on Low-Cycle Fatigue Behavior of Alloy 800H

    NASA Technical Reports Server (NTRS)

    Rao, K. Bhanu Sankara; Schiffers, H.; Schuster, H.; Halford, G. R.

    1996-01-01

    The effects of strain rate (4 x 10(exp -6) to 4 x 10(exp -3)/s) and temperature on the Low-Cycle Fatigue (LCF) behavior of alloy 800H have been evaluated in the range 750 C to 950 C. Total axial strain controlled LCF tests were conducted in air at a strain amplitude of +/- 0.30 pct. LCF life decreased with decreasing strain rate and increasing temperature. The cyclic stress response behavior showed a marked variation with temperature and strain rate. The time- and temperature- dependent processes which influence the cyclic stress response and life have been identified and their relative importance assessed. Dynamic strain aging, time-dependent deformation, precipitation of parallel platelets of M(23)C6 on grain boundaries and incoherent ledges of twins, and oxidation were found to operate depending on the test conditions. The largest effect on life was shown by oxidation processes.

  20. Effect of adjusting pulse durations of functional electrical stimulation cycling on energy expenditure and fatigue after spinal cord injury.

    PubMed

    Gorgey, Ashraf S; Poarch, Hunter J; Dolbow, David D; Castillo, Teodoro; Gater, David R

    2014-01-01

    The purpose of the current study was to determine the effects of three different pulse durations (200, 350, and 500 microseconds [P200, P350, and P500, respectively]) on oxygen uptake (VO2), cycling performance, and energy expenditure (EE) percentage of fatigue of the knee extensor muscle group immediately and 48 to 72 h after cycling in persons with spinal cord injury (SCI). A convenience sample of 10 individuals with motor complete SCI participated in a repeated-measures design using a functional electrical stimulation (FES) cycle ergometer over a 3 wk period. There was no difference among the three FES protocols on relative VO2 or cycling EE. Delta EE between exercise and rest was 42% greater in both P500 and P350 compared with P200 (p = 0.07), whereas recovery VO2 was 23% greater in P350 compared with P200 (p = 0.03). There was no difference in the outcomes of the three pulse durations on muscle fatigue. Knee extensor torque significantly decreased immediately after (p < 0.001) and 48 to 72 h after (p < 0.001) FES leg cycling. Lengthening pulse duration did not affect submaximal or relative VO2 or EE, total EE, and time to fatigue. Greater recovery VO2 and delta EE were noted in P350 and P500 compared with P200. An acute bout of FES leg cycling resulted in torque reduction that did not fully recover 48 to 72 h after cycling. PMID:25803753

  1. Review and Prospects for Current Studies on Very High Cycle Fatigue of Metallic Materials for Machine Structural Use

    NASA Astrophysics Data System (ADS)

    Sakai, Tatsuo

    In recent years, mechanical structures such as railway wheels, rails, offshore structures, bridges, engine components, load bearing parts of automobiles, etc. have to endure for a long term up to 108-1010 loading cycles in order to save resources and to reduce the cost together with the environmental load to the globe. Thus, the fatigue behavior of structural materials in the very high cycle regime of 108-1010 cycles has become an important subject of the research. In this paper, a review of the current studies in this area performed by many researchers is described in order to provide a certain milestone in the history of the research on fatigue behavior of the metallic materials in the very high cycle regime.

  2. Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    1989-01-01

    The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation. This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.

  3. Effects of Phase Difference and Mean Stress on the Fatigue Strength of Small-Hole-Containing Specimens Subjected to Combined Load

    NASA Astrophysics Data System (ADS)

    Endo, Masahiro; Ishimoto, Isao

    A unified criterion is proposed that allows one to predict the effects of phase difference and mean stress on the fatigue strength of components containing small holes under combined loading. Combined axial and torsional fatigue tests were conducted using annealed JIS S35C steel and quenched/tempered JIS SCM435 steel specimens containing a small hole of either 100 μm or 500 μm in diameter. The phase differences between axial and torsional loads were 0° and 90°. Non-propagating small cracks were observed to emanate in the radial direction from the holes at the fatigue limit. Moreover, these cracks were always in the plane of maximum principal stress. This indicates that a crack on this specific plane plays an important role in the determination of fatigue strength. A criterion was proposed on the basis of the assumption that at the threshold level, the time-variation in the Mode I stress intensity factor of a crack under multiaxial cyclic loading is equal to that under uniaxial cyclic loading. A predictive method for the determination of fatigue strength under combined loading conditions was also presented making use of this criterion. This method is useful in practice since no fatigue tests are necessary in making predictions. Good agreement between experimental results and predictions was obtained.

  4. LOW CYCLE FATIGUE OF COMPOSITE MATERIALS IN ARMY STRUCTURAL APPLICATIONS: A REVIEW OF LITERATURE AND RECOMMENDATIONS FOR RESEARCH

    EPA Science Inventory

    Low cycle fatigue (LCF) of laminate composite structures used in Army applications is assessed to identify the key physical phenomena occurring during LCF processes and to determine their main characteristics. Special attention is given to the LCF conditions inherent in Army stru...

  5. Fatigue strength of titanium alloys with a VK-type detonation coating

    SciTech Connect

    Fedorenko, V.K.; Sergeev, V.V.; Shkanov, I.N.

    1995-07-01

    The influence of the structural, phase, and size factors, and the bonding of hard tungsten alloys to titanium alloy bases on the mechanism by which the system fails under alternating loads is studied. The failure mechanism of materials with detonation coatings applied by different methods is discussed in regard to the classical sequence of fatigue phenomena, i.e., hardening-softening and crack nucleation and growth.

  6. Microstructural Features Controlling the Variability in Low-Cycle Fatigue Properties of Alloy Inconel 718DA at Intermediate Temperature

    NASA Astrophysics Data System (ADS)

    Texier, Damien; Gómez, Ana Casanova; Pierret, Stéphane; Franchet, Jean-Michel; Pollock, Tresa M.; Villechaise, Patrick; Cormier, Jonathan

    2016-03-01

    The low-cycle fatigue behavior of two direct-aged versions of the nickel-based superalloy Inconel 718 (IN718DA) was examined in the low-strain amplitude regime at intermediate temperature. High variability in fatigue life was observed, and abnormally short lifetimes were systematically observed to be due to crack initiation at (sub)-surface non-metallic inclusions. However, crack initiation within (sub)-surface non-metallic inclusions did not necessarily lead to short fatigue life. The macro- to micro-mechanical mechanisms of deformation and damage have been examined by means of detailed microstructural characterization, tensile and fatigue mechanical tests, and in situ tensile testing. The initial stages of crack micro-propagation from cracked non-metallic particles into the surrounding metallic matrix occupies a large fraction of the fatigue life and requires extensive local plastic straining in the matrix adjacent to the cracked inclusions. Differences in microstructure that influence local plastic straining, i.e., the δ-phase content and the grain size, coupled with the presence of non-metallic inclusions at the high end of the size distribution contribute strongly to the fatigue life variability.

  7. A surface crosslinked UHMWPE stabilized by vitamin E with low wear and high fatigue strength.

    PubMed

    Oral, Ebru; Ghali, Bassem W; Rowell, Shannon L; Micheli, Brad R; Lozynsky, Andrew J; Muratoglu, Orhun K

    2010-09-01

    Wear particle-induced periprosthetic osteolysis has been a clinical problem driving the development of wear resistant ultrahigh molecular weight polyethylene (UHMWPE) for total joint replacement. Radiation crosslinking has been used to decrease wear through decreased plastic deformation; but crosslinking also reduces mechanical properties including fatigue resistance, a major factor limiting the longevity of joint implants. Reducing UHMWPE wear with minimal detriment to mechanical properties is an unaddressed need for articular bearing surface development. Here we report a novel approach to achieve this by limiting crosslinking to the articular surface. The antioxidant vitamin E reduces crosslinking efficiency in UHMWPE during irradiation with increasing concentration, thus we propose to spatially control the crosslink density distribution by controlling the vitamin E concentration profile. Surface crosslinking UHMWPE prepared using this approach had high wear resistance and decreased crosslinking in the bulk resulting in high fatigue crack propagation resistance. The interface region did not represent a weakness in the material due to the gradual change in the crosslink density. Such an implant has the potential of decreasing risk of fatigue fracture of total joint implants as well as expanding the use of UHMWPE to younger and more active patients. PMID:20579730

  8. The comparison of cold-water immersion and cold air therapy on maximal cycling performance and recovery markers following strength exercises

    PubMed Central

    Hayter, Kane J.; Schumann, Moritz; Deakin, Glen B.

    2016-01-01

    This study examined the effects of cold-water immersion (CWI) and cold air therapy (CAT) on maximal cycling performance (i.e. anaerobic power) and markers of muscle damage following a strength training session. Twenty endurance-trained but strength-untrained male (n = 10) and female (n = 10) participants were randomised into either: CWI (15 min in 14 °C water to iliac crest) or CAT (15 min in 14 °C air) immediately following strength training (i.e. 3 sets of leg press, leg extensions and leg curls at 6 repetition maximum, respectively). Creatine kinase, muscle soreness and fatigue, isometric knee extensor and flexor torque and cycling anaerobic power were measured prior to, immediately after and at 24 (T24), 48 (T48) and 72 (T72) h post-strength exercises. No significant differences were found between treatments for any of the measured variables (p > 0.05). However, trends suggested recovery was greater in CWI than CAT for cycling anaerobic power at T24 (10% ± 2%, ES = 0.90), T48 (8% ± 2%, ES = 0.64) and T72 (8% ± 7%, ES = 0.76). The findings suggest the combination of hydrostatic pressure and cold temperature may be favourable for recovery from strength training rather than cold temperature alone. PMID:27069791

  9. Effects of Stretch Shortening Cycle Exercise Fatigue on Stress Fracture Injury Risk during Landing

    ERIC Educational Resources Information Center

    James, C. Roger; Dufek, Janet S.; Bates, Barry T.

    2006-01-01

    The purpose of this study was to examine changes in landing performance during fatigue that could result in increased stress fracture injury risk. Five participants performed nonfatigued and fatigued drop landings (0.60 m), while ground reaction force (GRF), electromyographic (EMG) activity, and kinematics were recorded. Fatigue was defined as a…

  10. Influence of Secondary Cyclic Hardening on the Low Cycle Fatigue Behavior of Nitrogen Alloyed 316LN Stainless Steel

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    In this article, the occurrence of secondary cyclic hardening (SCH) and its effect on high-temperature cyclic deformation and fatigue life of 316LN Stainless steel are presented. SCH is found to result from planar slip mode of deformation and enhance the degree of hardening over and above that resulted from dynamic strain aging. The occurrence of SCH is strongly governed by the applied strain amplitude, test temperature, and the nitrogen content in the 316LN SS. Under certain test conditions, SCH is noticed to decrease the low cycle fatigue life with the increasing nitrogen content.

  11. Fatigue Strength and Related Characteristics of Joints in 24s-t Alclad Sheet

    NASA Technical Reports Server (NTRS)

    Russell, H W; Jackson, L R; Grover, H J; Beaver, W W

    1944-01-01

    Report includes tension fatigue test results on the following types of samples of 0.040-inch alclad 24s-t: (1) monoblock sheet samples as received and after a post-aging heat treatment, (2) "sheet efficiency" samples (two equally stressed sheets joined by a single transverse row of spot welds) both as received and after post-aging, (3) spot-welded lap-joint samples as received and after post-aging, and (4) roll-welded lap-joint samples. (author)

  12. Effect of repeated preheating cycles on flexural strength of resin composites.

    PubMed

    D'Amario, M; Pacioni, S; Capogreco, M; Gatto, R; Baldi, M

    2013-01-01

    The aim of this study was to assess the flexural strengths of three resin composites prepared at room temperature or cured after 20 or 40 cycles of preheating to a temperature of 45°C. Three resin composites were evaluated: Enamel Plus HFO (Micerium) (HFO), Enamel Plus HRi (Micerium) (HRi), Opallis + (FGM) (OPA). One group of specimens for each composite was fabricated under ambient laboratory conditions, whereas in the other groups, the composites were cured after 20 or 40 preheating cycles to a temperature of 45°C in a preheating device. Ten specimens were prepared for each group. A three-point bending test was performed using a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed with a two-way analysis of variance (ANOVA) test and a Games-Howell test (α = 0.05). The two-way ANOVA showed that both the material and the number of heating cycles were significant factors, able to influence the flexural strength values (p<0.05). However, there was not a statistically significant interaction (p>0.05). For all three composites flexural strengths were not affected after 20 preheating cycles in comparison with the control groups (0 preheating cycles) but were, however, significantly decreased when 40 prewarming cycles were conducted. The HRi and OPA groups had the highest flexural strengths, with no statistically significant differences among them. HFO presented significantly lower flexural strengths in comparison with HRi. PMID:22770484

  13. NDE detectability of fatigue-type cracks in high-strength alloys: NDI reliability assessments

    NASA Technical Reports Server (NTRS)

    Christner, Brent K.; Long, Donald L.; Rummel, Ward D.

    1988-01-01

    This program was conducted to generate quantitative flaw detection capability data for the nondestructive evaluation (NDE) techniques typically practiced by aerospace contractors. Inconel 718 and Haynes 188 alloy test specimens containing fatigue flaws with a wide distribution of sizes were used to assess the flaw detection capabilities at a number of contractor and government facilities. During this program 85 inspection sequences were completed presenting a total of 20,994 fatigue cracks to 53 different inspectors. The inspection sequences completed included 78 liquid penetrant, 4 eddy current, and 3 ultrasonic evaluations. The results of the assessment inspections are presented and discussed. In generating the flaw detection capability data base, procedures for data collection, data analysis, and specimen care and maintenance were developed, demonstrated, and validated. The data collection procedures and methods that evolved during this program for the measurement of flaw detection capabilities and the effects of inspection variables on performance are discussed. The Inconel 718 and Haynes 188 test specimens that were used in conducting this program and the NDE assessment procedures that were demonstrated, provide NASA with the capability to accurately assess the flaw detection capabilities of specific inspection procedures being applied or proposed for use on current and future fracture control hardware program.

  14. Influence of temperature, environment, and thermal aging on the continuous cycle fatigue behavior of Hastelloy X and Inconel 617

    SciTech Connect

    Strizak, J.P.; Brinkman, C.R.; Booker, M.K.; Rittenhouse, P.L.

    1982-04-01

    Results are presented for strain-controlled fatigue and tensile tests for two nickel-base, solution-hardened reference structural alloys for use in several High-Temperature Gas-Cooled Reactor (HTGR) concepts. These alloys, Hastelloy X and Inconel 617, were tested from room temperature to 871/sup 0/C in air and impure helium. Materials were tested in both the solution-annealed and the preaged conditios, in which aging consisted of isothermal exposure at one of several temperatures for periods of up to 20,000 h. Comparisons are given between the strain-controlled fatigue lives of these and several other commonly used alloys, all tested at 538/sup 0/C. An analysis is also presented of the continuous cycle fatigue data obtained from room temperature to 427/sup 0/C for Hastelloy G, Hastelloy X, Hastelloy C-276, and Hastelloy C-4, an effort undertaken in support of ASME code development.

  15. Dynamic strain aging behavior of modified 9Cr-1Mo and reduced activation ferritic martensitic steels under low cycle fatigue

    NASA Astrophysics Data System (ADS)

    Mariappan, K.; Shankar, Vani; Sandhya, R.; Prasad Reddy, G. V.; Mathew, M. D.

    2013-04-01

    Influence of temperature and strain rate on low cycle fatigue (LCF) behavior of modified 9Cr-1Mo ferritic martensitic steel and 1.4W-0.06Ta reduced activation ferritic martensitic (RAFM) steel in normalized and tempered conditions was studied. Total strain controlled LCF tests between 300 and 873 K on modified 9Cr-1Mo steel and RAFM steel and at various strain rates on modified 9Cr-1Mo steel were performed at total strain amplitude of ±0.6%. Both the steels showed continuous cyclic softening at all temperatures. Whereas manifestations of dynamic strain aging (DSA) were observed in both the steels which decreased fatigue life at intermediate temperatures, at higher temperatures, oxidation played a crucial role in decreasing fatigue life.

  16. The role of microstructural variability on the very high cycle fatigue lifetime variability of the alpha + beta titanium alloy, Ti-6246

    NASA Astrophysics Data System (ADS)

    Szczepanski, Christopher J.

    2008-12-01

    The fatigue behavior of structural components in the regime of very high cycle fatigue (VHCF) (106-109 cycles) has been attracting increased commercial interest as components are increasingly being called upon to perform in this regime of lifetimes. In VHCF, the applied stresses relative to the yield stress are very low. Therefore, it is presumed that a substantial portion of fatigue lifetime is consumed by the fatigue crack initiation process, and that cyclic plasticity only accumulates in microstructural neighborhoods that are susceptible to fatigue damage accumulation. Thus, microstructural heterogeneity is believed to significantly effect the fatigue lifetime variability. The very high cycle fatigue behavior of Ti-6246 has been investigated using ultrasonic fatigue techniques, and lifetimes ranging from 10 6-109 cycles have been observed. Fatigue cracks initiate by facet formation within alphap grains. It has been found that the facets form in grains that are slightly larger than average and that the facets appear to form by a process of slip since the facet plane normals are oriented approximately 35-55° with respect to the tensile axis. Three characteristic fatigue crack initiation sites have been identified. These initiation sites, ranked in order of increasing fatigue resistance are: surface, subsurface with isolated facets, and subsurface with contiguous transgranular faceting. The texture of the material in these initiation regions is favorable for basal and prism slip. This texture is derived from the prior beta texture, and a mechanism of fatigue crack initiation resulting from strain incompatibility has been proposed. Fatigue crack growth experiments have been completed to measure the influence of local texture on the ease of fatigue crack initiation and the resulting fatigue crack growth rates. These experiments have found that the controlling microstructural dimension is on the order of 20-25 mum. The texture appears to affect initiation of fatigue

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  18. Statistical analysis of the time and fatigue strength of aircraft wing structures

    NASA Technical Reports Server (NTRS)

    Kaul, Hans W

    1941-01-01

    The results from stress measurements in flight operation afford data for analyzing the frequency of appearance of certain parts of the static breaking strength during a specified number of operating hours. Appropriate frequency evaluations furnish data for the prediction of the required strength under repeated stress in the wing structures of aircraft of the different stress categories for the specified number of operating hours demanded during the life of a component.

  19. Influence Of Holes On The In-Plane Tensile Strength And Fatigue Durability Of A NICALON(Trademark)/Si-N-C Ceramic Matrix Composite

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Verrilli, Michael J.

    2003-01-01

    Effects of different sizes of holes as well as different percentages of open areas on the in-plane tensile strength and fatigue durability of the SiC/Si-N-C composite were investigated in this study. Test specimens with no holes, four different diameters of holes (1.0 to 3.2 mm), and four different open areas (20 to 35%) were machined. All mechanical testing was performed in air at a temperature of 910 C. Fatigue tests were conducted with a load ratio, R = 0.05, and a frequency of 0.33 Hz. In general, both the in-plane tensile strength of the composite and its fatigue durability decreased with an increase in the size of the hole and percentage of the open area. Reductions in the in-plane tensile strength and cyclic fatigue life of the composite were described by empirical equations with the diameter of the hole and the percent open area as the independent variables. The validity of these two empirical equations was verified with additional tensile and fatigue test data generated on the composite specimens.

  20. Low cycle fatigue properties of reduced activation ferritic/martensitic steels after high-dose neutron irradiation

    NASA Astrophysics Data System (ADS)

    Gaganidze, E.; Petersen, C.; Aktaa, J.; Povstyanko, A.; Prokhorov, V.; Diegele, E.; Lässer, R.

    2011-08-01

    This paper focuses on the low cycle fatigue (LCF) behaviour of reduced activation ferritic/martensitic steels irradiated to a displacement damage dose of up to 70 dpa at 330-337 °C in the BOR 60 reactor within the ARBOR 2 irradiation programme. The influence of neutron irradiation on the fatigue behaviour was determined for the as-received EUROFER97, pre-irradiation heat-treated EUROFER97 HT and F82H-mod steels. Strain-controlled push-pull loading was performed using miniaturized cylindrical specimens at a constant temperature of 330 °C with total strain ranges between 0.8% and 1.1%. Comparison of the LCF behaviour of irradiated and reference unirradiated specimens was performed for both the adequate total and inelastic strains. Neutron irradiation-induced hardening may have various effects on the fatigue behaviour of the steels. The reduction of inelastic strain in the irradiated state compared with the reference unirradiated state at common total strain amplitudes may increase fatigue lifetime. The increase in the stress at the adequate inelastic strain, by contrast, may accelerate fatigue damage accumulation. Depending on which of the two effects mentioned dominates, neutron irradiation may either extend or reduce the fatigue lifetime compared with the reference unirradiated state. The results obtained for EUROFER97 and EUROFER97 HT confirm these considerations. Most of the irradiated specimens show fatigue lifetimes comparable to those of the reference unirradiated state at adequate inelastic strains. Some irradiated specimens, however, show lifetime reduction or increase in comparison with the reference state at adequate inelastic strains.

  1. Influence of preliminary tension on the low-cycle fatigue of 40Kh13 steel in gaseous hydrogen

    SciTech Connect

    Romaniv, A.N.

    1985-05-01

    Information is lacking on the influence of hydrogen entering from an electrolyte or an external gaseous medium on the low-cycle fatigue of steels after preliminary tension. Since preliminary plastic deformation by tension increases the elastic limit and hardness of the steel while reducing its toughness, this must be reflected in the processes of crack origin and propagation in low-cycle loading in hydrogen. The purpose of this work was to study the influence of the degree of preliminary tension on the low-cycle failure resistance of 40Kh13 martensitic class steel in an atmosphere of gaseous hydrogen.

  2. Strain-Controlled Low-Cycle Fatigue Behavior of Friction Stir-Welded AZ31 Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Yang, J.; Ni, D. R.; Wang, D.; Xiao, B. L.; Ma, Z. Y.

    2014-04-01

    Strain-controlled low-cycle fatigue (LCF) behavior of friction stir-welded (FSW) AZ31 joints, produced at rotation rates of 800 and 3500 rpm, was studied. The joints exhibited symmetric hysteresis loops, whereas asymmetric loops were observed for the parent material (PM). The fatigue resistance of the FSW joints was slightly improved as the rotation rate increased, and both the FSW joints possessed a fatigue life similar to that of the PM at the low strain amplitude of 0.1 pct. The obtained fatigue data for the PM and FSW joints can be well described using the Coffin-Manson and Basquin's relationships. For the FSW joints, during LCF deformation, the twinning originated from the nugget zone (NZ)/thermomechanically affected zone (TMAZ) boundary and then propagated to the NZ interior. This was attributed to different textures in these regions: the center of the NZ exhibited a hard orientation, whereas a soft orientation was observed in the region around the NZ/TMAZ boundary. The fatigue cracks initiated at the bottom of the joints and propagated along the NZ/TMAZ boundary or the NZ adjacent to the NZ/TMAZ boundary.

