The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Yukitaka Murakami - One of the best experts on this subject based on the ideXlab platform.
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Effect of Hydrogen on High Cycle Fatigue Failure of High Strength Steel, SCM435
Journal of The Society of Materials Science Japan, 2020Co-Authors: Yukitaka Murakami, Junji NagataAbstract:High cycle fatigue properties of high strength steel were investigated. In the Fuel Cell(FC) system, various metals are used in hydrogen environment under cyclic loading. In this study, hydrogen was artificially charged into specimen of a Cr-Mo high strength steel, and the fatigue properties were compared with those of the specimens without hydrogen charge. Fatigue strength and fatigue life decreased with increasing hydrogen content. The Fracture Origin of hydrogen charged specimens showed smaller ODAs than as-heat-treated specimens. It implies that the fatigue threshold of the microstructure which contains high hydrogen content is much lower than that of the as-heat-treated microstructure, and the upper bound of the critical hydrogen content level resulting ODA lies between 1.5ppm and 2.3ppm. Hydrogen desorption properties near the Fracture Origin were measured with Secondary Ion Mass Spectrometer(SIMS) and Thermal Desorption Spectrometer(TDS). Measurements with TDS and SIMS revealed that hydrogen trapped in microstructure is diffusive one and the hydrogen trapped by inclusion is non-diffusive one.
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Mechanism of fatigue failure in ultralong life regime
Fatigue & Fracture of Engineering Materials & Structures, 2002Co-Authors: Yukitaka Murakami, N. N. Yokoyama, Junji NagataAbstract:The fatigue Fracture surfaces of specimens of heat treated hard steels which failed in the regime of N =10 5 to 5 x 10 8 cycles , were investigated by optical microscopy and SEM. Specimens having a longer fatigue life had a particular morphology beside the inclusion at the Fracture Origin. The particular morphology looked optically dark and in the previous paper it was named the Optically Dark Area, ODA. The roughness inside ODA is larger than outside ODA. The relative size of the ODA to the size of the inclusion at the Fracture Origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of ultra long life fatigue failure. Direct evidences of existence of hydrogen at the inclusion at Fracture Origin are presented. It is presumed that the ODA is made by the cyclic stress coupled with the hydrogen which is trapped by the inclusion at the Fracture Origin. To verify the influence of hydrogen, specimens containing different levels of hydrogen were prepared by different heat treatments. The results obtained by fatigue tests of these specimens suggest that the hydrogen trapped by inclusions is a crucial factor which causes the ultra long fatigue failure of high strength steels. Aspects of the double S-N curve are also discussed in terms of experimental methods, specimen size and statistical distribution of inclusions sizes.
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Mechanism of superlong fatigue failure in the regime of N>107 cycles and fractography of the Fracture surface
Transactions of the Japan Society of Mechanical Engineers. A, 2000Co-Authors: Yukitaka Murakami, Toru Ueda, Tetsushi Nomoto, Yasuo MurakamiAbstract:In order to elucidate the mechanism of superlong fatigue failure in the regime of N>107 cycles, the Fracture surfaces of specimens of heat treated hard steel, SCM 435 and 0.46% medium carbon steel were investigated by optical microscope, SEM and AFM. It has been revealed that specimens having longer life have a particular morphology beside the inclusion at Fracture Origin. The particular morphology looks optically dark by the observation of optical microscope and it has been named the optically dark area, ODA. The ODA looks a rough area in the observation by SEM and AFM. The relative size of ODA to the size of inclusion at Fracture Origin increases with increase in fatigue life. Thus, ODA has a crucial importance for the mechanism of superlong fatigue failure. It has been assumed that ODA is made by the fatigue due to cyclic stress coupled with hydrogen which is trapped by the inclusion at Fracture Origin. To verify the hypothesis, specimens annealed at 300°C in a vacuum (VA specimens) and quenched in a vacuum (VQ specimens) are prepared to desorp the hydrogen trapped by inclusions. The specimens VA and VQ, had a much smaller ODA than conventionally heat treated specimens. Thus, it has been concluded that hydrogen trapped by inclusion is the crucial factor which causes superlong fatigue failure of high strength steels.
