Keio University · Engineering
Professor Motoaki Hayama's research lab specializes in the mechanics and metallurgy of surface integrity, with a primary focus on residual stress evolution and phase transformation behavior in steels under cyclic loading. The lab investigates the relaxation of compressive residual stresses induced by surface treatments such as fine particle peening, particularly during the initial fatigue cycles, using in situ X-ray diffraction techniques. A key research direction involves understanding the interplay between retained austenite transformation and residual stress changes in carburized steels, especially under varying stress ratios and loading modes. The lab also examines how material properties such as yield strength and surface condition influence fatigue performance and residual stress stability.
Figures are computed from collected data and may differ slightly.
To clarify the relaxation behavior of compressive residual stress during the first push and pull loading cycle, an in situ X-ray stress measurement method was formulated, in which a fine particle peening-treated hourglass-shaped specimen was fixed on an axial-loading fatigue testing machine, and the surface stress of the specimen—which is the sum of applied stress and residual stress—was directly measured via X-ray diffraction without removing the specimen from the testing machine. A noticeable
The transformation behavior of retained austenite in carburized SCM420H steel and its effect on the change in residual stress on a surface are investigated. The retained austenite on the carburized steel is transformed significantly in the first cycle of fatigue loading with a stress ratio of -1, and the transformation is less significant thereafter. Tensile loading significantly affects the transformation of retained austenite as compared with compressive loading. This is because the mechanical
The transformation behavior of retained austenite in carburized SCM420H steel and its effect on the change in residual stress on a surface are investigated. The retained austenite on the carburized steel is transformed significantly in the first cycle of fatigue loading with a stress ratio of −1, and the transformation is less significant thereafter. Tensile loading significantly affects the transformation of retained austenite as compared with compressive loading. This is because the mechanical
To clarify the relaxation behavior of compressive residual stress during the first push and pull loading cycle, an in situ X-ray stress measurement method was formulated, in which a fine particle peening-treated hourglass-shaped specimen was fixed on an axial-loading fatigue testing machine, and the surface stress of the specimen—which is the sum of applied stress and residual stress—was directly measured via X-ray diffraction without removing the specimen from the testing machine. A noticeable
The difference of the effects of residual stress and stress ratio on fatigue properties of S45C steel was examined. Two types of specimens were prepared, one is polished to mirror finish (P series) and the other is treated by fine particle peening (FPP series). The residual stress of the specimens was measured by X-ray diffraction residual stress measurement system. The surface roughness of the specimens was measured by a laser microscope. FPP series exhibited higher compressive residual stress
Compressive residual stress formed by fine particle peening improves the fatigue properties of steel. However, it is relaxed during the fatigue process particularly during the first cycle of fatigue because of the compressive residual stress layer yield. In this study, the compressive residual stress was induced for specimens with different yield strength by fine particle peening, and the residual stress relaxation behavior was measured and compared using in situ X-ray stress measurement. The re
The formation of a compressive residual stress layer on surfaces improves the fatigue properties of steel. However, compressive residual stress relaxation occurs during the fatigue process, necessitating the examination of this behavior. Herein, an on-site residual stress measurement system that can measure the residual stress under various load conditions was built. The load was changed in a stepwise manner and the residual stress was measured at each step to investigate compressive residual st
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