  3. Reproducibility and Repeatability of Tensile and Low-Cycle Fatigue Properties in Propulsion Grade Hydrogen

    NASA Technical Reports Server (NTRS)

    Vesely, E. J.; Bhat, B. N.; McPherson, W. B.; Grethlein, C. E.; Jones, Clyde S. (Technical Monitor)

    2002-01-01

    Hydrogen has the potential of increased use in the future as an environmentally friendly fuel. It has, however, shown a tendency to embrittle some materials. To be used in a safe manner and to exploit its full potential, it will be necessary to develop a database of material properties in hydrogen environment. The tests needed to produce this data are costly to perform (tensile test cost 25 times more and low cycle fatigue test are 55 times as expensive). Moreover, there is presently a lack of universal test methods to ensure standardized data within the hydrogen community. Each of the industries that work with hydrogen (aerospace, petroleum, fuel cells, etc.) performs tests by their own laboratory-developed methods, thus rendering cross- comparisons of material property data highly questionable. It is extremely important that data generated in a hydrogen environment be done to a standard that reduces variance to a minimum and allows direct comparison of test results from different laboratories. Doing so will assure that all data generated can be used to further our understanding of the hydrogen effects and to make sure components/products designed for hydrogen are the safest and most reliable possible. This paper reviews the results of two 'round-robin' programs conducted by NASA-MSFC. These two programs examined the reproducibility and repeatability of tensile and low-cycle fatigue test results in high-pressure hydrogen environments. The studies indicated that even with the tightest controls available from current commercial standards, the reproducibility (between different laboratories) and repeatability (within a laboratory) results of the tensile tests exhibited five times the variance as in standard ambient air tests. The variance with the LCF tests were on the same order as with air tests, but that was due to the large variation present in the last Interlaboratory air program. The paper concludes with a recommendation for a program that would allow the

  4. The importance of isometric maximum strength and peak rate-of-force development in sprint cycling.

    PubMed

    Stone, Michael H; Sands, William A; Carlock, Jon; Callan, Sam; Dickie, Des; Daigle, Karen; Cotton, John; Smith, Sarah L; Hartman, Michael

    2004-11-01

    This study was designed to investigate the relationship of whole-body maximum strength to variables potentially associated with track sprint-cycling success. These variables included body composition, power measures, coach's rank, and sprint-cycling times. The study was carried out in 2 parts. The first part (n = 30) served as a pilot for the second part (n = 20). Subjects for both parts ranged from international-caliber sprint cyclists to local-level cyclists. Maximum strength was measured using an isometric midthigh pull (IPF). Explosive strength was measured as the peak rate-of-force development (IPRFD) from the isometric force-time curve. Peak power was estimated from countermovement (CMJPP) and static vertical jumps (SJPP) and measured by modified Wingate tests. Athletes were ranked by the U.S. national cycling coach (part 1). Sprint times (from a standing start) were measured using timing gates placed at 25, 82.5, 165, 247.5, and 330 m of an outdoor velodrome (part 2). Maximum strength (both absolute and body-mass corrected) and explosive strength were shown to be strongly correlated with jump and Wingate power. Additionally, maximum strength was strongly correlated with both coach's rank (parts 1 and 2) and sprint cycling times (part 2). The results suggest that larger, stronger sprint cyclists have an advantage in producing power and are generally faster sprint cyclists. PMID:15574097

  5. Life cycle CO{sub 2} evaluation on reinforced concrete structures with high-strength concrete

    SciTech Connect

    Tae, Sungho; Baek, Cheonghoon Shin, Sungwoo

    2011-04-15

    The purpose of this study is to evaluate the environment performance of high-strength concrete used in super tall buildings as material of environmental load reduction. To this end, this study proposed a plan for the evaluation of energy consumption and CO{sub 2} emission throughout the life cycle of the building, and calculated the energy consumption and CO{sub 2} emission throughout the life cycle of tall apartment building that was actually constructed using this plan. Then, we evaluated the energy consumption and CO{sub 2} emission reduction performance for the life cycle of the building by the decrease of concrete and reinforced rebar quantities and the increase of building lifespan obtained through conversion of existing building's concrete compressive strength to 40 MPa high-strength concrete. As a result, the life cycle energy consumption in case 3, a high-strength concrete building, decreased 15.53% and 2.95% respectively compared with cases 1 and 2. The evaluation of the general strength concrete buildings and the life cycle CO{sub 2} emission also decreased 16.70% and 3.37% respectively, compared with cases 1 and 2.

  6. Effects of laser-weld joint opening size on fatigue strength of Ti-6Al-4V structures with several diameters.

    PubMed

    Nuñez-Pantoja, J M C; Vaz, L G; Nóbilo, M A A; Henriques, G E P; Mesquita, M F

    2011-03-01

    This study was conducted to evaluate the fatigue strength of Ti-6Al-4V laser-welded joints with several diameters and joint openings. Sixty dumbbell rods were machined in Ti-6Al-4V alloy with central diameters of 1·5, 2·0 and 3·5 mm. The specimens were sectioned and then welded using two joint openings (0·0 and 0·6 mm). The combination of variables created six groups, which when added to the intact groups made a total of nine groups (n = 10). Laser welding was executed as follows: 360 V per 8 ms (1·5 and 2·0 mm) and 380 V per 9 ms (3·5 mm) with focus and frequency regulated to zero. The joints were finished, polished and submitted to radiographic examination to be analysed visually for the presence of porosity. The specimens were then subjected to a mechanical cyclic test, and the number of cycles until failure was recorded. The fracture surface was examined with a scanning electron microscope (SEM). The Kruskal-Wallis test and Dunn test (α = 0·05) indicated that the number of cycles required for fracture was lower for all specimens with joint openings of 0·6 mm, and for 3·5-mm-diameter specimens with joint openings of 0·0 mm. The Spearman correlation coefficient (α = 0·05) indicated that there was a negative correlation between the number of cycles and the presence of porosity. So, laser welding of Ti-6Al-4V structures with a thin diameter provides the best conditions for the juxtaposition of parts. Radiographic examination allows for the detection of internal voids in titanium joints. PMID:20678101

  7. Bending Fatigue of Carburized Steel at Very Long Lives

    NASA Astrophysics Data System (ADS)

    Nelson, D. V.; Long, Z.

    2016-01-01

    The bending fatigue behavior of two carburized steels is investigated for lives between approximately 105 and 108 cycles. Cracks are observed to start at sub-surface inclusions and develop features on fracture surfaces resembling "fish eyes" in appearance. This type of sub-surface cracking tends to govern fatigue strength at long lives. Previous studies of "fish eye" fatigue in carburized steel have been relatively few and have mainly considered failures originating at depths beneath a carburized case, where compressive residual stresses are minimal and hardness values approach those in the core. This study provides fatigue data for cracks originating within cases at various depths where compressive residual stresses are substantial and hardness is much higher than in the core. Fatigue strength is predicted by a simple model, accounting for the influence of residual stresses and hardness values at the different depths at which cracks started. Predictions of fatigue strength are compared with data generated in this study.

  8. Effect of Processing Route on Strain Controlled Low Cycle Fatigue Behavior of Polycrystalline NiAl

    NASA Technical Reports Server (NTRS)

    Rao, K. Bhanu Sankara; Lerch, B. A.; Noebe, R. D.

    1995-01-01

    The present investigation examines the effects of manufacturing process on the total axial strain controlled low cycle fatigue behavior of polycrystalline NiAl at 1000 K, a temperature above the monotonic Brittle-to-Ductile Transition Temperature (BDTT). The nickel aluminide samples were produced by three different processing routes: hot isostatic pressing of pre- alloyed powders, extrusion of prealloyed powders, and extrusion of vacuum induction melted ingots. The LCF behavior of the cast plus extruded material was also determined at room temperature (below the BD77) for comparison to the high temperature data. The cyclic stress response, cyclic stress-strain behavior, and strain-life relationships were influenced by the alloy preparation technique and the testing temperature. Detailed characterization of the LCF tested samples was conducted by optical and electron microscopy to determine the variations in fracture and deformation modes and to determine any microstructural changes that occurred during LCF testing. The dependence of LCF properties on processing route was rationalized on the basis of starting microstructure, brittle-to-ductile transition temperature, deformation induced changes in the basic microstructure, deformation substructure, and synergistic interaction between the damage modes.

  9. Accelerated multiscale space-time finite element simulation and application to high cycle fatigue life prediction

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Wen, Lihua; Naboulsi, Sam; Eason, Thomas; Vasudevan, Vijay K.; Qian, Dong

    2016-05-01

    A multiscale space-time finite element method based on time-discontinuous Galerkin and enrichment approach is presented in this work with a focus on improving the computational efficiencies for high cycle fatigue simulations. While the robustness of the TDG-based space-time method has been extensively demonstrated, a critical barrier for the extensive application is the large computational cost due to the additional temporal dimension and enrichment that are introduced. The present implementation focuses on two aspects: firstly, a preconditioned iterative solver is developed along with techniques for optimizing the matrix storage and operations. Secondly, parallel algorithms based on multi-core graphics processing unit are established to accelerate the progressive damage model implementation. It is shown that the computing time and memory from the accelerated space-time implementation scale with the number of degree of freedom N through {˜ }{O}(N^{1.6}) and {˜ }{O}(N) , respectively. Finally, we demonstrate the accelerated space-time FEM simulation through benchmark problems.

  10. Accelerated multiscale space-time finite element simulation and application to high cycle fatigue life prediction

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Wen, Lihua; Naboulsi, Sam; Eason, Thomas; Vasudevan, Vijay K.; Qian, Dong

    2016-08-01

    A multiscale space-time finite element method based on time-discontinuous Galerkin and enrichment approach is presented in this work with a focus on improving the computational efficiencies for high cycle fatigue simulations. While the robustness of the TDG-based space-time method has been extensively demonstrated, a critical barrier for the extensive application is the large computational cost due to the additional temporal dimension and enrichment that are introduced. The present implementation focuses on two aspects: firstly, a preconditioned iterative solver is developed along with techniques for optimizing the matrix storage and operations. Secondly, parallel algorithms based on multi-core graphics processing unit are established to accelerate the progressive damage model implementation. It is shown that the computing time and memory from the accelerated space-time implementation scale with the number of degree of freedom N through ˜ O(N^{1.6}) and ˜ O(N), respectively. Finally, we demonstrate the accelerated space-time FEM simulation through benchmark problems.

  11. Predicting Blood Lactate Concentration and Oxygen Uptake from sEMG Data during Fatiguing Cycling Exercise.

    PubMed

    Ražanskas, Petras; Verikas, Antanas; Olsson, Charlotte; Viberg, Per-Arne

    2015-01-01

    This article presents a study of the relationship between electromyographic (EMG) signals from vastus lateralis, rectus femoris, biceps femoris and semitendinosus muscles, collected during fatiguing cycling exercises, and other physiological measurements, such as blood lactate concentration and oxygen consumption. In contrast to the usual practice of picking one particular characteristic of the signal, e.g., the median or mean frequency, multiple variables were used to obtain a thorough characterization of EMG signals in the spectral domain. Based on these variables, linear and non-linear (random forest) models were built to predict blood lactate concentration and oxygen consumption. The results showed that mean and median frequencies are sub-optimal choices for predicting these physiological quantities in dynamic exercises, as they did not exhibit significant changes over the course of our protocol and only weakly correlated with blood lactate concentration or oxygen uptake. Instead, the root mean square of the original signal and backward difference, as well as parameters describing the tails of the EMG power distribution were the most important variables for these models. Coefficients of determination ranging from R(2) = 0:77 to R(2) = 0:98 (for blood lactate) and from R(2) = 0:81 to R(2) = 0:97 (for oxygen uptake) were obtained when using random forest regressors. PMID:26295396

  12. Predicting Blood Lactate Concentration and Oxygen Uptake from sEMG Data during Fatiguing Cycling Exercise

    PubMed Central

    Ražanskas, Petras; Verikas, Antanas; Olsson, Charlotte; Viberg, Per-Arne

    2015-01-01

    This article presents a study of the relationship between electromyographic (EMG) signals from vastus lateralis, rectus femoris, biceps femoris and semitendinosus muscles, collected during fatiguing cycling exercises, and other physiological measurements, such as blood lactate concentration and oxygen consumption. In contrast to the usual practice of picking one particular characteristic of the signal, e.g., the median or mean frequency, multiple variables were used to obtain a thorough characterization of EMG signals in the spectral domain. Based on these variables, linear and non-linear (random forest) models were built to predict blood lactate concentration and oxygen consumption. The results showed that mean and median frequencies are sub-optimal choices for predicting these physiological quantities in dynamic exercises, as they did not exhibit significant changes over the course of our protocol and only weakly correlated with blood lactate concentration or oxygen uptake. Instead, the root mean square of the original signal and backward difference, as well as parameters describing the tails of the EMG power distribution were the most important variables for these models. Coefficients of determination ranging from R2=0.77 to R2=0.98 (for blood lactate) and from R2=0.81 to R2=0.97 (for oxygen uptake) were obtained when using random forest regressors. PMID:26295396

  13. The J-2X Fuel Turbopump - Turbine Nozzle Low Cycle Fatigue Acceptance Rationale

    NASA Technical Reports Server (NTRS)

    Hawkins, Lakiesha V.; Duke, Gregory C.; Newman, Wesley R.; Reynolds, David C.

    2011-01-01

    The J-2X Fuel Turbopump (FTP) turbine, which drives the pump that feeds hydrogen to the J-2X engine for main combustion, is based on the J-2S design developed in the early 1970 s. Updated materials and manufacturing processes have been incorporated to meet current requirements. This paper addresses an analytical concern that the J-2X Fuel Turbine Nozzle Low Cycle Fatigue (LCF) analysis did not meet safety factor requirements per program structural assessment criteria. High strains in the nozzle airfoil during engine transients were predicted to be caused by thermally induced stresses between the vane hub, vane shroud, and airfoil. The heritage J-2 nozzle was of a similar design and experienced cracks in the same area where analysis predicted cracks in the J-2X design. Redesign options that did not significantly impact the overall turbine configuration were unsuccessful. An approach using component tests and displacement controlled fracture mechanics analysis to evaluate LCF crack initiation and growth rate was developed. The results of this testing and analysis were used to define the level of inspection on development engine test units. The programmatic impact of developing crack initiation/growth rate/arrest data was significant for the J-2X program. Final Design Certification Review acceptance logic will ultimately be developed utilizing this test and analytical data.

  14. Strength training improves cycling performance, fractional utilization of VO2max and cycling economy in female cyclists.

    PubMed

    Vikmoen, O; Ellefsen, S; Trøen, Ø; Hollan, I; Hanestadhaugen, M; Raastad, T; Rønnestad, B R

    2016-04-01

    The purpose of this study was to investigate the effect of adding heavy strength training to well-trained female cyclists' normal endurance training on cycling performance. Nineteen female cyclists were randomly assigned to 11 weeks of either normal endurance training combined with heavy strength training (E+S, n = 11) or to normal endurance training only (E, n = 8). E+S increased one repetition maximum in one-legged leg press and quadriceps muscle cross-sectional area (CSA) more than E (P < 0.05), and improved mean power output in a 40-min all-out trial, fractional utilization of VO2 max and cycling economy (P < 0.05). The proportion of type IIAX-IIX muscle fibers in m. vastus lateralis was reduced in E+S with a concomitant increase in type IIA fibers (P < 0.05). No changes occurred in E. The individual changes in performance during the 40-min all-out trial was correlated with both change in IIAX-IIX fiber proportion (r = -0.63) and change in muscle CSA (r = 0.73). In conclusion, adding heavy strength training improved cycling performance, increased fractional utilization of VO2 max , and improved cycling economy. The main mechanisms behind these improvements seemed to be increased quadriceps muscle CSA and fiber type shifts from type IIAX-IIX toward type IIA. PMID:25892654

  15. The effect of Zr on the low-cycle fatigue behavior of NiAl at 1000 K

    SciTech Connect

    Lerch, B.A.; Noebe, R.D.; Rao, K.B.S.

    1998-04-01

    The effect of a 0.1 at.% alloying addition of Zr on the low-cycle fatigue behavior of polycrystalline NiAl was determined at 1,000 K and compared to that of binary NiAl. Samples of binary NiAl and the Zr-doped alloy were processed by either HIP consolidation or extrusion of prealloyed intermetallic powders. The cyclic stress response, cyclic stress-strain behavior, and strain-life relationships were all significantly influenced by the microalloying addition of Zr, regardless of the processing technique. A detailed examination of the post-tested low-cycle fatigue (LCF) samples was conducted by optical and electron microscopy to determine variations in fracture and deformation modes and to characterize any microstructural changes that occurred during LCF testing. Differences in LCF behavior due to the Zr addition are attributed to the strong effect that Zr has on modifying the deformation behavior of the intermetallic.

  16. The effect of Zr on the low-cycle fatigue behavior of NiAl at 1000 K

    NASA Astrophysics Data System (ADS)

    Lerch, B. A.; Noebe, R. D.; Rao, K. B. S.

    1998-04-01

    The effect of a 0.1 at. % alloying addition of Zr on the low-cycle fatigue behavior of polycrystalline NiAl was determined at 1000 K and compared to that of binary NiAl. Samples of binary NiAl and the Zr-doped alloy were processed by either HIP consolidation or extrusion of prealloyed intermetallic powders. The cyclic stress response, cyclic stress-strain behavior, and strain-life relationships were all significantly influenced by the microalloying addition of Zr, regardless of the processing technique. A detailed examination of the post-tested low-cycle fatigue (LCF) samples was conducted by optical and electron microscopy to determine variations in fracture and deformation modes and to characterize any microstructural changes that occurred during LCF testing. Differences in LCF behavior due to the Zr addition are attributed to the strong effect that Zr has on modifying the deformation behavior of the intermetallic.

  17. Tensile, low cycle fatigue and fracture toughness behaviour of type 316L steel irradiated to 0.3 dpa

    NASA Astrophysics Data System (ADS)

    Josefsson, Bertil; Bergenlid, Ulf

    1994-09-01

    The effect of a low dose neutron irradiation on the tensile, low cycle fatigue and fracture toughness properties of type 316L steel plate and weld material was investigated. The specimens were irradiated at a temperature of about 35°C to a neutron fluence of approximately 2.5 × 10 20 n/cm 2 ( E > 1 MeV). The testing was performed at 75, 250 and 450°C. Irradiated tensile specimens showed a substantial radiation hardening combined with some reduction of elongations. There was no significant effect of the irradiation on the low cycle fatigue endurances. The fracture toughness of the TIG weld specimens was roughly half of that of the 316L plate and electron beam weld. Some reductions of toughness owing to the irradiation were observed.

  18. Influence of different pre-etching times on fatigue strength of self-etch adhesives to dentin.

    PubMed

    Takamizawa, Toshiki; Barkmeier, Wayne W; Tsujimoto, Akimasa; Suzuki, Takayuki; Scheidel, Donal D; Erickson, Robert L; Latta, Mark A; Miyazaki, Masashi

    2016-04-01

    The purpose of this study was to use shear bond strength (SBS) and shear fatigue strength (SFS) testing to determine the influence on dentin bonding of phosphoric acid pre-etching times before the application of self-etch adhesives. Two single-step self-etch universal adhesives [Prime & Bond Elect (EL) and Scotchbond Universal (SU)], a conventional single-step self-etch adhesive [G-aenial Bond (GB)], and a two-step self-etch adhesive [OptiBond XTR (OX)] were used. The SBS and SFS values were obtained with phosphoric acid pre-etching times of 3, 10, or 15 s before application of the adhesives, and for a control without pre-etching. For groups with 3 s of pre-etching, SU and EL showed higher SBS values than control groups. No significant difference was observed for GB among the 3 s, 10 s, and control groups, but the 15 s pre-etching group showed significantly lower SBS and SFS values than the control group. No significant difference was found for OX among the pre-etching groups. Reducing phosphoric acid pre-etching time can minimize the adverse effect on dentin bonding durability for the conventional self-etch adhesives. Furthermore, a short phosphoric acid pre-etching time enhances the dentin bonding performance of universal adhesives. PMID:26918658

  19. Ultrasonic evaluation of the effects of compressive residual stresses on aircraft engine turbine blades subjected to high cycle fatigue

    NASA Astrophysics Data System (ADS)

    Bray, Don E.; Suh, Ui; Hough, C. L. ``Mickey''

    2002-05-01

    Experiments conducted on titanium (Ti-64) turbine blades with the LCR ultrasonic wave at 20 MHz showed significant differences in untreated blades and blades treated to increase the subsurface compressive residual stress. Group 1 showed significant differences in the treated and untreated areas, the top and bottom of the blades, high cycle fatigue and cracked and uncracked conditions. Group 2 blades showed significant difference between untreated and treated travel-times at probes located at the blade leading edge.

  20. Fatigue performance and cyclic softening of F82H, a ferritic martensic steel

    SciTech Connect

    Stubbins, J.F.; Gelles, D.S.

    1996-04-01

    The room temperature fatigue performance of F82H has been examined. The fatigue life was determined in a series of strain-controlled tests where the stress level was monitored as a function of the number of accrued cycles. Fatigue lives in the range of 10{sup 3} to 10{sup 6} cycles to failure were examined. The fatigue performance was found to be controlled primarily by the elastic strain range over most of the range of fatigue lives examined. Only at low fatigue lives did the plastic strain range contribute to the response. However, when the significant plastic strain did contribute, the material showed a tendency to cyclically soften. That is the load carrying capability of the material degrades with accumulated fatigue cycles. The overall fatigue performance of the F82H alloy was found to be similiar to other advanced martensitic steels, but lower than more common low alloy steels which possess lower yield strengths.