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On the mechanism of fatigue failure in the superlong life regime (N>107 cycles). Part 1: influence of hydrogen trapped by inclusions
Fatigue & Fracture of Engineering Materials & Structures, 2000Co-Authors: Yukitaka Murakami, Tetsushi Nomoto, Toru UedaAbstract:The Fracture surfaces of specimens of a heat-treated hard steel, namely Cr-Mo steel SCM435, which failed in the regime of N= 10 5 to 5 x 10 8 cycles, were investigated by optical microscopy and scanning electron microscopy (SEM). Specimens having a longer fatigue life had a particular morphology beside the inclusion at the Fracture Origin. The particular morphology looked optically dark when observed by an optical microscope and it was named the optically dark area (ODA). The ODA looks a rough area when observed by SEM and atomic force microscope (AFM). The relative size of the ODA to the size of the inclusion at the Fracture Origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of superlong fatigue failure. It has been assumed that the ODA is made by the cyclic fatigue stress and the synergetic effect of the hydrogen which is trapped by the inclusion at the Fracture Origin. To verify this hypothesis, in addition to conventionally heat-treated specimens (specimen QT, i.e. quenched and tempered), specimens annealed at 300 °C in a vacuum (specimen VA) and the specimens quenched in a vacuum (specimen VQ) were prepared to remove the hydrogen trapped by inclusions. The specimens VA and VQ, had a much smaller ODA than the specimen QT. Some other evidence of the influence of hydrogen on superlong fatigue failure are also presented. Thus, it is concluded that the hydrogen trapped by inclusions is a crucial factor which causes the superlong fatigue failure of high strength steels.
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Super-long life tension–compression fatigue properties of quenched and tempered 0.46% carbon steel
International Journal of Fatigue, 1998Co-Authors: Yukitaka Murakami, Masayuki Takada, Toshiyuki ToriyamaAbstract:Abstract To investigate the effect of non-metallic inclusions on fatigue properties of quenched and tempered 0.46% carbon steel (HV≅650) in super-long life fatigue range (107≤N≤5.0×108), tension–compression fatigue tests were carried out. The fatigue strength was discussed based on the area parameter model. The results obtained are: 1. Fatigue Fracture Origins were mostly at a non-metallic inclusion. 2. However, the location of the inclusion at Fracture Origin were not uniformly distributed over the specimen section due to the non-uniform distribution of residual stress induced by heat treatment. 3. The fatigue limit by the cycle N=5.0×108 can be predicted by the area parameter model, i.e. with three parameters, the Vickers hardness, HV, of the matrix, the square root of the projected area of inclusions, area , and residual stress. 4. The expected value of inclusion size area max of 0.46% carbon steel in a definite number of specimens can be estimated using the statistics of extreme values. The lower bound of the scatter of fatigue strength was predicted with the combination of the area parameter model and the value of area max .
Yoshiyuki Furuya - One of the best experts on this subject based on the ideXlab platform.
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size effects in gigacycle fatigue of high strength steel under ultrasonic fatigue testing
Procedia Engineering, 2010Co-Authors: Yoshiyuki FuruyaAbstract:Abstract Ultrasonic fatigue testing was conducted for high-strength steel using enlarged specimens with a straight section. The results showed good agreement with conventional servo-hydraulic fatigue test results under conditions where fish-eye Fracture occurs, showing the validity of ultrasonic fatigue testing using the enlarged specimens. When the results were compared with those using conventional specimens, size effects were clearly observed: enlarged specimens showed lower fatigue strength due to appearance of larger inclusions in the fish-eye Fracture Origin.
