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3/19(一)演講公告-演講人:Masahiro Goto日本大分大學教授
主題: Unique crack growth behavior of ultrafine grained copper processed by equal channel angular pressing under cyclic stresses
演講人:Masahiro Goto(Department of Mechanical Engineering, Oita University)
Purpose of the Course
The severe plastic deformation technique, such as the equal channel angular pressing (ECAP), has been used to obtain ultrafine grains (UFG), which are tenfold to hundred fold finer than those of conventional materials. These materials generally possess many unique properties such as high tensile strength, and fairly large plasticity at low temperature. These unique properties of UFG materials are due to their unusual microstructure which is often regarded as a ‘non-equilibrium’ state.
Regarding the fatigue on ECAPed UFG materials, most studies have concentrated on cyclic deformation, fatigue life, shear bands and underlying microstructural mechanisms. Since the fatigue life of machine components and structures is mainly controlled by the growth life of a fatigue crack, the crack growth behavior should be clarified for the design of safe machine components and structures. Recently, the growth behaviors of high-cycle-fatigue (HCF) cracks in UFG metals were studied, showing the higher growth rates in low and medium values of the stress intensity factor range and the lower growth thresholds. On the other hand, in stain-controlled low-cycle-fatigue (LCF) tests and stress-controlled fatigue tests at high stress amplitudes corresponding to an LCF regime, many investigators indicated a linear crack path with 45° inclination to the loading axis, however only a few reports on growth mechanism of LCF cracks can be found.
The objective of this study was to investigate the physical basis of the formation of growth paths of fatal cracks under high and low stress amplitudes corresponding to the LCF and HCF regimes, from the