  1. Ultrasonic fatigue of E319 cast aluminum alloy in the long lifetime regime

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaoxia

    2007-12-01

    The fatigue behavior of an E319 cast aluminum alloy used in the production of automotive cylinder heads, was studied by using both ultrasonic and conventional fatigue techniques in order to understand the potential effect of frequency on fatigue behavior of cast aluminum alloys. The effect of frequency, environment and temperature on S-N behavior, fatigue crack initiation and propagation behavior of E319 cast aluminum alloy was investigated. It was observed that, at room temperature, in the lifetime regime of less than 107 cycles, fatigue lives at 20 kHz are approximately five to ten times longer than fatigue lives at 75 Hz; while at 107 cycles, the effect of frequency is substantially reduced. At elevated temperature (150 and 250°C), however, the difference in fatigue lives between 20 kHz and 75 Hz persists over the entire range of stress examined. The effect of frequency on fatigue resistance is attributable to an environmental effect on fatigue crack growth rate at all temperatures. For E319 cast aluminum alloy, fatigue crack growth rates increase with increasing water exposure, P/f, which can be estimated by a modified superposition model. Fatigue resistance decreased with increasing temperature and the temperature dependence of fatigue strength at 108 cycles follows closely the temperature dependence of yield and tensile strength. The effect of temperature on fatigue resistance primarily results from the intrinsic effect of temperature on Young's modulus and yield strength. The environmental contribution to fatigue crack growth rates modestly decreases with increasing temperature. At room temperature, an endurance limit is demonstrated in the lifetime regime beyond 107 cycles and the fatigue strength at 10 8 cycles was investigated using the ultrasonic fatigue technique. The fatigue strength is correlated with both size and location of the initiating pores through a threshold stress intensity factor for fatigue crack growth. A probabilistic model was

  2. Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength

    PubMed Central

    RIPPE, Marília Pivetta; SANTINI, Manuela Favarin; BIER, Carlos Alexandre Souza; BALDISSARA, Paolo; VALANDRO, Luiz Felipe

    2014-01-01

    Objective To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred. Results The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario. PMID:25025556

  3. White-light corona and solar polar magnetic field strength over solar cycles

    NASA Astrophysics Data System (ADS)

    Rušin, V.; Saniga, M.; Komžík, R.

    2014-10-01

    We discuss the large-scale structure of the solar corona, in particular its helmet streamers, as observed during total solar eclipses around maxima of solar cycles and make its comparison with solar polar magnetic field strength as observed by the Wilcox Solar Observatory (WSO) since 1976. Even though the magnetic field strength at the solar poles around cycle minima decreased minimally twice in the last forty years, distributions of helmet streamers around the Sun in different cycles around cycle maxima remain nearly the same. This indicates that large-scale magnetic structures governing the shape and evolution of helmet streamers must be of a different nature than those related with solar polar fields.

  4. Strain-cycling fatigue behavior of ten structural metals tested in liquid helium (4 K), in liquid nitrogen (78 K), and in ambient air (300 K)

    NASA Technical Reports Server (NTRS)

    Nachtigall, A. J.

    1974-01-01

    Strain-cycling fatigue behavior of 10 different structural alloys and metals was investigated in liquid helium (4 K), in liquid nitrogen (78 K), and in ambient air (300 K). At high cyclic lives, fatigue resistance increased with decreasing temperature for all the materials investigated. At low cyclic lives, fatigue resistance generally decreased with decreasing temperature for the materials investigated. Only for Inconel 718 did fatigue resistance increase with decreasing temperature over the entire life range investigated. Comparison of the experimental fatigue behavior with that predicted by the Manson method of universal slopes showed that the fatigue behavior of these materials can be predicted for cryogenic temperatures by using material tensile properties obtained at those same temperatures.

  5. 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.

  6. Strength of graphite/epoxy bolted wing-skin splice specimens subjected to outdoor exposure under constant load and yearly fatigue loading

    NASA Technical Reports Server (NTRS)

    Wichorek, G. R.; Crews, J. H., Jr.

    1986-01-01

    The results of an experimental study to provide long-term durability data on detailed full-scale graphite/epoxy wing-skin joint designs under environmental exposure and cyclic loading associated with commercial transport aircraft are reported. The specimens consisted of a single-row bolt configuration fabricated from T300/5208 and a double-row bolt configuration fabricated from T300/5209. The unpainted specimens were exposed to the outdoor environment under a sustained tensile load, and at yearly intervals, they were subjected to fatigue loading. Experimental results showed a slight reduction in residual tensile strength for both graphite/epoxy joints under the exposure times and fatigue loadings reported. A 7.5-percent decrease in residual strength was observed for the T300/5208 single-row joint after 5 years exposure and two lifetimes of fatigue loading. A 5.3-percent decrease in residual strength was observed for the T300/5209 double-row joint after 7 years exposure and 2.8 lifetimes of fatigue loading. The 5208 epoxy material was more susceptible to degradation by ultraviolet radiation than the 5209 epoxy material.

  7. Ceramic Inlays: Effect of Mechanical Cycling and Ceramic Type on Restoration-dentin Bond Strength.

    PubMed

    Trindade, F Z; Kleverlaan, C J; da Silva, L H; Feilzer, A J; Cesar, P F; Bottino, M A; Valandro, L F

    2016-01-01

    This study aimed to evaluate the bond strength between dentin and five different ceramic inlays in permanent maxillary premolars, with and without mechanical cycling. One hundred permanent maxillary premolars were prepared and divided into 10 groups (n=10) according to the ceramic system (IPS e.Max Press; IPS e.Max CAD; Vita PM9; Vita Mark II; and Vita VM7) and the mechanical cycling factor (with and without [100 N, 2 Hz, 1.2×10(6) cycles]). The inlays were adhesively cemented, and all of the specimens were cut into microbars (1×1 mm, nontrimming method), which were tested under microtensile loading. The failure mode was classified and contact angle, roughness, and microtopographic analyses were performed on each ceramic surface. The mechanical cycling had a significant effect (p=0.0087) on the bond strength between dentin and IPS e.max Press. The Vita Mark II group had the highest bond strength values under both conditions, with mechanical cycling (9.7±1.8 MPa) and without (8.2±1.9 MPa), while IPS e.Max CAD had the lowest values (2.6±1.6 and 2.2±1.4, respectively). The adhesive failure mode at the ceramic/cement interface was the most frequent. Vita Mark II showed the highest value of average roughness. IPS e.max Press and Vita Mark II ceramics presented the lowest contact angles. In conclusion, the composition and manufacturing process of ceramics seem to have an influence on the ceramic surface and resin cement bond strength. Mechanical cycling did not cause significant degradation on the dentin and ceramic bond strength under the configuration used. PMID:27455117

  8. Low-Cycle Fatigue Behavior of 95.8Sn-3.5Ag-0.7Cu Solder Joints

    NASA Astrophysics Data System (ADS)

    Tang, Y.; Li, G. Y.; Shi, X. Q.

    2013-01-01

    Low-cycle fatigue (LCF) behavior of 95.8Sn-3.5Ag-0.7Cu solder joints was investigated over a range of test temperatures (25°C, 75°C, and 125°C), frequencies (0.001 Hz, 0.01 Hz, and 0.1 Hz), and strain ranges (0.78%, 1.6%, and 3.1%). Effects of temperature and frequency on the LCF life were studied. Results show that the LCF lifetime decreases with an increase in test temperature or a decrease of test frequency, which is attributed to the longer exposure time to creep and the stress relaxation mechanism during fatigue testing. A modified Coffin-Manson model considering effects of temperature and frequency on the LCF life is proposed. The fatigue exponent and ductility coefficient were found to be influenced by both the temperature and frequency. By fitting the experimental data, the mathematical relations between the fatigue exponent and temperature, and ductility coefficient and temperature, were analyzed. Scanning electron microscopy (SEM) of the cross-sections and fracture surfaces of failed specimens at different temperature and frequency was applied to verify the failure mechanisms.

  9. On the nature and crystallographic orientation of subsurface cracks in high cycle fatigue of Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Gilbert, Jeremy L.; Piehler, Henry R.

    1993-03-01

    Subsurface fatigue damage, in the form of cracking of the α phase, was observed in Ti-6A1-4V during high cycle fatigue of total hip prostheses tested in a simulated physiological test geometry and environment. The subsurface cracking was found only in the region of highest fatigue stresses and was present in a zone between 50 and 700 μm beneath the surface. The density of these cracks appeared to depend on the fabrication process used to form the part, where the direction of forging deformation strongly influenced the texture and grain morphology of the near-α bimodal microstructure. A novel scanning electron microscopy (SEM) technique, using selected area channeling patterns (SACPs) and electron channeling contrast imaging (ECCI), is described and was used to determine the crystallographic orientation of the fracture plane in the a phase. The texture resulting from the forming operation appeared to be such that the basal pole of the hcp lattice became oriented in the direction of flow. Also, the deformation substructure (in the form of dislocation subcells) influenced the formation of the subsurface cracks. Observations based on four independent fractured grains, using the channeling analysis techniques, indicated that the fracture plane for these subsurface fatigue cracks is the pyramidal plane of the hcp lattice.

  10. Strain Ratio Effects on Low-Cycle Fatigue Behavior of Gravity Cast Al-Si-Cu Alloys

    NASA Astrophysics Data System (ADS)

    Fan, K. L.; Liu, X. S.; He, G. Q.; Cheng, H.; Lv, S. Q.

    2015-10-01

    The strain-controlled low-cycle fatigue properties of gravity cast Al-Si-Cu alloys for engine cylinder heads were investigated. At strain ratios of R ɛ = -2, 0, and 0.1, the cyclic stress amplitude progressively increased from initiation to the 450th cycle, and then proceeded into a steady stage until failure. At a strain ratio of R ɛ = -∞, the material exhibited a continuous cyclic hardening. The hysteresis loops in this alloy for the 2nd and half-life cycle were tension/compression asymmetry, which also corresponded well to the evolution of peak/valley stress. Transmission electron microscopy analysis suggested that cyclic hardening was caused by the dislocations multiplication/tangles at strain ratios of R ɛ = -∞ and 0. Besides, the presence of dislocation cross slip contributed to cyclic stabilization observed at later stage of deformation at a strain ratio of R ɛ = 0. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain ratios. It showed that the fatigue cracks initiated basically at the internal defects in the samples. Meanwhile, at strain ratios of R = -∞ and 0, the fracture surface was rough with a large number of small unequiaxed dimples and some tear ridges. Moreover, the localized pores offered a preferential crack path in the samples, where they were surrounded by silicon particles. At a strain ratio of R ɛ = -∞, the fatigue cracks preferentially initiated at pores rather than α-Fe phases. At a strain ratio of R ɛ = 0, where fatigue crack initiation was observed at the interface between plate-like branch of α-Fe phase and aluminum matrix.

  11. A Cycling Movement Based System for Real-Time Muscle Fatigue and Cardiac Stress Monitoring and Analysis

    PubMed Central

    Chen, Szi-Wen; Liaw, Jiunn-Woei; Chang, Ya-Ju; Chan, Hsiao-Lung; Chiu, Li-Yu

    2015-01-01

    In this study, we defined a new parameter, referred to as the cardiac stress index (CSI), using a nonlinear detrended fluctuation analysis (DFA) of heart rate (HR). Our study aimed to incorporate the CSI into a cycling based fatigue monitoring system developed in our previous work so the muscle fatigue and cardiac stress can be both continuously and quantitatively assessed for subjects undergoing the cycling exercise. By collecting electrocardiogram (ECG) signals, the DFA scaling exponent α was evaluated on the RR time series extracted from a windowed ECG segment. We then obtained the running estimate of α by shifting a one-minute window by a step of 20 seconds so the CSI, defined as the percentage of all the less-than-one α values, can be synchronously updated every 20 seconds. Since the rating of perceived exertion (RPE) scale is considered as a convenient index which is commonly used to monitor subjective perceived exercise intensity, we then related the Borg RPE scale value to the CSI in order to investigate and quantitatively characterize the relationship between exercise-induced fatigue and cardiac stress. Twenty-two young healthy participants were recruited in our study. Each participant was asked to maintain a fixed pedaling speed at a constant load during the cycling exercise. Experimental results showed that a decrease in DFA scaling exponent α or an increase in CSI was observed during the exercise. In addition, the Borg RPE scale and CSI were positively correlated, suggesting that the factors due to cardiac stress might also contribute to fatigue state during physical exercise. Since the CSI can effectively quantify the cardiac stress status during physical exercise, our system may be used in sports medicine, or used by cardiologists who carried out stress tests for monitoring heart condition in patients with heart diseases. PMID:26115515

  12. Fatigue of insect cuticle.

    PubMed

    Dirks, Jan-Henning; Parle, Eoin; Taylor, David

    2013-05-15

    Many parts of the insect exoskeleton experience repeated cyclic loading. Although the cuticle of insects and other arthropods is the second most common natural composite material in the world, so far nothing is known about its fatigue properties, despite the fact that fatigue undoubtedly limits the durability of body parts in vivo. For the first time, we here present experimental fatigue data of insect cuticle. Using force-controlled cyclic loading, we determined the number of cycles to failure for hind legs (tibiae) and hind wings of the locust Schistocerca gregaria, as a function of the applied cyclic stress. Our results show that, although both are made from cuticle, these two body parts behave very differently. Wing samples showed a large fatigue range, failing after 100,000 cycles when we applied 46% of the stress needed for instantaneous failure [the ultimate tensile strength (UTS)]. Legs, in contrast, were able to sustain a stress of 76% of the UTS for the same number of cycles to failure. This can be explained by the difference in the composition and structure of the material, two factors that, amongst others, also affect the well-known behaviour of engineering composites. Final failure of the tibiae occurred via one of two different failure modes--propagation in tension or buckling in compression--indicating that the tibia is 'optimized' by evolution to resist both failure modes equally. These results are further discussed in relation to the evolution and normal use of these two body parts. PMID:23393276

  13. Menstrual Cycle Effects on Anaerobic Power, Muscular Strength, and Muscular Endurance in Trained and Untrained Females.

    ERIC Educational Resources Information Center

    Rosenburg, Beth S.; And Others

    A study determined if anaerobic power, isometric strength, and isometric endurance are affected by the menstrual cycle and if endurance trained females and untrained females are affected in the same manner on these performance parameters. Subjects were healthy, normally menstruating females, ages 18-34 years who were classified as either trained…

  14. Fatigue Properties of Cast Magnesium Wheels

    NASA Astrophysics Data System (ADS)

    Li, Zhenming; Luo, Alan A.; Wang, Qigui; Peng, Liming; Zhang, Peng

    2016-05-01

    This paper investigates the fatigue properties and deformation behavior of a newly developed Mg-2.96Nd-0.21Zn-0.39Zr magnesium alloy wheel in both as-cast and T6 conditions. Compared with the as-cast alloy, the T6-treated alloy shows a significant increase in fatigue strength and cyclic stress amplitude. This is believed to be attributed to the change of defect type from porosity to oxides and the increased matrix strength in the T6 (peak-aged) condition. For the as-cast alloy wheel, fatigue failure mainly originated from the cast defects including porosity, oxide film, and inclusion at or near the sample surface. In the T6-treated alloy, however, oxides and inclusions or slip bands initiate the fatigue cracks. Solution treatment appears to reduce or eliminate the shrinkage porosity because of grain growth and dissolution of as-cast eutectic phases in the grain boundaries. The cyclic stress amplitude of the as-cast alloy increases with increasing the number of cycles, while the T6-treated alloy shows cyclic softening after the stress reaches a maximum value. The Coffin-Manson law and Basquin equation can be used to evaluate the life of low cycle fatigue. The developed long crack model and multi-scale fatigue (MSF) models can be used to predict high-cycle fatigue life of the Mg-2.96Nd-0.21Zn-0.39Zr alloys with or without casting defects.

  15. Fatigue Properties of Cast Magnesium Wheels

    NASA Astrophysics Data System (ADS)

    Li, Zhenming; Luo, Alan A.; Wang, Qigui; Peng, Liming; Zhang, Peng

    2016-08-01

    This paper investigates the fatigue properties and deformation behavior of a newly developed Mg-2.96Nd-0.21Zn-0.39Zr magnesium alloy wheel in both as-cast and T6 conditions. Compared with the as-cast alloy, the T6-treated alloy shows a significant increase in fatigue strength and cyclic stress amplitude. This is believed to be attributed to the change of defect type from porosity to oxides and the increased matrix strength in the T6 (peak-aged) condition. For the as-cast alloy wheel, fatigue failure mainly originated from the cast defects including porosity, oxide film, and inclusion at or near the sample surface. In the T6-treated alloy, however, oxides and inclusions or slip bands initiate the fatigue cracks. Solution treatment appears to reduce or eliminate the shrinkage porosity because of grain growth and dissolution of as-cast eutectic phases in the grain boundaries. The cyclic stress amplitude of the as-cast alloy increases with increasing the number of cycles, while the T6-treated alloy shows cyclic softening after the stress reaches a maximum value. The Coffin-Manson law and Basquin equation can be used to evaluate the life of low cycle fatigue. The developed long crack model and multi-scale fatigue (MSF) models can be used to predict high-cycle fatigue life of the Mg-2.96Nd-0.21Zn-0.39Zr alloys with or without casting defects.

  16. Fatigue Strength and Related Characteristics of Aircraft Joints I : Comparison of Spot-Weld and Rivet Patterns in 24s-t Alclad and 75s-t Alclad

    NASA Technical Reports Server (NTRS)

    Russell, H W; Jackson, L R; Grover, H J; Beaver, W W

    1944-01-01

    Report contains detailed results of a number of fatigue tests on spot-welded joints in aluminum alloys. The tests described include: (1) fatigue tests on spot-welded lap joints in sheets of unequal thickness of alclad 24s-t. These tests indicate that the fatigue strength of a spot-welded joint in sheets of two different gages is slightly higher than that of a similar joint in two sheets of the thinner gage but definitely lower than that of a similar joint in two sheets of the thicker gage. (2) Fatigue tests on spot-welded alclad 75s-t spot-welded lap-joint specimens of alclad 75s-t were not any stronger in fatigue than similar specimens of alclad 24s-t. (3) Fatigue tests on lap-joint specimens spot -welded after various surface preparations--these included ac welding wire-brushed surfaces, dc welding wire-brushed surfaces, and dc welding chemically cleaned surfaces. While the ac welds were strongest statically, the dc welds on wire-brushed surfaces were strongest in fatigue. Specimens prepared in this way were very nearly as strong as the best riveted specimens tested for comparison. (4) Fatigue tests on specimens spot-welded with varying voltage so as to include a wide range of static spot-weld strengths. The fatigue strengths were in the same order as the static strengths but showed less range. (author)

  17. Limitations of Spectral Electromyogramic Analysis to Determine the Onset of Neuromuscular Fatigue Threshold during Incremental Ergometer Cycling

    PubMed Central

    Latasa, Iban; Cordova, Alfredo; Malanda, Armando; Navallas, Javier; Lavilla-Oiz, Ana; Rodriguez-Falces, Javier

    2016-01-01

    Recently, a new method has been proposed to detect the onset of neuromuscular fatigue during an incremental cycling test by assessing the changes in spectral electromyographic (sEMG) frequencies within individual exercise periods of the test. The method consists on determining the highest power output that can be sustained without a significant decrease in spectral frequencies. This study evaluated the validity of the new approach by assessing the changes in spectral indicators both throughout the whole test and within individual exercise periods of the test. Fourteen cyclists performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. The mean and median frequencies (Fmean and Fmedian, respectively) of the sEMG power spectrum were calculated. The main findings were: (1) Examination of spectral indicators within individual exercise periods of the test showed that neither Fmean nor Fmedian decreased significantly during the last (most fatiguing) exercise periods. (2) Examination of the whole incremental test showed that the behaviour of Fmean and Fmedian with increasing power output was highly inconsistent and varied greatly among subjects. (3) Over the whole incremental test, half of the participants exhibited a positive relation between spectral indicators and workload, whereas the other half demonstrated the opposite behavior. Collectively, these findings indicate that spectral sEMG indexes do not provide a reliable measure of the fatigue state of the muscle during an incremental cycling test. Moreover, it is concluded that it is not possible to determine the onset of neuromuscular fatigue during an incremental cycling test by examining spectral indicators within individual exercise periods of the test. Key points The behaviour of spectral EMG indicators during the incremental test exhibited a high heterogeneity among individuals, with approximately half of the participants showing a positive

  18. The effect of HVOF sprayed coatings on the elevated temperature high cycle fatigue behavior of a martensitic stainless steel

    SciTech Connect

    Tipton, A.A.

    1995-12-31

    This study reports the influence of three High Velocity Oxy-Fuel (HVOF) applied coatings on the high cycle fatigue resistance of a martensitic stainless steel substrate at room and elevated temperatures. It was found that chromium carbide and tungsten carbide coated specimens exhibited significantly lower fatigue capability compared to the substrate material at elevated temperatures while IN625 coated specimens exhibited a small beneficial effect. An attempt is made to explain the observed behavior in terms of elastic modulus mismatch, thermal expansion mismatch, residual stress and coating/substrate properties. It is concluded that coated metallic components must be analyzed as composite structures and that data generated for design properties must be performed on specimens which represent the geometry and characteristics of intended component.

  19. In situ neutron diffraction study of the low cycle fatigue of the α-γ duplex stainless steel

    NASA Astrophysics Data System (ADS)

    Jenčuš, Peter; Polák, Jaroslav; Lukáš, Petr; Muránsky, Ondrej

    2006-11-01

    In duplex stainless steels, significant thermal stresses are generated during the cooling from the homogenization temperature due to different thermal expansion coefficients of the austenitic and ferritic phases. The results of the in situ neutron diffraction examination of the evolution of the internal stresses during the low cycle fatigue in the SAF 2507 duplex stainless steel are reported. Stress response of both constituent components resulting from the load sharing between austenitic and ferritic grains was measured. It was found that the initial thermal residual stresses were relaxed rapidly at the beginning of the cyclic loading. Whereas initial hardening was identified in both phases, the subsequent fatigue softening was fully attributed to the austenitic phase.

  20. Simulation of Delamination Propagation in Composites Under High-Cycle Fatigue by Means of Cohesive-Zone Models

    NASA Technical Reports Server (NTRS)

    Turon, Albert; Costa, Josep; Camanho, Pedro P.; Davila, Carlos G.

    2006-01-01

    A damage model for the simulation of delamination propagation under high-cycle fatigue loading is proposed. The basis for the formulation is a cohesive law that links fracture and damage mechanics to establish the evolution of the damage variable in terms of the crack growth rate dA/dN. The damage state is obtained as a function of the loading conditions as well as the experimentally-determined coefficients of the Paris Law crack propagation rates for the material. It is shown that by using the constitutive fatigue damage model in a structural analysis, experimental results can be reproduced without the need of additional model-specific curve-fitting parameters.

  1. Twinning Behaviors During Thermomechanical Fatigue Cycling of a Nickel-Base Single-Crystal TMS-82 Superalloy

    NASA Astrophysics Data System (ADS)

    Lv, X. Z.; Zhang, J. X.; Harada, H.

    2014-03-01

    This paper provides further insight into the formation of deformation twins at different stages during the whole thermomechanical fatigue cycling in a nickel-base single-crystal TMS-82 superalloy. In general, it is found that twinning behaviors can always be associated with the applied stress orientation. The preferred twinning direction at the primary stage is <001>-compression since the tangled dislocations which appear after the first plastic deformation provide an opportunity for twinning nucleation in compression. At the intermediate stage, the applied stress required for formation of twins in tension is much larger than that in compression; hence, twinning behaviors show distinct tension/compression asymmetry. A thick twin plate and a great many dislocations can be found after fatigue failure, and one can rationalize the reason for this twinning being associated with the TMF procedure. Twins at the tip of the crack in tension occur owing to the existence of compressive strain field.

