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Sample records for fatigue fracture behavior

  1. Fatigue and fracture behavior of low alloy ferritic forged steels

    International Nuclear Information System (INIS)

    Chaudhry, V.; Sharma, A.K.; Muktibodh, U.C.; Borwankar, Neeraj; Singh, D.K.; Srinivasan, K.N.; Kulkarni, R.G.

    2016-01-01

    Low alloy ferritic steels are widely used in nuclear industry for the construction of pressure vessels. Pressure vessel forged low alloy steels 20MnMoNi55 (modified) have been developed indigenously. Experiments have been carried out to study the Low Cycle Fatigue (LCF) and fracture behavior of these forged steels. Fully reversed strain controlled LCF testing at room temperature and at 350 °C has been carried out at a constant strain rate, and for different axial strain amplitude levels. LCF material behavior has been studied from cyclic stress-strain responses and the strain-life relationships. Fracture behavior of the steel has been studied based on tests carried out for crack growth rate and fracture toughness (J-R curve). Further, responses of fatigue crack growth rate tests have been compared with the rate evaluated from fatigue precracking carried out for fracture toughness (J-R) tests. Fractography of the samples have been carried out to reveal dominant damage mechanisms in crack propagation and fracture. The fatigue and fracture properties of indigenously developed low alloy steel 20MnMoNi55 (modified) steels are comparable with similar class of steels. (author)

  2. Fatigue crack growth and fracture behavior of bainitic rail steels.

    Science.gov (United States)

    2011-09-01

    "The microstructuremechanical properties relationships, fracture toughness, fatigue crack growth and fracture surface morphology of J6 bainitic, manganese, and pearlitic rail steels were studied. Microstructuremechanical properties correlation ...

  3. Fatigue Fracture Behaviors of Transparent Polycarbonate Materials

    OpenAIRE

    ZHANG Xiao-wen; WU Nan; ZHANG Xuan; MA Li-ting; LI Lei

    2017-01-01

    The effect of the different stress ratios (R) and annealing treatment on the fatigue properties of the transparent polycarbonate (PC) sheet and the mechanism behind were studied, the fatigue crack propagation (FCP) process and mechanism were analyzed. The results show that after annealing, the residual stress of the PC samples decreases obviously and the fatigue properties are greatly improved. This is because the machining process results in tensile stress in the PC samples, eliminating the ...

  4. Flexural fracture and fatigue behavior of steel-fiber-reinforced concrete structures

    International Nuclear Information System (INIS)

    Chang, D.I.

    1995-01-01

    Fracture and fatigue tests were performed in order to investigate the fracture and fatigue behavior of steel-fibre-reinforced concrete (SFRC) structures. 33 SFRC beams were used in the fracture and fatigue tests. The relationship between loading, strain and midspan deflection of the beams was observed under the three-point loading system.From the test results, the effects of the fiber content, fiber aspect ratio and notch-to-depth ratio on the concrete fracture and fatigue behavior were studied, and the fatigue strengths of SFRC beams were calculated. According to the regression technique, some empirical formulae for predicting the fatigue strength of SFRC beams were also suggested. (orig.)

  5. The concept of fatigue fracture toughness in fatigue delamination growth behavior

    NARCIS (Netherlands)

    Yao, L.; Alderliesten, R.C.; Benedictus, R.

    2015-01-01

    This paper provides a study on mode I fatigue delamination growth in composite laminates using energy principles. Experimental data has been obtained from fatigue tests conducted on Double Cantilever Beam (DCB) specimens at various stress ratios. A concept of fatigue fracture toughness is proposed

  6. The fracture behavior of an Al-Mg-Si alloy during cyclic fatigue

    International Nuclear Information System (INIS)

    Azzam, Diya; Menzemer, Craig C.; Srivatsan, T.S.

    2010-01-01

    In this paper, is presented and discussed the cyclic fracture behavior of the Al-Mg-Si alloy 6063 that is a candidate used in luminaire light poles. The light poles were subject to fatigue deformation. Test sections were taken from the failed region of the light pole and carefully examined in a scanning electron microscope with the objective of rationalizing the macroscopic fracture mode and intrinsic micromechanisms governing fracture under cyclic loading. The fatigue fracture surface of the alloy revealed distinct regions of early microscopic crack growth, stable crack growth and unstable crack growth and overload. An array of fine striations was found covering the regions of early and stable crack growth. Both macroscopic and fine microscopic cracks were found in the region of unstable crack growth. Very few microscopic voids and shallow dimples were evident on the fatigue fracture surface indicative of the limited ductility of the alloy under cyclic loading conditions.

  7. Fatigue damage and fracture behavior of tungsten fiber reinforced Zr-based metallic glassy composite

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zhang, Z.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)]. E-mail: zhfzhang@imr.ac.cn; Wang, Z.G. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Qiu, K.Q. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zhang, H.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zang, Q.S. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Hu, Z.Q. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)

    2006-02-25

    The fatigue life, damage and fracture behavior of tungsten fiber reinforced metallic glass Zr{sub 41.25}Ti{sub 13.75}Ni{sub 10}Cu{sub 12.5}Be{sub 22.5} composites are investigated under cyclic push-pull loading. It is found that the fatigue life of the composite increases with increasing the volume fraction of tungsten fibers. Similar to crystalline metals, the regions of crack initiation, propagation and overload fracture can be discerned on the fracture surface of the specimen. Fatigue crack normally initiates in the metallic glass matrix at the outer surface of the composite specimen and propagates predominantly in the matrix. Different crack front profile around the tungsten fibers and fiber pullout demonstrate that fatigue crack may propagate around the fiber, leading to bridging of the crack faces by the unbroken fiber and hence improved fatigue crack-growth resistance. Locally decreased effective stiffness in the region where fiber distribution is sparse may provide preferential crack path in the composite. A proposed model was exercised to elucidate different tungsten fiber fracture morphologies in the fatigue crack propagation and overload fracture regions in the light of Poisson's ratio effect during fatigue loading.

  8. Fatigue damage and fracture behavior of tungsten fiber reinforced Zr-based metallic glassy composite

    International Nuclear Information System (INIS)

    Zhang, H.; Zhang, Z.F.; Wang, Z.G.; Qiu, K.Q.; Zhang, H.F.; Zang, Q.S.; Hu, Z.Q.

    2006-01-01

    The fatigue life, damage and fracture behavior of tungsten fiber reinforced metallic glass Zr 41.25 Ti 13.75 Ni 10 Cu 12.5 Be 22.5 composites are investigated under cyclic push-pull loading. It is found that the fatigue life of the composite increases with increasing the volume fraction of tungsten fibers. Similar to crystalline metals, the regions of crack initiation, propagation and overload fracture can be discerned on the fracture surface of the specimen. Fatigue crack normally initiates in the metallic glass matrix at the outer surface of the composite specimen and propagates predominantly in the matrix. Different crack front profile around the tungsten fibers and fiber pullout demonstrate that fatigue crack may propagate around the fiber, leading to bridging of the crack faces by the unbroken fiber and hence improved fatigue crack-growth resistance. Locally decreased effective stiffness in the region where fiber distribution is sparse may provide preferential crack path in the composite. A proposed model was exercised to elucidate different tungsten fiber fracture morphologies in the fatigue crack propagation and overload fracture regions in the light of Poisson's ratio effect during fatigue loading

  9. Fracture Toughness and Fatigue Crack Growth Behavior of As-Cast High-Entropy Alloys

    Science.gov (United States)

    Seifi, Mohsen; Li, Dongyue; Yong, Zhang; Liaw, Peter K.; Lewandowski, John J.

    2015-08-01

    The fracture toughness and fatigue crack growth behavior of two as-vacuum arc cast high-entropy alloys (HEAs) (Al0.2CrFeNiTi0.2 and AlCrFeNi2Cu) were determined. A microstructure examination of both HEA alloys revealed a two-phase structure consisting of body-centered cubic (bcc) and face-centered cubic (fcc) phases. The notched and fatigue precracked toughness values were in the range of those reported in the literature for two-phase alloys but significantly less than recent reports on a single phase fcc-HEA that was deformation processed. Fatigue crack growth experiments revealed high fatigue thresholds that decreased significantly with an increase in load ratio, while Paris law slopes exhibited metallic-like behavior at low R with significant increases at high R. Fracture surface examinations revealed combinations of brittle and ductile/dimpled regions at overload, with some evidence of fatigue striations in the Paris law regime.

  10. High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

    Science.gov (United States)

    Zhao, Jing; Ji, Honghong

    2017-01-01

    The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite. PMID:29286325

  11. High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

    Directory of Open Access Journals (Sweden)

    Jing Zhao

    2017-12-01

    Full Text Available The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite.

  12. Fatigue and fracture: Overview

    Science.gov (United States)

    Halford, G. R.

    1984-01-01

    A brief overview of the status of the fatigue and fracture programs is given. The programs involve the development of appropriate analytic material behavior models for cyclic stress-strain-temperature-time/cyclic crack initiation, and cyclic crack propagation. The underlying thrust of these programs is the development and verification of workable engineering methods for the calculation, in advance of service, of the local cyclic stress-strain response at the critical life governing location in hot section compounds, and the resultant crack initiation and crack growth lifetimes.

  13. Correlation between Fatigue Crack Growth Behavior and Fracture Surface Roughness on Cold-Rolled Austenitic Stainless Steels in Gaseous Hydrogen

    Directory of Open Access Journals (Sweden)

    Tai-Cheng Chen

    2018-03-01

    Full Text Available Austenitic stainless steels are often considered candidate materials for use in hydrogen-containing environments because of their low hydrogen embrittlement susceptibility. In this study, the fatigue crack growth behavior of the solution-annealed and cold-rolled 301, 304L, and 310S austenitic stainless steels was characterized in 0.2 MPa gaseous hydrogen to evaluate the hydrogen-assisted fatigue crack growth and correlate the fatigue crack growth rates with the fracture feature or fracture surface roughness. Regardless of the testing conditions, higher fracture surface roughness could be obtained in a higher stress intensity factor (∆K range and for the counterpart cold-rolled specimen in hydrogen. The accelerated fatigue crack growth of 301 and 304L in hydrogen was accompanied by high fracture surface roughness and was associated with strain-induced martensitic transformation in the plastic zone ahead of the fatigue crack tip.

  14. The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

    OpenAIRE

    Wenke Li; Lihua Zhan; Lingfeng Liu; Yongqian Xu

    2016-01-01

    Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that t...

  15. Ti–6Al–4V welded joints via electron beam welding: Microstructure, fatigue properties, and fracture behavior

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiaoguang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China); Li, Shaolin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Qi, Hongyu, E-mail: qhy@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China)

    2014-03-01

    The effect of microstructural characteristics on the fatigue properties of electron beam-welded joints of forged Ti–6Al–4V and its fracture behavior were investigated. Tensile tests and fatigue tests were conducted at room temperature in air atmosphere. The test data were analyzed in relation to microstructure, high-cycle fatigue properties, low-cycle fatigue properties, and fatigue crack propagation properties. The high-cycle fatigue test results indicated that the fatigue strength of the joint welded via electron beam welding was higher than that of the base metal because the former had a high yield strength and all high-cycle fatigue specimens were fractured in the base metal. Although the joint specimens had a lower low-cycle fatigue life than the base metal, they mainly ruptured at the fusion zone of the joint specimen and their crack initiation mechanism is load-dependent. The fatigue crack propagation test results show that the joint had a slower crack propagation rate than the base metal, which can be attributed to the larger grain in the fusion zone.

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

    Science.gov (United States)

    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.

  17. Influence of Nickel Particle Reinforcement on Cyclic Fatigue and Final Fracture Behavior of a Magnesium Alloy Composite

    Directory of Open Access Journals (Sweden)

    Manoj Gupta

    2012-06-01

    Full Text Available The microstructure, tensile properties, cyclic stress amplitude fatigue response and final fracture behavior of a magnesium alloy, denoted as AZ31, discontinuously reinforced with nano-particulates of aluminum oxide and micron size nickel particles is presented and discussed. The tensile properties, high cycle fatigue and final fracture behavior of the discontinuously reinforced magnesium alloy are compared with the unreinforced counterpart (AZ31. The elastic modulus and yield strength of the dual particle reinforced magnesium alloy is marginally higher than of the unreinforced counterpart. However, the tensile strength of the composite is lower than the monolithic counterpart. The ductility quantified by elongation to failure over 0.5 inch (12.7 mm gage length of the test specimen showed minimal difference while the reduction in specimen cross-section area of the composite is higher than that of the monolithic counterpart. At the microscopic level, cyclic fatigue fractures of both the composite and the monolithic alloy clearly revealed features indicative of the occurrence of locally ductile and brittle mechanisms. Over the range of maximum stress and at two different load ratios the cyclic fatigue resistance of the magnesium alloy composite is superior to the monolithic counterpart. The mechanisms responsible for improved cyclic fatigue life and resultant fracture behavior of the composite microstructure are highlighted.

  18. Microstructural effects on constitutive and fatigue fracture behavior of TinSilverCopper solder

    Science.gov (United States)

    Tucker, Jonathon P.

    As microelectronic package construction becomes more diverse and complex, the need for accurate, geometry-independent material constitutive and failure models increases. Evaluations of packages based on accelerated environmental tests (such as accelerated thermal cycling or power cycling) only provide package-dependent reliability information. In addition, extrapolations of such test data to life predictions under field conditions are often empirical. Besides geometry, accelerated environmental test data must account for microstructural factors such as alloy composition or isothermal aging condition, resulting in expensive experimental variation. In this work, displacement-controlled, creep, and fatigue lap shear tests are conducted on specially designed SnAgCu test specimens with microstructures representative to those found in commercial microelectronic packages. The data are used to develop constitutive and fatigue fracture material models capable of describing deformation and fracture behavior for the relevant temperature and strain rate ranges. Furthermore, insight is provided into the microstructural variation of solder joints and the subsequent effect on material behavior. These models are appropriate for application to packages of any geometrical construction. The first focus of the thesis is on Pb-mixed SnAgCu solder alloys. During the transition from Pb-containing solders to Pb-free solders, joints composed of a mixture of SnPb and SnAgCu often result from either mixed assemblies or rework. Three alloys of 1, 5 and 20 weight percent Pb were selected so as to represent reasonable ranges of Pb contamination expected from different 63Sn37Pb components mixed with Sn3.0Ag0.5Cu. Displacement-controlled (constant strain rate) and creep tests were performed at temperatures of 25°C, 75°C, and 125°C using a double lap shear test setup that ensures a nearly homogeneous state of plastic strain at the joint interface. Rate-dependent constitutive models for Pb

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

    Science.gov (United States)

    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.

  20. The effect of manufacturing conditions on discontinuity population and fatigue fracture behavior in carbon/epoxy composites

    Science.gov (United States)

    Hakim, Issa; Laquai, Rene; Walter, David; Mueller, Bernd; Graja, Paul; Meyendorf, Norbert; Donaldson, Steven

    2017-02-01

    Carbon fiber composites have been increasingly used in aerospace, military, sports, automotive and other fields due to their excellent properties, including high specific strength, high specific modulus, corrosion resistance, fatigue resistance, and low thermal expansion coefficient. Interlaminar fracture is a serious failure mode leading to a loss in composite stiffness and strength. Discontinuities formed during manufacturing process degrade the fatigue life and interlaminar fracture resistance of the composite. In his study, three approaches were implemented and their results were correlated to quantify discontinuities effecting static and fatigue interlaminar fracture behavior of carbon fiber composites. Samples were fabricated by hand layup vacuum bagging manufacturing process under three different vacuum levels, indicated High (-686 mmHg), Moderate (-330 mmHg) and Poor (0 mmHg). Discontinuity content was quantified through-thickness by destructive and nondestructive techniques. Eight different NDE methods were conducted including imaging NDE methods: X-Ray laminography, ultrasonic, high frequency eddy current, pulse thermography, pulse phase thermography and lock-in-thermography, and averaging NDE techniques: X-Ray refraction and thermal conductivity measurements. Samples were subsequently destructively serial sectioned through-thickness into several layers. Both static and fatigue interlaminar fracture behavior under Mode I were conducted. The results of several imaging NDE methods revealed the trend in percentages of discontinuity. However, the results of averaging NDE methods showed a clear correlation since they gave specific values of discontinuity through-thickness. Serial sectioning exposed the composite's internal structure and provided a very clear idea about the type, shape, size, distribution and location of most discontinuities included. The results of mechanical testing showed that discontinuities lead to a decrease in Mode I static interlaminar

  1. Investigation of the effect of vacuum environment on the fatigue and fracture behavior of 7075-T6.

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

    Axial-load fatigue-life, fatigue-crack propagation, and fracture-toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at air pressures ranging from 101 kN/sq m to 7 micronewtons/sq m to determine the effect of air pressure on fatigue behavior. Analysis of the results from the fatigue-life experiments indicated that for a given stress level, the lower the air pressure was the longer the fatigue life. At a pressure of 7 micronewtons/sq m, fatigue lives were 15 to 30 times longer than at 101 kN/sq m. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue-crack-growth rates were approximately twice as high at atmospheric pressure as in vacuum. However, at higher values of stress-intensity range, the fatigue-crack-growth rates were nominally the same in vacuum and at atmospheric pressure.

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

    Science.gov (United States)

    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.

  3. Fatigue and fracture behavior of coiled pipes; Comportamento a fratura e fadiga de tubos bobinados

    Energy Technology Data Exchange (ETDEWEB)

    Pope, Alexandre M.; Silva, Renato M.C. [PETROBRAS, Rio de Janeiro, RJ (Brazil); Frainer, Vitor J; Tarnowski, Gabriel A.; Strohaecker, Telmo R. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil)

    2005-07-01

    The possibility of applying coiled pipes in dynamic situations, such as risers, was investigated through full scale fatigue and fracture tests. A total of sixteen X-65 pipe specimens 41/2'' Od x 0.3'' x 13', containing a bias weld at the mid length, were fatigue tested in a resonance rig at 27 Hz. Six specimens were tested in the as fabricated condition while the ten others were previously subjected to five plastic deformation cycles, simulating reeling operations.. Tests were run until a crack propagated through thickness or 10{sup 7} cycles were achieved. Two cracked specimens were fracture tested in tension. All tests were carried out at room temperature. Test results showed that the fatigue lives were above the Bs-7608 mean class 'B' curves independently whether the specimen were plastically deformed or not. Post fatigue inspection and fractographic examination revealed that fatigue cracks propagate mostly from pits or surface scratches rather than from the bias weld. The two full size tensile specimens failed by ductile fracture at 80% of the material measured strength. (author)

  4. Effect of Process Parameters on Fatigue and Fracture Behavior of Al-Cu-Mg Alloy after Creep Aging

    Directory of Open Access Journals (Sweden)

    Lihua Zhan

    2018-04-01

    Full Text Available A set of creep aging tests at different aging temperatures and stress levels were carried out for Al-Cu-Mg alloy, and the effects of creep aging on strength and fatigue fracture behavior were studied through tensile tests and fatigue crack propagation tests. The microstructures were further analyzed by using scanning electron microscopy (SEM and transmission electron microscopy (TEM. The results show that temperature and stress can obviously affect the creep behavior, mechanical properties, and fatigue life of Al-Cu-Mg alloy. As the aging temperature increases, the fatigue life of alloy first increases, and then decreases. The microstructure also displays a transition from the Guinier-Preston-Bagaryatsky (GPB zones to the precipitation of S phase in the grain interior. However, the precipitation phases grow up and become coarse at excessive temperatures. Increasing stress can narrow the precipitation-free zone (PFZ at the grain boundary and improve the fatigue life, but overhigh stress can produce the opposite result. In summary, the fatigue life of Al-Cu-Mg alloy can be improved by fine-dispersive precipitation phases and a narrow PFZ in a suitable creep aging process.

  5. Observation of fracture behavior of 3-D printed specimens under rolling contact fatigue in water

    Directory of Open Access Journals (Sweden)

    Mizobe Koshiro

    2017-01-01

    Full Text Available Polymer bearing was widely used in the corrosive conditions because of its high corrosion durability. The polymer bearing had been formed using molding and machining until the new 3-D printing method was developed. In this study, we performed the rolling contact fatigue tests of the 3-D printed specimens in water and observed the fracture behaviour of the specimens. We found that the surface cracks are related to both the rolling direction and the lamination directions.

  6. The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Wenke Li

    2016-09-01

    Full Text Available Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that treated by artificial aging is lower than T3; T3 alloy is mainly dominated by GPB region. Meanwhile, the crystal boundary displays continuously distributed fine precipitated phases; after artificial aging and creep aging treatment, a large amount of needle-shaped S′ phases precipitate inside the alloy, while there are wide precipitated phases at the crystal boundary. Wide precipitation free zones appear at the crystal boundary of artificial-aging samples, but precipitation free zones at the alloy crystal boundary of creep aging become narrower and even disappear. It can be seen that creep aging can change the precipitation features of the alloy and improve its fatigue life.

  7. Effect of Si content on fatigue fracture behavior of hot-rolled high-silicon steels

    Science.gov (United States)

    Umezawa, Osamu; Kanda, Jyunichi; Yamazaki, Takao

    2017-05-01

    As the Si content was increased from 1.5 to 5 mass%, both the yield stress and ultimate tensile strength were increased, respectively. The work hardening rate was also increased as the increase of Si content. On the contrary, the elongation was decreased as the increase of Si content, and the fracture manner was shifted from ductile to brittle. The 107 cycles fatigue strength was higher as the increase of Si content. The small misorientation distribution as ladder-like was detected in the grains of 1.5 mass%Si steel. Around the grain boundary, the strain incompatibility was detected in the steels containing over 3 mass%Si. The lattice rotation was locally detected in the vicinity of grain boundaries.

  8. Effect of weld metal toughness on fracture behavior under ultra-low cycle fatigue loading (earthquake)

    Energy Technology Data Exchange (ETDEWEB)

    Kermajani, M. [School of Materials Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Ghaini, F. Malek, E-mail: Fmalek@modares.ac.ir [School of Materials Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Miresmaeili, R. [School of Materials Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Aghakouchak, A.A. [School of Civil Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Shadmand, M. [Department of Research and Development, MAPNA Electric and Control (MECO) Company, Karaj (Iran, Islamic Republic of)

    2016-06-21

    Results from 12 ultra-low cycle fatigue tests performed on the weld metals of both toughness and non-toughness rated grades are presented. Fracture resistance under these loadings seemed to be dependent on materials' toughness, displacement amplitude, and stress state triaxiality, while the toughness effect was more highlighted at high stress levels and concentrations. To study the effect of microstructures on these failures, supporting ancillary tests including all-weld tension coupons, Charpy V-notched impact tests, and optical and scanning electron microscope analyses were performed. The favored microstructures appeared to be those which absorbed energy by plastic deformation and, hence, hindered void formation and/or could avoid crack propagation by deflection. Considering the response of the tested materials to cyclic loadings and the requirements of the materials specified in AISC341 Provisions could question the adequacy of these requirements for weld metals. However, the role of microstructural features like inclusions would be the same in both the Charpy impact tests and ultra-low cycle loadings.

  9. Fatigue and insufficiency fractures

    International Nuclear Information System (INIS)

    Lodwick, G.S.; Rosenthal, D.I.; Kattapuram, S.V.; Hudson, T.M.

    1987-01-01

    The incidence of stress fracture is increasing. In our younger society this is due largely to a preocupation with physical conditioning, but in our elderly population it is due to improved recognition and better methods of detection and diagnosis. Stress fracture of the elderly is an insufficiency fracture which occurs in the spine, the pelvis, the sacrum and other bones afflicted with disorders which cause osteopenia. Stress fracture is frequently misdiagnosed as a malignant lesion of bone resulting in biopsy. Scintiscanning provides the greatest frequency of detection, while computed tomography often provides the definitive diagnosis. With increased interest and experience a better insight into the disease has been achieved, and what was once thought of as a simple manifestation of mechanical stress is now known to be an orderly, complex pattern of physiological changes in bone which conform to a model by Frost. The diffuse nature of these changes can be recognized by scintigraphy, radiography and magnetic resonance imaging. 27 refs.; 8 figs

  10. Two Parameter Fracture Mechanics: Fatigue Crack Behavior under Mixed Mode Conditions

    Czech Academy of Sciences Publication Activity Database

    Seitl, Stanislav; Knésl, Zdeněk

    2008-01-01

    Roč. 75, č. 3-4 (2008), s. 857-865 ISSN 0013-7944. [Crack Paths 2006. Parma, 14.09.2006-16.09.2006] R&D Projects: GA ČR GP101/04/P001 Institutional research plan: CEZ:AV0Z20410507 Keywords : Constraint * Mixed-mode loading * Fatigue crack * Crack growth * Crack path Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.713, year: 2008

  11. An investigation of the fatigue and fracture behavior of a Nb-12Al-44Ti-1.5Mo intermetallic alloy

    International Nuclear Information System (INIS)

    Soboyejo, W.O.; Dipasquale, J.; Ye, F.; Mercer, C.

    1999-01-01

    This article presents the results of a study of the fatigue and fracture behavior of a damage-tolerant Nb-12Al-44Ti-1.5Mo alloy. This partially ordered B2 + orthorhombic intermetallic alloy is shown to have attractive combinations of room-temperature ductility (11 to 14 pct), fracture toughness (60 to 92 MPa√m), and comparable fatigue crack growth resistance to IN718, Ti-6Al-4V, and pure Nb at room temperature. The studies show that tensile deformation in the Nb-12Al-44Ti-1.5Mo alloy involves localized plastic deformation (microplasticity via slip-band formation) which initiates at stress levels that are significantly below the uniaxial yield stress (∼9.6 pct of the 0.2 pct offset yield strength (YS)). The onset of bulk yielding is shown to correspond to the spread of microplasticity completely across the gage sections of the tensile specimen. Fatigue crack initiation is also postulated to occur by the accumulation of microplasticity (coarsening of slip bands). Subsequent fatigue crack growth then occurs by the unzipping of cracks along slip bands that form ahead of the dominant crack tip. The proposed mechanism of fatigue crack growth is analogous to the unzipping crack growth mechanism that was suggested originally by Neumann for crack growth in single-crystal copper. Slower near-threshold fatigue crack growth rates at 750 C are attributed to the shielding effects of oxide-induced crack closure. The fatigue and fracture behavior are also compared to those of pure Nb and emerging high-temperature niobium-based intermetallics

  12. Application of fracture mechanics to fatigue in pressure vessels

    International Nuclear Information System (INIS)

    Ghavami, K.

    1982-01-01

    The methods of application of fracture mechanics to predict fatigue crack propagation in welded structures and pressure vessels are described with the following objectives: i) To identify the effect of different variables such as crack tip plasticity, free surface, finite plate thickness, stress concentration and type of the structure, on the magnitude of stress intensity factor K in Welded joint. ii) To demonstrate the use of fracture mechanics for analysing fatigue crack propagation data. iii) To show how a law of fatigue crack propagation based on fracure mechanics, may be used to predict fatigue behavior of welded structures such as pressure vessel. (Author) [pt

  13. Quantifying voids effecting delamination in carbon/epoxy composites: static and fatigue fracture behavior

    Science.gov (United States)

    Hakim, I.; May, D.; Abo Ras, M.; Meyendorf, N.; Donaldson, S.

    2016-04-01

    On the present work, samples of carbon fiber/epoxy composites with different void levels were fabricated using hand layup vacuum bagging process by varying the pressure. Thermal nondestructive methods: thermal conductivity measurement, pulse thermography, pulse phase thermography and lock-in-thermography, and mechanical testing: modes I and II interlaminar fracture toughness were conducted. Comparing the parameters resulted from the thermal nondestructive testing revealed that voids lead to reductions in thermal properties in all directions of composites. The results of mode I and mode II interlaminar fracture toughness showed that voids lead to reductions in interlaminar fracture toughness. The parameters resulted from thermal nondestructive testing were correlated to the results of mode I and mode II interlaminar fracture toughness and voids were quantified.

  14. Study of Fatigue and Fracture Behavior of Cr-Based Alloys and Intermetallic Materials

    Energy Technology Data Exchange (ETDEWEB)

    He, YH

    2001-01-31

    The microhardness, and tensile and fracture-toughness properties of drop-cast and directionally-solidified Cr-9.25 at.% (atomic percent) Ta alloys have been investigated. Directional solidification was found to soften the alloy, which could be related to the development of equilibrium and aligned microstructures. It was observed that the tensile properties of the Cr-Ta alloys at room and elevated temperatures could be improved by obtaining aligned microstructures. The directionally-solidified alloy also showed increased fracture toughness at room temperature. This trend is mainly associated with crack deflection and the formation of shear ribs in the samples with aligned microstructures. The sample with better-aligned lamellar exhibits greater fracture toughness.

  15. Effect of aging time and aging temperature on fatigue and fracture behavior of 6063 aluminum alloy under seawater influence

    International Nuclear Information System (INIS)

    Siddiqui, R.A.; Abdul-Wahab, S.A.; Pervez, T.

    2008-01-01

    This paper describes experimentally the effect of seawater corrosion, aging time, and aging temperature on the fatigue resistance property of 6063 aluminum alloy. The 6063 aluminum alloy that was used for the study was heat treated and soaked in seawater for different intervals of time between 2 and 30 weeks. It was found that the maximum fatigue resistance property in the 6063 aluminum alloy was observed when aged between 7 and 9 h and heat treated at temperatures between 160 o C and 200 o C. Generally at constant load, the results indicated that the number of cycles to fail the 6063 aluminum alloy decreased with increasing the soaking time in seawater. Moreover, fracture surfaces were considered and studied under a scanning electron microscope (SEM). The results showed that the brittle fracture pattern tended to occur with the increase in aging time and temperature. The fatigue striations were observed very clearly at low and peak aging temperature. The increase in the fatigue resistance property with aging time was linked with the vacancies assisted diffusion mechanism and also by the hindering of dislocation movement by impure atoms

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

    Science.gov (United States)

    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.

  17. Cyclic fatigue-crack propagation, stress-corrosion, and fracture-toughness behavior in pyrolytic carbon-coated graphite for prosthetic heart valve applications.

    Science.gov (United States)

    Ritchie, R O; Dauskardt, R H; Yu, W K; Brendzel, A M

    1990-02-01

    Fracture-mechanics tests were performed to characterize the cyclic fatigue, stress-corrosion cracking, and fracture-toughness behavior of a pyrolytic carbon-coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing "atomically" sharp precracks, both in room-temperature air and principally in a simulated physiological environment of 37 degrees C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistance-curve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa square root of m, and subcritical stress-corrosion crack velocities (da/dt) which were a function of the stress intensity K raised to the 74th power (over the range approximately 10(-9) to over 10(-5) m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue-crack growth rates (da/dN) were seen to be a function of the 19th power of the stress-intensity range delta K (over the range approximately 10(-11) to over 10(-8) m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress-intensity levels, cyclic fatigue in pyrolytic carbon-coated graphite is reasoned to be a vital consideration in the design and life-prediction procedures of prosthetic devices manufactured from this material.

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

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

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

  19. Fatigue Behavior of Inconel 718 TIG Welds

    Science.gov (United States)

    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.

  20. Fatigue fracture modes of a stainless steel

    International Nuclear Information System (INIS)

    Pacheco, D.J.; Souza e Silva, A.S. de; Monteiro, S.N.

    1977-01-01

    The influence of strain hardening and martensite phase transformation on the fatigue fracture regions (pulsative tension) of a Stainless Steel type AISI 316 was investigated. This lead to the conclusion that the greater austenite strain hardening level only favours the occurrence of a brittle fracture. Also, in as much as the static induced martensite is concerned, a direct influence on the failure process was not observed, whereas, apparently, the one transformed under cyclic loading has no contribution to the rupture mechanisms. (author) [pt

  1. Creep, Fatigue and Fracture Behavior of Environmental Barrier Coating and SiC-SiC Ceramic Matrix Composite Systems: The Role of Environment Effects

    Science.gov (United States)

    Zhu, Dongming; Ghosn, Louis J.

    2015-01-01

    Advanced environmental barrier coating (EBC) systems for low emission SiCSiC CMC combustors and turbine airfoils have been developed to meet next generation engine emission and performance goals. This presentation will highlight the developments of NASAs current EBC system technologies for SiC-SiC ceramic matrix composite combustors and turbine airfoils, their performance evaluation and modeling progress towards improving the engine SiCSiC component temperature capability and long-term durability. Our emphasis has also been placed on the fundamental aspects of the EBC-CMC creep and fatigue behaviors, and their interactions with turbine engine oxidizing and moisture environments. The EBC-CMC environmental degradation and failure modes, under various simulated engine testing environments, in particular involving high heat flux, high pressure, high velocity combustion conditions, will be discussed aiming at quantifying the protective coating functions, performance and durability, and in conjunction with damage mechanics and fracture mechanics approaches.

  2. Fatigue and Fracture Characterization of Aircraft Aluminum Alloys Damaged by Prior Corrosion

    National Research Council Canada - National Science Library

    Baldwin, J

    2002-01-01

    At the time of the initiation of this project, there was no comprehensive data describing corrosion's effect on the fatigue and fracture behavior of aluminum alloys typically found in aging aircraft...

  3. Computational predictive methods for fracture and fatigue

    Science.gov (United States)

    Cordes, J.; Chang, A. T.; Nelson, N.; Kim, Y.

    1994-09-01

    The damage-tolerant design philosophy as used by aircraft industries enables aircraft components and aircraft structures to operate safely with minor damage, small cracks, and flaws. Maintenance and inspection procedures insure that damages developed during service remain below design values. When damage is found, repairs or design modifications are implemented and flight is resumed. Design and redesign guidelines, such as military specifications MIL-A-83444, have successfully reduced the incidence of damage and cracks. However, fatigue cracks continue to appear in aircraft well before the design life has expired. The F16 airplane, for instance, developed small cracks in the engine mount, wing support, bulk heads, the fuselage upper skin, the fuel shelf joints, and along the upper wings. Some cracks were found after 600 hours of the 8000 hour design service life and design modifications were required. Tests on the F16 plane showed that the design loading conditions were close to the predicted loading conditions. Improvements to analytic methods for predicting fatigue crack growth adjacent to holes, when multiple damage sites are present, and in corrosive environments would result in more cost-effective designs, fewer repairs, and fewer redesigns. The overall objective of the research described in this paper is to develop, verify, and extend the computational efficiency of analysis procedures necessary for damage tolerant design. This paper describes an elastic/plastic fracture method and an associated fatigue analysis method for damage tolerant design. Both methods are unique in that material parameters such as fracture toughness, R-curve data, and fatigue constants are not required. The methods are implemented with a general-purpose finite element package. Several proof-of-concept examples are given. With further development, the methods could be extended for analysis of multi-site damage, creep-fatigue, and corrosion fatigue problems.

  4. Fatigue and fracture of fibre metal laminates

    CERN Document Server

    Alderliesten, René

    2017-01-01

    This book contributes to the field of hybrid technology, describing the current state of knowledge concerning the hybrid material concept of laminated metallic and composite sheets for primary aeronautical structural applications. It is the only book to date on fatigue and fracture of fibre metal laminates (FMLs). The first section of the book provides a general background of the FML technology, highlighting the major FML types developed and studied over the past decades in conjunction with an overview of industrial developments based on filed patents. In turn, the second section discusses the mechanical response to quasi-static loading, together with the fracture phenomena during quasi-static and cyclic loading. To consider the durability aspects related to strength justification and certification of primary aircraft structures, the third section discusses thermal aspects related to FMLs and their mechanical response to various environmental and acoustic conditions.

  5. Fatigue behavior of niobium--hydrogen alloys

    International Nuclear Information System (INIS)

    Chung, D.W.; Stoloff, N.S.

    1978-01-01

    The effects of hydrogen on room temperature fatigue behavior of niobium were investigated under both high frequency stress control and low frequency strain control conditions, in air. Hydrogen markedly improved the fatigue life in high frequency tests, while low frequency tests resulted in decreased fatigue life with increasing hydrogen content. Notches in hydrogen-charged alloys reduced high cycle life significantly but had little effect on low cycle tests. Fracture surfaces of annealed niobium mainly exhibited striations, with numerous cracks originating at troughs of striated bands in both stress and strain control tests. The fracture mode for alloys with hydrogen in solution was mixed, with striations interspersed with cleavage facets at high frequencies but generally cleavage steps at low frequencies. For the hydrided alloys, distinctive steps of mixed ductile-brittle appearance were revealed under high frequency conditions, but large cleavage facets only were observed for low frequency tests. The results are discussed in terms of the effects of hydrogen on the cyclic strain hardening rate, as well as on fatigue strength and ductility of niobium

  6. Mechanical behavior and fatigue in polymeric composites at low temperatures

    International Nuclear Information System (INIS)

    Katz, Y.; Bussiba, A.; Mathias, H.

    1986-01-01

    Advanced fiber reinforced polymeric composite materials are often suggested as structural materials at low temperature. In this study, graphite epoxy and Kevlar-49/epoxy systems were investigated. Fatigue behavior was emphasized after establishing the standard monotonic mechanical properties, including fracture resistance parameters at 77, 190, and 296 K. Tension-tension fatigue crack propagation testing was carried out at nominal constant stress intensity amplitudes using precracked compact tensile specimens. The crack tip damage zone was measured and tracked by an electro-potential device, opening displacement gage, microscopic observation, and acoustic emission activity recording. Fractograhic and metallographic studies were performed with emphasis on fracture morphology and modes, failure processes, and description of sequential events. On the basis of these experimental results, the problem of fatigue resistance, including low temperature effects, is analyzed and discussed. The fundamental concepts of fatigue in composites are assessed, particularly in terms of fracture mechanics methods

  7. Fracture Mechanics Prediction of Fatigue Life of Aluminum Highway Bridges

    DEFF Research Database (Denmark)

    Rom, Søren; Agerskov, Henning

    2015-01-01

    Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations. The fati......Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations...... against fatigue in aluminum bridges, may give results which are unconservative. Furthermore, it was in both investigations found that the validity of the results obtained from Miner's rule will depend on the distribution of the load history in tension and compression....

  8. Evaluation of fatigue crack growth and fracture resistance of SA350 LF2 material

    International Nuclear Information System (INIS)

    Singh, P.K.; Dubey, J.S.; Chakrabarty, J.K.; Vaze, K.K.; Kushwaha, H.S.

    2003-01-01

    The aim of the present paper is to evaluate the tensile and fracture mechanics properties of the SA350 LF2 carbon steel material used as the Header material in the primary heat transport (PHT) system piping of the Indian pressurized heavy water reactors (PHWR). Tensile, fatigue crack growth rate and fracture toughness tests have been carried out on specimens machined from the Header of the actual PHT pipes. The effect of temperature on tensile properties has been discussed. The effect of temperature and notch orientation on fracture resistance behavior of the material and fatigue crack growth rate dependence on the notch orientation and stress ratio has also been discussed. (author)

  9. Fatigue fracture of the sacrum in an adolescent

    International Nuclear Information System (INIS)

    Patterson, Scott P.; Daffner, Richard H.; Sciulli, Robert L.; Schneck-Jacob, Stephanie L.

    2004-01-01

    There are relatively few reports of sacral stress fractures in children. In adolescents, sacral stress fractures have been reported in patients involved in vigorous athletic activity. Recognition of these fractures is important to avoid unnecessary biopsy if the findings are confused with tumor or infection. We report a sacral fatigue fracture in a 15-year-old without a history of athletic participation or trauma. (orig.)

  10. Hydrologic behavior of fracture networks

    International Nuclear Information System (INIS)

    Long, J.C.S.; Endo, H.K.; Karasaki, K.; Pyrak, L.; MacLean, P.; Witherspoon, P.A.

    1985-01-01

    This paper reviews recent research on the nature of flow and transport in discontinuous fracture networks. The hydrologic behavior of these networks has been examined using two- and three-dimensional numerical models. The numerical models represent random realizations of fracture networks based on statistical field measurements of fracture geometry and equivalent hydraulic aperture. The authors have compared the flux and mechanical transported behavior of these networks to the behavior of equivalent continua. In this way they were able to determine whether a given fracture network could be modeled as an equivalent porous media in both flux and advective transport studies. They have examined departures from porous media behavior both as a function of interconnectivity and heterogeneity. Parameter studies have revealed behavior patterns such as: given a fracture frequency that can be measured in the field, porous media like behavior and the magnitude of permeability are both enhanced if the fractures are longer and the standard deviation of fracture permeabilities is smaller. The behavior of well tests in fractured networks has been modeled and compared to a new analytical well test solution which accounts for the early time dominance of the fractures intersecting the well. Finally, a three-dimensional fracture flow model has been constructed which assumes fractures are randomly located discs. This model has been constructed which assumes fractures are randomly located discs. This model uses a semi-analytical solution for flow such that it is relatively easy to use the model as a tool for stochastic analysis. 13 references, 12 figures

  11. Fatigue-crack propagation behavior of Inconel 600

    International Nuclear Information System (INIS)

    James, L.A.

    1976-05-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effects of several parameters upon the fatigue-crack propagation behavior of Inconel 600. The parameters studied included temperature, cyclic frequency, stress ratio, thermal aging, and a limited amount of testing in a liquid sodium environment

  12. Fatigue-crack propagation behavior of Inconel 718

    International Nuclear Information System (INIS)

    James, L.A.

    1975-09-01

    The techniques of linear-elastic fracture mechanics were used to characterize the effect of several variables (temperature, environment, cyclic frequency, stress ratio, and heat-treatment variations) upon the fatigue-crack growth behavior of Inconel 718 base metal and weldments. Relevant crack growth data on this alloy from other laboratories is also presented. (33 fig, 39 references)

  13. Thermal fatigue behavior of valves

    International Nuclear Information System (INIS)

    Moinereau, D.; Scliffet, L.; Capion, J.C.; Genette, P.

    1991-01-01

    This paper reports that valves of pressurized water reactors are exposed to thermal shocks during transient operations. The numerous thermal shock tests performed on valves on the EDF test facilities have shown the sensibility of fillets and geometrical discontinuities to thermal fatigue: cracks can appear in those areas and grow through the valve body. Valves systems designated as level 1 must be designed to withstand fatigue up to the second isolation valve: the relevant rule is specified in the paragraph B 3500 of the French RCCM code. It is a simplified method which doesn't require finite element calculations. Many valve systems have been designed according to this rule and have been operated without accident. However, in one case, important cracks were found in the fillet of a check-valve after numerous thermal shocks. Calculation of the valve's behavior according to the RCCM code to estimate the fatigue damage resulting from thermal shocks led to a low damage factor, which doesn't agree with the experimental results. This was confirmed by new testings and showed the inadequacy of B 3500 rule for thermal transients. On this base a new rule is proposed to estimate fatigue damage resulting from thermal shocks. An experimental program has been realized to validate this rule. Axisymetrical analytical mock-ups with different geometries and one check-valve in austenitic stainless steel 316 L have been submitted to hot thermal shocks of 210 degrees C magnitude

  14. Failure by fracture and fatigue in 'NANO' and 'BIO'materials

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, R.O.; Muhlstein, C.L.; Nalla, R.K.

    2003-12-19

    The behavior of nanostructured materials/small-volumestructures and biologi-cal/bio-implantable materials, so-called "nano"and "bio" materials, is currently much in vogue in materials science. Oneaspect of this field, which to date has received only limited attention,is their fracture and fatigue properties. In this paper, we examine twotopics in this area, namely the premature fatigue failure ofsilicon-based micron-scale structures for microelectromechanical systems(MEMS), and the fracture properties of mineralized tissue, specificallyhuman bone.

  15. 2014 New Trends in Fatigue and Fracture Conference

    CERN Document Server

    Milovic, Ljubica

    2017-01-01

    This book is a compilation of selected papers from the 2014 New Trends in Fatigue and Fracture (NT2F14) Conference, which was held in Belgrade, Serbia. This prestigious conference brought together delegates from around the globe to discuss how to characterize, predict and analyze the fatigue and fracture of engineering materials, components, and structures using theoretical, experimental, numerical and practical approaches. It highlights some important new trends in fracture mechanics presented at the conference, such as: • two-parameter fracture mechanics, arising from the coupling of fracture toughness and stress constraints • high-performance steel for gas and oil transportation and production (pressure vessels and boilers) • safety and reliability of welded joints This book includes 12 contributions from well-known international scientists and a special tribute dedicated to the scientific contributions of Stojan Sedmark, who passed away in 2014.

  16. Corrosion fatigue behavior of high strength brass in aqueous solutions

    Energy Technology Data Exchange (ETDEWEB)

    Hamada, A.S.; Kassem, M.A.; Ramadan, R.M.; El-Zeky, M.A. [Suez Canal Univ., Dept. of Metallurgy and Materials Engineering (Egypt)

    2000-07-01

    Corrosion fatigue behavior of British Standard high strength brass, CZ 127 has been studied in various environments, 3.5%NaC1 solution and 3.5%NaC1 containing 1000ppm ammonia by applying the reverse bending technique, strain-controlled cyclic, at 67 cycles/min. Characteristics of the produced alloy were studied using differential thermal analysis with applying its results in heat treating of the alloy; metallographic examinations; hardness measurements; X-ray; and electrochemical behavior of the unstressed alloy. CZ 127 was fatigued at three different conditions, solution treated, peak aged, and over aged at a fixed strain amplitude, 0.03 5. Solution treated alloy gave the best fatigue properties in all environments tested among the other materials. Results of the alloy studied were compared with that obtained of 70/30 {alpha}-brass. Fracture surface of the fatigued alloy was examined using optical microscope and scanning electron microscope equipped with EDX. (author)

  17. Corrosion fatigue behavior of high strength brass in aqueous solutions

    International Nuclear Information System (INIS)

    Hamada, A.S.; Kassem, M.A.; Ramadan, R.M.; El-Zeky, M.A.

    2000-01-01

    Corrosion fatigue behavior of British Standard high strength brass, CZ 127 has been studied in various environments, 3.5%NaC1 solution and 3.5%NaC1 containing 1000ppm ammonia by applying the reverse bending technique, strain-controlled cyclic, at 67 cycles/min. Characteristics of the produced alloy were studied using differential thermal analysis with applying its results in heat treating of the alloy; metallographic examinations; hardness measurements; X-ray; and electrochemical behavior of the unstressed alloy. CZ 127 was fatigued at three different conditions, solution treated, peak aged, and over aged at a fixed strain amplitude, 0.03 5. Solution treated alloy gave the best fatigue properties in all environments tested among the other materials. Results of the alloy studied were compared with that obtained of 70/30 α-brass. Fracture surface of the fatigued alloy was examined using optical microscope and scanning electron microscope equipped with EDX. (author)

  18. Three-point bending fatigue behavior of WC–Co cemented carbides

    International Nuclear Information System (INIS)

    Li, Anhai; Zhao, Jun; Wang, Dong; Gao, Xinliang; Tang, Hongwei

    2013-01-01

    Highlights: ► Mechanical fatigue tests were conducted on a specific designed jig. ► Three-point bending fatigue behavior of WC–Co cemented carbides was studied. ► Fatigue mechanisms of WC–Co cemented carbides with different WC grain sizes and Co binder contents were revealed. -- Abstract: WC–Co cemented carbides with different WC grain sizes and Co binder contents were sintered and fabricated. The three-point bending specimens with a single edge notch were prepared for tests. In the experiments, the mechanical properties of materials were investigated under static and cyclic loads (20 Hz) in air at room temperature. The fatigue behaviors of the materials under the same applied loading conditions are presented and discussed. Optical microscope and scanning electron microscopy were used to investigate the micro-mechanisms of damage during fatigue, and the results were used to correlate with the mechanical fatigue behavior of WC–Co cemented carbides. Experimental results indicated that the fatigue fracture surfaces exhibited more fracture origins and diversification of crack propagation paths than the static strength fracture surfaces. The fatigue fracture typically originates from inhomogeneities or defects such as micropores or aggregates of WC grains near the notch tip. Moreover, due to the diversity and complexity of the fatigue mechanisms, together with the evolution of the crack tip and the ductile deformation zone, the fatigue properties of WC–Co cemented carbides were largely relevant with the combination of transverse rupture strength and fracture toughness, rather than only one of them. Transverse rupture strength dominated the fatigue behavior of carbides with low Co content, whilst the fatigue behavior of carbides with high Co content was determined by fracture toughness.

  19. Hydrologic behavior of fracture networks

    International Nuclear Information System (INIS)

    Long, J.C.S.; Endo, H.K.; Karasaki, K.; Pyrak, L.; MacLean, P.; Witherspoon, P.A.

    1984-10-01

    This paper reviews recent research on the nature of flow and transport in discontinuous fracture networks. The hydrologic behavior of these networks has been examined using two- and three-dimensional numerical models. The numerical models represent random realizations of fracture networks based on statistical field measurements of fracture geometry and equivalent hydraulic aperture. We have compared the flux and mechanical transport behavior of these networks to the behavior of equivalent continua. In this way we are able to determine whether a given fracture network can be modeled as an equivalent porous media in both flux and advective transport studies. We have examined departures from porous media behavior both as a function of interconnectivity and heterogeneity. Parameter studies have revealed behavior patterns such as: given a fracture frequency that can be measured in the field, porous media like behavior and the magnitude of permeability are both enhanced if the fractures are longer and the standard deviation of fracture permeabilities is smaller. Transport studies have shown that the ratio between flux and velocity is not necessarily constant when the direction of flow is changed in systems which do behave like a porous media for flux. Thus the conditions under which porous media analysis can be used in transport studies are more restrictive than the condition for flux studies. We have examined systems which do not behave like porous media and have shown how the in situ behavior varies as a function of scale of observation. The behavior of well tests in fractured networks has been modeled and compared to a new analytical well test solution which accounts for the early time dominance of the fractures intersecting the well. Finally, a three-dimensional fracture flow model has been constructed which assumes fractures are randomly located discs. 13 references, 12 figures

  20. Quantitative x-ray fractographic analysis of fatigue fractures

    International Nuclear Information System (INIS)

    Saprykin, Yu.V.

    1983-01-01

    The study deals with quantitative X-ray fractographic investigation of fatigue fractures of samples with sharp notches tested at various stresses and temperatures with the purpose of establishing a connection between material crack resistance parameters and local plastic instability zones restraining and controlling the crack growth. At fatigue fractures of notched Kh18N9T steel samples tested at +20 and -196 deg C a zone of sharp ring notch effect being analogous to the zone in which crack growth rate is controlled by the microshifting mechanisms is singled out. The size of the notched effect zone in the investigate steel is unambiguosly bound to to the stress amplitude. This provides the possibility to determine the stress value by the results of quantitative fractographic analysis of notched sample fractures. A possibility of determining one of the threshold values of cyclic material fracture toughness by the results of fatigue testing and fractography of notched sample fractures is shown. Correlation between the size of the hsub(s) crack effect zone in the notched sample, delta material yield limit and characteristic of cyclic Ksub(s) fracture toughness has been found. Such correlation widens the possibilities of quantitative diagnostics of fractures by the methods of X-ray fractography

  1. Cyclic Fracture Toughness of Railway Axle and Mechanisms of its Fatigue Fracture

    Directory of Open Access Journals (Sweden)

    Sorochak Andriy

    2015-06-01

    Full Text Available The main regularities in fatigue fracture of the railway axle material - the OSL steel - are found in this paper. Micromechanisms of fatigue crack propagation are described and systematized, and a physical-mechanical interpretation of the relief morphology at different stages of crack propagation is proposed for fatigue cracks in specimens cut out of the surface, internal and central layers of the axle.

  2. Mean load effect on fatigue of welded joints using structural stress and fracture mechanics approach

    International Nuclear Information System (INIS)

    Kim, Jong Sung; Kim, Cheol; Jin, Tae Eun; Dong, P.

    2006-01-01

    In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B and PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ΔK characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints

  3. Fracture and Fatigue: Some New Insights

    Indian Academy of Sciences (India)

    It is over nine decades since fracture mechanics found its importance in the design of mechanical, aerospace and civil engineering structures. Its application started in naval structures during the early part of 20th century. The theory of fracture mechanics was initially found ideal to explain the failure of brittle materials like ...

  4. Cyclic deformation and fatigue behaviors of Hadfield manganese steel

    Energy Technology Data Exchange (ETDEWEB)

    Kang, J. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, F.C., E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Long, X.Y. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, B. [School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2014-01-03

    The cyclic deformation characteristics and fatigue behaviors of Hadfield manganese steel have been investigated by means of its ability to memorize strain and stress history. Detailed studies were performed on the strain-controlled low cycle fatigue (LCF) and stress-controlled high cycle fatigue (HCF). Initial cyclic hardening to saturation or peak stress followed by softening to fracture occurred in LCF. Internal stress made the dominant contribution to the fatigue crack propagation until failure. Effective stress evolution revealed the existence of C–Mn clusters with short-range ordering in Hadfield manganese steel and demonstrated that the interaction between C atoms in the C–Mn cluster and dislocation was essential for its cyclic hardening. The developing/developed dislocation cells and stacking faults were the main cyclic deformation microstructures on the fractured sample surface in LCF and HCF, which manifested that fatigue failure behavior of Hadfield manganese steel was induced by plastic deformation during strain-controlled or stress-controlled testing.

  5. Micro- and macroapproaches in fracture mechanics for interpreting brittle fracture and fatigue crack growth

    International Nuclear Information System (INIS)

    Ekobori, T.; Konosu, S.; Ekobori, A.

    1980-01-01

    Classified are models of the crack growth mechanism, and in the framework of the fracture mechanics suggested are combined micro- and macroapproaches to interpreting the criterion of the brittle fracture and fatigue crack growth as fracture typical examples, when temporal processes are important or unimportant. Under the brittle fracture conditions the crack propagation criterion is shown to be brought with the high accuracy to a form analogous to one of the crack propagation in a linear fracture mechanics although it is expressed with micro- and macrostructures. Obtained is a good agreement between theoretical and experimental data

  6. Creep fracture and creep-fatigue fracture in ceramics and ceramic composites

    International Nuclear Information System (INIS)

    Suresh, S.

    1993-01-01

    This paper summarizes recent advances in the areas of subcritical crack growth in ceramics subjected to static and cyclic loads at elevated temperatures. Attention is devoted to the specific role of pre-existing and in-situ-formed glass films in influencing creep fracture and creep-fatigue fracture. Experimental results on the effects of cyclic frequency and load ratio, along with detailed transmission electron microscopy of crack-tip and crack-wake damage are highlighted. Some general conclusions are drawn about the dependence of high-temperature damage tolerance on interfacial glass films and about the susceptibility of ceramic materials to cyclic fatigue fracture

  7. Fatigue-crack growth behavior in dissimilar metal weldments

    International Nuclear Information System (INIS)

    James, L.A.

    1977-03-01

    The techniques of linear-elastic fracture mechanics were used to characterize fatigue-crack propagation behavior in three dissimilar metal weldments at test temperatures of 800 0 F (427 0 C) and 1000 0 F (538 0 C). The weldments studied included Inconel 718/Type 316, all using Inconel 82 as the filler metal. In general, fatigue-crack growth rates in the weldments were equal to, or less than, those observed in the base metals. Crack deviation from the expected path perpendicular to the loading axis was noted in some cases, and is discussed

  8. Probabilistic finite elements for fatigue and fracture analysis

    Science.gov (United States)

    Belytschko, Ted; Liu, Wing Kam

    1993-04-01

    An overview of the probabilistic finite element method (PFEM) developed by the authors and their colleagues in recent years is presented. The primary focus is placed on the development of PFEM for both structural mechanics problems and fracture mechanics problems. The perturbation techniques are used as major tools for the analytical derivation. The following topics are covered: (1) representation and discretization of random fields; (2) development of PFEM for the general linear transient problem and nonlinear elasticity using Hu-Washizu variational principle; (3) computational aspects; (4) discussions of the application of PFEM to the reliability analysis of both brittle fracture and fatigue; and (5) a stochastic computational tool based on stochastic boundary element (SBEM). Results are obtained for the reliability index and corresponding probability of failure for: (1) fatigue crack growth; (2) defect geometry; (3) fatigue parameters; and (4) applied loads. These results show that initial defect is a critical parameter.

  9. Fatigue stress fractures of the sacrum: diagnosis with MR imaging

    International Nuclear Information System (INIS)

    Ahovuo, J.A.; Vusuri, T.

    2004-01-01

    The aim of this study was to describe the MRI findings and clinical observations in a fatigue stress fracture of the sacrum. In this retrospective study, 380 conscripts (53 women, 327 men; age range 18-29 years, mean age 20.7 years) who suffered from stress-related hip pain were studied with MRI of the pelvis. The findings of MRI were evaluated with regard to stress fracture of the sacrum. Thirty-one (8%) patients had MRI changes in signal intensity of the cranial part of the sacrum, extending to the first and second sacral foramina. The MRI changes in signal intensity were intermediate on T1-weighted images, and high on short tau inversion recovery or T2-weighted fat-suppressed images. A linear signal void fracture line was also seen. Multiple stress injuries to the pelvic bones were also seen in 7 of 31 (23%) patients. Five patients (16%) had bilateral sacral stress fracture. Fatigue sacral stress fractures appeared more commonly in women than in men (p<0.001). During recovery time 20 of the 31 patients underwent control MRI, and fatty marrow conversion was seen in 8 (40%) cases as high signal intensity on T1-weighted images, which disappeared 5-6 months after the onset of symptoms. Fatigue sacral stress fractures are associated with stress-related hip pain. These fractures were more common in women than in men. Other stress injuries of the pelvis may be seen simultaneously with sacral stress fractures. Signal intensity of the sacrum was normal after 5-6 months

  10. Static and Fatigue Behavior Investigation of Artificial Notched Steel Reinforcement

    Directory of Open Access Journals (Sweden)

    Yafei Ma

    2017-05-01

    Full Text Available Pitting corrosion is one of the most common forms of localized corrosion. Corrosion pit results in a stress concentration and fatigue cracks usually initiate and propagate from these corrosion pits. Aging structures may fracture when the fatigue crack reaches a critical size. This paper experimentally simulates the effects of pitting morphologies on the static and fatigue behavior of steel bars. Four artificial notch shapes are considered: radial ellipse, axial ellipse, triangle and length-variable triangle. Each shape notch includes six sizes to simulate a variety of pitting corrosion morphologies. The stress-strain curves of steel bars with different notch shape and depth are obtained based on static tensile testing, and the stress concentration coefficients for various conditions are determined. It was determined that the triangular notch has the highest stress concentration coefficient, followed by length-variable triangle, radial ellipse and axial ellipse shaped notches. Subsequently, the effects of notch depth and notch aspect ratios on the fatigue life under three stress levels are investigated by fatigue testing, and the equations for stress range-fatigue life-notch depth are obtained. Several conclusions are drawn based on the proposed study. The established relationships provide an experimental reference for evaluating the fatigue life of concrete bridges.

  11. Effect of temperature upon the fatigue-crack propagation behavior of Inconel X-750

    International Nuclear Information System (INIS)

    James, L.A.

    1976-05-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of precipitation heat-treated Inconel X-750 in an air environment over the range 75-1200 0 F. In general, fatigue-crack growth rates increased with increasing test temperature

  12. Committee III.2 Fatigue and Fracture

    DEFF Research Database (Denmark)

    Brennan, F. P.; Branner, Kim; den Besten, J.H.

    2015-01-01

    Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service. Consider......Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service...

  13. Fracture behavior of human molars.

    Science.gov (United States)

    Keown, Amanda J; Lee, James J-W; Bush, Mark B

    2012-12-01

    Despite the durability of human teeth, which are able to withstand repeated loading while maintaining form and function, they are still susceptible to fracture. We focus here on longitudinal fracture in molar teeth-channel-like cracks that run along the enamel sidewall of the tooth between the gum line (cemento-enamel junction-CEJ) and the occlusal surface. Such fractures can often be painful and necessitate costly restorative work. The following study describes fracture experiments made on molar teeth of humans in which the molars are placed under axial compressive load using a hard indenting plate in order to induce longitudinal cracks in the enamel. Observed damage modes include fractures originating in the occlusal region ('radial-median cracks') and fractures emanating from the margin of the enamel in the region of the CEJ ('margin cracks'), as well as 'spalling' of enamel (the linking of longitudinal cracks). The loading conditions that govern fracture behavior in enamel are reported and observations made of the evolution of fracture as the load is increased. Relatively low loads were required to induce observable crack initiation-approximately 100 N for radial-median cracks and 200 N for margin cracks-both of which are less than the reported maximum biting force on a single molar tooth of several hundred Newtons. Unstable crack growth was observed to take place soon after and occurred at loads lower than those calculated by the current fracture models. Multiple cracks were observed on a single cusp, their interactions influencing crack growth behavior. The majority of the teeth tested in this study were noted to exhibit margin cracks prior to compression testing, which were apparently formed during the functional lifetime of the tooth. Such teeth were still able to withstand additional loading prior to catastrophic fracture, highlighting the remarkable damage containment capabilities of the natural tooth structure.

