Effect of Stress Ratio on Axial-Loading Fatigue Characteristics of High Carbon-Chromium Bearing Steel in Very High Cycle Fatigue Regime
Kazuaki SHIOZAWA, Takayuki HASEGAWA and Seiichi NISHINO
Abstract: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 106 cycles. 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. Key Words:Very high cycle fatigue, Axial loading, Stress ratio, Subsurface crack, Fracture mode, Residual stress, High carbon-chromium bearing steel