  2. Adaptations to isolated shoulder fatigue during simulated repetitive work. Part II: Recovery.

    PubMed

    McDonald, Alison C; Tse, Calvin T F; Keir, Peter J

    2016-08-01

    The shoulder allows kinematic and muscular changes to facilitate continued task performance during prolonged repetitive work. The purpose of this work was to examine changes during simulated repetitive work in response to a fatigue protocol. Participants performed 20 one-minute work cycles comprised of 4 shoulder centric tasks, a fatigue protocol, followed by 60 additional cycles. The fatigue protocol targeted the anterior deltoid and cycled between static and dynamic actions. EMG was collected from 14 upper extremity and back muscles and three-dimensional motion was captured during each work cycle. Participants completed post-fatigue work despite EMG manifestations of muscle fatigue, reduced flexion strength (by 28%), and increased perceived exertion (∼3 times). Throughout the post-fatigue work cycles, participants maintained performance via kinematic and muscular adaptations, such as reduced glenohumeral flexion and scapular rotation which were task specific and varied throughout the hour of simulated work. By the end of 60 post-fatigue work cycles, signs of fatigue persisted in the anterior deltoid and developed in the middle deltoid, yet perceived exertion and strength returned to pre-fatigue levels. Recovery from fatigue elicits changes in muscle activity and movement patterns that may not be perceived by the worker which has important implications for injury risk. PMID:26076931

  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. Effects of a high mean stress on the high cycle fatigue life of PWA 1480 and correlation of data by linear elastic fracture mechanics

    NASA Technical Reports Server (NTRS)

    Majumdar, S.; Kwasny, R.

    1985-01-01

    High-cycle fatigue tests using 5-mm-diameter smooth specimens were performed on the single crystal alloy PWA 1480 (001 axis) at 70F (room temperature) in air and at 100F (538C) in vacuum (10 to the -6 power torr). Tests were conducted at zero mean stress as well as at high tensile mean stress. The results indicate that, although a tensile mean stress, in general, reduces life, the reduction in fatigue strength, for a given mean stress at a life of one million cycles, is much less than what is predicted by the usual linear Goodman plot. Further, the material appears to be significantly more resistant to mean stress effects at 1000F than at 70F. Metallographic examinations of failed specimens indicate that failures in all cases are initiated from micropores of sizes of the order of 30 to 40 microns. Since the macroscopic stress-strain response in all cases was observed to be linear elastic, linear elastic fracture mechanics (LEFM) analyses were carried out to determine the crack growth curves of the material assuming that crack initiation from a micropore (a sub o = 40 microns) occurs very early in life. The results indicate that the calculated crack growth rates at an R (defined as the ratio between minimum stress to maximum stress) value of zero are approximately the same at 70F as at 1000F. However, the calculated crack growth rates at other R ratios, both positive and negative, tend to be higher at 70F than at 1000F. Calculated threshold effects at large R values tend to be independent of temperature in the temperature regime studied. They are relatively constant with increasing R ratio up to a value of about 0.6, beyond which the calculated threshold stress intensity factor range decreases rapidly with increasing R ratios.

  5. The effect of two configuration factors, time, and thermal cycling on resin to dentin bond strengths.

    PubMed

    Price, Richard B; Dérand, Tore; Andreou, Pantelis; Murphy, Darcy

    2003-03-01

    Most in vitro testing of bonding systems is performed using specimens made in a mold with a low configuration (C) factor (ratio of bonded/unbonded surfaces) whereas clinically the C-factor is usually much greater. This study compared the effect of thermal cycling on the measured shear bond strength of 3M Single Bond dental adhesive bonded to dentin using molds with two different C-factors. The hypothesis was that neither C-factor nor thermal cycling would affect measured bond strengths. Resin composite was bonded to human dentin in cylindrical molds with an internal diameter of 3.2mm and either 1mm or 2.5mm deep. The 1mm deep molds had a C-factor of 2.2 and the 2.5mm deep molds had a C-factor of 4.1. Specimens were debonded either 10min after they had been bonded to dentin, or after they had been stored for 7 days in water at 37+/-1 degrees C, or after thermal cycling 5000 times for 7 days. Two-way ANOVA showed that overall both the C-factor and the storage condition had a significant effect on bond strength (p<0.001). There was a significant interaction (p<0.001) between the C-factor and how the specimens had been stored. The GLM/LSMEANS procedure with Sidak's adjustment for multiple comparisons showed that overall the specimens made in the mold with a high C-factor (4.1) had a lower bond strength than those that had been made in the mold with a lower (2.2) C-factor (p<0.001). Thermal cycling had a negative effect on the bond strength only for specimens made in molds with a C-factor of 4.1 (p<0.001). PMID:12504523

  6. Acute prior heavy strength exercise bouts improve the 20-km cycling time trial performance.

    PubMed

    Silva, Renato A S; Silva-Júnior, Fernando L; Pinheiro, Fabiano A; Souza, Patrícia F M; Boullosa, Daniel A; Pires, Flávio O

    2014-09-01

    This study verified if a prior 5 repetition maximum (5RM) strength exercise would improve the cycling performance during a 20-km cycling time trial (TT20km). After determination of the 5RM leg press exercise load, 11 trained cyclists performed a TT20km in a control condition and 10-minute after 4 sets of 5RM strength exercise bouts (potentiation condition). Oxygen uptake, blood lactate concentration, ratings of perceived exertion (RPE), and power output data were recorded during the TT20km. Cycling economy index was assessed before the TT20km, and pacing strategy was analyzed assuming a "J-shaped" power output distribution profile. Results were a 6.1% reduction (p ≤ 0.05) in the time to complete the TT20km, a greater cycling economy (p < 0.01), and power output in the first 10% of the TT20km (i.e., trend; p = 0.06) in the potentiation condition. However, no differences were observed in pacing strategy, physiological parameters, and RPE between the conditions. These results suggest that 5RM strength exercise bouts improve the performance in a subsequent TT20km. PMID:24584047

  7. The effect of pre-stress cycles on fatigue crack growth - An analysis of crack growth mechanism. [in Al alloy plates

    NASA Technical Reports Server (NTRS)

    Kang, T. S.; Liu, H. W.

    1974-01-01

    Cyclic prestress increases subsequent fatigue crack growth rate in 2024-T351 aluminum alloy. This increase in growth rate, caused by the prestress, and the increased rate, caused by temper embrittlement as observed by Ritchie and Knott (1973), cannot be explained by the crack tip blunting model alone. Each fatigue crack increment consists of two components, a brittle and a ductile component. They are controlled by the ductility of the material and its cyclic yield strength, respectively.

  8. Peroxide bond strength of antimalarial drugs containing an endoperoxide cycle. Relation with biological activity.

    PubMed

    Fernández, Israel; Robert, Anne

    2011-06-01

    Several endoperoxide compounds are very efficient antimalarial analogues of the natural drug artemisinin. Quantum chemical calculations have been used to correlate the computed free energies of the O-O bond with respect to the total number of oxygen atoms contained in the cycle, and with the size/strain of the cycle (5- or 6-membered cycles). The gas-phase homolysis of the O-O bond has been studied for five- and six-membered oxygenated cycles which are models of the "real" drugs. Our results indicate that, in 6-membered cycles, the stability order is the following: 1,2-dioxane > 1,2,4-trioxane > 1,2,4,5-tetraoxane. In cycles containing 3 oxygen atoms, the 5-membered cycle 1,2,4-trioxolane was found much less stable than its 6-membered counterpart 1,2,4-trioxane. This feature indicates the possible role of the cycle strain for the O-O bond stability, and may also explain the high antimalarial activity of some trioxolane derivatives. Similar trends in the O-O bond strength have been found for the real antimalarial drugs. However, the O-O bond stability is not in itself a decisive argument to anticipate the antimalarial activity of drugs. PMID:21487624

  9. Effect of Forging Parameters on Low Cycle Fatigue Behaviour of Al/Basalt Short Fiber Metal Matrix Composites

    PubMed Central

    Karthigeyan, R.; Ranganath, G.

    2013-01-01

    This paper deals with metal matrix composites (MMCs) of Al 7075 alloy containing different weight percentage (2.5, 5, 7.5, and 10) basalt short fiber reinforcement and unreinforced matrix alloy. The samples were produced by the permanent stir casting technique. The casting ingots were cut into blanks to be forged in single stage and double stage, using MN press and graphite-based lubricant. The microstructures and fatigue properties of the matrix alloy and MMC samples were investigated in the as cast state and in the single and double stage forging operations. The microstructure results showed that the forged sample had a uniform distribution of the basalt short fiber throughout the specimens. Evaluation of the fatigue properties showed that the forged samples had higher values than those of the as cast counterparts. After forging, the enhancement of the fatigue strength of the matrix alloy was so significant and high in the case of 2.5 and 5.0 wt. percentage basalt short fiber reinforced MMC, and there was no enhancement in 7.5 and 10 weight percentages short fiber reinforced MMCs. The fracture damage was mainly due to decohesion at the matrix-fiber interface. PMID:24298207

  10. Effect of forging parameters on low cycle fatigue behaviour of Al/basalt short fiber metal matrix composites.

    PubMed

    Karthigeyan, R; Ranganath, G

    2013-01-01

    This paper deals with metal matrix composites (MMCs) of Al 7075 alloy containing different weight percentage (2.5, 5, 7.5, and 10) basalt short fiber reinforcement and unreinforced matrix alloy. The samples were produced by the permanent stir casting technique. The casting ingots were cut into blanks to be forged in single stage and double stage, using MN press and graphite-based lubricant. The microstructures and fatigue properties of the matrix alloy and MMC samples were investigated in the as cast state and in the single and double stage forging operations. The microstructure results showed that the forged sample had a uniform distribution of the basalt short fiber throughout the specimens. Evaluation of the fatigue properties showed that the forged samples had higher values than those of the as cast counterparts. After forging, the enhancement of the fatigue strength of the matrix alloy was so significant and high in the case of 2.5 and 5.0 wt. percentage basalt short fiber reinforced MMC, and there was no enhancement in 7.5 and 10 weight percentages short fiber reinforced MMCs. The fracture damage was mainly due to decohesion at the matrix-fiber interface. PMID:24298207

  11. The low cycle fatigue behavior of a plasma-sprayed coating material

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V., Jr.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  12. Low cycle fatigue behaviour of a plasma-sprayed coating material

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  13. Studies of Microtexture and Its Effect on Tensile and High-Cycle Fatigue Properties of Laser-Powder-Deposited INCONEL 718

    NASA Astrophysics Data System (ADS)

    Qi, Huan; Azer, Magdi; Deal, Andrew

    2012-11-01

    The current work studies the microstructure, texture, and mechanical properties of INCONEL 718 alloy (IN718) produced by laser direct metal deposition. The grain microstructure exhibits an alternative distribution of banded fine and coarse grain zones as a result of the rastering scanning pattern. The effects of the anisotropic crystallographic texture on the tensile and high-cycle fatigue (HCF) properties at room temperature are investigated. Tensile test results showed that the tensile strength of laser-deposited IN718 after direct aging or solution heat treatment is equivalent to the minimum-forged IN718 properties. The transverse direction (relative to the laser scanning direction) produces >10 pct stiffer modulus of elasticity but 3 to 6 pct less tensile strength compared to the longitudinal direction due to the preferential alignment of grains having <111> and <100> directions parallel to the tensile loading direction. Laser-deposited IN718 with good metallurgical integrity showed equivalent HCF properties compared to the direct-aged wrought IN718, which can be attributed to the banded grain size variation and cyclic change of inclining grain orientations resulted from alternating rastering deposition path.

  14. Stretch shortening cycle fatigue: interactions among joint stiffness, reflex, and muscle mechanical performance in the drop jump [corrected].

    PubMed

    Horita, T; Komi, P V; Nicol, C; Kyröläinen, H

    1996-01-01

    The purpose of the present study was to investigate the effect of strenuous stretch-shortening cycle exercise on the relationship between reflex and stiffness regulation during the drop jump. Ten healthy male subjects performed submaximal stretch-shortening cycle exercise on a special sledge apparatus. Exhaustion occurred on average within 3 min. A drop jump test from a 50-cm height was performed immediately before and after the sledge exercise, as well as 2 h, 2 days and 4 days later. The fatigue exercise showed relatively high blood lactate concentrations 12.5 (SD 2.6) mmol.l-1 and a 2-day delayed increase of serum cretaine kinase concentration. In drop jumps, the short latency M1 component of the vastus lateralis muscle electromyogram (EMG) response showed a continuous decline throughout the entire follow-up period after fatigue (NS), whereas the medium latency EMG component increased 2 days after the postfatigue sessions (P < 0.05). Immediately after the fatigue exercise a positive correlation (P < 0.05) was found between the changes in the short latency EMG response and in the amount of knee joint stiffness during the early postlanding phase of the drop jump. This suggests that the M1 response was closely related to the stiffness changes during the initial braking phase of the drop jump. Increase of creatine kinase concentration on the 2nd day correlated negatively with the changes in the drop jump performance (P < 0.05). Since the short latency EMG component has almost recovered on the 2nd day, impairment of the mechanical function of the muscle might have taken place. In conclusion, exhausting stretch-shortening cycle exercise induced local muscle impairment, which resulted in modulation of the reflex and stiffness interaction in the drop jump as well as compensation by central motor command. PMID:8803498

  15. Fatigue failure kinetics and structural changes in lead-free interconnects due to mechanical and thermal cycling

    NASA Astrophysics Data System (ADS)

    Fiedler, Brent Alan

    Environmental and human health concerns drove European parliament to mandate the Reduction of Hazardous Substances (RoHS) for electronics. This was enacted in July 2006 and has practically eliminated lead in solder interconnects. There is concern in the electronics packaging community because modern lead-free solder is rich in tin. Presently, near-eutectic tin-silver-copper solders are favored by industry. These solders are stiffer than the lead-tin near-eutectic alloys, have a higher melting temperature, fewer slip systems, and form intermetallic compounds (IMC) with Cu, Ni and Ag, each of which tend to have a negative effect on lifetime. In order to design more reliable interconnects, the experimental observation of cracking mechanisms is necessary for the correct application of existing theories. The goal of this research is to observe the failure modes resulting from mode II strain and to determine the damage mechanisms which describe fatigue failures in 95.5 Sn- 4.0 Ag - 0.5 Cu wt% (SAC405) lead-free solder interconnects. In this work the initiation sites and crack paths were characterized for SAC405 ball-grid array (BGA) interconnects with electroless-nickel immersion-gold (ENIG) pad-finish. The interconnects were arranged in a perimeter array and tested in fully assembled packages. Evaluation methods included monotonic and displacement controlled mechanical shear fatigue tests, and temperature cycling. The specimens were characterized using metallogaphy, including optical and electron microscopy as well as energy dispersive spectroscopy (EDS) and precise real-time electrical resistance structural health monitoring (SHM). In mechanical shear fatigue tests, strain was applied by the substrates, simulating dissimilar coefficients of thermal expansion (CTE) between the board and chip-carrier. This type of strain caused cracks to initiate in the soft Sn-rich solder and grow near the interface between the solder and intermetallic compounds (IMC). The growth near

  16. (abstract) A Brief, Selective Review of Thermal Cycling Fatigue in Eutectic Tin-Lead Solder

    NASA Technical Reports Server (NTRS)

    Winslow, J. W.; Silveira, C. de

    1993-01-01

    This paper reviews selected parts of the current literature relevant to thermo-mechanical fatigue mechanisms in eutectic tin-lead solder, and suggests a general outline to account for some observed failures. The field is found to be complex. One recent experimental study finds some failure modes to be sensitive to joint geometry. Attempts to extrapolate from test environments to service environments have had only limited success. Much work remains to be done before fatigue failures in this material can be considered as under practical control.

  17. Muscle Strength Enhancement Following Home-Based Virtual Cycling Training in Ambulatory Children with Cerebral Palsy

    ERIC Educational Resources Information Center

    Chen, Chia-Ling; Hong, Wei-Hsien; Cheng, Hsin-Yi Kathy; Liaw, Mei-Yun; Chung, Chia-Ying; Chen, Chung-Yao

    2012-01-01

    This study is the first well-designed randomized controlled trial to assess the effects of a novel home-based virtual cycling training (hVCT) program for improving muscle strength in children with spastic cerebral palsy (CP). Twenty-eight ambulatory children with spastic CP aged 6-12 years were randomly assigned to an hVCT group (n = 13) or a…

  18. Bond and low cycle fatigue behavior of thermoset composite reinforcing for the concrete industry

    SciTech Connect

    Barnes, B.

    1990-09-21

    This thesis encompasses two separate research projects. The first project, described in Chapter 2 was a project investigating the fatigue behavior of thermoset Fiber Composite (FC) sandwich wall ties. The second research project detailed in this thesis was a project studying the bond and tensile properties of FC rod and FC fibers.

  19. Effectiveness of a tailored neck training program on neck strength, movement, and fatigue in under-19 male rugby players: a randomized controlled pilot study

    PubMed Central

    Barrett, Matthew D; McLoughlin, Terence F; Gallagher, Kieran R; Gatherer, Don; Parratt, Michael TR; Perera, Jonathan R; Briggs, Tim WR

    2015-01-01

    Purpose To investigate the effect of a tailored neck muscle conditioning program on neck muscle strength, neck muscle fatigue, and range of neck movement in 16–18-year-old male rugby players. Materials and methods Thirty-four male rugby players were divided into forward and back playing positions and randomized within these groups. Seventeen players were randomly assigned to each group. The test group was given a tailored 6-week exercise regime based on their baseline measurements to be performed three times a week in addition to their normal training and playing. The control group trained and played as normal. The outcome measures used were cervical spine range of movement, neck strength, and neck muscle fatigability. Results There were no clinically relevant statistically significant differences between the two groups. Trends identified between the two groups suggest that a tailored neck exercise program increases neck strength, particularly neck extension, and increases resistance to fatigue, as well as influencing right- and left-sided neck muscle balance. A reduction in range of movement was also demonstrated in the test group. There was a great deal of variability in range of movement and strength within this age group. No previously undiagnosed neck conditions were detected, and there were no adverse events reported. Conclusion This study has shown that neck strength, range of movement, and susceptibility of the neck muscles to fatigue can be influenced using a focused neck training regime. It forms an important basis for a larger, multicenter study to ensure the neck is given due attention in rugby training and receives the same focus of conditioning as other parts of the body. PMID:25999771

  20. Fatigue Behavior of Inconel 718 TIG Welds

    NASA Astrophysics Data System (ADS)

    Alexopoulos, Nikolaos D.; Argyriou, Nikolaos; Stergiou, Vasillis; Kourkoulis, Stavros K.

    2014-08-01

    Mechanical behavior of reference and TIG-welded Inconel 718 specimens was examined in the present work. Tensile, constant amplitude fatigue, and fracture toughness tests were performed in ambient temperature for both, reference and welded specimens. Microstructure revealed the presence of coarse and fine-grained heat-affected zones. It has been shown that without any post-weld heat treatment, welded specimens maintained their tensile strength properties while their ductility decreased by more than 40%. It was found that the welded specimens had lower fatigue life and this decrease was a function of the applied fatigue maximum stress. A 30% fatigue life decrease was noticed in the high cycle fatigue regime for the welded specimens while this decrease exceeded 50% in the low cycle fatigue regime. Cyclic stress-strain curves showed that Inconel 718 experiences a short period of hardening followed by softening for all fatigue lives. Cyclic fatigue response of welded specimens' exhibited cyclically stable behavior. Finally, a marginal decrease was noticed in the Mode I fracture toughness of the welded specimens.

  1. Effect of thermal cycling on the bond strength of self-adhesive cements to fiber posts.

    PubMed

    Mazzitelli, Claudia; Monticelli, Francesca; Toledano, Manuel; Ferrari, Marco; Osorio, Raquel

    2012-06-01

    The aim of this study was to assess the push-out bond strengths of self-adhesive resin cements to epoxy resin-based fiber posts after challenging by thermocycling. Thirty-six single-rooted premolars were endodontically treated, and the post-spaces were drilled to receive RelyX Fiber posts #1. Three self-adhesive resin cements (RelyX Unicem, G-Cem, and Breeze) were used for luting fiber posts. The bonded specimens were either stored for 1 month in a moist field (37°C) or submitted to thermocycling (5,000 times) prior to push-out test. The maximum force required to dislodge the post via an apical-coronal direction was recorded (megapascal). The data were statistically analyzed with two-way ANOVA and Tukey tests (p < 0.05). The factors "luting cement" and "thermocycling" significantly influenced bond strengths. The initial push-out values of RelyX Unicem and Breeze were higher than those of G-Cem. After thermocycling, the bond strength of G-Cem increased and no differences were found between groups. RelyX Unicem and Breeze bond strengths were not affected by the thermal challenge. Thermal cycling and cement type differently influence the bond strengths of self-adhesive resin cements. Self-adhesive cements can represent an option for luting fiber posts into root canal. PMID:21670983

  2. Evaluation of the Effect of Surface Finish on High-Cycle Fatigue for SLM-IN718

    NASA Technical Reports Server (NTRS)

    Lambert, Dennis M.

    2016-01-01

    A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the selective laser melt (SLM) process. This factor is the reduction at a common fatigue life from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition. Various vendors provided specimens. To reduce the number of degrees-of-freedom, only one heat treat condition was evaluated. Testing temperatures included room temperature, 800F, 1000F, and 1200F. The two surface conditions were compared at constant lives, where data was available. The recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness <= 4 micro-inches/inch) is approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce the same life in the as built surface condition. As an alternative method, the surface finish was incorporated into a new parameter with the maximum stress. The new parameter was formulated to be similar to the fracture mechanics stress intensity factor, and it was named the pseudo stress intensity factor, Kp. Using Kp, the variance seemed acceptable across all sources, and the knockdown factor was estimated over the range of data identified by Kp where data occurred. A plot of the results suggests that the knockdown factor is a function of temperature, and that for low lives the knockdown is greater than the knockdown observed above about one million cycles, where it stabilizes. One data point at room temperature was clearly different, and the sparsity of data in the higher life region reduces the value of these results. The method does appear to provide useful results, and further characterization of the method is suggested.

  3. Thermal-Fatigue Crack-Growth Characteristics and Mechanical Strain Cycling Behavior of A-286 Discaloy, and 16-25-6 Austenitic Steels

    NASA Technical Reports Server (NTRS)

    Smith, Robert W.; Smith, Gordon T.