  14. Hydrogen effect on the fatigue behavior of LBM Inconel 718

    Directory of Open Access Journals (Sweden)

    Puydebois Simon

    2018-01-01

    Full Text Available For several years, Inconel 718 made by Laser Beam Melting (LBM has been used for components of the Ariane propulsion systems manufactured by ArianeGroup. In the aerospace field, many components of space engines are used under hydrogen environment. The risk of hydrogen embrittlement (HE can be therefore a first order problem. Consequently, to improve the HE sensitivity of LBM Inconel 718, a systematic approach needs to be developed to characterize the microstructure at different scales and its interaction with hydrogen. This study addresses the impact of gaseous hydrogen on the material mechanical behavior under fatigue loadings. In a first step, the low cycle fatigue behavior under 300 bar of hydrogen gas has been evaluated with specimen loaded at a constant load ratio of R=0.1 and a frequency of 0.5 Hz. A reduction in the cycle number of fracture is shown. This reduction of fatigue life is a consequence of the impact of hydrogen damage processes. The impact of hydrogen is evaluated at the stages of crack initiation, crack propagation. These results are discussed in relation with the hydrogen embrittlement mechanisms and particularly in terms of hydrogen / plasticity interactions. To achieve this, the fracture surface morphology was first examined using scanning electron microscopy and second samples near the fracture surface were extracted using Focused-Ion Beam machining from regions containing striation. The main result observed is a reduction of the size of dislocation organization in relation with a decrease of the striation distance.

  15. Experimental study on creep-fatigue interaction behavior of GH4133B superalloy

    International Nuclear Information System (INIS)

    Hu Dianyin; Wang Rongqiao

    2009-01-01

    The creep-fatigue tests have been conducted with nickel-based superalloy GH4133B at 600 deg. C in three cases of type loading to study the creep-fatigue behavior of the alloy and the loading history effect on the creep-fatigue damage. Since the conventional linear cumulative damage rule failed in evaluating the creep-fatigue life based on experimental data, a continuous non-linear model proposed by Mao et al. was employed to describe the creep-fatigue interaction. The creep-fatigue damage in the cases of continuous cyclic creep loading (CF) and prior fatigue followed by creep loading (F + C) was larger than unity and smaller than unity when the type loading was prior creep followed by fatigue loading (C + F). Scanning electron microscope (SEM) analyses of the fracture surface showed that the cracks initiated from the specimen surface and the fracture modes in different loading history were different. The crack mode at CF loading depended on the cyclic period. In the case of F + C loading, the primary fracture mode was transgranular, and in the condition where the type of waveform was C + F, the fracture mode was of mixed transgranular and intergranular type. In addition, the origin of the history effect on creep-fatigue interaction was explained by the SEM observations.

  16. Probabilistic finite elements for fracture and fatigue analysis

    Science.gov (United States)

    Liu, W. K.; Belytschko, T.; Lawrence, M.; Besterfield, G. H.

    1989-01-01

    The fusion of the probabilistic finite element method (PFEM) and reliability analysis for probabilistic fracture mechanics (PFM) is presented. A comprehensive method for determining the probability of fatigue failure for curved crack growth was developed. The criterion for failure or performance function is stated as: the fatigue life of a component must exceed the service life of the component; otherwise failure will occur. An enriched element that has the near-crack-tip singular strain field embedded in the element is used to formulate the equilibrium equation and solve for the stress intensity factors at the crack-tip. Performance and accuracy of the method is demonstrated on a classical mode 1 fatigue problem.

  17. Fatigue fracture of steel after mechanical and ultrasonic strengthening

    International Nuclear Information System (INIS)

    Stotskij, I.M.

    1978-01-01

    Fatigue fracture surfaces of samples after mechanical and ultrasonic strengthening have been studied metallographically and by electron fractography. Studied was the 40Kh steel hardened from 850 deg and then tempered at 180 deg or at 550 deg C. The ultrasound power was 25 kWt, the frequency was 20 kHz, the sample rotation velocity was 39.5 m/min. Mechanical and ultrasonic treatment was found to cause structural changes (formation of a white layer) and deformation of the material under the layer. The fatigue cracks were extending beyond the white layer; their propagation involved generation and coalescence of microcracks on account of segregation of carbides. It is concluded that mechanical and ultrasonic treatment should be used for increasing the fatigue strength of low and average strength materials rather than hardened or low-tempered ones

  18. X-ray fractography of fatigue fracture surface under mode I and mode III loading

    International Nuclear Information System (INIS)

    Akiniwa, Yoshiaki; Tanaka, Keisuke; Tsumura, Tsuyoshi

    2001-01-01

    The propagation behavior of a circumferential fatigue crack in cylindrical bars of a carbon steel (JIS SGV410) and a stainless steel (JIS SUS316NG) was investigated under cyclic axial and torsional loadings. The J-integral range was used as a fracture mechanics parameter. When compared at the same J-integral range, the crack propagation rate under mode III was smaller than that under mode I. Parallel markings perpendicular to the crack propagation direction were observed on the fatigue fracture surface obtained under mode III loading. The residual stresses in the radial direction, σ r , and in the tangential direction, σ θ , were measured for both mode I and mode III fatigue fracture surfaces. For mode I fracture surface, σ r was tension, and was almost constant irrespective of the applied J-integral range. σ θ was close to zero for both materials. On the other hand, for mode III, σ r and σ θ were compression. For SUS316NG steel, the compressive stress of σ θ increased with the J-integral range. For SGV410 steel, the change of σ θ with the J-integral range was small. The breadth of diffraction profiles increased with J-integral range for both mode I and III. The breadth was found to be a good parameter to evaluate the applied J-integral range. (author)

  19. Corrosion fatigue behaviors of steel wires used in coalmine

    International Nuclear Information System (INIS)

    Wang, Songquan; Zhang, Dekun; Chen, Kai; Xu, Linmin; Ge, Shirong

    2014-01-01

    Highlights: • The CF life of steel wire in acid solution is the shortest. • The fatigue source zone showed dimple morphology when coupled with anode potential. • The area of dimple increases with the increase of the applied anode potential. • The strong cathode potential cannot reduce the CF life of the smooth steel wire. • The hydrogen impacted mainly on the plastic deformation of the wire surface. - Abstract: The corrosion fatigue (CF) behaviors of the mining steel wire in different solutions at different applied polarization potentials were investigated in this paper. The surfaces and fracture morphologies of the steel wire at different applied potentials were observed by scanning electron microscope (SEM). The results showed that the CF life of steel wire in acid solution is the shortest. Moreover, the strong anodic polarization potential greatly reduced the CF life of steel wire, while the strong cathode potential did not reduce the CF life. For the smooth steel wire, the hydrogen impacted mainly on the plastic deformation of the wire surface. There was obvious dimple in the fatigue source zone of the wire when coupled with anode potential, and the area of the dimple increased with the increase of the applied anode potential. Conversely, the fatigue source zone of the fracture was relatively smooth at cathode polarization potential, which indicated that the crack propagation followed the mechanism of hydrogen induced cracking

  20. Fatigue and fracture mechanics in pressure vessels and piping. PVP-Volume 304

    International Nuclear Information System (INIS)

    Mehta, H.S.; Wilkowski, G.; Takezono, S.; Bloom, J.; Yoon, K.; Aoki, S.; Rahman, S.; Nakamura, T.; Brust, F.; Yoshimura, S.

    1995-01-01

    Fracture mechanics and fatigue evaluations are an important part of the structural integrity analyses to assure safe operation of pressure vessels and piping components during their service life. The paper presented in this volume illustrate the application of fatigue and fracture mechanics techniques to assess the structural integrity of a wide variety of Pressure Vessels and Piping components. The papers are organized in six sections: (1) fatigue and fracture--vessels; (2) fatigue and fracture--piping; (3) fatigue and fracture--material property evaluations; (4) constraint effects in fracture mechanics; (5) probabilistic fracture mechanics analyses; and (6) user's experience with failure assessment diagrams. Separate abstracts were prepared for most of the papers in this book

  1. Low cycle fatigue behavior of die cast Mg-Al-Mn-Ce magnesium alloy

    Directory of Open Access Journals (Sweden)

    Wu Wei

    2013-11-01

    Full Text Available Fatigue failure is a main failure mode for magnesium and other alloys. It is beneficial for fatigue design and fatigue life improvement to investigate the low cycle fatigue behavior of magnesium alloys. In order to investigate the low cycle fatigue behavior of die cast Mg-Al-Mn-Ce magnesium alloy, the strain controlled fatigue experiments were performed at room temperature and fatigue fracture surfaces of specimens were observed with scanning election microscopy for the alloys under die-cast and aged states. Cyclic stress response curves, strain amplitude versus reversals to failure curve, total strain amplitude versus fatigue life curves and cyclic stress-strain curves of Mg-Al-Mn-Ce alloys were analyzed. The results show that the Mg-Al-Mn-Ce alloys under die-cast (F and aged (T5 states exhibit cyclic strain hardening under the applied total strain amplitudes, and aging treatment could greatly increase the cyclic stress amplitudes of die cast Mg-Al-Mn-Ce alloys. The relationships between the plastic strain amplitude, the elastic strain amplitude and reversals to failure of Mg-Al-Mn-Ce magnesium alloy under different treatment states could be described by Coffin-Manson and Basquin equations, respectively. Observations on the fatigue fracture surface of specimens reveal that the fatigue cracks initiate on the surface of specimens and propagate transgranularly.

  2. The Fatigue Behavior of Steel Structures under Random Loading

    DEFF Research Database (Denmark)

    Agerskov, Henning

    2008-01-01

    Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part...... and variable amplitude fatigue test results. Both the fracture mechanics analysis and the fatigue test results indicate that Miner’s rule, which is normally used in the design against fatigue in steel structures, may give results, which are unconservative, and that the validity of the results obtained from...

  3. Experimental Investigation and Finite Element Analysis on Fatigue Behavior of Aluminum Alloy 7050 Single-Lap Joints

    Science.gov (United States)

    Zhou, Bing; Cui, Hao; Liu, Haibo; Li, Yang; Liu, Gaofeng; Li, Shujun; Zhang, Shangzhou

    2018-03-01

    The fatigue behavior of single-lap four-riveted aluminum alloy 7050 joints was investigated by using high-frequency fatigue test and scanning electron microscope (SEM). Stress distributions obtained by finite element (FE) analysis help explain the fatigue performance. The fatigue test results showed that the fatigue lives of the joints depend on cold expansion and applied cyclic loads. FE analysis and fractography indicated that the improved fatigue lives can be attributed to the reduction in maximum stress and evolution of fatigue damage at the critical location. The beneficial effects of strengthening techniques result in tearing ridges or lamellar structure on fracture surface, decrease in fatigue striations spacing, delay of fatigue crack initiation, crack deflection in fatigue crack propagation and plasticity-induced crack closure.

  4. Effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280

    International Nuclear Information System (INIS)

    James, L.A.

    1976-05-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280 in an air environment. Also included in this study are survey tests to determine the effects of thermal aging and stress ratio upon crack growth behavior in this alloy

  5. Fatigue and fracture toughness characteristics of laser rapid manufactured Inconel 625 structures

    International Nuclear Information System (INIS)

    Ganesh, P.; Kaul, R.; Paul, C.P.; Tiwari, Pragya; Rai, S.K.; Prasad, R.C.; Kukreja, L.M.

    2010-01-01

    Research highlights: → Mechanical test results of Laser rapid manufactured (LRM) Inconel 625 are reported. → 12 and 25 mm thick CT specimens of LRM Inconel 625 showed similar fatigue crack growth. → Stage II crack growth behavior is observed in the investigated ΔK range. → Fracture toughness testing by J-integral method yielded J 1c of about 200-250 kJ/m 2 . - Abstract: Fatigue crack growth and fracture toughness characteristics of laser rapid manufactured (LRMed) Inconel 625 compact tension specimens of thickness 12 and 25 mm were investigated. Fatigue crack propagation in all the specimens investigated in the stress intensity range (ΔK) of 14-38 MPa√m, exhibited stage II crack growth in Paris' regime with nearly same slopes of crack growth per cycle versus ΔK plot. Fatigue crack growth rates in the LRMed specimens of present study were found to be lower than the reported values for wrought Inconel 625 in the ΔK range of 14-24 MPa√m and above this range they tended to coincide. X-ray diffraction patterns of the fractured surfaces revealed that the crack propagated along the growth direction of the specimens which was predominantly along the (1 1 1) plane. The fracture toughness values (J 0.2 ) for LRMed Inconel 625 specimens were found to be in the range of about 200-255 kJ/m 2 . The LRMed specimens exhibited stable crack growth during the J-integral test.

  6. Fatigue and fracture toughness characteristics of laser rapid manufactured Inconel 625 structures

    Energy Technology Data Exchange (ETDEWEB)

    Ganesh, P., E-mail: ganesh@rrcat.gov.in [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India); Kaul, R.; Paul, C.P. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India); Tiwari, Pragya; Rai, S.K. [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India); Prasad, R.C. [Metallurgy and Materials Science Department, IIT Bombay, Mumbai 400 076 (India); Kukreja, L.M. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India)

    2010-11-15

    Research highlights: {yields} Mechanical test results of Laser rapid manufactured (LRM) Inconel 625 are reported. {yields} 12 and 25 mm thick CT specimens of LRM Inconel 625 showed similar fatigue crack growth. {yields} Stage II crack growth behavior is observed in the investigated {Delta}K range. {yields} Fracture toughness testing by J-integral method yielded J{sub 1c} of about 200-250 kJ/m{sup 2}. - Abstract: Fatigue crack growth and fracture toughness characteristics of laser rapid manufactured (LRMed) Inconel 625 compact tension specimens of thickness 12 and 25 mm were investigated. Fatigue crack propagation in all the specimens investigated in the stress intensity range ({Delta}K) of 14-38 MPa{radical}m, exhibited stage II crack growth in Paris' regime with nearly same slopes of crack growth per cycle versus {Delta}K plot. Fatigue crack growth rates in the LRMed specimens of present study were found to be lower than the reported values for wrought Inconel 625 in the {Delta}K range of 14-24 MPa{radical}m and above this range they tended to coincide. X-ray diffraction patterns of the fractured surfaces revealed that the crack propagated along the growth direction of the specimens which was predominantly along the (1 1 1) plane. The fracture toughness values (J{sub 0.2}) for LRMed Inconel 625 specimens were found to be in the range of about 200-255 kJ/m{sup 2}. The LRMed specimens exhibited stable crack growth during the J-integral test.

  7. A discrete element model for damage and fracture of geomaterials under fatigue loading

    Science.gov (United States)

    Gao, Xiaofeng; Koval, Georg; Chazallon, Cyrille

    2017-06-01

    Failure processes in geomaterials (concrete, asphalt concrete, masonry, etc.) under fatigue loading (repeated moving loads, cycles of temperature, etc.) are responsible for most of the dysfunctions in pavements, brick structures, etc. In the beginning of the lifetime of a structure, the material presents only inner defects (micro cracks, voids, etc.). Due to the effect of the cyclic loading, these small defects tend to grow in size and quantity which damage the material, reducing its stiffness. With a relatively high number of cycles, these growing micro cracks become large cracks, which characterizes the fracture behavior. From a theoretical point of view, both mechanisms are treated differently. Fracture is usually described locally, with the propagation of cracks defined by the energy release rate at the crack tip; damage is usually associated to non-local approaches. In the present work, damage and fracture mechanics are combined in a local discrete element approach.

  8. Effect of temperature upon the fatigue-crack propagation behavior of Inconel 625

    International Nuclear Information System (INIS)

    James, L.A.

    1977-03-01

    The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of mill-annealed Inconel 625 in an air environment over the range 75 0 - 1200 0 F (24 0 - 649 0 C). In general, fatigue-crack growth rates increased with increasing test temperature. Two different specimen sizes were employed at each test temperature, and no effects of specimen size upon crack growth were noted

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

    Science.gov (United States)

    Fletcher, Lloyd; Codrington, John; Parkinson, Ian

    2014-07-01

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

  10. Research on fatigue behavior and residual stress of large-scale cruciform welding joint with groove

    International Nuclear Information System (INIS)

    Zhao, Xiaohui; Liu, Yu; Liu, Yong; Gao, Yuan

    2014-01-01

    Highlights: • The fatigue behavior of the large-scale cruciform welding joint with groove was studied. • The longitudinal residual stress of the large-scale cruciform welding joint was tested by contour method. • The fatigue fracture mechanism of the large-scale cruciform welding joint with groove was analyzed. - Abstract: Fatigue fracture behavior of the 30 mm thick Q460C-Z steel cruciform welded joint with groove was investigated. The fatigue test results indicated that fatigue strength of 30 mm thick Q460C-Z steel cruciform welded joint with groove can reach fatigue level of 80 MPa (FAT80). Fatigue crack source of the failure specimen initiated from weld toe. Meanwhile, the microcrack was also found in the fusion zones of the fatigue failure specimen, which was caused by weld quality and weld metal integrity resulting from the multi-pass welds. Two-dimensional map of the longitudinal residual stress of 30 mm thick Q460C-Z steel cruciform welded joint with groove was obtained by using the contour method. The stress nephogram of Two-dimensional map indicated that longitudinal residual stress in the welding center is the largest

  11. Failure of metals III: Fracture and fatigue of nanostructured metallic materials

    International Nuclear Information System (INIS)

    Pineau, André; Amine Benzerga, A.; Pardoen, Thomas

    2016-01-01

    Pushing the internal or external dimensions of metallic alloys down to the nanometer scale gives rise to strong materials, though most often at the expense of a low ductility and a low resistance to cracking, with negative impact on the transfer to engineering applications. These characteristics are observed, with some exceptions, in bulk ultra-fine grained and nanocrystalline metals, nano-twinned metals, thin metallic coatings on substrates and freestanding thin metallic films and nanowires. This overview encompasses all these systems to reveal commonalities in the origins of the lack of ductility and fracture resistance, in factors governing fatigue resistance, and in ways to improve properties. After surveying the various processing methods and key deformation mechanisms, we systematically address the current state of the art in terms of plastic localization, damage, static and fatigue cracking, for three classes of systems: (1) bulk ultra-fine grained and nanocrystalline metals, (2) thin metallic films on substrates, and (3) 1D and 2D freestanding micro and nanoscale systems. In doing so, we aim to favour cross-fertilization between progress made in the fields of mechanics of thin films, nanomechanics, fundamental researches in bulk nanocrystalline metals and metallurgy to impart enhanced resistance to fracture and fatigue in high-strength nanostructured systems. This involves exploiting intrinsic mechanisms, e.g. to enhance hardening and rate-sensitivity so as to delay necking, or improve grain-boundary cohesion to resist intergranular cracks or voids. Extrinsic methods can also be utilized such as by hybridizing the metal with another material to delocalize the deformation - as practiced in stretchable electronics. Fatigue crack initiation is in principle improved by a fine structure, but at the expense of larger fatigue crack growth rates. Extrinsic toughening through hybridization allows arresting or bridging cracks. The content and discussions are based on

  12. Analysis of the cyclic behavior and fatigue damage of extruded AA2017 aluminum alloy

    International Nuclear Information System (INIS)

    May, A.; Taleb, L.; Belouchrani, M.A.

    2013-01-01

    The present work is devoted to study the anisotropic behavior of an extruded aluminum alloy under cyclic loading in axial and shear directions. In first, we have studied its elastoplastic behavior through the evolution of stress–strain loops, isotropic and kinematic hardening and we have associated this behavior with the evolution of its elastic adaptation (shakedown). In second, we have studied the behavior of the material in fatigue damage using the evolution of stiffness. Finally, microstructural investigations were performed on fractured surfaces using scanning electron microscope (SEM) in order to understand the evolution of fatigue damage during cyclic loading

  13. Study of fatigue and fracture behavior of NbCr{sub 2}-based alloys: Phase stability in Nb-Cr-Ni ternary system

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, J.H.; Liaw, P.K. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering; Liu, C.T. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.

    1997-12-01

    Phase stability in a ternary Nb-Cr-Ni Laves phase system was studied in this paper. Their previous study in NbCr{sub 2}-based transition-metal Laves phases has shown that the average electron concentration factor, e/a, is the dominating factor in controlling the phase stability of NbCr{sub 2}-based Laves phases when the atomic size ratios are kept identical. Since Ni has ten out-shell electrons, the substitution of Ni for Cr in NbCr{sub 2} will increase the average electron concentration of the alloy, thus leading to the change of the crystal structures from C15 to C14. In this paper, a number of pseudo-binary Nb(Cr,Ni){sub 2} alloys were prepared, and the crystal structures of the alloys after a long heat-treatment at 1000 C as a function of the Ni content were determined by the X-ray diffraction technique. The boundaries of the C15/C14 transition were determined and compared to their previous predictions. It was found that the electron concentration and phase stability correlation is obeyed in the Nb-Cr-Ni system. However, the e/a ratio corresponding to the C15/C14 phase transition was found to move to a higher value than the predicted one. The changes in the lattice constant, Vickers hardness and fracture toughness were also determined as a function of the Ni content, which were discussed in light of the phase stability difference of the alloys.

  14. Influence of steel-making process and heat-treatment temperature on the fatigue and fracture properties of pressure vessel steels

    International Nuclear Information System (INIS)

    Koh, S. K.; Na, E. G.; Baek, T. H.; Won, S. Y.; Park, S. J.; Lee, S. W.

    2001-01-01

    In this paper, high strength pressure vessel steels having the same chemical compositions were manufactured by the two different steel-making processes, such as Vacuum Degassing(VD) and Electro-Slag Remelting(ESR) methods. After the steel-making process, they were normalized at 955 deg. C, quenched at 843 .deg. C, and finally tempered at 550 .deg. C or 450 deg. C, resulting in tempered martensitic microstructures with different yielding strengths depending on the tempering conditions. Low-Cycle Fatigue(LCF) tests, Fatigue Crack Growth Rate(FCGR) tests, and fracture toughness tests were performed to investigate the fatigue and fracture behaviors of the pressure vessel steels. In contrast to very similar monotonic, LCF, and FCGR behaviors between VD and ESR steels, a quite difference was noticed in the fracture toughness. Fracture toughness of ESR steel was higher than that of VD steel, being attributed to the removal of impurities in steel-making process

  15. X-ray fractographic study on fatigue fracture surface of structural steels

    International Nuclear Information System (INIS)

    Ogura, Keiji; Miyoshi, Yoshio; Kawaguchi, Masahiro; Kayama, Masahiro.

    1985-01-01

    An X-ray fractographic study was made on the fatigue fracture surface of the structural steels with various strength levels. An emphasis was put on examining the effect of strength level on the residual stress and half-value breadth on and under the fracture surface. It was found that the residual stress on the fracture surface was controlled by Ksub(max) in a low Ksub(max) or ΔK region (Region I), while it was controlled by ΔK rather than Ksub(max) in a high Ksub(max) or ΔK region (Region III). It was also found that another transitional region (Region II) was observed between these two regions in SNCM 815 steel. An explanation for all these behavior was discussed by a proposed model. The distribution of the residual stress and half-value breadth under the fracture surface was found to be usefull for estimating the value of Ksub(max), although the distribution itself was strongly influenced by strength level, particularly the work-softening behavior, of the materials. (author)

  16. Fracture probability properties of pure and cantilever bending fatigue of STS304 steel

    International Nuclear Information System (INIS)

    Roh, Sung Kuk; Park, Dae Hyun; Jeong, Soon Uk

    2001-01-01

    Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frequently. Therefore many people are suffering harm of property. The destruction cause of marcaine components is almost accused by fatigue. This study is test for STS304 specimen using pure and cantilever bending state. Rounded and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress, the fatigue life of the test specimen was higher at high speed than low speed

  17. Effect of a new specimen size on fatigue crack growth behavior in thick-walled pressure vessels

    International Nuclear Information System (INIS)

    Shariati, Mahmoud; Mohammadi, Ehsan; Masoudi Nejad, Reza

    2017-01-01

    Fatigue crack growth in thick-walled pressure vessels is an important factor affecting their fracture. Predicting the path of fatigue crack growth in a pressure vessel is the main issue discussed in fracture mechanics. The objective of this paper is to design a new geometrical specimen in fatigue to define the behavior of semi-elliptical crack growth in thick-walled pressure vessels. In the present work, the importance of the behavior of fatigue crack in test specimen and real conditions in thick-walled pressure vessels is investigated. The results of fatigue loading on the new specimen are compared with the results of fatigue loading in a cylindrical pressure vessel and a standard specimen. Numerical and experimental methods are used to investigate the behavior of fatigue crack growth in the new specimen. For this purpose, a three-dimensional boundary element method is used for fatigue crack growth under stress field. The modified Paris model is used to estimate fatigue crack growth rates. In order to verify the numerical results, fatigue test is carried out on a couple of specimens with a new geometry made of ck45. A comparison between experimental and numerical results has shown good agreement. - Highlights: • This paper provides a new specimen to define the behavior of fatigue crack growth. • We estimate the behavior of fatigue crack growth in specimen and pressure vessel. • A 3D finite element model has been applied to estimate the fatigue life. • We compare the results of fatigue loading for cylindrical vessel and specimens. • Comparison between experimental and numerical results has shown a good agreement.

  18. Stresses, fatigue and fracture analysis in the tube sheets

    International Nuclear Information System (INIS)

    Billon, F.

    1986-05-01

    The purpose of the present work is to study the behaviour of the nuclear PWR steam generator tube sheet. But the methods developed in this field can easily be generalized in order to study tube sheets from any other type of heat exchangers. The aim of the stress analysis of these sheets is to verify their correct design, to quantify the risk of fatigue damage in the areas submitted to a high stress concentration and through the fracture mechanic, to make sure there is no risk of fast fracture resulting from initiated or pre-existing defects. This analysis necessarily relates to the calculation of stresses in all parts of the multidrilled area, mainly around the holes where they are concentrated. However the tube sheets are so complexe structures that their direct modelization cannot be envisaged within the context of the finite element method. We then must refer to the concept of equivalent medium in order to calculate the nominal stresses. Then using the stresses multiple fonctions appropriate to the net geometry, we can calculate the actual stresses concentrated around the holes. The method depends on the behaviour of the elementary volume which represents the behaviour of the multidrilled medium. This approach must allow to correctly take account of the ''thermal skin effect'', which is a phenomenon particular to the tube sheets with thermal loads. It must as well be generalized in order to analyse the irregular ligaments which affect the periodical stresses distribution and locally overconcentrate them [fr

  19. Microstructural Characterization Of Laser Heat Treated AISI 4140 Steel With Improved Fatigue Behavior

    Directory of Open Access Journals (Sweden)

    Oh M.C.

    2015-06-01

    Full Text Available The influence of surface heat treatment using laser radiation on the fatigue strength and corresponding microstructural evolution of AISI 4140 alloy steel was investigated in this research. The AISI 4140 alloy steel was radiated by a diode laser to give surface temperatures in the range between 600 and 800°C, and subsequently underwent vibration peening. The fatigue behavior of surface-treated specimens was examined using a giga-cycle ultrasonic fatigue test, and it was compared with that of non-treated and only-peened specimens. Fatigue fractured surfaces and microstructural evolution with respect to the laser treatment temperatures were investigated using an optical microscope. Hardness distribution was measured using Vickers micro-hardness. Higher laser temperature resulted in higher fatigue strength, attributed to the phase transformation.

  20. Environmental fatigue behaviors of wrought and cast stainless steels in 310degC deoxygenated water

    International Nuclear Information System (INIS)

    Cho, Pyung-Yeon; Jang, Hun; Jang, Changheui; Jeong, Ill-Seok; Lee, Jae-Gon

    2009-01-01

    Environmental fatigue behaviors of wrought type 316LN stainless steel and cast CF8M stainless steel were investigated. Low cycle fatigue tests were performed in a 310degC deoxygenated water environment at a strain rate of 0.04%/s with various strain amplitudes. It was shown that the low cycle fatigue life of CF8M was slightly longer than that of 316LN. To understand the causes of the difference, fracture surface was observed and material factors like microstructure, mechanical properties, and chemical compositions of both materials were analyzed. In a duplex microstructure of CF8M, the fatigue crack growth was affected by barrier role of ferrite phase and acceleration role of microvoids in ferrite phase. Test results indicate that the former is greater than the latter, resulting in slower fatigue crack growth rate, or longer LCF lives in CF8M than in 316LN. (author)

  1. NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

    Science.gov (United States)

    Forman, Royce; Shivakumar, V.; Mettu, Sambi; Beek, Joachim; Williams, Leonard; Yeh, Feng; McClung, Craig; Cardinal, Joe

    2004-01-01

    This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

  2. Tensile and fracture behavior of polymer foams

    International Nuclear Information System (INIS)

    Kabir, Md. E.; Saha, M.C.; Jeelani, S.

    2006-01-01

    Tensile and mode-I fracture behavior of cross-linked polyvinyl chloride (PVC) and rigid polyurethane (PUR) foams are examined. Tension tests are performed using prismatic bar specimens and mode-I fracture tests are performed using single edge notched bend (SENB) specimens under three-point bending. Test specimens are prepared from PVC foams with three densities and two different levels of cross-linking, and PUR foam with one density. Tension and quasi-static fracture tests are performed using a Zwick/Rowell test machine. Dynamic fracture tests are performed using a DYNATUP model 8210 instrumented drop-tower test set up at three different impact energy levels. Various parameters such as specimen size, loading rate, foam density, cross-linking, crack length, cell orientation (flow and rise-direction) and solid polymer material are studied. It is found that foam density and solid polymer material have a significant effect on tensile strength, modulus, and fracture toughness of polymer foams. Level of polymer cross-linking is also found to have a significant effect on fracture toughness. The presence of cracks in the rise- and flow direction as well as loading rate has minimal effect. Dynamic fracture behavior is found to be different as compared to quasi-static fracture behavior. Dynamic fracture toughness (K d ) increases with impact energy. Examination of fracture surfaces reveals that the fracture occurs in fairly brittle manner for all foam materials

  3. Study on high-cycle fatigue behavior of candidate Fe-Cr-Ni alloys for SCWR

    International Nuclear Information System (INIS)

    Zhao Yuxiang; Liu Guiliang; Tang Rui; Xiong Ru; Qiao Yingjie

    2014-01-01

    In the design for supercritical water reactor (SCWR), the operating temperature, pressure, burn up and irradiation damage are very high, so it seems vital to make correct choice of structural materials in core and obtain their key application behavior which would beneficial the research and development of SCWR. In this paper, the high cycle fatigue (HCF) tests of commerce austenite alloys including 6XN and 825 were conducted under bending and rotating loads at room temperature (RT) as well as at 550 ℃ in air. The experimental data were analyzed and the S-N curves were processed, the fracture morphology was also observed by SEM. The results indicate that the fatigue limited stresses at RT for the 2 Fe-Cr-Ni alloy were in such order of 825 < 6XN, which consistent with the order of their tensile strength. Elevated temperature would accelerate the oxidation of the specimen and therefore the fatigue life would decrease, among them 6XN was more sensitive to high temperature with the larger decreasing tendency which make the fatigue limited stress of the two alloys more closer at 550 ℃. While 825 is more sensitive to the stress cycles. All the two alloys have good resistance to high cycle fatigue when comparing their experimental data with the calculated value from the empirical formula. The fracture morphology presents areas of crack initiation, crack growth and fracture, the fracture area has much dimples. This work can be applied to the conceptional design for SCWR. (authors)

  4. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    Science.gov (United States)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.

  5. The Fatigue Behavior of Steel Structures under Random Loading

    DEFF Research Database (Denmark)

    Agerskov, Henning

    2009-01-01

    of the investigation, fatigue test series with a total of 540 fatigue tests have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel or high-strength steel. The fatigue tests......Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part...... and the fracture mechanics analyses have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude...

  6. Correction of fatigue parameters of concrete using approximation of mechanical-Fracture parameters in time

    Czech Academy of Sciences Publication Activity Database

    Šimonová, H.; Keršner, Z.; Seitl, Stanislav; Pryl, D.; Pukl, R.

    -, č. 1 (2012), s. 57-59 ISSN 1213-3116 R&D Projects: GA ČR(CZ) GAP104/11/0833 Institutional support: RVO:68081723 Keywords : fatigue * concrete * correction * fracture parameters Subject RIV: JL - Materials Fatigue, Friction Mechanics

  7. Prediction of fretting fatigue behavior under elastic-plastic conditions

    International Nuclear Information System (INIS)

    Shin, Ki Su

    2009-01-01

    Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. While many studies have evaluated fretting fatigue behavior under elastic deformation conditions, few have focused on fretting fatigue behavior under elastic-plastic deformation conditions, especially the crack orientation and fatigue life prediction for Ti-6Al-4V. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. Several parametric approaches were used to predict fretting fatigue life along with stress distribution resulting from FEA. However, those parameters using surface stresses were unable to establish an equivalence between elastic fretting fatigue data and elastic-plastic fretting fatigue data. Based on this observation, the critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations

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

    Energy Technology Data Exchange (ETDEWEB)

    Fan, K.L., E-mail: 12klfan@tongji.edu.cn; 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.

  9. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination...... of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....

  10. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination...

  11. Ductile fracture behavior of cast structure containing voids

    International Nuclear Information System (INIS)

    Gilles, Ph.; Migne, C.; Chapuliot, S.

    2001-01-01

    In pressurized water reactors, the primary loop contains cast-piping components made of duplex stainless steel. Due to the presence of ferrite, such steels are susceptible to thermal aging embrittlement, which decrease their fracture resistance. The cast process induces shrinkage cavities, therefore all these components are submitted to liquid penetrant examination and all surface defects are repaired. EDF, CEA and Framatome have conducted experimental and analytical analysis of fatigue and fracture behavior of aged cast stainless steel structures containing shrinkage cavities. The present study considers only ductile tearing and is based on specimen test results and a fracture mechanics model of the interaction between shrinkage cavities. The experimental results presented here show that large groups of shrinkage cavities have almost no influence on the global behavior of the structure. Only for the specimen with the largest reduction of area, a significant reduction of strength has been registered. Using elementary fracture mechanics models, it has been evidenced that failure mechanism of structures containing shrinkage cavities consists in 3 phases: local initiation, macro-crack formation by coalescence and failure by crack instability or collapse depending if J resistance is low or not. No significant changes in global behavior appear in the first phase. (A.C.)

  12. Ductile fracture behavior of cast structure containing voids

    Energy Technology Data Exchange (ETDEWEB)

    Gilles, Ph.; Migne, C. [FRAMATOME ANP, 92 - Paris-La-Defence (France); Chapuliot, S. [CEA Saclay, 91 - Gif-sur-Yvette (France). Dept. de Mecanique et de Technologie

    2001-07-01

    In pressurized water reactors, the primary loop contains cast-piping components made of duplex stainless steel. Due to the presence of ferrite, such steels are susceptible to thermal aging embrittlement, which decrease their fracture resistance. The cast process induces shrinkage cavities, therefore all these components are submitted to liquid penetrant examination and all surface defects are repaired. EDF, CEA and Framatome have conducted experimental and analytical analysis of fatigue and fracture behavior of aged cast stainless steel structures containing shrinkage cavities. The present study considers only ductile tearing and is based on specimen test results and a fracture mechanics model of the interaction between shrinkage cavities. The experimental results presented here show that large groups of shrinkage cavities have almost no influence on the global behavior of the structure. Only for the specimen with the largest reduction of area, a significant reduction of strength has been registered. Using elementary fracture mechanics models, it has been evidenced that failure mechanism of structures containing shrinkage cavities consists in 3 phases: local initiation, macro-crack formation by coalescence and failure by crack instability or collapse depending if J resistance is low or not. No significant changes in global behavior appear in the first phase. (A.C.)

  13. Quantitative analysis by X-ray fractography of fatigue fractured surface under variable amplitude loading

    International Nuclear Information System (INIS)

    Akita, Koichi; Kodama, Shotaro; Misawa, Hiroshi

    1994-01-01

    X-ray fractography is a method of analysing the causes of accidental fracture of machine components or structures. Almost all of the previous research on this problem has been carried out using constant amplitude fatigue tests. However, the actual loads on components and structures are usually of variable amplitudes. In this study, X-ray fractography was applied to fatigue fractured surfaces produced by variable amplitude loading. Fatigue tests were carried out on Ni-Cr-Mo steel CT specimens under the conditions of repeated, two-step and multiple-step loading. Residual stresses were measured on the fatigue fractured surface by an X-ray diffraction method. The relationships between residual stress and stress intensity factor or crack propagation rate were studied. They were discussed in terms of the quantitative expressions under constant amplitude loading, proposed by the authors in previous papers. The main results obtained were as follows : (1) It was possible to estimate the crack propagation rate of the fatigue fractured surface under variable amplitude loading by using the relationship between residual stress and stress intensity factor under constant amplitude loading. (2) The compressive residual stress components on the fatigue fractured surface correspond with cyclic softening of the material rather than with compressive plastic deformation at the crack tip. (author)

  14. Low-cycle fatigue behavior of HT-9 alloy in a flowing-lithium environment

    International Nuclear Information System (INIS)

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

    1983-06-01

    Low-cycle fatigue data have been obtained on normalized/tempered or lithium-preexposed HT-9 alloy at 755 K in flowing lithium of controlled purity. The results show that the fatigue life of this material decreases with an increase in nitrogen content in lithium. A reduction in strain rate also decreases the fatigue life in high-nitrogen lithium. However, in the range from approx. 4 x 10 - 4 to 4 x 10 - 2 s - 1 , the strain rate has no effect on fatigue life in lithium containing <200 wppM nitrogen. The fatigue life of the HT-9 alloy in low-nitrogen lithium is significantly greater than the fatigue life of Fe-9Cr-1Mo steel or Type 403 martensitic steel in air. Furthermore, a 4.0-Ms preexposure to low-nitrogen lithium has no influence on fatigue life. The reduction in fatigue life in high-nitrogen lithium is attributed to internal corrosive attack of the material. The specimens tested in high-nitrogen lithium show internal corrosion along grain and martensitic lathe boundaries and intergranular fracture. This behavior is not observed in specimens tested in low-nitrogen lithium. Results for a constant-load corrosion test in flowing lithium are also presented

  15. Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, L. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, M. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-05-01

    Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatigue for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.

  16. High temperature low cycle fatigue behavior of Ni-base superalloy M963

    International Nuclear Information System (INIS)

    He, L.Z.; Zheng, Q.; Sun, X.F.; Guan, H.R.; Hu, Z.Q.; Tieu, A.K.; Lu, C.; Zhu, H.T.

    2005-01-01

    The cyclic stress-strain response and the low cycle fatigue life behavior of solution treated Ni-base superalloy M963 were studied. Fully reversed strain-controlled tests were performed at temperature range from 700 to 950 deg. C in air at a constant total strain rate. The dislocation characteristics and failed surface observation were evaluated through scanning electron microscopy and transmission electron microscopy, respectively. The alloy exhibited the cyclic hardening, softening, or stable cyclic stress response, which was dependent on the temperature and total strain range. The fracture surface observation revealed that fatigue crack initiation was transgranular and closely related to the total strain range; however, fatigue crack propagation exhibited a strong dependence on testing temperature. The dramatic reduction in fatigue life and intergranular cracking observed at 900 and 950 deg. C were attributed to oxidation

  17. Fatigue behavior of partially stabilized zirconia ceramics

    International Nuclear Information System (INIS)

    Ferber, M.K.; Hine, T.

    1986-01-01

    The time-dependent strength variations of two grades of MgO stabilized materials (Mg-PSZ) were measured as a function of temperature and applied stress level. The strength was determined using an interrupted fatigue (I.F.) test in which flexure samples were exposed at temperatures between 500 and 100 0 C for times up to 1008 h. During testing, the applied stress was maintained at a percentage of the short-term strength value measured at the same T. The resulting I.F. data gave evidence of both strengthening and weakening processes. The dominant mechanism at a given temperature was primarily dictated by the stress level. In the present investigation, the fatigue behavior for two grades of Mg-PSZ was evaluated by measuring the time-dependent strength variations as a function of temperature and applied stress level. Changes in microstructure resulting from the high-temperature exposure were determined from subsequent ceramographic, SEM and TEM studies. In addition, x-ray diffraction and dilatometry measurements were used to examine time-dependent variations in the phase assemblage

  18. Experimental Investigation on Fatigue Behavior of Epoxy Resin under Load and Displacement Controls

    Directory of Open Access Journals (Sweden)

    Mahmood Mehrdad Shokrieh

    2014-12-01

    Full Text Available The mechanical properties of epoxy resin including tensile and flexural modulus, tensile and flexural strength for static conditions are currently studied. The frequency effect as significant parameter at room temperature is investigated and fatigue behavior of the epoxy resin in tension-tension loading conditions for different frequencies of 2, 3 and 5 Hz are obtained. The epoxy resin has been taken under flexural bending fatigue loading and fatigue life is investigated. The results of the experiments show the values of 2.5 and 3 GPa of tensile and flexural modules and 59.98 and 110.02 MPa of tensile and flexural strengths for the resin, respectively. To achieve a linear load-deflection relationship in a three-point bending experiment, a maximum allowable deflection of 5 mm is acquired. The relationship between the frequency and fatigue life shows higher frequency results in lower fatigue life. Loading with frequency of 2 Hz has provided 5.8 times more fatigue life compared with 5 Hz loading. For a tension-tension fatigue loading condition, the variation of tensile module of epoxy resin shows no noticeable change during the fatigue loading condition. This module decreases significantly only in the primary and failure cycles close to the fracture point. In further experiments, fatigue behavior of epoxy resin was tested under flexural bending fatigue loadings with controlled deflection at room temperature. Maximum applied normalized stresses versus the number of cycles to failure curve are illustrated and it can be performed in order to predict the number of cycles to failure for the resin in arbitrary applied normal stresses as well.

  19. Taltirelin alleviates fatigue-like behavior in mouse models of cancer-related fatigue.

    Science.gov (United States)

    Dougherty, John P; Wolff, Brian S; Cullen, Mary J; Saligan, Leorey N; Gershengorn, Marvin C

    2017-10-01

    Fatigue affects most cancer patients and has numerous potential causes, including cancer itself and cancer treatment. Cancer-related fatigue (CRF) is not relieved by rest, can decrease quality of life, and has no FDA-approved therapy. Thyrotropin-releasing hormone (TRH) has been proposed as a potential novel treatment for CRF, but its efficacy against CRF remains largely untested. Thus, we tested the TRH analog, taltirelin (TAL), in mouse models of CRF. To model fatigue, we used a mouse model of chemotherapy, a mouse model of radiation therapy, and mice bearing colon 26 carcinoma tumors. We used the treadmill fatigue test to assess fatigue-like behavior after treatment with TAL. Additionally, we used wild-type and TRH receptor knockout mice to determine which TRH receptor was necessary for the actions of TAL. Tumor-bearing mice displayed muscle wasting and all models caused fatigue-like behavior, with mice running a shorter distance in the treadmill fatigue test than controls. TAL reversed fatigue-like behavior in all three models and the mouse TRH 1 receptor was necessary for the effects of TAL. These data suggest that TAL may be useful in alleviating fatigue in all cancer patients and provide further support for evaluating TAL as a potential therapy for CRF in humans. Published by Elsevier Ltd.

  20. Flexural fatigue behavior of steel fiber reinforced concrete structures

    International Nuclear Information System (INIS)

    Chang, G.I.; Chai, W.K.; Park, C.W.; Min, I.K.

    1993-01-01

    In this thesis, the fatigue tests are performed on a series of SFRC (steel fiber reinforced concrete) to investigate the fatigue behavior of SFRC varing with the steel fiber contents and the steel fiber aspect ratios. Thirty SFRC beams are used in this test. The relationships between repeated loading cycle and mid-span deflection of the beams are observed under the three-point loading system. From the test results, the effects of the fiber content and the fiber aspect ratio on the concrete fatigue behavior were studied. According to the regression technique, some empirical formulae for predicting the fatigue strength of SFRC beams are also suggested. (author)

  1. Effect of heat-treatment on elevated temperature fatigue-crack growth behavior of two heats of Alloy 718

    International Nuclear Information System (INIS)

    Mills, W.J.; James, L.A.

    1978-05-01

    The room temperature and elevated temperature fatigue-crack growth behavior of two heats of Alloy 718 was characterized within a linear-elastic fracture mechanics framework. Two different heat-treatments were used: the ''conventional'' (ASTM A637) treatment, and a ''modified'' heat-treatment designed to improve the toughness of Alloy 718 base metal and weldments. Heat-to-heat variations in the fatigue-crack propagation behavior were observed in the conventionally-treated material. On the other hand, no heat-to-heat variations were observed in the modified condition. Furthermore, both heats of Alloy 718 exhibited superior fatigue-crack growth resistance when given the modified heat-treatment. Electron fractographic examination of Alloy 718 fatigue fracture surfaces revealed that the operative crack growth mechanisms were dependent on heat-treatment, temperature, and ΔK level

  2. Tensile and fatigue behaviors of printed Ag thin films on flexible substrates

    International Nuclear Information System (INIS)

    Sim, Gi-Dong; Won, Sejeong; Lee, Soon-Bok

    2012-01-01

    Flexible electronics using nanoparticle (NP) printing has been highlighted as a key technology enabling eco-friendly, low-cost, and large-area fabrication. For NP-based printing to be used as a successive alternative to photolithography and vacuum deposition, stretchability and long term reliability must be considered. This paper reports the stretchability and fatigue behavior of 100 nm thick NP-based silver thin films printed on polyethylene-terephthalate substrate and compares it to films deposited by electron-beam evaporation. NP-based films show stretchability and fatigue life comparable to evaporated films with intergranular fracture as the dominant failure mechanism.

  3. Tensile and fatigue behaviors of printed Ag thin films on flexible substrates

    Science.gov (United States)

    Sim, Gi-Dong; Won, Sejeong; Lee, Soon-Bok

    2012-11-01

    Flexible electronics using nanoparticle (NP) printing has been highlighted as a key technology enabling eco-friendly, low-cost, and large-area fabrication. For NP-based printing to be used as a successive alternative to photolithography and vacuum deposition, stretchability and long term reliability must be considered. This paper reports the stretchability and fatigue behavior of 100 nm thick NP-based silver thin films printed on polyethylene-terephthalate substrate and compares it to films deposited by electron-beam evaporation. NP-based films show stretchability and fatigue life comparable to evaporated films with intergranular fracture as the dominant failure mechanism.

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

    Science.gov (United States)

    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

  5. Fatigue behavior and failure mechanisms of direct laser deposited Ti–6Al–4V

    Energy Technology Data Exchange (ETDEWEB)

    Sterling, Amanda J.; Torries, Brian [Department of Mechanical Engineering, Mississippi State University, Box 9552, Mississippi State, MS 39762 (United States); Shamsaei, Nima, E-mail: shamsaei@me.msstate.edu [Department of Mechanical Engineering, Mississippi State University, Box 9552, Mississippi State, MS 39762 (United States); Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Box 5405, , Mississippi State, MS 39762 (United States); Thompson, Scott M. [Department of Mechanical Engineering, Mississippi State University, Box 9552, Mississippi State, MS 39762 (United States); Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Box 5405, , Mississippi State, MS 39762 (United States); Seely, Denver W. [Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Box 5405, , Mississippi State, MS 39762 (United States)

    2016-02-08

    In order for additive-manufactured parts to become more widely utilized and trusted in application, it is important to have their mechanical properties well-characterized and certified. The fatigue behavior and failure mechanisms of Ti–6Al–4V specimens fabricated using Laser Engineered Net Shaping (LENS), a Direct Laser Deposition (DLD) additive manufacturing (AM) process, are investigated in this study. A series of fully-reversed strain-controlled fatigue tests is conducted on Ti–6Al–4V specimens manufactured via LENS in their as-built and heat-treated conditions. Scanning Electron Microscopy (SEM) is used to examine the fracture surfaces of fatigue specimens to qualify the failure mechanism, crack initiation sites, and defects such as porosity. Due to the relatively high localized heating and cooling rates experienced during DLD, fabricated parts are observed to possess anisotropic microstructures, and thus, different mechanical properties than those of their traditionally-manufactured wrought counterparts. The fatigue lives of the investigated LENS specimens were found to be shorter than those of wrought specimens, and porosity was found to be the primary contributor to these shorter fatigue lives, with the exception of the heat-treated LENS samples. The presence of pores promotes more unpredictable fatigue behavior, as evidenced by data scatter. Pore shape, size, location, and number were found to impact the fatigue behavior of the as-built and annealed DLD parts. As porosity seems to be the main contributor to the fatigue behavior of DLD parts, it is important to optimize the manufacturing process and design parameters to minimize and control pore generation during the build.

  6. Evaluation of local deformation behavior accompanying fatigue damage in F82H welded joint specimens by using digital image correlation

    International Nuclear Information System (INIS)

    Nakata, Toshiya; Tanigawa, Hiroyasu

    2012-01-01

    Highlights: ► In tensile, the TIG welded joint material was concentrated in the THAZ. ► In tensile, fracture occurred at the point where the axial strain converged. ► In fatigue, fracture occurred at the point where the Max. shear strain converged. ► Many macrocracks and cavities formed in the FGHAZ and THAZ of the cross section. - Abstract: By using digital image correlation, the deformation behaviors of local domains of F82H joint specimens welded using tungsten inert gas (TIG) and electron beam (EB) welding were evaluated during tensile and fatigue testing. In the tensile test specimens, the tensile strength decreased in the TIG-welded joints, and ductility decreased in both the EB- and TIG-welded joints. Because axial strain increased in the tempered heat-affected zone (HAZ) and led to the fracture of the TIG-welded joint, the strength was considered to have decreased because of welding. In fatigue testing, the number of cycles to fracture for the welded joint decreased to less than 40–60% of that for the base metal. For both fracture specimens, the largest value of shear strain was observed in the region approximately between the fine-grained HAZ and tempered HAZ; this shear strain ultimately led to fracture. Cavities and macrocracks were observed in the fine-grained HAZ and tempered HAZ in the cross sections of the fracture specimens, and geometrical damage possibly resulted in the reduction of fatigue lifetime.

  7. Influence of cyclical fatigue on torsional fracture morphology in endodontic instruments.

    Science.gov (United States)

    Lopreite, Gustavo; Basilaki, Jorge; Hecht, Pedro

    2013-01-01

    Cyclical fatigue may influence the appearance and propagation of the type of fracture of an endodontic instrument. The aim of this study was to assess the influence of cyclic fatigue on morphological features of torsional fracture in Pathfile nickel-titanium rotary instruments for surgical preparation in endodontics. Thirty new Pathfile instruments (Dentsply- Maillefer. Ballaigues-Switzerland) diameter .13 and taper .02 were randomly divided into 5 groups (n = 6). Twenty-four of them were subject to cyclical fatigue by continuous rotation using a stainless steel cylinder with internal bore 0.5 mm, length 25 mm, with a curve of 45 degrees and radius 8 mm at 5 mm from the tip, at 300 rpm and 1 Ncm torque for different times: A: 15 sec, B: 75 sec, C: 150 sec and D: 300 sec, while the fifth group was kept as a control (group N). As a second step, the instruments were rotated at 2 rpm and 1 Ncm torque, with their apical 3 mm fixed in a resin block until they suffered torsional fracture. The fracture surfaces were analyzed using a conventional high-vacuum scanning electron microscope (Phillips mod. 515) at 400x. All instruments had ductile fracture areas of different sizes. The ductile fracture areas were measured as percentages of the total area of the instrument by means of Golden Ratio (Softonic) software for measuring images. The data obtained were analyzed statistically using one-way variance analysis followed by Tukey's multiple comparison test. There were significant differences among groups regarding cyclic fatigue time and fragile fracture area (P fatigue to which the rotating PathFile instrument is subject significantly increases the percentage of ductile fracture area produced by torsion.

  8. Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material

    Science.gov (United States)

    O'Brien, T. Kevin; Johnston, William M.; Toland, Gregory J.

    2010-01-01

    Mode II interlaminar fracture toughness and delamination onset and growth characterization data were generated for IM7/8552 graphite epoxy composite materials from two suppliers for use in fracture mechanics analyses. Both the fracture toughness testing and the fatigue testing were conducted using the End-notched Flexure (ENF) test. The ENF test for mode II fracture toughness is currently under review by ASTM as a potential standard test method. This current draft ASTM protocol was used as a guide to conduct the tests on the IM7/8552 material. This report summarizes the test approach, methods, procedures and results of this characterization effort.

  9. Probabilistic Fatigue Life Prediction of Bridge Cables Based on Multiscaling and Mesoscopic Fracture Mechanics

    Directory of Open Access Journals (Sweden)

    Zhongxiang Liu

    2016-04-01

    Full Text Available Fatigue fracture of bridge stay-cables is usually a multiscale process as the crack grows from micro-scale to macro-scale. Such a process, however, is highly uncertain. In order to make a rational prediction of the residual life of bridge cables, a probabilistic fatigue approach is proposed, based on a comprehensive vehicle load model, finite element analysis and multiscaling and mesoscopic fracture mechanics. Uncertainties in both material properties and external loads are considered. The proposed method is demonstrated through the fatigue life prediction of cables of the Runyang Cable-Stayed Bridge in China, and it is found that cables along the bridge spans may have significantly different fatigue lives, and due to the variability, some of them may have shorter lives than those as expected from the design.

  10. Fatigue fracture of cutter blade made of high-speed steel

    Directory of Open Access Journals (Sweden)

    Beata Letkowska

    2015-04-01

    Full Text Available The quality of the surface of cyclically loaded components is very important. Many observations confirm that the root cause of the micro cracks (causing the fatigue fracture are primarily a surface's defects appearing during production process. These surface defects can be also caused by engraving processes used to perform identification marks. This paper presents the failure analysis of broken blade of the cutter Ku 500VX. The blade was subject of standard metallographic examination, hardness measurements, fractography analysis and metallographic studies using stereoscopic, light and scanning electron microscopes. The damage of the blade was caused by changes of the structure (formation of the brittle micro dendritic structure that occurred during manual electric engraving process when the material was heated till its melting point. As a result the stresses occurred in surface what provided to micro cracking and to propagate the fatigue fracture. The origin of this fatigue fracture was in the place where the inscription was made.

  11. Evaluation of hot hardness, creep, fatigue and fracture properties of zirconia ceramics by an indentation technique

    International Nuclear Information System (INIS)

    Kutty, T.R.G.; Ganguly, C.; Upadhyaya, D.D.

    1996-01-01

    Zirconia ceramics have wide range engineering applications at room and elevated temperatures. For understanding the mechanical behaviour, the indentation technique was adapted for quick evaluation of hot hardness, creep, fatigue and fracture properties. A Vicker's diamond indentor with 10 N load was employed for hot hardness and creep measurement up to 1300 deg. The fatigue data were evaluated at room temperature by repeated indentation with a constant load (10-2500N) at the same location for a dwell time of 5s until it resulted in the formation of a lateral chip on the sample surface. Thus, the number of cycles for chip formation at a specific indentation load was obtained. The fracture toughness was evaluated at room temperature with a load of 300N using a Vicker's diamond indentor. The results of hot hardness, creep, fatigue, and fracture data ol 3Y-TZP and Mg-PSZ are discussed along with their microstructural features. (authors)

  12. Influence of Aging Conditions on Fatigue Fracture Behaviour of 6063 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Rafiq Ahmed Siddiqui

    2001-12-01

    Full Text Available Aluminum - Magnesium - Silicon (Al-Mg-Si 6063 alloy was heat-treated using under aged, peak aged and overage temperatures. The numbers of cycles required to cause the fatigue fracture, at constant stress, was considered as criteria for the fatigue resistance. Moreover, the fractured surface of the alloy at different aging conditions was evaluated by optical microscopy and the Scanning Electron Microscopy (SEM. The SEM micrographs confirmed the cleavage surfaces with well-defined fatigue striations. It has been observed that the various aging time and temperature of the 6063 Al-alloy, produces different modes of fractures. The most suitable age hardening time and temperature was found to be between 4 to 5 hours and to occur at 460 K. The increase in fatigue fracture property of the alloy due to aging could be attributed to a vacancy assisted diffusion mechanism or due to pinning of dislocations movement by the precipitates produced during aging. However, the decrease in the fatigue resistance, for the over aged alloys, might be due to the coalescence of precipitates into larger grains.

  13. Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments

    International Nuclear Information System (INIS)

    Mills, W.J.; James, L.A.

    1981-05-01

    The microstructural features that influenced the room and elevated temperature fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination of fatigue fracture surfaces revealed that operative fatigue mechanisms were dependent on microstructure, temperatures and stress intensity factor. All specimens exhibited three basic fracture surface appearances at temperatures up to 538 degrees C: crystallographic faceting at low stress intensity range (ΔK) levels, striation, formation at intermediate values, and dimples coupled with striations in the highest (ΔK) regime. At 649 degrees C, the heat-treated welds exhibited extensive intergranular cracking. Laves and δ particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused on overall acceleration in crack growth rates at intermediate and high ΔK levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material was attributed to compressive residual stresses introduced by the welding process. 19 refs., 16 figs

  14. Low cycle fatigue behavior of titanium carbide coated molybdenum

    International Nuclear Information System (INIS)

    Nishi, Hiroshi; Oku, Tatsuo; Kodaira, Tsuneo; Kikuyama, Toshihiko

    1985-09-01

    Sintered molybdenum coated by TiC is used for the first wall such as a troidal fixed limiter and a magnetic limiter plate in JT-60, that is being operated at JAERI presently. This report describes the low cycle fatigue behavior of sintered molybdenum and the influence of TiC coating on fatigue strength. The low cycle fatigue test was conducted at room temperature and 500 0 C. The test results was also analyzed by fractographic observation, metallography and element analysis using EPMA. The low cycle fatigue strength of the molybdenum coated by TiC at 500 0 C is decreased compared with the one at room temperature. (author)

  15. Fatigue behavior of lubricated Ni-Ti endodontic rotary instruments

    Directory of Open Access Journals (Sweden)

    A. Brotzu

    2014-04-01

    Full Text Available The use of Ni-Ti alloys in the practice of endodontic comes from their important properties such as shape memory and superelasticity phenomena, good corrosion resistance and high compatibility with biological tissues. In the last twenty years a great variety of nickel-titanium rotary instruments, with various sections and taper, have been developed and marketed. Although they have many advantages and despite their increasing popularity, a major concern with the use of Ni-Ti rotary instruments is the possibility of unexpected failure in use due to several reasons: novice operator handling, presence manufacturing defects, fatigue etc. Recently, the use of an aqueous gel during experimental tests showed a longer duration of the instruments. The aim of the present work is to contribute to the study of the fracture behavior of these endodontic rotary instruments particularly assessing whether the use of the aqueous lubricant gel can extend their operative life stating its reasons. A finite element model (FEM has been developed to support the experimental results. The results were rather contradictory, also because the Perspex (Poly-methyl methacrylate, PMMA cannot simulate completely the dentin mechanical behavior; however the results highlight some interesting points which are discussed in the paper.

  16. High-Temperature Creep-Fatigue Behavior of Alloy 617

    Directory of Open Access Journals (Sweden)

    Rando Tungga Dewa

    2018-02-01

    Full Text Available This paper presents the high-temperature creep-fatigue testing of a Ni-based superalloy of Alloy 617 base metal and weldments at 900 °C. Creep-fatigue tests were conducted with fully reversed axial strain control at a total strain range of 0.6%, 1.2%, and 1.5%, and peak tensile hold time of 60, 180, and 300 s. The effects of different constituents on the combined creep-fatigue endurance such as hold time, strain range, and stress relaxation behavior are discussed. Under all creep-fatigue tests, weldments’ creep-fatigue life was less than base metal. In comparison with the low-cycle fatigue condition, the introduction of hold time decreased the cycle number of both base metal and weldments. Creep-fatigue lifetime in the base metal was continually decreased by increasing the tension hold time, except for weldments under longer hold time (>180 s. In all creep-fatigue tests, intergranular brittle cracks near the crack tip and thick oxide scales at the surface were formed, which were linked to the mixed-mode creep and fatigue cracks. Creep-fatigue interaction in the damage-diagram (D-Diagram (i.e., linear damage summation was evaluated from the experimental results. The linear damage summation was found to be suitable for the current limited test conditions, and one can enclose all the data points within the proposed scatter band.

  17. Creep-fatigue behavior of turbine disc of superalloy GH720Li at 650 °C and probabilistic creep-fatigue modeling

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Dianyin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China); Ma, Qihang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Shang, Lihong [Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5 (Canada); Gao, Ye [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Wang, Rongqiao, E-mail: wangrq@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China)

    2016-07-18

    Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li at an elevated temperature of 650 °C with a stress ratio of 0.1, based on which, different dwell times at the maximum loading were applied to investigate the effect of dwell time on the creep-fatigue behaviors. The tested specimens were cut from the rim region of an actual turbine disc in the hoop direction. The grain size and precipitates of the GH720Li superalloy were examined through scanning electronic microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. Experimental data shows creep-fatigue lifetime decreases as the dwell time prolongs. Further, different scattering was observed in the creep-fatigue lifetime at different dwell times. Then a probabilistic model based on the applied mechanical work density (AMWD), with a linear heteroscedastic function that evaluates the non-constant deviation in the creep-fatigue lifetime, was formulated to describe the dependence of creep-fatigue lifetime on the dwell time. Finally, the possible microscopic mechanism of the creep-fatigue behavior has been discussed by SEM with EDS on the fracture surfaces.