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specimen size effects on gigacycle fatigue properties of high strength steel under ultrasonic fatigue testing
Scripta Materialia, 2008Co-Authors: Yoshiyuki FuruyaAbstract:Ultrasonic fatigue testing was conducted for high-strength steel, employing enlarged specimens with a straight section. The results showed good agreement with conventional servohydraulic fatigue test results, demonstrating the validity of ultrasonic fatigue testing using these enlarged specimens under conditions where fish-eye Fractures occur. When the results were compared with those using conventional specimens, specimen size effects were clearly observed: enlarged specimens showed lower fatigue strength due to appearance of larger inclusions in the fish-eye Fracture Origin.
Andreas Krell - One of the best experts on this subject based on the ideXlab platform.
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Fracture Origin and strength in advanced pressureless sintered alumina
Journal of the American Ceramic Society, 2005Co-Authors: Andreas KrellAbstract:Advanced raw materials and shaping approaches enable the production of pressureless-sintered alumina parts where, in bending, the average maximum stress at the Fracture Origin is as high as 800 MPa. In individual specimens that Fracture at lower stresses (450-600 MPa), failure often Originates at volume flaws, as known for hot-pressed alumina with a similar strength. Also, transgranular and intergranular Fracture modes along the crack path are the same as those observed in hot-pressed alumina. If the size and the frequency of volume flaws are reduced, Fracture initiates at smaller defects in the ground surfaces and bodies with a bending strength of >800 MPa are produced without hot pressing. The grain-size dependence of grinding-induced surface damage contributes to a grain-size effect for the strength.
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Fracture Origin and Strength in Advanced Pressureless‐Sintered Alumina
Journal of the American Ceramic Society, 2005Co-Authors: Andreas KrellAbstract:Advanced raw materials and shaping approaches enable the production of pressureless-sintered alumina parts where, in bending, the average maximum stress at the Fracture Origin is as high as 800 MPa. In individual specimens that Fracture at lower stresses (450-600 MPa), failure often Originates at volume flaws, as known for hot-pressed alumina with a similar strength. Also, transgranular and intergranular Fracture modes along the crack path are the same as those observed in hot-pressed alumina. If the size and the frequency of volume flaws are reduced, Fracture initiates at smaller defects in the ground surfaces and bodies with a bending strength of >800 MPa are produced without hot pressing. The grain-size dependence of grinding-induced surface damage contributes to a grain-size effect for the strength.
Koji Hayashi - One of the best experts on this subject based on the ideXlab platform.
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Applicabilities of σm=ψKICSmf1/2 and σd-1=σo-1+Ka1/2to KIC Estimation of Hardmetals Cermets and Ceramics
Journal of The Japan Society of Powder and Powder Metallurgy, 2001Co-Authors: Yutaka Yanaba, Koji HayashiAbstract:We have proposed two new estimation methods for the Fracture toughness (KIC) of hard or brittle materials by each use of our newly derived two equations of σm=ψKICSmf1/2 and σd-1=σ0-1+Ka1/2 (σm: transverse-rupture strength of artificially un-notched test piece, ψ: shape factor, Smf: total macroscopic Fracture surface area of one test piece, σd: maximum external Fracture stress which operated on the Fracture Origin, σ0: intrinsic Fracture strength, 2a: maximum Fracture Origin diameter, K: 2σ0-1ρ-1/2, which is nearly proportional to KIC-1, ρ: Fracture Origin tip radius). And we have clarified that these two equations and two methods are applicable to some hard or brittle materials such as high speed steel, WC-16.4vol%Co hardmetal, Si3N4 ceramics and Mn-Zn ferrite.In this study, we clarified that the above two equations and two methods are applicable also to another eight kinds of hard or brittle materials such as WC-Co hardmetals, TiC- and Ti(C, N)-base cermets and Al2O3-base ceramics. The Ψ and K values for each material were clarified to be commonly about 14×103 m-3/2 and 0.70KIC-1 respectively, in the same way as for the above previously studied materials. Thus, it was concluded that the KIC of general new hard or brittle materials can be estimated from σm and Smf or σd and 2a by each use of the above two equations or modified equations where these concrete experimental values of Ψ and K were substituted, respectively.
