高炭素クロム軸受鋼の超高サイクル軸荷重疲労特性に及ぼす応力比の影響

概要

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Axial-reversed loading fatigue tests under three applied stress ratios of –1, 0 and 0.5 were carried out in air at room temperature using hour-glass shaped specimen of high carbon-chromium bearing steel, JIS SUJ2, to investigate fatigue fracture characteristic in very high cycle regime. A granular bright facet (GBF) was observed around subsurface inclusion in all specimens ruptured at long-life fatigue over 106cycles. Three types of fracture mode were observed from the fracture surface, such as surface-induced fracture, subsurface inclusion-induced fracture without GBF area and that with GBF area. Number of cycles to transition in the fracture mode depended on the applied stress ratio. Shape of the S–N curve obtained from the axial loading fatigue was a smooth and continuous in spite of the occurrence on three types of fracture mode, and was different from that of rotary bending fatigue. The characteristic of fatigue fracture behavior was discussed from point of view in fracture mechanics and also residual stress distribution on the specimen surface.