  18. MR imaging findings of fatigue fractures of lower extremity in young soldiers

    International Nuclear Information System (INIS)

    Mo, Jong Hyun; Moon, Sung Hee; Kim, Young Bok; Park, Yang Hee; Park, Jin Kyoon

    1999-01-01

    To evaluate the MR imaging findings of fatigue fractures of the lower extremity in young soldiers. In 22 cases of fatigue fractures of the lower extremity in young soldiers proven by clinical findings and radiological follow up, the MRI findings were retrospectively evalvated. All patients were male and aged between 19 and 21 years. As seen on MRI, the bone marrow edema, intramedullary low signal intensity band, cortical fracture line, periosteal reaction, surrounding soft tissue edema, and enhancement pattern were analyzed and the site of involvement was determined in the axial plane. The locations of fatigue fractures of the lower extremity were the tibia (n=12), fibula (n=8), femur (n=1) and second metatarsus (n=1). All occurred in diaphyses: the junction of the proximal and middle (n=10), middle (n=9), proximal (n=2), and distal shaft (n=1). The sites of involvement were the posteromedial (n=6) and medial side (n=6) of the tibia, and the entire portion of the fibula(n=5) in the axial plane. MRI findings were bone marrow edema in 20 cases, intramedullary low signal intensity band in 14 (which were continuous with the cortex or cortical fracture line), cortical fracture line in 13, and periosteal reaction and surrounding soft tissue edema in all. On gadolinium-enhanced images, enhancement was seen in the bone marrow in 19 cases, in the subperiosteal region in 18, and in the surrounding soft tissue in 22. In fatigue fractures of the lower extremity in young soldiers, the main locations were the tibia and fibula, and characteristic MR imaging findings were intramedullary low signal intensity bands, which were continuous with the cortex or cortical fracture line and often accompanied by bone marrow edema, periosteal reaction, and surrounding soft tissue edema

  19. Fatigue crack propagation behavior under creep conditions

    International Nuclear Information System (INIS)

    Ohji, Kiyotsugu; Kubo, Shiro

    1991-01-01

    The crack propagation behavior of the SUS 304 stainless steel under creep-fatigue conditions was reviewed. Cracks propagated either in purely time-dependent mode or in purely cycle-dependent mode, depending on loading conditions. The time-dependent crack propagation rate was correlated with modified J-integral J * and the cycle-dependent crack propagation rate was correlated with J-integral range ΔJ f . Threshold was observed in the cycle-dependent crack propagation, and below this threshold the time-dependent crack propagation appeared. The crack propagation rates were uniquely characterized by taking the effective values of J * and ΔJ f , when crack closure was observed. Change in crack propagation mode occurred reversibly and was predicted by the competitive damage model. The threshold disappeared and the cycle-dependent crack propagation continued in a subthreshold region under variable amplitude conditions, where the threshold was interposed between the maximum and minimum ΔJ f . (orig.)

  20. The stability of a hip fracture determines the fatigue of an intramedullary nail.

    Science.gov (United States)

    Eberle, S; Bauer, C; Gerber, C; von Oldenburg, G; Augat, P

    2010-01-01

    The purpose of this study was to address the question of how the stability of a proximal hip fracture determines the fatigue and failure mechanism of an intramedullary implant. To answer this question, mechanical experiments and finite element simulations with two different loading scenarios were conducted. The two load scenarios differed in the mechanical support of the fracture by an artificial bone sleeve, representing the femoral head and neck. The experiments confirmed that an intramedullary nail fails at a lower load in an unstable fracture situation in the proximal femur than in a stable fracture. The nails with an unstable support failed at a load 28 per cent lower than the nails with a stable support by the femoral neck. Hence, the mechanical support of a fracture is crucial to the fatigue failure of an implant. The simulation showed why the fatigue fracture of the nail starts at the aperture of the lag screw. It is the location of the highest von Mises stress, which is the failure criterion for ductile materials.

  1. Fracture mechanics of ceramics. Vol. 8. Microstructure, methods, design, and fatigue

    International Nuclear Information System (INIS)

    Bradt, R.C.; Evans, A.G.; Hasselman, D.P.H.; Lange, F.F.

    1986-01-01

    This paper presents information on the following topics: fracture mechanics and microstructures; non-lubricated sliding wear of Al 2 O 3 , PSZ and SiC; mixed-mode fracture of ceramics; some fracture properties of alumina-containing electrical porcelains; transformation toughening in the Al 2 O 3 -Cr 2 O 3 /ZrO 2 -HfO 2 system; strength toughness relationships for transformation toughened ceramics; tensile strength and notch sensitivity of Mg-PSZ; fracture mechanisms in lead zirconate titanate ceramics; loading-unloading techniques for determining fracture parameters of brittle materials utilizing four-point bend, chevron-notched specimens; application of the potential drop technique to the fracture mechanics of ceramics; ceramics-to-metal bonding from a fracture mechanics perspective; observed changes in fracture strength following laser irradiation and ion beam mixing of Ni overlayers on sintered alpha-SiC; crack growth in single-crystal silicon; a fracture mechanics and non-destructive evaluation investigation of the subcritical-fracture process in rock; slow crack growth in sintered silicon nitride; uniaxial tensile fatigue testing of sintered silicon carbide under cyclic temperature change; and effect of surface corrosion on glass fracture

  2. Role of intermetallics on the mechanical fatigue behavior of Cu–Al ball bond interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Lassnig, A., E-mail: alice.lassnig@univie.ac.at [University of Vienna, Faculty of Physics, Physics of Nanostructured Materials, Boltzmanngasse 5, 1090 Wien (Austria); Pelzer, R. [Infineon Technologies Austria AG, Siemensstrae 2, 9500 Villach (Austria); Gammer, C. [University of Vienna, Faculty of Physics, Physics of Nanostructured Materials, Boltzmanngasse 5, 1090 Wien (Austria); National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Khatibi, G. [Vienna University of Technology, Institute of Chemical Technology and Analytics, Getreidemarkt 9, 1060 Wien (Austria)

    2015-10-15

    The mechanical fatigue behavior of Cu–Al interfaces occurring in thermosonic ball bonds –typically used in microelectronic packages for automotive applications – is investigated by means of a specially designed fatigue test technique. Fully reversed cyclic shear stresses are induced at the bond interface, leading to subsequent fatigue lift off failure and revealing the weakest site of the bond. A special focus is set on the role of interfacial intermetallic compounds (IMC) on the fatigue performance of such interfaces. Therefore fatigue life curves were obtained for three representative microstructural states: The as-bonded state is compared to two annealed states at 200 °C for 200 h and at 200 °C for 2000 h respectively. In the moderately annealed state two IMC layers (Al{sub 2}Cu, Al{sub 4}Cu{sub 9}) could be identified, whereas in the highly aged state the original pad metallization was almost entirely consumed and AlCu is formed as a third IMC. Finally, the crack path is traced back as a function of interfacial microstructure by means of electron microscopy techniques. Whereas conventional static shear tests reveal no significant decrease of the bond shear force with increased IMC formation the fatigue tests prove a clear degradation in the cyclic mechanical performance. It can be concluded that during cycling the crack deflects easily into the formed intermetallics, leading to early failure of the ball bonds due to their brittle nature. - Highlights: • High cycle fatigue of various miniaturized Cu–Al interfaces is investigated. • Interfacial intermetallic compounds consist of Al2Cu, AlCu and Al4Cu9. • Static shear strength shows minor dependency on interfacial phase formation. • Fatigue tests prove significant degradation with intermetallic compound evolution. • Fatigue fracture surface analysis reveal microstructure dependent crack path.

  3. Role of intermetallics on the mechanical fatigue behavior of Cu–Al ball bond interfaces

    International Nuclear Information System (INIS)

    Lassnig, A.; Pelzer, R.; Gammer, C.; Khatibi, G.

    2015-01-01

    The mechanical fatigue behavior of Cu–Al interfaces occurring in thermosonic ball bonds –typically used in microelectronic packages for automotive applications – is investigated by means of a specially designed fatigue test technique. Fully reversed cyclic shear stresses are induced at the bond interface, leading to subsequent fatigue lift off failure and revealing the weakest site of the bond. A special focus is set on the role of interfacial intermetallic compounds (IMC) on the fatigue performance of such interfaces. Therefore fatigue life curves were obtained for three representative microstructural states: The as-bonded state is compared to two annealed states at 200 °C for 200 h and at 200 °C for 2000 h respectively. In the moderately annealed state two IMC layers (Al 2 Cu, Al 4 Cu 9 ) could be identified, whereas in the highly aged state the original pad metallization was almost entirely consumed and AlCu is formed as a third IMC. Finally, the crack path is traced back as a function of interfacial microstructure by means of electron microscopy techniques. Whereas conventional static shear tests reveal no significant decrease of the bond shear force with increased IMC formation the fatigue tests prove a clear degradation in the cyclic mechanical performance. It can be concluded that during cycling the crack deflects easily into the formed intermetallics, leading to early failure of the ball bonds due to their brittle nature. - Highlights: • High cycle fatigue of various miniaturized Cu–Al interfaces is investigated. • Interfacial intermetallic compounds consist of Al2Cu, AlCu and Al4Cu9. • Static shear strength shows minor dependency on interfacial phase formation. • Fatigue tests prove significant degradation with intermetallic compound evolution. • Fatigue fracture surface analysis reveal microstructure dependent crack path

  4. Localized bending fatigue behavior of high-strength steel monostrands

    DEFF Research Database (Denmark)

    Winkler, Jan; Fischer, Gregor; Georgakis, Christos T.

    2012-01-01

    In this paper, the localized bending fatigue behavior of pretensioned high strength steel monostrands is investigated. Furthermore, a new methodology using an optical photogrammetry system, which can quantify surface deformations on the strand is presented. The system allows measurement of the st......In this paper, the localized bending fatigue behavior of pretensioned high strength steel monostrands is investigated. Furthermore, a new methodology using an optical photogrammetry system, which can quantify surface deformations on the strand is presented. The system allows measurement...... displacement (opening/closing and sliding) of the helically wound wires. Moreover, the results are a step towards understanding the bending fatigue damage mechanisms of monostrand cables....

  5. The effect of carbon nanotube dimensions and dispersion on the fatigue behavior of epoxy nanocomposites

    International Nuclear Information System (INIS)

    Zhang, W; Picu, R C; Koratkar, N

    2008-01-01

    Fatigue is one of the primary reasons for failure in structural materials. It has been demonstrated that carbon nanotubes can suppress fatigue in polymer composites via crack-bridging and a frictional pull-out mechanism. However, a detailed study of the effects of nanotube dimensions and dispersion on the fatigue behavior of nanocomposites has not been performed. In this work, we show the strong effect of carbon nanotube dimensions (i.e. length, diameter) and dispersion quality on fatigue crack growth suppression in epoxy nanocomposites. We observe that the fatigue crack growth rates can be significantly reduced by (1) reducing the nanotube diameter, (2) increasing the nanotube length and (3) improving the nanotube dispersion. We qualitatively explain these observations by using a fracture mechanics model based on crack-bridging and pull-out of the nanotubes. By optimizing the above parameters (tube length, diameter and dispersion) we demonstrate an over 20-fold reduction in the fatigue crack propagation rate for the nanocomposite epoxy compared to the baseline (unfilled) epoxy

  6. Low cycle fatigue and creep fatigue behavior of alloy 617 at high temperature

    International Nuclear Information System (INIS)

    Cabet, Celine; Carroll, Laura; Wright, Richard

    2013-01-01

    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 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 mechanisms and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle fatigue specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens and the addition of a hold time at peak tensile strain degraded the cycle life. This suggests that creep-fatigue interaction occurs and that the environment may be partially responsible for accelerating failure. (authors)

  7. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    Energy Technology Data Exchange (ETDEWEB)

    Margolin, B., E-mail: margolinbz@yandex.ru; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-15

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  8. Fracture strength and fatigue resistance of dental resin-based composites

    NARCIS (Netherlands)

    Keulemans, F.; Palav, P.; Aboushelib, M.M.N.; van Dalen, A.; Kleverlaan, C.J.; Feilzer, A.J.

    2009-01-01

    Objectives: The aim of this study was to evaluate in vitro the influence of fiber-reinforcement on the fracture strength and fatigue resistance of resin-based composites. Methods: One hundred rectangular bar-shaped specimens (2 mm × 2 mm × 25 mm) made of resin-based composite were prepared in a

  9. Probabilistic model for fatigue crack growth and fracture of welded joints in civil engineering structures

    NARCIS (Netherlands)

    Maljaars, J.; Steenbergen, H.M.G.M.; Vrouwenvelder, A.C.W.M.

    2012-01-01

    This paper presents a probabilistic assessment model for linear elastic fracture mechanics (LEFM). The model allows the determination of the failure probability of a structure subjected to fatigue loading. The distributions of the random variables for civil engineering structures are provided, and

  10. Fracture and fatigue considerations in the development of ductile-phase reinforced intermetallic-matrix composites

    International Nuclear Information System (INIS)

    Venkateswara Rao, K.T.; Ritchie, R.O.

    1994-01-01

    The salient microstructural factors influencing fracture and fatigue-crack growth resistance of ductile-particle reinforced intermetallic-matrix composites at ambient temperature are reviewed through examples from the Nb/MoSi 2 , TiNb/TiAl, Nb/TiAl and Nb/Nb 3 Al systems; specific emphasis is placed on properties and morphology of the reinforcement and its interfacial properties with the matrix. It is shown that composites must be fabricated with a high aspect ratio ductile-reinforcement morphology in order to promote crack-particle interception and resultant crack bridging for improved fracture and fatigue properties. Concurrently, however, the ductile phases have contrasting effects on crack growth under monotonic vs. cyclic loading suggesting that composite microstructures tailored for optimal toughness may not necessarily yield optimal fatigue resistance. Perspectives for the future development of damage-tolerant intermetallic-composite microstructures are discussed

  11. Crack growth and fracture in fiber reinforced concrete beams under static and fatigue loading

    International Nuclear Information System (INIS)

    Jeanfreau, J.; Arockiasamy, M.; Reddy, D.V.

    1987-01-01

    The paper presents the results of a two-phase experimental investigation on the fatigue and fracture of six different types of concrete: plain, 0.5%, 1.0%, 1.5%, and 2.0% steel fibers and 0.5% kevlar fibers. In the first phase the J-integral was evaluated for different types of concrete from load-displacement curves. The value shows a marked increase in the energy required to fracture concrete when fibers are added. The values did not vary substantially for different notch depths. In the second phase concrete beams were subjected to fatigue by applying a pure bending on the notch. The effect of fiber addition was examined with emphasis on the crack propagation and the increase in the fatigue strength. The crack pattern was mainly influenced by the presence, amount, and the distribution of the fibers in the concrete. (orig./HP)

  12. Detection of fatigue fracture in pearlitic flake graphite cast iron with the help of scanning and transmission electron microscopy

    International Nuclear Information System (INIS)

    Dunger, B.; Hunger, J.

    1976-01-01

    To prove the existence of the characteristic features of fatigue fracture in a pearlitic flake graphite cast iron, its fracture surface topography revealed by scanning electron microscopy has been compared with that of a pearlitic steel, the fractures having been caused by static tensile and by cyclic bending tests. The characteristic features of fatigue fracture were visible in the pearlitic matrix of the steel and of the flake graphite cast iron as well. These features differ characteristically from the lamellar structure of the pearlite, particularly after etching the surface area of the fractures. The graphite structures as viewed on the electron scanning and the electron transmission microscope are described. (orig.) [de

  13. Correlating Scatter in Fatigue Life with Fracture Mechanisms in Forged Ti-6242Si Alloy

    Science.gov (United States)

    Sinha, V.; Pilchak, A. L.; Jha, S. K.; Porter, W. J.; John, R.; Larsen, J. M.

    2018-04-01

    Unlike the quasi-static mechanical properties, such as strength and ductility, fatigue life can vary significantly (by an order of magnitude or more) for nominally identical material and test conditions in many materials, including Ti-alloys. This makes life prediction and management more challenging for components that are subjected to cyclic loading in service. The differences in fracture mechanisms can cause the scatter in fatigue life. In this study, the fatigue fracture mechanisms were investigated in a forged near- α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si, which had been tested under a condition that resulted in life variations by more than an order of magnitude. The crack-initiation and small crack growth processes, including their contributions to fatigue life variability, were elucidated via quantitative characterization of fatigue fracture surfaces. Combining the results from quantitative tilt fractography and electron backscatter diffraction, crystallography of crack-initiating and neighboring facets on the fracture surface was determined. Cracks initiated on the surface for both the shortest and the longest life specimens. The facet plane in the crack-initiating grain was aligned with the basal plane of a primary α grain for both the specimens. The facet planes in grains neighboring the crack-initiating grain were also closely aligned with the basal plane for the shortest life specimen, whereas the facet planes in the neighboring grains were significantly misoriented from the basal plane for the longest life specimen. The difference in the extent of cracking along the basal plane can explain the difference in fatigue life of specimens at the opposite ends of scatter band.

  14. Talar body fatigue stress fractures: three cases observed in elite female gymnasts

    International Nuclear Information System (INIS)

    Rossi, F.; Dragoni, S.

    2005-01-01

    To introduce and emphasize the clinical and radiological findings of three talar body fatigue stress fractures in competitive athletes. Clinical and radiographic skeletal records of 24,562 athletes taken between 1962 and 2002 were retrospectively reviewed. Among these, 6851 files related to acute foot and ankle injuries or chronic post-traumatic sequelae were found. There were 925 (3.76%) stress fatigue fractures selected from the whole collection. Among these there were three cases (0.32%) of talar body stress fractures diagnosed in elite female gymnasts 15 - 17 years old. The negative first radiograph become positive 4-6 weeks later. Scintigraphy was positive at an early stage and consistent for the diagnosis. CT and MRI gave positive results 1-2 weeks after the beginning of symptoms which were always greatly diagnostic. The sports medicine literature lacks reports of talar body fatigue stress fractures. The poor initial sensitivity of radiography makes it problematic to establish an early diagnosis. A wise combination of scintigraphy, CT and MRI has therefore to be relied upon. Familiarity with this rare location for a stress fracture may prevent delayed diagnosis and long-lasting damage, both of which are important factors in competitive athletes. (orig.)

  15. Talar body fatigue stress fractures: three cases observed in elite female gymnasts

    Energy Technology Data Exchange (ETDEWEB)

    Rossi, F. [National Institute of Sports Medicine of the Italian Olympic Committee, Rome (Italy); Dragoni, S. [National Institute of Sports Medicine of the Italian Olympic Committee, Rome (Italy); Istituto Nazionale di Medicina dello Sport, Rome (Italy)

    2005-07-01

    To introduce and emphasize the clinical and radiological findings of three talar body fatigue stress fractures in competitive athletes. Clinical and radiographic skeletal records of 24,562 athletes taken between 1962 and 2002 were retrospectively reviewed. Among these, 6851 files related to acute foot and ankle injuries or chronic post-traumatic sequelae were found. There were 925 (3.76%) stress fatigue fractures selected from the whole collection. Among these there were three cases (0.32%) of talar body stress fractures diagnosed in elite female gymnasts 15 - 17 years old. The negative first radiograph become positive 4-6 weeks later. Scintigraphy was positive at an early stage and consistent for the diagnosis. CT and MRI gave positive results 1-2 weeks after the beginning of symptoms which were always greatly diagnostic. The sports medicine literature lacks reports of talar body fatigue stress fractures. The poor initial sensitivity of radiography makes it problematic to establish an early diagnosis. A wise combination of scintigraphy, CT and MRI has therefore to be relied upon. Familiarity with this rare location for a stress fracture may prevent delayed diagnosis and long-lasting damage, both of which are important factors in competitive athletes. (orig.)

  16. Microstructural modeling of fatigue fracture of shape memory alloys at thermomechanical cyclic loading

    Science.gov (United States)

    Belyaev, Fedor S.; Evard, Margarita E.; Volkov, Aleksandr E.

    2018-05-01

    A microstructural model of shape memory alloys (SMA) describing their deformation and fatigue fracture is presented. A new criterion of fracture has been developed which takes into account the effect of hydrostatic pressure, deformation defects and material damage. It is shown that the model can describe the fatigue fracture of SMA under various thermomechanical cycling regimes. Results of calculating the number of cycles to failure at thermocycling under a constant stress, at symmetric two-sided cyclic deformation, at straining-unloading cycles, at cycling in the regime of the thermodynamic cycles of a SMA working body in the hard (strain controlled) and soft (stress controlled) working cycles, is studied. Results of calculating the number of cycles to failure are presented for different parameters of these cycles.

  17. X-ray analysis on the fatigue fracture surface of stainless steels

    International Nuclear Information System (INIS)

    Yoshioka, Yasuo; Guimard, B.

    1986-01-01

    Several X-ray diffraction parameters were observed on the fatigue fracture surface and its vicinity of both of SUS420J1 martensitic and SUS304 austenitic stainless steels and we discussed the relation between the stress intensity factor and these parameters. Monotonic plastic zone depth determined by the measurement of residual stress distribution proportionals to the squre of the maximum stress intensity factor as well as the case of ferritic steel. However, it is very difficult to find the relation between the stress intensity factor and residual stress or half value breadth of X-ray diffraction profile in the fracture surface for both materials. On the other hand, the amount of martensite induced by the transformation during fatigue process in SUS304 is related to the maximum stress intensity factor in the fracture surface regardless the stress ratio R. (author)

  18. Fatigue Stress Fracture of the Talar Body: An Uncommon Cause of Ankle Pain.

    Science.gov (United States)

    Kim, Young Sung; Lee, Ho Min; Kim, Jong Pil; Moon, Han Sol

    2016-01-01

    Fatigue stress fractures of the talus are rare and usually involve the head of the talus in military recruits. We report an uncommon cause of ankle pain due to a fatigue stress fracture of the body of the talus in a 32-year-old male social soccer player. Healing was achieved after weightbearing suppression for 6 weeks. Although rare, a stress fracture of the body of the talus should be considered in an athlete with a gradual onset of chronic ankle pain. Magnetic resonance imaging and bone scan are useful tools for early diagnosis. Copyright © 2016 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  19. Fatigue Behavior of Modified Asphalt Concrete Pavement

    Directory of Open Access Journals (Sweden)

    saad I. Sarsam

    2016-02-01

    Full Text Available Fatigue cracking is the most common distress in road pavement. It is mainly due to the increase in the number of load repetition of vehicles, particularly those with high axle loads, and to the environmental conditions. In this study, four-point bending beam fatigue testing has been used for control and modified mixture under various micro strain levels of (250 μƐ, 400 μƐ, and 750 μƐ and 5HZ. The main objective of the study is to provide a comparative evaluation of pavement resistance to the phenomenon of fatigue cracking between modified asphalt concrete and conventional asphalt concrete mixes (under the influence of three percentage of Silica fumes 1%, 2%, 3% by the weight of asphalt content, and (changing in the percentage of asphalt content by (0.5% ± from the optimum. The results show that when Silica fumes content was 1%, the fatigue life increases by 17%, and it increases by 46% when Silica fumes content increases to 2%, and that fatigue life increases to 34 % when Silica fumes content increases to 3% as compared with control mixture at (250 μƐ, 20°C and optimum asphalt content. From the results above, we can conclude the optimum Silica fumes content was 2%. When the asphalt content was 4.4%, the fatigue life has increased with the use of silica fumes by (50%, when asphalt content was 5.4%, the additives had led to increasing the fatigue life by (69%, as compared with the conventional asphalt concrete pavement.

  20. Fatigue behavior of ULTIMETRTM alloy: Experiment and theoretical modeling

    Science.gov (United States)

    Jiang, Liang

    ULTIMETRTM alloy is a commercial Co-26Cr-9Ni (weight percent) superalloy, which possesses excellent resistance to both wear and corrosion. In order to extend the structural applications of this alloy and improve the fundamental understanding of the fatigue damage mechanisms, stress- and strain-controlled fatigue tests were performed at various temperatures and in different environments. The stress- and strain-life data were developed for the structural design and engineering applications of this material. Fractographic studies characterized the crack-initiation and propagation behavior of the alloy. Microstructure evolution during fatigue was revealed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Specifically, it was found that the metastable face-centered-cubic structure of this alloy in the as-received condition could be transformed into a hexagonal-close-packed structure either under the action of plastic deformation at room temperature, or due to the aging and cyclic deformation at intermediate temperatures. This interesting observation constructed a sound basis for the alloy development. The dominant mechanisms, which control the fatigue behavior of ULTIMET alloy, were characterized. High-speed, high-resolution infrared (IR) thermography, as a non-contact, full-field, and nondestructive technique, was used to characterize the damage during fatigue. The temperature variations during each fatigue cycle, which were due to the thermal-elastic-plastic effect, were observed and related to stress-strain analyses. The temperature evolution during fatigue manifested the cumulative fatigue damage process. A constitutive model was developed to predict thermal and mechanical responses of ULTIMET alloy subjected to cyclic deformation. The predicted cyclic stress-strain responses and temperature variations were found to be in good agreement with the experimental results. In addition, a fatigue life prediction model was developed

  1. Seismic Behavior of Fatigue-Retrofitted Steel Frame Piers

    Directory of Open Access Journals (Sweden)

    Kinoshita K.

    2013-01-01

    Full Text Available Fatigue retrofit works have been conducted on severely fatigue damaged beam-to-column connections of existing steel frame bridge piers in Japan. It is clear that retrofit works provides additional stiffness but the significance on the seismic behavior of steel frame piers is not clear. Since fatigue retrofit works have become prevalent, the effect of fatigue retrofit works on the seismic behavior of steel frame piers need to be understood. The objective of this study is therefore to investigate these effects of the retrofit work, especially installation of bolted splices, which is the most common technique. Elasto-plastic finite element earthquake response analyses were carried out. It is shown that the existence of bolted splices may increase seismic demand on the piers when plastic hinge zone is located on the beam. In addition, longer bolted splices using low yield strength steel are proposed to overcome this problem and are shown to give beneficial effects.

  2. Static and fatigue mechanical behavior of three dental CAD/CAM ceramics.

    Science.gov (United States)

    Homaei, Ehsan; Farhangdoost, Khalil; Tsoi, James Kit Hon; Matinlinna, Jukka Pekka; Pow, Edmond Ho Nang

    2016-06-01

    The aim of this study was to measure the mechanical properties and fatigue behavior of three contemporary used dental ceramics, zirconia Cercon(®) (ZC), lithium disilicate e.max(®) CAD (LD), and polymer-infiltrated ceramic Enamic(®) (PIC). Flexural strength of each CAD/CAM ceramic was measured by three point bending (n=15) followed by Weibull analysis. Elastic modulus was calculated from the load-displacement curve. For cyclic fatigue loading, sinusoidal loading with a frequency of 8Hz with minimum load 3N were applied to these ceramics (n=24) using three point bending from 10(3) to 10(6) cycles. Fatigue limits of these ceramics were predicted with S-N fatigue diagram. Fracture toughness and Vickers hardness of the ceramics were measured respectively by single edge V-notch beam (SEVNB) and microindentation (Hv 0.2) methods. Chemical compositions of the materials׳ surfaces were analyzed by EDS, and microstructural analysis was conducted on the fracture surfaces by SEM. One-way ANOVA was performed and the level of significance was set at 0.05 to analyze the numerical results. The mean flexural strength of ZC, LD, and PIC was respectively 886.9, 356.7, and 135.8MPa. However, the highest Weibull modulus belonged to PIC with 19.7 and the lowest was found in LD with 7.0. The fatigue limit of maximum load for one million cycles of ZC, LD, and PIC was estimated to be 500.1, 168.4, and 73.8GPa. The mean fracture toughness of ZC, LD, and PIC was found to be respectively 6.6, 2.8, and 1.4MPam(1/2), while the mean Vickers hardness was 1641.7, 676.7, and 261.7Hv. Fracture surfaces followed fatigue loading appeared to be smoother than that after monotonic loading. Mechanical properties of ZC were substantially superior to the two other tested ceramics, but the scattering of data was the least in PIC. The fatigue limit was found to be approximately half of the mean flexural strength for all tested ceramics. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Length scale of secondary stresses in fracture and fatigue

    International Nuclear Information System (INIS)

    Dong, P.

    2008-01-01

    In an attempt to provide a consistent framework for the analysis and treatment of secondary stresses associated with welding and thermal loading in the context of fracture mechanics, this paper starts with an effective stress characterization procedure by introducing a length-scale concept. With it, a traction-based stress separation procedure is then presented to provide a consistent characterization of stresses from various sources based on their length scale. Their relative contributions to fracture driving force are then quantified in terms of their characteristic length scales. Special attention is given to the implications of the length-scale argument on both analysis and treatment of welding residual stresses in fracture assessment. A series of examples is provided to demonstrate how the present developments can be applied for treating not only secondary stresses but also externally applied stresses, as well as their combined effects on the structural integrity of engineering components

  4. High-temperature fracture and fatigue resistance of a ductile β-TiNb reinforced γ-TiAl intermetallic composite

    International Nuclear Information System (INIS)

    Rao, K.T.V.; Ritchie, R.O.

    1998-01-01

    The high-temperature fatigue-crack propagation and fracture resistance of a model γ-TiAl intermetallic composite reinforced with 20 vol. % ductile β-TiNb particles is examined at elevated temperatures of 650 and 800 C and compared with behavior at room temperature. TiNb reinforcements are found to enhance the fracture toughness of γ-TiAl, even at high temperatures, from about 123 to ∼40 MPa m 1/2 , although their effectiveness is lower compared to room temperature due to the reduction in strength of TiNb particles. Under monotonic loading, crack-growth response in the composite is characterized by resistance-curve behavior arising from crack trapping, renucleation and resultant crack bridging effects attributable to the presence of TiNb particles. In addition, crack-tip blunting associated with plasticity increases the crack-initiation (matrix) toughness of the composite, particularly at 800 C, above the ductile-to-brittle transition temperature (DBTT) for γ-TiAl. High-temperature fatigue-crack growth resistance, however, is marginally degraded by the addition of TiNb particles in the C-R (edge) orientation, similar to observations made at room temperature; premature fatigue failure of TiNb ligaments in the crack wake diminishes the role of bridging under cyclic loading. Both fatigue and fracture resistance of the composite are slightly lower at 650 C (just below the DBTT for TiAl) compared to the behavior at ambient and 800 C. Overall, the beneficial effect of adding ductile TiNb reinforcements to enhance the room-temperature fracture and fatigue resistance of γ-TiAl alloys is retained up to 800 C, in air environments. There is concern, however, regarding the long-term environmental stability of these composite microstructures in unprotected atmospheres

  5. Fatigue and Fracture Resistance of Heavy-Section Ferritic Ductile Cast Iron

    Directory of Open Access Journals (Sweden)

    Matteo Benedetti

    2017-03-01

    Full Text Available In this paper, we explore the effect of a long solidification time (12 h on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI. For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried out on specimens extracted from the same casting. The obtained results are compared with those of similar materials published in the technical literature. Moreover, the discussion is complemented with metallurgical and fractographic analyses. It has been found that the long solidification time, representative of conditions arising in heavy-section castings, leads to an overgrowth of the graphite nodules and a partial degeneration into chunky graphite. With respect to minimum values prescribed for thick-walled (t > 60 mm EN-GJS-400-15, the reduction in tensile strength and total elongation is equal to 20% and 75%, respectively. The rotating bending fatigue limit is reduced by 30% with respect to the standard EN-1563, reporting the results of fatigue tests employing laboratory samples extracted from thin-walled castings. Conversely, the resistance to fatigue crack growth is even superior and the fracture toughness comparable to that of conventional DCI.

  6. Reliability Analysis of Fatigue Fracture of Wind Turbine Drivetrain Components

    DEFF Research Database (Denmark)

    Berzonskis, Arvydas; Sørensen, John Dalsgaard

    2016-01-01

    in the volume of the casted ductile iron main shaft, on the reliability of the component. The probabilistic reliability analysis conducted is based on fracture mechanics models. Additionally, the utilization of the probabilistic reliability for operation and maintenance planning and quality control is discussed....

  7. Fatigue Behavior of 2A12 Aluminum Alloy Under Multiaxial Loading

    Directory of Open Access Journals (Sweden)

    CHEN Ya-jun

    2017-08-01

    Full Text Available The multiaxial fatigue behavior of 2A12 aluminum alloy was studied with SDN100/1000 electro-hydraulic servo tension-torsion fatigue tester under multiple variables, and the failure mechanism was investigated by scanning electron microscopy (SEM. The results show that under the loading condition of equivalent stress, the fatigue life decreases with the increase of phase angle. For the phase angle 0°, some special features can be observed in the crack initial zone, such as the tire pattern,fishbone pattern and stalactite pattern. There are secondary cracks and vague fatigue striations in the crack propagation zone; the multiaxial fatigue life decreases with the change of mean stress for tension or torsion. Some white flocculent oxides can be found in the crack initiation zone, and secondary crack as well as shear-type elongated dimples in the instantaneous fracture zone; facing different loading waveforms, the multiaxial life of sine wave is the longest, triangle wave in the second place, and the square wave is the shortest, under the loading condition of equivalent stress, square wave leads to the maximum structural energy dissipation. Under the low and high two step loading, 2A12 shows training effect.

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

    Energy Technology Data Exchange (ETDEWEB)

    Sarkar, Apu, E-mail: asarkar@barc.gov.in; Kumawat, Bhupendra K.; Chakravartty, J.K.

    2015-07-15

    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.

  9. Influence of low temperature on kinetics of magnesium alloy fatigue fracture

    International Nuclear Information System (INIS)

    Serdyuk, V.A.; Grinberg, N.M.; Malinkina, T.I.; Kamyshkov, A.S.

    1980-01-01

    Studied is the effect of low temperature on kinetics of fatigue fracture in a number of magnesium alloys (MA2-1, MA15, IMV6, MA21, MA12). Cylindrical samples have been tested in vacuum at 20 deg C and at -120 deg C using cyclic symmetric tension-compression. Presented is a dependence of residual durability of alloys at low temperature on the number of preliminary deformation reversals at room temperature. It is shown that for the MA15, MA 12 alloys the durability increases at low temperature due to increasing crack initiation duration, and the out-of-grain crack growth rate is higher at low temperature than at room temperature; whereas for the second group alloys (IMV6, MA21, MA2-1) an increase in the crack initiation stage and a decrease in the crack growth at temperature decreasing are characteristic. A conclusion is made that different behavior of Mg alloys at low temperature is conditioned by their different structural states

  10. The effect of advanced ultrasonic forging on fatigue fracture mechanisms of welded Ti-6A1-4V alloy

    Science.gov (United States)

    Smirnova, A.; Pochivalov, Yu.; Panin, V.; Panin, S.; Eremin, A.; Gorbunov, A.

    2017-12-01

    The current study is devoted to application of advanced postwelding ultrasonic forging to joints formed by laser welding of Ti-6A1-4V alloy in order to enhance their mechanical properties and fatigue durability. Low cycle fatigue tests were performed via digital image correlation technique used to obtain strain fields and in situ characterization of deformation, crack growth and fracture. Fracture surfaces were studied by SEM analysis accompanied with calculation of fracture patterns percentage. The fatigue tests demonstrate the high increase in the number of cycles until fracture (from 17 000 to 32 000 cycles) which could be explained by high ductility of welded material after treatment. This leads to lower fatigue crack growth rate due to higher energy dissipation. The obtained effect is attributable only for small cracks on micro-/mesoscales and fails to play a significant role for macro cracks.

  11. X-ray fractography on fatigue fracture surface of high manganese austenitic steel

    International Nuclear Information System (INIS)

    Akita, Koichi; Misawa, Hiroshi; Kodama, Shotaro; Saito, Tetsuro.

    1997-01-01

    Fatigue tests were carried out under constant stress amplitude, using a non-magnetic high manganese Mn-Cr steel. X-ray fractography was applied on the fatigue fractured surface to investigate the relationship between stress intensity factor and residual stress or half-value breadth of the X-ray diffraction profile. The fatigue crack propagation rate of this non-magnetic Mn-Cr steel had the same tendency as in the ordinary structural ferritic steels. The relationship between stress intensity factor and the residual stress or half-value breadth of the steel was almost the same as that of the ferritic cyclic work hardening steels. No stress induced transformation was observed on the fracture surface, but the residual stress on the fractured surface was compressive in the high stress intensity factors range, which is typical in the cyclic work hardening steels. The half-value breadth on the fractured surface increased with increasing effective stress intensity factor range. The relationship between the half-value breadth and stress intensity factor range was represented by a linear line regardless of the stress ratio. Therefore, the acting stress intensity factor range at the time of fracture can be estimated from the half-value breadth. The depth of monotonic plastic zone was estimated from the distribution of half-value breadth beneath the fractured surface. The relationship between the maximum stress intensity factor and half-value breadth was expressed by the equation ω m α(K max /σ y ) 2 , where the value of α was 0.025. This is about one sixth of the value for ferritic steels, and the fact shows the severe work hardening occuring in the plastic zone in this manganese steel. (author)

  12. Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification

    Directory of Open Access Journals (Sweden)

    Xiaojian Cao

    2018-01-01

    Full Text Available The influence of ultrasonic nanocrystal surface modification (UNSM on the fatigue fracture characteristics of Ti6Al4V was investigated. Two groups of specimens were separated due to different heat treatment conditions. Group one was stress-relief annealed at 650 °C, and group two was then treated with solid solution-aging. UNSM with the conditions of a static load of 25 N, vibration amplitude of 30 μm, and 36,000 strikes per unit produced about 40 μm surface severe plastic deformation (SPD layers on both groups of specimens. UNSM improved the microhardness and the compressive residual stress. UNSM also helped achieve a neat surface, almost without changing the surface roughness. The fatigue strengths of these two groups were improved by 7% and 11.7%, respectively. After UNSM, fatigue cracks mainly initiated from the surface of the specimen before the fatigue life of 106 cycles, while they appeared at the internal compress deformed α-phase at the zone between the SPD layer and the core after the fatigue life of 106 cycles. The cracks usually extended along the deformation overflow bands and the process traces on the surface. Through the change of micro-dimples in the fatigue final rupture region, nanocrystals were achieved in the SPD layer. The crystal slip and the surface remodeling together influenced the energy field of crack evolution.

  13. Fatigue behavior of RC T-beams

    Directory of Open Access Journals (Sweden)

    Omar A. Farghal

    2014-09-01

    Full Text Available The objective of this research is to study the fatigue performance of reinforced concrete (RC T-beams strengthened in shear with Carbon Fiber Reinforced Polymer (CFRP composite. Experiments were conducted on RC beams with and without CFRP sheets bonded on their web surfaces and subjected to static and cycling loading. The obtained results showed that the strengthened beams could survive one million cycles of cyclic loading (=50% of maximum static load with no apparent signs of damage (premature failure demonstrating the effectiveness of CFRP strengthening system on extending the fatigue life of structures. Also, for beams having the same geometry, the applied strengthening technique can significantly enhance the cycling load particularly, in case of beams provided with U-jacket sheets. Moreover, although the failure mode for the different beams was a brittle one, the strengthened beams provided with U-jacket sheets approved an acceptable enhancement in the structural ductility.

  14. Third metacarpal condylar fatigue fractures in equine athletes occur within previously modelled subchondral bone.

    Science.gov (United States)

    Whitton, R Christopher; Trope, Gareth D; Ghasem-Zadeh, Ali; Anderson, Garry A; Parkin, Timothy D H; Mackie, Eleanor J; Seeman, Ego

    2010-10-01

    Bone modelling and remodelling reduce the risk of fatigue fractures; the former by adapting bone to its loading circumstances, the latter by replacing fatigued bone. Remodelling transiently increases porosity because of the normal delay in onset of the formation phase of the remodelling sequence. Protracted intense loading suppresses remodelling leaving modelling as the only means of maintaining bone strength. We therefore hypothesized that race horses with fatigue fractures of the distal third metacarpal bone (MC3) will have reduced porosity associated with suppressed remodelling while continued adaptive modelling will result in higher volume fraction (BV/TV) at this site. Using high resolution peripheral quantitative computed tomography (HR-pQCT), we measured the distal aspect of the MC3 obtained at postmortem from 13 thoroughbred race horses with condylar fractures of the MC3 (cases), 8 horses without fractures (training controls), 14 horses with a fracture at another site (fractured controls) and 9 horses resting from training (resting controls). Porosity of the subchondral bone of MC3 was lower in cases than resting controls (12±1.4% vs. 18±1.6%, P=0.017) although areas of focal porosity were observed adjacent to fractures in 6/13 horses. BV/TV of the distal metacarpal epiphysis tended to be higher in horses with condylar fractures (0.79±0.015) than training controls (0.74±0.019, P=0.070), but also higher in controls with a fracture elsewhere (0.79±0.014) than the training controls (0.74±0.019, P=0.040). BV/TV was higher in horses over three years of age than those aged two or three years (0.79±0.01 vs. 0.74±0.01, P=0.016). All metacarpal condylar fractures occurred within focal areas of high BV/TV. We infer that intense training in equine athletes suppresses remodelling of third metacarpal subchondral bone limiting damage repair while modelling increases regional bone volume in an attempt to minimise local stresses but may fail to offset bone

  15. Fatigue behavior of porous biomaterials manufactured using selective laser melting.

    Science.gov (United States)

    Yavari, S Amin; Wauthle, R; van der Stok, J; Riemslag, A C; Janssen, M; Mulier, M; Kruth, J P; Schrooten, J; Weinans, H; Zadpoor, A A

    2013-12-01

    Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4). © 2013.

  16. The fatigue life and fatigue crack through thickness behavior of a surface cracked plate, 2

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Fujibayashi, Shinpei; Ando, Kotoji; Ogura, Nobukazu.

    1987-01-01

    Most structures have a region where stresses concentrate, and the probability of fatigue crack initiation may be higher than in other parts. Therefore, to improve the reliability of an LBB design, it is necessary to evaluate the growth and through thickness behavior of fatigue cracks in the stress concentration part. In this paper, a fatigue crack growth test at a stress concentration region has been made on 3 % NiCrMo and HT 80 steel. Stress concentration is caused by a fillet on the plate. The main results obtained are as follows : (1) Before cracking through the plate thickness, stress concentration has a remarkable effect on the fatigue crack growth behavior and it flatens the shape of a surface crack. The crack growth behavior can be explained quantatively by using the Newman-Raju equation and the stress resolving method proposed by ASME B and P Code SecXI. (2) The da/dN-ΔK relation obtained in a stress concentration specimen shows good agreement with that obtained in a surface cracked smooth specimen. (3) It is shown that stress concentration caused by a fillet has little effect on the crack growth rate after cracking through the plate thickness. (4) By using the K value based on eq. (1), (2), particular crack growth behavior and the change in crack shape after cracking through thickness can be explained quantatively. (author)

  17. Fatigue stress fractures of the pubic ramus in the army: imaging features with radiographic, scintigraphic and MR imaging findings

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sang Woo; Lee, Chang Hyun [The Armed Forces Capital Hospital, Seongnam (Korea, Republic of)

    2005-03-15

    Although fatigue fractures are not unusual in athletes and military personnel those of the pubic ramus are rare. We report three cases of fatigue fractures of the inferior pubic rami in two male recruits and one female military cadet. On the initial radiograph, most of the lesions were subtle and easy to overlook. However, bone scintigraphy provided more distinct images that allowed easy and early detection of lesion, and MR imaging presented more diagnostic information, which allowed a precise diagnosis.

  18. The fatigue behavior of composite laminates under various mean stresses

    Science.gov (United States)

    Rotem, A.

    1991-01-01

    A method is developed for predicting the S-N curve of a composite laminate which is subjected to an arbitrary stress ratio, R (minimum stress/maximum stress). The method is based on the measuring of the S-N behavior of two distinct cases, tension-tension and compression-compression fatigue loadings. Using these parameters, expressions are formulated that estimate the fatigue behavior under any stress ratio loading. Experimental results from the testing of graphite/epoxy laminates, with various structures, are compared with the predictions and show good agreement.

  19. Macro and Microscopic Investigation on Fracture Specimen of Alloy 617 Base Metal and Weldment in Low Cycle Fatigue Regime

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seon Jin; Dewa, Rando Tungga [Pukyung National Univ., Busan (Korea, Republic of); Kim, Won Gon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-06-15

    This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction.

  20. Macro and Microscopic Investigation on Fracture Specimen of Alloy 617 Base Metal and Weldment in Low Cycle Fatigue Regime

    International Nuclear Information System (INIS)

    Kim, Seon Jin; Dewa, Rando Tungga; Kim, Won Gon

    2016-01-01

    This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction

  1. Micromechanisms of fracture and fatigue in Ti3Al based and TiAl based intermetallics

    International Nuclear Information System (INIS)

    James, A.W.; Chave, R.A.; Hippsley, C.A.; Bowen, P.

    1993-01-01

    Micromechanisms of fracture and fatigue crack growth resistance in specific Ti 3 Al based and TiAl based intermetallics are reviewed. Effects of test temperature, environment and microstructure on crack growth resistance are considered in detail for several Ti 3 Al and Ti'Al based intermetallic systems under development. The implications of these studies for the structural reliability of these materials is also addressed briefly. (orig.)

  2. Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13

    Science.gov (United States)

    Brnic, Josip; Krscanski, Sanjin; Lanc, Domagoj; Brcic, Marino; Turkalj, Goran; Canadija, Marko; Niu, Jitai

    2017-01-01

    The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R=0.25 and R=−1 are shown in the form of S–N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy. PMID:28772749

  3. A study of fatigue and fracture response of cantilevered luminaire structures made from aluminum alloy 6063

    Energy Technology Data Exchange (ETDEWEB)

    Menzemer, Craig C. [Department of Civil Engineering, University of Akron, Akron, OH 443265 (United States); Azzam, Diya [Department of Civil Engineering, University of Akron, Akron, OH 443265 (United States); California Department of Transportation (Caltrans), Bridge Structure Design (Branch, 10) Los Angeles Projects, 1801 30th Street, Sacramento, CA 95816 (United States); Srivatsan, T.S., E-mail: TSrivatsan@uakron.edu [Division of Materials Science and Engineering, Department of Mechanical Engineering, University of Akron, Akron, OH 44325-3903 (United States)

    2010-07-15

    In the experimental results elegantly and exhaustively elaborated upon in this paper the local stresses, obtained from finite element analysis, was used to develop estimates of the stress intensity factor (SIF). In combination with crack growth data, the fatigue lives of both the through-plate and an integrally stiffened socket connection were estimated using software developed by the U.S. Air Force (and referred to as AFGROW). The fatigue life estimates correlated well with the test results provided the crack growth rate data was obtained under conditions of minimal closure at higher stress ratios (of the order R = 0.7). In an attempt to establish the fatigue lives in the high cycle regime, the measured residual stresses had to be included in the analysis. For identical stress ranges, the 25 mm thick through-plate socket connection exhibited noticeably lower fatigue lives when compared to the integrally stiffened shoe-base structure. Scanning electron microscopy observations revealed pockets of well-defined striations consistent with stable growth of the crack through the microstructure prior to the onset of unstable crack growth culminating in catastrophic fracture. In the slow growth region, the fracture surface revealed pockets of shallow, well-defined striations that were uniformly spaced indicative of the occurrence of localized microplastic deformation.

  4. Corrosion fatigue behaviors of two biomedical Mg alloys - AZ91D and WE43 - In simulated body fluid.

    Science.gov (United States)

    Gu, X N; Zhou, W R; Zheng, Y F; Cheng, Y; Wei, S C; Zhong, S P; Xi, T F; Chen, L J

    2010-12-01

    Magnesium alloys have been recently developed as biodegradable implant materials, yet there has been no study concerning their corrosion fatigue properties under cyclic loading. In this study the die-cast AZ91D (A for aluminum 9%, Z for zinc 1% and D for a fourth phase) and extruded WE43 (W for yttrium 4%, E for rare earth mischmetal 3%) alloys were chosen to evaluate their fatigue and corrosion fatigue behaviors in simulated body fluid (SBF). The die-cast AZ91D alloy indicated a fatigue limit of 50MPa at 10⁷ cycles in air compared to 20MPa at 10⁶ cycles tested in SBF at 37°C. A fatigue limit of 110MPa at 10⁷ cycles in air was observed for extruded WE43 alloy compared to 40MPa at 10⁷ cycles tested in SBF at 37°C. The fatigue cracks initiated from the micropores when tested in air and from corrosion pits when tested in SBF, respectively. The overload zone of the extruded WE43 alloy exhibited a ductile fracture mode with deep dimples, in comparison to a brittle fracture mode for the die-cast AZ91D. The corrosion rate of the two experimental alloys increased under cyclic loading compared to that in the static immersion test. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  5. The effects of Nitinol phases on corrosion and fatigue behavior

    Science.gov (United States)

    Denton, Melissa

    The purpose of these studies was to provide a detailed understanding of Nitinol phases and their effects on corrosion and fatigue life. The two primary phases, austenite and martensite, were carefully evaluated with respect to material geometry, corrosion behavior, wear, and fatigue life. Material characterization was performed using several techniques that include metallography, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray photoelectron spectrum (XPS), and Auger electron spectroscopy (AES). Uniaxial tensile tests were conducted to determine the mechanical properties such as elongation, ultimate tensile strength, modulus, transformation strain, and plateau stress. In addition, accelerated wear testing and four point bend fatigue testing were completed to study the fatigue life and durability of the material. The corrosion of Nitinol was found to be dependent on various surface conditions. Electrochemical corrosion behavior of each phase was investigated using cyclic potentiodyamic polarization testing. The corrosion response of electropolished Nitinol was found to be acceptable, even after durability testing. Stress-induced martensite had a lower breakdown potential due to a rougher surface morphology, while thermally induced martensite and austenite performed similarly well. The surface conditioning also had a significant effect on Nitinol mechanical properties. Electropolishing provided a smooth mirror finish that reduced localized texture and enhanced the ductility of the material. Quasi-static mechanical properties can be good indicators of fatigue life, but further fatigue testing revealed that phase transformations had an important role as well. The governing mechanisms for the fatigue life of Nitinol were determined to be both martesitic phase transformations and surface defects. A new ultimate dislocation strain model was proposed based on specific accelerated step-strain testing.

  6. Cyclic Deformation and Fatigue Behaviors of Alloy 617 Base Metal and Weldments at 900℃ for VHTR Applications

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seon Jin; Kim, Byung Tak; Dewa, Rando T.; Hwang, Jeong Jun; Kim, Tae Su [Pukyong National Univ., Busan (Korea, Republic of); Kim, Woo Gon; Kim, Eung Seon [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    An analysis of cyclic deformation can contribute to a deeper understanding of the fatigue fracture mechanisms as well as to improvements in the design and application of VHTR system. However, the studies associated with cyclic deformation and low cycle fatigue (LCF) properties of Alloy 617 have focused mainly on the base metal, with little attention given to the weldments. Totemeier studied on high-temperature creep-fatigue of Alloy 617 base metal and weldments. Current research activities at PKNU and KAERI focus on the study of cyclic deformation and LCF behaviors of Alloy 617 base metal (BM) and weldments (WM) specimens were machined from GTAW buttwelded plates at very high-temperature of 900℃. In this work, the cyclic deformation characteristics and fatigue behaviors of Alloy 617 BM and WM are studied and discussed with respect to LCF. In this paper, cyclic deformation and low cycle fatigue behaviors of Alloy 617 base metal and weldments was evaluated using strain-controlled LCF tests at 900℃for 0.6% total strain range. Results of the current experiments can be concluded; The WM specimen has shown a higher cyclic stress response than the BM specimen. The fatigue life of WM specimen was reduced relative to that of BM specimen.

  7. Fatigue and pain limit independent mobility and physiotherapy after hip fracture surgery

    DEFF Research Database (Denmark)

    Münter, Kristine H.; Clemmesen, Christopher G.; Foss, Nicolai B.

    2017-01-01

    Purpose: The patient’s ability to complete their planned physiotherapy session after hip fracture surgery has been proposed as an independent predictor for achieving basic mobility independency upon hospital discharge. However, knowledge of factors limiting mobility is sparse. We therefore examined...... patient reported factors limiting ability to complete planned physiotherapy sessions as well as limitations for not achieving independency in basic mobility early after hip fracture surgery. Methods: A total of 204 consecutive patients with a hip fracture (mean (SD) age of 80 (9.9) years, 47 patients were......; pain, motor blockade, dizziness, fatigue, nausea, acute cognitive dysfunction and “other limitations”, for not achieving a full Cumulated Ambulation Score or inability to complete planned physiotherapy sessions were noted by the physiotherapist on each of the three first postoperative days. This period...

  8. Bilateral Femoral Neck Fatigue Fracture due to Osteomalacia Secondary to Celiac Disease: Report of Three Cases.

    Science.gov (United States)

    Selek, Ozgur; Memisoglu, Kaya; Selek, Alev

    2015-08-01

    Bilateral non traumatic femoral neck fatigue fracture is a rare condition usually occurring secondary to medical conditions such as pregnancy, pelvic irradiation, corticosteroid exposure, chronic renal failure and osteomalacia. In this report, we present three young female patients with bilateral femoral neck fracture secondary to osteomalacia. The underlying cause of osteomalacia was Celiac disease in all patients. The patients were treated with closed reduction and internal fixation with cannulated lag screws. They were free of pain and full weight bearing was achieved at three months. There were no complications, avascular necrosis and nonunion during the follow up period. In patients with bone pain, non traumatic fractures and muscle weakness, osteomalacia should be kept in mind and proper diagnostic work-up should be performed to identify the underlying cause of osteomalacia such as celiac disease.

  9. Thermal fatigue behavior of thermal barrier coatings by air plasma spray

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Han Sang; Kim, Eui Hyun [Korea Electric Power Research Institute, Daejeon (Korea, Republic of); Lee, Jung Hyuk [Korea Plant Service and Engineering Co. Ltd., Incheon (Korea, Republic of)

    2008-06-15

    Effects of top coat morphology and thickness on thermal fatigue behavior of Thermal Barrier Coatings (TBC) were investigated in this study. Thermal fatigue tests were conducted on three coating specimens with different top coat morphology and thickness, and then the test data were compared via microstructures, cycles to failure, and fracture surfaces. In the air plasma spray specimens (APS1, APS2), top coat were 200 and 300 {mu}m respectively. The thickness of top coat was about 700 {mu}m in the Perpendicular Cracked Specimen (PCS). Under thermal fatigue condition at 1,100 .deg. C, the cycles to top coat failure of APS1, APS2, and PCS were 350, 560 and 480 cycles, respectively. The cracks were initiated at the interface of top coat and Thermally Grown Oxide (TGO) and propagated into TGO or top coat as the number of thermal fatigue cycles increased. For the PCS specimen, additive cracks were initiated and propagated at the starting points of perpendicular cracks in the top coat. Also, the thickness of TGO and the decrease of aluminium concentration in bond coat do not affect the cycles to failure.

  10. Effects of Stress Ratio and Microstructure on Fatigue Failure Behavior of Polycrystalline Nickel Superalloy

    Science.gov (United States)

    Zhang, H.; Guan, Z. W.; Wang, Q. Y.; Liu, Y. J.; Li, J. K.

    2018-05-01

    The effects of microstructure and stress ratio on high cycle fatigue of nickel superalloy Nimonic 80A were investigated. The stress ratios of 0.1, 0.5 and 0.8 were chosen to perform fatigue tests in a frequency of 110 Hz. Cleavage failure was observed, and three competing failure crack initiation modes were discovered by a scanning electron microscope, which were classified as surface without facets, surface with facets and subsurface with facets. With increasing the stress ratio from 0.1 to 0.8, the occurrence probability of surface and subsurface with facets also increased and reached the maximum value at R = 0.5, meanwhile the probability of surface initiation without facets decreased. The effect of microstructure on the fatigue fracture behavior at different stress ratios was also observed and discussed. Based on the Goodman diagram, it was concluded that the fatigue strength of 50% probability of failure at R = 0.1, 0.5 and 0.8 is lower than the modified Goodman line.

  11. Relationships among the Microstructure, Mechanical Properties, and Fatigue Behavior in Thin Ti6Al4V

    Directory of Open Access Journals (Sweden)

    Y. Fan

    2016-01-01

    Full Text Available The microstructures of Ti6Al4V are complex and strongly affect its mechanical properties and fatigue behavior. This paper investigates the role of microstructure on mechanical and fatigue properties of thin-section Ti6Al4V sheets, with the aim of reviewing the effects of microstructure on fatigue properties where suboptimal microstructures might result following heat treatment of assemblies that may not be suited to further annealing, for example, following laser welding. Samples of Ti6Al4V sheet were subjected to a range of heat treatments, including annealing and water quenching from temperatures ranging from 650°C to 1050°C. Micrographs of these samples were inspected for microstructure, and hardness, 0.2% proof stress, elongation, and fracture strength were measured and attributed back to microstructure. Fractography was used to support the findings from microstructure and mechanical analyses. The strength ranking from high to low for the microstructures of thin Ti6Al4V sheets observed in this study is as follows: acicular α′ martensite, Widmanstätten, bimodal, and equiaxed microstructure. The fatigue strength ranking from high to low is as follows: equiaxed, bimodal, Widmanstätten, and acicular α′ martensite microstructure.

  12. Modeling of the mechanical behavior of austenitic stainless steels under pure fatigue and fatigue relaxation loadings

    International Nuclear Information System (INIS)

    Hajjaji-Rachdi, Fatima

    2015-01-01

    Austenitic stainless steels are potential candidates for structural components of sodium-cooled fast neutron reactors. Many of these components will be subjected to cyclic loadings including long hold times (1 month) under creep or relaxation at high temperature. These hold times are unattainable experimentally. The aim of the present study is to propose mechanical models which take into account the involved mechanisms and their interactions during such complex loadings. First, an experimental study of the pure fatigue and fatigue-relaxation behavior of 316L(N) at 500 C has been carried out with very long hold times (10 h and 50 h) compared with the ones studied in literature. Tensile tests at 600 C with different applied strain rates have been undertaken in order to study the dynamic strain ageing phenomenon. Before focusing on more complex loadings, the mean field homogenization approach has been used to predict the mechanical behavior of different FCC metals and alloys under low cycle fatigue at room temperature. Both Hill-Hutchinson and Kroener models have been used. Next, a physically-based model based on dislocation densities has been developed and its parameters measured. The model allows predictions in a qualitative agreement with experimental data for tensile loadings. Finally, this model has been enriched to take into account visco-plasticity, dislocation climb and interaction between dislocations and solute atoms, which are influent during creep-fatigue or fatigue relaxation at high temperature. The proposed model uses three adjustable parameters only and allows rather accurate prediction of the behavior of 316L(N) steel under tensile loading and relaxation. (author) [fr

  13. Effect of fiber fabric orientation on the flexural monotonic and fatigue behavior of 2D woven ceramic matrix composites

    International Nuclear Information System (INIS)

    Chawla, N.; Liaw, P.K.; Lara-Curzio, E.; Ferber, M.K.; Lowden, R.A.

    2012-01-01

    The effect of fiber fabric orientation, i.e., parallel to loading and perpendicular to the loading axis, on the monotonic and fatigue behavior of plain-weave fiber reinforced SiC matrix laminated composites was investigated. Two composite systems were studied: Nextel 312 (3M Corp.) reinforced SiC and Nicalon (Nippon Carbon Corp.) reinforced SiC, both fabricated by Forced Chemical Vapor Infiltration (FCVI). The behavior of both materials was investigated under monotonic and fatigue loading. Interlaminar and in-plane shear tests were conducted to further correlate shear properties with the effect of fabric orientation, with respect to the loading axis, on the orientation effects in bending. The underlying mechanisms, in monotonic and fatigue loading, were investigated through post-fracture examination using scanning electron microscopy (SEM).

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

    International Nuclear Information System (INIS)

    Booker, M.K.; Majumdar, S.

    1982-01-01

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

  15. Fatigue Fracture Strength of Implant-Supported Full Contour Zirconia and Metal Ceramic Fixed Partial Dentures

    Directory of Open Access Journals (Sweden)

    Fariborz Vafaee

    2017-10-01

    Full Text Available Objectives: Zirconia restorations have been suggested as a more durable and more appealing alternative to metal restorations. However, their mechanical properties may be negatively affected by fatigue due to superficial stresses or low temperature degradation. This study aimed to assess the fatigue fracture strength of three-unit implant-supported full contour zirconia and pre-sintered cobalt-chromium (Co-Cr alloy posterior fixed partial dentures (FPDs.Materials and Methods: In this in-vitro experimental study, 28 posterior three-unit implant-supported FPDs were fabricated of full contour zirconia and pre-sintered Co-Cr alloy, and were cemented on implant abutments. To simulate the oral environment, FPDs were subjected to 10,000 thermal cycles between 5-55°C for 30 seconds, and were then transferred to a chewing simulator (100,000 cycles, 50 N, 0.5 Hz. Afterwards, fatigue fracture strength was measured using a universal testing machine. Data were analyzed by Mann-Whitney U test.Results: The mean and standard deviation of fracture strength were 2108.6±440.1 N in full contour zirconia, and 3499.9±1106.5 N in pre-sintered Co-Cr alloy. According to Mann- Whitney U test, the difference in this respect was statistically significant between the two groups (P=0.007.Conclusions: Since the fracture strength values obtained in the two groups were significantly higher than the maximum mean masticatory load in the oral environment, both materials can be used for fabrication of posterior three-unit FPDs, depending on the esthetic demands of patients.