    1960-01-01

    Thermal-fatigue crack-growth characteristics of notched- and unnotched-disk specimens of A-286, Discaloy, hot-cold worked 16-25-6, and overaged 16-25-6 were experimentally studied. Separately controlled variables were total strain range (0.0043 to 0.0079 in./in.), maximum cycle temperature (1300 and 1100 F), and hold time at maximum temperature (O and 5 min). A limited number of mechanical, push-pull, constant-strain cycle tests at room temperature were made using notched and un-notched bars of the same materials. In these tests the number of cycles to failure as well as the variation of load change with accumulated cycles was measured, and the effects of mean stress were observed. Constant-strain-range mechanical-fatigue tests at room temperature revealed notched-bar fatigue life to be strongly influenced by mean stress. For a specific strain range, the longest fatigue life was always found to be associated with the least-tensile (or most compressive) mean stress. By defining thermal-fatigue life as the number of cycles required to produce a crack area of 6000 square mils, the relative thermal-fatigue resistances of the test materials were established. Notched-disk specimens of A-286 and Discaloy steels exhibited longer fatigue lives than either hot-cold worked or overaged 16-25-6. On the other hand, unnotched-disk specimens of Discaloy and hot-cold worked 16-25-6 had longer lives than A-286 and overaged 16-25-6. Separation of the crack-growth data into microstage and macrostage periods revealed that the macrostage period accounted for the greatest part of the difference among materials when tested in the notched configuration, while the microstage was largely responsible for the differences encountered in unnotched disks.

  4. Effects of microstructure on the strength and fatigue behavior of a silicon carbide fiber-reinforced titanium matrix composite and its constituents

    SciTech Connect

    Soboyejo, W.O.; Rabeeh, B.M.; Li, Y.; Chu, Y.C.; Lavrentenyev, A.; Rokhlin, S.I.

    1997-08-01

    The results of a systematic study of the effects of microstructure on the strength and fatigue behavior of a symmetric [0/90]{sub 2s} Ti-15V-3Cr-3Al-3Sn/SiC (SCS-6) composite are presented along with relevant information on failure mechanisms in the composite constituents, i.e., the interface, fiber, and matrix materials. Damage micromechanisms are elucidated via optical microscopy, scanning electron microscopy (SEM), and nondestructive acoustic emission (AE) and ultrasonic techniques. Composite damage is shown to initiate early under cyclic loading conditions and is dominated by longitudinal and transverse interfacial cracking. Subsequent fatigue damage occurs by matrix slip band formation, matrix and fiber cracking, and crack coalescence, prior to the onset of catastrophic failure. However, the sequence of the damage is different in material annealed above or below the {beta} solvus of the Ti-15-3 matrix material. Mechanistically based micromechanics models are applied to the prediction of the changes in modulus induced by fatigue damage. Idealized fracture mechanics models are also employed in the prediction of the fatigue lives of smooth specimens deformed to failure at room temperature. The article highlights the potential to develop mechanistically based predictive models based on simplified mechanics idealizations of experimental observations.

  5. Fatigue properties of shuttle thermal protection system

    NASA Technical Reports Server (NTRS)

    Sawyer, J. W.; Cooper, P. A.

    1980-01-01

    Static and cyclic load tests were conducted to determine the static and fatigue strength of the RIS tile/SIP thermal protection system used on the orbiter of the space shuttle. The material systems investigated include the densified and undensified LI-900 tile system on the .40 cm thick SIP and the densified and undensified LI-2200 tile system on the .23 cm (.090 inch) thick SIP. The tests were conducted at room temperature with a fully reversed uniform cyclic loading at 1 Hertz. Cyclic loading causes a relatively large reduction in the stress level that each of the SIP/tile systems can withstand for a small number of cycles. For example, the average static strength of the .40 cm thick SIP/LI-900 tile system is reduced from 86 kPa to 62 kPa for a thousand cycles. Although the .23 cm thick SIP/LI-2200 tile system has a higher static strength, similar reductions in the fatigue strength are noted. Densifying the faying surface of the RSI tile changes the failure mode from the SIP/tile interface to the parent RSI or the SIP and thus greatly increases the static strength of the system. Fatigue failure for the densified tile system, however, occurs due to complete separation or excessive elongation of the SIP and the fatigue strength is only slightly greater than that for the undensified tile system.

  6. Effect of Polymerization Cycles on Gloss, Roughness, Hardness and Impact Strength of Acrylic Resins.

    PubMed

    Consani, Rafael Leonardo Xediek; Folli, Bianca L; Nogueira, Moises C F; Correr, Americo Bortolazzo; Mesquita, Marcelo F

    2016-04-01

    The aim of this study was to evaluate the conventional and boiled polymerization cycles on gloss, roughness, hardness and impact strength of acrylic resins. Samples were made for each Classico and QC-20 materials (n=10) in dental stone molds obtained from rectangular metallic matrices embedded in metallic flasks. The powder-liquid ratio and manipulation of the acrylic resins' were accomplished according to manufacturers' instructions and the resins were conventionally packed in metallic flasks. After polymerization by (1) conventional: 74 °C for 9 h (Classico) and (2) boiled: 20 min (QC-20) cycles, the samples were deflasked after cooling at room temperature and conventionally finished and polished. The properties were evaluated after storage in water at 37 °C for 24 h. Gloss was verified with Multi Gloss 268 meter (Konica Minolta), surface roughness was measured with Surfcorder SE 1700 rugosimeter (Kosaka), Knoop hardness number was obtained with HMV-200 microdurometer, and impact strength was measured in an Otto Wolpert-Werke device by Charpy system (40 kpcm). Data were subjected to Student's t-test (at α=0.05). The results were: Gloss: 67.7 and 62.2 for Classico and QC-20 resins, respectively; Surface roughness: 0.874 and 1.469 Ra-µm for Classico and QC-20, respectively; Knoop hardness: 27.4 and 26.9 for Classico and QC-20, respectively; and Impact strength: 37.6 and 33.6 kgf/cm2 for Classico and QC-20, respectively. No statistically significant difference (p>0.05)were found between the resins for the evaluated properties. In conclusion, conventional and boiled polymerization cycles had similar effects on gloss, roughness, hardness and impact strength of both Classico and QC-20 resins. PMID:27058380

  7. Benefits of thread rolling process to the stress corrosion cracking and fatigue resistance of high strength fasteners

    SciTech Connect

    Kephart, A.R.; Hayden, S.Z.

    1993-05-01

    Stress corrosion cracking (SCC) behavior of cut (machined) vice thread rolled Alloy X-750 and Alloy 625 fasteners in a simulated high temperature primary water environment has been evaluated. SCC testing at 360 and 338C included 157 small and 40 large 60{degree} Vee thread studs. Thread rolled fasteners had improved resistance relative to cut fasteners. Tests of fatigue resistance in air at room temperature and both air and primary water at 315C were conducted on smaller studs with both cut and rolled threads. Results showed rolled threads can have significantly improved fatigue lives over those of cut threads in both air and primary water. Fasteners produced by two different thread rolling methods, in-feed (radial) and through-feed (axial), revealed similar SCC initiation test results. Testing of thread rolled fasteners revealed no significant SCC or fatigue growth of rolling induced thread crest laps typical of the thread rolling process. While fatigue resistance differed between the two rolled thread supplier`s studs, neither of the suppliers studs showed SCC initiation at exposure times beyond that of cut threads with SCC. In contrast to rolling at room temperature, warm rolled (427C) threads showed no improvement over cut threads in terms of fatigue resistance. The observed improved SCC and fatigue performance of rolled threads is postulated to be due to interactive factors, including beneficial residual stresses in critically stressed thread root region, reduction of plastic strains during loading and formation of favorable microstructure.

  8. Benefits of thread rolling process to the stress corrosion cracking and fatigue resistance of high strength fasteners

    NASA Astrophysics Data System (ADS)

    Kephart, A. R.; Hayden, S. Z.

    1993-05-01

    Stress corrosion cracking (SCC) behavior of cut (machined) vice thread rolled Alloy X-750 and Alloy 625 fasteners in a simulated high temperature primary water environment has been evaluated. SCC testing at 360 and 338 C included 157 small and 40 large 60 degree thread studs. Thread rolled fasteners had improved resistance relative to cut fasteners. Tests of fatigue resistance in air at room temperature and both air and primary water at 315 C were conducted on smaller studs with both cut and rolled threads. Results showed rolled threads can have significantly improved fatigue lives over those of cut threads in both air and primary water. Fasteners produced by two different thread rolling methods, in-feed (radial) and through-feed (axial), revealed similar SCC initiation test results. Testing of thread rolled fasteners revealed no significant SCC or fatigue growth of rolling induced thread crest laps typical of the thread rolling process. While fatigue resistance differed between the two rolled thread supplier's studs, neither of the suppliers studs showed SCC initiation at exposure times beyond that of cut threads with SCC. In contrast to rolling at room temperature, warm rolled (427 C) threads showed no improvement over cut threads in terms of fatigue resistance. The observed improved SCC and fatigue performance of rolled threads is postulated to be due to interactive factors, including beneficial residual stresses in critically stressed thread root region, reduction of plastic strains during loading and formation of favorable microstructure.

  9. Dynamic speckle interferometry of high-cycle material fatigue: Theory and some experiments

    NASA Astrophysics Data System (ADS)

    Vladimirov, A. P.

    2016-06-01

    The objective of this paper was theoretical analysis of speckle dynamics in the image plane of a thin transparent object. It was suggested that speckle dynamics develops in simultaneous periodic motion of the sample, micro- and macro-variations of its refraction index and its translational motion. The results of the theory were contrasted with the data obtained in the fatigue tests with transparent object.

  10. Assessment of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720

    NASA Technical Reports Server (NTRS)

    Gabb, Tomothy P.; Bonacuse, Peter J.; Ghosn, Louis J.; Sweeney, Joseph W.; Chatterjee, Amit; Green, Kenneth A.

    2000-01-01

    The fatigue lives of modem powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538 C (1000 F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions. Significant variations in life were observed as functions of the disk processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio R(sub epsilon) = epsilon(sub min)/epsilon(sub max) of 0 were different from those in tests at a strain ratio of -1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.

  11. Fatigue behavior of SiC reinforced Ti/6Al-4V/ at 650 C

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Grimes, H. H.

    1982-01-01

    Axial, low cycle fatigue properties of 25 and 44 fiber vol pct SiC/Ti(6Al-4V) composites, measured at 650 C, were compared with the fatigue properties of unreinforced Ti(6Al-4V) at the same temperature. A prior study of the fatigue behavior of this composite system at room temperature indicated that the SiC fiber reinforcement did not provide the anticipated improvement of fatigue resistance of this alloy. At 650 C, the composite fatigue properties degraded somewhat from those at room temperature. However, these properties degraded more for the unreinforced matrix at 650 C with the result that the composite fatigue strength was two to three times the fatigue strength of the matrix alloy. The reasons for this reversal are discussed in terms of crack initiation at broken fibers and residual matrix stresses.

  12. Fatigue Behavior of TiN and TiCN Coated a Rotor Turbine Steel

    NASA Astrophysics Data System (ADS)

    Suh, Chang Min; Kim, Kyung Ryul; Kang, Yong Goo; Suh, Duck Young; Kim, Chang Keun

    In order to clarify the effect of ceramic coating films on the fatigue strength, and crack initiation of material, fatigue tests were carried out in room air, using the round plain specimens and compact tension specimens of 1Cr-1Mo-0.25V steel coated with TiN and TiCN are ion plating (AIP) process. It was observed that the scatter band of fatigue life at low fatigue strengths was wider than that at high fatigue strengths. The obvious improvement of fatigue life was confirmed in TiCN coated specimens for the region of low fatigue strengths, as compared with uncoated and TiN coated specimens. It was explained that the increase of fatigue life in the TiCN coated material was attributed to the retardation of crack initiation due to the restriction of surface plastic deformation in the substrate with hard coating layer. Also, the fatigue strength at 107 cycles of ceramic coated material was increased about 15 ~ 21% higher than that of base material. The fatigue crack of TiCN coated material was mainly initiated at the inclusions of Al compositions near the substrate under coating film.

  13. Influence of microstructure on high-cycle fatigue of Ti-6Al-4V: Bimodal vs. lamellar structures

    NASA Astrophysics Data System (ADS)

    Nalla, R. K.; Ritchie, R. O.; Boyce, B. L.; Campbell, J. P.; Peters, J. O.

    2002-03-01

    The high-cycle fatigue (HCF) of titanium alloy turbine engine components remains a principal cause of failures in military aircraft engines. A recent initiative sponsored by the United States Air Force has focused on the major drivers for such failures in Ti-6Al-4V, a commonly used turbine blade alloy, specifically for fan and compressor blades. However, as most of this research has been directed toward a single processing/heat-treated condition, the bimodal (solution-treated and overaged (STOA)) microstructure, there have been few studies to examine the role of microstructure. Accordingly, the present work examines how the overall resistance to high-cycle fatigue in Ti-6Al-4V compares between the bimodal microstructure and a coarser lamellar ( β-annealed) microstructure. Several aspects of the HCF problem are examined. These include the question of fatigue thresholds for through-thickness large and short cracks; microstructurally small, semi-elliptical surface cracks; and cracks subjected to pure tensile (mode I) and mixed-mode (mode I+II) loading over a range of load ratios (ratio of minimum to maximum load) from 0.1 to 0.98, together with the role of prior damage due to sub-ballistic impacts (foreign-object damage (FOD)). Although differences are not large, it appears that the coarse lamellar microstructure has improved smooth-bar stress-life (S-N) properties in the HCF regime and superior resistance to fatigue-crack propagation (in pure mode I loading) in the presence of cracks that are large compared to the scale of the microstructure; however, this increased resistance to crack growth compared to the bimodal structure is eliminated at extremely high load ratios. Similarly, under mixed-mode loading, the lamellar microstructure is generally superior. In contrast, in the presence of microstructurally small cracks, there is little difference in the HCF properties of the two microstructures. Similarly, resistance to HCF failure following FOD is comparable in the

  14. Three-dimensional characterization of fatigue-relevant intermetallic particles in high-strength aluminium alloys using synchrotron X-ray nanotomography

    NASA Astrophysics Data System (ADS)

    Nizery, E.; Proudhon, H.; Buffiere, J.-Y.; Cloetens, P.; Morgeneyer, T. F.; Forest, S.

    2015-09-01

    Second-phase particles and small porosities are known to favour fatigue crack initiation in high-strength aluminium alloys 2050-T8 and 7050-T7451. Using high-resolution X-ray tomography (320 nm voxel size), with Paganin reconstruction algorithms, the probability that large clusters of particles contain porosities could be measured for the first time in 3D, as well as precise 3D size distributions. Additional holotomography imaging provided improved spatial resolution (50 nm voxel size), allowing to estimate the probability of finding cracked particles in the as-received material state. The extremely precise 3D shape (including cracks) as well as local chemistry of the particles has been determined. This experiment enabled unprecedented 3D identification of detrimental stress risers relevant for fatigue in as-received aluminium alloys.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    This study discussed the change of residual fracture torque and the fatigue damage process of thin CFRP plates clamped by bolts for axial coupling joint, in which flexible deformation was allowed in the direction of off-set angle by the deflection of the CFRP plates while effective stiffness was obtained in rotational direction. Mechanically laminated 4 layers of the CFRP plates were repeatedly deflected during the rotation of axial coupling, when two axes were jointed with 3 degree of off-set angle, in which number of revolution was 1,800 rpm (30Hz of loading frequency). At first, the fracture morphology of specimen and the residual fracture torque was investigated after 1.0×107 cycles of repeated revolutions. The reduction ratio of spring constant was also determined by simple bending test after the fatigue. The residual fracture torque of the joint was determined on the rotational test machine after 1.0×107 cycles of fatigue. After rotations of cyclic fatigue, fiber breaking and wear of matrix were observed around the fixed parts compressed by washers for setting bolts. The reduction of spring constant of the CFRP plates was caused by the initiation of cyclic fatigue damages around the fixed parts, when the axial coupling joint was rotated with off-set angle. It was found that residual fracture torque of the joint was related with the specific fatigue damage of the CFRP observed in this study.

  16. Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Figert, J.; Beek, J.; Ventura, J.; Martinez, J.; Samonski, F.

    2011-01-01

    This presentation describes results obtained from a research project conducted at the NASA Johnson Space Center (JSC) that was jointly supported by the FAA Technical Center and JSC. The JSC effort was part of a multi-task FAA program involving several U.S. laboratories and initiated for the purpose of developing enhanced analysis tools to assess damage tolerance of rotorcraft and aircraft propeller systems. The research results to be covered in this presentation include a new understanding of the behavior of fatigue crack growth in the threshold region. This behavior is important for structural life analysis of aircraft propeller systems and certain rotorcraft structural components (e.g., the mast). These components are often designed to not allow fatigue crack propagation to exceed an experimentally determined fatigue crack growth threshold value. During the FAA review meetings for the program, disagreements occurred between the researchers regarding the observed fanning (spread between the da/dN curves of constant R) in the threshold region at low stress ratios, R. Some participants believed that the fanning was a result of the ASTM load shedding test method for threshold testing, and thus did not represent the true characteristics of the material. If the fanning portion of the threshold value is deleted or not included in a life analysis, a significant penalty in the calculated life and design of the component would occur. The crack growth threshold behavior was previously studied and reported by several research investigators in the time period: 1970-1980. Those investigators used electron microscopes to view the crack morphology of the fatigue fracture surfaces. Their results showed that just before reaching threshold, the crack morphology often changed from a striated to a faceted or cleavage-like morphology. This change was reported to have been caused by particular dislocation properties of the material. Based on the results of these early investigations, a

  17. Fatigue behavior and recommended design rules for an automotive composite

    SciTech Connect

    Corum, J.M.; Battiste, R.L.; Ruggles, M.B.

    1998-11-01

    Fatigue curves (stress vs cycles to failure) were generated under a variety of conditions (temperatures, fluid environments, mean stresses, block loadings) for a candidate automotive structural composite. The results were used to (1) develop observations regarding basic fatigue behavioral characteristics and (2) establish fatigue design rules. The composite was a structural reaction injection-molded polyurethane reinforced with continuous strand, swirl-mat E-glass fibers. Tensile fatigue tests on specimens from a single plaque at {minus}40 F, room temperature, and 250 F provided the basic behavioral characteristics. It was found that when stress was normalized by the at-temperature ultimate tensile strength, the fatigue curves at the three temperatures collapsed into a single master curve. An assessment of the individual stress-strain loops throughout each test showed a progressive loss in stiffness and an increase in permanent strain, both of which are indicative of increasing damage. Fatigue tests on specimens from several plaques were used to develop a design fatigue curve, which was established by using a reduction factor of 20 on average cycles to failure. This factor assures that the stiffness loss during the design life is no greater than 10 percent. Fatigue reduction factors were established to account for various fluids. Reversed stress fatigue tests allowed a mean stress rule to be validated, and block loading tests were used to demonstrate the adequacy of Miner`s rule for cumulative fatigue damage.

  18. Effect of Al-Si Pack Cementation Diffusion Coating on High-Temperature Low-Cycle Fatigue Behavior of Inconel 713LC

    NASA Astrophysics Data System (ADS)

    Mansuri, Mohammadreza; Hadavi, Seyed Mohammad Mehdi; Zare, Esmail

    2016-01-01

    In this research, an Al-Si protective coating was applied on the surface of an IN713LC specimen using pack cementation method. Surface-treated and untreated specimens were exposed to low-cycle fatigue by tension-tension loading under total strain control at 1173 K (900 °C) in air. Based on the obtained results, the hardening/softening, cyclic stress-strain, and fatigue life curves were plotted and analyzed. The results showed that both the single-stage and two-stage coatings improved the fatigue life of the substrate. However, owing to more silicon content of single-stage coating compared to that of two-stage coating, the effect of single-stage coating was superior. The stress response of the treated material was lower compared with the untreated one. Observations of the specimen section and fracture surface examinations were used to analyze fatigue behavior of both coated and uncoated materials.

  19. Evaluation of the Effect of Dynamic Sodium on the Low Cycle Fatigue Properties of 316L(N) Stainless Steel Base and Weld Joints

    NASA Astrophysics Data System (ADS)

    Ganesan, V.; Kannan, R.; Mariappan, K.; Sukumaran, G.; Sandhya, R.; Rao, K. Bhanu Sankara

    2012-06-01

    Low cycle fatigue (LCF) tests on 316L(N) austenitic stainless steel base and weld joints were at 823 K and 873 K at a constant strain rate of 3 × 10 -3 s -1 with strain ranges varying from {±}0.4% to {±}1.0% in a servo-hydraulic fatigue test system under flowing sodium environment. The cyclic stress response exhibited a similar trend as that in air comprising of an initial rapid hardening, followed by a slight softening stage before saturation. The fatigue lives are significantly improved in sodium environment when compared to identical testing conditions in air environment. The lack of oxidation in sodium environment is attributed to the delayed crack initiation, reduced crack propagation rate and consequent increase in fatigue life. Comparison of the data evaluated in sodium with RCC-MR design code, derived on the basis of data obtained from air shows that the design based on air tests is conservative.

  20. Statistical summaries of fatigue data for design purposes

    NASA Technical Reports Server (NTRS)

    Wirsching, P. H.

    1983-01-01

    Two methods are discussed for constructing a design curve on the safe side of fatigue data. Both the tolerance interval and equivalent prediction interval (EPI) concepts provide such a curve while accounting for both the distribution of the estimators in small samples and the data scatter. The EPI is also useful as a mechanism for providing necessary statistics on S-N data for a full reliability analysis which includes uncertainty in all fatigue design factors. Examples of statistical analyses of the general strain life relationship are presented. The tolerance limit and EPI techniques for defining a design curve are demonstrated. Examples usng WASPALOY B and RQC-100 data demonstrate that a reliability model could be constructed by considering the fatigue strength and fatigue ductility coefficients as two independent random variables. A technique given for establishing the fatigue strength for high cycle lives relies on an extrapolation technique and also accounts for "runners." A reliability model or design value can be specified.

  1. Bithermal low-cycle fatigue behavior of a NiCoCrAlY-coated single crystal superalloy

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V.; Halford, G. R.

    1987-01-01

    Specimens of a single crystal superalloy, PWA 1480, both bare and coated with a NiCoCrAlY alloy, PWA 276, were tested in low-cycle fatigue at 650 and 1050 C, and in bithermal thermomechanical fatigue tests. In the two bithermal test types, tensile strain was imposed at one of the two temperatures and reversed in compression at the other. In the high-strain regime, lives for both bithermal test types approached that for the 650 C isothermal test on an inelastic strain basis, all being controlled by the low ductility of the superalloy at 650 C. In the low-strain regime, coating cracking reduced life in the 650 C isothermal test. The bithermal test imposing tension at 650 C, termed out-of-phase, also produced rapid surface cracking, but in both coated and bare specimens. Increased crack growth rates also occurred for the out-of-phase test. Increased lives in vacuum suggested that there is a large environmental contribution to damage in the out-of-phase test due to the 1050 C exposure followed by tensile straining at the low temperature.

  2. Bithermal Low-Cycle Fatigue Behavior of a NiCoCrAlY-Coated Single Crystal Superalloy

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V.; Halford, G. R.