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Applicabilities of Equations of σm=ΨKICSmf1/2 and σd-1=σ0-1+Ka1/2 to Soda Lime Glass
Journal of The Japan Society of Powder and Powder Metallurgy, 2000Co-Authors: Yoshihiro Kawaguchi, Yutaka Yanaba, Koji HayashiAbstract:We have already clarified that our derived equations of σm=ΨKICSmf1/2 as well as σd-1=σo-1+Ka1/2 are applicable to various hard or brittle sintered materials such as WC-Co hardmetal and Si3N4 ceramics (σm: flexural strength, Ψ: shape factor, KIC: Fracture toughness, Smf: total macroscopic Fracture surface area of fragments, σd: external stress which operated on the Fracture Origin, σo: intrinsic or attainable Fracture strength, K: material factor, a: half length of Fracture Origin). In this study, we investigated whether these two equations are applicable to soda lime glass which is non-crystalline and has extremely low KIC. It was found that both equations are also applicable to soda lime glass, when Smf+Sc is used in the application of the former equation, instead of Smf (Sc: the total macroscopic Fracture surface area of internally stopped cracks). The Fracture started from a visible microstructural defect with sizes of 10-30μm even for polished test pieces with σm values of 180-78 MPa. A correction was made in the derivation process of the former equation: the equation itself, however, was not changed.
Toshiyuki Toriyama - One of the best experts on this subject based on the ideXlab platform.
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Super-long life tension–compression fatigue properties of quenched and tempered 0.46% carbon steel
International Journal of Fatigue, 1998Co-Authors: Yukitaka Murakami, Masayuki Takada, Toshiyuki ToriyamaAbstract:Abstract To investigate the effect of non-metallic inclusions on fatigue properties of quenched and tempered 0.46% carbon steel (HV≅650) in super-long life fatigue range (107≤N≤5.0×108), tension–compression fatigue tests were carried out. The fatigue strength was discussed based on the area parameter model. The results obtained are: 1. Fatigue Fracture Origins were mostly at a non-metallic inclusion. 2. However, the location of the inclusion at Fracture Origin were not uniformly distributed over the specimen section due to the non-uniform distribution of residual stress induced by heat treatment. 3. The fatigue limit by the cycle N=5.0×108 can be predicted by the area parameter model, i.e. with three parameters, the Vickers hardness, HV, of the matrix, the square root of the projected area of inclusions, area , and residual stress. 4. The expected value of inclusion size area max of 0.46% carbon steel in a definite number of specimens can be estimated using the statistics of extreme values. The lower bound of the scatter of fatigue strength was predicted with the combination of the area parameter model and the value of area max .
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Fatigue. Super-Long Life Tension-Compression Fatigue Properties of Quenched and Tempered 0.46% Carbon Steel.
Journal of The Society of Materials Science Japan, 1997Co-Authors: Yukitaka Murakami, Masayuki Takada, Toshiyuki ToriyamaAbstract:To investigate the effect of non-metallic inclusions on the fatigue properties of quenched and tempered 0.46% carbon steel (HV≅650) in the super-long life fatigue range (N≤5.0×108), tension-compression fatigue tests were carried out. The fatigue strength was discussed based on the √area parameter model.The results obtained are:(1) Fatigue Fracture Origins were mostly at a non-metallic inclusion.(2) However, the locations of the inclusion at Fracture Origin were not uniformly distributed over the specimen section due to the nonuniform distribution of residual stress induced by heat treatment.(3) The fatigue limit defined by the cycle N=5.0×108 can be predicted by the √area parameter model, i.e. with three parameters, the Vickers hardness, HV, of the matrix, the square root of the projected area of inclusions, √area, and residual stress.(4) The expected value of inclusion size √areamax of 0.46% carbon steel in a definite number of specimens can be estimated using the statics of extreme values. The lower bound of the scatter of fatigue strength was predicted with the combination of the √area parameter model and the value of √areamax.