  16. Fatigue

    Science.gov (United States)

    ... to help you find out what's causing your fatigue and recommend ways to relieve it. Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include Taking certain medicines, such as antidepressants, ...

  17. Fracture and fatigue of high strength filaments. Final report, September 25, 1974--August 30, 1975

    International Nuclear Information System (INIS)

    Holt, N.L.; Finnie, I.

    1975-01-01

    The history of high strength filamentary materials is traced and it is seen that their use has been widespread. It is shown that today's demands upon these materials require a better understanding of their behavior than is presently available. Current theories for both the static and fatigue strength of filamentary materials are reviewed. An analysis of static strength tests on short filaments is presented that explains seemingly anomalous test behavior which has been reported in the literature. The proposed approach is supported by experiments and computer analysis. A new machine for the fatigue testing of filaments or wires was designed and is described in detail. Results are presented for fatigue tests on tungsten wire, graphite filaments and glass filaments. Graphite filaments showed an unexpected deterioration in strength after very many cycles (10 8 ). An explanation of this effect is offered and supported by scanning electron microscope observations. The work concludes with some suggestions for further research

  18. Anatomical Thin Titanium Mesh Plate Structural Optimization for Zygomatic-Maxillary Complex Fracture under Fatigue Testing

    Directory of Open Access Journals (Sweden)

    Yu-Tzu Wang

    2018-01-01

    Full Text Available This study performs a structural optimization of anatomical thin titanium mesh (ATTM plate and optimal designed ATTM plate fabricated using additive manufacturing (AM to verify its stabilization under fatigue testing. Finite element (FE analysis was used to simulate the structural bending resistance of a regular ATTM plate. The Taguchi method was employed to identify the significance of each design factor in controlling the deflection and determine an optimal combination of designed factors. The optimal designed ATTM plate with patient-matched facial contour was fabricated using AM and applied to a ZMC comminuted fracture to evaluate the resting maxillary micromotion/strain under fatigue testing. The Taguchi analysis found that the ATTM plate required a designed internal hole distance to be 0.9 mm, internal hole diameter to be 1 mm, plate thickness to be 0.8 mm, and plate height to be 10 mm. The designed plate thickness factor primarily dominated the bending resistance up to 78% importance. The averaged micromotion (displacement and strain of the maxillary bone showed that ZMC fracture fixation using the miniplate was significantly higher than those using the AM optimal designed ATTM plate. This study concluded that the optimal designed ATTM plate with enough strength to resist the bending effect can be obtained by combining FE and Taguchi analyses. The optimal designed ATTM plate with patient-matched facial contour fabricated using AM provides superior stabilization for ZMC comminuted fractured bone segments.

  19. The theory of critical distances applied to problems in fracture and fatigue of bone

    Directory of Open Access Journals (Sweden)

    Emma Brazel

    2009-10-01

    Full Text Available The theory of critical distances (TCD has been applied to predict notch-based fracture and fatigue in a wide range of materials and components. The present paper describes a series of projects in which we applied this approach to human bone. Using experimental data from the literature, combined with finite element analysis, we showed that the TCD was able to predict the effect of notches and holes on the strength of bone failing in brittle fracture due to monotonic loading, in different loading regimes. Bone also displays short crack effects, leading to R-curve data for both fracture toughness and fatigue crack propagation thresholds; we showed that the TCD could predict this data. This analysis raised a number of questions for discussion, such as the significance of the L value itself in this and other materials. Finally, we applied the TCD to a practical problem in orthopaedic surgery: the management of bone defects, showing that predictions could be made which would enable surgeons to decide on whether a bone graft material would be needed to repair a defect, and to specify what mechanical properties this material should have.

  20. The Fracture Mechanical Markov Chain Fatigue Model Compared with Empirical Data

    DEFF Research Database (Denmark)

    Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard

    The applicability of the FMF-model (Fracture Mechanical Markov Chain Fatigue Model) introduced in Gansted, L., R. Brincker and L. Pilegaard Hansen (1991) is tested by simulations and compared with empirical data. Two sets of data have been used, the Virkler data (aluminium alloy) and data...... established at the Laboratory of Structural Engineering at Aalborg University, the AUC-data, (mild steel). The model, which is based on the assumption, that the crack propagation process can be described by a discrete Space Markov theory, is applicable to constant as well as random loading. It is shown...

  1. Variable amplitude fatigue crack growth behavior - a short overview

    International Nuclear Information System (INIS)

    Singh, Konjengbam Darunkumar; Parry, Matthew Roger; Sinclair, Ian

    2011-01-01

    A short overview concerning variable amplitude (VA) fatigue crack growth behavior is presented in this paper. The topics covered in this review encompass important issues pertaining to both single and repeated overload transients. Reviews on transient post overload effects such as plasticity induced crack closure, crack tip blunting, residual stresses, crack deflection and branching, activation of near threshold mechanisms, strain hardening are highlighted. A brief summary on experimental trends and finite element modelling of overload induced crack closure is also presented

  2. Variable amplitude fatigue crack growth behavior - a short overview

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Konjengbam Darunkumar [Indian Institute of Technology, Guwahati (India); Parry, Matthew Roger [Airbus Operations Ltd, Bristol (United Kingdom); Sinclair, Ian [University of Southampton, Southampton (United Kingdom)

    2011-03-15

    A short overview concerning variable amplitude (VA) fatigue crack growth behavior is presented in this paper. The topics covered in this review encompass important issues pertaining to both single and repeated overload transients. Reviews on transient post overload effects such as plasticity induced crack closure, crack tip blunting, residual stresses, crack deflection and branching, activation of near threshold mechanisms, strain hardening are highlighted. A brief summary on experimental trends and finite element modelling of overload induced crack closure is also presented.

  3. A study on fatigue crack growth behavior subjected to a single tensile overload

    International Nuclear Information System (INIS)

    Lee, S.Y.; Liaw, P.K.; Choo, H.; Rogge, R.B.

    2011-01-01

    Neutron diffraction and electric potential experiments were carried out to investigate the growth behavior of a fatigue crack subjected to a single tensile overload. The specific objectives were to (i) probe the crack tip deformation and fracture behaviors under applied loads; (ii) examine the overload-induced transient crack growth micromechanism; (iii) validate the effective stress intensity factor range based on the crack closure approach as the fatigue crack tip driving force; and (iv) establish a quantitative relationship between the crack tip driving force and crack growth behavior. Immediately after a single tensile overload was introduced and then unloaded, the crack tip became blunt and enlarged compressive residual stresses in both magnitude and zone size were observed around the crack tip. The results show that the combined contributions of the overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are responsible for the observed changes in the crack opening load and the resultant post-overload transient crack growth behavior.

  4. Fracture mechanical evaluation of high temperature structure and creep-fatigue defect assessment

    Energy Technology Data Exchange (ETDEWEB)

    Park, Chang Gyu; Kim, Jong Bum; Lee, Jae Han

    2004-02-01

    This study proposed the evaluation procedure of high temperature structures from the viewpoint of fracture mechanics on the cylindrical structure applicable to the KALIMER, which is developed by KAERI. For the evaluation of structural integrity, linear and non-linear fracture mechanics parameters were analyzed. Parameters used in creep defect growth applicable to high temperature structure of liquid metal reactor and the evaluation codes with these parameters were analyzed. The evaluation methods of defect initiation and defect growth which were established in R5/R6 code(UK), JNC method (Japan) and RCC-MR A16(France) code were analyzed respectively. The evaluation procedure of leak before break applicable to KALIMER was preliminarily developed and proposed. As an application example of defect growth, the creep-fatigue defect growth on circumferential throughwall defect in high temperature cylindrical structure was evaluated by RCC-MR A16 and this application technology was established.

  5. Effects of laser peening treatment on high cycle fatigue and crack propagation behaviors in austenitic stainless steel

    International Nuclear Information System (INIS)

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

    2010-01-01

    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 10 8 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. (author)

  6. Fatigue Crack Growth Behavior of Austempered AISI 4140 Steel with Dissolved Hydrogen

    Directory of Open Access Journals (Sweden)

    Varun Ramasagara Nagarajan

    2017-11-01

    Full Text Available The focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behavior of an austempered low-alloy AISI 4140 steel. The investigation also examined the influence of dissolved hydrogen on the fatigue threshold in this material. The material was tested in two conditions, as-received (cold rolled and annealed and austempered (austenitized at 882 °C for 1 h and austempered at 332 °C for 1 h. The microstructure of the annealed specimens consisted of a mix of ferrite and fine pearlite; the microstructure of the austempered specimens was lower bainite. Tensile and Compact Tension specimens were prepared. To examine the influence of dissolved hydrogen, two subsets of the CT specimens were charged with hydrogen for three different time periods between 150 and 250 h. All of the CT samples were then subjected to fatigue crack growth tests in the threshold and linear regions at room temperature. The test results indicate that austempering resulted in significant improvement in the yield and tensile strength as well as the fracture toughness of the material. The test results also show that, in the absence of dissolved hydrogen, the crack growth rate in the threshold and linear regions was lower in austempered samples compared to the as-received (annealed samples. The fatigue threshold was also slightly greater in the austempered samples. In presence of dissolved hydrogen, the crack growth rate was dependent upon the ∆K value. In the low ∆K region (<30 MPa√m, the presence of dissolved hydrogen caused the crack growth rate to be higher in the austempered samples as compared to annealed samples. Above this value, the crack growth rate was increasingly greater in the annealed specimens when compared to the austempered specimens in presence of dissolved hydrogen. It is concluded that austempering of 4140 steel appears to provide a processing route by which the strength, hardness, and fracture toughness of

  7. Fatigue fracture analysis in medium carbon structural steel and austenitic stainless steel by X-ray fractography

    International Nuclear Information System (INIS)

    Rao, N.N.; Azmi bin Rahmat

    1994-01-01

    Apart from the reidual stresses present in the bulk material, a growing fatigue crack may develop its own stress field ahead of the crack tip which in turn could influence the crack propagation behaviour. A fracture surface analysis through measurement of the residual stress of a failed component may provide some additional useful information to that obtained through conventional metallurgical and fracture mechanics investigations. This method of fracture surface analysis using x-ray diffraction technique is known as X -ray Fractography . Residual stress (ρ sub γ) and the full width at half maximum (FWHM) of the x-ray diffraction profile of any reflection are determined at different crack lengths on the fracture surface. These are then corelated to the fracture toughness parameters such as fracture toughness K sub I sub C, the maximum stress intensity factor K sub max and the stress intensity factor range δK. The present investigation aims at detailed x-ray analysis of the fatigue fractured surfaces of the compact tension specimens prepared from ferritic and austenitic stainless steels. The ferritic steel has been subjected to various heat treatments to obtain different microstructures and mechanical properties. The overall observations are analyzed through fatigue (cumulative) damage and material science concepts

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

    International Nuclear Information System (INIS)

    Wong, F.M.G.

    1990-06-01

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

  9. Low Cycle Fatigue behavior of SMAW welded Alloy28 superaustenitic stainless steel at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kchaou, Y., E-mail: yacinekchaou@yahoo.fr [Institut Pprime, Département Physique et Mécanique des Matériaux, UPR 3346 CNRS ISAE-ENSMA Université de Poitiers, Téléport 2, 1, avenue Clément Ader, BP 40109, F – 86961 Futuroscope Chasseneuil Cedex (France); Laboratoire de Génie des Matériaux et Environnement (LGME), ENIS, BPW 1173, Sfax (Tunisia); Pelosin, V.; Hénaff, G. [Institut Pprime, Département Physique et Mécanique des Matériaux, UPR 3346 CNRS ISAE-ENSMA Université de Poitiers, Téléport 2, 1, avenue Clément Ader, BP 40109, F – 86961 Futuroscope Chasseneuil Cedex (France); Haddar, N.; Elleuch, K. [Laboratoire de Génie des Matériaux et Environnement (LGME), ENIS, BPW 1173, Sfax (Tunisia)

    2016-01-10

    This paper focused on the study of Low Cycle Fatigue of welded joints of superaustenitic (Alloy28) stainless steels. Chemical composition and microstructure investigation of Base Metal (BM) and Weld Metal (WM) were identified. The results showed that both of composition is fully austenitic with a dendritic microstructure in the WM. Low cycle fatigue tests at different strain levels were performed on Base Metal (BM) and Welded Joint (WJ) specimens with a strain ratio R{sub ε}=−1. The results indicated that the fatigue life of welded joints is lower than the base metal. This is mainly due to the low ductility of the Welded Metal (WM) and the presence of welding defects. Simultaneously, Scanning Electron Microscope (SEM) observations of fractured specimens show that WJ have brittle behavior compared to BM with the presence of several welding defects especially in the crack initiation site. An estimation of the crack growth rate during LCF tests of BM and WJ was performed using distance between striations. The results showed that the crack initiation stage is shorter in the case of WJ compared to BM because of the presence of welding defects in WJ specimens.

  10. Tensile and fatigue behavior of polymer composites reinforced with superelastic SMA strands

    Science.gov (United States)

    Daghash, Sherif M.; Ozbulut, Osman E.

    2018-06-01

    This study explores the use of superelastic shape memory alloy (SMA) strands, which consist of seven individual small-diameter wires, in an epoxy matrix and characterizes the tensile and fatigue responses of the developed SMA/epoxy composites. Using a vacuum assisted hand lay-up technique, twelve SMA fiber reinforced polymer (FRP) specimens were fabricated. The developed SMA-FRP composites had a fiber volume ratio of 50%. Tensile response of SMA-FRP specimens were characterized under both monotonic loading and increasing amplitude loading and unloading cycles. The degradation in superelastic properties of the developed SMA-FRP composites during fatigue loading at different strain amplitudes was investigated. The effect of loading rate on the fatigue response of SMA-FRP composites was also explored. In addition, fractured specimens were examined using the scanning electron microscopy (SEM) technique to study the failure mechanisms of the tested specimens. A good interfacial bonding between the SMA strands and epoxy matrix was observed. The developed SMA-FRP composites exhibited good superelastic behavior at different strain amplitudes up to at least 800 cycle after which significant degradation occurred.

  11. High temperature fracture and fatigue of ceramics. Annual technical progress report No. 6, August 15, 1994--August 14, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Cox, B.

    1996-04-01

    This report covers work done in the first year of our new contract {open_quotes}High Temperature Fracture and Fatigue of Ceramics,{close_quotes} which commenced in August, 1995 as a follow-on from our prior contract {open_quotes}Mechanisms of Mechanical Fatigue in Ceramics.{close_quotes} Our activities have consisted mainly of studies of the failure of fibrous ceramic matrix composites (CMCs) at high temperature; with a little fundamental work on the role of stress redistribution in the statistics of fracture and cracking in the presence of viscous fluids.

  12. Fatigue crack growth behavior under cyclic thermal transient stress

    International Nuclear Information System (INIS)

    Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.

    1986-01-01

    Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)

  13. Fatigue crack growth behavior under cyclic transient thermal stress

    International Nuclear Information System (INIS)

    Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.

    1987-01-01

    Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)

  14. Fatigue crack growth behavior in niobium-hydrogen alloys

    International Nuclear Information System (INIS)

    Lin, M.C.C.; Salama, K.

    1997-01-01

    Near-threshold fatigue crack growth behavior has been investigated in niobium-hydrogen alloys. Compact tension specimens (CTS) with three hydrogen conditions are used: hydrogen-free, hydrogen in solid solution, and hydride alloy. The specimens are fatigued at a temperature of 296 K and load ratios of 0.05, 0.4, and 0.75. The results at load ratios of 0.05 and 0.4 show that the threshold stress intensity range (ΔK th ) decreases as hydrogen is added to niobium. It reaches a minimum at the critical hydrogen concentration (C cr ), where maximum embrittlement occurs. The critical hydrogen concentration is approximately equal to the solubility limit of hydrogen in niobium. As the hydrogen concentration exceeds C cr , ΔK th increases slowly as more hydrogen is added to the specimen. At load ratio 0.75, ΔK th decreases continuously as the hydrogen concentration is increased. The results provide evidence that two mechanisms are responsible for fatigue crack growth behavior in niobium-hydrogen alloys. First, embrittlement is retarded by hydride transformation--induced and plasticity-induced crack closures. Second, embrittlement is enhanced by the presence of hydrogen and hydride

  15. Fracture mechanics and residual fatigue life analysis for complex stress fields. Technical report

    International Nuclear Information System (INIS)

    Besuner, P.M.

    1975-07-01

    This report reviews the development and application of an influence function method for calculating stress intensity factors and residual fatigue life for two- and three-dimensional structures with complex stress fields and geometries. Through elastic superposition, the method properly accounts for redistribution of stress as the crack grows through the structure. The analytical methods used and the computer programs necessary for computation and application of load independent influence functions are presented. A new exact solution is obtained for the buried elliptical crack, under an arbitrary Mode I stress field, for stress intensity factors at four positions around the crack front. The IF method is then applied to two fracture mechanics problems with complex stress fields and geometries. These problems are of current interest to the electric power generating industry and include (1) the fatigue analysis of a crack in a pipe weld under nominal and residual stresses and (2) fatigue analysis of a reactor pressure vessel nozzle corner crack under a complex bivariate stress field

  16. Fatigue crack growth monitoring: fracture mechanics and non-destructive testing requirements

    International Nuclear Information System (INIS)

    Williams, S.; Mudge, P.J.

    1982-01-01

    If a fatigue crack is found in a component in service, two options exist if plant integrity is to be maintained: first, the plant can be removed from service and repairs effected or replacements fitted; second, the growth of the crack can be monitored non-destructively until it is either considered to be too large to tolerate, in which case it must be repaired, or until a convenient down time when repair can be effected. The second option has obvious benefits for plant operators, but in such a situation it is essential that errors of the non-destructive estimate of defect size, which will undoubtedly exist, and uncertainties in the fatigue crack growth laws in operation must both be allowed for if a safe extension of service life is to be obtained; i.e. without failure by leakage or fast fracture arising from the fatigue crack. This paper analyses the accuracy required of non-destructive crack measurement techniques to permit the safe monitoring of crack growth by periodic inspection. It then demonstrates that it is possible to achieve adequate crack monitoring using conventional ultrasonic techniques. (author)

  17. Behavior of Steel Branch Connections during Fatigue Loading

    Directory of Open Access Journals (Sweden)

    Sládek A.

    2017-09-01

    Full Text Available Fatigue behavior of the branch connection made of low-alloyed steel with yield stress of 355 MPa during low-cycle bending test is investigated in the article. Numerical prediction of the stress and strain distribution are described and experimentally verified by fatigue test of the branch connection sample. Experimental verification is based on low-cycle bending testing of the steel pipes welded by manual metal arc process and loaded by external force in the appropriate distance. Stresses and displacement of the samples induced by bending moment were measured by unidirectional strain gauges and displacement transducers. Samples were loaded in different testing levels according to required stress for 2.106 cycles. Increase of the stress value was applied until the crack formation and growth was observed. Results showed a high agreement of numerical and experimental results of stress and displacement.

  18. Fracture behavior of W based materials

    International Nuclear Information System (INIS)

    Hack, J.E.

    1991-01-01

    This report describes the results of a program to investigate the fracture properties of tungsten based materials. In particular, the role of crack velocity on crack instability was determined in a W-Fe-Ni-Co ''heavy alloy'' and pure polycrystalline tungsten. A considerable effort was expended on the development of an appropriate crack velocity gage for use on these materials. Having succeeded in that, the gage technology was employed to determine the crack velocity response to the applied level of stress intensity factor at the onset of crack instability in pre-cracked specimens. The results were also correlated to the failure mode observed in two material systems of interest. Major results include: (1) unstable crack velocity measurements on metallic specimens which require high spatial resolution require the use of brittle, insulating substrates, as opposed to the ductile, polymer based substrates employed in low spatial resolution measurements; and (2) brittle failure modes, such as cleavage, are characterized by relatively slow unstable crack velocities while evidence of high degrees of deformation are associated with failures which proceed at high unstable crack velocities. This latter behavior is consistent with the predictions of the modeling of Hack et al and may have a significant impact on the interpretation of fractographs in general

  19. Fracture Mechanics

    International Nuclear Information System (INIS)

    Jang, Dong Il; Jeong, Gyeong Seop; Han, Min Gu

    1992-08-01

    This book introduces basic theory and analytical solution of fracture mechanics, linear fracture mechanics, non-linear fracture mechanics, dynamic fracture mechanics, environmental fracture and fatigue fracture, application on design fracture mechanics, application on analysis of structural safety, engineering approach method on fracture mechanics, stochastic fracture mechanics, numerical analysis code and fracture toughness test and fracture toughness data. It gives descriptions of fracture mechanics to theory and analysis from application of engineering.

  20. Fatigue behavior of welded austenitic stainless steel in different environments

    Directory of Open Access Journals (Sweden)

    D.S. Yawas

    2014-01-01

    Full Text Available The fatigue behavior of welded austenitic stainless steel in 0.5 M hydrochloric acid and wet steam corrosive media has been investigated. The immersion time in the corrosive media was 30 days to simulate the effect on stainless steel structures/equipment in offshore and food processing applications and thereafter annealing heat treatment was carried out on the samples. The findings from the fatigue tests show that seawater specimens have a lower fatigue stress of 0.5 × 10−5 N/mm2 for the heat treated sample and 0.1 × 10−5 N/mm2 for the unheat-treated sample compared to the corresponding hydrochloric acid and steam samples. The post-welding heat treatment was found to increase the mechanical properties of the austenitic stainless steel especially tensile strength but it reduces the transformation and thermal stresses of the samples. These findings were further corroborated by the microstructural examination of the stainless steel specimen.

  1. Biaxial fatigue crack propagation behavior of perfluorosulfonic-acid membranes

    Science.gov (United States)

    Lin, Qiang; Shi, Shouwen; Wang, Lei; Chen, Xu; Chen, Gang

    2018-04-01

    Perfluorosulfonic-acid membranes have long been used as the typical electrolyte for polymer-electrolyte fuel cells, which not only transport proton and water but also serve as barriers to prevent reactants mixing. However, too often the structural integrity of perfluorosulfonic-acid membranes is impaired by membrane thinning or cracks/pinholes formation induced by mechanical and chemical degradations. Despite the increasing number of studies that report crack formation, such as crack size and shape, the underlying mechanism and driving forces have not been well explored. In this paper, the fatigue crack propagation behaviors of Nafion membranes subjected to biaxial loading conditions have been investigated. In particular, the fatigue crack growth rates of flat cracks in responses to different loading conditions are compared, and the impact of transverse stress on fatigue crack growth rate is clarified. In addition, the crack paths for slant cracks under both uniaxial and biaxial loading conditions are discussed, which are similar in geometry to those found after accelerated stress testing of fuel cells. The directions of initial crack propagation are calculated theoretically and compared with experimental observations, which are in good agreement. The findings reported here lays the foundation for understanding of mechanical failure of membranes.

  2. The effect of aging treatment on the high temperature fatigue strength and fatigue fracture behaviour of friction welded domestic heat resisting steels (SUH3-SUS303)

    International Nuclear Information System (INIS)

    Lee, K.Y.; Oh, S.K.; Kim, H.J.

    1981-01-01

    In this study the experiment was carried out as the high temperature rotary bending fatigue testing under the condition of 700 0 C high temperature to the friction welded domestic heat resisting steels, SUH3-SUS303, which were 10 hr., 100 hr. aging heat treated at 700 0 C after solution treatment 1 hr. at 1060 0 C for the purpose of observing the effects of the high temperature fatigue strength and fatigue fracture behaviours as well as with various mechanical properties of welded joints. The results obtained are summarized as follows: 1) Through mechanical tests and microstructural examinations, the determined optimum welding conditions, rotating speed 2420 rpm, heating pressure 8 kg/mm 2 , upsetting pressure 22 kg/mm 2 , the amount of total upset 7 mm (heating time 3 sec and upsetting time 2 sec) were satisfied. 2) The solution treated material SUH3, SUS303 and SUH3-SUS303, have the highest inclination gradiant on S-N curve due to the high temperature fatigue testing for long time at 700 0 C. 3) The optimum aging time of friction welded SUH3-SUS303, has been recognized near the 10 hr. at 700 0 C after the solution treatment of 1 hr. at 1060 0 C. 4) The high temperature fatigue limits of aging treated materials were compared with those of raw material according to the extender of aging time, on 10 hr. aging, fatigue limits were increased by SUH3 75.4%, SUS303 28.5%, friction welded joints SUH3-SUS303 44.2% and 100 hr. aging the rate were 64.9%, 30.4% and 36.6% respectively. 5) The fatigue fractures occurred at the side of the base metal SUS303 of the friction welded joints SUH3-SUS303 and it is difficult to find out fractures at the friction welding interfaces. 6) The cracking mode of SUS303, SUH3-SUS303 is intergranular in any case, but SUH3 is fractured by transgranular cracking. (author)

  3. Survey of the effect of heat-to-heat variations upon the fatigue-crack propagation behavior of types 304 and 316 stainless steels

    International Nuclear Information System (INIS)

    James, L.A.

    1975-05-01

    The fatigue-crack growth behavior of four heats of annealed Type 304 stainless steel and three heats of annealed Type 316 stainless steel were studied at elevated temperature using the techniques of linear-elastic fracture mechanics. It is estimated that a factor of 1.5 applied above and below the mean line would provide upper and lower bounds that would account for heat-to-heat variations. In addition, the three heats of Type 316 represented three different melt practices: air-melt, vacuum-arc-remelt, and double-vacuum-melt processes. No effect on fatigue-crack growth behavior was noted due to melt practice. (U.S.)

  4. High cycle fatigue behavior of the IN718/M247 hybrid element fabricated by friction welding at elevated temperatures

    Directory of Open Access Journals (Sweden)

    Tran Hung Tra

    2016-12-01

    Full Text Available A hybrid element has been fabricated by friction welding, joining two superalloys Inconel 718 and Mar-M247. The high cycle fatigue behavior of this welded element was investigated at 500 °C and 700 °C. The fabrication could obtain excellent fatigue strength in which the fracture is located in the base metal Mar-M247 side and takes place outside the welded zone. The behavior of the joint under loadings is discussed through a simulation by the numerical finite element method.

  5. Fatigue crack propagation behavior of stainless steel welds

    Science.gov (United States)

    Kusko, Chad S.

    The fatigue crack propagation behavior of austenitic and duplex stainless steel base and weld metals has been investigated using various fatigue crack growth test procedures, ferrite measurement techniques, light optical microscopy, stereomicroscopy, scanning electron microscopy, and optical profilometry. The compliance offset method has been incorporated to measure crack closure during testing in order to determine a stress ratio at which such closure is overcome. Based on this method, an empirically determined stress ratio of 0.60 has been shown to be very successful in overcoming crack closure for all da/dN for gas metal arc and laser welds. This empirically-determined stress ratio of 0.60 has been applied to testing of stainless steel base metal and weld metal to understand the influence of microstructure. Regarding the base metal investigation, for 316L and AL6XN base metals, grain size and grain plus twin size have been shown to influence resulting crack growth behavior. The cyclic plastic zone size model has been applied to accurately model crack growth behavior for austenitic stainless steels when the average grain plus twin size is considered. Additionally, the effect of the tortuous crack paths observed for the larger grain size base metals can be explained by a literature model for crack deflection. Constant Delta K testing has been used to characterize the crack growth behavior across various regions of the gas metal arc and laser welds at the empirically determined stress ratio of 0.60. Despite an extensive range of stainless steel weld metal FN and delta-ferrite morphologies, neither delta-ferrite morphology significantly influence the room temperature crack growth behavior. However, variations in weld metal da/dN can be explained by local surface roughness resulting from large columnar grains and tortuous crack paths in the weld metal.

  6. Ductile-reinforcement toughening in γ-TiAl intermetallic-matrix composites: Effects on fracture toughness and fatigue-crack propagation resistance

    International Nuclear Information System (INIS)

    Venkateswara Rao, K.T.; Ritchie, R.O.; Odette, G.R.

    1994-01-01

    The influence of the type, volume fraction, thickness and orientation of ductile phase reinforcements on the room temperature fatigue and fracture resistance of γ-TiAl intermetallic alloys is investigated. Large improvements in toughness compared to monolithic γ-TiAl are observed in both the TiNb- and Nb-reinforced composites under monotonic loading. Toughness increases with increasing ductile phase content, reinforcement thickness and strength; orientation effect are minimal. Crack-growth behavior is characterized by steep resistance curves primarily due to crack trapping/renucleation and extensive crack bridging by the ductile-phase particles. In contrast, under cyclic loading the influence of ductile phases on fatigue resistance is strongly dependent upon reinforcement orientation. Compared to monolithic γ-TiAl, improvements in fatigue-crack growth resistance are observed in TiNb-reinforced composites only in the face (C-L) orientation; crack-growth rates for the edge (C-R) orientation are actually faster in the composite. In comparison, Nb-particle reinforcements offer less toughening under monotonic loading but enhance the fatigue properties compared to TiNb reinforcements under cyclic loading

  7. The effects of strain-induced martensitic transformation and temperature on impact fatigue crack propagation behavior of SUS 304 at low temperature

    International Nuclear Information System (INIS)

    Murakami, Ri-ichi; Akizono, Koichi; Kusukawa, Kazuhiro.

    1988-01-01

    The fatigue crack propagation behavior in fatigue impact at room temperature and 103 K was investigated by means of fracture mechanics, X-ray diffraction analysis and fractography for an austenitic stainless steel, SUS 304. The crack growth rate in fatigue impact decreased with decreasing temperature. The crack growth rate at room temperature was scarcely influenced by the microstructure, while at low temperature it was markedly influenced by the microstructure. The effects of microstructure and temperature on the crack growth rate were closely related to the strain-induced martensitic transformation. The martensitic transformation was influenced by the microstructure, the temperature, the fracture morphology and the stress intensity level and resulted in a decrease in crack growth rate with increasing crack opening level. (author)

  8. Strain-rate dependent fatigue behavior of 316LN stainless steel in high-temperature water

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Jibo [CAS Key Laboratory of Nuclear Materials and Safety Assessment, Liaoning Key Laboratory for Safety and Assessment Technique of Nuclear Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Wu, Xinqiang, E-mail: xqwu@imr.ac.cn [CAS Key Laboratory of Nuclear Materials and Safety Assessment, Liaoning Key Laboratory for Safety and Assessment Technique of Nuclear Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Han, En-Hou; Ke, Wei; Wang, Xiang [CAS Key Laboratory of Nuclear Materials and Safety Assessment, Liaoning Key Laboratory for Safety and Assessment Technique of Nuclear Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Sun, Haitao [Nuclear and Radiation Safety Center, SEPA, Beijing 100082 (China)

    2017-06-15

    Low cycle fatigue behavior of forged 316LN stainless steel was investigated in high-temperature water. It was found that the fatigue life of 316LN stainless steel decreased with decreasing strain rate from 0.4 to 0.004 %s{sup −1} in 300 °C water. The stress amplitude increased with decreasing strain rate during fatigue tests, which was a typical characteristic of dynamic strain aging. The fatigue cracks mainly initiated at pits and slip bands. The interactive effect between dynamic strain aging and electrochemical factors on fatigue crack initiation is discussed. - Highlights: •The fatigue lives of 316LN stainless steel decrease with decreasing strain rate. •Fatigue cracks mainly initiated at pits and persistent slip bands. •Dynamic strain aging promoted fatigue cracks initiation in high-temperature water.

  9. Fractal cluster modeling of the fatigue behavior of lead zirconate titanate

    OpenAIRE

    Priya, Shashank; Kim, Hyeoung Woo; Ryu, Jungho; Uchino, Kenji; Viehland, Dwight D.

    2002-01-01

    The fatigue behavior of lead zirconate titanate ceramics (PZT) has been studied under electrical and mechanical drives. Piezoelectric fatigue was studied using a mechanical method. Under ac mechanical drive, hard and soft PZTs showed an increase in the longitudinal piezoelectric constant at short times, reaching a maximum at intermediate times. Systematic investigations were performed to characterize the electrical fatigue behavior. A decrease in the magnitude of the remanent polarization was...

  10. Low-Cycle Fatigue Behavior of 10CrNi3MoV High Strength Steel and Its Undermatched Welds.

    Science.gov (United States)

    Song, Wei; Liu, Xuesong; Berto, Filippo; Razavi, S M J

    2018-04-24

    The use of high strength steel allows the design of lighter, more slender and simpler structures due to high strength and favorable ductility. Nevertheless, the increase of yield strength does not guarantee the corresponding improvement of fatigue resistance, which becomes a major concern for engineering structure design, especially for the welded joints. The paper presents a comparison of the low cycle fatigue behaviors between 10CrNi3MoV high strength steel and its undermatched weldments. Uniaxial tension tests, Push-pull, strain-controlled fatigue tests were conducted on base metal and weldments in the strain range of 0.2⁻1.2%. The monotonic and cyclic stress-strain curves, stress-life, strain-life and energy-life in terms of these materials were analyzed for fatigue assessment of materials discrepancy. The stress-life results of base metal and undermatched weld metal exhibit cyclic softening behaviors. Furthermore, the shapes of 10CrNi3MoV steel hysteresis loops show a satisfactory Masing-type behavior, while the weld metal shows a non-Masing type behavior. Strain, plastic and total strain energy density amplitudes against the number of reversals to failure results demonstrate that the undermatched weld metal presents a higher resistance to fatigue crack initiation than 10CrNi3MoV high strength steel. Finally, fatigue fracture surfaces of specimens were compared by scanning electron microscopy to identify the differences of crack initiation and the propagation between them.

  11. Fatigue behavior of an insulation system for the ITER magnets

    International Nuclear Information System (INIS)

    Prokopec, R.; Humer, K.; Weber, H.W.

    2006-01-01

    The application of glass-fiber reinforced plastics as insulation materials for fusion magnet coils (e.g. the Toroidal Field Coils of ITER) requires the full characterization of their mechanical performance under ITER-relevant conditions. One of the methods of testing material's response under dynamic load is the tension-tension fatigue procedure. This test can be used to simulate the pulsed tokamak-operation of the ITER coils over a lifetime of more than 20 years. Furthermore, it provides information on the maximum tensile or shear stress in the ITER-relevant range of 10 4 -10 5 cycles. In order to simulate the operation conditions of ITER as closely as possible, several fatigue parameters can be set in the test programme, e.g., the minimum-to-peak stress ratio R and the frequency ν of the sinusoidal load function. Further, the fatigue process can be run under load or strain control. All of these parameters may influence the mechanical response of the insulation system under cyclic load. Therefore, it is highly desirable to investigate the influence of test parameter variations on the measured stress-lifetime diagrams. The investigations were performed at 77 K using an industrial glass-fiber reinforced composite impregnated with epoxy resin. For both the load and the strain controlled mode, R-values of 0.3 and 0.5 and a frequency of 10 Hz were chosen. The results showed almost no deviations in the lifetime behavior between the load and the strain controlled mode, up to the ITER specified number of pulses, i.e. 3 x 10 4 cycles. Beyond this point, the residual strength levels were lower by 5-30 % under strain control than under load control. This effect is more pronounced at higher cycle numbers and for lower R-ratios. (author)

  12. Statistical analysis of fatigue crack growth behavior for grade B cast steel

    International Nuclear Information System (INIS)

    Li, W.; Sakai, T.; Li, Q.; Wang, P.

    2011-01-01

    Tests for fatigue crack growth rate (FCGR) and crack-tip opening displacement (CTOD) were performed to clarify the fatigue crack growth behavior of a railway grade B cast steel. The threshold values of this steel with specific survival probabilities are evaluated, in which the mean value is 8.3516 MPa m 1/2 , very similar to the experimental value, about 8.7279 MPa m 1/2 . Under the conditions of plane strain and small-scale yielding, the values of fracture toughness for this steel with specific survival probabilities are converted from the corresponding critical CTOD values, in which the mean value is about 138.4256 MPa m 1/2 . In consideration of the inherent variability of crack growth rates, six statistical models are proposed to represent the probabilistic FCGR curves of this steel in entire crack propagation region from the viewpoints of statistical evaluation on the number of cycles at a given crack size and the crack growth rate at a given stress intensity factor range, stochastic characteristic of crack growth as well as statistical analysis of coefficient and exponent in FCGR power law equation. Based on the model adequacy checking, result shows that all models are basically in good agreement with test data. Although the probabilistic damage-tolerant design based on some models may involve a certain amount of risk in stable crack propagation region, they just accord with the fact that the dispersion degree of test data in this region is relatively smaller.

  13. Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography

    Directory of Open Access Journals (Sweden)

    Gheorghe Hutiu

    2018-02-01

    fatigue fracture of metals, and we demonstrate that OCT is able to replace SEM for such investigations as well.

  14. Effect of laser shock processing on fatigue crack growth and fracture toughness of 6061-T6 aluminum alloy

    International Nuclear Information System (INIS)

    Rubio-Gonzalez, C.; Ocana, J.L.; Gomez-Rosas, G.; Molpeceres, C.; Paredes, M.; Banderas, A.; Porro, J.; Morales, M.

    2004-01-01

    Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm 2 with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy

  15. Effects of irradiation and thermal aging upon fatigue-crack growth behavior of reactor pressure boundary materials. [Neutrons

    Energy Technology Data Exchange (ETDEWEB)

    James, L. A.

    1978-10-01

    Two processes that have the potential to produce degradation in the properties of pressure boundary materials are neutron irradiation and long-time thermal aging. This paper uses linear-elastic fracture mechanics techniques to assess the effect of these two processes upon the fatigue-crack growth behavior of a number of alloys commonly employed in reactor pressure boundaries. The materials evaluated include ferritic steels, austenitic stainless steels, and nickel-base alloys typical of those employed in a number of reactor types including water-cooled, gas-cooled, and liquid-metal-cooled designs.

  16. Fatigue Crack Growth Behavior of Gas Metal Arc Welded AISI 409 Grade Ferritic Stainless Steel Joints

    Science.gov (United States)

    Lakshminarayanan, A. K.; Shanmugam, K.; Balasubramanian, V.

    2009-10-01

    The effect of filler metals such as austenitic stainless steel, ferritic stainless steel, and duplex stainless steel on fatigue crack growth behavior of the gas metal arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Center cracked tensile specimens were prepared to evaluate fatigue crack growth behavior. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN was used to evaluate the fatigue crack growth behavior of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.

  17. Triphasic behavioral response of motor units to submaximal fatiguing exercise.

    Science.gov (United States)

    Dorfman, L J; Howard, J E; McGill, K C

    1990-07-01

    We have measured the firing rate and amplitude of 4551 motor unit action potentials (MUAPs) recorded with concentric needle electrodes from the brachial biceps muscles of 10 healthy young adults before, during, and after 45 minutes of intermittent isometric exercise at 20% of maximum voluntary contraction (MVC), using an automatic method for decomposition of electromyographic activity (ADEMG). During and after exercise, MUAPs derived from contractions of 30% MVC showed progressive increase in mean firing rate (P less than or equal to .01) and amplitude (P less than or equal to .05). The firing rate increase preceded the rise in mean amplitude, and was evident prior to the development of fatigue, defined as reduction of MVC. Analysis of individual potentials revealed that the increase in firing rate and in amplitude reflected different MUAP subpopulations. A short-term (less than 1 minute) reduction in MUAP firing rates (P less than or equal to .05) was also observed at the onset of each test contraction. These findings suggest that motor units exhibit a triphasic behavioral response to prolonged submaximal exercise: (1) short-term decline and stabilization of onset firing rates, followed by (2) gradual and progressive increase in firing rates and firing variability, and then by (3) recruitment of additional (larger) motor units. The (2) and (3) components presumably compensate for loss of force-generating capacity in the exercising muscle, and give rise jointly to the well-known increase in total surface EMG which accompanies muscle fatigue.

  18. Study on high-cycle fatigue behavior of candidate stainless steels for SCWR

    International Nuclear Information System (INIS)

    Xiong Ru; Zhao Yuxiang; Zhang Qiang; Wang Hao; Tang Rui; Qiao Yingjie

    2013-01-01

    The fatigue experiments of commerce stainless steels including 347, 316Ti and 310 were conducted under bending and rotating loadings. The environments were at room temperature (RT) as well as at 550℃ in air. The fracture morphology was observed by SEM, and the S-N curves were processed according to the experimental data. The results indicate the fatigue limited stresses for the 3 stainless steels were in the order of 347 < 316Ti < 310, which consistent with the order of their tensile strength. Elevated temperature would accelerate the oxidation and therefore the fatigue life would decrease, among them 347 was more sensitive to temperature with the maximum decreasing tendency. All the 3 stainless steels have good resistance to high cycle fatigue when comparing their experimental data with the calculated value from the empirical formula. The fracture morphology presents areas of crack initiation, crack growth and fracture, the width of fatigue ripples is about 1 μm, the fracture area has much dimples, and 347 presents much cavities of different sizes in dimples. (authors)

  19. Effects of micro arc oxidation on fatigue limits and fracture morphologies of 7475 high strength aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Dejun, Kong, E-mail: kong-dejun@163.com [College of Mechanical Engineering, Changzhou University, Changzhou, 213164 (China); Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou, 213164 (China); Hao, Liu; Jinchun, Wang [College of Mechanical Engineering, Changzhou University, Changzhou, 213164 (China)

    2015-11-25

    The oxide coatings with thicknesses of 8 μm, 10 μm, and 15 μm were prepared on 7475 aluminum alloy with micro arc oxidation (MAO) by controlling MAO time, the fatigue limits of original and MAO samples were contrastively measured by the Roccati method. The surface-interface morphologies, fracture morphologies, surface phases, and residual stresses of MAO coating were analyzed with a scanning electron microscopy (SEM), X-ray diffractometer (XRD) and XRD stress tester, respectively. The results show that fatigue limits of the MAO samples decreases as the coating thickness increasing. The fatigue limit of MAO sample with thickness of 8 μm, 10 μm, and 15 μm decreases by 6.48%, 8.33%, and 11.11%, respectively, compared with the original sample. The residual stress and defects introduced by MAO were the main factors of decreasing fatigue limits. - Graphical abstract: The fatigue limit of original sample was 216 MPa (a), while that of MAO samples with thickness of 8 μm, 10 μm and 15 μm was 202 MPa, 198 MPa and 192 MPa (b). The fatigue limit of MAO samples with thickness of 8 μm, 10 μm and 15 μm decreased by 6.48%, 8.33% and 11.11% compared with that of the original sample, as a result, the fatigue limit decreased with the MAO film thickness increasing. - Highlights: • The fatigue limits of MAO samples decrease with the oxide thickness increasing. • The overgrowth regions cause the crack source expanding. • The overgrowth of MAO film and tensile residual stress decrease fatigue limit.

  20. How driving duration influences drivers' visual behaviors and fatigue ...

    African Journals Online (AJOL)

    unhcc

    Eye fixations express the focus of driver's visual attention on driving, ... driver's attention is attracted by fatigue. The second ... was divided into seven refined categories (see Table 1), ...... driver fatigue in terms of line crossing: a pilot study.

  1. A literature review and inventory of the effects of environment on the fatigue behavior of metals

    Science.gov (United States)

    Hudson, C. M.; Seward, S. K.

    1976-01-01

    The current state of knowledge of the effects of gas environments (at atmospheric pressure and below) on the fatigue behavior of metals is reviewed. Among the topics considered are the mechanisms proposed to explain the differences observed in the fatigue behavior of vacuum- and air-tested specimens, the effects of environment on the surface topography of fatigue cycled specimens, the effect of environment on the various phases of the fatigue phenomenon, the effect of prolonged exposure to vacuum on fatigue life, the variation of fatigue life with decreasing gas pressure, and gas evolution during fatigue cycling. Analysis of the findings of this review indicates that hydrogen embrittlement is primarily responsible for decreased fatigue resistance in humid environments, and that dislocations move more easily during tests in vacuum than during test in air. It was found that fatigue cracks generally initiated and propagated more rapidly in air than in vacuum. Prolonged exposure to vacuum does not adversely affect fatigue resistance. The variation of fatigue life with decreasing gas pressure is sometimes stepped and sometimes continuous.

  2. Influence of shear cutting parameters on the fatigue behavior of a dual-phase steel

    Science.gov (United States)

    Paetzold, I.; Dittmann, F.; Feistle, M.; Golle, R.; Haefele, P.; Hoffmann, H.; Volk, W.

    2017-09-01

    The influence of the edge condition of car body and chassis components made of steel sheet on fatigue behavior under dynamic loading presents a major challenge for automotive manufacturers and suppliers. The calculated lifetime is based on material data determined by the fatigue testing of specimens with polished edges. Prototype components are often manufactured by milling or laser cutting, whereby in practice, the series components are produced by shear cutting due to its cost-efficiency. Since the fatigue crack in such components usually starts from a shear cut edge, the calculated and experimental determined lifetime will vary due to the different conditions at the shear cut edges. Therefore, the material data determined with polished edges can result in a non-conservative component design. The aim of this study is to understand the relationship between the shear cutting process and the fatigue behavior of a dual-phase steel sheet. The geometry of the shear cut edge as well as the depth and degree of work hardening in the shear affected zone can be adjusted by using specific shear cutting parameters, such as die clearance and cutting edge radius. Stress-controlled fatigue tests of unnotched specimens were carried out to compare the fatigue behavior of different edge conditions. By evaluating the results of the fatigue experiments, influential shear cutting parameters on fatigue behavior were identified. It was possible to assess investigated shear cutting strategies regarding the fatigue behavior of a high-strength steel DP800.

  3. Age-related mechanical strength evolution of trabecular bone under fatigue damage for both genders: Fracture risk evaluation.

    Science.gov (United States)

    Ben Kahla, Rabeb; Barkaoui, Abdelwahed; Merzouki, Tarek

    2018-05-04

    Bone tissue is a living composite material, providing mechanical and homeostatic functions, and able to constantly adapt its microstructure to changes in long term loading. This adaptation is conducted by a physiological process, known as "bone remodeling". This latter is manifested by interactions between osteoclasts and osteoblasts, and can be influenced by many local factors, via effects on bone cell differentiation and proliferation. In the current work, age and gender effects on damage rate evolution, throughout life, have been investigated using a mechanobiological finite element modeling. To achieve the aim, a mathematical model has been developed, coupling both cell activities and mechanical behavior of trabecular bone, under cyclic loadings. A series of computational simulations (ABAQUS/UMAT) has been performed on a 3D human proximal femur, allowing to investigate the effects of mechanical and biological parameters on mechanical strength of trabecular bone, in order to evaluate the fracture risk resulting from fatigue damage. The obtained results revealed that mechanical stimulus amplitude affects bone resorption and formation rates, and indicated that age and gender are major factors in bone response to the applied loadings. Copyright © 2018 Elsevier Ltd. All rights reserved.

  4. Fatigue crack closure behavior at high stress ratios

    Science.gov (United States)

    Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

    1988-01-01

    Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

  5. Fatigue

    Science.gov (United States)

    ... sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of not caring ... Call your provider right away if you have any of the following: Confusion or dizziness Blurred vision Little or no urine, or recent ...

  6. Fatigue crack growth resistance and crack closure behavior in two aluminum alloys for aeronautical applications

    Directory of Open Access Journals (Sweden)

    Elenice Maria Rodrigues

    2005-09-01

    Full Text Available Aluminum-lithium alloys are candidate materials for many aerospace applications because of their high specific strength and elastic modulus. These alloys have several unique characteristics such as excellent fatigue crack growth resistance when compared with that of the conventional 2000 and 7000 series alloys. In this study, fatigue crack propagation behavior has been examined in a commercial thin plate of Al-Li-Cu-Mg alloy (8090, with specific emphasis at the fatigue threshold. The results are compared with those of the traditional Al-Cu-Mg alloy (2024. Fatigue crack closure is used to explain the different behavior of the compared alloys.

  7. Heat affected zone and fatigue crack propagation behavior of high performance steel

    International Nuclear Information System (INIS)

    Choi, Sung Won; Kang, Dong Hwan; Kim, Tae Won; Lee, Jong Kwan

    2009-01-01

    The effect of heat affected zone in high performance steel on fatigue crack propagation behavior, which is related to the subsequent microstructure, was investigated. A modified Paris-Erdogan equation was presented for the analysis of fatigue crack propagation behavior corresponding to the heat affected zone conditions. Fatigue crack propagation tests under 0.3 stress ratio and 0.1 load frequency were conducted for both finegrained and coarse-grained heat affected zones, respectively. As shown in the results, much higher crack growth rate occurred in a relatively larger mean grain size material under the same stress intensity range of fatigue crack propagation process for the material.

  8. A study on the fatigue behavior of Steel Fiber Reinforced Concrete structures with initial cracks

    International Nuclear Information System (INIS)

    Chang, Dong-Il; Chai, Won-Kyu; Son, Young-Hyun; Park, Cheol-Woo

    1992-01-01

    Fatigue tests are performed in order to investigate the fatigue behavior of SFRC (Steel Fiber Reinforced Concrete) structures. Thirty SFRC beams are used in this test. The relationships between repeated loading cycle and mid-span deflection of the beams are observed under the three-point loading system. From the test results, the effects of the fiber content and the fiber aspect ratio on the concrete fatigue behavior were studied. According to the regression technique, some empirical formulae for predicting the fatigue strength of SFRC beams are also suggested. (author)

  9. Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

    Institute of Scientific and Technical Information of China (English)

    SI Tingzhi; LIU Ning; ZHANG Qingan; YOU Xianqing

    2008-01-01

    The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt. % TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δα). The mechanical properties and thermal fatigue resistance of TiC/Al2O3 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.

  10. Relationship Between Unusual High-Temperature Fatigue Crack Growth Threshold Behavior in Superalloys and Sudden Failure Mode Transitions

    Science.gov (United States)

    Telesman, J.; Smith, T. M.; Gabb, T. P.; Ring, A. J.

    2017-01-01

    An investigation of high temperature cyclic fatigue crack growth (FCG) threshold behavior of two advanced nickel disk alloys was conducted. The focus of the study was the unusual crossover effect in the near-threshold region of these type of alloys where conditions which produce higher crack growth rates in the Paris regime, produce higher resistance to crack growth in the near threshold regime. It was shown that this crossover effect is associated with a sudden change in the fatigue failure mode from a predominant transgranular mode in the Paris regime to fully intergranular mode in the threshold fatigue crack growth region. This type of a sudden change in the fracture mechanisms has not been previously reported and is surprising considering that intergranular failure is typically associated with faster crack growth rates and not the slow FCG rates of the near-threshold regime. By characterizing this behavior as a function of test temperature, environment and cyclic frequency, it was determined that both the crossover effect and the onset of intergranular failure are caused by environmentally driven mechanisms which have not as yet been fully identified. A plausible explanation for the observed behavior is proposed.

  11. Impact fracture behavior of HT9 duct

    International Nuclear Information System (INIS)

    Huang, F.H.; Gelles, D.S.

    1994-07-01

    Ferritic alloys are known to undergo a ductile-brittle transition as the test temperature is decreased. This inherent problem has limited their applications to reactor component materials subjected to low neutron exposures. However, the excellent resistance to void swelling exhibited by these alloys has led to choosing the materials as candidate materials for fast and fusion reactor applications. Despite the ductile-brittle transition problem, results show that the materials exhibit superior resistance to fracture under very high neutron fluences at irradiation temperatures above 380 degrees C. Impact testing on FFTF duct sections of HT9 indicates that HT9 ducts have adequate fracture toughness at much higher temperatures for handling operations at room temperature and refueling operations

  12. Fatigue Behavior of Steel Fiber Reinforced High-Strength Concrete under Different Stress Levels

    Science.gov (United States)

    Zhang, Chong; Gao, Danying; Gu, Zhiqiang

    2017-12-01

    The investigation was conducted to study the fatigue behavior of steel fiber reinforced high-strength concrete (SFRHSC) beams. A series of 5 SFRHSC beams was conducted flexural fatigue tests at different stress level S of 0.5, 0.55, 0.6, 0.7 and 0.8 respectively. Static test was conducted to determine the ultimate static capacity prior to fatigue tests. Fatigue modes and S-N curves were analyzed. Besides, two fatige life prediction model were analyzed and compared. It was found that stress level S significantly influenced the fatigue life of SFRHSC beams and the fatigue behavior of SFRHSC beams was mainly determined by the tensile reinforcement.

  13. Correlation of nodular austempered ductile iron (ADI) microstructural parameters and fatigue properties using an approach based on fracture mechanics

    International Nuclear Information System (INIS)

    Dias, Jose Felipe; Fonseca, Vinicius Rizzuti; Godefroid, Leonardo Barbosa; Ribeiro, Gabriel de Oliveira

    2010-01-01

    An investigation has been accomplished to check the effect of temperature and austempering time on austempered ductile iron (ADI) properties by means of fracture toughness (K_C) and fatigue threshold (∆K_t_h) tests. The correlation of ADI microstructural parameters and ADI two mechanical parameters: KC and Kth, is evaluated. Three sets of samples have ben extracted from ADI casting Y blocks produced in industrial conditions.and austenitized at 900°C for 1.5 hour. The austempering process has been performed in the following ways: the first set was austenitized at 300 deg C for 4 hours, the second set at 360°C for 1.5 hour and the third at 360°C for 0.6 hour. These distinct austempering processes have been adopted in order to obtain distinct microstructures containing austenite with two different carbon rates and two ferritic cell sizes. The materials have been characterized by means of optical and electronic microscopy, X-ray diffraction and mechanical tests. All materials have presented equivalent fatigue crack propagation rates, fracture toughness in the range between 94 and 128 MPa·m"1"/"2 and ∆K_t_h in the range between 5,7 and 6,4 MPa·m"1"/"2. The experimental results have confirmed the effect of microstructural properties (austenitic volumetric rate, austenitic carbon rate, ferritic cell size, total matrix carbon content) on fracture toughness (K_C) and fatigue threshold (∆K_t_h). Further, it was found that following parameters: fracture toughness (K_C), fatigue threshold ((∆K_t_h) and impact strength are correlated with the total matrix carbon content and ferritic cell size. (author)

  14. Thermal Exposure and Environment Effects on Tension, Fracture and Fatigue of 5XXX Alloys Tested in Different Orientations

    Science.gov (United States)

    2017-12-27

    Thermal Exposure and Environment Effects on Tension, Fracture and Fatigue of 5XXX Alloys Tested in Different Orientations Sb. GRANT NUMBER ONR-N000 14...e.g.Hl31, HI 16, HI 28), thermal exposure conditions (i .e. time, temperature), and environment (e.g. dry air, humid air, solutions) on the... environmental cracking susceptibility at different load ing rates in both the S-T and L-T orientations. Experiments were conducted using slow strain rate

  15. Fatigue crack growth behavior in equine cortical bone

    Science.gov (United States)

    Shelton, Debbie Renee

    2001-07-01

    Objectives for this research were to experimentally determine crack growth rates, da/dN, as a function of alternating stress intensity factor, DeltaK, for specimens from lateral and dorsal regions of equine third metacarpal cortical bone tissue, and to determine if the results were described by the Paris law. In one set of experiments, specimens were oriented for crack propagation in the circumferential direction with the crack plane transverse to the long axis of the bone. In the second set of experiments, specimens were oriented for radial crack growth with the crack plane parallel to the long axis of the bone. Results of fatigue tests from the latter specimens were used to evaluate the hypothesis that crack growth rates differ regionally. The final experiments were designed to determine if crack resistance was dependent on region, proportion of hooped osteons (those with circumferentially oriented collagen fibers in the outer lamellae) or number of osteons penetrated by the crack, and to address the hypothesis that hooped osteons resist invasion by cracks better than other osteonal types. The transverse crack growth data for dorsal specimens were described by the Paris law with an exponent of 10.4 and suggested a threshold stress intensity factor, DeltaKth, of 2.0 MPa·m1/2 and fracture toughness of 4.38 MPa·m 1/2. Similar results were not obtained for lateral specimens because the crack always deviated from the intended path and ran parallel to the loading direction. Crack growth for the dorsal and lateral specimens in the radial orientation was described by the Paris law with exponents of 8.7 and 10.2, respectively, and there were no regional differences in the apparent DeltaK th (0.5 MPa·m1/2) or fracture toughness (1.2 MPa·m 1/2). Crack resistance was not associated with cortical region, proportion of hooped osteons or the number of osteons penetrated by the crack. The extent to which cracks penetrate osteons was influenced by whether the collagen fiber

  16. Fatigue behavior of Type 316 stainless steel following neutron irradiation inducing helium

    International Nuclear Information System (INIS)

    Grossbeck, M.L.; Liu, K.C.

    1980-01-01

    Since a tokamak reactor operates in a cyclic mode, thermal stresses will result in fatigue in structural components, especially in the first wall and blanket. There has been limited work on fatigue in irradiated alloys but none on irradiated materials containing significant amounts of irradiation-induced helium. To provide scoping data and to study the effects of irradiation on fatigue behavior, 20%-cold-worked type 316 stainless steel from the MFE reference heat was studied

  17. Fatigue behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP)

    Science.gov (United States)

    Jinghao Li; John F. Hunt; Shaoqin Gong; Zhiyong Cai

    2015-01-01

    The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP) has been investigated by four-point bending tests. Fatigue panels and weakened panels (wESCP) with an initial interface defect were manufactured for the fatigue tests. Stress σ vs. number of cycles curves (S-N) were recorded under the different stress...

  18. Measurement of Solute Diffusion Behavior in Fractured Waste Glass Media

    International Nuclear Information System (INIS)

    Saripalli, Kanaka P.; Lindberg, Michael J.; Meyer, Philip D.

    2008-01-01

    Determination of aqueous phase diffusion coefficients of solutes through fractured media is essential for understanding and modeling contaminants transport at many hazardous waste disposal sites. No methods for earlier measurements are available for the characterization of diffusion in fractured glass blocks. We report here the use of time-lag diffusion experimental method to assess the diffusion behavior of three different solutes (Cs, Sr and Pentafluoro Benzoic Acid or PFBA) in fractured, immobilized low activity waste (ILAW) glass forms. A fractured media time-lag diffusion experimental apparatus that allows the measurement of diffusion coefficients has been designed and built for this purpose. Use of time-lag diffusion method, a considerably easier experimental method than the other available methods, was not previously demonstrated for measuring diffusion in any fractured media. Hydraulic conductivity, porosity and diffusion coefficients of a solute were experimentally measured in fractured glass blocks using this method for the first time. Results agree with the range of properties reported for similar rock media earlier, indicating that the time-lag experimental method can effectively characterize the diffusion coefficients of fractured ILAW glass media

  19. Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite–pearlite and ferrite–bainite microstructures

    International Nuclear Information System (INIS)

    Guan, Mingfei; Yu, Hao

    2013-01-01

    The roles of microstructure types in fatigue crack growth behaviors in ferrite–pearlite steel and ferrite–bainite steel were investigated. The ferrite–bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite–pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F–P steel could become unstable more ealier compared with that in F–B steel. The fatigue cracks in ferrite–pearlite were more tortuous and could propagate more freely than that in ferrite–bainite microstructures. However, frequent crack branching were observed in ferrite–bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate (da/dN) with stress intensity factor range (ΔK) for F–P and F–B steels was discussed within the Paris region. It was shown that FCG rate of F–P steel was higher than that of F–B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

  20. X-ray fractography by using synchrotron radiation source. Residual stress distribution just beneath fatigue fracture surface

    International Nuclear Information System (INIS)

    Akita, Koichi; Yoshioka, Yasuo; Suzuki, Hiroshi; Sasaki, Toshihiko

    2000-01-01

    The residual stress distributions just beneath the fatigue fracture surface were measured using synchrotron radiation with three different wavelengths, i.e., three different penetration depths. The residual stress distributions were estimated from three kinds of diffraction data by the following process. First, a temporary residual stress distribution in the depth direction is assumed. Theoretical 2θ-sin 2 ψ diagrams for each wavelength, where each has a different penetration depth, are calculated by the cosψ method developed by one of the authors. The sum total of the differences between the theoretical and experimental values of the diffraction angle in 2θ-sin 2 ψ diagrams is calculated. This total value is minimized by changing the assumed stress distribution by the quasi-Newton optimization method. Finally, optimized 2θ-sin 2 ψ diagrams for each penetration depth and detailed stress distribution are determined. The true surface residual stress is obtained from this stress distribution. No effect of load ratio R (= P min /P max ) on the residual stresses of the fatigue fracture surfaces in low-carbon steels was observed when the sin 2 ψ method was used for stress measurement. However, the residual stresses became higher with increasing R when these were measured by the proposed method. On the basis of this, the stress intensity factor range, ΔK, can be estimated from the residual stress on the fatigue fracture surface. (author)

  1. Tensile Fracture Behavior of Progressively-Drawn Pearlitic Steels

    Directory of Open Access Journals (Sweden)

    Jesús Toribio

    2016-05-01

    Full Text Available In this paper a study is presented of the tensile fracture behavior of progressively-drawn pearlitic steels obtained from five different cold-drawing chains, including each drawing step from the initial hot-rolled bar (not cold-drawn at all to the final commercial product (pre-stressing steel wire. To this end, samples of the different wires were tested up to fracture by means of standard tension tests, and later, all of the fracture surfaces were analyzed by scanning electron microscopy (SEM. Micro-fracture maps (MFMs were assembled to characterize the different fractographic modes and to study their evolution with the level of cumulative plastic strain during cold drawing.