    1987-01-01

    Specimens of a single crystal superalloy, PWA 1480, both bare and coated with a NiCoCrAlY alloy, PWA 276, were tested in low-cycle fatigue at 650 and 1050 C, and in bithermal thermomechanical fatigue tests. In the two bithermal test types, tensile strain was imposed at one of the two temperatures and reversed in compression at the other. In the high-strain regime, lives for both bithermal test types approached that for the 650 C isothermal test on an inelastic strain basis, all being controlled by the low ductility of the superalloy at 650 C. In the low-strain regime, coating cracking reduced life in the 650 C isothermal test. The bithermal test imposing tension at 650 C, termed out-of-phase, also produced rapid surface cracking, but in both coated and bare specimens. Increased crack growth rates also occurred for the out-of-phase test. Increased lives in vacuum suggested that there is a large environmental contribution to damage in the out-of-phase test due to the 1050 C exposure followed by tensile straining at the low temperature.

  3. Improving High-Temperature Tensile and Low-Cycle Fatigue Behavior of Al-Si-Cu-Mg Alloys Through Micro-additions of Ti, V, and Zr

    NASA Astrophysics Data System (ADS)

    Shaha, S. K.; Czerwinski, F.; Kasprzak, W.; Friedman, J.; Chen, D. L.

    2015-07-01

    High-temperature tensile and low-cycle fatigue tests were performed to assess the influence of micro-additions of Ti, V, and Zr on the improvement of the Al-7Si-1Cu-0.5Mg (wt pct) alloy in the as-cast condition. Addition of transition metals led to modification of microstructure where in addition to conventional phases present in the Al-7Si-1Cu-0.5Mg base, new thermally stable micro-sized Zr-Ti-V-rich phases Al21.4Si4.1Ti3.5VZr3.9, Al6.7Si1.2TiZr1.8, Al2.8Si3.8V1.6Zr, and Al5.1Si35.4Ti1.6Zr5.7Fe were formed. The tensile tests showed that with increasing test temperature from 298 K to 673 K (25 °C to 400 °C), the yield stress and tensile strength of the present studied alloy decreased from 161 to 84 MPa and from 261 to 102 MPa, respectively. Also, the studied alloy exhibited 18, 12, and 5 pct higher tensile strength than the alloy A356, 354 and existing Al-Si-Cu-Mg alloy modified with additions of Zr, Ti, and Ni, respectively. The fatigue life of the studied alloy was substantially longer than those of the reference alloys A356 and the same Al-7Si-1Cu-0.5Mg base with minor additions of V, Zr, and Ti in the T6 condition. Fractographic analysis after tensile tests revealed that at the lower temperature up to 473 K (200 °C), the cleavage-type brittle fracture for the precipitates and ductile fracture for the matrix were dominant while at higher temperature fully ductile-type fracture with debonding and pull-out of cracked particles was identified. It is believed that the intermetallic precipitates containing Zr, Ti, and V improve the alloy performance at increased temperatures.

  4. High Cycle Fatigue Properties Of Electron Beam Melted TI-6AL-4V Samples Without And With Integrated Defects ("Effects Of Defects")

    NASA Astrophysics Data System (ADS)

    Brandl, Erhard; Greitemeier, Daniel; Maier, Hans Jurgen; Syassen, Freerk

    2012-07-01

    The understanding of additive manufactured material properties is still at an early stage and mostly not profound. Nowadays, there is only little experience in predicting the effect of defects (e.g. porosity, unmelted spots, insufficient bonding between the layers) on the fatigue behaviour. In this paper, some of these questions are adressed. An electron beam melting process is used to manufacture Ti-6Al-4V high cycle fatigue samples without and with intentionally integrated defects inside of the samples. The samples were annealed or hot isostatically pressed. The defects were analysed by non- destructive methods before and by light/electron microscopy after the tests. In order to predict the high cycle fatigue properties, the crack propagation properties of the material (da/dN - ΔK curve) were tested and AFGROW simulation was used.

  5. Estimation of high temperature low cycle fatigue on the basis of inelastic strain and strainrate

    NASA Technical Reports Server (NTRS)

    Berkovits, A.

    1986-01-01

    Fatigue life at elevated temperature can be predicted by introducing parametric values obtained from monotonic constitutive behavior into the Universal-Slopes Equation. For directionally solidified MAR-M200+HF at 975 C, these parameters are the maximum stress achievable under entirely plastic (time-independent) and purely creep (time-dependent) conditions and the corresponding inelastic strains, as well as the elastic modulus. For materials which exhibit plasticity/creep interaction, two more pairs of monotonic parameters must be evaluated for fatigue life prediction. This life-prediction method based on the Universal-Slopes Equation, resulted from a constitutive model characterizing monotonic and cyclic data as inelastic strainrate as a function of inelastic strain. Characterizing monotonic data is this way, permitted distinction between different material responses such as strain-hardening, strain-softening, and dynamic recovery effects. Understanding and defining the region of influence of each of these effects facilitated formulation of the constitutive model in relation to the mechanical and microstructural processes occurring in the material under cyclic loading.

  6. High temperature fatigue behavior of Haynes 188

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.; Saltsman, James F.; Kalluri, Sreeramesh

    1988-01-01

    The high temperature, creep-fatigue behavior of Haynes 188 was investigated as an element in a broader thermomechanical fatigue life prediction model development program at the NASA-Lewis. The models are still in the development stage, but the data that were generated possess intrinsic value on their own. Results generated to date is reported. Data were generated to characterize isothermal low cycle fatigue resistance at temperatures of 316, 704, and 927 C with cyclic failure lives ranging from 10 to more than 20,000. These results follow trends that would be predicted from a knowledge of tensile properties, i.e., as the tensile ductility varies with temperature, so varies the cyclic inelastic straining capacity. Likewise, as the tensile strength decreases, so does the high cyclic fatigue resistance. A few two-minute hold-time cycles at peak compressive strain were included in tests at 760 C. These results were obtained in support of a redesign effort for the Orbital Maneuverable System engine. No detrimental effects on cyclic life were noted despite the added exposure time for creep and oxidation. Finally, a series of simulated thermal fatigue tests, referred to as bithermal fatigue tests, were conducted using 316 C as the minimum and 760 C as the maximum temperature. Only out-of-phase bithermal tests were conducted to date. These test results are intended for use as input to a more general thermomechanical fatigue life prediction model based on the concepts of the total strain version of Strainrange Partitioning.

  7. What the diurnal cycle of precipitation tells us about land-atmosphere coupling strength

    NASA Astrophysics Data System (ADS)

    Ferguson, Craig; Song, Hyojong; Roundy, Joshua

    2015-04-01

    The key attributes of a coupled forecast model are the coupling strengths between the land-atmosphere and ocean-atmosphere schemes. If a model cannot skillfully capture the diurnal cycle of clouds and precipitation, then it likely cannot be expected to yield accurate long-term climate projections. The seasonal drought forecast skill shortfalls of the U.S. NCEP Coupled Forecast System Version 2 (CFSv2) have been directly linked to its unrealistically strong land-atmosphere coupling strength. Most models can be similarly categorized, which is to say, sensitivity to the land physics (i.e., soil moisture constraints on evapotranspiration) is too strong. In nature, the land signal: noise ratio appears to be at a much lower value. Diagnosing land-atmosphere coupling strength requires at a minimum: surface soil moisture state, surface turbulent heat fluxes, and atmospheric moisture and instability. Full-on diagnosis would entail hacking into the code and inserting a number of tracers. This study addresses the question: What if, given the soil wetness anomaly, model biases in coupling sign and/or strength could be diagnosed from phase shifts in the diurnal precipitation frequency cycle? We use 34-years of output from the North American Regional Reanalysis (NARR) and North American Land Data Assimilation System Phase 2 (NLDAS-2) to investigate the variation in diurnal precipitation frequency cycle between so-called "wet-advantage" and "dry-advantage" coupling regimes over the U.S. southern Great Plains. Wet-advantage occurs when the atmospheric state is closer to the wet adiabatic rate and convection is triggered by a strong increase in the moist static energy from the surface. In contrast, dry-advantage occurs when the atmosphere is drier and the temperature profile is close to the dry adiabatic lapse rate, which favors convection over areas of large boundary layer growth due to high sensible heat fluxes at the surface. We find that there is a significant difference in the

  8. Adaptations to isolated shoulder fatigue during simulated repetitive work. Part I: Fatigue.

    PubMed

    Tse, Calvin T F; McDonald, Alison C; Keir, Peter J

    2016-08-01

    Upper extremity muscle fatigue is challenging to identify during industrial tasks and places changing demands on the shoulder complex that are not fully understood. The purpose of this investigation was to examine adaptation strategies in response to isolated anterior deltoid muscle fatigue while performing simulated repetitive work. Participants completed two blocks of simulated repetitive work separated by an anterior deltoid fatigue protocol; the first block had 20 work cycles and the post-fatigue block had 60 cycles. Each work cycle was 60s in duration and included 4 tasks: handle pull, cap rotation, drill press and handle push. Surface EMG of 14 muscles and upper body kinematics were recorded. Immediately following fatigue, glenohumeral flexion strength was reduced, rating of perceived exertion scores increased and signs of muscle fatigue (increased EMG amplitude, decreased EMG frequency) were present in anterior and posterior deltoids, latissimus dorsi and serratus anterior. Along with other kinematic and muscle activity changes, scapular reorientation occurred in all of the simulated tasks and generally served to increase the width of the subacromial space. These findings suggest that immediately following fatigue people adapt by repositioning joints to maintain task performance and may also prioritize maintaining subacromial space width. PMID:26208429

  9. Plastic Behavior of a Nickel-Based Alloy under Monotonic-Tension and Low-Cycle-Fatigue Loading

    SciTech Connect

    Huang, E-Wen; Barabash, Rozaliya; Wang, Yandong; Clausen, Bjorn; Li, Li; Liaw, Peter K; Ice, Gene E; Yang, Dr Ren; Choo, Hahn; Pike, Lee M; Klarstrom, Dwaine L

    2008-01-01

    The plasticity behavior of the annealed HASTELLOY C-22HSTM alloy, a face-centered cubic (FCC), nickel-based superalloy, was examined by the in-situ neutron-diffraction experiments at room temperature. Monotonic-tension and low-cycle-fatigue experiments were conducted to observe the plastic behavior of the alloy. The tension straining and cyclic-loading deformation were studied as a function of the stress. The plastic behaviors during the deformation are discussed in the light of the relationship between the stress and dislocation-density evolutions. The calculated dislocation-density evolutions within the alloys reflect the strain hardening and cyclic hardening/softening. Experimental lattice strains are compared to verify the hardening mechanism at the selected stress levels for tension and cyclic loadings. Combining with the calculations of the dislocation densities, the neutron-diffraction experiments give an evidence of the strain and cyclic hardening of the alloy.

  10. Mechanisms of deformation and fracture in high temperature low cycle fatigue of Rene 80 and IN 100

    NASA Technical Reports Server (NTRS)

    Romanoski, G. R., Jr.

    1982-01-01

    Specimens tested for the AGARD strain range partitioning program were investigated. Rene 80 and IN 100 were tested in air and in vacuum; at 871 C, 925 C, and 1000 C; and in the coated and uncoated condition. The specimens exhibited a multiplicity of high-temperature low-cycle fatigue damage. Observations of the various forms of damage were consistent with material and testing conditions and were generally in agreement with previous studies. In every case observations support a contention that failure occurs at a particular combination of crack length and maximum stress. A failure criterion which is applicable in the regime of testing studied is presented. The predictive capabilities of this criterion are straight forward.

  11. Effects of geometry and materials on low cycle fatigue life of turbine blades in LOX/hydrogen rocket engines

    NASA Technical Reports Server (NTRS)

    Ryan, R. M.; Gross, L. A.

    1986-01-01

    This paper presents the results of an advanced turbine blade test program aimed at improving turbine blade low cycle fatigue (LCF) life. A total of 21 blades were tested in a blade thermal tester. The blades were made of MAR-M-246(Hf)DS and PWA-1480SC in six different geometries. The test results show that the PWA-1480SC material improved life by a factor of 1.7 to 3.0 over the current MAR-M-246(Hf)DS. The geometry changes yielded life improvements as high as 20 times the baseline blade made of PWA-1480SC and 34 times the baseline MAR-M-246DS blade.

  12. Current activities in standardization of high-temperature, low-cycle-fatigue testing techniques in the United States

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Ellis, J. Rodney; Swindeman, Robert W.

    1990-01-01

    The American Society for Testing and Materials (ASTM) standard E606-80 is the most often used recommended testing practice for low-cycle-fatigue (LCF) testing in the United States. The standard was first adopted in 1977 for LCF testing at room temperature and was modified in 1980 to include high-temperature testing practices. Current activity within ASTM is aimed at extending the E606-80 recommended practices to LCF under thermomechanical conditions, LCF in high-pressure hydrogen, and LCF in metal-matrix composite materials. Interlaboratory testing programs conducted to generate a technical base for modifying E606-80 for the aforementioned LCF test types are discussed.

  13. Fatigue and fracture behavior of U-6 wt. pct. Nb

    SciTech Connect

    Strum, M.J.; Freeman, D.C.; Elmer, J.W.

    1993-05-21

    The fatigue and fracture properties of U6Nb were measured to provide the materials property data needed for structural designs in material processed by solution quenching and aging 200 C/2h. Limited testing was also performed on as-quenched U6Nb. The authors have extended the database on fatigue properties in U6Nb to include both crack initiation data and crack propagation data. The static load carrying capabilities have been characterized through fracture toughness and tensile property measurements. Using a rotating beam fatigue machine, a fatigue strength of 248 MPa was measured at 10{sup 8} cycles for smooth bars at zero mean load. As is typical of nonferrous alloys, U6Nb does not exhibit a fatigue endurance limit. Reductions in fatigue strength for notched bars and for mean loads of 276 MPa and 483 MPa (70 ksi) were also determined. The predominant sites for fatigue crack initiation were identified as niobium carbide and uranium oxide inclusion clusters and the distribution of these inclusions are presented. Fatigue crack propagation rates were measured in the near-threshold regime using compact tension specimens. The fatigue threshold for crack growth rates below 10{sup {minus}7} mm/cycle were measured at both R = 0.1, for which a fatigue threshold of 3.2 MPa{radical}m was measured, and for constant Kmax cycles with Kmax values of 14.6 MPa{radical}m and 30.5 MPa{radical}m, for which the fatigue threshold was reduced to 0.9 MPa{radical} and 0.6 MPa{radical}m, respectively.

  14. Changes in Muscle Strength in U19 Soccer Players During an Annual Training Cycle

    PubMed Central

    Lehnert, Michal; Xaverová, Zuzana; De Ste Croix, Mark

    2014-01-01

    The aim of the study was to investigate the seasonal variation in isokinetic strength of the knee flexors and extensors, and conventional (H/QCONV) and functional (H/QFUNC) hamstring to quadriceps strength ratios in highly trained adolescent soccer players. The players (n=11; age 17.8±0.3) were measured at the end of the competitive season (autumn), at the beginning and the end of pre-season (winter) and during the sixth week of a new competitive season. Isokinetic peak torque (concentric and eccentric) was measured at 60°·s-1 in a sitting position with the hip flexed at 100°. The testing range of motion was set from 10 – 90° of knee flexion. The players performed a set of five maximum repetitions for both the dominant and non-dominant leg. Statistically significant differences (p<0.001) between the four seasonal measurements were noted for peak torque of the dominant leg knee flexors in concentric muscle action only. A post hoc analysis revealed a statistically significant increase in peak torque from the 1st to the 4th measurement (p<0.001; d=0.692) and from the 2nd to the 4th (p<0.01; d=0.564). The differences in the changes of peak torque of the knee flexors and extensors depending on type of muscle action and tendencies found in the H/Q ratios throughout the annual training cycle indicate that strength assessment of the knee flexors and extensors and their balance throughout the annual training cycle could be beneficial for elite male adolescent soccer players both in terms of performance and risk of injury. PMID:25414751

  15. Effect of formoterol, a long-acting β2-adrenergic agonist, on muscle strength and power output, metabolism, and fatigue during maximal sprinting in men.

    PubMed

    Kalsen, Anders; Hostrup, Morten; Backer, Vibeke; Bangsbo, Jens

    2016-06-01

    The aim was to investigate the effect of the long-acting β2-adrenergic agonist formoterol on muscle strength and power output, muscle metabolism, and phosphorylation of CaMKII Thr(287) and FXYD1 during maximal sprinting. In a double-blind crossover study, 13 males [V̇o2 max: 45.0 ± 0.2 (means ± SE) ml·min(-1)·kg(-1)] performed a 30-s cycle ergometer sprint after inhalation of either 54 μg of formoterol (FOR) or placebo (PLA). Before and after the sprint, muscle biopsies were collected from vastus lateralis and maximal voluntary contraction (MVC), and contractile properties of quadriceps were measured. Oxygen uptake was measured during the sprint. During the sprint, peak power, mean power, and end power were 4.6 ± 0.8, 3.9 ± 1.1, and 9.5 ± 3.2% higher (P < 0.05) in FOR than in PLA, respectively. Net rates of glycogenolysis and glycolysis were 45.7 ± 21.0 and 28.5 ± 13.4% higher (P < 0.05) in FOR than in PLA, respectively, and the decrease in ATP content was lower (P < 0.05) in FOR than in PLA (3.7 ± 1.5 vs. 8.0 ± 1.6 mmol/kg dry weight). There was no difference in breakdown of phosphocreatine and oxygen uptake between treatments. Before and after the sprint, MVC and peak twitch force were higher (P < 0.05) in FOR than in PLA. No differences were observed in phosphorylation of CaMKII Thr(287) and FXYD1 between treatments before the sprint, whereas phosphorylation of CaMKII Thr(287) and FXYD1 was greater (P < 0.05) in FOR than in PLA after the sprint. In conclusion, formoterol-induced enhancement in power output during maximal sprinting is associated with increased rates of glycogenolysis and glycolysis that may counteract development of fatigue. PMID:27147617

  16. Rieger-type Periodicity during Solar Cycles 14–24: Estimation of Dynamo Magnetic Field Strength in the Solar Interior

    NASA Astrophysics Data System (ADS)

    Gurgenashvili, Eka; Zaqarashvili, Teimuraz V.; Kukhianidze, Vasil; Oliver, Ramon; Ballester, Jose Luis; Ramishvili, Giorgi; Shergelashvili, Bidzina; Hanslmeier, Arnold; Poedts, Stefaan

    2016-07-01

    Solar activity undergoes a variation over timescales of several months known as Rieger-type periodicity, which usually occurs near maxima of sunspot cycles. An early analysis showed that the periodicity appears only in some cycles and is absent in other cycles. But the appearance/absence during different cycles has not been explained. We performed a wavelet analysis of sunspot data from the Greenwich Royal Observatory and the Royal Observatory of Belgium during cycles 14–24. We found that the Rieger-type periods occur in all cycles, but they are cycle dependent: shorter periods occur during stronger cycles. Our analysis revealed a periodicity of 185–195 days during the weak cycles 14–15 and 24 and a periodicity of 155–165 days during the stronger cycles 16–23. We derived the dispersion relation of the spherical harmonics of the magnetic Rossby waves in the presence of differential rotation and a toroidal magnetic field in the dynamo layer near the base of the convection zone. This showed that the harmonics of fast Rossby waves with m = 1 and n = 4, where m (n) indicates the toroidal (poloidal) wavenumbers, perfectly fit with the observed periodicity. The variation of the toroidal field strength from weaker to stronger cycles may lead to the different periods found in those cycles, which explains the observed enigmatic feature of the Rieger-type periodicity. Finally, we used the observed periodicity to estimate the dynamo field strength during cycles 14–24. Our estimations suggest a field strength of ∼40 kG for the stronger cycles and ∼20 kG for the weaker cycles.

  17. High-Temperature, Low-Cycle Fatigue of Copper-Base Alloys for Rocket Nozzles. Part 1: Data Summary for Materials Tested in Prior Programs

    NASA Technical Reports Server (NTRS)

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1975-01-01

    A more detailed analysis of the results obtained in 188 previously reported low-cycle fatigue tests of various candidate materials for regeneratively-cooled, reusable rocket nozzle liners was reported. Plots of load range versus cycles were reported for each test along with a stress-strain hysteresis loop near half-life. In addition, a summary table was provided to compare N5 (cycles to a five percent load range drop) and Nf (cycles to complete specimen separation) values for each test.

  18. Microstructure Evolution Associated with a Superior Low-Cycle Fatigue Resistance of the Fe-30Mn-4Si-2Al Alloy

    NASA Astrophysics Data System (ADS)

    Nikulin, Ilya; Sawaguchi, Takahiro; Ogawa, Kazuyuki; Tsuzaki, Kaneaki

    2015-11-01

    The microstructure evolution responsible for the superior low-cycle fatigue (LCF) resistance ( N f > 8000 cycles at a total strain range of 2 pct) was studied in the Fe-30Mn-4Si-2Al alloy susceptible to strain-induced martensitic transformation. To investigate the microstructure effect on the LCF behaviors of the alloy, a series of interrupted fatigue tests at total strain range of 2 pct were carried out. A characteristic softening stage followed by the secondary hardening was observed during cyclic loading of the studied alloy. This softening is associated with the strain localization caused by persistent Lüders bands formation and the transformation of Lüders bands into strain-induced ɛ-martensite is found to have a key role in the delayed fatigue fracture of the alloy being studied. Therefore, the continuous transformation process involving Lüders bands and ɛ-martensite formation associated with intermediate stacking fault energy (SFE) ( γ SF of 14 mJ/m2) is necessary to prevent the rearrangement of dislocations into walls/channels and substructures inherent to high-SFE ( γ SF higher 20 mJ/m2) alloys capable to accelerated fatigue damage. However, sluggish martensite transformation kinetics is necessary to delay the formation of the ɛ-martensite associated with the development and propagation of fatigue crack in alloys with very low SFE.

  19. Effect of initiation chemistry on the fracture toughness, fatigue strength, and residual monomer content of a novel high-viscosity, two-solution acrylic bone cement.

    PubMed

    Hasenwinkel, Julie M; Lautenschlager, Eugene P; Wixson, Richard L; Gilbert, Jeremy L

    2002-03-01

    Porous-free, two-solution bone cements have been developed in our laboratory as an alternative to commercial powder/liquid formulations. Each pair of solutions consist of poly(methyl methacrylate) (PMMA) powder dissolved in methyl methacrylate (MMA) monomer, with benzoyl peroxide (BPO) added to one solution as the initiator and N,N-dimethyl-p-toluidine (DMPT) added to the other as the activator. When mixed, the solutions polymerize via a free radical reaction, which is governed by the concentrations of initiator and activator and their molar stoichiometry. Previous work by the authors has demonstrated that these two-solution cement compositions are comparable to Simplex P bone cement in polymerization exotherm, setting time, and flexural mechanical properties. This study was designed to evaluate the effect of BPO and DMPT concentrations, along with their molar ratio, on the fracture toughness, fatigue strength, and residual monomer content of the experimental compositions. The results showed that fracture toughness and fatigue strength for the solution cements were comparable to Simplex P and were not significantly affected by the BPO concentration or the BPO:DMPT molar ratio; however, the highest DMPT concentration yielded significantly lower values for both variables. Residual monomer content was significantly affected by both the individual concentrations of BPO and DMPT and their molar ratios. The two-solution cements had significantly higher residual monomer contents versus Simplex P; however, this can be attributed to their higher initial monomer concentration rather than a lower degree of conversion. PMID:11774298

  20. Arm-cycling sprints induce neuromuscular fatigue of the elbow flexors and alter corticospinal excitability of the biceps brachii.