  2. Orientation dependent fracture behavior of nanotwinned copper

    Energy Technology Data Exchange (ETDEWEB)

    Kobler, Aaron, E-mail: aaron.kobler@kit.edu; Hahn, Horst, E-mail: ahodge@usc.edu, E-mail: horst.hahn@kit.edu, E-mail: christian.kuebel@kit.edu [Technische Universität Darmstadt (TUD), KIT-TUD Joint Research Laboratory Nanomaterials, 64287 Darmstadt (Germany); Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Hodge, Andrea M., E-mail: ahodge@usc.edu, E-mail: horst.hahn@kit.edu, E-mail: christian.kuebel@kit.edu [University of Southern California (USC), Department of Aerospace and Mechanical Engineering, Los Angeles, California 90089-1453 (United States); Kübel, Christian, E-mail: ahodge@usc.edu, E-mail: horst.hahn@kit.edu, E-mail: christian.kuebel@kit.edu [Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2015-06-29

    Columnar grown nanotwinned Cu was tensile tested in-situ inside the TEM in combination with automated crystal orientation mapping scanning transmission electron microscopy to investigate the active deformation mechanisms present in this material. Two tensile directions were applied, one parallel to the twin boundaries and the other perpendicular to the twin boundaries. In case of tensile testing perpendicular to the twin boundaries, the material deformed by detwinning and the formation of new grains, whereas in the parallel case, no new grains were formed and the fracture happened along the twin boundaries and a boundary that has formed during the deformation.

  3. Orientation dependent fracture behavior of nanotwinned copper

    International Nuclear Information System (INIS)

    Kobler, Aaron; Hahn, Horst; Hodge, Andrea M.; Kübel, Christian

    2015-01-01

    Columnar grown nanotwinned Cu was tensile tested in-situ inside the TEM in combination with automated crystal orientation mapping scanning transmission electron microscopy to investigate the active deformation mechanisms present in this material. Two tensile directions were applied, one parallel to the twin boundaries and the other perpendicular to the twin boundaries. In case of tensile testing perpendicular to the twin boundaries, the material deformed by detwinning and the formation of new grains, whereas in the parallel case, no new grains were formed and the fracture happened along the twin boundaries and a boundary that has formed during the deformation

  4. Thermo-hydro-mechanical behavior of fractured rock mass

    International Nuclear Information System (INIS)

    Coste, F.

    1997-12-01

    The purpose of this research is to model Thermo-Hydro-Mechanical behavior of fractured rock mass regarding a nuclear waste re-depository. For this, a methodology of modeling was proposed and was applied to a real underground site (EDF site at Nouvelle Romanche). This methodology consists, in a first step, to determine hydraulic and mechanical REV. Beyond the greatest of these REV, development of a finite element code allows to model all the fractures in an explicit manner. The homogenized mechanical properties are determined in drained and undrained boundary conditions by simulating triaxial tests that represent rock mass subject to loading. These simulations allow to study the evolution of hydraulic and mechanical properties as a function of stress state. Drained and undrained boundary conditions enable to discuss the validity of assimilation of a fractured rock mass to a porous medium. The simulations lead to a better understanding of the behavior of the fractured rock masses and allow to show the dominant role of the shear behavior of the fractures on the hydraulic and mechanical homogenized properties. From a thermal point of view, as long as conduction is dominant, thermal properties of the rock mass are almost the same as those the intact rock. (author)

  5. Fatigue behavior of Ti–6Al–4V alloy in saline solution with the surface modified at a micro- and nanoscale by chemical treatment

    Energy Technology Data Exchange (ETDEWEB)

    Claros, Cesar Adolfo Escobar; Oliveira, Diego Pedreira; Campanelli, Leonardo Contri; Pereira da Silva, Paulo Sergio Carvalho; Bolfarini, Claudemiro

    2016-10-01

    This work evaluated the influence of the surface modification using acid etching combined with alkaline treatment on the fatigue strength of Ti–6Al–4V ELI alloy. The topography developed by chemical surface treatments (CST) was examined by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Increased roughness and effective surface area were investigated and compared with the Ti–6Al–4V samples without modification. Surface composition was analyzed by energy dispersive X-ray spectroscopy (EDS). Axial fatigue resistance of polished and modified surfaces was determined by stepwise load increase tests and staircase test method. Light microscopy and SEM were employed to examine the fracture surface of the tested specimens. According to the results, a similar fatigue behavior was found and a negligible difference in the fatigue crack nucleation was observed for the Ti–6Al–4V with CST in comparison to the samples without treatment. - Highlights: • Fatigue behavior of Ti–6Al–4V with the surface modified by chemical treatments • The topography developed did not induce differences in the fatigue resistance. • Untreated and chemically treated surfaces presented fractographic similarities.

  6. Fatigue behavior of Ti–6Al–4V alloy in saline solution with the surface modified at a micro- and nanoscale by chemical treatment

    International Nuclear Information System (INIS)

    Claros, Cesar Adolfo Escobar; Oliveira, Diego Pedreira; Campanelli, Leonardo Contri; Pereira da Silva, Paulo Sergio Carvalho; Bolfarini, Claudemiro

    2016-01-01

    This work evaluated the influence of the surface modification using acid etching combined with alkaline treatment on the fatigue strength of Ti–6Al–4V ELI alloy. The topography developed by chemical surface treatments (CST) was examined by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Increased roughness and effective surface area were investigated and compared with the Ti–6Al–4V samples without modification. Surface composition was analyzed by energy dispersive X-ray spectroscopy (EDS). Axial fatigue resistance of polished and modified surfaces was determined by stepwise load increase tests and staircase test method. Light microscopy and SEM were employed to examine the fracture surface of the tested specimens. According to the results, a similar fatigue behavior was found and a negligible difference in the fatigue crack nucleation was observed for the Ti–6Al–4V with CST in comparison to the samples without treatment. - Highlights: • Fatigue behavior of Ti–6Al–4V with the surface modified by chemical treatments • The topography developed did not induce differences in the fatigue resistance. • Untreated and chemically treated surfaces presented fractographic similarities.

  7. Effect of shot peening process on fatigue behavior of an alloyed austempered ductile iron

    Directory of Open Access Journals (Sweden)

    Amir Sadighzadeh Benam

    2011-08-01

    Full Text Available Shot peening is one of the most common surface treatments to improve the fatigue behavior of metallic parts. In this study the effect of shot peening process on the fatigue behavior of an alloyed austempered ductile iron (ADI has been studied. Austempering heat treatment consisted of austenitizing at 875℃ for 90 min followed by austempering at three different temperatures of 320, 365 and 400℃. Rotating-bending fatigue test was carried out on samples after shot peening by 0.4 – 0.6 mm shots. XRD and SEM analysis, micro hardness and roughness tests were carried out to study the fatigue behavior of the samples. Results indicate that the fatigue strengths of samples austempered at 320, 365 and 400℃ are increased by 27.3%, 33.3% and 48.4%, respectively, after shot peening process.

  8. A computer-controlled automated test system for fatigue and fracture testing

    International Nuclear Information System (INIS)

    Nanstad, R.K.; Alexander, D.J.; Swain, R.L.; Hutton, J.T.; Thomas, D.L.

    1989-01-01

    A computer-controlled system consisting of a servohydraulic test machine, an in-house designed test controller, and a desktop computer has been developed for performing automated fracture toughness and fatigue crack growth testing both in the laboratory and in hot cells for remote testing of irradiated specimens. Both unloading compliance and dc-potential drop can be used to monitor crack growth. The test controller includes a dc-current supply programmer, a function generator for driving the servohydraulic test machine to required test outputs, five measurement channels (each consisting of low-pass filter, track/hold amplifier, and 16-bit analog-to-digital converter), and digital logic for various control and data multiplexing functions. The test controller connects to the computer via a 16-bit wide photo-isolated bidirectional bus. The computer, a Hewlett-Packard series 200/300, inputs specimen and test parameters from the operator, configures the test controller, stores test data from the test controller in memory, does preliminary analysis during the test, and records sensor calibrations, specimen and test parameters, and test data on flexible diskette for later recall and analysis with measured initial and final crack length information. During the test, the operator can change test parameters as necessary. 24 refs., 6 figs

  9. Analysis of Flow Behavior for Acid Fracturing Wells in Fractured-Vuggy Carbonate Reservoirs

    Directory of Open Access Journals (Sweden)

    Mingxian Wang

    2018-01-01

    Full Text Available This study develops a mathematical model for transient flow analysis of acid fracturing wells in fractured-vuggy carbonate reservoirs. This model considers a composite system with the inner region containing finite number of artificial fractures and wormholes and the outer region showing a triple-porosity medium. Both analytical and numerical solutions are derived in this work, and the comparison between two solutions verifies the model accurately. Flow behavior is analyzed thoroughly by examining the standard log-log type curves. Flow in this composite system can be divided into six or eight main flow regimes comprehensively. Three or two characteristic V-shaped segments can be observed on pressure derivative curves. Each V-shaped segment corresponds to a specific flow regime. One or two of the V-shaped segments may be absent in particular cases. Effects of interregional diffusivity ratio and interregional conductivity ratio on transient responses are strong in the early-flow period. The shape and position of type curves are also influenced by interporosity coefficients, storativity ratios, and reservoir radius significantly. Finally, we show the differences between our model and the similar model with single fracture or without acid fracturing and further investigate the pseudo-skin factor caused by acid fracturing.

  10. Fracture toughness and fatigue crack propagation in cast irons with spheroidal vanadium carbides dispersed within martensitic matrix microstructure

    International Nuclear Information System (INIS)

    Uematsu, Y.; Tokaji, K.; Horie, T.; Nishigaki, K.

    2007-01-01

    Fracture toughness and fatigue crack propagation (FCP) have been studied using compact tension (CT) specimens of as-cast and subzero-treated materials in a cast iron with spheroidal vanadium carbides (VCs) dispersed in the martensitic matrix microstructure. X-ray diffraction (XRD) analysis revealed that retained austenite was transformed to martensite by subzero treatment. Vickers hardness was increased from 738 for the as-cast material to 782 for the subzero-treated material, which could be attributed to retained austenite to martensite transformation. The subzero-treated material exhibited lower fracture toughness than the as-cast material because soft and ductile retained austenite which possesses high fracture toughness was transformed to martensite in the subzero-treated material. Intrinsic FCP resistance after taking account of crack closure was decreased by the subzero treatment, which was attributed to the predominant crack propagation through the interface between VCs and the matrix and the straight crack path in the matrix microstructure

  11. Evaluation of Mechanical Properties and Fatigue Behavior of STS 304L due to Plastic Working

    Energy Technology Data Exchange (ETDEWEB)

    Shim, Hyun-Bo [Yeungnam Univ., Daegu (Korea, Republic of); Kim, Young-Kyun [KOGAS Research Institute, Seoul (Korea, Republic of); Suh, Chang-Min [Kyungpook Nat’l Univ., Daegu (Korea, Republic of)

    2017-07-15

    The purpose of this study is to investigate the influence of the cold reduction rate and an ultrasonic fatigue test (UFT) on the fatigue behaviors of STS 304L. The tensile strength, yield strength, hardness value and fatigue limit in the UFT fatigue test linearly increased as thickness decreased from 1.5 mm to 1.1 mm, as the cold reduction rate of STS 304L increased. As a result of the UFT fatigue test (R = -1) of four specimens, the fatigue limit of the S-N curve formed a knee point in the region of 10{sup 6}, and the 2nd fatigue limit caused by giga cycle fatigue did not appeared. In the case of t = 1.1 mm, the highest fatigue limit was 345 MPa, which was 64.3% higher than the original material (t = 1.5 mm). As a result of the UFT fatigue test of STS 304L, many small surface cracks occurred, grown, coalesced while tearing.

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

    Science.gov (United States)

    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.

  13. High-cycle fatigue behavior of ultrafine-grained austenitic stainless and TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Hamada, A.S. [Materials Engineering Laboratory (4KOMT), Box 4200, University of Oulu, 90014 Oulu (Finland); Metallurgical and Materials Engineering Department, Faculty of Petroleum and Mining Engineering, Suez Canal University, Box 43721, Suez (Egypt); Karjalainen, L.P., E-mail: pentti.karjalainen@oulu.fi [Materials Engineering Laboratory (4KOMT), Box 4200, University of Oulu, 90014 Oulu (Finland)

    2010-08-20

    High-cycle fatigue behavior of ultrafine-grained (UFG) 17Cr-7Ni Type 301LN austenitic stainless and high-Mn Fe-22Mn-0.6C TWIP steels were investigated in a reversed plane bending fatigue and compared to the behavior of steels with conventional coarse grain (CG) size. Optical, scanning and transmission electron microscopy were used to examine fatigue damage mechanisms. Testing showed that the fatigue limits leading to fatigue life beyond 4 x 10{sup 6} cycles were about 630 MPa for 301LN while being 560 MPa for TWIP steel, and being 0.59 and 0.5 of the tensile strength respectively. The CG counterparts were measured to have the fatigue limits of 350 and 400 MPa. The primary damage caused by fatigue took place by grain boundary cracking in UFG 301LN, while slip band cracking occurred in CG 301LN. However, in the case of TWIP steel, the fatigue damage mechanism is similar in spite of the grain size. In the course of cycling neither the formation of a martensite structure nor mechanical twinning occurs, but intense slip bands are created with extrusions and intrusions. Fatigue crack initiates preferentially on grain and twin boundaries, and especially in the intersection sites of slip bands and boundaries.

  14. A Study on the VHCF Fatigue Behaviors of Hydrogen Attacked Inconel 718 Alloy

    Energy Technology Data Exchange (ETDEWEB)

    Suh, Chang-Min [Kyungpook National Univ., DMI Senior Fellow, Daegu (Korea, Republic of); Nahm, Seung-Hoon [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Kim, Jun-Hyong; Pyun, Young-Sik [Sun Moon Univ., Chunan (Korea, Republic of)

    2016-07-15

    This study is to investigate the influence of hydrogen attack and UNSM on fatigue behaviors of the Inconel 718 alloy. The decrease of the fatigue life between the untreated and the hydrogen attacked material is 10-20%. The fatigue lives of hydrogen attacked specimen decreased without a fatigue limit, similar to those of nonferrous materials. Due to hydrogen embrittlement, about 80% of the surface cracks were smaller than the average grain size of 13 μm. Many small surface cracks caused by the embrittling effect of hydrogen attack were initiated at the grain boundaries and surface scratches. Cracks were irregularly distributed, grew, and then coalesced through tearing, leading to a reduction of fatigue life. Results revealed that the fatigue lives of UNSM-treated specimens were longer than those of the untreated specimens.

  15. Incomplete longitudinal fractures and fatigue injury of the proximopalmar medial aspect of the third metacarpal bone in 55 horses.

    Science.gov (United States)

    Morgan, R; Dyson, S

    2012-01-01

    Previous descriptions of incomplete longitudinal fractures and fatigue injury of the proximopalmar aspect of the third metacarpal bone (McIII) have focused on diagnostic imaging findings, especially in racehorses. To document the case details, clinical features, response to diagnostic analgesia, diagnostic imaging findings and follow-up data in a large group of horses with an incomplete longitudinal fracture or fatigue injury of the proximopalmar medial aspect of the McIII. Horses were included in the study if pain was localised to the proximopalmar aspect of the metacarpal region, with radiological evidence of an incomplete longitudinal fracture or generalised increased radiopacity in the proximopalmar medial aspect of the McIII, or focal increased radiopharmaceutical uptake (IRU) in the proximopalmar aspect of the McIII. Age, breed, gender, height, bodyweight, work discipline, work history, duration of lameness, clinical signs and responses to diagnostic analgesia were recorded. Radiographic and scintigraphic images were assessed subjectively and objectively. There were 55 horses representing a broad spectrum of ages and work disciplines, 73% of which had radiological abnormalities. The majority had no localising clinical signs, although 73% of horses with radiological abnormalities showed a characteristic pattern of lameness. Lameness was generally worse in straight lines than in circles. Increased radiopharmaceutical uptake ranged from mild to intense in the lame limb; 14% of nonlame limbs had mild IRU. Of horses for which long-term follow-up was available, 98% returned to full athletic function. Incomplete longitudinal fractures and fatigue injury of the proximopalmar medial aspect of the McIII may occur in horses of many types and sports disciplines, and are not confined to immature performance horses. They should be considered an important differential diagnosis for proximal metacarpal region pain. © 2011 EVJ Ltd.

  16. Effects of fine porosity on the fatigue behavior of a powder metallurgy superalloy

    Science.gov (United States)

    Miner, R. V.; Dreshfield, R. L.

    1980-01-01

    Hot-isostatically-pressed powder-metallurgy Astroloy was obtained which contained 1.4 percent porosity at the grain boundaries produced by argon entering the powder container during pressing. This material was tested at 650 C in fatigue, creep-fatigue, tension, and stress-rupture and the results compared with data on sound Astroloy. They influenced fatigue crack initiation and produced a more intergranular mode of propagation but fatigue life was not drastically reduced. Fatigue behavior of the porous material showed typical correlation with tensile behavior. The plastic strain range-life relation was reduced proportionately with the reduction in tensile ductility, but the elastic strain range-life relation was changed little.

  17. Self-Regulatory Fatigue, Quality of Life, Health Behaviors, and Coping in Patients with Hematologic Malignancies

    Science.gov (United States)

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

    2015-01-01

    Background Self-regulatory fatigue may play an important role in a complex medical illness. Purpose Examine associations between self-regulatory fatigue, quality of life, and health behaviors in patients pre- (N=213) and 1-year post-hematopoietic stem cell transplantation (HSCT; N=140). Associations between self-regulatory fatigue and coping strategies pre-HSCT were also examined. Method Pre- and 1-year post-HSCT data collection. Hierarchical linear regression modeling. Results Higher self-regulatory fatigue pre-HSCT associated with lower overall, physical, social, emotional, and functional quality of life pre- (p’sself-regulatory fatigue pre-HSCT relating to decreased quality of life and health behaviors, and predicting changes in these variables 1-year post-HSCT. PMID:24802991

  18. Characterization of high cycle fatigue behavior of a new generation aluminum lithium alloy

    International Nuclear Information System (INIS)

    De, P.S.; Mishra, R.S.; Baumann, J.A.

    2011-01-01

    Highlights: → Effect of microstructure on fatigue fracture of an advanced Al-Li alloy was studied in detail. → Preferential crack propagation in T3 state at specific orientations was analyzed. → Fatigue crack propagation difference between T3 and T8 tempers and friction stir welded condition was rationalized. → The effect of grain size on fatigue life for T3 and T8 tempers was justified based on current theories. → Delamination in T3 and T8 tempers was rationalized using microstructural analysis and FEA simulation. - Abstract: The high cycle fatigue life characteristics of an Al-Li alloy were studied as a function of microstructure. While for the parent microstructure fatigue life decreased as grain size increased, no such effect was noted at high stresses. This decrease in fatigue life was correlated with lower crack initiation life due to small crack effect. Under multiaxial stress conditions, the alloy exhibited intergranular cracking. The cross-linking of intergranular cracks (in the T8 condition) caused a further deterioration in fatigue life. Additionally, planar slip movements (in the T3 condition) in stage I crack propagation were observed. Slip planarity depended on both the sample texture and the nature of the precipitates. Fractographic and textural evidence is presented.

  19. Characterization of high cycle fatigue behavior of a new generation aluminum lithium alloy

    Energy Technology Data Exchange (ETDEWEB)

    De, P.S. [Center for Friction Stir Processing, Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409 (United States); Mishra, R.S., E-mail: rsmishra@mst.edu [Center for Friction Stir Processing, Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409 (United States); Baumann, J.A. [Boeing Company, St. Louis, MO 631666 (United States)

    2011-09-15

    Highlights: {yields} Effect of microstructure on fatigue fracture of an advanced Al-Li alloy was studied in detail. {yields} Preferential crack propagation in T3 state at specific orientations was analyzed. {yields} Fatigue crack propagation difference between T3 and T8 tempers and friction stir welded condition was rationalized. {yields} The effect of grain size on fatigue life for T3 and T8 tempers was justified based on current theories. {yields} Delamination in T3 and T8 tempers was rationalized using microstructural analysis and FEA simulation. - Abstract: The high cycle fatigue life characteristics of an Al-Li alloy were studied as a function of microstructure. While for the parent microstructure fatigue life decreased as grain size increased, no such effect was noted at high stresses. This decrease in fatigue life was correlated with lower crack initiation life due to small crack effect. Under multiaxial stress conditions, the alloy exhibited intergranular cracking. The cross-linking of intergranular cracks (in the T8 condition) caused a further deterioration in fatigue life. Additionally, planar slip movements (in the T3 condition) in stage I crack propagation were observed. Slip planarity depended on both the sample texture and the nature of the precipitates. Fractographic and textural evidence is presented.

  20. Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

    National Research Council Canada - National Science Library

    Zhu, Dongming

    2004-01-01

    .... In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz...

  1. Fatigue crack behavior on a Cu-Zn-Al SMA

    Directory of Open Access Journals (Sweden)

    V. Di Cocco

    2014-10-01

    Optical Microscope (LOM observations. Furthermore a fatigue crack propagation and fracture surface scanning electron microscope (SEM observations have been performed in order to evaluate the crack path and the main crack micromechanisms.

  2. The Mechanical Behaviors of Various Dental Implant Materials under Fatigue

    Directory of Open Access Journals (Sweden)

    Fatma Bayata

    2018-01-01

    Full Text Available The selection of materials has a considerable role on long-term stability of implants. The materials having high resistance to fatigue are required for dental implant applications since these implants are subjected to cyclic loads during chewing. This study evaluates the performance of different types of materials (AISI 316L stainless steel, alumina and its porous state, CoCr alloys, yttrium-stabilized zirconia (YSZ, zirconia-toughened alumina (ZTA, and cp Ti with the nanotubular TiO2 surface by finite element analysis (FEA under real cyclic biting loads and researches the optimum material for implant applications. For the analysis, the implant design generated by our group was utilized. The mechanical behavior and the life of the implant under biting loads were estimated based on the material and surface properties. According to the condition based on ISO 14801, the FEA results showed that the equivalent von Mises stress values were in the range of 226.95 MPa and 239.05 MPa. The penetration analysis was also performed, and the calculated penetration of the models onto the bone structure ranged between 0.0037389 mm and 0.013626 mm. L-605 CoCr alloy-assigned implant model showed the least penetration, while cp Ti with the nanotubular TiO2 surface led to the most one. However, the difference was about 0.01 mm, and it may not be evaluated as a distinct difference. As the final numerical evaluation item, the fatigue life was executed, and the results were achieved in the range of 4 × 105 and 1 × 109 cycles. These results indicated that different materials showed good performance for each evaluation component, but considering the overall mechanical performance and the treatment process (implant adsorption by means of surface properties, cp Ti with the nanotubular TiO2 surface material was evaluated as the suitable one, and it may also be implied that it displayed enough performance in the designed dental implant model.

  3. Low cycle fatigue and creep-fatigue interaction behavior of nickel-base superalloy GH4169 at elevated temperature of 650 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G., E-mail: agang@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Y. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xu, D.K. [Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Lin, Y.C. [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

    2016-02-08

    Total strain-controlled low cycle fatigue (LCF) tests of a nickel based superalloy were performed at 650 °C. Various hold times were introduced at the peak tensile strain to investigate the high-temperature creep-fatigue interaction (CFI) effects under the same temperature. A substantial decrease in fatigue life occurred as the total strain amplitude increased. Moreover, tensile strain holding further reduced fatigue life. The saturation phenomenon of holding effect was found when the holding period reached 120 s. Cyclic softening occurred during the LCF and CFI process and it was related to the total strain amplitude and the holding period. The relationship between life-time and total strain amplitude was obtained by combining Basquin equation and Coffin-Manson equation. The surface and fracture section of the fatigued specimens were observed via scanning electronic microscope (SEM) to determine the failure mechanism.

  4. Ratcheting fatigue behavior of Zircaloy-2 at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Rajpurohit, R.S., E-mail: rsrajpurohit.rs.met13@iitbhu.ac.in [Department of Metallurgical Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi, 221005 (India); Sudhakar Rao, G. [Nuclear Energy and Safety Department, Paul Scherrer Institute, Villigen, CH-5232 (Switzerland); Chattopadhyay, K.; Santhi Srinivas, N.C.; Singh, Vakil [Department of Metallurgical Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi, 221005 (India)

    2016-08-15

    Nuclear core components of zirconium alloys experience asymmetric stress or strain cycling during service which leads to plastic strain accumulation and drastic reduction in fatigue life as well as dimensional instability of the component. Variables like loading rate, mean stress, and stress amplitude affect the influence of asymmetric loading. In the present investigation asymmetric stress controlled fatigue tests were conducted with mean stress from 80 to 150 MPa, stress amplitude from 270 to 340 MPa and stress rate from 30 to 750 MPa/s to study the process of plastic strain accumulation and its effect on fatigue life of Zircaloy-2 at room temperature. It was observed that with increase in mean stress and stress amplitude accumulation of ratcheting strain was increased and fatigue life was reduced. However, increase in stress rate led to improvement in fatigue life due to less accumulation of ratcheting strain. - Highlights: • Ratcheting strain accumulation occurred due to asymmetric cyclic loading. • Accumulation of ratcheting strain increased with mean stress and stress amplitude. • Ratcheting strain accumulation decreased with increase in stress rate. • With increase in mean stress and stress amplitude there was reduction in fatigue life. • Fatigue life is improved with increase in stress rate.

  5. Room temperature fatigue behavior of OFHC copper and CuAl25 specimens of two sizes

    DEFF Research Database (Denmark)

    Singhal, A.; Stubbins, J.F.; Singh, B.N.

    1994-01-01

    requiring an understanding of their fatigue behavior.This paper describes the room temperature fatigue behavior of unirradiated OFHC (oxygen-free high-conductivity) copper and CuAl25 (copper strengthened with a 0.25% atom fraction dispersion of alumina). The response of two fatigue specimen sizes to strain......Copper and its alloys are appealing for application in fusion reactor systems for high heat flux components where high thermal conductivities are critical, for instance, in divertor components. The thermal and mechanical loading of such components will be, at least in part, cyclic in nature, thus...

  6. Fatigue behavior of thick composite single lap joints

    Energy Technology Data Exchange (ETDEWEB)

    Tang, J.H.; Sridhar, I.; Srikanth, N. [Nanyang Technological Univ., Singapore (Singapore)

    2012-07-01

    In consideration of bondline thickness variability, in bonded joints where thick adherend is adopted, relative thick adhesive layer (2-5 mm) is preferable. This paper aims to give some insight in fatigue strength of adhesively bonded structures involving thick adherend coupled with thick adhesive layer. Single lap joints with nominal adherend thickness of 8 mm and two different nominal thicknesses (2.5 mm and 5.5 mm) were made and tested under fatigue loading. The failure mode exhibits always a tendency for interfacial initiation, followed by interlaminar separation. Fatigue strength for higher adhesive thickness is found to be lower. (Author)

  7. Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures.

    Science.gov (United States)

    Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S

    2016-03-01

    In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Evolution of dislocation structure and fatigue crack behavior in Fe-Si alloys during cyclic bending test

    International Nuclear Information System (INIS)

    Ushioda, Kohsaku; Takebayashi, Shigeto; Goto, Shoji; Komatsu, Yoshinari; Hoshino, Akinori

    2010-01-01

    The evolution of dislocation structures was investigated by means of TEM in Fe-Si alloys with 0, 0.5 and 1.0 mass% Si during a cyclic bending test in conjunction with fatigue crack behavior. The addition of Si increased the fatigue strength. In steel without Si the cell structure develops, whereas in steel with 1%Si the vein structure evolves, which is considered to lead to the increased fatigue strength. The cell structure in 0%Si steel is postulated to be caused by the easy cross slip of dislocations, whereas the vein structure in the steels with Si is inferred to be caused by the difficulty in cross slip presumably due to the decrease in stacking fault energy. Furthermore, the steel containing Si shows a dislocation free zone (DFZ) along grain boundaries. A transgranular fracture takes place in 0%Si steel, while in 1%Si steel many intergranular cracks were observed just beneath the top surface, which was thought to be caused by the fact that a) strains are dispersed within grains owing to the vein structure and b) micro cracks are initiated and propagated along a DFZ.

  9. Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure

    Directory of Open Access Journals (Sweden)

    Ungyu Paik

    2013-08-01

    Full Text Available The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF for 1429 cycles. The TBC with the bond coat prepared by the air-plasma spray (APS method showed a good condition at the interface between the top and bond coats after cyclic furnace thermal fatigue (CFTF for 1429 cycles, whereas the TBCs with the bond coats prepared by the high-velocity oxygen fuel (HVOF and low-pressure plasma spray (LPPS methods showed a partial cracking (and/or delamination and a delamination after 780 cycles, respectively. The TBCs with the bond coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50% after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the bond coat prepared by the APS showed the highest adhesive strength before and after the FTF.

  10. Effect of Ultrasonic Surface Impact on the Fatigue Behavior of Ti-6Al-4V Subject to Simulated Body Fluid

    Directory of Open Access Journals (Sweden)

    Xiaojian Cao

    2017-10-01

    Full Text Available The effect of ultrasonic nanocrystal surface modification (UNSM on the fatigue behavior of Ti6Al4V (TC4 in simulated body fluid (SBF was investigated. UNSM with the condition of a static load of 25 N, vibration amplitude of 30 μm and 36,000 strikes per unit produced about 35 μm surface severe plastic deformation (SPD layers on the TC4 specimens. One group was treated with a hybrid surface treatment (UNSM + TiN film. UNSM technique improves the micro hardness and the compressive residual stress. The surface roughness is increased slightly, but it can be remarkably improved by the TiN film. The fatigue strength of TC4 is improved by about 7.9% after UNSM. Though the current density of corrosion is increased and the pitting corrosion is accelerated, UNSM still improved the fatigue strength of TC4 after pre-soaking in SBF by 10.8%. Interior cracks initiate at the deformed carbide and oxide inclusions due to the ultrasonic impacts of UNSM. Corrosion products are always observed at the edge of fracture surface to both interior cracks and surface cracks. Coating a TiN film on the UNSMed surface helps to improve the whole properties of TC4 further.

  11. Advances in fatigue lifetime predictive techniques; Proceedings of the Symposium, San Francisco, CA, Apr. 24, 1990

    International Nuclear Information System (INIS)

    Mitchell, M.R.; Landgraf, R.W.

    1992-01-01

    Recent progress in the development of methods to predict fatigue performance of materials and structures is reviewed. Attention is given to general approaches to fatigue mechanics, elevated temperature phenomena, spectrum loading, the multiaxial behavior, and applications. Particular attention is given to a fracture-mechanics-based model for cumulative damage assessment, thermo-mechanical fatigue life prediction methods, a probabilistic fracture mechanics approach for structural reliability assessment of space flight systems, a multiaxial fatigue life estimation technique, plasticity and fatigue damage modeling of severely loaded tubing, damage evaluation in composite materials using thermographic stress analysis, and fatigue lifetime monitoring in power plants

  12. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    International Nuclear Information System (INIS)

    Park, H. B.; Chopra, O. K.

    2000-01-01

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of ΔJ and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values

  13. Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures

    Energy Technology Data Exchange (ETDEWEB)

    Zargarian, A.; Esfahanian, M. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kadkhodapour, J., E-mail: j.kad@srttu.edu [Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of); Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart, Stuttgart (Germany); Ziaei-Rad, S. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)

    2016-03-01

    In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1–0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. - Highlights: • Numerical simulation was used to predict fatigue behavior of titanium scaffolds. • Good agreement between numerical and experimental results • S–N curves obeyed the power law. • Fatigue strength of scaffolds was proportional to their Young's modulus. • Failure surface of scaffolds was inclined at an angle of 45° to loading.

  14. The fatigue life and fatigue-crack-through-thickness behavior of a surface-cracked plate, 3

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Matsui, Kentaro; Ando, Kotoji; Ogura, Nobukazu

    1989-01-01

    The LBB (leak-before-break) design is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LNG carriers and various other structures. In the LBB design, it is necessary to evaluate precisely the lifetime of steel plate. Furthermore, the change in crack shape that occurs during the propagation after through thickness is of paramount importance. For this reason, in a previous report, the authors proposed a simplified evaluation model for the stress intensity factor after cracking through thickness. Using this model, the crack propagation behavior, crack-opening displacement and crack shape change of surface-cracked smooth specimens and surface-cracked specimens with a stress concentration were evaluated quantitatively. The present study was also done to investigate the fatigue crack propagation behavior of surface cracks subjected to combined tensile and bending stress. Estimation of fatigue crack growth was done using the Newman-Raju formula before through thickness, and using formula (7) and (8) after through thickness. Crack length a r at just through thickness increases with increasing a bending stress. Calculated fatigue crack shape showed very good agreement with experimental one. It was also found that particular crack growth behavior and change in crack shape after cracking through thickness can be explained quantitatively using the K value based on Eqs. (7) and (8). (author)

  15. Elevated temperature axial and torsional fatigue behavior of Haynes 188

    Science.gov (United States)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1992-06-01

    The results of high-temperature axial and torsional low-cycle fatigue experiments performed on Haynes 188, a wrought cobalt-base superalloy, are reported. Fatigue tests were performed at 760 C in air on thin-walled tubular specimens at various ranges under strain control. Data are also presented for coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. The data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME boiler and pressure vessel code), Manson-Halford, Modified Multiaxiality Factor (proposed here), Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.

  16. Cement based composites for thin building elements: Fracture and fatigue parameters

    Czech Academy of Sciences Publication Activity Database

    Seitl, Stanislav; Bílek, V.; Keršner, Z.; Veselý, J.

    2010-01-01

    Roč. 2, č. 1 (2010), s. 911-916 E-ISSN 1877-7058. [Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GA103/08/0963 Institutional research plan: CEZ:AV0Z20410507 Keywords : Cement-based composites * Fatigue concrete * Wöhler curve * Fibers Subject RIV: JL - Materials Fatigue, Friction Mechanics

  17. Fatigue Crack Behavior of Stainless Steel 304 by the Addition of Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Rizwanulhaque Syed

    2014-01-01

    Full Text Available Fatigue is the main source of almost half of whole mechanical failures. This research investigated the effect on cyclic fatigue behavior of stainless steel 304 (SS304 when including carbon nanotubes (CNTs at the crack tip. The cyclic fatigue tests were conducted on compact tension (CT specimens to establish the relationship between crack growth and the number of cycles (a-N. It is found that the incorporation of a small amount of CNTs increased the fatigue life of the SS304/metal. Micrographs showed that the enhancement in fatigue life is caused by CNTs dense arrangement around the crack tip, entangled with each other, and finer grain size. Smooth bonding at the interface of the CNTs and SS304 grains is also observed.

  18. Low cycle fatigue behavior of Sanicro25 steel at room and at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Polák, Jaroslav, E-mail: polak@ipm.cz [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno (Czech Republic); CEITEC, Institute of Physics of Materials Academy of Sciences of the Czech Republic, Žižkova 22, Brno (Czech Republic); Petráš, Roman; Heczko, Milan; Kuběna, Ivo [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno (Czech Republic); Kruml, Tomáš [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno (Czech Republic); CEITEC, Institute of Physics of Materials Academy of Sciences of the Czech Republic, Žižkova 22, Brno (Czech Republic); Chai, Guocai [Sandvik Materials Technology, SE-811 81 Sandviken (Sweden); Linköping University, Engineering Materials, SE-581 83 Linköping (Sweden)

    2014-10-06

    Austenitic heat resistant Sanicro 25 steel developed for high temperature applications in power generation industry has been subjected to strain controlled low cycle fatigue tests at ambient and at elevated temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress–strain curves and fatigue life curves were evaluated at room temperature and at 700 °C. The internal dislocation structures of the material at room and at elevated temperature were studied using transmission electron microscopy. High resolution surface observations and FIB cuts revealed early damage at room temperature in the form of persistent slip bands and at elevated temperature as oxidized grain boundary cracks. Dislocation arrangement study and surface observations were used to identify the cyclic slip localization and to discuss the fatigue softening/hardening behavior and the temperature dependence of the fatigue life.

  19. Effect of Various Heat Treatment Processes on Fatigue Behavior of Tool Steel for Cold Forging Die

    Science.gov (United States)

    Jin, S. U.; Kim, S. S.; Lee, Y. S.; Kwon, Y. N.; Lee, J. H.

    Effects of various heat treatment processes, including "Q/T (quenching and tempering)", "Q/CT/T (Quenching, cryogenic treatment and tempering)", "Q/T (quenching and tempering) + Ti-nitriding" and "Q/CT/T (Cryogenic treatment and tempering) + Ti-nitriding", on S-N fatigue behavior of AISI D2 tool steel were investigated. The optical micrographs and Vicker's hardness values at near surface and core area were examined for each specimen. Uniaxial fatigue tests were performed by using an electro-magnetic resonance fatigue testing machine at a frequency of 80 Hz and an R ratio of -1. The overall resistance to fatigue tends to decrease significantly with Ti-nitriding treatment compared to those for the general Q/T and Q/CT/T specimens. The reduced resistance to fatigue with Ti-nitriding is discussed based on the microstructural and fractographic analyses.

  20. Fatigue behavior of a bolted assembly - a comparison between numerical analysis and experimental analysis

    International Nuclear Information System (INIS)

    Bosser, M.; Vagner, J.

    1987-01-01

    The fatigue behavior of a bolted assembly can be analysed, either by fatigue tests, or by computing the stress variations and using a fatigue curve. This paper presents the fatigue analysis of a stud-bolt and stud-flange of a steam generator manway carried out with the two methods. The experimental analysis is performed for various levels of load, according to the recommandations of the ASME code section III appendix II. The numerical analysis of the stresses is based on the results of a finite element analysis performed with the program SYSTUS. The maximum stresses are obtained in the first bolt threads. In using these stresses, the allowable number of cycles for each level of loading analysed, is obtained from fatigue curves, as defined in appendix I section III of the ASME code. The analysis underlines that, for each level of load the purely numerical approach is highly conservative, compared to the experimental approach. (orig.)

  1. Corrosion and Corrosion-Fatigue Behavior of 7075 Aluminum Alloys Studied by In Situ X-Ray Tomography

    Science.gov (United States)

    Stannard, Tyler

    7XXX Aluminum alloys have high strength to weight ratio and low cost. They are used in many critical structural applications including automotive and aerospace components. These applications frequently subject the alloys to static and cyclic loading in service. Additionally, the alloys are often subjected to aggressive corrosive environments such as saltwater spray. These chemical and mechanical exposures have been known to cause premature failure in critical applications. Hence, the microstructural behavior of the alloys under combined chemical attack and mechanical loading must be characterized further. Most studies to date have analyzed the microstructure of the 7XXX alloys using two dimensional (2D) techniques. While 2D studies yield valuable insights about the properties of the alloys, they do not provide sufficiently accurate results because the microstructure is three dimensional and hence its response to external stimuli is also three dimensional (3D). Relevant features of the alloys include the grains, subgrains, intermetallic inclusion particles, and intermetallic precipitate particles. The effects of microstructural features on corrosion pitting and corrosion fatigue of aluminum alloys has primarily been studied using 2D techniques such as scanning electron microscopy (SEM) surface analysis along with post-mortem SEM fracture surface analysis to estimate the corrosion pit size and fatigue crack initiation site. These studies often limited the corrosion-fatigue testing to samples in air or specialized solutions, because samples tested in NaCl solution typically have fracture surfaces covered in corrosion product. Recent technological advancements allow observation of the microstructure, corrosion and crack behavior of aluminum alloys in solution in three dimensions over time (4D). In situ synchrotron X-Ray microtomography was used to analyze the corrosion and cracking behavior of the alloy in four dimensions to elucidate crack initiation at corrosion pits

  2. Low-cycle fatigue behaviors of pre-hardening Hadfield steel

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Chen [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, Bo [College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China); Wang, Fei [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, Fucheng, E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China)

    2017-05-17

    Low-cycle fatigue behaviors of the pre-hardening (PH) and the water-quenching (WQ) Hadfield steel were studied using optical microscopy, transmission electron microscopy, and electron backscatter diffraction technique. The effect of the PH treatment on low-cycle fatigue behavior of the Hadfield steel was analyzed through comparing the cyclic hardening/softening behaviors and the changing regulations of stress amplitude, internal stress, and effective stress at different total strain amplitudes. Results showed obvious differences in fatigue behaviors between the PH (with a cold rolling deformation degree of 40%) and the WQ Hadfield steels. Transient hardening followed by cyclic stability behavior occurred in the PH Hadfield steel under cyclic loading, whereas cyclic softening behavior was barely observed. The fatigue life of the PH Hadfield steel was higher than that of the WQ Hadfield steel at relatively low strain amplitudes, while a contrary result was obtained at relatively high strain amplitudes. At low strain amplitudes, the deformation twins induced in the PH Hadfield steel could enhance the multiplication and slip process of dislocations, which actually improved the deformation uniformity. The long-range motion of dislocations was intensified at high strain amplitudes. However, the dislocation motion was also blocked by twin boundaries. As a result, the interactions between dislocations and deformation twins enhanced, finally causing severe dislocation accumulation. These two effects of deformation twins on dislocation motion eventually resulted in different low-cycle fatigue behaviors of the PH Hadfield steel.

  3. Compressive and fatigue behavior of beta-type titanium porous structures fabricated by electron beam melting

    International Nuclear Information System (INIS)

    Liu, Y.J.; Wang, H.L.; Li, S.J.; Wang, S.G.; Wang, W.J.; Hou, W.T.; Hao, Y.L.; Yang, R.; Zhang, L.C.

    2017-01-01

    β-type titanium porous structure is a new class of solution for implant because it offers excellent combinations of high strength and low Young's modulus. This work investigated the influence of porosity variation in electron beam melting (EBM)-produced β-type Ti2448 alloy samples on the mechanical properties including super-elastic property, Young's modulus, compressive strength and fatigue properties. The relationship between the misorientation angle of adjacent grains and fatigue crack deflection behaviors was also observed. The super-elastic property is improved as the porosity of samples increases because of increasing tensile/compressive ratio. For the first time, the position of fatigue crack initiation is defined in stress-strain curves based on the variation of the fatigue cyclic loops. The unique manufacturing process of EBM results in the generation of different sizes of grains, and the apparent fatigue crack deflection occurs at the grain boundaries in the columnar grain zone due to substantial misorientation between adjacent grains. Compared with Ti-6Al-4V samples, the Ti2448 porous samples exhibit a higher normalized fatigue strength owing to super-elastic property, greater plastic zone ahead of the fatigue crack tip and the crack deflection behavior. - Highlights: • The super-elastic property is improved with increasing porosity of Ti2448 porous samples. • The position of fatigue crack initiation on the strain curve is defined. • The unique EBM-produced microstructure leads to apparent fatigue crack deflection occurring at columnar grain boundary. • Ti2448 porous samples display only half of the Young's modulus of Ti-6Al-4V porous samples at same fatigue strength level.

  4. Proceedings of the 1985 pressure vessels and piping conference. Volume PVP-98-8. Fracture, fatigue and advanced mechanics

    International Nuclear Information System (INIS)

    Short, W.E.; Zamrik, S.Y.

    1985-01-01

    State-of-the-art engineering practices in pressure vessel and piping technology are the result of continual efforts in the evaluation of problems which have been experienced and the development of appropriate design and analysis methods for those applications. The resulting advances in technology benefit industry with properly engineered, safe, cost-effective pressure vessels and piping systems. To this end, advanced study continues in specialized areas of mechanical engineering such as fracture mechanics, experimental stress analysis, high pressure applications and related material considerations, as well as advanced techniques for evaluation of commonly encountered design problems. This volume is comprised of current technical papers on various aspects of fracture, fatigue and advanced mechanics as related to the design and analysis of pressure vessels and piping

  5. The compensatory interaction between motor unit firing behavior and muscle force during fatigue.

    Science.gov (United States)

    Contessa, Paola; De Luca, Carlo J; Kline, Joshua C

    2016-10-01

    Throughout the literature, different observations of motor unit firing behavior during muscle fatigue have been reported and explained with varieties of conjectures. The disagreement amongst previous studies has resulted, in part, from the limited number of available motor units and from the misleading practice of grouping motor unit data across different subjects, contractions, and force levels. To establish a more clear understanding of motor unit control during fatigue, we investigated the firing behavior of motor units from the vastus lateralis muscle of individual subjects during a fatigue protocol of repeated voluntary constant force isometric contractions. Surface electromyographic decomposition technology provided the firings of 1,890 motor unit firing trains. These data revealed that to sustain the contraction force as the muscle fatigued, the following occurred: 1) motor unit firing rates increased; 2) new motor units were recruited; and 3) motor unit recruitment thresholds decreased. Although the degree of these adaptations was subject specific, the behavior was consistent in all subjects. When we compared our empirical observations with those obtained from simulation, we found that the fatigue-induced changes in motor unit firing behavior can be explained by increasing excitation to the motoneuron pool that compensates for the fatigue-induced decrease in muscle force twitch reported in empirical studies. Yet, the fundamental motor unit control scheme remains invariant throughout the development of fatigue. These findings indicate that the central nervous system regulates motor unit firing behavior by adjusting the operating point of the excitation to the motoneuron pool to sustain the contraction force as the muscle fatigues. Copyright © 2016 the American Physiological Society.

  6. Effects of warm laser peening at elevated temperature on the low-cycle fatigue behavior of Ti6Al4V alloy

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J.Z.; Meng, X.K., E-mail: mengdetiankong10@126.com; Huang, S.; Sheng, J.; Lu, J.Z.; Yang, Z.R.; Su, C.

    2015-09-03

    This study focused on the effects of warm laser peening (WLP) on the fatigue behavior of Ti6Al4V titanium alloy during low-cycle fatigue (LCF) tests. The Ti6Al4V specimens were treated by laser peening at room temperature (RT-LP) and WLP at elevated temperatures from 100 °C to 400 °C. The residual stress relaxation (RSR) tests and LCF tests were conducted subsequently. In addition, the microstructure analysis of fracture surfaces was performed using scanning electron microscope (SEM). Finally, the fracture mechanism of the untreated, RT-LPed and 300 °C-WLPed samples during LCF was revealed. It is found that although the compressive residual stress (CRS) induced by WLP decreases at elevated temperatures, the depth and stability of CRS increase with the increasing treatment temperature, which help to retard the early fatigue crack initiation. Moreover, for the 300 °C-WLPed specimens, the growth rate of effective cracks is decreased and the lengths of crack growth paths are increased by the induced high angle boundaries (HABs) and nano-precipitates. Therefore, specimens treated by WLP at 300 °C are found to have a significantly extended fatigue life when subjected to low-cycle loads. This extended fatigue life is attributed to the great depth and stability of introduced CRS, as well as the enhanced fracture toughness. It can be concluded that 300 °C is the optimal temperature for WLP of Ti6Al4V titanium alloy from the perspective of LCF improvement.

  7. Atomistic origin of size effects in fatigue behavior of metallic glasses

    Science.gov (United States)

    Sha, Zhendong; Wong, Wei Hin; Pei, Qingxiang; Branicio, Paulo Sergio; Liu, Zishun; Wang, Tiejun; Guo, Tianfu; Gao, Huajian

    2017-07-01

    While many experiments and simulations on metallic glasses (MGs) have focused on their tensile ductility under monotonic loading, the fatigue mechanisms of MGs under cyclic loading still remain largely elusive. Here we perform molecular dynamics (MD) and finite element simulations of tension-compression fatigue tests in MGs to elucidate their fatigue mechanisms with focus on the sample size effect. Shear band (SB) thickening is found to be the inherent fatigue mechanism for nanoscale MGs. The difference in fatigue mechanisms between macroscopic and nanoscale MGs originates from whether the SB forms partially or fully through the cross-section of the specimen. Furthermore, a qualitative investigation of the sample size effect suggests that small sample size increases the fatigue life while large sample size promotes cyclic softening and necking. Our observations on the size-dependent fatigue behavior can be rationalized by the Gurson model and the concept of surface tension of the nanovoids. The present study sheds light on the fatigue mechanisms of MGs and can be useful in interpreting previous experimental results.

  8. Fatigue during breast cancer radiotherapy: an initial randomized study of cognitive-behavioral therapy plus hypnosis.

    Science.gov (United States)

    Montgomery, Guy H; Kangas, Maria; David, Daniel; Hallquist, Michael N; Green, Sheryl; Bovbjerg, Dana H; Schnur, Julie B

    2009-05-01

    The study purpose was to test the effectiveness of a psychological intervention combining cognitive-behavioral therapy and hypnosis (CBTH) to treat radiotherapy-related fatigue. Women (n = 42) scheduled for breast cancer radiotherapy were randomly assigned to receive standard medical care (SMC) (n = 20) or a CBTH intervention (n = 22) in addition to SMC. Participants assigned to receive CBTH met individually with a clinical psychologist. CBTH participants received training in hypnosis and CBT. Participants assigned to the SMC control condition did not meet with a study psychologist. Fatigue was measured on a weekly basis by using the fatigue subscale of the Functional Assessment of Chronic Illness Therapy (FACIT) and daily using visual analogue scales. Multilevel modeling indicated that for weekly FACIT fatigue data, there was a significant effect of the CBTH intervention on the rate of change in fatigue (p < .05), such that on average, CBTH participants' fatigue did not increase over the course of treatment, whereas control group participants' fatigue increased linearly. Daily data corroborated the analyses of weekly data. The results suggest that CBTH is an effective means for controlling and potentially preventing fatigue in breast cancer radiotherapy patients.

  9. Investigation of thermal fatigue behavior of thermal barrier coating systems

    International Nuclear Information System (INIS)

    Zhu Dongming; Miller, R.A.

    1997-01-01

    In the present study, the mechanisms of fatigue crack initiation and propagation, and of coating failure under thermal loads that simulate those in diesel engines are investigated. Surface cracks initiate early and grow continuously under thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) 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. Significant LCF and HCF interactions have been observed in the thermal fatigue tests. The fatigue crack growth rate in the ceramic coating strongly depends on the characteristic HCF cycle number, N* HCF which is defined as the number of HCF cycles per LCF cycle. The crack growth rate is increased from 0.36 μm/LCF cycle for a pure LCF test to 2.8 μm/LCF cycle for a combined LCF and HCF test at N* HCF about 20 000. A surface wedging model has been proposed to account for the HCF crack growth in the coating systems. This mechanism predicts that the HCF damage effect increases with heat flux and thus with increasing surface temperature swing, thermal expansion coefficient and elastic modulus of the ceramic coating, as well as with the HCF interacting depth. Good correlation has been found between the analysis and experimental evidence. (orig.)

  10. Low-Cycle Fatigue Behavior of 10CrNi3MoV High Strength Steel and Its Undermatched Welds

    Directory of Open Access Journals (Sweden)

    Wei Song

    2018-04-01

    Full Text Available The use of high strength steel allows the design of lighter, more slender and simpler structures due to high strength and favorable ductility. Nevertheless, the increase of yield strength does not guarantee the corresponding improvement of fatigue resistance, which becomes a major concern for engineering structure design, especially for the welded joints. The paper presents a comparison of the low cycle fatigue behaviors between 10CrNi3MoV high strength steel and its undermatched weldments. Uniaxial tension tests, Push-pull, strain-controlled fatigue tests were conducted on base metal and weldments in the strain range of 0.2–1.2%. The monotonic and cyclic stress-strain curves, stress-life, strain-life and energy-life in terms of these materials were analyzed for fatigue assessment of materials discrepancy. The stress-life results of base metal and undermatched weld metal exhibit cyclic softening behaviors. Furthermore, the shapes of 10CrNi3MoV steel hysteresis loops show a satisfactory Masing-type behavior, while the weld metal shows a non-Masing type behavior. Strain, plastic and total strain energy density amplitudes against the number of reversals to failure results demonstrate that the undermatched weld metal presents a higher resistance to fatigue crack initiation than 10CrNi3MoV high strength steel. Finally, fatigue fracture surfaces of specimens were compared by scanning electron microscopy to identify the differences of crack initiation and the propagation between them.

  11. Tension and fatigue behavior of 316LVM 1x7 multi-strand cables used as implantable electrodes.

    Science.gov (United States)

    Lewandowski, John J; Varadarajan, Ravikumar; Smith, Brian; Tuma, Chris; Shazly, Mostafa; Vatamanu, Luciano O

    2008-07-15

    The mechanical behavior of 316LVM 1x7 cables were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a Flex tester operated to provide fully reversed bending fatigue. The magnitude of cyclic strains imparted to each cable tested was controlled via the use of different diameter mandrels. Smaller diameter mandrels produced higher values of cyclic strain and lower fatigue life. Multiple samples were tested and analyzed via scanning electron microscopy. The fatigue results were analyzed via a Coffin-Manson-Basquin approach and compared to fatigue data obtained from the literature where testing was conducted on similar materials, but under rotating bending fatigue conditions.

  12. A Study on the Fatigue-Fractured Surface of Normalized SS41 Steel and M.E.F. Dual Phase Steel by an X-ray Diffraction Technique

    International Nuclear Information System (INIS)

    Oh, Sae Wook; Park, Young Chul; Park, Soo Young; Kim, Deug Jin; Hue, Sun Chul

    1996-01-01

    This study verified the relationship between fracture mechanics parameters and X-ray parameters for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation test were carried out and X-ray diffraction technique was applied to fatigue fractured surface. The change in X-ray parameters(residual stress, half-value breadth) according to the depth of fatigue fractured surface were investigated. The depth of maximum plastic zone, W y , were determined on the basis of the distribution of the half-value breadth for normalized SS41 steel and that of the residual stress for M.E.F. dual phase steel. K max could be estimated by the measurement of W y

  13. Low-cycle fatigue behavior of oxygen-free high-conductivity copper at 3000C in high vacuum

    International Nuclear Information System (INIS)

    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 0 C. Excessive recrystallization due to exposure in the 1025 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

  14. Low Cycle Fatigue Behavior of Alloy617 Weldment at 850°C

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Jeong Jun; Kim, Seon Jin [Pukyong Nat’l Univ., Busan (Korea, Republic of); Kim, Woo Gon; Kim, Eung-Seon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2017-03-15

    Alloy 617 is one of the primary candidate materials to be used in a very high temperature reactor (VHTR) system as an intermediate heat exchanger (IHX). To investigate the low cycle fatigue behavior of Alloy 617 weldments at a high temperature of 850℃, fully reversed strain-controlled fatigue tests were conducted with the total strain values ranging from 0.6~1.5%. The weldment specimens were machined using the weld pads fabricated with a single V-grove configuration by gas tungsten arc welding (GTAW) process. The fatigue life is reduced as the total strain range increases. For all testing conditions, the cyclic stress response behavior of the Alloy 617 weldments exhibited the initial cyclic strain hardening phenomenon during the initial small number of cycles. Furthermore, the overall fatigue cracking and the propagation or cracks showed a transgranular failure mode.

  15. Tension-Compression Fatigue Behavior of Plain Woven Kenaf/Kevlar Hybrid Composites

    Directory of Open Access Journals (Sweden)

    Suhad D. Salman

    2016-02-01

    Full Text Available The applications of hybrid natural/synthetic reinforced polymer composites have been rapidly gaining market share in structural applications due to their remarkable characteristics and the fact that most of the components made of these materials are subjected to cyclic loading. Their fatigue properties have received a lot of attention because predicting their behavior is a challenge due to the effects of the synergies between the fibers. The purpose of this work is to characterize the tension, compression, and tensile-compression fatigue behavior of six layers of Kevlar hybridized with one layer of woven kenaf reinforced epoxy, at a 35% weight fraction. Fatigue tests were carried out and loaded cyclically at 60%, 70%, 80%, and 90% of their ultimate compressive stress. The results give a complete description for tensile and compression properties and could be used to predict fatigue-induced failure mechanisms.

  16. Fracture mechanics

    CERN Document Server

    Perez, Nestor

    2017-01-01

    The second edition of this textbook includes a refined presentation of concepts in each chapter, additional examples; new problems and sections, such as conformal mapping and mechanical behavior of wood; while retaining all the features of the original book. The material included in this book is based upon the development of analytical and numerical procedures pertinent to particular fields of linear elastic fracture mechanics (LEFM) and plastic fracture mechanics (PFM), including mixed-mode-loading interaction. The mathematical approach undertaken herein is coupled with a brief review of several fracture theories available in cited references, along with many color images and figures. Dynamic fracture mechanics is included through the field of fatigue and Charpy impact testing. Explains computational and engineering approaches for solving crack-related problems using straightforward mathematics that facilitate comprehension of the physical meaning of crack growth processes; Expands computational understandin...

  17. Fatigue Behaviors of Materials Processed by Planar Twist Extrusion

    Science.gov (United States)

    Ebrahimi, Mahmoud

    2017-12-01

    Since the last decade, the fabrication of ultrafine grain and nanostructure metals and alloys has attracted much attention in the field of materials engineering. The present study aimed at experimentally investigating the fatigue properties that are of great importance in dynamic structures before and after the planar twist extrusion process for both commercially pure copper and 6061 aluminum alloy. The results indicated that the yield strength, tensile strength, hardness, and fatigue endurance of copper increased by about 398, 122, 198, and 183 pct, respectively, while they improved by about 429, 212, 227, and 148 pct, respectively, in aluminum alloy as compared to the initial conditions. The stress-strain curves displayed sizable reduction of strain hardening. Furthermore, grain-size correction factors based on the empirical results were introduced to include the effect of the grain-size effect on both low and high-cycle fatigue strengths of the material.

  18. Characterization of uniaxial fatigue behavior of precipitate strengthened Cu-Ni-Si alloy (SICLANIC(TM

    Directory of Open Access Journals (Sweden)

    B. Saadouki

    2018-01-01

    Full Text Available Fatigue tests were conducted on cylindrical bars specimens to understand the fatigue behavior of SICLANIC. Although it displays good resistance in monotonic tension, this material weakens and shows a softening in repeated solicitation. This has been verified through a SEM observation, the Cu-Ni-Si alloy presents transgranular failure by cleavage. The MansonCoffin diagram exhibited the plastic deformation accommodation. The plastic deformation becomes periodic and decreases progressively as the cycle number increases. The approximations of Manson Coffin give fatigue parameters values which are in good agreement with the experience

  19. Fretting fatigue behavior of high-strength steel monostrands under bending load

    DEFF Research Database (Denmark)

    Winkler, Jan; Georgakis, Christos T.; Fischer, Gregor

    2015-01-01

    In this paper, the fretting fatigue behavior of pretensioned high-strength steel monostrands is investigated. To measure the local deformations on the strands, a novel method based on the digital image correlation (DIC) technique was used to quantify the relative movement between individual wires...... along the length of the monostrand. Information about the monostrand bending stiffness and the extent of relative displacement between core and outer wires of a monostrand undergoing flexural deformations is provided. From the series of dynamic fatigue tests, a fretting fatigue spectrum is derived...

  20. Fatigue crack growth rates and fracture toughness of rapidly solidified Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloys

    International Nuclear Information System (INIS)

    Hariprasad, S.; Sastry, S.M.L.; Jerina, K.L.

    1994-01-01

    The room-temperature fatigue crack growth rates (FCGR) and fracture toughness were evaluated for different crack plane Orientations of an Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloy produced by planar flow casting (PFC) and atomized melt deposition (AMD) processes. For the alloy produced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. Diffusion bonding and adhesive bonding methods were used to prepare specimens for determining FCGR and fracture toughness in the short transverse direction. Interparticle boundaries control fracture properties in the alloy produced by PFC. Fracture toughness of the PFC alloy varies from 13.4 MPa√ bar m to 30.8 MPa√ bar m, depending on the orientation of the crack plane relative to the interparticle boundaries. Fatigue crack growth resistance and fracture toughness are greater in the L-T, L-S, and T-S directions than in the T-L, S-T, and S-L orientations. The alloy produced by AMD does not exhibit anisotropy in fracture toughness and fatigue crack growth resistance in the as-deposited condition or in the extruded condition. The fracture toughness varies from 17.2 MPa√ bar m to 18.5 MPa√ bar m for the as-deposited condition and from 19.8 MPa√ bar m to 21.0 MPa√ bar m for the extruded condition. Fracture properties are controlled by intrinsic factors in the alloy produced by AMD. Fatigue crack growth rates of the AMD alloy are comparable to those of the PFC alloy in the L-T orientation. The crack propagation modes were studied by optical metallographic examination of crack-microstructure interactions and scanning electron microscopy of the fracture surfaces

  1. Thermal-stress fatigue behavior of twenty-six superalloys

    Science.gov (United States)

    Bizon, P. T.; Spera, D. A.

    1976-01-01

    The comparative thermal-stress fatigue resistances of 26 nickeland cobalt-base alloys were determined by fluidized bed tests. Cycles to cracking differed by almost three orders of magnitude for these materials, with directional solidification and surface protection showing definite benefit. The alloy-coating combination with the highest thermal-stress fatigue resistance was directionally solidified NASA TAZ-8A with an RT-SP coating. Its oxidation resistance was also excellent, showing approximately a 1/2 percent weight loss after 14,000 fluidized bed cycles.

  2. Fatigue Behavior of Long and Short Cracks in Wrought and Powder Aluminum Alloys.

    Science.gov (United States)

    1984-05-01

    The effects of cyclic frequency, electrochemical potential and bulk solution composition on the kinetics of small corrosion fatigue cracks have not...threshold behavior between cast iron (co = 113 MPa) and maraging steel (co = 1906 MPa), as a function of surface roughness (to simulate crack size) (after...4130 steel the crack size effect on corrosion fatigue, Fig. 2, is predicted in part based on linear superposition of stress corrosion growth rates for

  3. Thermo-mechanical response and fatigue behavior of shape memory alloy

    International Nuclear Information System (INIS)

    Kusagawa, Masaki; Asada, Yasuhide; Nakamura, Toshiya

    1998-01-01

    Mechanical, thermo-mechanical and fatigue behaviors of Ni-Ti-Nb shape memory alloy (SMA) have been studied to prepare material data for a design purpose. Presented are testing devices, testing procedure and test results of monotonic tensile, recovery of inelastic deformation due to post heating (thermo-mechanical recovery) and fatigue for future use of the SMA as a structural material of nuclear incore structures. (orig.)

  4. Effects of high mean stress on the high-cycle fatigue behavior of PWA 1480

    International Nuclear Information System (INIS)

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

    1985-03-01

    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. This paper describes results obtained in an ongoing program to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material

  5. Thermo-mechanical response and fatigue behavior of shape memory alloy

    Energy Technology Data Exchange (ETDEWEB)

    Kusagawa, Masaki; Asada, Yasuhide; Nakamura, Toshiya [Tokyo Univ. (Japan). Dept. of Mechanical Engineering

    1998-11-01

    Mechanical, thermo-mechanical and fatigue behaviors of Ni-Ti-Nb shape memory alloy (SMA) have been studied to prepare material data for a design purpose. Presented are testing devices, testing procedure and test results of monotonic tensile, recovery of inelastic deformation due to post heating (thermo-mechanical recovery) and fatigue for future use of the SMA as a structural material of nuclear incore structures. (orig.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Nikulin, S.A.; Rozhnov, A.B. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Gusev, A.Yu. [A.A. Bochvar All-Russia Research Institute of Inorganic Materials (VNIINM), Rogova St. 5a, 123060 Moscow (Russian Federation); Nechaykina, T.A. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Rogachev, S.O., E-mail: csaap@mail.ru [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Zadorozhnyy, M.Yu. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation)

    2014-03-15

    Highlights: •Low-cycle fatigue tests of Zr–Nb alloys using DMA have been carried out. •The characteristics of low-cycle fatigue of the Zr–Nb alloy at 25/350 °C were determined. •Increasing test temperature up to 350 °C leads to a decrease of fatigue life. •The test temperature doesn’t have an effect on the character of fatigue curves. -- Abstract: 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.

  7. Prediction of inelastic behavior and creep-fatigue life of perforated plates

    International Nuclear Information System (INIS)

    Igari, Toshihide; Setoguchi, Katsuya; Nakano, Shohki; Nomura, Shinichi

    1991-01-01

    Prediction methods of macroscopic and local stress-strain behavior of perforated plates in plastic and creep regime which are proposed by the authors are applied to the inelastic analysis and creep-fatigue life prediction of perforated cylinder subjected to cyclic thermal stress. Stress-strain behavior of perforated cylinder is analyzed by modeling the perforated portion to cylinder with equivalent-solid-plate properties. Creep-fatigue lives at around a hole of perforated plates are predicted by using the local stress-strain behavior and are compared with experimentally observed lives. (author)

  8. Os peroneum friction syndrome complicated by sesamoid fatigue fracture: a new radiological diagnosis? Case report and literature review

    Energy Technology Data Exchange (ETDEWEB)

    Bashir, Waseem A.; Connell, David A. [Royal National Orthopaedic Hospital NHS Trust, Department of Radiology, London, Middlesex (United Kingdom); Lewis, Steve [Craven Cottage, Fulham Football Club, London (United Kingdom); Cullen, Nicholas [The Royal National Orthopaedic Hospital NHS Trust, Department of Orthopaedics, London, Middlesex (United Kingdom)

    2009-02-15

    Injuries to the peroneal tendons are relatively common worldwide but tendon rupture without significant trauma is uncommon. Ankle mechanics can be seriously affected by disruption of one or both of the peroneal tendons although complete rupture can also remain asymptomatic. Accessory ossicles are sesamoid bones and are common findings in routine radiology of the foot and ankle. Although in the vast majority these ''os'' are normal variants of anatomy, they can lead to painful syndromes and suffer fractures and even undergo degenerative changes in response to overuse and trauma. Although similar syndromes have been discussed in the surgical literature, there is a lack of literature describing the use of modern imaging in the accurate diagnosis and its subsequent assistance towards appropriate management of os peroneum friction syndrome complicated by sesamoid fatigue syndrome. This article presents the plain film, sonographic and magnetic resonance imaging findings in a case of os peroneum friction syndrome complicated by a sesamoid fatigue fracture as well as reviewing the pertinent literature. (orig.)

  9. Os peroneum friction syndrome complicated by sesamoid fatigue fracture: a new radiological diagnosis? Case report and literature review.

    Science.gov (United States)

    Bashir, Waseem A; Lewis, Steve; Cullen, Nicholas; Connell, David A

    2009-02-01

    Injuries to the peroneal tendons are relatively common worldwide but tendon rupture without significant trauma is uncommon. Ankle mechanics can be seriously affected by disruption of one or both of the peroneal tendons although complete rupture can also remain asymptomatic. Accessory ossicles are sesamoid bones and are common findings in routine radiology of the foot and ankle. Although in the vast majority these "os" are normal variants of anatomy, they can lead to painful syndromes and suffer fractures and even undergo degenerative changes in response to overuse and trauma. Although similar syndromes have been discussed in the surgical literature, there is a lack of literature describing the use of modern imaging in the accurate diagnosis and its subsequent assistance towards appropriate management of os peroneum friction syndrome complicated by sesamoid fatigue syndrome. This article presents the plain film, sonographic and magnetic resonance imaging findings in a case of os peroneum friction syndrome complicated by a sesamoid fatigue fracture as well as reviewing the pertinent literature.

  10. Os peroneum friction syndrome complicated by sesamoid fatigue fracture: a new radiological diagnosis? Case report and literature review

    International Nuclear Information System (INIS)

    Bashir, Waseem A.; Connell, David A.; Lewis, Steve; Cullen, Nicholas

    2009-01-01

    Injuries to the peroneal tendons are relatively common worldwide but tendon rupture without significant trauma is uncommon. Ankle mechanics can be seriously affected by disruption of one or both of the peroneal tendons although complete rupture can also remain asymptomatic. Accessory ossicles are sesamoid bones and are common findings in routine radiology of the foot and ankle. Although in the vast majority these ''os'' are normal variants of anatomy, they can lead to painful syndromes and suffer fractures and even undergo degenerative changes in response to overuse and trauma. Although similar syndromes have been discussed in the surgical literature, there is a lack of literature describing the use of modern imaging in the accurate diagnosis and its subsequent assistance towards appropriate management of os peroneum friction syndrome complicated by sesamoid fatigue syndrome. This article presents the plain film, sonographic and magnetic resonance imaging findings in a case of os peroneum friction syndrome complicated by a sesamoid fatigue fracture as well as reviewing the pertinent literature. (orig.)

  11. Experimental verification of the statistical theories of scaling factor effect in fatigue fracture of steel

    International Nuclear Information System (INIS)

    Svistun, R.P.; Babej, Yu.I.; Tkachenko, N.N.

    1976-01-01

    Statistical theories of the scale effect in the fatigue failure of 40KH18N9T, 10 and 20 steels have been verified. The theories are shown to be not invariably suitable for a satisfactory exlanation of the fatigue strength of the samples with respect to their dimensions. One of the main reasons for displaying the scale effect in the process of steel fatigue is the sample self-heating, i.e. a temperature factor which in many cases overlaps a statistical one

  12. Experimental verification of the statistical theories of scaling factor effect in fatigue fracture of steel

    Energy Technology Data Exchange (ETDEWEB)

    Svistun, R P; Babei, Yu I; Tkachenko, N N [AN Ukrainskoj SSR, Lvov. Fiziko-Mekhanicheskij Inst.; L' vovskij Lesotekhnicheskij Inst. (Ukrainian SSR))

    1976-01-01

    Statistical theories of the scale effect in the fatigue failure of 40KH18N9T, 10 and 20 steels have been verified. The theories are shown to be not invariably suitable for a satisfactory exlanation of the fatigue strength of the samples with respect to their dimensions. One of the main reasons for displaying the scale effect in the process of steel fatigue is the sample self-heating, i.e. a temperature factor which in many cases overlaps a statistical one.

  13. Computational prediction of the fatigue behavior of additively manufactured porous metallic biomaterials

    NARCIS (Netherlands)

    Hedayati, R.; Hosseini-Toudeshky, H; Sadighi, M.; Mohammadi-Aghdam, M; Zadpoor, A.A.

    2016-01-01

    The mechanical behavior of additively manufactured porous biomaterials has recently received increasing attention. While there is a relatively large body of data available on the static mechanical properties of such biomaterials, their fatigue behavior is not yet well-understood. That is partly

  14. Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism.

    Science.gov (United States)

    Gludovatz, Bernd; Demetriou, Marios D; Floyd, Michael; Hohenwarter, Anton; Johnson, William L; Ritchie, Robert O

    2013-11-12

    Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ~1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly "zig-zag" manner, creating a rough "staircase-like" profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability.

  15. S-N Fatigue and Fatigue Crack Propagation Behaviors of X80 Steel at Room and Low Temperatures

    Science.gov (United States)

    Jung, Dae-Ho; Kwon, Jae-Ki; Woo, Nam-Sub; Kim, Young-Ju; Goto, Masahiro; Kim, Sangshik

    2014-02-01

    In the present study, the S-N fatigue and the fatigue crack propagation (FCP) behaviors of American Petroleum Institute X80 steel were examined in the different locations of the base metal (BM), weld metal (WM), and heat-affected zone (HAZ) at 298 K, 223 K, and 193 K (25 °C, -50 °C, and -80 °C). The resistance to S-N fatigue of X80 BM specimen increased greatly with decreasing temperature from 298 K to 193 K (25 °C to -80 °C) and showed a strong dependency on the flow strength (½(yield strength + tensile strength)). The FCP rates of X80 BM specimen were substantially reduced with decreasing temperature from 298 K to 223 K (25 °C to -50 °C) over the entire ∆ K regime, while further reduction in FCP rates was not significant with temperature from 223 K to 193 K (-50 °C to -80 °C). The FCP rates of the X80 BM and the WM specimens were comparable with each other, while the HAZ specimen showed slightly better FCP resistance than the BM and the WM specimens over the entire ∆K regime at 298 K (25 °C). Despite the varying microstructural characteristics of each weld location, the residual stress appeared to be a controlling factor to determine the FCP behavior. The FCP behaviors of high strength X80 steel were discussed based on the microstructural and the fractographic observations.

  16. Competing fatigue failure behaviors of Ni-based superalloy FGH96 at elevated temperature

    International Nuclear Information System (INIS)

    Miao, Guolei; Yang, Xiaoguang; Shi, Duoqi

    2016-01-01

    Fatigue experiments were performed on a polycrystalline P/M processed nickel-based superalloy, FGH96 at 600 °C to investigate competing fatigue failure behaviors of the alloy. The experiments were performed at four levels of stress (from high cycle fatigue to low cycle fatigue) at stress ratio of 0.05. There was large variability in fatigue life at both high and low stresses. Scanning electron microscopy (SEM) was used to analyze the failure surfaces. Three types of competing failure modes were observed (surface, sub-surface and internal initiated failures). Crack initiation sites were gradually changed from the surface to the interior with the decreasing of stress level. Roles of microstructures in competing failure mechanism were analyzed. There were six kinds of fatigue crack initiation modes: (1) surface inclusion initiated; (2) surface facet initiated; (3) sub-surface inclusion initiated; (4) sub-surface facet initiated; (5) internal inclusion initiated; (6) internal facet initiated. Inclusions at surface were the life-limiting microstructures at higher stress levels. The probability of occurrence of inclusions initiated is gradually reduced with decreasing of stress level, simultaneously the probability of occurrence of facets initiated is increasing. The existence of the inclusions resulted in large life variability at higher stress levels, while heterogeneity of material caused by random combinations of grains was the main cause of fatigue variability at lower stress levels.

  17. Competing fatigue failure behaviors of Ni-based superalloy FGH96 at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Miao, Guolei [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Yang, Xiaoguang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-engine(CICAAE), Beihang University, Beijing 100191 (China); Shi, Duoqi, E-mail: shdq@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-engine(CICAAE), Beihang University, Beijing 100191 (China)

    2016-06-21

    Fatigue experiments were performed on a polycrystalline P/M processed nickel-based superalloy, FGH96 at 600 °C to investigate competing fatigue failure behaviors of the alloy. The experiments were performed at four levels of stress (from high cycle fatigue to low cycle fatigue) at stress ratio of 0.05. There was large variability in fatigue life at both high and low stresses. Scanning electron microscopy (SEM) was used to analyze the failure surfaces. Three types of competing failure modes were observed (surface, sub-surface and internal initiated failures). Crack initiation sites were gradually changed from the surface to the interior with the decreasing of stress level. Roles of microstructures in competing failure mechanism were analyzed. There were six kinds of fatigue crack initiation modes: (1) surface inclusion initiated; (2) surface facet initiated; (3) sub-surface inclusion initiated; (4) sub-surface facet initiated; (5) internal inclusion initiated; (6) internal facet initiated. Inclusions at surface were the life-limiting microstructures at higher stress levels. The probability of occurrence of inclusions initiated is gradually reduced with decreasing of stress level, simultaneously the probability of occurrence of facets initiated is increasing. The existence of the inclusions resulted in large life variability at higher stress levels, while heterogeneity of material caused by random combinations of grains was the main cause of fatigue variability at lower stress levels.

  18. A comparison of tensile, fracture and fatigue mechanical behaviour of structural reinforcing bars made with different steels

    Directory of Open Access Journals (Sweden)

    Rodríguez, C.

    2013-09-01

    Full Text Available The use of austenitic stainless steels as rebar is an option increasingly used in reinforced concrete structures exposed to aggressive environments and especially those that have to work in marine environments. The same is true for duplex stainless steel rebars, although nowadays they have a lower use, mainly due to the fact that their inclusion in the reinforced concrete standards was delayed 10 years compared to austenitic stainless steel ones, and consequently their in-service behavior is not as well known. A study of the mechanical properties, including fracture toughness, fatigue behaviour and corrosion resistance in saline alkaline environments of austenitic (AISI 304LN and 316LN and duplex (D2205 stainless steel reinforcing bars was performed in this work. Bars made on a high ductility carbon steel (B500SD that are normally used to reinforce concrete were also characterized and used as a comparison. Stainless steel reinforcing bars show mechanical properties at least similar but usually higher than one of the best carbon steel re-bars (B500SD, along with a significantly higher ductility and, of course, much better corrosion behaviour in saline alkaline environments.El uso de aceros inoxidables austeníticos como armaduras de refuerzo es una opción cada vez más utilizada en estructuras de hormigón armado expuestas a ambientes agresivos y especialmente en las que han de trabajar en ambientes marinos. Lo mismo cabe decir de las armaduras de acero inoxidable dúplex, si bien su uso es menor, debido sobre todo a que su inclusión en la normativa aplicable al armado de hormigón se retrasó 10 años con respecto a los inoxidables austeníticos y, consecuentemente, su comportamiento en servicio es menos conocido. En este trabajo se analiza el comportamiento mecánico, incluyendo fractura y fatiga, así como la resistencia a la corrosión en medios que simulan un hormigón contaminado de cloruros, de armaduras fabricadas tanto con

  19. Role of prism decussation on fatigue crack growth and fracture of human enamel.

    Science.gov (United States)

    Bajaj, Devendra; Arola, Dwayne

    2009-10-01

    The role of prism decussation on the crack growth resistance of human enamel is evaluated. Miniature inset compact tension (CT) specimens embodying a section of cuspal enamel were subjected to Mode I cyclic or monotonic loads. Cracks were grown in either the forward (from outer enamel inwards) or reverse (from inner enamel outwards) direction and the responses were compared quantitatively. Results showed that the outer enamel exhibits lower resistance to the inception and growth of cracks. Regardless of the growth direction, the near-threshold region of cyclic extension was typical of "short crack" behavior (i.e. deceleration of growth with an increase in crack length). Cyclic crack growth was more stable in the forward direction and occurred over twice the spatial distance achieved in the reverse direction. In response to the monotonic loads, a rising R-curve response was exhibited by growth in the forward direction only. The total energy absorbed in fracture for the forward direction was more than three times that in the reverse. The rise in crack growth resistance was largely attributed to a combination of mechanisms that included crack bridging, crack bifurcation and crack curving, which were induced by decussation in the inner enamel. An analysis of the responses distinguished that the microstructure of enamel appears optimized for resisting crack growth initiating from damage at the tooth's surface.

  20. Behavior of Fatigue Crack Tip Opening in Air and Corrosive Atmosphere

    Science.gov (United States)

    Hayashi, Morihito; Toeda, Kazunori

    In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

  1. Epigallocatechin gallate ameliorates chronic fatigue syndrome in mice: behavioral and biochemical evidence.

    Science.gov (United States)

    Sachdeva, Anand Kamal; Kuhad, Anurag; Tiwari, Vinod; Chopra, Kanwaljit

    2009-12-28

    Three decades after the coining of the term chronic fatigue syndrome, the diagnosis of this illness is still symptom based and the aetiology remains elusive. Chronic fatigue syndrome pathogenesis seems to be multifactorial and the possible involvement of immune system is supported. The present study was designed to evaluate the effects of the epigallocatechin gallate in a mouse model of immunologically induced chronic fatigue. On 19th day, after lipopolysaccharide/Brucella abortus administration, the mice showed significant increase in immobility period, post swim fatigue and thermal hyperalgesia. Behavioral deficits were coupled with enhanced oxidative-nitrosative stress as evident by increased lipid peroxidation, nitrite levels and decreased endogenous antioxidant enzymes (superoxide dismutase, reduced glutathione and catalase) and inflammation (increased levels of tumor necrosis factor-alpha and tissue growth factor-beta). Chronic treatment with epigallocatechin gallate restored these behavioral and biochemical alterations in mice. The present study points out towards the beneficial effect of epigallocatechin gallate in the amelioration of chronic fatigue syndrome and thus may provide a new, effective and powerful strategy to treat chronic fatigue syndrome.

  2. Cognitive behavioral therapies and multiple sclerosis fatigue: A review of literature.

    Science.gov (United States)

    Chalah, Moussa A; Ayache, Samar S

    2018-03-30

    Patients with multiple sclerosis (MS) commonly suffer from fatigue, a multidimensional symptom with physical, cognitive and psychosocial components that can drastically alter the quality of life. Despite its debilitating nature, the current treatment options are limited by their modest efficacy and numerous side effects. Cognitive behavioral therapies (CBT) have been applied in MS patients and might be of help in relieving fatigue. This constitutes the main objective of the current review. Computerized databases (Medline/PubMed, Scopus) were consulted till January 2018, and a research was conducted according to PRISMA guidelines in order to identify original research articles published at any time in English and French languages on cognitive behavioral therapies and MS fatigue as a primary outcome. The following key terms were used: ('multiple sclerosis' OR 'MS') AND ('fatigue') AND ('cognitive behavioral therapy' OR 'CBT' OR 'cognitive therapy' OR 'CT' OR 'behavioral therapy' OR 'BT' OR 'psychotherapy'). Fourteen papers matched the above criteria (11 trials, 2 methods and 1 study addressing CBT mechanisms of action). CBT seems to have positive effects on MS fatigue. However, the onset and duration of effects varied across the studies. These data highlight the promising effects of CBT in MS fatigue. Admitting the limited number of studies, more protocols are needed before drawing any conclusion. Future works might benefit from combining CBT with emerging therapies such as non-invasive brain stimulation techniques which also yielded promising results in the setting of MS. This may help in long-term maintenance of fatigue relief. Copyright © 2018 Elsevier Ltd. All rights reserved.

  3. Effects of pulse current stimulation on the thermal fatigue crack propagation behavior of CHWD steel

    International Nuclear Information System (INIS)

    Lin, H.Q.; Zhao, Y.G.; Gao, Z.M.; Han, L.G.

    2008-01-01

    The fatigue crack propagating behaviors of cast hot working die (CHWD) steel untreated and treated by an electric current in the intermediate stage of thermal fatigue were investigated in the present study. The circle/elliptical heating affected zone (HAZ) was formed ahead of the notch tip on the fatigued specimens after pulse electric current stimulation. Both SEM observation and X-ray diffraction analysis revealed that pulse electric current stimulation refined grains/subgrains in the HAZs. With the prolonging of discharging duration, the grains/subgrains decreased in size and the dislocation density and microhardness increased gradually. The grain refinement and dislocation density increase played an important role in the material strengthening, which inevitably enhanced the propagation resistance and delayed the propagation of thermal fatigue cracks. Therefore, the pulse electric current stimulation was an effective method to improve the service lifetime of die material

  4. Corrosion fatigue cracking behavior of Inconel 690 (TT) in secondary water of pressurized water reactors

    International Nuclear Information System (INIS)

    Xiao Jun; Chen Luyao; Qiu Shaoyu; Chen Yong; Lin Zhenxia; Fu Zhenghong

    2015-01-01

    Inconel 690 (TT) is one of the key materials for tubes of steam generators for pressurized water reactors, where it is susceptible to corrosion fatigue cracking. In this paper, the corrosion fatigue cracking behavior of Inconel 690 (TT) was investigated under small scale yielding conditions, in the simulated secondary water of pressurized water reactor. It was observed that the fatigue crack growth rate was accelerated by a maximum factor up to 3 in the simulated secondary water, comparing to that in room temperature air. In addition, it was found that the accelerating effect was influenced by out-of-plane cracking of corrosion fatigue cracks and also correlated with stress intensity factor range, maximum stress intensity factor and stress ratio. (authors)

  5. Effect of an amorphous titania nanotubes coating on the fatigue and corrosion behaviors of the biomedical Ti-6Al-4V and Ti-6Al-7Nb alloys.

    Science.gov (United States)

    Campanelli, Leonardo Contri; Bortolan, Carolina Catanio; da Silva, Paulo Sergio Carvalho Pereira; Bolfarini, Claudemiro; Oliveira, Nilson Tadeu Camarinho

    2017-01-01

    An array of self-organized TiO 2 nanotubes with an amorphous structure was produced on the biomedical Ti-6Al-4V and Ti-6Al-7Nb alloys, and the resulting fatigue and corrosion behaviors were studied. The electrochemical response of the nanotubular oxide surfaces was investigated in Ringer physiological solution through potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The absence of transpassivation in the chloride-containing solution, in addition to the micron-scale values of the passivation current density, indicated the excellent corrosion behavior of the coating and the satisfactory protection against the creation of potential stress concentrators in the surface. Axial fatigue tests were performed in physiological solution on polished and coated conditions, with characterization of the treated surfaces by scanning electron microscopy before and after the tests. The surface modification was not deleterious to the fatigue response of both alloys mainly due to the nano-scale dimension of the nanotubes layer. An estimation based on fracture mechanics revealed that a circumferential crack in the range of 5μm depth would be necessary to affect the fatigue performance, which is far from the thickness of the studied coating, although no cracks were actually observed in the oxide surfaces after the tests. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Rotary bending fatigue behavior of A356 –T6 aluminum alloys by vacuum pressurizing casting

    Directory of Open Access Journals (Sweden)

    Yong-qin Liu

    2015-09-01

    Full Text Available Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigue properties of A356-T6 alloys prepared by vacuum pressurizing casting were investigated. The S-N curve and limit strength 90 MPa under fatigue life of 107 cycles were obtained. The analyses on the fatigue fractography and microstructure of specimens showed that the fatigue fracture mainly occurs at the positions with casting defects in the subsurface, especially at porosities regions, which attributed to the crack propagation during the fatigue fracture process. Using the empirical crack propagation law of Pairs-Erdogon, the quantitative relationship among the initial crack size, fatigue life and applied stress was established. The fatigue life decreases with an increase in initial crack size. Two constants in the Pairs-Erdogon equation of aluminum alloy A356-T6 were calculated using the experimental data.

  7. Effect of strain rate and temperature at high strains on fatigue behavior of SAP alloys

    DEFF Research Database (Denmark)

    Blucher, J.T.; Knudsen, Per; Grant, N.J.

    1968-01-01

    Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased with decre......Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased...

  8. Fracture behavior of nuclear graphites under tensile impact loading

    International Nuclear Information System (INIS)

    Ugachi, Hirokazu; Ishiyama, Shintaro; Eto, Motokuni

    1994-01-01

    Impact tensile strength test was performed with two kinds of HTTR graphites, fine grained isotropic graphite, IG-11 and coarse grained near isotropic graphite, PGX and deformation and fracture behavior under the strain rate of over 100s -1 was measured and the following results were derived: (1) Tensile strength for IG-11 graphite does not depend on the strain rate less than 1 s -1 , but over 1 s -1 , tensile strength for IG-11 graphite increase larger than that measured under 1 s -1 . At the strain rate more than 100 s -1 , remarkable decrease of tensile strength for IG-11 graphite was found. Tensile strength of PGX graphite does not depend on the strain rate less than 1 s -1 , but beyond this value, the sharp tensile strength decrease occurs. (2) Under 100 s -1 , fracture strain for both graphites increase with increase of strain rate and over 100 s -1 , drastic increase of fracture strain for IG-11 graphite was found. (3) At the part of gage length, volume of specimen increase with increase of tensile loading level and strain rate. (4) Poisson's ratio for both graphites decrease with increase of tensile loading level and strain rate. (5) Remarkable change of stress-strain curve for both graphites under 100 s -1 was not found, but over 100 s -1 , the slope of these curve for IG-11 graphite decrease drastically. (author)

  9. Acoustic emission technique for characterisation of deformation, fatigue, fracture and phase transformation and for leak detection with high sensitivity- our experiences

    International Nuclear Information System (INIS)

    Jayakumar, T.; Mukhopadhyay, C.K.; Baldev Raj

    1996-01-01

    Acoustic emission technique has been used for studying tensile deformation, fracture behaviour, detection and assessment of fatigue crack growth and α-martensite phase transformation in austenitic alloys. A methodology for amplification of weak acoustic emission signals has been established. Acoustic emission technique with advanced spectral analysis has enabled detection with high sensitivity of minute leaks in noisy environments. (author)

  10. Effect of tungsten and tantalum on the low cycle fatigue behavior of reduced activation ferritic/martensitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Shankar, Vani, E-mail: vani@igcar.gov.in [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603102 (India); Mariappan, K.; Nagesha, A.; Prasad Reddy, G.V.; Sandhya, R.; Mathew, M.D.; Jayakumar, T. [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603102 (India)

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Effect of tungsten and tantalum on low cycle fatigue behavior of RAFM steels. Black-Right-Pointing-Pointer Both alloying elements W and Ta improved fatigue life. Black-Right-Pointing-Pointer Increase in Ta content improved fatigue life more than W. Black-Right-Pointing-Pointer Optimization of W content at 1.4 wt.%. Black-Right-Pointing-Pointer Softening behavior closely related to W and Ta content. - Abstract: Reduced activation ferritic/martensitic (RAFM) steels are candidate materials for the test blanket modules of International Thermonuclear Experimental Reactor (ITER). Several degradation mechanisms such as thermal fatigue, low cycle fatigue, creep fatigue interaction, creep, irradiation hardening, swelling and phase instability associated irradiation embrittlement must be understood in order to estimate the component lifetime and issues concerning the structural integrity of components. The current work focuses on the effect of tungsten and tantalum on the low cycle fatigue (LCF) behavior of RAFM steels. Both alloying elements tungsten and tantalum improved the fatigue life. Influence of Ta on increasing fatigue life was an order of magnitude higher than the influence of W on improving the fatigue life. Based on the present study, the W content was optimized at 1.4 wt.%. Softening behavior of RAFM steels showed a strong dependence on W and Ta content in RAFM steels.

  11. FRACTURE MECHANICS APPROACH TO ESTIMATE FATIGUE LIVES OF WELDED LAP-SHEAR SPECIMENS

    Energy Technology Data Exchange (ETDEWEB)

    Lam, P.; Michigan, J.

    2014-04-25

    A full range of stress intensity factor solutions for a kinked crack is developed as a function of weld width and the sheet thickness. When used with the associated main crack solutions (global stress intensity factors) in terms of the applied load and specimen geometry, the fatigue lives can be estimated for the laser-welded lap-shear specimens. The estimations are in good agreement with the experimental data. A classical solution for an infinitesimal kink is also employed in the approach. However, the life predictions tend to overestimate the actual fatigue lives. The traditional life estimations with the structural stress along with the experimental stress-fatigue life data (S-N curve) are also provided. In this case, the estimations only agree with the experimental data under higher load conditions.

  12. Resistance to corrosion fatigue fracture in heat resistant steels and their welded joints

    International Nuclear Information System (INIS)

    Timofeev, B.T.; Fedorova, V.A.; Zvezdin, Yu.I.; Vajner, L.A.; Filatov, V.M.

    1987-01-01

    Experimental data on cyclic crack resistance of heat-resistant steels and their welded joints employed for production of the reactor bodies are for the first time generalized and systematized. The formula is suggested accounting for surface and inner defects to calculate the fatigue crack growth in the process of operation. This formula for surface defects regards also the effect of the corrosion factor. Mechanisms of the reactor water effect on the fatigue crack growth rate are considered as well as a combined effect of radiation and corrosive medium on this characteristic

  13. Effects of a laser surface processing induced heat-affected zone on the fatigue behavior of AISI 4340 steel

    International Nuclear Information System (INIS)

    McDaniels, R.L.; White, S.A.; Liaw, K.; Chen, L.; McCay, M.H.; Liaw, P.K.

    2008-01-01

    The effects of the heat-affected zone (HAZ) in AISI 4340 steel created by laser-surface alloying (LSA) on high-cycle fatigue behavior have been investigated. This research was performed by producing several lots of laser-processed AISI 4340 steel using different laser processing parameters, and then subjecting the samples to high-cycle fatigue and Knoop microindentation hardness studies. Samples of tested material from each lot were examined using scanning-electron microscopy (SEM) in order to establish the effects of laser processing on the microstructure of the fatigue-tested AISI 4340 steel. When these three techniques, microindentation hardness testing, high-cycle fatigue testing, and SEM, are combined, a mechanistic understanding of the effect of the HAZ on the fatigue behavior of this alloy might be gained. It was found that the HAZ did not appear to have an adverse effect on the high-cycle fatigue behavior of LSA-processed AISI 4340 steel

  14. Fracture Behavior in Nylon 6 Fibers. Ph.D. Thesis

    Science.gov (United States)

    Lloyd, B. A.

    1972-01-01

    Electron paramagnetic resonance (EPR) techniques are used to determine the number of free radicals produced during deformation leading to fracture of nylon 6 fibers. A reaction rate molecular model is proposed to explain some of the deformation and bond rupture behavior leading to fracture. High-strength polymer fibers are assumed to consist of a sandwich structure of disordered and ordered regions along the fiber axis. In the disordered or critical flaw regions, tie chains connecting the ordered or crystalline block regions are assumed to have a statistical distribution in length. These chains are, therefore, subjected to different stresses. The effective length distribution was determined by EPR. The probability of bond rupture was assumed to be controlled by reaction-rate theory with a stress-aided activation energy and behavior of various loadings determined by numerical techniques. The model is successfully correlated with experimental stress, strain, and bond rupture results for creep, constant rate loadings, cyclic stress, stress relaxation and step strain tests at room temperature.

  15. Research on the fracture behavior of PBX under static tension

    Directory of Open Access Journals (Sweden)

    Hu Guo

    2014-06-01

    Full Text Available The fracture behavior of polymer-bonded explosive (PBX seriously affects the safety and reliability of weapon system. The effects of interface debonding and initial meso-damage on the fracture behavior of PBX under quasi-static tension are studied using numerical method. A two-dimensional representative volume element (RVE is established based on Voronoi model in which the component contents could be regulated and the particles are randomly distributed. A nonlinear damage model of polymer matrix relative to matrix depth between particles is constructed. The results show that the simulated strain-stress relation is coincident with experiment data. It is found that interface debonding leads to the nucleation and propagation of meso-cracks, and a main crack approximately perpendicular to the loading direction is generated finally. The interface debonding tends to occur in the interface perpendicular to the loading direction. There seems to be a phenomenon that strain softening and hardening alternatively appear around peak stress of stress and strain curve. It is shown that the initial damages of intragranular and interfacial cracks both decrease the modulus and failure stress, and the main crack tends to propagate toward the initial meso-cracks.

  16. Low cycle fatigue behavior in a medium-carbon carbide-free bainitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Kang, J. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, F.C., E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Long, X.Y. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, B. [College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2016-06-01

    In the paper, different morphologies of bainite were obtained through isothermal quenching at 320 °C and 395 °C in a medium-carbon carbide-free bainitic steel. The cyclic deformation mechanism was explored by using low cycle fatigue testing. The volume fraction of retained austenite was measured by X-ray diffraction and the space partitioning of the solute atoms was constructed by three-dimensional atom probe. Results showed that the fatigue life at 320 °C was always higher than that at 395 °C under low and high total strain amplitude. The cyclic softening at the early fatigue stage increased the plastic strain of the sample which was responsible for the reduction of the fatigue life at 395 °C. Strain-induced retained austenite to martensite contributed to initial cyclic hardening, but almost having no effect on the subsequent cyclic stable/softening behaviors. The finer bainitic ferrite sheaves obtained at 320 °C changed the small fatigue crack propagation direction and delayed the crack propagation rate, which was beneficial for the fatigue properties. In addition, the substitutional atoms did not redistribute between the retained austenite and bainitic ferrite before and after cyclic deformation.

  17. Effects of environment on the low-cycle fatigue behavior of Type 304 stainless steel

    International Nuclear Information System (INIS)

    Maiya, P.S.; Burke, W.F.

    1979-12-01

    The low-cycle fatigue behavior of Type 304 stainless steel has been investigated at 593 0 C in a dynamic vacuum of better than 1.3 x 10 -6 Pa (10 -8 torr). The results concerning the effects of strain range, strain rate and tensile hold time on fatigue life are presented and compared with results of similar tests performed in air and sodium environments. Under continuous symmetrical cycling, fatigue life is significantly longer in vacuum than in air; in the low strain range regime, the effect of sodium on fatigue life appears to be similar to that of vacuum. Strain rate (or frequency) strongly influences fatigue life in both air and vacuum. In compressive hold-time tests, the effect of environment on life is similar to that in a continuous-cycling test. However, tensile hold times are nearly as damaging in vacuum as in air. Thus, at least for austenitic stainless steels, the influence of the environment of fatigue life appears to depend on the loading waveshape

  18. Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

    Science.gov (United States)

    Ren, Huai-Hui; Wang, Xi-Shu

    2014-04-01

    This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

  19. An experimental method to quantify the impact fatigue behavior of rocks

    International Nuclear Information System (INIS)

    Wu, Bangbiao; Xia, Kaiwen; Kanopoulos, Patrick; Luo, Xuedong

    2014-01-01

    Fatigue failure is an important failure mode of engineering materials. The fatigue behavior of both ductile and brittle materials has been under investigation for many years. While the fatigue failure of ductile materials is well established, only a few studies have been carried out on brittle materials. In addition, most fatigue studies on rocks are conducted under quasi-static loading conditions. To address engineering applications involving repeated blasting, this paper proposes a method to quantify the impact fatigue properties of rocks. In this method, a split Hopkinson pressure bar system is adopted to exert impact load on the sample, which is placed in a specially designed steel sleeve to limit the displacement of the sample and thus to enable the recovery of the rock after each impact. The method is then applied to Laurentian granite, which is fine-grained and isotropic material. The results demonstrate that this is a practicable means to conduct impact fatigue tests on rocks and other brittle solids. (paper)

  20. An experimental method to quantify the impact fatigue behavior of rocks

    Science.gov (United States)

    Wu, Bangbiao; Kanopoulos, Patrick; Luo, Xuedong; Xia, Kaiwen

    2014-07-01

    Fatigue failure is an important failure mode of engineering materials. The fatigue behavior of both ductile and brittle materials has been under investigation for many years. While the fatigue failure of ductile materials is well established, only a few studies have been carried out on brittle materials. In addition, most fatigue studies on rocks are conducted under quasi-static loading conditions. To address engineering applications involving repeated blasting, this paper proposes a method to quantify the impact fatigue properties of rocks. In this method, a split Hopkinson pressure bar system is adopted to exert impact load on the sample, which is placed in a specially designed steel sleeve to limit the displacement of the sample and thus to enable the recovery of the rock after each impact. The method is then applied to Laurentian granite, which is fine-grained and isotropic material. The results demonstrate that this is a practicable means to conduct impact fatigue tests on rocks and other brittle solids.

  1. Fatigued and drowsy driving: a survey of attitudes, opinions and behaviors.

    Science.gov (United States)

    Vanlaar, Ward; Simpson, Herb; Mayhew, Dan; Robertson, Robyn

    2008-01-01

    There is evidence suggesting that the problem of fatigued or drowsy driving is an important contributor to road crashes. However, not much is known about public perceptions of the issue. The purpose of this study was to obtain information on attitudes, opinions, and professed practices related to fatigued or drowsy driving. The data were gathered by means of a public opinion poll among a representative sample of 750 Ontario drivers. A majority of drivers (58.6%) admitted that they occasionally drive while fatigued or drowsy. Of greater importance, 14.5% of respondents admitted that they had fallen asleep or "nodded off" while driving during the past year. Nearly 2% were involved in a fatigue or drowsy driving related crash in the past year. Respondents were also asked about measures they take to overcome fatigue or drowsiness. Results indicate that relatively ineffective measures such as opening the window or playing music are the most popular; the most effective preventive measure--taking a rest--is the least popular. The prevalence of the behavior, coupled with the ineffective prevention measures favored by the public suggest there is a need for increasing their level of awareness and knowledge about the problem. Results from this study further emphasize the importance of increasing the fatigued and drowsy driving knowledge base and the need to educate the public about it.

  2. Effect of substructure on mechanical properties and fracture behavior of lath martensite in 0.1C–1.1Si–1.7Mn steel

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shengci [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Zhu, Guoming, E-mail: zhuguoming@ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Kang, Yonglin, E-mail: kangylin@ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China)

    2016-08-05

    The purpose of this study was to analyze the microstructure of lath martensite in 0.1C–1.1Si–1.7Mn (wt.%) steel and its effect on mechanical properties and fracture behavior. The microstructure was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron back scattering diffraction (EBSD). Charpy V-notch impact samples and compact tension (CT) samples were used to investigate the Charpy impact properties and fatigue crack growth behavior of the steel, respectively. The propagation of cleavage crack and fatigue crack were analyzed to figure out the effective grain size. The results showed that the typical hierarchical lath martensite structure contained prior austenite grains, packets, blocks and laths; packet size and block width were positively correlated to prior austenite grain size, while lath width was maintained at about 0.29 μm. Yield strength was related to prior austenite grain size, packet size and block width, and obeyed Hall–Petch relationship. Grain refinement was effective in improving the resistance to cleavage fracture by introducing barriers to crack propagation; packet boundaries and block boundaries hold similar ability to impede the propagation of crack. Paris model can well describe the FCG behavior of the investigated steel. Block width governs the effective grain size for strength, toughness and fatigue crack propagation. - Graphical abstract: Mechanical properties and fracture behavior of 0.1C–1.1Si–1.7Mn steel. - Highlights: • Hall–Petch relationship is obeyed between yield strength and martensite microstructure size. • Packet boundaries and block boundaries hold similar ability to impede the propagation of crack. • Block width is the effective grain size for strength, toughness and fatigue crack propagation.

  3. Effect of biomimetic non-smooth unit morphology on thermal fatigue behavior of H13 hot-work tool steel

    Science.gov (United States)

    Meng, Chao; Zhou, Hong; Cong, Dalong; Wang, Chuanwei; Zhang, Peng; Zhang, Zhihui; Ren, Luquan

    2012-06-01

    The thermal fatigue behavior of hot-work tool steel processed by a biomimetic coupled laser remelting process gets a remarkable improvement compared to untreated sample. The 'dowel pin effect', the 'dam effect' and the 'fence effect' of non-smooth units are the main reason of the conspicuous improvement of the thermal fatigue behavior. In order to get a further enhancement of the 'dowel pin effect', the 'dam effect' and the 'fence effect', this study investigated the effect of different unit morphologies (including 'prolate', 'U' and 'V' morphology) and the same unit morphology in different sizes on the thermal fatigue behavior of H13 hot-work tool steel. The results showed that the 'U' morphology unit had the optimum thermal fatigue behavior, then the 'V' morphology which was better than the 'prolate' morphology unit; when the unit morphology was identical, the thermal fatigue behavior of the sample with large unit sizes was better than that of the small sizes.

  4. Deformation and fatigue behavior of hot dip galvanized coatings

    International Nuclear Information System (INIS)

    Camurri, Carlos P.; Benavente, Raul G.; Roa, Isidoro S.; Carrasco, Claudia C.

    2005-01-01

    This paper reports on the results of a study of the effect of static and dynamic stresses on hot dip galvanized coatings on SAE 1020 steel substrates. Galvanizing was performed using baths maintained at 450 deg. C, the zinc containing 0.16% Ti and 0.02% Fe and with Al and Ni in the ranges 0-0.20% and 0-0.30%, respectively. Static three-point bend tests were conducted with applied stresses in the range 428-790 MPa. Dynamic bend-fatigue tests involved stresses in the range 228-578 MPa at a cyclic frequency of 0.25 Hz for up to 700 cycles. The total crack density in the coatings was measured before and after the tests using light optical and electron microscopy. The results showed that the crack density increased as the applied stress increased and crack propagation was promoted perpendicular to the substrate. The number of cycles had no effect on the crack density and propagation at stresses lower than 386 MPa. At higher stresses the number of applied cycles contributed only to crack propagation. It was concluded that the best bath composition for preventing fatigue crack propagation is one that minimized the formation of thinner brittle layers in the galvanized coatings

  5. Effect of tensile mean stress on fatigue behavior of single-crystal and directionally solidified superalloys

    Science.gov (United States)

    Kalluri, Sreeramesh; Mcgaw, Michael A.

    1990-01-01

    Two nickel base superalloys, single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf, were studied in view of the potential usage of the former and usage of the latter as blade materials for the turbomachinery of the space shuttle main engine. The baseline zero mean stress (ZMS) fatigue life (FL) behavior of these superalloys was established, and then the effect of tensile mean stress (TMS) on their FL behavior was characterized. At room temperature these superalloys have lower ductilities and higher strengths than most polycrystalline engineering alloys. The cycle stress-strain response was thus nominally elastic in most of the fatigue tests. Therefore, a stress range based FL prediction approach was used to characterize both the ZMS and TMS fatigue data. In the past, several researchers have developed methods to account for the detrimental effect of tensile mean stress on the FL for polycrystalline engineering alloys. However, the applicability of these methods to single crystal and directionally solidified superalloys has not been established. In this study, these methods were applied to characterize the TMS fatigue data of single crystal PWA 1480 and directionally solidified MAR-M 246 + Hf and were found to be unsatisfactory. Therefore, a method of accounting for the TMS effect on FL, that is based on a technique proposed by Heidmann and Manson was developed to characterize the TMS fatigue data of these superalloys. Details of this method and its relationship to the conventionally used mean stress methods in FL prediction are discussed.

  6. NLRP3 inflammasome activation mediates fatigue-like behaviors in mice via neuroinflammation.

    Science.gov (United States)

    Zhang, Ziteng; Ma, Xiujuan; Xia, Zhenna; Chen, Jikuai; Liu, Yangang; Chen, Yongchun; Zhu, Jiangbo; Li, Jinfeng; Yu, Huaiyu; Zong, Ying; Lu, Guocai

    2017-09-01

    Numerous experimental and clinical studies have suggested that the interaction between the immune system and the brain plays an important role in the pathophysiology of chronic fatigue syndrome (CFS). The NLRP3 inflammasome is an important part of the innate immune system. This complex regulates proinflammatory cytokine interleukin-1β (IL-1β) maturation, which triggers different kinds of immune-inflammatory reactions. We employed repeated forced swims to establish a model of CFS in mice. NLRP3 knockout (KO) mice were also used to explore NLRP3 inflammasome activation in the mechanisms of CFS, using the same treatment. After completing repeated swim tests, the mice displayed fatigue-like behaviors, including locomotor activity and reduced fall-off time on the rota-rod test, which was accompanied by significantly higher mature IL-1β level in the prefrontal cortex (PFC) and malondialdehyde (MDA) level in serum. We also found increased NLRP3 protein expression, NLRP3 inflammasome formation and increased mature IL-1β production in the PFC, relative to untreated mice. The NLRP3 KO mice displayed significantly moderated fatigue behaviors along with decreased PFC and serum IL-1β levels under the same treatment. These findings demonstrated the involvement of NLRP3 inflammasome activation in the mechanism of swimming-induced fatigue. Future therapies targeting the NLRP3/IL-1β pathway may have significant potential for fatigue prevention and treatment. Copyright © 2017. Published by Elsevier Ltd.

  7. Randomized Evaluation of Cognitive-Behavioral Therapy and Graded Exercise Therapy for Post-Cancer Fatigue.

    Science.gov (United States)

    Sandler, Carolina X; Goldstein, David; Horsfield, Sarah; Bennett, Barbara K; Friedlander, Michael; Bastick, Patricia A; Lewis, Craig R; Segelov, Eva; Boyle, Frances M; Chin, Melvin T M; Webber, Kate; Barry, Benjamin K; Lloyd, Andrew R

    2017-07-01

    Cancer-related fatigue is prevalent and disabling. When persistent and unexplained, it is termed post-cancer fatigue (PCF). Cognitive behavioral therapy (CBT) and graded exercise therapy (GET) may improve symptoms and functional outcomes. To evaluate the outcomes of a randomized controlled trial, which assigned patients with post-cancer fatigue to education, or 12 weeks of integrated cognitive-behavioral therapy (CBT) and graded exercise therapy (GET). Three months after treatment for breast or colon cancer, eligible patients had clinically significant fatigue, no comorbid medical or psychiatric conditions that explained the fatigue, and no evidence of recurrence. The CBT/GET arm included individually tailored consultations at approximately two weekly intervals. The education arm included a single visit with clinicians describing the principles of CBT/GET and a booklet. The primary outcome was clinically significant improvement in self-reported fatigue (Somatic and Psychological HEalth REport 0-12), designated a priori as greater than one SD of improvement in fatigue score. The secondary outcome was associated improvement in function (role limitation due to physical health problems-36-Item Short Form Health Survey 0-100) comparing baseline, end treatment (12 weeks), and follow-up (24 weeks). There were 46 patients enrolled, including 43 women (94%), with a mean age of 51 years. Fatigue severity improved in all subjects from a mean of 5.2 (±3.1) at baseline to 3.9 (±2.8) at 12 weeks, suggesting a natural history of improvement. Clinically significant improvement was observed in 7 of 22 subjects in the intervention group compared with 2 of 24 in the education group (P < 0.05, χ 2 ). These subjects also had improvement in functional status compared with nonresponders (P < 0.01, t-test). Combined CBT/GET improves fatigue and functional outcomes for a subset of patients with post-cancer fatigue. Further studies to improve the response rate and the magnitude of

  8. Childhood maltreatment and the response to cognitive behavior therapy for chronic fatigue syndrome.

    NARCIS (Netherlands)

    Heins, M.J.; Knoop, H.; Lobbestael, J.; Bleijenberg, G.

    2011-01-01

    Objective: To examine the relationship between a history of childhood maltreatment and the treatment response to cognitive behavior therapy for chronic fatigue syndrome (CFS). Methods: A cohort study in a tertiary care clinic with a referred sample of 216 adult patients meeting the Centers for

  9. Fatigue crack layer propagation in silicon-iron

    Science.gov (United States)

    Birol, Y.; Welsch, G.; Chudnovsky, A.

    1986-01-01

    Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

  10. The Effect of Material Variability on Fatigue Behaviors of Low Alloy Steels in 310 .deg. C Deoxygenated Water

    International Nuclear Information System (INIS)

    Jang, Hun; Jang, Changheui; Kim, Insup; Cho, Hyunchul

    2008-01-01

    As environmental fatigue damage is one of the main crack initiation mechanisms in nuclear power plants (NPPs), it is most important factor to assess the integrity and safety of NPPs. So, based on extensive researches, argon nation laboratory (ANL) suggested the statistical model to predict fatigue life of low alloy steels (LASs) which are widely used as structural material in NPPs. Also, we reported the environmental fatigue behaviors of SA508 Gr.1a LAS. However, from comparison between our experimental fatigue data and ANL's statistical model, our fatigue life data showed poor agreement with the ANL's statistical model. In this regard, the additional low cycle fatigue (LCF) tests were performed in 310 .deg. C deoxygenated water, and compared with ANL's statistical model to evaluate reliability of the data. And then, the effect of material variability on the fatigue life of LASs was investigated through microstructure analysis

  11. Dynamic Torsional and Cyclic Fracture Behavior of ProFile Rotary Instruments at Continuous or Reciprocating Rotation as Visualized with High-speed Digital Video Imaging.

    Science.gov (United States)

    Tokita, Daisuke; Ebihara, Arata; Miyara, Kana; Okiji, Takashi

    2017-08-01

    This study examined the dynamic fracture behavior of nickel-titanium rotary instruments in torsional or cyclic loading at continuous or reciprocating rotation by means of high-speed digital video imaging. The ProFile instruments (size 30, 0.06 taper; Dentsply Maillefer, Ballaigues, Switzerland) were categorized into 4 groups (n = 7 in each group) as follows: torsional/continuous (TC), torsional/reciprocating (TR), cyclic/continuous (CC), and cyclic/reciprocating (CR). Torsional loading was performed by rotating the instruments by holding the tip with a vise. For cyclic loading, a custom-made device with a 38° curvature was used. Dynamic fracture behavior was observed with a high-speed camera. The time to fracture was recorded, and the fractured surface was examined with scanning electron microscopy. The TC group initially exhibited necking of the file followed by the development of an initial crack line. The TR group demonstrated opening and closing of a crack according to its rotation in the cutting and noncutting directions, respectively. The CC group separated without any detectable signs of deformation. In the CR group, initial crack formation was recognized in 5 of 7 samples. The reciprocating rotation exhibited a longer time to fracture in both torsional and cyclic fatigue testing (P rotary instruments, as visualized with high-speed digital video imaging, varied between the different modes of rotation and different fatigue testing. Reciprocating rotation induced a slower crack propagation and conferred higher fatigue resistance than continuous rotation in both torsional and cyclic loads. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  12. Experimental Behavior of Fatigued Single Stiffener PRSEUS Specimens

    Science.gov (United States)

    Jegley, Dawn C.

    2009-01-01

    NASA, the Air Force Research Laboratory and The Boeing Company have worked to develop new low-cost, light-weight composite structures for aircraft. A Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept has been developed which offers advantages over traditional metallic structure. In this concept a stitched carbon-epoxy material system has been developed with the potential for reducing the weight and cost of transport aircraft structure by eliminating fasteners, thereby reducing part count and labor. By adding unidirectional carbon rods to the top of stiffeners, the panel becomes more structurally efficient. This combination produces a more damage tolerant design. This document describes the results of experimentation on PRSEUS specimens loaded in unidirectional compression in fatigue and to failure.

  13. Thermal fatigue behavior of US and Russian grades of beryllium

    International Nuclear Information System (INIS)

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

    1996-01-01

    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 degrees C for each pass of the beam. Large thermal stress in excess of the yield strength are generated due to very high spot heat flux, 250 MW/m 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-300F-H, Sr-200, I-400, extruded high purity. HIP'd sperical powder, porous beryllium (94% and 98% dense), Be/30% BeO, Be/60% BeO, and TiBe 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

  14. Experimental evaluation of the fretting fatigue behavior of high-strength steel monostrands

    DEFF Research Database (Denmark)

    Winkler, Jan; Fischer, Gregor; Georgakis, Christos T.

    2013-01-01

    In this paper, the fretting fatigue behavior of pretensioned high-strength steel monostrands is investigated. A method based on the digital image correlation (DIC) technique was used to quantify the relative movement between individual wires along the length of the monostrand. The experimental data....... Moreover, the paper provides relevant information about the monostrand bending stiffness and the extent of relative displacement between core and outer wires of the monostrand undergoing flexural deformations. The results presented herein are of special interest for the fatigue analysis of modern stay...

  15. Fatigue crack growth behavior and AE signal recognition from a composite patch repaired Ai thein plate

    International Nuclear Information System (INIS)

    Kim, Sung Jin; Kwon, Oh Yang

    2004-01-01

    The fatigue crack growth behavior of a fatigue-cracked and patch-repaired AA2024-T3 plate has been monitored. It was found that the overall crack growth rate was reduced and the crack propagation into the adjacent hole was also retarded. Signals due to crack growth after patch-repair and those due to debonding of the plate-patch interface were discriminated each other by using principal component analysis. The former showed higher center frequency and lower amplitude, whereas the latter showed longer rise time, lower frequency and higher amplitude.

  16. The cyclic fatigue behavior of a Nicalon/SiC composite

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; McHargue, C.J. [Univ. of Tennessee, Knoxville, TN (United States); Snead, L.L. [Oak Ridge National Lab., TN (United States)

    1996-10-01

    Cyclic fatigue tests were performed at ambient temperature on a Nicalon/SiC composite to study the effects of fabric orientation on the mechanical behavior. Four-point bend specimens were loaded either parallel or normal to the braided fabric plies. The maximum stresses chosen during the fatigue tests were 60, 70, and 80% of the monotonic strengths, respectively, in both orientations. Specimen failure did not occur in any case even after one million loading cycles. However, it was observed that much of the decrease in the composite modulus occurred in the first few (<10) cycles, and the fabric orientation did not significantly affect the effective modulus or midspan deflection trends.

  17. The Fracture of Plasma-Treated Polyurethane Surface under Fatigue Loading

    Directory of Open Access Journals (Sweden)

    Ilya A. Morozov

    2018-02-01

    Full Text Available Plasma treatment of soft polymers is a promising technique to improve biomedical properties of the materials. The response to the deformation of such materials is not yet clear. Soft elastic polyurethane treated with plasma immersion ion implantation is subjected to fatigue uniaxial loading. The influence of the strain amplitude and the plasma treatment regime on damage character is discussed. Surface defects are studied in unloaded and stretched states of the material. As a result of fatigue loading, transverse cracks (with closed overlapping edges as well as with open edges deeply propagating into the polymer and longitudinal folds which are break and bend inward, appear on the surface. Hard edges of cracks cut the soft polymer which is squeezed from the bulk to the surface. The observed damages are related to the high stiffness of the modified surface and its transition to the polymer substrate.

  18. The bridge crane mechanism shaft reliability calculating in case of the fatigue fracture parameters correlation

    Directory of Open Access Journals (Sweden)

    Krutitskiy M.N.

    2016-03-01

    Full Text Available The method of statistical tests examines the impact of the correlation of the parameters of fatigue-such as the durability of the shaft mechanism of an overhead traveling crane for General use is under consideration in this article. It is be-lieved that the normal and shear stresses together affect the overall durability of the shaft. There may be a correlation between endurance limits and coefficients of block similarity of loading. To calculate resource used corrected linear theory of fatigue damage accumulation. Parameters on the reliability are computed after building the function, the reli-ability function directly or through private functions the reliability function for each type of stress.

  19. Low cycle fatigue behaviors of low alloy steels in 310 .deg. C deoxygenated water

    International Nuclear Information System (INIS)

    Jang, Hun

    2008-02-01

    After low cycle fatigue tests of SA508 Gr.1a low alloy steel in 310 .deg. C deoxygenated water, the fatigue surface and the sectioned area of specimens were observed to understand the effect of the cyclic strain rate on the environmentally assisted cracking behaviors. From the fatigue crack morphologies of the specimen tested at a strain rate of 0.008 %/s, unclear ductile striations and blunt crack tip were observed. So, metal dissolution could be the main cracking mechanism of the material at the strain rate. On the other hand, on the fatigue surface of the specimen tested at strain rates of 0.04 and 0.4 %/s, the brittle cracks and the flat facets, which are the evidence of the hydrogen induced cracking, were observed. Also, the tendency of linkage between the main crack and micro-cracks was observed on the sectioned area. Therefore, the main cracking mechanism at the strain rates of 0.04 and 0.4 %/s could be the hydrogen induced cracking. Additionally, the evidence of the dissolved MnS inclusions was observed on the fatigue surface from energy dispersive x-ray spectrometer analyses. So, despite of the low sulfur content of the test material, the sulfides seem to contribute to environmentally assisted cracking of SA508 Gr.1a low alloy steel in 310 .deg. C deoxygenated water. Additionally, our experimental fatigue life data of SA508 Gr.1a low alloy steel (heat A) showed a consistent difference with statistical model produced in argon national laboratory. So, additional low cycle fatigue tests of other heat SA508 Gr.1a (heat B) and SA508 Gr.3 low alloy steels were performed to investigate the effect of material variability on fatigue behaviors of low alloy steels in 310 .deg. C deoxygenated water. In results, the fatigue lives of three low alloy steels were increased following order: SA508 Gr.1a low alloy steel - heat A, SA508 Gr.3 low alloy steel, and SA508 Gr.1a low alloy steel - heat B. From microstructure observation, the fatigue surface of SA508 Gr.1a low alloy

  20. Fatigue-type stress fractures of the lower limb associated with fibrous cortical defects/non-ossifying fibromas in the skeletally immature

    Energy Technology Data Exchange (ETDEWEB)

    Shimal, A.; Davies, A.M. [Department of Radiology, Royal Orthopaedic Hospital, Birmingham B31 2AP (United Kingdom); James, S.L.J., E-mail: steven.james@roh.nhs.u [Department of Radiology, Royal Orthopaedic Hospital, Birmingham B31 2AP (United Kingdom); Grimer, R.J. [Department of Orthopaedic Oncology, Royal Orthopaedic Hospital, Birmingham B31 2AP (United Kingdom)

    2010-05-15

    Aim: To investigate the association of a fatigue-type stress fracture and a fibrous cortical defect/non-ossifying fibroma (FCD/NOF) of the lower limb long bones in skeletally immature patients. Materials and methods: The patient database of a specialist orthopaedic oncology centre was searched to determine the number of skeletally immature patients (<=16 years of age) over an 18 year period with a lower limb long bone lesion ultimately shown to be a fatigue-type stress fracture. The diagnosis was established by a combination of typical imaging findings of a fatigue-type stress fracture, the absence of aggressive features suggestive of a sarcoma (e.g., interrupted periosteal reaction, cortical breach, and a soft-tissue mass) together with evidence of consolidation or healing on follow-up radiographs and resolution of symptoms over the subsequent weeks. The database was also used to determine the number of skeletally immature cases (<=16 years of age) referred in the same period in which the principal lesion was shown to be a fibrous cortical defect (FCD) or non-ossifying fibroma (NOF) of the lower limb long bones. The clinical and imaging features of those cases common to both groups (i.e., with both a fatigue-type stress fracture and a FCD or NOF) were reviewed. Results: Six percent of patients (five cases) referred to an orthopaedic oncology unit, who were subsequently shown to have a stress fracture of the lower limb long bones, were found to have a related FCD/NOF. All had been referred with a suggested diagnosis of a bone sarcoma and/or osteomyelitis. The possibility of a stress fracture had been raised in only one case. Four cases involved the proximal tibia and one the distal femur. Radiographs revealed that both lesions arose in the posteromedial cortex in all but one of the cases. The radiographs and magnetic resonance imaging (MRI) features were considered typical of the overlapping pathological features of the lesions. Conclusions: A sarcoma could be

  1. Fatigue-type stress fractures of the lower limb associated with fibrous cortical defects/non-ossifying fibromas in the skeletally immature.

    Science.gov (United States)

    Shimal, A; Davies, A M; James, S L J; Grimer, R J

    2010-05-01

    To investigate the association of a fatigue-type stress fracture and a fibrous cortical defect/non-ossifying fibroma (FCD/NOF) of the lower limb long bones in skeletally immature patients. The patient database of a specialist orthopaedic oncology centre was searched to determine the number of skeletally immature patients (lower limb long bone lesion ultimately shown to be a fatigue-type stress fracture. The diagnosis was established by a combination of typical imaging findings of a fatigue-type stress fracture, the absence of aggressive features suggestive of a sarcoma (e.g., interrupted periosteal reaction, cortical breach, and a soft-tissue mass) together with evidence of consolidation or healing on follow-up radiographs and resolution of symptoms over the subsequent weeks. The database was also used to determine the number of skeletally immature cases (lower limb long bones. The clinical and imaging features of those cases common to both groups (i.e., with both a fatigue-type stress fracture and a FCD or NOF) were reviewed. Six percent of patients (five cases) referred to an orthopaedic oncology unit, who were subsequently shown to have a stress fracture of the lower limb long bones, were found to have a related FCD/NOF. All had been referred with a suggested diagnosis of a bone sarcoma and/or osteomyelitis. The possibility of a stress fracture had been raised in only one case. Four cases involved the proximal tibia and one the distal femur. Radiographs revealed that both lesions arose in the posteromedial cortex in all but one of the cases. The radiographs and magnetic resonance imaging (MRI) features were considered typical of the overlapping pathological features of the lesions. A sarcoma could be effectively excluded in the absence of true cortical destruction and soft-tissue extension. Both fatigue-type stress fractures and FCD/NOFs occur at similar sites in the long bones. It is postulated that the existence of the latter may cause localized weakening of

  2. Fatigue-type stress fractures of the lower limb associated with fibrous cortical defects/non-ossifying fibromas in the skeletally immature

    International Nuclear Information System (INIS)

    Shimal, A.; Davies, A.M.; James, S.L.J.; Grimer, R.J.