    PubMed

    Pearcey, Gregory E P; Bradbury-Squires, David J; Monks, Michael; Philpott, Devin; Power, Kevin E; Button, Duane C

    2016-02-01

    We examined the effects of arm-cycling sprints on maximal voluntary elbow flexion and corticospinal excitability of the biceps brachii. Recreationally trained athletes performed ten 10-s arm-cycling sprints interspersed with 150 s of rest in 2 separate experiments. In experiment A (n = 12), maximal voluntary contraction (MVC) force of the elbow flexors was measured at pre-sprint 1, post-sprint 5, and post-sprint 10. Participants received electrical motor point stimulation during and following the elbow flexor MVCs to estimate voluntary activation (VA). In experiment B (n = 7 participants from experiment A), supraspinal and spinal excitability of the biceps brachii were measured via transcranial magnetic and transmastoid electrical stimulation that produced motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs), respectively, during a 5% isometric MVC at pre-sprint 1, post-sprint 1, post-sprint 5, and post-sprint 10. In experiment A, mean power output, MVC force, potentiated twitch force, and VA decreased 13.1% (p < 0.001), 8.7% (p = 0.036), 27.6% (p = 0.003), and 5.6% (p = 0.037), respectively, from pre-sprint 1 to post-sprint 10. In experiment B, (i) MEPs decreased 42.1% (p = 0.002) from pre-sprint 1 to post-sprint 5 and increased 40.1% (p = 0.038) from post-sprint 5 to post-sprint 10 and (ii) CMEPs increased 28.5% (p = 0.045) from post-sprint 1 to post-sprint 10. Overall, arm-cycling sprints caused neuromuscular fatigue of the elbow flexors, which corresponded with decreased supraspinal and increased spinal excitability of the biceps brachii. The different post-sprint effects on supraspinal and spinal excitability may illustrate an inhibitory effect on supraspinal drive that reduces motor output and, therefore, decreases arm-cycling sprint performance. PMID:26799694

  1. Experimental study of cyclic creep and high-cycle fatigue of welded joints of St3 steel by the DIC technique

    SciTech Connect

    Kibitkin, Vladimir V. Solodushkin, Andrey I. Pleshanov, Vasily S.

    2015-10-27

    In the paper the mechanisms of plastic deformation and fracture of welded joints of steel St3 were investigated at high-cycle fatigue and cyclic creep by the digital image correlation (DIC) technique. The evolution of strain rate is studied for the following regions: base metal, HAZ, and fusion zone. This strain rate evolution can be considered as a mechanical response of material. Three stages of deformation evolution are shown: deformation hardening (I), fatigue crack initiation (II), and the last stage is related to main crack (III). Two criteria are offered to evaluate the current mechanical state of welded joints.

  2. Experimental study of cyclic creep and high-cycle fatigue of welded joints of St3 steel by the DIC technique

    NASA Astrophysics Data System (ADS)

    Kibitkin, Vladimir V.; Solodushkin, Andrey I.; Pleshanov, Vasily S.

    2015-10-01

    In the paper the mechanisms of plastic deformation and fracture of welded joints of steel St3 were investigated at high-cycle fatigue and cyclic creep by the digital image correlation (DIC) technique. The evolution of strain rate is studied for the following regions: base metal, HAZ, and fusion zone. This strain rate evolution can be considered as a mechanical response of material. Three stages of deformation evolution are shown: deformation hardening (I), fatigue crack initiation (II), and the last stage is related to main crack (III). Two criteria are offered to evaluate the current mechanical state of welded joints.

  3. Use of ultrasonic back-reflection intensity for predicting the onset of crack growth due to low-cycle fatigue in stainless steel under block loading.

    PubMed

    Islam, Md Nurul; Arai, Yoshio; Araki, Wakako

    2015-02-01

    The present study proposes the use of ultrasonic back-reflected waves for evaluating low cycle fatigue crack growth from persistent slip bands (PSBs) of stainless steel under block loading. Fatigue under high-low block loading changes the back-reflected intensity of the ultrasonic wave that emanates from the surface. Measuring the change in ultrasonic intensity can predict the start of crack growth with reasonable accuracy. The present study also proposes a modified constant cumulative plastic strain method and a PSB damage evolution model to predict the onset of crack growth under block loads. PMID:25287974

  4. Longitudinally polarized single-cycle terahertz pulses generated with high electric field strengths

    NASA Astrophysics Data System (ADS)

    Cliffe, M. J.; Graham, D. M.; Jamison, S. P.

    2016-05-01

    We demonstrate the generation of single-cycle longitudinally polarized terahertz pulses with field amplitudes in excess of 11 kV/cm using the interferometric recombination of two linearly polarized terahertz beams. High field strength transversely polarized pulses were generated by optical rectification in a matched pair of magnesium-oxide doped stoichiometric lithium niobate (MgO:SLN) crystals with a reversal in the χ333 ( 2 ) orientation. The discontinuity in χ333 ( 2 ) produces a polarity flip in the transverse field; the longitudinal field produced as a consequence of the transverse field discontinuity was measured in the far-field. Both the spatial and temporal profiles of the measured longitudinally polarized terahertz radiation were consistent with the propagation of the transverse discontinuity.

  5. A comparison of the effects of fatigue on subjective and objective assessment of situation awareness in cycling.

    PubMed

    Knez, Wade L; Ham, Daniel J

    2006-01-01

    Maximal effort on a 30 km Time Trial (TT30) was examined to assess whether it would elicit changes in objective and subjective tests of the participants' perception of the environment and their ability to anticipate future occurrences (situation awareness; SA) and to determine the effect of post-exercise recovery on SA. Nine experienced (5.22 ± 2.77 years) road cyclists had their objective and subjective levels of SA assessed prior to and at the completion of two TT30. The participants' results were compared to measurements of maximal oxygen uptake (VO2max), peak power output (PPO), age and years of competitive cycle racing experience. Fatigue resulting from maximal effort on a TT30 produced significant changes in both the objective and subjective test of SA. Effect sizes of 0.93 and 0.99 indicated that the first and second TT30 were likely or almost certain to have a beneficial effect on the objective assessment of SA. However, the effect sizes of 0.97 and 0.95 relating to the subjective assessment of cognitive performance on the first and second TT30 showed that it was very likely the participants' had an increased difficulty in maintaining SA. A recovery period of up to three minutes post TT30 had no effect on SA. Changes in SA had no relationship with measurements of VO2max, peak power output (PPO), age and years of competitive cycle racing experience. The findings suggest that within a laboratory environment, participants consistently underestimate their ability to make accurate assessments of their cycling environment compared to objective measures of their SA. Key PointsExhaustive exercise from a TT30 produces significant changes in both subjective and objective SA.This study indicates that fatigued participants underestimate their ability to maintain SA.A time period of three minutes is not enough to observe a recovery effect on subjective or objective SA.Both the objective and subjective tests proved to be reliable assessments of SA. PMID:24198685

  6. Low-cycle fatigue of Type 347 stainless steel and Hastelloy alloy X in hydrogen gas and in air at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Jaske, C. E.; Rice, R. C.; Buchheit, R. D.; Roach, D. B.; Porfilio, T. L.

    1976-01-01

    An investigation was conducted to assess the low-cycle fatigue resistance of two alloys, Type 347 stainless steel and Hastelloy Alloy X, that were under consideration for use in nuclear-powered rocket vehicles. Constant-amplitude, strain-controlled fatigue tests were conducted under compressive strain cycling at a constant strain rate of 0.001/sec and at total axial strain ranges of 1.5, 3.0, and 5.0 %, in both laboratory-air and low-pressure hydrogen-gas environments at temperatures from 538 to 871 C. Specimens were obtained from three heats of Type 347 stainless steel bar and two heats of Hastelloy Alloy X. The tensile properties of each heat were determined at 21, 538, 649, and 760 C. The continuous cycling fatigue resistance was determined for each heat at temperatures of 538, 760, and 871 C. The Type 347 stainless steel exhibited equal or superior fatigue resistance to the Hastelloy Alloy X at all conditions of this study.

  7. Management of Total Pressure Recovery, Distortion and High Cycle Fatigue in Compact Air Vehicle Inlets

    NASA Technical Reports Server (NTRS)

    Anderson, Bernhard H.; Baust, Henry D.; Agrell, Johan

    2002-01-01

    It is the purpose of this study to demonstrate the viability and economy of Response Surface Methods (RSM) and Robustness Design Concepts (RDC) to arrive at micro-secondary flow control installation designs that maintain optimal inlet performance over a range of the mission variables. These statistical design concepts were used to investigate the robustness properties of 'low unit strength' micro-effector installations. 'Low unit strength' micro-effectors are micro-vanes set at very low angles-of-incidence with very long chord lengths. They were designed to influence the near wall inlet flow over an extended streamwise distance, and their advantage lies in low total pressure loss and high effectiveness in managing engine face distortion.

  8. Cavitation Fatigue. Embolism and Refilling Cycles Can Weaken the Cavitation Resistance of Xylem1

    PubMed Central

    Hacke, Uwe G.; Stiller, Volker; Sperry, John S.; Pittermann, Jarmila; McCulloh, Katherine A.

    2001-01-01

    Although cavitation and refilling cycles could be common in plants, it is unknown whether these cycles weaken the cavitation resistance of xylem. Stem or petiole segments were tested for cavitation resistance before and after a controlled cavitation-refilling cycle. Cavitation was induced by centrifugation, air drying of shoots, or soil drought. Except for droughted plants, material was not significantly water stressed prior to collection. Cavitation resistance was determined from “vulnerability curves” showing the percentage loss of conductivity versus xylem pressure. Two responses were observed. “Resilient” xylem (Acer negundo and Alnus incana stems) showed no change in cavitation resistance after a cavitation-refilling cycle. In contrast, “weakened” xylem (Populus angustifolia, P. tremuloides, Helianthus annuus stems, and Aesculus hippocastanum petioles) showed considerable reduction in cavitation resistance. Weakening was observed whether cavitation was induced by centrifugation, air dehydration, or soil drought. Observations from H. annuus showed that weakening was proportional to the embolism induced by stress. Air injection experiments indicated that the weakened response was a result of an increase in the leakiness of the vascular system to air seeding. The increased air permeability in weakened xylem could result from rupture or loosening of the cellulosic mesh of interconduit pit membranes during the water stress and cavitation treatment. PMID:11161035

  9. The Effect of a Non-Gaussian Random Loading on High-Cycle Fatigue of a Thermally Post-Buckled Structure

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A.; Behnke, marlana N.; Przekop, Adam

    2010-01-01

    High-cycle fatigue of an elastic-plastic beam structure under the combined action of thermal and high-intensity non-Gaussian acoustic loadings is considered. Such loadings can be highly damaging when snap-through motion occurs between thermally post-buckled equilibria. The simulated non-Gaussian loadings investigated have a range of skewness and kurtosis typical of turbulent boundary layer pressure fluctuations in the vicinity of forward facing steps. Further, the duration and steadiness of high excursion peaks is comparable to that found in such turbulent boundary layer data. Response and fatigue life estimates are found to be insensitive to the loading distribution, with the minor exception of cases involving plastic deformation. In contrast, the fatigue life estimate was found to be highly affected by a different type of non-Gaussian loading having bursts of high excursion peaks.

  10. Effect of Cryorolling and Aging on Fatigue Behavior of Ultrafine-grained Al6061

    NASA Astrophysics Data System (ADS)

    Yadollahpour, M.; Hosseini-Toudeshky, H.; Karimzadeh, F.

    2016-05-01

    The effects of cryorolling (rolling at liquid nitrogen temperature) and heat treatment on tensile and high-cycle fatigue properties and fatigue crack growth rate of Al6061 alloy have been investigated in the present work. First, the solid solution-treated bulk Al6061 alloy was subjected to cryorolling with 90% total thickness reduction and subsequent short annealing at 205°C for 5 min and peak aging at 148°C for 39 h to achieve grain refinement and simultaneous improvement of the strength and ductility. Then, hardness measurements, tensile tests, fatigue life, and fatigue crack growth rate tests including fractography analyses using scanning electron microscopy were performed on bulk Al6061 alloy, cryorolled (CR), and cryorolled material followed by peak aging (PA). The PA specimen showed improved yield strength by 24%, ultimate tensile strength by 20%, and ductility by 12% as compared with the bulk Al6061 alloy. It is shown that the fatigue strength of both CR and PA specimens under a high-cycle fatigue regime are larger than that of the bulk Al6061 alloy. Also, fatigue crack growth rates of the CR and PA specimens show significant enhancement in fatigue crack growth resistances as compared with the bulk Al6061 alloy, as a result of grain refinement.

  11. Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Zanganehgheshlaghi, Mohannad

    2014-01-01

    The research results described in this paper presents a new understanding of the behavior of fatigue crack growth in the threshold region. It is believed by some crack growth experts that the ASTM load shedding test method does not produce true or valid threshold properties. The concern involves the observed fanning of threshold region da/dN data plots for some materials in which the low R-ratio data fans out or away from the high R-ratio data. This data fanning or elevation of threshold values is obviously caused by an increase in crack closure in the low R-ratio tested specimens. This increase in crack closure is assumed by some investigators to be caused by a plastic wake on the crack surfaces that was created during the load shedding test phase. This study shows that the increase in crack closure is the result of an extensive occurrence of crack bifurcation behavior in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the particular fanning behavior in aluminum alloys is a function of intrinsic dislocation property of the materials and that the fanned data represents valid material properties. However, for corrosion sensitive steel alloys used in this study the fanning was caused by a build-up of iron oxide at the crack tip from fretting corrosion.

  12. The high-cycle-fatigue performance of lightweight titanium automotive suspensions

    NASA Astrophysics Data System (ADS)

    Kocan, Marcin; Wagner, L.; Yazgan-Kokuoz, B.; Rack, H. J.

    2005-11-01

    Although suspension spring materials traditionally have been made of steel, metastable beta-titanium alloys are being considered as possible alternative materials. Among their benefits, metastable beta-titanium alloys offer high specific strength, low elastic moduli, high corrosion resistance, and manufacturability. However, the cost-effective substitution of metastable beta-titanium for steel will require that titanium suspension springs be manufactured using existing steel suspension fabrication equipment and techniques. These techniques involve coil winding followed by short-time aging and shot peening. This paper describes an evaluation of the effects of the steel suspension fabrication techniques on a prominent metastable beta-titanium alloy.

  13. A study on the role of grain boundary engineering in promoting high-cycle fatigue resistance and improving reliability in nickel base superalloys for propulsion systems

    NASA Astrophysics Data System (ADS)

    Gao, Yong

    High-cycle fatigue, involving the premature initiation and/or rapid propagation of small cracks to failure due to high-frequency (vibratory) loading, remains the principal cause of failures in military gas-turbine propulsion systems. The objective of this study is to examine whether the resistance to high-cycle fatigue failures can be enhanced by grain-boundary engineering, i.e., through the modification of the spatial distribution and topology of the grain boundaries in the microstructure. While grain boundary engineering has been used to obtain significant improvements in intergranular corrosion and cracking, creep and cavitation behavior, toughness and plasticity, cold-work embrittlement, and weldability, only very limited, but positive, results exist for fatigue. Accordingly, using a commercial polycrystalline nickel base gamma/gamma' superalloy, ME3, as a typical engine disk material, sequential thermomechanical processing, involving alternate cycles of strain and annealing, is used to (i) modify the proportion of special grain boundaries, and (ii) interrupt the connectivity of the random boundaries in the grain boundary network. The processed microstructures are then subjected to fracture-mechanics based high cycle fatigue testing to evaluate how the crack initiation and small- and large-crack growth properties are affected and to examine how the altered grain boundary population and connectivity can influence growth rates and overall lifetimes. The effect of such grain-boundary engineering on the fatigue-crack-propagation behavior of large (˜8 to 20 mm), through-thickness cracks at 25, 700, and 800°C was examined. Although there was little influence of an increased special boundary fraction at ambient temperatures, the resistance to near-threshold crack growth was definitively improved at elevated temperatures, with fatigue threshold-stress intensities some 10 to 20% higher than at 25°C, concomitant with a lower proportion (˜20%) of intergranular

  14. The effects of short-cycle sprints on power, strength, and salivary hormones in elite rugby players.

    PubMed

    Crewther, Blair T; Cook, Christian J; Lowe, Tim E; Weatherby, Robert P; Gill, Nicholas

    2011-01-01

    This study examined the effects of short-cycle sprints on power, strength, and salivary hormones in elite rugby players. Thirty male rugby players performed an upper-body power and lower-body strength (UPLS) and/or a lower-body power and upper-body strength (LPUS) workout using a crossover design (sprint vs. control). A 40-second upper-body or lower-body cycle sprint was performed before the UPLS and LPUS workouts, respectively, with the control sessions performed without the sprints. Bench throw (BT) power and box squat (BS) 1 repetition maximum (1RM) strength were assessed in the UPLS workout, and squat jump (SJ) power and bench press (BP) 1RM strength were assessed in the LPUS workout. Saliva was collected across each workout and assayed for testosterone (Sal-T) and cortisol (Sal-C). The cycle sprints improved BS (2.6 ± 1.2%) and BP (2.8 ± 1.0%) 1RM but did not affect BT and SJ power. The lower-body cycle sprint produced a favorable environment for the BS by elevating Sal-T concentrations. The upper-body cycle sprint had no hormonal effect, but the workout differences (%) in Sal-T (r = -0.59) and Sal-C (r = 0.42) concentrations correlated to the BP, along with the Sal-T/C ratio (r = -0.49 to -0.66). In conclusion, the cycle sprints improved the BP and BS 1RM strength of elite rugby players but not power output in the current format. The improvements noted may be explained, in part, by the changes in absolute or relative hormone concentrations. These findings have practical implications for prescribing warm-up and training exercises. PMID:20093968

  15. Deer Antler Extract Improves Fatigue Effect through Altering the Expression of Genes Related to Muscle Strength in Skeletal Muscle of Mice

    PubMed Central

    Hsiang, Chien-Yun; Lin, Yung-Chang; Ho, Tin-Yun

    2014-01-01

    Deer antler is a well-known traditional Chinese medicine used in Asian countries for the tonic and the improvement of aging symptoms. The present study was designed to investigate the antifatigue effect and mechanism of Formosan sambar deer tip antler extract (FSDTAE). The swimming times to exhaustion of mice administered FSDTAE (8.2 mg/day) for 28 days were apparently longer than those of the vehicle-treated mice in forced swim test. However, the indicators of fatigue, such as the reduction in glucose level and the increases in blood urea nitrogen and lactic acid levels, were not significantly inhibited by FSDTAE. Therefore, microarray analysis was further used to examine the anti-fatigue mechanism of FSDTAE. We selected genes with fold changes >2 or <−2 in skeletal muscle for pathway analysis. FSDTAE-affected genes were involved in 9 different signaling pathways, such as GnRH signaling pathway and insulin signaling pathway. All of the significantly expressed genes were classified into 8 different categories by their functions. The most enriched category was muscular system, and 6 upregulated genes, such as troponin I, troponin T1, cysteine and glycine-rich protein 2, myosin heavy polypeptide 7, tropomyosin 2, and myomesin family member 3, were responsible for the development and contraction of muscle. Real-time PCR analysis indicated that FSDTAE increased troponins mRNA expression in skeletal muscle. In conclusion, our findings suggested that FSDTAE might increase the muscle strength through the upregulation of genes responsible for muscle contraction and consequently exhibited the anti-fatigue effect in mice. PMID:24701242

  16. Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

    NASA Technical Reports Server (NTRS)

    Forman, R. G.; Zanganeh, M.

    2014-01-01

    This paper describes the results of a research program conducted to improve the understanding of fatigue crack growth rate behavior in the threshold growth rate region and to answer a question on the validity of threshold region test data. The validity question relates to the view held by some experimentalists that using the ASTM load shedding test method does not produce valid threshold test results and material properties. The question involves the fanning behavior observed in threshold region of da/dN plots for some materials in which the low R-ratio data fans out from the high R-ratio data. This fanning behavior or elevation of threshold values in the low R-ratio tests is generally assumed to be caused by an increase in crack closure in the low R-ratio tests. Also, the increase in crack closure is assumed by some experimentalists to result from using the ASTM load shedding test procedure. The belief is that this procedure induces load history effects which cause remote closure from plasticity and/or roughness changes in the surface morphology. However, experimental studies performed by the authors have shown that the increase in crack closure is a result of extensive crack tip bifurcations that can occur in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the fanning behavior which occurs in aluminum alloys is a function of intrinsic dislocation property of the alloy, and therefore, the fanned data does represent the true threshold properties of the material. However, for the corrosion sensitive steel alloys tested in laboratory air, the occurrence of fanning results from fretting corrosion at the crack tips, and these results should not be considered to be representative of valid threshold properties because the fanning is

  17. Structure-phase states evolution in Al-Si alloy under electron-beam treatment and high-cycle fatigue

    SciTech Connect

    Konovalov, Sergey Alsaraeva, Krestina Gromov, Victor Semina, Olga; Ivanov, Yurii

    2015-10-27

    By methods of scanning and transmission electron diffraction microscopy the analysis of structure-phase states and defect substructure of silumin subjected to high-intensity electron beam irradiation in various regimes and subsequent fatigue loading up to failure was carried out. It is revealed that the sources of fatigue microcracks are silicon plates of micron and submicron size are not soluble in electron beam processing. The possible reasons of the silumin fatigue life increase under electron-beam treatment are discussed.