    2010-01-01

    Aim: To investigate the association of a fatigue-type stress fracture and a fibrous cortical defect/non-ossifying fibroma (FCD/NOF) of the lower limb long bones in skeletally immature patients. Materials and methods: The patient database of a specialist orthopaedic oncology centre was searched to determine the number of skeletally immature patients (≤16 years of age) over an 18 year period with a lower limb long bone lesion ultimately shown to be a fatigue-type stress fracture. The diagnosis was established by a combination of typical imaging findings of a fatigue-type stress fracture, the absence of aggressive features suggestive of a sarcoma (e.g., interrupted periosteal reaction, cortical breach, and a soft-tissue mass) together with evidence of consolidation or healing on follow-up radiographs and resolution of symptoms over the subsequent weeks. The database was also used to determine the number of skeletally immature cases (≤16 years of age) referred in the same period in which the principal lesion was shown to be a fibrous cortical defect (FCD) or non-ossifying fibroma (NOF) of the lower limb long bones. The clinical and imaging features of those cases common to both groups (i.e., with both a fatigue-type stress fracture and a FCD or NOF) were reviewed. Results: Six percent of patients (five cases) referred to an orthopaedic oncology unit, who were subsequently shown to have a stress fracture of the lower limb long bones, were found to have a related FCD/NOF. All had been referred with a suggested diagnosis of a bone sarcoma and/or osteomyelitis. The possibility of a stress fracture had been raised in only one case. Four cases involved the proximal tibia and one the distal femur. Radiographs revealed that both lesions arose in the posteromedial cortex in all but one of the cases. The radiographs and magnetic resonance imaging (MRI) features were considered typical of the overlapping pathological features of the lesions. Conclusions: A sarcoma could be

  3. Strain rate effects on fracture behavior of Austempered Ductile Irons

    Science.gov (United States)

    Ruggiero, Andrew; Bonora, Nicola; Gentile, Domenico; Iannitti, Gianluca; Testa, Gabriel; Hörnqvist Colliander, Magnus; Masaggia, Stefano; Vettore, Federico

    2017-06-01

    Austempered Ductile Irons (ADIs), combining high strength, good ductility and low density, are candidates to be a suitable alternative to high-strength steels. Nevertheless, the concern about a low ductility under dynamic loads often leads designers to exclude cast irons for structural applications. However, results from dynamic tensile tests contradict this perception showing larger failure strain with respect to quasistatic data. The fracture behaviour of ADIs depends on damage mechanisms occurring in the spheroids of graphite, in the matrix and at their interface, with the matrix (ausferrite) consisting of acicular ferrite in carbon-enriched austenite. Here, a detailed microstructural analysis was performed on the ADI 1050-6 deformed under different conditions of strain rates, temperatures, and states of stress. Beside the smooth specimens used for uniaxial tensile tests, round notched bars to evaluate the ductility reduction with increasing stress triaxiality and tophat geometries to evaluate the propensity to shear localization and the associated microstructural alterations were tested. The aim of the work is to link the mechanical and fracture behavior of ADIs to the load condition through the microstructural modifications that occur for the corresponding deformation path.

  4. The effect of ion implantation on the fatigue behavior of metals and alloys

    International Nuclear Information System (INIS)

    Chakrabortty, S.B.; Kujore, A.; Legg, K.O.; Starke, E.A.

    1981-01-01

    The effect of ion implantation on the strain and stress controlled fatigue behavior of polycrystalline copper has been investigated. The cyclic stress-strain response, strain-life and stress-life relationships and fatigue crack nucleation behavior have been studied. The results from the non-implanted materials have been compared with those from the implanted materials. Four implant species, one with a positive misfit, one with a negative misfit, one with a zero misfit, and one insoluble under equilibrium conditions have been used. Most of the fatigue tests were performed in laboratory air. Ion implantation changes the surface deformation behavior for both monotonic and cyclic loading with a corresponding change in hardening rate. Larger changes are observed for the cyclic loading. Implantations which lead to a more homogeneous deformation (fine slip) near the surface, improves the resistance to fatigue crack initiation. Surface compressive residual stresses, induced from implanting a positive misfit species, have a major influence on crack initiation in the stress-life regime

  5. Protective effects of antidepressants against chronic fatigue syndrome-induced behavioral changes and biochemical alterations.

    Science.gov (United States)

    Kumar, Anil; Garg, Ruchika

    2009-02-01

    Chronic fatigue syndrome (CFS) is characterized by profound fatigue, which substantially interferes with daily activities. The aim of this study was to explore the protective effects of antidepressants in an animal model of CFS in mice. Male albino mice were forced to swim individually for a period of 6-min session each for 7 days. Imipramine (10 and 20 mg/kg), desipramine (10 and 20 mg/kg) and citalopram (5 and 10 mg/kg) were administered 30 min before forced swimming test on each day. Various behavior tests (immobility time, locomotor activity, anxiety-like behavior by plus maze and mirror chamber) followed by biochemical parameters (lipid peroxidation, reduced glutathione, catalase and nitrite level) were assessed in chronic stressed mice. Chronic forced swimming for 7 days significantly caused increase in immobility period, impairment in locomotor activity, anxiety-like behavior, and oxidative stress (raised lipid peroxidation, nitrite activity and reduced glutathione and catalase activity) as compared with naïve mice (P immobility time, improved locomotor activity and anti-anxiety effect (in both plus maze and mirror chamber test), and attenuated oxidative stress in chronic stressed mice as compared with control (chronic fatigues) (P < 0.05). These results suggested that these drugs have protective effect and could be used in the management of chronic fatigue like conditions.

  6. Tensile and high cycle fatigue behaviors of high-Mn steels at 298 and 110 K

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Wongyu; Jeong, Daeho; Sung, Hyokyung; Kim, Sangshik, E-mail: sang@gnu.ac.kr

    2017-02-15

    Tensile and high cycle fatigue behaviors of high-Mn austenitic steels, including 25Mn, 25Mn0.2Al, 25Mn0.5Cu, 24Mn4Cr, 22Mn3Cr and 16Mn2Al specimens, were investigated at 298 and 110 K. Depending on the alloying elements, tensile ductility of high-Mn steels either increased or decreased with decreasing temperature from 298 to 110 K. Reasonable correlation between the tendency for martensitic tranformation, the critical twinning stress and the percent change in tensile elongation suggested that tensile deformation of high-Mn steels was strongly influenced by SFE determining TRIP and TWIP effects. Tensile strength was the most important parameter in determining the resistance to high cycle fatigue of high-Mn steels with an exceptional work hardening capability at room and cryogenic temperatures. The fatigue crack nucleation mechanism in high-Mn steels did not vary with decreasing tempertature, except Cr-added specimens with grain boundary cracking at 298 K and slip band cracking at 110 K. The EBSD (electron backscatter diffraction) analyses suggested that the deformation mechanism under fatigue loading was significantly different from tensile deformation which could be affected by TRIP and TWIP effects. - Highlights: •The resistances to HCF of various high-Mn steels were measured. •The variables affecting tensile and HCF behaviors of high-Mn steels were assessed. •The relationship between tensile and the HCF behaviors of high-Mn steels was established.

  7. Effect of oxide film formation on the fatigue behavior of aluminum alloy

    International Nuclear Information System (INIS)

    Kim, Jong Cheon; Cheong, Seong Kyun

    2012-01-01

    In this study, the effects of surface oxide film formation on the fatigue behavior of 7075-T6 aluminum alloy were analyzed in terms of the corrosion time of the alloy. The aluminum material used is known to have high corrosion resistance due to the passivation phenomenon that prevents corrosion. Aluminum alloys have been widely used in various industrial applications such as aircraft component manufacturing because of their lighter weight and higher strength than other materials. Therefore, studies on the fatigue behavior of materials and passivation properties that prevent corrosion are required. The fatigue behavior in terms of the corrosion time was analyzed by using a four pointing bending machine, and the surface corrosion level of the aluminum material in terms of the corrosion time was estimated by measuring the surface were studied by scanning electron microscopy (SEM). The results indicated that corrosion actively progressed for four weeks during the initial corrosion phase, the fatigue life significantly decreased, and the surface roughness increased. However, after four weeks, the corrosion reaction tended to slow down due to the passivation phenomenon of the material. Therefore, on the basis of SEM analysis results, it was concluded that the growth of the surface oxide film was reduced after four weeks and then the oxide film on the material surface served as a protection layer and prevented further corrosion

  8. Consideration of the environmental effects on fatigue behavior of austenitic components. Calculation methods and practical application

    International Nuclear Information System (INIS)

    Seichter, Johannes; Reese, Sven H.; Klucke, Dietmar

    2012-01-01

    During the last years environmental effects on the fatigue behavior of nuclear power plant components has worldwide been discussed controversial with respect to the transferability of laboratory data on real components. A publication from Argonne National Laboratory on experimental results concerning environmental effects (air and LWR coolant) on fatigue of austenitic steels included a proposal on calculation methods concerning the lifetime reduction due to environmental effects. This calculation method, i.e. multiplication of the usage factor by a F(en), has been included into the ASME Code, Section III, Division I, as Code Case N-792 (fatigue evaluations including environmental effects). The presented contribution evaluates the practical application of this calculation procedure and demonstrates the determination of the usage factor of an austenitic component under environmental exposure.

  9. Influence of De-icers on the Corrosion and Fatigue Behavior of 4140 Steel

    Science.gov (United States)

    Dean, William P.; Sanford, Brittain J.; Wright, Matthew R.; Evans, Jeffrey L.

    2012-11-01

    The purpose of this test was to evaluate the effects of calcium magnesium acetate (CMA) and sodium chloride (NaCl)—two common substances used to de-ice roadways—on the corrosion and fatigue behavior of annealed AISI 4140 steel. When CMA-corroded, NaCl-corroded, and as-machined samples were tested using R = 0.1, and f = 20 Hz, it was found that, within the scope of this study, samples corroded in both 3.5% CMA solution and 3.5% NaCl solution exhibited a lower fatigue strength than samples tested in the as-machined, uncorroded condition. For the short lives tested in this study, the difference in the effects of CMA and NaCl is minimal. However, at longer lives it is suspected, based on the trends, that the CMA solution would be less detrimental to the fatigue life.

  10. An investigation of the mechanical and hydrologic behavior of tuff fractures under saturated conditions

    International Nuclear Information System (INIS)

    Voss, C.F.; Shotwell, L.R.

    1990-04-01

    The mechanical and hydrologic behavior of natural fractures in a partially welded tuff rock were investigated. Tuff cores, each containing part of the same natural fracture oriented subparallel to the core axis, were subjected a range of stress and hydraulic gradients while simultaneously monitoring changes in the fracture aperture and volumetric flow rate. The fractures were tested in three configurations: intact, mated, and offset. Fracture deformation was nonlinear over the stress range tested with permanent deformation and hysteresis occurring with each loading cycle. The offset samples had larger permanent deformation and significantly reduced normal stiffness at lower stress levels. The cubic flow law appears to be valid for the relatively undisturbed tuff fractures at the scale tested. The cubic law did not explain the observed hydraulic behavior of the offset fractures. 6 refs., 10 figs., 2 tabs

  11. The effect of multiaxial stress state on creep behavior and fracture mechanism of P92 steel

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Yuan; Xu, Hong, E-mail: xuhong@ncepu.edu.cn; Ni, Yongzhong; Lan, Xiang; Li, Hongyuan

    2015-06-11

    The creep experiments on plain and double U-typed notched specimens were conducted on P92 steel at 650 °C. The notch strengthening effect was found in the notched specimens. Fracture appearance observed by scanning electron microscopy revealed that dimpled fracture for relatively blunt notched specimen, and dimpled fracture doubled with intergranular brittle fracture for relatively sharp notched specimen, which meant that fracture mechanism of P92 steel altered due to the presence of the notch. Meanwhile, based on Norton–Bailey and Kachanov–Robotnov constitutive models, a modified model was proposed. Finite element simulations were carried out to investigate the effect of multiaxial stress state on the creep behavior, fracture mechanism and damage evolvement of P92 steel. The simulation results agreed well with the fracture behaviors observed experimentally.

  12. Spot weld arrangement effects on the fatigue behavior of multi-spot welded joints

    International Nuclear Information System (INIS)

    Hassanifard, Soran; Zehsaz, Mohammad; Esmaeili, Firooz

    2011-01-01

    In the present study, the effects of spot weld arrangements in multi-spot welded joints on the fatigue behavior of the joints are studied. Three different four-spot welded joints are considered: one-row four-spot parallel to the loading direction, one-row four-spot perpendicular to the loading direction and two-row four-spot weld specimens. The experimental fatigue test results reveal that the differences between the fatigue lives of three spot welded types in the low cycle regime are more considerable than those in the high cycle regime. However, all kinds of spot weld specimens have similar fatigue strength when approaching a million cycles. A non-linear finite element analysis is performed to obtain the relative stress gradients, effective distances and notch strength reduction factors based on the volumetric approach. The work here shows that the volumetric approach does a very good job in predicting the fatigue life of the multi-spot welded joints

  13. Fatigue life assessment based on crack growth behavior in reduced activation ferritic/martensitic steel

    International Nuclear Information System (INIS)

    Nogami, Shuhei; Sato, Yuki; Hasegawa, Akira

    2010-01-01

    Crack growth behavior under low cycle fatigue in reduced activation ferritic/martensitic steel, F82H IEA-heat (Fe-8Cr-2W-0.2V-0.02Ta), was investigated to improve the fatigue life assessment method of fusion reactor structural material. Low cycle fatigue test was carried out at room temperature in air at a total strain range of 0.4-1.5% using an hourglass-type miniature fatigue specimen. The relationship between the surface crack length and life fraction was described using one equation independent of the total strain range. Therefore, the fatigue life and residual life could be estimated using the surface crack length. Moreover, the microcrack initiation life could be estimated using the total strain range if there was a one-to-one correspondence between the total strain range and number of cycles to failure. The crack growth rate could be estimated using the total strain range and surface crack length by introducing the concept of the normalized crack growth rate. (author)

  14. "Well, I'm tired of tryin'!" Organizational citizenship behavior and citizenship fatigue.

    Science.gov (United States)

    Bolino, Mark C; Hsiung, Hsin-Hua; Harvey, Jaron; LePine, Jeffery A

    2015-01-01

    This study seeks to identify workplace conditions that influence the degree to which employees feel worn out, tired, or on edge attributed to engaging in organizational citizenship behavior (OCB) and also how this phenomenon, which we refer to as citizenship fatigue, is associated with future occurrences of OCB. Using data collected from 273 employees and their peers at multiple points in time, we found that the relationship between OCB and citizenship fatigue depends on levels of perceived organizational support, quality of team-member exchange relationships, and pressure to engage in OCB. Specifically, the relationship between OCB and citizenship fatigue is significantly stronger and positive when perceived organizational support is low, and it is significantly stronger and negative when the quality of team-member exchange is high and pressure to engage in OCB is low. Our results also indicate that citizenship fatigue is negatively related to subsequent acts of OCB. Finally, supplemental analyses reveal that the relationship between OCB and citizenship fatigue may vary as a function of the specific facet of OCB. We conclude with a discussion of the key theoretical and practical implications of our findings. (c) 2015 APA, all rights reserved.

  15. High temperature mechanical properties and surface fatigue behavior improving of steel alloy via laser shock peening

    International Nuclear Information System (INIS)

    Ren, N.F.; Yang, H.M.; Yuan, S.Q.; Wang, Y.; Tang, S.X.; Zheng, L.M.; Ren, X.D.; Dai, F.Z.

    2014-01-01

    Highlights: • The properties of 00C r 12 were improved by laser shock processing. • A deep layer of residual compressive stresses was introduced. • Fatigue life was enhanced about 58% at elevated temperature up to 600 °C. • The pinning effect is the reason of prolonging fatigue life at high temperature. - Abstract: Laser shock peening was carried out to reveal the effects on ASTM: 410L 00C r 12 microstructures and fatigue resistance in the temperature range 25–600 °C. The new conception of pinning effect was proposed to explain the improvements at the high temperature. Residual stress was measured by X-ray diffraction with sin 2 ψ method, a high temperature extensometer was utilized to measure the strain and control the strain signal. The grain and precipitated phase evolutionary process were observed by scanning electron microscopy. These results show that a deep layer of compressive residual stress is developed by laser shock peening, and ultimately the isothermal stress-controlled fatigue behavior is enhanced significantly. The formation of high density dislocation structure and the pinning effect at the high temperature, which induces a stronger surface, lower residual stress relaxation and more stable dislocation arrangement. The results have profound guiding significance for fatigue strengthening mechanism of components at the elevated temperature

  16. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    alloys (2). [--I Fig. 6. Fatigue fracture in Nitrile- butadien rubber ( NBR ). Fig. 7. The characteristic features of fatigue fracture in press moulded...in plastics and even in rubber . It follows therefore, that fatigue fractures must also occur in the mineral layers of our earth or in the rock on...effective until the weakest point yields and forms a crack. To get a feeling for this process, you can imagine that the stressed article is made of rubber

  17. Two different mechanisms of fatigue damage due to cyclic stress loading at 77 K for MOCVD-YBCO-coated conductors

    International Nuclear Information System (INIS)

    Sugano, M; Yoshida, Y; Hojo, M; Shikimachi, K; Hirano, N; Nagaya, S

    2008-01-01

    Tensile fatigue tests were carried out at 77 K for YBCO-coated conductors fabricated by metal-organic chemical vapor deposition (MOCVD). The S-N relationship, variation of critical current (I c ) during cyclic loading and microscopic fatigue damage were investigated. Fatigue strength at 10 6 cycles was evaluated to be σ max = 1300 MPa and 890 MPa under the stress ratios of 0.5 and 0.1. Two different mechanisms of fatigue damage, depending on the number of stress cycles to failure, were observed. In one of the fracture mechanisms, fatigue behavior is characterized by overall fracture which occurs at 10 4 -10 5 cycles. For these specimens, I c after unloading does not degrade before overall fracture. Although only shallow slip bands were found at the Ag surface, fatigue cracks were found on the Hastelloy C-276 surface of the fractured specimen. These results suggest that overall fracture due to cyclic stress was caused by fatigue of the Hastelloy substrate. In the other fracture mechanism, even though overall fracture did not occur at 10 6 cycles, a slight decrease of I c was detected after 10 5 cycles. No fatigue crack was found on the Hastelloy surface, while deep slip bands corresponding to the initial stage of fatigue crack were observed on the Ag surface. From these results, we concluded that I c degradation at a high cycle number is attributed to the fatigue of the Ag stabilizing layer

  18. Mechanical behavior and fatigue performance of SMA short fiber reinforced MMC

    Science.gov (United States)

    Al-Matar, Basem Jawad

    The mechanical behavior and performance of Shape Memory Alloy (SMA) short fiber NiTi reinforced Al was experimentally investigated for monotonic and fatigue test Al 6061 NiTi-SiC T6 was superior to unreinforced materials as well as to the reinforced Al T4. Taya three-dimensional model was performed on the monotonic tensile test at room temperature. It showed good agreement with experimental results. In order to utilize the compressive criterion for SMA, the NiTi reinforced Al composite was cooled at -10°C and prestrained at 1.2%. Beyond this limit composite suffered from damage. The net enhancement of SMA effect was around 10 MPa on composite yield stress. Results showed that the elastic constant for the composite did not change with loading and unloading suggesting that the inelastic behavior is plasticity. Further investigation on the inelastic behavior model as damage and/or plasticity by evaluating Poisson's ratio during loading was carried out by Adaptive Image Correlation Technique for Full-Field Strain Measurement. Poisson's ratio increased from around 0.33 to 0.5 demonstrating that it is plasticity that is responsible for the inelastic behavior. Scanning electron microscopy was also used and confirmed model results. The overall damage-behavior was quantified in terms of the post fatigue failure strength for low-cycle fatigue tests. Power law model was best to fit experimental findings.

  19. Prediction of inelastic behavior and creep-fatigue life of perforated plates

    International Nuclear Information System (INIS)

    Igari, Toshihide; Yamauchi, Masafumi; Nomura, Shinichi.

    1992-01-01

    Prediction methods of macroscopic and local stress-strain behaviors of perforated plates in plastic and creep regime are proposed in this paper, and are applied to the creep-fatigue life prediction of perforated plates. Both equivalent-solid-plate properties corresponding to the macroscopic behavior and the stress-strain concentration around a hole were obtained by assuming the analogy between plasticity and creep and also by extending the authors' proposal in creep condition. The perforated plates which were made of Hastelloy XR were subjected to the strain-controlled cyclic test at 950degC in air in order to experimentally obtain the macroscopic behavior such as the cyclic stress-strain curve and creep-fatigue life around a hole. The results obtained are summarized as follows. (1) The macroscopic behavior of perforated plates including cyclic stress-strain behavior and relaxation is predictable by using the proposed method in this paper. (2) The creep-fatigue life around a hole can be predicted by using the proposed method for stress-strain concentration around a hole. (author)

  20. Fatigue crack growth behavior and tearing instability characteristics under cyclic high stress, 2

    International Nuclear Information System (INIS)

    Mogami, Kazunari; Yamakawa, Jun; Ando, Kotoji; Ogura, Nobukazu

    1990-01-01

    The J-R curve, fatigue crack growth rate and characteristics of ductile unstable fracture under monotonic and cyclic load were investigated using 1TCT test specimens which were cut out from A508 steel for reactor pressure vessels. All the tests were carried out at 100degc. The main results obtained were as follows. (1) The J-R curve under the cyclic load is not a material constant but is dependent on the test conditions. (2) da/dN from typical fatigue data cannot be extrapolated by ΔJ only if the value of da/dN is above 5x10 -4 mm/cycles. However, it can be extrapolated by using the following equation in which J max is used: da/dN=C{√(ΔJ)/(B-√J max )} m . (3) The J values at instability obtained from the ductile unstable fracture test carried out under the cyclic load of stress ratio R=0, 01 and -1.0 were compared with those from the monotonically increasing load. These J values at instability were almost the same as that for the monotonically increasing load. (author)

  1. Ibuprofen Ameliorates Fatigue- and Depressive-like Behavior in Tumor-bearing Mice

    Science.gov (United States)

    Norden, Diana M.; McCarthy, Donna O.; Bicer, Sabahattin; Devine, Raymond; Reiser, Peter J.; Godbout, Jonathan P.; Wold, Loren E.

    2015-01-01

    Aims Cancer-related fatigue (CRF) is often accompanied by depressed mood, both of which reduce functional status and quality of life. Research suggests that increased expression of pro-inflammatory cytokines are associated with skeletal muscle wasting and depressive- and fatigue- like behaviors in rodents and cancer patients. We have previously shown that treatment with ibuprofen, a nonsteroidal anti-inflammatory drug, preserved muscle mass in tumor-bearing mice. Therefore, the purpose of the present study was to determine the behavioral effects of ibuprofen in a mouse model of CRF. Main Methods Mice were injected with colon-26 adenocarcinoma cells and treated with ibuprofen (10mg/kg) in the drinking water. Depressive-like behavior was determined using the forced swim test (FST). Fatigue-like behaviors were determined using voluntary wheel running activity (VWRA) and grip strength. The hippocampus, gastrocnemius muscle, and serum were collected for cytokine analysis. Key Findings Tumor-bearing mice showed depressive-like behavior in the FST, which was not observed in mice treated with ibuprofen. VWRA and grip strength declined in tumor-bearing mice, and ibuprofen attenuated this decline. Tumor-bearing mice had decreased gastrocnemius muscle mass and increased expression of IL-6, MAFBx and MuRF mRNA, biomarkers of protein degradation, in the muscle. Expression of IL-1β and IL-6 was also increased in the hippocampus. Treatment with ibuprofen improved muscle mass and reduced cytokine expression in both the muscle and hippocampus of tumor-bearing mice. Significance Ibuprofen treatment reduced skeletal muscle wasting, inflammation in the brain, and fatigue- and depressive-like behavior in tumor-bearing mice. Therefore, ibuprofen warrants evaluation as an adjuvant treatment for CRF. PMID:26498217

  2. Effects of microstructures on low cycle fatigue behavior in Al-Si-Mg cast alloys

    International Nuclear Information System (INIS)

    Han, Sang Won; Kim, Sug Won

    2002-01-01

    Low cycle fatigue tests were carried out using four kinds of Al-7%Si-0.4Mg cast alloys, i.e., two kinds of sand mold casts, permanent mold cast and semi-solid die cast. They were heat-treated in the condition of under aging and over aging to investigate effects of precipitates on fatigue. All tests were conducted under axial plastic strain amplitude control. Stress level of cyclic hardening curves increased sensitively with needle like eutectic Si particle, refine grain size and dendrite arm spacing (DAS). In particular, the refined grain structure of under aged matrix was more effective encourager for cyclic hardening compared with DAS and eutectic Si particle size. After rapid increase in cyclic hardening during several number of cycles, the stress amplitude kept increasing steadily until fracture in under aged alloys strengthened by shearable G.P. zone. On the other hand, over aged alloys strengthened by non-shearable β ' precipitates generated more drastic initial hardening and the stress amplitude reached the saturation state in quite early stage of the fatigue

  3. The Effects of Cognitive Behavioral Therapy for Postcancer Fatigue on Perceived Cognitive Disabilities and Neuropsychological Test Performance

    NARCIS (Netherlands)

    Goedendorp, Martine M.; Knoop, Hans; Gielissen, Marieke F. M.; Verhagen, Constans A. H. H. V. M.; Bleijenberg, Gijs

    Context. After successful cancer treatment, a substantial number of survivors continue to experience fatigue and related concentration and memory problems. Severe fatigue after cancer treatment can be treated effectively with cognitive behavioral therapy (CBT), but it is unclear whether CBT has an

  4. Influence of dwell times on the thermomechanical fatigue behavior of a directionally solidified Ni-base superalloy

    Czech Academy of Sciences Publication Activity Database

    Guth, S.; Petráš, Roman; Škorík, Viktor; Kruml, Tomáš; Man, Jiří; Lang, K. H.; Polák, Jaroslav

    2015-01-01

    Roč. 80, NOV (2015), s. 426-433 ISSN 0142-1123 R&D Projects: GA MŠk(CZ) EE2.3.30.0063 Institutional support: RVO:68081723 Keywords : Nickel base superalloy * Thermomechanical fatigue * Dwell time * Lifetime behavior * Damage mechanisms Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.162, year: 2015

  5. Low-cyclic fatigue behavior of modified 9Cr–1Mo steel at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Guguloth, Krishna; Sivaprasad, S. [CSIR-National Metallurgical laboratory, Material Science and Technology Division, Jamshedpur 831007 (India); Chakrabarti, D. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur 721302 (India); Tarafder, S. [CSIR-National Metallurgical laboratory, Material Science and Technology Division, Jamshedpur 831007 (India)

    2014-05-01

    The low-cycle fatigue behavior of indigenously developed modified 9Cr–1Mo steel has been evaluated using a constant strain rate (1×10{sup −3} s{sup −1}) at ambient temperature (25 °C) and at elevated temperatures (500–600 °C) over the strain amplitudes varying between ±0.7% and ±1.2%. Cyclic stress response showed a gradual softening regime that ended in a stress plateau until complete failure of the specimens. The estimated fatigue life decreased with the increase in test temperature. The effect of temperature on fatigue life was more pronounced at lower strain amplitudes. The cyclic deformation behavior at different temperatures has been analyzed from hysteresis loop and also in view of the changes taking place in dislocation structure and dislocation–precipitation interaction. Evaluation of low-cycle fatigue properties of modified 9Cr–1Mo steel over a range of test temperature can help in designing components for in-core applications in fast breeder reactors and in super heaters for nuclear power plants.

  6. The Study on Environmental Fatigue Behavior of Low Alloy Steel and Stainless Steel Pipes Using the Simplified Plant Transients

    International Nuclear Information System (INIS)

    Yoo, One; Song, M. S.; Kim, I. Y.; Park, S. H.; Lee, B. S.

    2010-01-01

    Nuclear components categorized as ASME Code Class 1 shall be evaluated for the fatigue and satisfy the fatigue acceptance criteria, CUF(cumulative usage factor) < 1 in accordance with ASME Code. However, recent studies have shown the fatigue evaluation procedure may not give conservative results when the components operate in the water environment. NRC issued Regulatory Guide 1.207 which enforces the new fatigue evaluation method or Fen(environmental fatigue correction factor) method to nuclear plants to be newly constructed. This paper describes the characteristics of the behavior of low alloy and austenitic stainless steel straight pipe related to environmental fatigue, which are obtained by using the method suggested by Regulatory Guide 1.207 and simplified plant transients

  7. Fracture Behavior and Properties of Functionally Graded Fiber-Reinforced Concrete

    International Nuclear Information System (INIS)

    Roesler, Jeffery; Bordelon, Amanda; Gaedicke, Cristian; Park, Kyoungsoo; Paulino, Glaucio

    2008-01-01

    In concrete pavements, a single concrete mixture design is selected to resist mechanical loading without attempting to adversely affect the concrete pavement shrinkage, ride quality, or noise attenuation. An alternative approach is to design distinct layers within the concrete pavement surface which have specific functions thus achieving higher performance at a lower cost. The objective of this research was to address the structural benefits of functionally graded concrete materials (FGCM) for rigid pavements by testing and modeling the fracture behavior of different combinations of layered plain and synthetic fiber-reinforced concrete materials. Fracture parameters and the post-peak softening behavior were obtained for each FGCM beam configuration by the three point bending beam test. The peak loads and initial fracture energy between the plain, fiber-reinforced, and FGCM signified similar crack initiation. The total fracture energy indicated improvements in fracture behavior of FGCM relative to full-depth plain concrete. The fracture behavior of FGCM depended on the position of the fiber-reinforced layer relative to the starter notch. The fracture parameters of both fiber-reinforced and plain concrete were embedded into a finite element-based cohesive zone model. The model successfully captured the experimental behavior of the FGCMs and predicted the fracture behavior of proposed FGCM configurations and structures. This integrated approach (testing and modeling) demonstrates the viability of FGCM for designing layered concrete pavements system

  8. Development, Characterization and Piezoelectric Fatigue Behavior of Lead-Free Perovskite Piezoelectric Ceramics

    Science.gov (United States)

    Patterson, Eric Andrew

    Much recent research has focused on the development lead-free perovskite piezoelectrics as environmentally compatible alternatives to lead zirconate titanate (PZT). Two main categories of lead free perovskite piezoelectric ceramic systems were investigated as potential replacements to lead zirconate titanate (PZT) for actuator devices. First, solid solutions based on Li, Ta, and Sb modified (K0.5Na0.5)NbO3 (KNN) lead-free perovskite systems were created using standard solid state methods. Secondly, Bi-based materials a variety of compositions were explored for (1-x)(Bi 0.5Na0.5)TiO3-xBi(Zn0.5Ti0.5)O 3 (BNT-BZT) and Bi(Zn0.5Ti0.5)O3-(Bi 0.5K0.5)TiO3-(Bi0.5Na0.5)TiO 3 (BZT-BKT-BNT). It was shown that when BNT-BKT is combined with increasing concentrations of Bi(Zn1/2i1/2)O3 (BZT), a transition from normal ferroelectric behavior to a material with large electric field induced strains was observed. The higher BZT containing compositions are characterized by large hysteretic strains(> 0.3%) with no negative strains that might indicate domain switching. This work summarizes and analyzes the fatigue behavior of the new generation of Pb-free piezoelectric materials. In piezoelectric materials, fatigue is observed as a degradation in the electromechanical properties under the application of a bipolar or unipolar cyclic electrical load. In Pb-based materials such as lead zirconate titanate (PZT), fatigue has been studied in great depth for both bulk and thin film applications. In PZT, fatigue can result from microcracking or electrode effects (especially in thin films). Ultimately, however, it is electronic and ionic point defects that are the most influential mechanism. Therefore, this work also analyzes the fatigue characteristics of bulk polycrystalline ceramics of the modified-KNN and BNT-BKT-BZT compositions developed. The defect chemistry that underpins the fatigue behavior will be examined and the results will be compared to the existing body of work on PZT. It will

  9. Fatigue crack growth behavior of a new single crystal nickel-based superalloy (CMSX-4) at 650 C

    International Nuclear Information System (INIS)

    Sengupta, A.; Putatunda, S.K.

    1994-01-01

    CMSX-4 is a recently developed rhenium containing single crystal nickel-based superalloy. This alloy has potential applications in many critical high-temperature applications such as turbine blades, rotors, nuclear reactors, etc. The fatigue crack growth rate and the fatigue threshold data of this material is extremely important for accurate life prediction, as well as failure safe design, at elevated temperatures. In this paper, the fatigue crack growth behavior of CMSX-4 has been studied at 650 C. The investigation also examined the influence of γ' precipitates (size and distribution) on the near-threshold fatigue crack growth rate and the fatigue threshold. The influence of load ratio on the fatigue crack growth rate and the fatigue threshold was also examined. Detailed fractographic studies were carried out to determine the crack growth mechanism in fatigue in the threshold region. Compact tension specimens were prepared from the single crystal nickel-based superalloy CMSX-4 with [001] orientation as the tensile loading axis direction. These specimens were given three different heat treatments to produce three different γ' precipitate sizes and distributions. Fatigue crack growth behavior of these specimens was studied at 650 C in air. The results of the present investigation indicate that the near-threshold fatigue crack growth rate decreases and that the fatigue threshold increases with an increase in the γ' precipitate size at 650 C. The fatigue threshold decreased linearly with an increase in load ratio. Fractographs at 650 C show a stage 2 type of crack growth along {100} type of crystal planes in the threshold region, and along {111} type of crystal planes in the high ΔK region

  10. The monitoring and fatigue behavior of CFCCs at ambient temperature and 1000{degrees}C

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; McHargue, C.J. [Univ. of Tennessee, Knoxville, TN (United States)] [and others

    1997-04-01

    Metallographically polished flexure bars of Nicalon/SiC and Nicalon/alumina composites were subjected to monotonic and cycle-fatigue loadings, with loading either parallel or normal to the fabric plies. The fabric orientation did not significantly affect the mechanical behavior of the Nicalon/SiC composite at ambient temperature. However, the mechanical behavior of the Nicalon/alumina composite was significantly affected by the fabric orientation at ambient temperature in air and at 1000{degrees}C in argon atmosphere. In addition, there was a significant degradation in the fatigue performance of the alumina matrix composite at the elevated temperature, owing to creep in the material and degradation in the fiber strength.

  11. The monitoring and fatigue behavior of CFCCs at ambient temperature and 1000 degrees C

    International Nuclear Information System (INIS)

    Miriyala, N.; Liaw, P.K.; McHargue, C.J.

    1997-01-01

    Metallographically polished flexure bars of Nicalon/SiC and Nicalon/alumina composites were subjected to monotonic and cycle-fatigue loadings, with loading either parallel or normal to the fabric plies. The fabric orientation did not significantly affect the mechanical behavior of the Nicalon/SiC composite at ambient temperature. However, the mechanical behavior of the Nicalon/alumina composite was significantly affected by the fabric orientation at ambient temperature in air and at 1000 degrees C in argon atmosphere. In addition, there was a significant degradation in the fatigue performance of the alumina matrix composite at the elevated temperature, owing to creep in the material and degradation in the fiber strength

  12. Influence of the geometry of curved artificial canals on the fracture of rotary nickel-titanium instruments subjected to cyclic fatigue tests.

    Science.gov (United States)

    Lopes, Hélio P; Vieira, Márcia V B; Elias, Carlos N; Gonçalves, Lucio S; Siqueira, José F; Moreira, Edson J L; Vieira, Victor T L; Souza, Letícia C

    2013-05-01

    This study evaluated the influence of different features of canal curvature geometry on the number of cycles to fracture of a rotary nickel-titanium endodontic instrument subjected to a cyclic fatigue test. BioRaCe BR4C instruments (FKG Dentaire, La Chaux-de Fonds, Switzerland) were tested in 4 grooves simulating curved metallic artificial canals, each one measuring 1.5 mm in width, 20 mm in total length, and 3.5 mm in depth with a U-shaped bottom. The parameters of curvature including the radius and arc lengths and the position of the arc differed in the 4 canal designs. Fractured surfaces and helical shafts of the separated instruments were analyzed by scanning electron microscopy. The Student's t test showed that a significantly lower number of cycles to fracture values were observed for instruments tested in canals with the smallest radius, the longest arc, and the arc located in the middle portion of the canal. Scanning electron microscopic analysis of the fracture surfaces revealed morphologic characteristics of ductile fracture. Plastic deformation was not observed in the helical shaft of the fractured instruments. Curvature geometry including the radius and arc lengths and the position of the arc along the root canal influence the number of cycles to fracture of rotary nickel-titanium instruments subjected to flexural load. Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  13. Comportamiento a fatiga del vástago de una prótesis para cadera al caminar//Fatigue behavior stem hip prosthesis for walking

    Directory of Open Access Journals (Sweden)

    Ángel Martínez-Delfín

    2014-01-01

    Full Text Available La prótesis de cadera consiste en sustituir la parte superior fracturada del fémur por una pieza de material biocompatible. Debido a las cargas aleatorias que sobre esta prótesis actúan al caminar la persona injertada, surge la fatiga sobre la prótesis. En este trabajo se realiza el cálculo a fatiga del vástago de una prótesis de caderas fabricada con acero inoxidable austenítico AISI 316L GrQ y de uso actual. Para ellose emplea el método de los elementos finitos, considerando la compleja geometría del vástago, el material y las cargas variables resultantes del caminar de la persona con la prótesis artificial colocada. Se calcula el daño a fatiga que estas cargas provocan en la misma así como el número de pasos que pueden darse, garantizándose una larga vida útil de la prótesis por este concepto de resistencia.Palabras claves: fatiga, prótesis de cadera, ciclo, daño, elementos finitos.______________________________________________________________________________AbstractThe hip prosthesis consists in substituting the fractured femur part by a piece of biocompatible material. Because the random character of loads acting over this prosthesis while person walk, crop up the fatigue on the prosthesis. The fatigue behavior of austenitic stainless steel hips prosthesis is studied in this article. The method of finite elements is used, considering the complex geometry of the part, the material and the variable acting loads, as results of steps of walking person. The fatigue damages are calculated as well as the number of steps that can be given, guarantying a long life of the prosthesis for fatigue resistance concept.Key words: fatigue, hip prosthesis, cycle, damage, finite elements.

  14. The combined effects of prior-corrosion and aggressive chemical environments on fatigue crack growth behavior in aluminum alloy 7075-T651

    Science.gov (United States)

    Mills, Thomas Brian

    1997-11-01

    Exfoliation corrosion is a potentially severe form of corrosion that frequently affects high-strength aluminum, particularly 2xxx- and 7xxx-series alloys. Exfoliation degrades components such as sheets, plates, and extrusions that have highly elongated grain structures. Few attempts have been made to investigate the effects of this form of corrosion on the fatigue performance of these materials, so a preliminary study was conducted to determine the effects of exfoliation corrosion on the fatigue response of quarter-inch 7075-T651 aluminum alloy plate. This was accomplished by subjecting aluminum panels to an ASTM standard corrosive solution known as EXCO then fatiguing the panels in corrosion fatigue environments of dry air, humid air, and artificial acid rain. Statistical analyses of the fatigue crack growth data suggest that prior-corrosion and corrosion fatigue are competing mechanisms that both have the potential of accelerating crack growth rates. In the dry air cases, exfoliation accelerated crack growth rates a maximum of 4.75 times over the uncorroded material at lower stress intensities such as 5 ksi surdinch. This accelerated behavior dropped off rapidly, however, and was nonexistent at higher stress intensities. Humid air increased crack velocities considerably as compared to the dry air uncorroded case, but the addition of exfoliation corrosion to the humid cases did not have a significant effect on crack growth behavior. On the other hand, specimens containing exfoliation corrosion and then exposed to artificial acid rain had significantly higher crack growth rates than their uncorroded counterparts. Finally, fractographic examinations of the specimens revealed evidence of lower energy, quasi-cleavage fracture persisting near to the exfoliated edge of specimens tested in the dry air, humid air, and artificial acid rain environments. The implications of this research are that prior-corrosion damage has the ability to significantly increase crack growth

  15. Driver sleepiness, fatigue, careless behavior and risk of motor vehicle crash and injury: Population based case and control study

    Directory of Open Access Journals (Sweden)

    Abdulbari Bener

    2017-10-01

    Conclusion: The current study confirmed that drivers with chronic fatigue, acute sleepiness, and careless driver behavior may significantly increases the risk of road crash which can be lead to serious injury.

  16. Study on low cycle fatigue behavior of two titanium alloy materials with elevated temperature effects

    International Nuclear Information System (INIS)

    Cai Lixun; Sun Yafang; Wang Li; Huang Shuzhen

    2000-01-01

    A serial of tensional and low cycle fatigue tests for two titanium alloy materials:T42NG and T225NG under room temperature and 350 degree C elevated temperature are carried out. Based on the test results, four monotonic constitutive relationships between stress and strain and four relationships between life Nf and strain amplitude controlled are given. By three ratio λ σ , λ Δσ and λ Nf of the materials related to the elevated temperature, systematical investigations about the influence of the elevated temperature on monotonic tensional intensity, cyclic intensity and fatigue life are performed. According to the important rule opened out that it exists a linearity relationship between the ratio λ Nf and strain amplitude Δε/2, the author present a λ-M-C model for predicting the fatigue life of a exponential material under R= -1 and an elevated temperature. To get the λ-M-C model, the authors give available discussion about the method simplified test and regression. The authors know from test results that T42NG steel has better fatigue and tensional behaviors than those of T225NG steel

  17. Damage formation, fatigue behavior and strength properties of ZrO{sub 2}-based ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Kozulin, A. A., E-mail: kozulyn@ftf.tsu.ru; Kulkov, S. S. [Tomsk State University, Tomsk, 634050 (Russian Federation); Narikovich, A. S.; Leitsin, V. N. [Immanuel Kant Baltic Federal University, Kaliningrad, 236041 (Russian Federation); Kulkov, S. N., E-mail: kulkov@ispms.ru [Tomsk State University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2016-08-02

    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 ZrO{sub 2}-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 10{sup 5} 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.

  18. Hydrogen Embrittlement Mechanism in Fatigue Behavior of Austenitic and Martensitic Stainless Steels

    Directory of Open Access Journals (Sweden)

    Sven Brück

    2018-05-01

    Full Text Available In the present study, the influence of hydrogen on the fatigue behavior of the high strength martensitic stainless steel X3CrNiMo13-4 and the metastable austenitic stainless steels X2Crni19-11 with various nickel contents was examined in the low and high cycle fatigue regime. The focus of the investigations were the changes in the mechanisms of short crack propagation. Experiments in laboratory air with uncharged and precharged specimen and uncharged specimen in pressurized hydrogen were carried out. The aim of the ongoing investigation was to determine and quantitatively describe the predominant processes of hydrogen embrittlement and their influence on the short fatigue crack morphology and crack growth rate. In addition, simulations were carried out on the short fatigue crack growth, in order to develop a detailed insight into the hydrogen embrittlement mechanisms relevant for cyclic loading conditions. It was found that a lower nickel content and a higher martensite content of the samples led to a higher susceptibility to hydrogen embrittlement. In addition, crack propagation and crack path could be simulated well with the simulation model.

  19. Damage formation, fatigue behavior and strength properties of ZrO_2-based ceramics

    International Nuclear Information System (INIS)

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

    2016-01-01

    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 ZrO_2-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 10"5 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.

  20. Multifilamentary MgB2 wires fracture behavior during the drawing process

    International Nuclear Information System (INIS)

    Shan, D.; Yan, G.; Zhou, L.; Li, J.S.; Li, C.S.; Wang, Q.Y.; Xiong, X.M.; Jiao, G.F.

    2012-01-01

    The fracture behavior of 6 + 1 filamentary MgB 2 superconductive wires is presented here. The composite wires were fabricated by in situ Powder-in-Tube method using Nb as a barrier and copper as a stabilizer. The microstructure of the material has a great influence on its fracture behavior. The microstructural aspects of crack nucleation and propagation are discussed. It shows that there are complicated correlations between fracture behavior and the main influencing parameters, which contain specific drawing conditions (drawing velocity, reduction in area per pass), materials properties (strength, yield stress, microstructure) as well as the extent of bonding between the metal sheaths at their interface.

  1. The effect of different light-curing units on fatigue behavior and degree of conversion of a resin composite.

    Science.gov (United States)

    Lohbauer, Ulrich; Rahiotis, Christos; Krämer, Norbert; Petschelt, Anselm; Eliades, George

    2005-07-01

    The aim of this study was to investigate the effect of different light-curing units and irradiation modes on the mechanical fatigue strength and degree of conversion of a restorative resin composite. Conventional halogen, plasma arc and blue LED light-curing units were used for polymerization of a resin composite (Tetric) Ceram, Ivoclar, Vivadent, Liechtenstein). Initial fracture strength (FS) and flexural fatigue limit (FFL) as well as degree of conversion (DC) were measured. The FFL was determined under cyclic loading for 10(5) cycles in terms of a staircase approach. The specimens were stored for 14 days in 37 degrees C distilled water prior to testing. The curing efficiency was observed with Fourier transform infrared micromultiple internal reflectance spectroscopy. The measurements were carried out at 0.5 and 2.5 mm distance from the directly irradiated surface after 14 days storage in dark and dry conditions at 37 degrees C. The highest FS, FFL and DC were observed from high energy curing devices and from extended curing intervals. The conventional halogen light exhibited the most homogenous in-depth curing efficiency along with a low loss of mechanical resistance under cyclic fatigue. Evaluation of flexural fatigue limit and curing efficiency correlate in terms of decreased mechanical strength due to insufficient light-curing intervals or light intensities. Initial promising fracture strengths do not correlate with a clinically more relevant fatigue loading and with the in-depth degree of conversion, both accounting for a significantly reduced strength performance.

  2. Fatigue Behavior under Multiaxial Stress States Including Notch Effects and Variable Amplitude Loading

    Science.gov (United States)

    Gates, Nicholas R.

    The central objective of the research performed in this study was to be able to better understand and predict fatigue crack initiation and growth from stress concentrations subjected to complex service loading histories. As such, major areas of focus were related to the understanding and modeling of material deformation behavior, fatigue damage quantification, notch effects, cycle counting, damage accumulation, and crack growth behavior under multiaxial nominal loading conditions. To support the analytical work, a wide variety of deformation and fatigue tests were also performed using tubular and plate specimens made from 2024-T3 aluminum alloy, with and without the inclusion of a circular through-thickness hole. However, the analysis procedures implemented were meant to be general in nature, and applicable to a wide variety of materials and component geometries. As a result, experimental data from literature were also used, when appropriate, to supplement the findings of various analyses. Popular approaches currently used for multiaxial fatigue life analysis are based on the idea of computing an equivalent stress/strain quantity through the extension of static yield criteria. This equivalent stress/strain is then considered to be equal, in terms of fatigue damage, to a uniaxial loading of the same magnitude. However, it has often been shown, and was shown again in this study, that although equivalent stress- and strain-based analysis approaches may work well in certain situations, they lack a general robustness and offer little room for improvement. More advanced analysis techniques, on the other hand, provide an opportunity to more accurately account for various aspects of the fatigue failure process under both constant and variable amplitude loading conditions. As a result, such techniques were of primary interest in the investigations performed. By implementing more advanced life prediction methodologies, both the overall accuracy and the correlation of fatigue

  3. Efecto de la tenacidad del asfalto en la resistencia a fatiga de las mezclas asfálticas Asphalt toughness effect on bituminous mixture fatigue behavior

    Directory of Open Access Journals (Sweden)

    Alfredo H Noguera

    2011-08-01

    Full Text Available Uno de los parámetros más importantes para definir el comportamiento de la mezcla en servicio es la tenacidad que el asfalto proporciona al aglomerar los agregados, es decir, la energía que se disipa al fracturar la mezcla, entre mayor sea dicha energía mejor será su calidad. Y por lo tanto, deberá existir una relación si dicha cantidad de energía se disipa en un ciclo de carga (tracción o con muchos ciclos durante el tiempo (fatiga. El objetivo de éste trabajo es establecer una relación entre la tenacidad que ofrecen distintos asfaltos y el comportamiento a fatiga de sus correspondientes mezclas asfálticas, para lo cual, se ha obtenido la tenacidad mediante un ensayo de tracción directa y se ha comparado con los valores de las leyes de fatiga y energía disipada obtenidas del ensayo de flexo-tracción dinámica.One of the most important parameters to define bituminous mixture behavior in service is the toughness that the bitumen provides when binding the aggregate particles; that is; the dissipated energy during the materials fracture process. The greater the dissipated energy in fracture, the better the bituminous mixture quality is. Hence, a relationship will have to exist if the toughness is removed during one load cycle (direct tension or during many cycles along time (fatigue. The purpose of this study is to determinate relationships between the toughness of different bitumens and the fatigue behavior of their corresponding bituminous mixtures, for which, the toughness has been obtained by means of direct tension test and has been compared with the value of the fatigue law and dissipated energy obtained by fatigue bending test. Results showed that, this study expect to give important means for further research to predict fatigue life from a static test.

  4. Effect of corrosion and sandblasting on the high cycle fatigue behavior of reinforcing B500C steel bars

    Directory of Open Access Journals (Sweden)

    Marina C. Vasco

    2017-10-01

    Full Text Available In a series of applications, steel reinforced concrete structures are subjected to fatigue loads during their service life, what in most cases happens in corrosive environments. Surface treatments have been proved to represent proper processes in order to improve both fatigue and corrosion resistances. In this work, the effect of corrosion and sandblasting on the high cycle fatigue behavior reinforcing steel bars is investigated. The investigated material is the reinforcing steel bar of technical class B500C, of nominal diameter of 12 mm. Steel bars specimens were first exposed to corrosion in alternate salt spray environment for 30 and 60 days and subjected to both tensile and fatigue tests. Then, a series of specimens were subjected to common sandblasting, corroded and mechanically tested. Metallographic investigation and corrosion damage evaluation regarding mass loss and martensitic area reduction were performed. Tensile tests were conducted after each corrosion exposure period prior to the fatigue tests. Fatigue tests were performed at a stress ratio, R, of 0.1 and loading frequency of 20 Hz. All fatigue tests series as well as tensile test were also performed for as received steel bars to obtain the reference behavior. The results have shown that sandblasting hardly affects the tensile behavior of the uncorroded material. The effect of sandblasting on the tensile behavior of pre-corroded specimens seems to be also limited. On the other hand, fatigue results indicate an improved fatigue behavior for the sandblasted material after 60 days of corrosion exposure. Martensitic area reductions, mass loss and depth of the pits were significantly smaller for the case of sandblasted materials, which confirms an increased corrosion resistance

  5. Fatigue crack growth behavior of RAFM steel in Paris and threshold regimes at different temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Babu, M. Nani; Sasikala, G., E-mail: gsasi@igcar.gov.in; Dutt, B. Shashank; Venugopal, S.; Bhaduri, A.K.; Jayakumar, T.

    2014-04-01

    Fatigue crack growth (FCG) behavior of a reduced activation ferritic martensitic (indigenous RAFM) steel has been evaluated at 300, 653 and 823 K in Paris and threshold regimes. The effect of temperature on threshold stress intensity factor range and associated crack closure mechanisms is highlighted. The FCG results were compared with those for EUROFER 97. Further, crack tip effective stress intensity factor ranges (ΔK{sub tip,eff}) have been evaluated by taking crack tip shielding into account in order to examine the effect of temperature on true intrinsic FCG behavior.

  6. Microstructure characteristics and temperature-dependent high cycle fatigue behavior of advanced 9% Cr/CrMoV dissimilarly welded joint

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qingjun [Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240 (China); Lu, Fenggui, E-mail: Lfg119@sjtu.edu.cn [Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240 (China); Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China); Cui, Haichao [Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240 (China); Ding, Yuming; Liu, Xia [Shanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co. Ltd., Shanghai 200240 (China); Gao, Yulai, E-mail: ylgao@shu.edu.cn [Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China)

    2014-10-06

    Advanced 9% Cr and CrMoV steels chosen as candidate materials are first welded by narrow-gap submerged arc welding (NG-SAW) to fabricate the heavy section rotor. The present work focuses on studying the high-cycle fatigue (HCF) behavior of advanced 9% Cr/CrMoV dissimilarly welded joint at different temperatures. Conditional fatigue strength of this dissimilarly welded joint was obtained by HCF tests at room temperature (RT), 400 °C and 470 °C. It was observed that the failure occurred at the side of CrMoV base metal (BM), weld metal (WM) and heat affected zone (HAZ) of CrMoV side over 5×10{sup 7} cycles for the specimens tested at RT, 400 °C and 470 °C. The detailed microstructures of BMs, WMs and HAZs as well as fracture appearance were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Precipitation and aggregation of carbides along the grain boundaries were clearly detected with the increase of temperature, which brought a negative effect on the fatigue properties. It is interesting to note that the inclusion size leading to crack initiation became smaller for the HCF test at higher temperature. Therefore, reduction in the inclusion size in a welded joint helps to improve the HCF performance at high temperature.

  7. Microstructure characteristics and temperature-dependent high cycle fatigue behavior of advanced 9% Cr/CrMoV dissimilarly welded joint

    International Nuclear Information System (INIS)

    Wu, Qingjun; Lu, Fenggui; Cui, Haichao; Ding, Yuming; Liu, Xia; Gao, Yulai

    2014-01-01

    Advanced 9% Cr and CrMoV steels chosen as candidate materials are first welded by narrow-gap submerged arc welding (NG-SAW) to fabricate the heavy section rotor. The present work focuses on studying the high-cycle fatigue (HCF) behavior of advanced 9% Cr/CrMoV dissimilarly welded joint at different temperatures. Conditional fatigue strength of this dissimilarly welded joint was obtained by HCF tests at room temperature (RT), 400 °C and 470 °C. It was observed that the failure occurred at the side of CrMoV base metal (BM), weld metal (WM) and heat affected zone (HAZ) of CrMoV side over 5×10 7 cycles for the specimens tested at RT, 400 °C and 470 °C. The detailed microstructures of BMs, WMs and HAZs as well as fracture appearance were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Precipitation and aggregation of carbides along the grain boundaries were clearly detected with the increase of temperature, which brought a negative effect on the fatigue properties. It is interesting to note that the inclusion size leading to crack initiation became smaller for the HCF test at higher temperature. Therefore, reduction in the inclusion size in a welded joint helps to improve the HCF performance at high temperature

  8. Fatigue failure analysis of V-4Ti-4Cr alloy

    International Nuclear Information System (INIS)

    Aglan, H.; Gan, Y.X.; Grossbeck, M.

    1999-01-01

    In the present work, the fatigue fracture and failure behavior of a V-4Ti-4Cr has been studied. Static tests were conducted to study the overloading behavior and to select the magnitude of the stress level for the fatigue studies. Fatigue tests were performed using single edge notched (SEN) specimens under tension-tension load control conditions. Fatigue crack propagation (FCP) data such as the crack length, number of cycles, and hysteresis loops were recorded to calculate the crack speed, the energy release rate, and the change in work expended on damage formation and dissipative processes within the material. Parameters characterizing the fatigue fracture resistance of V-4Ti-4Cr alloy, namely the specific energy of damage (γ'), and the dissipative coefficient (β'), were determined from the fatigue data using the modified crack layer (MCL) theory. Fracture surface examination using scanning electron microscopy (SEM) revealed ductile failure mechanisms under tensile overloading conditions. The fatigue fracture surface of the V-4Ti-4Cr consists of three distinct regions, corresponding to the threshold, stable and unstable crack propagation stages. (orig.)

  9. Role of Lactobacillus acidophilus loaded floating beads in chronic fatigue syndrome: behavioral and biochemical evidences.

    Science.gov (United States)

    Singh, P K; Chopra, K; Kuhad, A; Kaur, I P

    2012-04-01

      In recent years the interface between neuropsychiatry and gastroenterology has converged in to a new discipline referred to as enteric neuroscience. Implications of brain-gut communication in the pathogenesis of psychiatric disorders indicate a possible role of suitably packaged/delivered probiotics as newer therapeutic options. In the present study probable role of per-oral administration of free Lactobacillus acidophilus (LAB) and LAB loaded alginate beads in attenuation of the symptoms associated with chronic fatigue syndrome (CFS) were evaluated.   Chronic fatigue syndrome following physical fatigue was induced in rats by forcing them to swim (forced swim test; FST) in water till exhaustion, after weighing them down with 10% their body weight, daily for 28 days. Immobility (I) and postswim fatigue time (PSF) were taken as suitable markers. Free LAB and LAB loaded floating beads (FBs) were administered, from 21 to 28 days.   Immobility and PSF were found to increase considerably in FST rats (665 ± 22 s and 196 ± 6 s) as compared with the naïve (32 ± 7 s and 22 ± 2 s) at 20 days, establishing severe fatigue like behavior. FST control group exhibited significant (P < 0.05) hypertrophy of spleen, hypotrophy of thymus, and increased oxido-nitrosative stress in brain and tumor necrosis factor-α (TNF-α) levels in serum. Treatment with LAB and LAB FBs significantly decreased I and PSF and attenuated (P < 0.05) oxido-nitrosative stress and TNF-α levels. Spleen and thymus were also restored to their original size in this group.   The findings suggest a valuable therapeutic role of LAB especially when incorporated into alginate beads for the treatment of CFS. © 2012 Blackwell Publishing Ltd.

  10. Effect of rare earth elements on high cycle fatigue behavior of AZ91 alloy

    International Nuclear Information System (INIS)

    Mokhtarishirazabad, M.; Boutorabi, S.M.A.; Azadi, M.; Nikravan, M.

    2013-01-01

    This article investigates effects of adding rare earth elements (RE) into a magnesium–aluminum–zinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of −1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al 11 RE 3 intermetallic particles which is associated to the reduction of β-(Mg 17 Al 12 ) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (S–N) shows an increase in the fatigue strength at 10 5 cycles, from 100±10 MPa to 135±10 MPa, when RE elements were added to the AZ91 alloy

  11. Effect of rare earth elements on high cycle fatigue behavior of AZ91 alloy

    Energy Technology Data Exchange (ETDEWEB)

    Mokhtarishirazabad, M., E-mail: mehdi-mokhtari@hotmail.com [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Boutorabi, S.M.A. [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Azadi, M.; Nikravan, M. [Irankhodro Powertrain Company (IPCO), Tehran (Iran, Islamic Republic of)

    2013-12-10

    This article investigates effects of adding rare earth elements (RE) into a magnesium–aluminum–zinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of −1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al{sub 11}RE{sub 3} intermetallic particles which is associated to the reduction of β-(Mg{sub 17}Al{sub 12}) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (S–N) shows an increase in the fatigue strength at 10{sup 5} cycles, from 100±10 MPa to 135±10 MPa, when RE elements were added to the AZ91 alloy.

  12. Association of fatigue with emotional-eating behavior and the response to mental stress in food intake in a young adult population.

    Science.gov (United States)

    Yoshikawa, Takahiro; Tanaka, Masaaki; Ishii, Akira; Watanabe, Yasuyoshi

    2014-01-01

    Fatigue is a common complaint among young adults. We investigated whether eating behaviors are associated with fatigue in this population. The participants consisted of 117 healthy students attending Osaka City University. They completed questionnaires assessing fatigue and eating behaviors. To identify the factors associated with the prevalence of fatigue, multivariate logistic regression analysis adjusted for gender was performed. The Emotional Eating subscale score of the Japanese version of Three-Factor Eating Questionnaire Revised 21-item and stress response in food intake (large decrease vs. no change) were positively associated with the prevalence of fatigue assessed by the Japanese version of the Chalder Fatigue Scale. The finding suggests that emotional eating and decrease in amount of food intake under mental stress were associated with fatigue in healthy young adults. Our findings may help to clarify the mechanisms underlying fatigue-eating coupling as well as the etiology of diseases related to abnormal eating behavior.

  13. Evaluation of long term creep-fatigue life for type 304 stainless steel

    International Nuclear Information System (INIS)

    Kawasaki, Hirotsugu; Ueno, Fumiyoshi; Aoto, Kazumi; Ichimiya, Masakazu; Wada, Yusaku

    1992-01-01

    The long term creep-fatigue life of type 304 stainless steel was evaluated by the creep-fatigue life prediction method based on a linear damage fraction rule. The displacement controlled creep-fatigue tests were carried out, and the time to failure of longer than 10000 hours was obtained. The creep damage of long term creep-fatigue was evaluated by taking into account the stress relaxation behavior with elastic follow-up during the hold period. The relationship between life reduction of creep-fatigue and fracture mode was provided by the creep cavity growth. The results of this study are summarized as follows; (1) The long term creep-fatigue data can be reasonably evaluated by the present method. The predicted lives were within a factor of 3 of the observed ones. (2) The present method provides the capability to predict the long term creep-fatigue life at lower temperatures as well as that at the creep dominant temperature. (3) The value of creep damage for the long term creep-fatigue data increased by elastic follow-up. The creep-fatigue damage diagram intercepted between 0.3 and 1 can represent the observed creep-fatigue damages. (4) The cavity growth depends on the hold time. The fracture of long term creep-fatigue is caused by the intergranular cavity growth. The intergranular fracture of creep-fatigue is initiated by the cavity growth and followed by the microcrack propagation along grain boundaries starting from creep cavities. (author)

  14. Effect of thermo-mechanical loading histories on fatigue crack growth behavior and the threshold in SUS 316 and SCM 440 steels. For prevention of high cycle thermal fatigue failures

    International Nuclear Information System (INIS)

    Okazaki, Masakazu; Muzvidziwa, Milton; Iwasaki, Akira; Kasahara, Naoto

    2014-01-01

    High cycle thermal fatigue failure of pipes induced by fluid temperature change is one of the interdisciplinary issues to be concerned for long term structural reliability of high temperature components in energy systems. In order to explore advanced life assessment methods to prevent the failure, fatigue crack propagation tests were carried out in a low alloy steel and an austenitic stainless steel under typical thermal and thermo-mechanical histories. Special attention was paid to both the effect of thermo-mechanical loading history on the fatigue crack threshold, as well as to the applicability of continuum fracture mechanics treatment to small or short cracks. It was shown experimentally that the crack-based remaining fatigue life evaluation provided more reasonable assessment than the traditional method based on the semi-empirical law in terms of 'usage factor' for high cycle thermal fatigue failure that is employed in JSME Standard, S017. The crack propagation analysis based on continuum fracture mechanics was almost successfully applied to the small fatigue cracks of which size was comparable to a few times of material grain size. It was also shown the thermo-mechanical histories introduced unique effects to the prior fatigue crack wake, resulting in occasional change in the fatigue crack threshold. (author)

  15. Fluoxetine prevents the development of depressive-like behavior in a mouse model of cancer related fatigue.

    Science.gov (United States)

    Norden, Diana M; Devine, Raymond; Bicer, Sabahattin; Jing, Runfeng; Reiser, Peter J; Wold, Loren E; Godbout, Jonathan P; McCarthy, Donna O

    2015-03-01

    Cancer patients frequently suffer from fatigue, a complex syndrome associated with tiredness and depressed mood. Cancer-related fatigue (CRF) can be present at the time of diagnosis, escalates during treatment, and can persist for years after treatment. CRF negatively influences quality of life, limits functional independence, and is associated with decreased survival in patients with incurable disease. We have previously shown that increased pro-inflammatory cytokine expression in the brain contributes to depressive- and fatigue-like behaviors in a mouse model of CRF. Inflammatory cytokines increase the activity of indoleamine 2,3-dioxygenase (IDO) and kynurenine 3-monooxygenase (KMO), which competitively reduce serotonin synthesis. Reduced serotonin availability in the brain and increased production of alternative neuroactive metabolites of tryptophan are thought to contribute to the development of depression and fatigue. The purpose of this study was to determine the effects of fluoxetine, a selective serotonin reuptake inhibitor (SSRI), on brain cytokines and behavioral measures of fatigue and depression in tumor-bearing mice. Here we show that tumor growth increased brain expression of pro-inflammatory cytokines and KMO. Treatment with fluoxetine had no effect on tumor growth, muscle wasting, fatigue behavior, or cytokine expression in the brain. Fluoxetine, however, reduced depressive-like behaviors in tumor bearing mice. In conclusion, our data confirm that increased brain expression of pro-inflammatory cytokines is associated with tumor-induced fatigue- and depressive-like behaviors. However, it is possible to separate the effects of tumor growth on mood and fatigue-like behaviors using SSRIs such as fluoxetine. Copyright © 2014 Elsevier Inc. All rights reserved.

  16. Cyclic fatigue and fracture in pyrolytic carbon-coated graphite mechanical heart-valve prostheses: role of small cracks in life prediction.

    Science.gov (United States)

    Dauskardt, R H; Ritchie, R O; Takemoto, J K; Brendzel, A M

    1994-07-01

    A fracture-mechanics based study has performed to characterize the fracture toughness and rates of cyclic fatigue-crack growth of incipient flaws in prosthetic heart-valve components made of pyrolytic carbon-coated graphite. Such data are required to predict the safe structural lifetime of mechanical heart-valve prostheses using damage-tolerant analysis. Unlike previous studies where fatigue-crack propagation data were obtained using through-thickness, long cracks (approximately 2-20 mm long), growing in conventional (e.g., compact-tension) samples, experiments were performed on physically small cracks (approximately 100-600 microns long), initiated on the surface of the pyrolytic-carbon coating to simulate reality. Small-crack toughness results were found to agree closely with those measured conventionally with long cracks. However, similar to well-known observations in metal fatigue, it was found that based on the usual computations of the applied (far-field) driving force in terms of the maximum stress intensity, Kmax, small fatigue cracks grew at rates that exceeded those of long cracks at the same applied stress intensity, and displayed a negative dependency on Kmax; moreover, they grew at applied stress intensities less than the fatigue threshold value, below which long cracks are presumed dormant. To resolve this apparent discrepancy, it is shown that long and small crack results can be normalized, provided growth rates are characterized in terms of the total (near-tip) stress intensity (incorporating, for example, the effect of residual stress); with this achieved, in principle, either form of data can be used for life prediction of implant devices. Inspection of the long and small crack results reveals extensive scatter inherent in both forms of growth-rate data for the pyrolytic-carbon material.

  17. Influence of stress change on the fatigue behavior and fatigue life of aluminum oxide-dispersion-strengthening copper alloy at room temperature and 350degC

    International Nuclear Information System (INIS)

    Kawagoishi, Norio; Kondo, Eiji; Nisitani, Hironobu; Shimamoto, Atsunori; Tashiro, Rieko

    2004-01-01

    In order to investigate the influence of stress change on the fatigue behavior and fatigue life of an aluminum oxide-dispersion-strengthening copper alloy at elevated temperature, rotating bending fatigue tests were carried out under two-step loading at room temperature and 350degC. Both of static strength and fatigue strength decreased at 350degC. However, at the same relative stress σ a /σ B , fatigue life was longer at 350degC than at room temperature. Although the cumulative ratios Σ(N/N f ) were nearly unity for both the low to high and the high to low block loadings at room temperature, Miner's rule did not hold at 350degC. These results were related to the stress dependence on the log l-N/N f relation. That is, the crack length initiated at the same N/N f was larger in higher stress level at 350degC, whereas there was no stress dependence in the relation at room temperature. The stress dependence on the relation at 350degC was caused by the suppression of crack initiation due to the surface oxidation. (author)

  18. Surface crack behavior in socket weld of nuclear piping under fatigue loading condition

    International Nuclear Information System (INIS)

    Choi, Y.H.; Kim, J.S.; Choi, S.Y.

    2005-01-01

    The ASME B and PV Code Sec. III allows the socket weld for the nuclear piping in spite of the weakness on the weld integrity. Recently, the integrity of the socket weld is regarded as a safety concern in nuclear power plants because many failures and leaks have been reported in the socket weld. OPDE (OECD Piping Failure Data Exchange) database lists 108 socket weld failures among 2,399 nuclear piping failure cases during 1970 to 2001. Eleven failures in the socket weld were also reported in Korean NPPs. Many failure cases showed that the root cause of the failure is the fatigue and the gap requirement for the socket weld given in ASME Code was not satisfied. The purpose of this paper is to evaluate the fatigue crack behavior of a surface crack in the socket weld under fatigue loading condition considering the gap effect. Three-dimensional finite element analysis was performed to estimate the fatigue crack behavior of the surface crack. Three types of loading conditions such as the deflection due to vibration, the pressure transient ranging from P=0 to 15.51 MPa, and the thermal transient ranging from T=25 C to 288 C were considered. The results are as follows; 1) The socket weld is susceptible to the vibration where the vibration levels exceed the requirement in the ASME operation and maintenance (OM) Code. 2) The effect of pressure or temperature transient load on the socket weld integrity is not significant. 3) No-gap condition gives very high possibility of the crack initiation at the socket weld under vibration loading condition. 4) For the specific systems having the vibration condition to exceed the requirement in the ASME Code OM and/or the transient loading condition from P=0 and T=25 C to P=15.51 MPa and T=288 C, radiographic examination to examine the gap during the construction stage is recommended. (orig.)

  19. Effect of Micro-Structure on Fatigue Behavior of Intact Rocks under Completely Reversed Loading

    Directory of Open Access Journals (Sweden)

    Saeed Jamali Zavareh

    2017-01-01

    Full Text Available Rock formations and structures can be subjected to both static and dynamic loadings. Static loadings resulting from different sources such as gravity and tectonic forces and dynamic forces are intermittently transmitted via vibrations of the earth’s crust, through major earthquakes, rock bursts, rock blasting and drilling and also, traffic. Reaction of rocks to cyclic and repetitive stresses resulting from dynamic loads has been generally neglected with the exception of a few rather limited studies. In this study, , two crystalline quarry stones in Iran; (Natanz gabbro and Green onyx and one non-crystalline rock (Asmari limestone are used to evaluate the effect of micro-structure of intact rock on fatigue behavior. These rocks have different mineral compositions and formation conditions. A new apparatus based on rotating beam fatigue testing machine (R.R.Moore, which is commonly used for laboratory fatigue test in metals, is developed and fatigue behavior and existence of the endurance limit were evaluated for the mentioned rocks based on stress-life method. The obtained results in the variation of applied amplitude stress versus loading cycle number (S-N diagram followed common relationship in other materials. In addition, the endurance limit is perceived for all tested rocks. The results also illustrated that the endurance limits for all types of tested rocks in this study are ranged between 0.4 and 0.6 of their tensile strengths. The endurance limit to tensile strength fraction of green onyx and Natanz gabbro were approximated in a higher value compared to the Asmari limestone with non-crystalline micro-structure.

  20. Experimental and Numerical Investigations of Fretting Fatigue Behavior for Steel Q235 Single-Lap Bolted Joints

    Directory of Open Access Journals (Sweden)

    Yazhou Xu

    2016-01-01

    Full Text Available This work aims to investigate the fretting fatigue life and failure mode of steel Q235B plates in single-lap bolted joints. Ten specimens were prepared and tested to fit the S-N curve. SEM (scanning electron microscope was then employed to observe fatigue crack surfaces and identify crack initiation, crack propagation, and transient fracture zones. Moreover, a FEM model was established to simulate the stress and displacement fields. The normal contact stress, tangential contact stress, and relative slipping displacement at the critical fretting zone were used to calculate FFD values and assess fretting fatigue crack initiation sites, which were in good agreement with SEM observations. Experimental results confirmed the fretting fatigue failure mode for these specimens. It was found that the crack initiation resulted from wear regions at the contact surfaces between plates, and fretting fatigue cracks occurred at a certain distance away from hole edges. The proposed FFD-N relationship is an alternative approach to evaluate fretting fatigue life of steel plates in bolted joints.

  1. The effect of low temperatures on the fatigue of high-strength structural grade steels

    NARCIS (Netherlands)

    Walters, C.L.

    2014-01-01

    It is well-known that for fracture, ferritic steels undergo a sudden transition from ductile behavior at higher temperatures to brittle cleavage failure at lower temperatures. However, this phenomenon has not received much attention in the literature on fatigue. The so-called Fatigue Ductile-Brittle

  2. Happy Now, Tired Later? Extraverted and Conscientious Behavior Are Related to Immediate Mood Gains, but to Later Fatigue.

    Science.gov (United States)

    Leikas, Sointu; Ilmarinen, Ville-Juhani

    2017-10-01

    Experience sampling studies on Big Five-related behavior show that people display the whole spectrum of each trait in their daily behavior, and that desirable Big Five states-especially state Extraversion-are related to positive mood. However, other research lines suggest that extraverted and conscientious behavior may be mentally depleting. The present research examined this possibility by extending the time frame of the measured personality processes. A 12-day experience sampling study (N = 48; observations = 2,328) measured Big Five states, mood, stress, and fatigue five times a day. Extraverted and conscientious behavior were concurrently related to positive mood and lower fatigue, but to higher fatigue after a 3-hour delay. These relations were not moderated by personality traits. The relation between extraverted behavior and delayed fatigue was mediated by the number of people the person had encountered. Whether the person had a goal mediated the relation between conscientious behavior and delayed fatigue. Extraverted and conscientious behavior predict mental depletion after a 3-hour delay. The results help reconcile previous findings regarding the consequences of state Extraversion and provide novel information about the consequences of state Conscientiousness. © 2016 Wiley Periodicals, Inc.

  3. Photoelastic study of the dynamic fracture behavior of Homalite 100

    International Nuclear Information System (INIS)

    Irwin, G.R.; Dally, J.W.; Kobayashi, T.; Etheridge, J.M.

    1975-09-01

    This report describes an experimental investigation of the dynamic behavior of cracks propagation in Homalite 100, a brittle thermosetting polymeric material. Dynamic photoelectric isochromatic fringe patterns associated with cracks propagating in center-pin-loaded, eccentric-pin-loaded and crack-line-loaded SEN specimens were recorded with a high speed multiple spark camera. Data was obtained from 11 tests over a range of crack velocities from arrest to the terminal velocity of 15,000 in/sec. The size and shape of the isochromatic loops was used to determine the instantaneous values of K by matching analytical and experimental results. The analytical results employed a Westergaard stress function of the form Z(z) = K/√ 2πz[1 + (z/a)] and a superimposed sigma/sub ox/ = αK/√ 2πa. Results were obtained by computer program (FRACTURE) for different values of α, β, K and a to give 8925 analytical fringe loops. Another computer program (SEARCH I) was used to find the best fit to each experimentally determined loop based on a comparison function. After a close fit was obtained, the instantaneous K was determined. Results show that K/sub a/ and K/sub IC/ are nearly the same and that a increases abruptly from 0 to about 10,000 in/sec for modest increases in K above 400 psi √in. Further increases in crack velocity require significant increases in K until terminal velocity is reached at K = 2000 psi√in. At this value of K the crack attempts to branch and produces a large number of small branches

  4. Surface modification and fatigue behavior of nitinol for load bearing implants

    Science.gov (United States)

    Bernard, Sheldon A.

    Musculoskeletal disorders are recognized amongst the most significant human health problems that exist today. Even though considerable research and development has gone towards understanding musculoskeletal disorders, there is still lack of bone replacement materials that are appropriate for restoring lost structures and functions, particularly for load-bearing applications. Many materials on the market today, such as titanium and stainless steel, suffer from significantly higher modulus than natural bone and low bioactivity leading to stress shielding and implant loosening over longer time use. Nitinol (NiTi) is an equiatomic intermetallic compound of nickel and titanium whose unique biomechanical and biological properties contributed to its increasing use as a biomaterial. An innovative method for creating dense and porous net shape NiTi alloy parts has been developed to improve biological properties while maintaining comparable or better mechanical properties than commercial materials that are currently in use. Laser engineered net shaping (LENS(TM)) and surface electrochemistry modification was used to create dense/porous samples and micro textured surfaces on NiTi parts, respectively. Porous implants are known to promote cell adhesion and have a low elastic modulus, a combination that can significantly increase the life of an implant. However, porosity can significantly reduce the fatigue life of an implant, and very little work has been reported on the fatigue behavior of bulk porous metals, specifically on porous nitinol alloy. High-cycle rotating bending and compression-compression fatigue behavior of porous NiTi fabricated using LENS(TM) were studied. In cyclic compression loading, plastic strain increased with increasing porosity and it was evident that maximum strain was achieved during the first 50000 cycles and remained constant throughout the remaining loading. No failures were observed due to loading up to 150% of the yield strength. When subjected

  5. Metal magnetic memory technique used to predict the fatigue crack propagation behavior of 0.45%C steel

    Energy Technology Data Exchange (ETDEWEB)

    Chongchong, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Lihong, Dong, E-mail: lihong.dong@126.com [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Haidou, Wang [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Guolu, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Binshi, Xu [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China)

    2016-05-01

    Monitoring fatigue crack propagation behavior of ferromagnetic components is very important. In this paper, the tension–tension fatigue tests of center cracked tension (CCT) specimens were carried out; the variation regularity of both tangential and normal components of magnetic signals during fatigue process were investigated. The results showed that the initial abnormal signals which appeared at the notch were reversed after cyclic loading. The abnormal magnetic signals became more significant with the increase of fatigue cycles and reversed again after failure. The characteristic parameters, i.e., the peak value of tangential component, B{sub tp}, and maximum gradient value of normal component, K{sub m}, showed similar variation trends during the fatigue process, which can be divided into three different stages. An approximate linear relationship was found between the characteristic parameters and fatigue crack length 2a. The feasibility of predicting the fatigue crack propagation using the abnormal magnetic signals was discussed. What's more, the variation and distribution of the magnetic signals were also analyzed based on the theory of magnetic charge. - Highlights: • A novel and passive NDT method, i.e. MMMT method, is proposed. • Both tangential and normal components of magnetic signals were investigated. • The prediction of crack propagation by abnormal magnetic signals was discussed. • A linear relationship was found between the parameters and fatigue crack length 2a. • The parameters can be potentially used to evaluate the crack propagation state.

  6. Fatigue behavior of alloy 600 in sodium chloride solution at room temperature

    International Nuclear Information System (INIS)

    Ho, J.-T.; Yu, G.-P.

    2004-01-01

    Fatigue crack growth (FCG) rates of mill annealed Alloy 600 in NaCI solution were studied by a fracture mechanics test method. Compact tension (CT) specimens were tested under load control with a sinusoidal wave form, in accordance with ASTM specification E647-83, to investigate the effects of environment, load frequency (f), load ratio (R=Pmin/Pmax). The FCG rates of Alloy 600, R=0.1, f=1Hz, were quite similar in air, distilled water, and NaCI (0.6 M, 0.1 M, and 0.001 M) solution at room temperature. Environmental enhancement effect on the FCG rate of Alloy 600 was not significant in NaCI solution. Variations of the load frequency (0.03Hz-3Hz) did not influence the FCG rates of Alloy 600 significantly in air and 0.1 M NaCI solution. The FCG rates of Alloy 600 in air and 0.1 M NaCI solution increased with increasing the load ratio. Compared with the corrosion effects, test results showed that the mechanical effects dominated on the FCG rates of Alloy 600 in chloride solution at room temperature. The SEM fractographs showed that significant striations and transgranular fracture modes were observed on tested specimens. (author)

  7. Mixed-mode fatigue fracture of adhesive joints in harsh environments and nonlinear viscoelastic modeling of the adhesive

    Science.gov (United States)

    Arzoumanidis, Alexis Gerasimos

    A four point bend, mixed-mode, reinforced, cracked lap shear specimen experimentally simulated adhesive joints between load bearing composite parts in automotive components. The experiments accounted for fatigue, solvent and temperature effects on a swirled glass fiber composite adherend/urethane adhesive system. Crack length measurements based on compliance facilitated determination of da/dN curves. A digital image processing technique was also utilized to monitor crack growth from in situ images of the side of the specimen. Linear elastic fracture mechanics and finite elements were used to determine energy release rate and mode-mix as a function of crack length for this specimen. Experiments were conducted in air and in a salt water bath at 10, 26 and 90°C. Joints tested in the solvent were fully saturated. In air, both increasing and decreasing temperature relative to 26°C accelerated crack growth rates. In salt water, crack growth rates increased with increasing temperature. Threshold energy release rate is shown to be the most appropriate design criteria for joints of this system. In addition, path of the crack is discussed and fracture surfaces are examined on three length scales. Three linear viscoelastic properties were measured for the neat urethane adhesive. Dynamic tensile compliance (D*) was found using a novel extensometer and results were considerably more accurate and precise than standard DMTA testing. Dynamic shear compliance (J*) was determined using an Arcan specimen. Dynamic Poisson's ratio (nu*) was extracted from strain gage data analyzed to include gage reinforcement. Experiments spanned three frequency decades and isothermal data was shifted by time-temperature superposition to create master curves spanning thirty decades. Master curves were fit to time domain Prony series. Shear compliance inferred from D* and nu* compared well with measured J*, forming a basis for finding the complete time dependent material property matrix for this

  8. Fracture behavior of the ODS steels prepared by internal oxidation

    Czech Academy of Sciences Publication Activity Database

    Stratil, Luděk; Šiška, Filip; Hadraba, Hynek; Bártková, Denisa; Fintová, Stanislava; Puchý, V.

    2017-01-01

    Roč. 124, NOV (2017), s. 1108-1111 ISSN 0920-3796 R&D Projects: GA ČR GJ15-21292Y; GA ČR(CZ) GA14-25246S Institutional support: RVO:68081723 Keywords : ODS * Internal oxidation * Fracture toughness * J-R curve * Fracture analysis Subject RIV: JG - Metallurgy OBOR OECD: Materials engineering Impact factor: 1.319, year: 2016

  9. High-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures

    OpenAIRE

    Wan, Aoshuang; Xiong, Junjiang; Lyu, Zhiyang; Li, Kuang; Du, Yisen; Chen, Kejiao; Man, Ziyu

    2016-01-01

    A modified model is developed to characterize and evaluate high-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures by considering the stress ratio effect. The model is informed by the relationship surface between maximum nominal stress, stress ratio and fatigue life. New formulae are derived to deal with the test data for estimating the parameters of the proposed model. Fatigue tests are performed on Co-based superalloy 9CrCo subjected to constant amplitude loading a...

  10. Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

    Science.gov (United States)

    Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

    2018-02-01

    Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

  11. Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

    Science.gov (United States)

    Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

    2018-03-01

    Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

  12. Polyphasic Temporal Behavior of Finger-Tapping Performance: A Measure of Motor Skills and Fatigue.

    Science.gov (United States)

    Aydin, Leyla; Kiziltan, Erhan; Gundogan, Nimet Unay

    2016-01-01

    Successive voluntary motor movement involves a number of physiological mechanisms and may reflect motor skill development and neuromuscular fatigue. In this study, the temporal behavior of finger tapping was investigated in relation to motor skills and fatigue by using a long-term computer-based test. The finger-tapping performances of 29 healthy male volunteers were analyzed using linear and nonlinear regression models established for inter-tapping interval. The results suggest that finger-tapping performance exhibits a polyphasic nature, and has several characteristic time points, which may be directly related to muscle dynamics and energy consumption. In conclusion, we believe that future studies evaluating the polyphasic nature of the maximal voluntary movement will lead to the definition of objective scales that can be used in the follow up of some neuromuscular diseases, as well as, the determination of motor skills, individual ability, and peripheral fatigue through the use of a low cost, easy-to-use computer-based finger-tapping test.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  15. Failure mode and fracture behavior evaluation of pipes with local wall thinning subjected to bending load

    International Nuclear Information System (INIS)

    Ahn, Seok Hwan; Nam, Ki Woo; Kim, Seon Jin; Kim, Jin Hwan; Kim, Hyun Soo; Do, Jae Yoon

    2003-01-01

    Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. In pipes of energy plants, sometimes, the local wall thinning may result from severe Erosion-Corrosion (E/C) damage. However, the effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. In this paper, the monotonic bending tests were performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and fracture strength of locally thinned pipe were manifested systematically. The observed failure modes were divided into four types; ovalization, crack initiation/growth after ovalization, local buckling and crack initiating/growth after local buckling. Also, the strength and the allowable limit of piping system with local wall thinning were evaluated

  16. Improvement of elastic-plastic fatigue crack growth evaluation method. 2. Crack opening behavior

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Yukio [Central Research Inst. of Electric Power Industry, Tokyo (Japan)

    2001-05-01

    Evaluation of crack growth behavior under cyclic loading is often required in the structural integrity assessment of cracked components. Closing and re-opening of the crack give large influence on crack growth rate through the change of fracture mechanics parameters. Based on the finite element analysis for a center-cracked plate, dependency of crack opening ratio on applied stress range and mean stress was examined. Simple formulae for representing the results were derived for plane stress and plane strain conditions. (author)

  17. Crack closure and growth behavior of short fatigue cracks under random loading (part I : details of crack closure behavior)

    International Nuclear Information System (INIS)

    Lee, Shin Young; Song, Ji Ho

    2000-01-01

    Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow-and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks

  18. Changes in motor unit behavior following isometric fatigue of the first dorsal interosseous muscle

    Science.gov (United States)

    Rymer, William Z.; Lowery, Madeleine M.; Suresh, Nina L.

    2015-01-01

    The neuromuscular strategies employed to compensate for fatigue-induced muscle force deficits are not clearly understood. This study utilizes surface electromyography (sEMG) together with recordings of a population of individual motor unit action potentials (MUAPs) to investigate potential compensatory alterations in motor unit (MU) behavior immediately following a sustained fatiguing contraction and after a recovery period. EMG activity was recorded during abduction of the first dorsal interosseous in 12 subjects at 20% maximum voluntary contraction (MVC), before and directly after a 30% MVC fatiguing contraction to task failure, with additional 20% MVC contractions following a 10-min rest. The amplitude, duration and mean firing rate (MFR) of MUAPs extracted with a sEMG decomposition system were analyzed, together with sEMG root-mean-square (RMS) amplitude and median frequency (MPF). MUAP duration and amplitude increased immediately postfatigue and were correlated with changes to sEMG MPF and RMS, respectively. After 10 min, MUAP duration and sEMG MPF recovered to prefatigue values but MUAP amplitude and sEMG RMS remained elevated. MU MFR and recruitment thresholds decreased postfatigue and recovered following rest. The increase in MUAP and sEMG amplitude likely reflects recruitment of larger MUs, while recruitment compression is an additional compensatory strategy directly postfatigue. Recovery of MU MFR in parallel with MUAP duration suggests a possible role for metabolically sensitive afferents in MFR depression postfatigue. This study provides insight into fatigue-induced neuromuscular changes by examining the properties of a large population of concurrently recorded single MUs and outlines possible compensatory strategies involving alterations in MU recruitment and MFR. PMID:25761952

  19. Modeling of the fracture behavior of spot welds using advanced micro-mechanical damage models

    International Nuclear Information System (INIS)

    Sommer, Silke

    2010-01-01

    This paper presents the modeling of deformation and fracture behavior of resistance spot welded joints in DP600 steel sheets. Spot welding is still the most commonly used joining technique in automotive engineering. In overloading situations like crash joints are often the weakest link in a structure. For those reasons, crash simulations need reliable and applicable tools to predict the load bearing capacity of spot welded components. Two series of component tests with different spot weld diameters have shown that the diameter of the weld nugget is the main influencing factor affecting fracture mode (interfacial or pull-out fracture), load bearing capacity and energy absorption. In order to find a correlation between nugget diameter, load bearing capacity and fracture mode, the spot welds are simulated with detailed finite element models containing base metal, heat affected zone and weld metal in lap-shear loading conditions. The change in fracture mode from interfacial to pull-out or peel-out fracture with growing nugget diameter under lap-shear loading was successfully modeled using the Gologanu-Leblond model in combination with the fracture criteria of Thomason and Embury. A small nugget diameter is identified to be the main cause for interfacial fracture. In good agreement with experimental observations, the calculated pull-out fracture initiates in the base metal at the boundary to the heat affected zone.

  20. Interaction between depolarization effects, interface layer, and fatigue behavior in PZT thin film capacitors

    Science.gov (United States)

    Böttger, U.; Waser, R.

    2017-07-01

    The existence of non-ferroelectric regions in ferroelectric thin films evokes depolarization effects leading to a tilt of the P(E) hysteresis loop. The analysis of measured hysteresis of lead zirconate titanate (PZT) thin films is used to determine a depolarization factor which contains quantitative information about interfacial layers as well as ferroelectrically passive zones in the bulk. The derived interfacial capacitance is smaller than that estimated from conventional extrapolation techniques. In addition, the concept of depolarization is used for the investigation of fatigue behavior of PZT thin films indicating that the mechanism of seed inhibition, which is responsible for the effect, occurs in the entire film.

  1. Mechanical behavior of 9Cr-1Mo-1V steel due to creep fatigue deformation

    International Nuclear Information System (INIS)

    Kim, Sang Tae; Kim, Jae Kyoung; Lee, Hak Sun; Oh, Sang Hyun; Kwun, Sook In; Kim, Chung Seok

    2005-01-01

    Creep-fatigue tests with trapezoid load wave were performed on a 9Cr-1Mo-1V steel at high temperature(550 .deg. C). Trapezoid load wave is considering about hold time for creep effects. we could find out some information in the relationship between number of cycles to failure and hold time. The number of cycles to failure depended on hold time. The cyclic behavior of 9Cr-1Mo-1V steel was characterized by cyclic softening with increasing number of cycles in high temperature. Also we could observe some cavity in the specimens. The size of cavity was different from each hold time

  2. Experimental investigation on low cycle fatigue and creep-fatigue interaction of DZ125 in different dwell time at elevated temperatures

    International Nuclear Information System (INIS)

    Shi Duoqi; Liu Jinlong; Yang Xiaoguang; Qi Hongyu; Wang Jingke

    2010-01-01

    Research highlights: → This paper has researched creep-fatigue interaction of directionally solidified superalloy DZ125 with different dwell time at high temperature combined with micro-mechanism by experiment. → The results indicated that the life of creep-fatigue decreases as dwell time increases, but the life of this alloy was almost unchanged when dwell time exceeds a critical value at 850 deg. C. - Abstract: The low cycle fatigue (LCF) and creep-fatigue tests have been conducted with directionally solidified nickel-based superalloy DZ125 at 850 and 980 deg. C to study the creep-fatigue interaction behavior of alloy with different dwell time. On the average, the life of creep-fatigue tests are about 70% less than the life of LCF tests under the same strain range at 850 deg. C. The life of creep-fatigue decreases as dwell time increases, but the life of this alloy was almost unchanged when dwell time exceeds a critical value at 850 deg. C. Scanning electron microscope (SEM) analyses of the fracture revealed that the fracture modes were influenced by different way of loading. In case of LCF, the primary fracture mode was transgranular, while in case of creep-fatigue, the primary fracture mode was mixed with transgranular and intergranular. There were also obvious different morphologies of surface crack between LCF and creep-fatigue.

  3. The Effects of Hot Bending on the Low Cycle Fatigue Behaviors of 347 SS in PWR Primary Environment

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ho-Sub; Hong, Jong-Dae; Lee, Junho; Jang, Changheui [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-10-15

    Fatigue damage could be significant for some locations, especially the welds and bends where stress concentration is typically high. As a possible solution, a large radius hot-bending method has been suggested to eliminate some weld joints and all tight bends. However, for the hot-bending process which involves a high temperature thermal cycle, there is a concern about changes in mechanical properties including low cycle fatigue behaviors. In APR1400, Type 347 SS have been used as surge line pipes. Therefore, to verify the applicability of hot-bending on 347 SS surge line pipes, an environmental fatigue test program was initiated. In this paper, the preliminary results of the on-going test program are introduced. Also, the low cycle fatigue behaviors of 347 SS are compared with those of other grade of stainless steels. The effects of hot bending on the low cycle fatigue behavior of 347 SS were quantitatively evaluated. The fatigue life was compared with the estimated values per NUREG 6909 rev. 1. There are no distinct differences between NUREG 6909 and LCF tests. According to fractography and cross section analysis in progress, basically, the reduction of LCF life of 347 SS in PWR water was caused by operation of HIC mechanism. The cyclic stress responses shows that there is no secondary hardening in 330 .deg.C air and PWR water.

  4. Thermo-mechanical fatigue behavior of the intermetallic gamma-TiAl alloy TNB-V5 with different microstructures

    International Nuclear Information System (INIS)

    Roth, M; Biermann, H

    2010-01-01

    The cyclic deformation and fatigue behavior of the γ-TiAl alloy TNB-V5 is studied under thermo-mechanical load for the three technically important microstructures Fully-Lamellar (FL), Near-Gamma (NG) and Duplex (DP), respectively. Thus, thermo-mechanical fatigue (TMF) tests were carried out with different temperature-strain cycles, different temperature ranges from 400 0 C to 800 0 C and with two different strain ranges. Cyclic deformation curves, stress-strain hysteresis loops and fatigue lives are presented. The type of microstructure shows a surprisingly small influence on the cyclic deformation and fatigue behavior under TMF conditions. For a general life prediction the damage parameter of Smith, Watson and Topper P SWT is well suitable, if the testing and the application temperature ranges, respectively, include temperatures above the ductile-brittle transition temperature (approx. 750 0 C). If the maximum temperature is below that temperature, the brittle materials' behavior yields a high scatter of fatigue lives and a low slope of the fatigue life curve and therefore the damage parameter P SWT cannot be applied for the live prediction.

  5. Thermo-mechanical fatigue behavior of the intermetallic gamma-TiAl alloy TNB-V5 with different microstructures

    Energy Technology Data Exchange (ETDEWEB)

    Roth, M [now at IAV GmbH, Kauffahrtei 25, D-09120 Chemnitz (Germany); Biermann, H, E-mail: marcel.roth@iav.d [TU Bergakademie Freiberg, Institute for Materials Engineering, Gustav-Zeuner-Strasse 5, D-09599 Freiberg (Germany)

    2010-07-01

    The cyclic deformation and fatigue behavior of the {gamma}-TiAl alloy TNB-V5 is studied under thermo-mechanical load for the three technically important microstructures Fully-Lamellar (FL), Near-Gamma (NG) and Duplex (DP), respectively. Thus, thermo-mechanical fatigue (TMF) tests were carried out with different temperature-strain cycles, different temperature ranges from 400{sup 0}C to 800{sup 0}C and with two different strain ranges. Cyclic deformation curves, stress-strain hysteresis loops and fatigue lives are presented. The type of microstructure shows a surprisingly small influence on the cyclic deformation and fatigue behavior under TMF conditions. For a general life prediction the damage parameter of Smith, Watson and Topper P{sub SWT} is well suitable, if the testing and the application temperature ranges, respectively, include temperatures above the ductile-brittle transition temperature (approx. 750{sup 0}C). If the maximum temperature is below that temperature, the brittle materials' behavior yields a high scatter of fatigue lives and a low slope of the fatigue life curve and therefore the damage parameter P{sub SWT} cannot be applied for the live prediction.

  6. Fracture toughness behavior of irradiated stainless steel in PWR systems

    Energy Technology Data Exchange (ETDEWEB)

    Xu, H.; Fyfitch, S. [AREVA NP Inc., Lynchburg, Pennsylvania (United States); Tang, H.T. [Electric Power Research Inst., Palo Alto, California (United States)

    2007-07-01

    Data from available research programs were collected and evaluated by the Electric Power Research Institute (EPRI) Materials Reliability Program (MRP) to determine the relationship between fracture toughness and neutron fluence for conditions representative of pressurized water reactor (PWR) conditions. It is shown that the reduction of fracture toughness with increasing neutron dose in both boiling water reactors (BWRs) and PWRs is consistent with that observed in fast reactors. The lower bound fracture toughness observed for irradiated stainless steels in PWRs is 38 MPa{radical}m (34.6 ksi{radical}in) at neutron exposures greater than 6.7 X 10{sup 21} n/cm{sup 2} (E > 1.0 MeV) or approximately 10 dpa. For such levels of fracture toughness, it is recommended that linear-elastic fracture mechanics (LEFM) analyses be considered for design and operational analyses. The results from this study can be used by the nuclear industry to assess the effects of irradiation on stainless steels in PWR systems. (author)

  7. Strength and fracture behavior of aluminide matrix composites with ceramic fibers

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, M.; Suganuma, K.; Niihara, K.

    1999-07-01

    This paper investigates the fracture behavior of FeAl and Ni{sub 3}Al matrix composites with ceramic continuous fibers 8.5--10 {micro}m in diameter. When stress is applied to these composites, multiple-fracture of fibers predominantly occurs before matrix cracking, because the load carried by the fibers reaches their fracture strength. Fragments which remain longer than the critical length can provide significant strengthening through load bearing even though fiber breaking has occurred. The ultimate fracture strength of the composites also depends on stress relaxation by plastic deformation of the matrix at a crack tip in the multiple-fractured fibers. Ductilizing of the matrix by B doping improves the ultimate strength at ambient temperatures in both composites. However, their mechanical properties at elevated temperatures are quite different. In the case of Ni{sub 3}Al matrix composites, embrittlement of the matrix is undesirable for high strength and reliability at 873--973 K.

  8. Low cycle fatigue behavior of ITER-like divertor target under DEMO-relevant operation conditions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Muyuan; Werner, Ewald [Lehrstuhl für Werkstoffkunde und Werkstoffmechanik, Technische Universität München, Boltzmannstr. 15, 85748 Garching (Germany); You, Jeong-Ha, E-mail: you@ipp.mpg.de [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching (Germany)

    2015-01-15

    Highlights: • LCF behavior of the cooling tube and the interlayer of an ITER-like divertor target is studied. • For the cooling tube, LCF failure will not be an issue under an HHF load of up to 18 MW/m{sup 2}. • Plastic strain in the interlayer is concentrated at the free surface edge of the bond interface. • The predicted LCF lifetime of the interlayer may not meet the design requirement. - Abstract: In this work the low cycle fatigue (LCF) behavior of the copper alloy cooling tube and the copper interlayer of an ITER-like divertor target is reported for nine different combinations of loading and cooling conditions relevant to DEMO divertor operation. The LCF lifetime is presented as a function of loading and cooling conditions considered here by means of cyclic plasticity simulation and using LCF data of materials relevant for ITER. The numerical predictions indicate, that fatigue failure will not be an issue for the copper alloy tube under a high heat flux (HHF) load of up to 18 MW/m{sup 2} as long as it preserves its initial strength. In contrast, the copper interlayer exhibits significant plastic dissipation at the free surface edge of the bond interface adjacent to the cooling tube, where the LCF lifetime is predicted to be below 3000 load cycles for HHF loads higher than 15 MW/m{sup 2}. Most of the bulk region of the copper interlayer away from the free surface edge does not experience severe plastic fatigue and hence does not pose any critical concern as the LCF lifetime is predicted to be at least 7000 load cycles. LCF lifetime decreases as HHF load is increased or coolant temperature is decreased.

  9. Influence of sodium on the low-cycle fatigue behavior of types 304 and 316 stainless steel

    International Nuclear Information System (INIS)

    Smith, D.L.; Zeman, G.J.; Natesan, K.; Kassner, T.F.

    1976-01-01

    Fatigue tests in sodium were conducted to investigate the influence of a high-temperature sodium environment on the low-cycle fatigue behavior of Types 304 and 316 stainless steel. The effects of testing in a sodium environment as well as long-term sodium exposure were investigated. The fatigue tests were conducted at 600 and 700 0 C in sodium of controlled purity, viz., approximately 1 ppM oxygen and 0.4 ppM carbon, at a strain rate of 4 x 10 -3 s -1 . The fatigue life of annealed Type 316 stainless steel is substantially greater in sodium than when tested in air; however, the fatigue life of annealed Type 304 stainless steel is altered much less when tested in sodium. A 1512-h preexposure to sodium had no significant effect on the fatigue life of Type 316 stainless steel tested in sodium. However, a similar exposure substantially increased the fatigue life of Type 304 stainless steel in sodium. 10 fig

  10. Effect of strain-induced martensitic transformation on high cycle fatigue behavior in cyclically-prestrained type 304

    International Nuclear Information System (INIS)

    Uematsu, Yoshihiko; Kakiuchi, Toshifumi; Akita, Masayuki; Nakajima, Masaki; Nakamura, Yuki; Yajima, Takumi

    2013-01-01

    The effects of the cyclic prestrain on the fatigue behavior in type 304 austenitic stainless steel were investigated. Rotating bending fatigue tests have been performed in laboratory air using the specimens subjected to ±5% cyclic prestrain at room temperature (R.T.) and -5°C. Martensitic phase volume fraction of the prestrained specimen at -5°C was 48% and larger than 3.8% at R.T. The prestrained specimens exhibited higher fatigue strengths than the as-received ones, and larger volume fraction of martensitic phase resulted in the higher fatigue limit. EBSD analysis revealed that the martensitic phases were more uniformly distributed in the austenitic matrix in the cyclically-prestrained specimens than in the monotonically-prestrained ones. Fatigue crack initiation from inclusion was observed only in the cyclically-prestrained specimens at -5°C. High volume fraction and uniform distribution of martensitic phase induced the transition of crack initiation mechanism and led to the higher fatigue limit. In type 304 stainless steel with high volume fraction of strain-induced martensitic phase, the prediction of fatigue limit based on Vickers hardness could give unconservative results. (author)

  11. Evaluation of Fatigue Behavior and Surface Characteristics of Aluminum Alloy 2024 T6 After Electric Discharge Machining

    Science.gov (United States)

    Mehmood, Shahid; Shah, Masood; Pasha, Riffat Asim; Sultan, Amir

    2017-10-01

    The effect of electric discharge machining (EDM) on surface quality and consequently on the fatigue performance of Al 2024 T6 is investigated. Five levels of discharge current are analyzed, while all other electrical and nonelectrical parameters are kept constant. At each discharge current level, dog-bone specimens are machined by generating a peripheral notch at the center. The fatigue tests are performed on four-point rotating bending machine at room temperature. For comparison purposes, fatigue tests are also performed on the conventionally machined specimens. Linearized SN curves for 95% failure probability and with four different confidence levels (75, 90, 95 and 99%) are plotted for each discharge current level as well as for conventionally machined specimens. These plots show that the electric discharge machined (EDMed) specimens give inferior fatigue behavior as compared to conventionally machined specimen. Moreover, discharge current inversely affects the fatigue life, and this influence is highly pronounced at lower stresses. The EDMed surfaces are characterized by surface properties that could be responsible for change in fatigue life such as surface morphology, surface roughness, white layer thickness, microhardness and residual stresses. It is found that all these surface properties are affected by changing discharge current level. However, change in fatigue life by discharge current could not be associated independently to any single surface property.

  12. Quasi-static analysis of elastic behavior for some systems having higher fracture densities.

    Energy Technology Data Exchange (ETDEWEB)

    Berryman, J.G.; Aydin, A.

    2009-10-15

    Elastic behavior of geomechanical systems with interacting (but not intersecting) fractures is treated using generalizations of the Backus and the Schoenberg-Muir methods for analyzing layered systems whose layers are intrinsically anisotropic due to locally aligned fractures. By permitting the axis of symmetry of the locally anisotropic compliance matrix for individual layers to differ from that of the layering direction, we derive analytical formulas for interacting fractured regions with arbitrary orientations to each other. This procedure provides a systematic tool for studying how contiguous, but not yet intersecting, fractured domains interact, and provides a direct (though approximate) means of predicting when and how such interactions lead to more dramatic weakening effects and ultimately to failure of these complicated systems. The method permits decomposition of the system elastic behavior into specific eigenmodes that can all be analyzed, and provides a better understanding about which of these specific modes are expected to be most important to the evolving failure process.

  13. Fracture behavior of C/SiC composites at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Dong Hyun; Lee, Jeong Won; Kim, Jae Hoon; Shin, Ihn Cheol; Lim, Byung Joo [Chungnam National University, Daejeon (Korea, Republic of)

    2017-08-15

    The fracture behavior of carbon fiber-reinforced silicon carbide (C/SiC) composites used in rocket nozzles has been investigated under tension, compression, and fracture conditions at room temperature, 773 K and 1173 K. The C/SiC composites used in this study were manufactured by liquid silicon infiltration process at ~1723 K. All experiments were conducted using two types of specimens, considering fiber direction and oxidation condition. Experimental results show that temperature, fiber direction, and oxidation condition affect the behavior of C/SiC composites. Oxidation was found to be the main factor that changes the strength of C/SiC composites. By applying an anti-oxidation coating, the tensile and compressive strengths of the C/SiC composites increased with temperature. The fracture toughness of the C/SiC composites also increased with increase temperature. A fractography analysis of the fractured specimens was conducted using a scanning electron microscope.

  14. Influence of weld discontinuities on strain controlled fatigue behavior of 308 stainless steel weld metal

    International Nuclear Information System (INIS)

    Bhanu Sankara Rao, K.; Valsan, M.; Sandhya, R.; Mannan, S.L.; Rodriguez, P.

    1994-01-01

    Detailed investigations have been performed for assessing the importance of weld discontinuities in strain controlled low cycle fatigue (LCF) behavior of 308 stainless steel (SS) welds. The LCF behavior of 308 SS welds containing defects was compared with that of type 304 SS base material and 308 SS sound weld metal. Weld pads were prepared by shielded metal arc welding process. Porosity and slag inclusions were introduced deliberately into the weld metal by grossly exaggerating the conditions normally causing such defects. Total axial strain controlled LCF tests have been conducted in air at 823 K on type 304 SS base and 308 SS sound weld metal employing strain amplitudes in the range from ±0.25 to ±0.8 percent. A single strain amplitude of ±0.25 percent was used for all the tests conducted on weld samples containing defects. The results indicated that the base material undergoes cyclic hardening whereas sound and defective welds experience cyclic softening. Base metal showed higher fatigue life than sound weld metal at all strain amplitudes. The presence of porosity and slag inclusions in the weld metal led to significant reduction in life. Porosity on the specimen surface has been found to be particularly harmful and caused a reduction in life by a factor of seven relative to sound weld metal

  15. Near-threshold fatigue crack growth behavior of AISI 316 stainless steel

    International Nuclear Information System (INIS)

    Tobler, R.L.

    1986-01-01

    The near-threshold fatigue behavior of an AISI 316 alloy was characterized using a newly developed, fully automatic fatigue test apparatus. Significant differences in the near-threshold behavior at temperatures of 295 and 4 K are observed. At 295 K, where the operationally defined threshold at 10 -10 m/cycle is insensitive contains stress ratio and strongly affected by crack closure, the effective threshold stress intensity factor (ΔK/sub Th/)/sub eff/) is about 4.65 MPa m/sub 1/2/ at R = 0.3. At 4 K, the threshold is higher, crack closure is less pronounced, and there is a stress ratio dependency: (ΔK/sub Th/)/sub eff/ is 5.1 MPa m/sup 1/2/ at R = 0.3 and 6.1 MPa m/sup 1/2/ at R - 0.1. There is also a significant difference in the form of the da/dN-versus-ΔK curves on log-log coordinates: at 4 K the curve has the expected sigmoidal shape, but at 295 K the trend is linear over the region of da/dN from 10 -7 to 10 -10 m/cycle. Other results suggest that the near-threshold measurements of a 6.4-mm-thick specimen of this alloy are insensitive to cyclic test frequency below 40 Hz

  16. Evaluation of Fatigue Behavior in Dental Implants from In Vitro Clinical Tests: A Systematic Review

    Directory of Open Access Journals (Sweden)

    Rosa Rojo

    2018-05-01

    Full Text Available In the area of dentistry, there is a wide variety of designs of dental implant and materials, especially titanium, which aims to avoid failures and increase their clinical durability. The purpose of this review was to evaluate fatigue behavior in different connections and implant materials, as well as their loading conditions and response to failure. In vitro tests under normal and dynamic loading conditions evaluating fatigue at implant and abutment connection were included. A search was conducted in PubMed, Scopus, and Science Direct. Data extraction was performed independently by two reviewers. The quality of selected studies was assessed using the Cochrane Handbook proposed by the tool for clinical trials. Nineteen studies were included. Fourteen studies had an unclear risk and five had high risk of bias. Due to the heterogeneity of the data and the evaluation of the quality of the studies, meta-analysis could not be performed. Evidence from this study suggests that both internal and morse taper connections presented a better behavior to failure. However, it is necessary to unify criteria in the methodological design of in vitro studies, following methodological guidelines and establishing conditions that allow the homogenization of designs in ISO (International Organization for Standardization standards.

  17. Creep-fatigue behavior of 2 1/4Cr-1Mo steel at 5500C in air and vacuum

    International Nuclear Information System (INIS)

    Asayama, T.; Cheng, S.Z.; Asada, Y.; Mitsuhashi, S.; Tachibana, Y.

    1987-01-01

    Following studies on creep-fatigue behaviors of 304 steel at 650 0 C (Asada et al (1980) and Morishita et al (1984), (1985), (1987)), 2 1/4Cr-1Mo steel was studied on its creep-fatigue behaviors at 550 0 C in air and vacuum of 100 and 0.1 μPa. The present study intends to give a base for an evaluation of the environmental effect through obtaining a pure creep-fatigue behavior of this steel which is free from the environmental effect. In the previous studies on 304 steel, tests were conducted in three kinds of environment of air, 100 and 0.1 μPa vacuum. It seemed to be plausible that the 0.1 μPa vacuum shows the pure creep-fatigue behavior of 304 steel at 650 0 C which is almost completely free from the environment. A creep-fatigue life in 0.1 μPa vacuum is almost one order of magnitude higher than that in air. The 100 μPa vacuum suggested that the environmental effect of air still remains but is so small that a creep-fatigue life in 100 μPa is same to that in 0.1 μPa in some strain wave forms. The present study intends to examine if similar observations are obtained with 2 1/4Cr-1Mo steel at 550 0 C. This paper describes the analysis of the overstress and damages, in addition to a creep-fatigue result. (orig.GL)

  18. In-situ Investigation of the Fracture Behaviors of 2195-T8 Aluminum-Lithium alloy

    Directory of Open Access Journals (Sweden)

    Wang Liang

    2016-01-01

    Full Text Available In this paper, the tensile crack initiation and propagation behavior of 2195-T8 Aluminum-Lithium alloy was studied by in situ scanning electron microscope observation at room temperature. It was found that cracks initiated at second phases which propagated along the grain boundaries only as T1 phases could retard crack growth inside grains. With further increase of strain, within the grain a large number of slip bands were produced, resulting in the deflection of the grains, which leaded to transgranular fracture at last. SEM examination show both intergranular and transgranular fracture surface morphology indicating that the 2195-T8 alloy revealed a mix mechanism for the fracture.

  19. Mechanical properties and fracture behavior of single-layer phosphorene at finite temperatures

    International Nuclear Information System (INIS)

    Sha, Zhen-Dong; Pei, Qing-Xiang; Ding, Zhiwei; Zhang, Yong-Wei; Jiang, Jin-Wu

    2015-01-01

    Phosphorene, a new two-dimensional (2D) material beyond graphene, has attracted great attention in recent years due to its superior physical and electrical properties. However, compared to graphene and other 2D materials, phosphorene has a relatively low Young’s modulus and fracture strength, which may limit its applications due to possible structure failures. For the mechanical reliability of future phosphorene-based nanodevices, it is necessary to have a deep understanding of the mechanical properties and fracture behaviors of phosphorene. Previous studies on the mechanical properties of phosphorene were based on first principles calculations at 0 K. In this work, we employ molecular dynamics simulations to explore the mechanical properties and fracture behaviors of phosphorene at finite temperatures. It is found that temperature has a significant effect on the mechanical properties of phosphorene. The fracture strength and strain reduce by more than 65% when the temperature increases from 0 K to 450 K. Moreover, the fracture strength and strain in the zigzag direction is more sensitive to the temperature rise than that in the armchair direction. More interestingly, the failure crack propagates preferably along the groove in the puckered structure when uniaxial tension is applied in the armchair direction. In contrast, when the uniaxial tension is applied in the zigzag direction, multiple cracks are observed with rough fracture surfaces. Our present work provides useful information about the mechanical properties and failure behaviors of phosphorene at finite temperatures. (paper)

  20. Why ductile fracture mechanics

    International Nuclear Information System (INIS)

    Ritchie, R.O.

    1983-01-01

    Until recently, the engineering application of fracture mechanics has been specific to a description of macroscopic fracture behavior in components and structural parts which remain nominally elastic under loading. While this approach, termed linear elastic fracture mechanics, has been found to be invaluable for the continuum analysis of crack growth in brittle and high strength materials, it is clearly inappropriate for characterizing failure in lower strength ductile alloys where extensive inelastic deformation precedes and accompanies crack initiation and subsequent propagation. Accordingly, much effort has been devoted in recent years toward the development of nonlinear or ductile fracture mechanics methodology to characterize fracture behavior under elastic/plastic conditions; an effort which has been principally motivated by problems in nuclear industry. In this paper, the concepts of ductile (elastic/plastic) fracture mechanics are introduced and applied to the problem of both stationary and nonstationary cracks. Specifically, the limitations inherent in this approach are defined, together with a description of the microstructural considerations and applications relevant to the failure of ductile materials by fracture, fatigue, and creep

  1. FATIGUE CRACK PROPAGATION THROUGH AUSTEMPERED DUCTILE IRON MICROSTRUCTURE

    Directory of Open Access Journals (Sweden)

    Lukáš Bubenko

    2010-10-01

    Full Text Available Austempered ductile iron (ADI has a wide range of application, particularly for castings used in automotive and earth moving machinery industries. These components are usually subjected to variable dynamic loading that may promote initiation and propagation of fatigue cracks up to final fracture. Thus, it is important to determine the fatigue crack propagation behavior of ADI. Since fatigue crack growth rate (da/dN vs. stress intensity factor K data describe fatigue crack propagation resistance and fatigue durability of structural materials, da/dN vs. Ka curves of ADI 1050 are reported here. The threshold amplitude of stress intensity factor Kath is also determined. Finally, the influence of stress intensity factor amplitude to the character of fatigue crack propagation through the ADI microstructure is described.

  2. Study on Tensile Fatigue Behavior of Thermal Butt Fusion in Safety Class III High-Density Polyethylene Buried Piping in Nuclear Power Plants

    International Nuclear Information System (INIS)

    Kim, Jong Sung; Lee, Young Ju; Oh, Young Jin

    2015-01-01

    High-density polyethylene (HDPE) piping, which has recently been applied to safety class III piping in nuclear power plants, can be butt-joined through the thermal fusion process, which heats two fused surfaces and then subject to axial pressure. The thermal fusion process generates bead shapes on the butt fusion. The stress concentrations caused by the bead shapes may reduce the fatigue lifetime. Thus, investigating the effect of the thermal butt fusion beads on fatigue behavior is necessary. This study examined the fatigue behavior of thermal butt fusion via a tensile fatigue test under stress-controlled conditions using finite element elastic stress analysis. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low-cycle fatigue region while having a negligible effect in the medium- and high-cycle fatigue regions

  3. Study on Tensile Fatigue Behavior of Thermal Butt Fusion in Safety Class III High-Density Polyethylene Buried Piping in Nuclear Power Plants

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jong Sung; Lee, Young Ju [Sunchon National University, Suncheon (Korea, Republic of); Oh, Young Jin [KEPCO E and C, Yongin (Korea, Republic of)

    2015-01-15

    High-density polyethylene (HDPE) piping, which has recently been applied to safety class III piping in nuclear power plants, can be butt-joined through the thermal fusion process, which heats two fused surfaces and then subject to axial pressure. The thermal fusion process generates bead shapes on the butt fusion. The stress concentrations caused by the bead shapes may reduce the fatigue lifetime. Thus, investigating the effect of the thermal butt fusion beads on fatigue behavior is necessary. This study examined the fatigue behavior of thermal butt fusion via a tensile fatigue test under stress-controlled conditions using finite element elastic stress analysis. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low-cycle fatigue region while having a negligible effect in the medium- and high-cycle fatigue regions.

  4. Determination of rat vertebral bone compressive fatigue properties in untreated intact rats and zoledronic-acid-treated, ovariectomized rats

    NARCIS (Netherlands)

    Brouwers, J.E.M.; Ruchselman, M.; Rietbergen, van B.; Bouxsein, M.L.

    2009-01-01

    Summary Compressive fatigue properties of whole vertebrae, which may be clinically relevant for osteoporotic vertebral fractures, were determined in untreated, intact rats and zoledronic-acid-treated, ovariectomized rats. Typical fatigue behavior was found and was similar to that seen in other

  5. Correlation of Stress Concentration Factors for T-Welded Connections – Finite Element Simulations and Fatigue Behavior

    Directory of Open Access Journals (Sweden)

    Gerardo Terán Méndez

    Full Text Available Abstract The stress concentration factors (SCFs in welded connections usually occur at zones with high stress levels. Stress concentrations reduce the fatigue behavior of welded connections in offshore structures and cracking can develop. By using the grinding technique, cracking can be eliminated. Stress concentration factors are defined as a ratio of maximum stress at the intersection to nominal stress on the brace. Defining the stress concentration factor is an important stage in the fatigue behavior of welded connections. Several approaches have evolved for designing structures with the classical S-N approach for estimating total life. This work correlates to the stress concentration factors of T-welded connections and the fatigue behavior. Stress concentration factors were computed with the finite element employing 3D T-welded connections with intact and grinding depth conditions. Then, T-welded connections were constructed with A36 plate steel and welded with E6013 electrodes to obtain the stress-life (S-N approach. The methodology from previous works was used to compute the SCF and fabricate the T-welded connections. The results indicated that the grinding process could restore the fatigue life of the T-welded connections for SCFs values in the range of 1.29. This value can be considered to be a low SCF value in T-welded connection. However, for higher SCF values, the fatigue life decreased, compromising and reducing the structural integrity of the T-welded connections.

  6. Stress-related psychosocial factors at work, fatigue, and risky driving behavior in bus rapid transport (BRT) drivers.

    Science.gov (United States)

    Useche, Sergio A; Ortiz, Viviola Gómez; Cendales, Boris E

    2017-07-01

    There is consistent scientific evidence that professional drivers constitute an occupational group that is highly exposed to work related stressors. Furthermore, several recent studies associate work stress and fatigue with unsafe and counterproductive work behaviors. This study examines the association between stress-related work conditions of Bus Rapid Transport (BRT) drivers and risky driving behaviors; and examines whether fatigue is a mechanism that mediates the association between the two. A sample of 524 male Bus Rapid Transit (BRT) operators were drawn from four transport companies in Bogotá, Colombia. The participants answered a survey which included an adapted version of the Driver Behavior Questionnaire (DBQ) for BRT operators, as well as the Effort-Reward Imbalance and Job Content Questionnaires, the Subjective Fatigue subscale of the Checklist Individual Strength (CIS) and the Need for Recovery after Work Scale (NFR). Utilizing Structural Equation Models (SEM) it was found that risky driving behaviors in BRT operators could be predicted through job strain, effort-reward imbalance and social support at work. It was also found that fatigue and need for recovery fully mediate the associations between job strain and risky driving, and between social support and risky driving, but not the association between effort/reward imbalance (ERI) and risky driving. The results of this study suggest that a) stress related working conditions (Job Strain, Social Support and ERI) are relevant predictors of risky driving in BRT operators, and b) that fatigue is the mechanism which links another kind of stress related to working conditions (job strain and low social support) with risky driving. The mechanism by which ERI increases risky driving in BRT operators remains unexplained. This research suggests that in addition to the individual centered stress-reduction occupational programs, fatigue management interventions aimed to changing some working conditions may reduce

  7. Fracture behavior and deformation mechanisms under fast neutron irradiation

    International Nuclear Information System (INIS)

    Boutard, J.L.; Dupouy, J.M.

    1980-09-01

    We have established the out-of-pile and in-pile deformation mechanism maps of a 316 stainless steel irradiated in a fast reactor. The knowledge of the dominating deformation mechanism either in post irradiation creep experiments or during the in-pile steady state operating conditions allows to rationalize the apparent discrepancy between the very low out-of-pile ductility and the rather high plastic diametral strains which are obtained in the fast reactor environment without fracture

  8. Investigation of dynamic fracture behavior in functionally graded materials

    International Nuclear Information System (INIS)

    Yang, X B; Qin, Y P; Zhuang, Z; You, X C

    2008-01-01

    The fast running crack in functionally graded materials (FGMs) is investigated through numerical simulations under impact loading. Some fracture characterizations such as crack propagation and arrest are evaluated by the criterion of the crack tip opening angle. Based on the experimental results, the whole propagation process of the fast running crack is simulated by the finite element program. Thus, the dynamic fracture parameters can be obtained during the crack growing process. In this paper, the crack direction is assumed to be the graded direction of the materials, and the property gradation in FGMs is considered by varying the elastic modulus exponentially along the graded direction and keeping the mass density and Poisson's ratio constant. The influences of the non-homogeneity, the loading ratio and the crack propagation speed on the dynamic fracture response of FGMs are analyzed through the test and numerical analysis. Considering the potential application of FGMs in natural-gas transmission engineering, a functionally graded pipeline is designed to arrest the fast running crack for a short period in high pressure large diameter natural-gas pipelines

  9. Fracture behavior of short circumferentially surface-cracked pipe

    International Nuclear Information System (INIS)

    Krishnaswamy, P.; Scott, P.; Mohan, R.

    1995-11-01

    This topical report summarizes the work performed for the Nuclear Regulatory Comniission's (NRC) research program entitled ''Short Cracks in Piping and Piping Welds'' that specifically focuses on pipes with short, circumferential surface cracks. The following details are provided in this report: (i) material property deteminations, (ii) pipe fracture experiments, (iii) development, modification and validation of fracture analysis methods, and (iv) impact of this work on the ASME Section XI Flaw Evaluation Procedures. The material properties developed and used in the analysis of the experiments are included in this report and have been implemented into the NRC's PIFRAC database. Six full-scale pipe experiments were conducted du