  18. The Florence Bird Lecture: "From Strength to Strength: The Interrelated Rights of Women and Children over the Life Cycle"

    ERIC Educational Resources Information Center

    Pearson, Landon

    2012-01-01

    This article presents the author's Florence Bird lecture, which was delivered at Carleton University in Ottawa, Canada on International Women's Day, March 8, 2012. In the lecture, the author focuses on the interrelated rights of women and children over the life cycle. The author explores this linkage and offers a caveat. The author shares a…

  19. Three-dimensional characterisation and modelling of small fatigue corner cracks in high strength Al-alloys

    NASA Astrophysics Data System (ADS)

    Proudhon, Henry; Moffat, A.; Sinclair, Ian; Buffiere, Jean-Yves

    2012-04-01

    The growth of fatigue cracks at small length scales is known to be influenced by a variety of factors, including local microstructure, varying stress states and crack shape. High resolution computed tomography allows for sub-micron resolution imaging of failure processes in small test coupons undergoing in situ cyclic loading, providing detailed three-dimensional (3D) assessment of propagation processes across the entire crack front (surface and depth). In this work fatigue crack growth has been examined in an advanced Direct Chill (DC) cast aluminium alloy, along with a fine grained powder-metallurgy alloy. The latter is identified as a model material, offering considerably simpler microscopic crack paths than the DC cast alloy, and hence a means of separating bulk mechanical effects (such as stress state variations across a crack front and plasticity induced closure) from microstructural effects (such as crystallographic deflection and roughness induced crack closure). Crack growth has been studied in both materials under both constant amplitude (CA) and single peak overload (OL) conditions. Experimental results are presented in the present paper, particularly in relation to micromechanical understanding of failure. A modelling approach based on those results, and some typical results, is also presented.

  20. Daily Social Enjoyment Interrupts the Cycle of Same-day and Next-day Fatigue in Women with Fibromyalgia

    PubMed Central

    Yeung, Ellen W.; Davis, Mary C.; Aiken, Leona S.; Tennen, Howard A.

    2014-01-01

    Background Fatigue is a debilitating symptom of fibromyalgia (FM) that has limited treatment options. Some evidence, however, has linked positive social engagement with reduced within-day fatigue. Purpose This study elaborated longitudinal within-day and across-day relations between FM fatigue and social enjoyment. Methods 176 women with FM completed 21-day automated diaries assessing morning and end-of-day fatigue, and both afternoon social enjoyment and stress within two social domains: non-spousal and spousal. Results In the non-spousal domain, analysis supported a mediational path from lower morning fatigue to higher afternoon social enjoyment, which predicted lower end-of-day fatigue, and subsequently, lower next-morning fatigue. Enjoyment exerted a greater impact on within-day fatigue than did stress. Patterns in the spousal domain were similar, but the mediated path was nonsignificant. Conclusions Positive social engagement offers relief from FM fatigue that carries over across days and may provide an additional target to enhance the effectiveness of current interventions. PMID:25380634

  1. Bond strength and bioactivity of Zn-doped dental adhesives promoted by load cycling.

    PubMed

    Toledano, Manuel; Aguilera, Fátima S; Osorio, Estrella; Cabello, Inmaculada; Toledano-Osorio, Manuel; Osorio, Raquel

    2015-02-01

    The purpose of this study was to evaluate if mechanical loading influences bioactivity and bond strength at the resin-dentin interface after bonding with Zn-doped etch-and-rinse adhesives. Dentin surfaces were subjected to demineralization by 37% phosphoric acid (PA) or 0.5 M ethylenediaminetetraacetic acid (EDTA). Single bond (SB) adhesive—3M ESPE—SB+ZnO particles 20 wt% and SB+ZnCl2 2 wt% were applied on treated dentin to create the groups PA+SB, SB+ZnO, SB+ZnCl2, EDTA+SB, EDTA+ZnO, and EDTA+ZnCl2. Bonded interfaces were stored in simulated body fluid for 24 h and tested or submitted to mechanical loading. Microtensile bond strength (MTBS) was assessed. Debonded dentin surfaces were studied by high-resolution scanning electron microscopy. Remineralization of the bonded interfaces was assessed by atomic force microscope imaging/nanoindentation, Raman spectroscopy/cluster analysis, and Masson's trichrome staining. Load cycling (LC) produced reduction in MTBS in all PA+SB, and no change was encountered in EDTA+SB specimens, regardless of zinc doping. LC increased the mineralization and crystallographic maturity at the interface; a higher effect was noticed when using ZnO. Trichrome staining reflected a narrow demineralized dentin matrix after loading of dentin surfaces that were treated with SB-doped adhesives. This correlates with an increase in mineral platforms or plate-like multilayered crystals in PA or EDTA-treated dentin surfaces, respectively. PMID:25499741

  2. Fatigue behavior of SiC reinforced titanium composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Grimes, H. H.

    1979-01-01

    The low cycle axial fatigue properties of 25 and 44 fiber volume percent SiC/Ti(6Al-4V) composites were measured at room temperature and at 650 deg C. The S-N curves for the composites showed no anticipated improvement over bulk matrix behavior at room temperature. Although axial and transverse tensile strength results suggest a degradation in SiC fiber strength during composite fabrication, it appears that the poor fatigue life of the composites was caused by a reduced fatigue resistance of the reinforced Ti(6Al-4V) matrix. The reduced matrix behavior was due, to the presence of flawed and fractured fibers created near the specimen surfaces by preparation techniques and to the large residual tensile stresses that can exist in fiber reinforced matrices. The effects of fatigue testing at high temperature are discussed.

  3. Fatigue behavior of SiC reinforced titanium composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Grimes, H. H.

    1979-01-01

    The low cycle axial fatigue properties of 25 and 44 fiber volume percent SiC/Ti(6Al-4V) composites were measured at room temperature and at 650 C. At room temperature, the S-N curves for the composites showed no anticipated improvement over bulk matrix behavior. Although axial and transverse tensile strength results suggest a degradation in SiC fiber strength during composite fabrication, it appears that the poor fatigue life of the composites was caused by a reduced fatigue resistance of the reinforced Ti(6Al-4V) matrix. Microstructural studies indicate that the reduced matrix behavior was due, in part, to the presence of flawed and fractured fibers created near the specimen surfaces by preparation techniques. Another possible contributing factor is the large residual tensile stresses that can exist in fiber-reinforced matrices. These effects, as well as the effects of fatigue testing at high temperature, are discussed.

  4. Dentin bond strength of a fluoride-releasing adhesive system submitted to pH-cycling.

    PubMed

    Costa, Ana Rosa; Correr-Sobrinho, Lourenço; Ambrosano, Glaucia Maria Bovi; Sinhoreti, Mario Alexandre Coelho; Borges, Gilberto Antonio; Platt, Jeffrey A; Puppin-Rontani, Regina Maria

    2014-01-01

    To evaluate the microtensile bond strength (µTBS) of a fluoride-containing adhesive system submitted to a pH-cycling and storage time regimen for primary outcomes. As secondary outcomes the fluoride released amount was evaluated. Twelve dentin surfaces from sound third molar were divided into 2 groups according to adhesive systems: Clearfil SE Protect (PB) and Clearfil SE Bond (SE). Sticks obtained (1.0 mm2) from teeth were randomly divided into 3 subgroups according to storage regimen model: immediate (24h); 5-month deionized water (W); and pH-cycling model (C). All sticks were tested for µTBS in a universal testing machine. Fluoride concentration was obtained from 1-4 days and 30-day in W and 1-4 days in demineralization (DE)/remineralization (RE) solutions from C, using a fluoride-specific electrode. µTBS and fluoride released data were, respectively, submitted to ANOVA in a split plot design and Tukey, and Friedman' tests (a=0.05). There was no significant interaction between adhesive system and storage regimen for µTBS. W showed the lowest µTBS values. There was no significant difference between 24 h and C models for µTBS. There was no significant difference between adhesive systems. Failure mode was predominantly cohesive within composite for the 24 h and W, for the C group it was mixed for SE and cohesive within composite for PB adhesive system. Fluoride concentrations in the DE/RE solutions were less than 0.03125 ppm and not detected in W. In conclusion, the fluoride-containing adhesive system performed similarly to the regular one. Hydrolytic degradation is the main problem with both adhesive systems, regardless of fluoride contents. PMID:25590191

  5. High temperature, low-cycle fatigue of copper-base alloys in argon. Part 1: Preliminary results for 12 alloys at 1000 F (538 C)

    NASA Technical Reports Server (NTRS)

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1973-01-01

    Short-term tensile evaluations at room temperature and 538 C and low-cycle fatigue evaluations at 538 C are presented for the following materials: Zirconium copper-annealed, Zirconium copper-1/4 hard, Zirconium copper-1/2 hard, Tellurium copper-1/2 hard, Chromium copper-SA and aged, OFHC copper-hard, OFHC copper-1/4 hard, OFHC copper-annealed, Silver-as drawn, Zr-Cr-Mg copper-SA, CW and aged, Electroformed copper-30-35 ksi, and Co-Be-Zr- copper-SA, aged. A total of 50 tensile tests and 76 low-cycle fatigue tests were performed using a strain rate of 0.2 percent per second.

  6. Acute effect of high-intensity aerobic exercise performed on treadmill and cycle ergometer on strength performance.

    PubMed

    Panissa, Valéria L G; Tricoli, Valmor A A; Julio, Ursula F; Ribeiro, Natalia; de Azevedo Neto, Raymundo M A; Carmo, Everton C; Franchini, Emerson

    2015-04-01

    Concurrent training (i.e., combination of endurance with strength training) may result in negative interference on strength performance. Moreover, there are indications that the magnitude of this interference is dependent on endurance exercise mode. Thus, this study aimed to verify the acute effects of previous running and cycling on strength endurance performance. After the determination of the maximum intensity reached (Imax) during treadmill running and cycle ergometer pedaling and half-squat maximum strength (1 repetition maximum [1RM]), 10 physically active men were submitted to 3 experimental conditions: control condition (S) comprised of 4 sets of maximum repetitions at 80% 1RM, intermittent running (RS), and cycling (CS) conditions (15 × 1 minute:1 minute in the Imax) followed by the strength exercise (S). Maximum number of repetitions (MNR), total session volume (TV), and vastus lateralis electromyographic signal (VLRMS) were analyzed. It was observed that MNR and TV performed in set 1 in the S condition was superior to that performed in set 1 in the RS (p < 0.001) and CS (p < 0.001) conditions; and set 2 in the S condition was superior to set 2 only in the CS for the MNR (p = 0.032) and TV (p = 0.012). For the VLRMS, there was a main effect for repetition, with higher values in the last repetition compared with the second one (p < 0.01). In conclusion, an aerobic exercise bout before strength exercise impairs the subsequent strength endurance performance. In addition, the magnitude of the interference effect was higher after the aerobic cycling exercise. PMID:25259468

  7. Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

    PubMed

    Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

    2014-07-01

    The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a “sandwich structure” as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50–55% of ultimate tensile strength). The dynamic modulus (E⁎) was found to stay almost constant at 47 GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials. PMID:24918250

  8. Ultrasonic Fatigue Endurance of Thin Carbon Fiber Sheets

    NASA Astrophysics Data System (ADS)

    Domínguez Almaraz, Gonzalo M.; Ruiz Vilchez, Julio A.; Dominguez, Aymeric; Meyer, Yann

    2016-04-01

    Ultrasonic fatigue tests were carried out on thin carbon fiber sheets (0.3 mm of thickness) to determine the fatigue endurance under very high-frequency loading (20 kHz). This material, called the gas diffusion layer (GDL), plays a major role in the overall performances of proton exchange membrane fuel cells (PEMFCs). The study of its physical-chemical properties is an on-going subject in the literature; nevertheless, no knowledge is available concerning the high-frequency fatigue endurance. A principal difficulty in carrying out ultrasonic fatigue tests on this material was to determine the dimensions of testing specimen to fit the resonance condition. This aspect was solved by modal numerical simulation: The testing specimen has been a combination of a low-strength steel frame (to facilitate the attachment to the ultrasonic machine and to increase the mass of the specimen), and the carbon fiber hourglass-shape profile. Under resonance condition, a stationary elastic wave is generated along the specimen that induces high stress at the neck section and high displacements at the ends. Results show that fatigue life was close to 3 × 108 cycles when the high Von Misses stress at the neck section was 170 MPa, whereas fatigue life attains the 4.5 × 109 cycles when stress decreases to 117 MPa. Crack initiation and propagation were analyzed, and conclusions were drawn concerning the fatigue endurance of these fiber carbon sheets under ultrasonic fatigue testing.

  9. Atmospheric cycles of nitrogen oxides and ammonia. [source strengths and destruction rates

    NASA Technical Reports Server (NTRS)

    Bottger, A.; Ehhalt, D. H.; Gravenhorst, G.

    1981-01-01

    The atmospheric cycles of nitrogenous trace compounds for the Northern and Southern Hemispheres are discussed. Source strengths and destruction rates for the nitrogen oxides: NO, NO2 and HNO3 -(NOX) and ammonia (NH3) are given as a function of latitude over continents and oceans. The global amounts of NOX-N and NH3-N produced annually in the period 1950 to 1975 (34 + 5 x one trillion g NOx-N/yr and 29 + or - 6 x one trillion g NH3-N/yr) are much less than previously assumed. Globally, natural and anthropogenic emissions are of similar magnitude. The NOx emission from anthropogenic sources is 1.5 times that from natural processes in the Northern Hemisphere, whereas in the Southern Hemisphere, it is a factor of 3 or 4 less. More than 80% of atmospheric ammonia seems to be derived from excrements of domestic animals, mostly by bulk deposition: 24 + or - 9 x one trillion g NO3 -N/yr and 21 + or - 9 x one trillion g NH4+-N/yr. Another fraction may be removed by absorption on vegetation and soils.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  11. Effect of Environment on Fatigue Behavior of a Nicalon(TM)/Si-N-C Ceramic Matrix Composite

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Ojard, Greg C.; Verrilli, Michael J.; Kiraly, Louis J. (Technical Monitor)

    2002-01-01

    The effect of environmental exposure on the fatigue life of Nicalon(TM) /Si-N-C composite was investigated in this study. Test specimens with arrays of 1.8 mm diameter holes and two different open areas, 25 and 35%, were machined. Three environmental conditions were studied: 1) continuous fatigue cycling in air, 2) fatigue cycling in air alternating with humidity exposure, and 3) fatigue cycling in air alternating with exposure to a salt-fog environment. All fatigue testing on specimens with holes was performed with a load ratio, R = 0.05, and at a temperature of 910 C. In general, fatigue lives were shortest for specimens subjected to salt-fog exposure and longest for specimens subjected to continuous fatigue cycling in air. The fatigue data generated on the specimens with holes were compared with fatigue data generated in air on specimens with no holes. Fatigue strength reduction factors for different environmental conditions and open areas investigated in the study were calculated for the Nicalon(TM) /Si-N-C composite.

  12. Journal of mechanical strength, Volume 20, Number 4, 1998

    SciTech Connect

    Chen, A.

    1998-12-01

    Partial contents include: Notch strength of spheroidal graphite cast iron under tension loading; Study on the susceptivity to welding cold crack of 30CrMo and 40CrNi steel; Studies on stress distribution in spot welded lap joints and the fatigue behavior of the joints; Application of H(infinity) method in active vibration robust control; Effect of torsional prestrain on low cycle fatigue behavior of 45 steel; and Reliability analysis of vibrating structural components.

  13. An engineering approach to the prediction of fatigue behavior of unnotched/notched fiber reinforced composite laminates

    NASA Technical Reports Server (NTRS)

    Kulkarni, S. V.; Mclaughlin, P. V., Jr.

    1978-01-01

    An engineering approach is proposed for predicting unnotched/notched laminate fatigue behavior from basic lamina fatigue data. The fatigue analysis procedure was used to determine the laminate property (strength/stiffness) degradation as a function of fatigue cycles in uniaxial tension and in plane shear. These properties were then introduced into the failure model for a notched laminate to obtain damage growth, residual strength, and failure mode. The approach is thus essentially a combination of the cumulative damage accumulation (akin to the Miner-Palmgren hypothesis and its derivatives) and the damage growth rate (similar to the fracture mechanics approach) philosophies. An analysis/experiment correlation appears to confirm the basic postulates of material wearout and the predictability of laminate fatigue properties from lamina fatigue data.

  14. Influence of duty cycle on the time course of muscle fatigue and the onset of neuromuscular compensation during exhaustive dynamic isolated limb exercise

    PubMed Central

    Sundberg, Christopher W.

    2015-01-01

    We investigated the influence of altered muscle duty cycle on the performance decrements and neuromuscular responses occurring during constant-load, fatiguing bouts of knee extension exercise. We experimentally altered the durations of the muscularly inactive portion of the limb movement cycle and hypothesized that greater relative durations of inactivity within the same movement task would 1) reduce the rates and extent of muscle performance loss and 2) increase the forces necessary to trigger muscle fatigue. In each condition (duty cycle = 0.6 and 0.3), male subjects [age = 25.9 ± 2.0 yr (SE); mass = 85.4 ± 2.6 kg], completed 9–11 exhaustive bouts of two-legged knee extension exercise, at force outputs that elicited failure between 4 and 290 s. The novel duty cycle manipulation produced two primary results; first, we observed twofold differences in both the extent of muscle performance lost (DC0.6 = 761 ± 35 N vs. DC0.3 = 366 ± 49 N) and the time course of performance loss. For example, exhaustive trials at the midpoint of these force ranges differed in duration by more than 30 s (t0.6 = 36 ± 2.6 vs. t0.3 = 67 ± 4.3 s). Second, both the minimum forces necessary to exceed the peak aerobic capacity and initiate a reliance on anaerobic metabolism, and the forces necessary to elicit compensatory increases in electromyogram activity were 300% greater in the lower vs. higher duty cycle condition. These results indicate that the fatigue-induced compensatory behavior to recruit additional motor units is triggered by a reliance on anaerobic metabolism for ATP resynthesis and is independent of the absolute level or fraction of the maximum force produced by the muscle. PMID:25876654

  15. Damage development during low cycle fatigue of carbon-black loaded SBR. [Styrene butadiene rubber containing 0, 15, 25, and 35 wt % carbon black

    SciTech Connect

    Lesuer, D.; Goldberg, A.; Hiromoto, D.; Patt, J.

    1984-06-18

    Fatigue of elastomers is a subject that has received considerable study over the years. This paper explores the problem of damage accumulation in a series of styrene butadiene rubber (SBR) based compounds containing 0, 15, 25, and 35 wt % carbon-black under conditions in which a limited number of higher stress cycles have been applied to the material (referred to here as low cycle fatigue). Damage development in elastomers can take many forms. Generally speaking, one can classify the degradation as mechanical or chemical in origin. The most obvious form of mechanical damage is flaw or cut growth, while typical examples of chemical damage include chain scission or thermal oxidation. The fatigue crack growth relationship given in Equation 1 obviously only applies to flaw growth. However, it does an excellent job of following the data and exhibits the threshold behavior observed in both SBR and SBR-35 at room temperature. At higher temperatures, the damaged material shows an increasing deviation from threshold behavior. The obvious implication is that some thermally activated damage mechanism is degrading the material. In previous work, carbon-black loaded SBR subjected to a high temperature, high stress environment was shown to undergo a thermal-mechanical oxidation process. Certainly, this process is a candidate for a damage mechanism in these studies. 6 references, 14 figures, 1 table.

  16. A comparative study on low cycle fatigue behaviour of nano and micro Al2O3 reinforced AA2014 particulate hybrid composites

    NASA Astrophysics Data System (ADS)

    Senthilkumar, R.; Arunkumar, N.; Manzoor Hussian, M.

    Aluminium based metal matrix composites have drawn more attraction due to their improved properties in structural applications for the past two decades. The fatigue behaviour of composite materials needs to be studied for their structural applications. In this work, powder metallurgy based aluminium (AA2014) alloy reinforced with micro and nano-sized alumina particles were fabricated and consolidated with the hot extrusion process. The evaluation of mechanical properties in the extruded composite was carried out. This composite was subjected to low cycle fatigue test with a constant strain rate. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images were used to evaluate the fatigue behaviour of aluminium-nano composite samples. Enhanced mechanical properties were exhibited by the nano alumina reinforced aluminium composites, when compared to the micron sized alumina reinforced composites. The failure cycle is observed to be higher for the nano alumina reinforced composites when compared with micron sized alumina composites due to a lower order of induced plastic strain.

  17. A strength-based wearout model for predicting the life of composite structures

    SciTech Connect

    Schaff, J.R.; Davidson, B.D.

    1997-12-31

    A model to predict the residual strength and life of polymeric composite structures subjected to spectrum fatigue loadings is described. The model is based on the fundamental assumptions that the structure undergoes proportional loading, that the residual strength is a monotonically decreasing function of the number of fatigue cycles, and that both the life distribution due to continuous constant amplitude cycling and the residual strength distribution after an arbitrary load history may be represented by two parameter Weibull functions. The model also incorporates a cycle mix factor to account for the drastic reduction of fatigue life that may be caused by a large number of changes in the stress amplitude of the loading. The model`s predictions are compared to experimentally determined fatigue life distributions for uniaxial loadings of a number of laminates comprised of different materials and layups. Constant-amplitude, two-stress level, and spectrum fatigue loadings, including the FALSTAFF (Fighter Aircraft Loading Standard for Fatigue) spectrum, are considered. The theoretical fatigue life distributions are shown to correlate well with the experimental results. Moreover, excellent correlation of theory and experiment is obtained for an average fatigue life that is based on the 63.2% probability of failure.

  18. Coupled modeling of a directly heated tubular solar receiver for supercritical carbon dioxide Brayton cycle: Structural and creep-fatigue evaluation

    DOE PAGESBeta

    Ortega, Jesus; Khivsara, Sagar; Christian, Joshua; Ho, Clifford; Dutta, Pradip

    2016-06-06

    A supercritical carbon dioxide (sCO2) Brayton cycle is an emerging high energy-density cycle undergoing extensive research due to the appealing thermo-physical properties of sCO2 and single phase operation. Development of a solar receiver capable of delivering sCO2 at 20 MPa and 700 °C is required for implementation of the high efficiency (~50%) solar powered sCO2 Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Moreover, temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used to evaluate the thermal andmore » mechanical stresses along with detailed creep-fatigue analysis of the tubes. For resulting body stresses were used to approximate the lifetime performance of the receiver tubes. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. The creep-fatigue analysis display the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver.« less

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  20. The Effects of Mechanical Properties on Fatigue Behavior of ECAPed AA7075

    NASA Astrophysics Data System (ADS)

    Kaya, Hasan; Uçar, Mehmet

    2016-03-01

    In this study, the effects of equal channel angular pressing (ECAP) on high-cycle fatigue and fatigue surface morphology of AA7075 have been investigated at a constant temperature (483 K) and the "C" route for four passes at ECAP process. ECAPed and as-received specimens were tested by four-point bending fatigue device. Fatigue tests were carried out by using 100, 120 and 140 MPa strength values. ECAPed specimens were characterized for each pass with optical microscope (OM), scanning electron microscope (SEM), energy-dispersive spectroscope (EDS), transmission electron microscope (TEM), selected area electron diffraction (SAED) and hardness measurements. Fracture surfaces of the specimens were also characterized with SEM. The results show that the highest hardness values (137 HV) and the best fatigue life (5.4 × 107 for 100 MPa) were measured in ECAPed four-pass sample. For this reason hardness values and fatigue life were increased with increasing number of severe plastic deformation (SPD) process.