A basic study on reliability of axles for high-speed railway

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(1) A new ultrasonic technique in combination of ultrasonic grazing SH wave inspection system and a wave forming method were proposed. Applying this technique, it became possible to detect the fretting fatigue cracks in wheel set axle of shinkansen train.(2) Fatigue test and ultrasonic test were performed for the hybrid surface improved axles. The results show that the fatigue limit of the axle increases but the detection of cracks becomes more difficult because of large compressive residual stresses.(3) Rotating bending, high-cycle fatigue tests under constant amplitude and variable amplitude land sequences were carried out on a high carbon chromium steel for bearings, JIS SUJ2. In the case of repeated two-step landing, fatigue crack origin sites change from the specimen surface to the subsurface due to the load variation. The usefulness of linear damage accumulation law under variable amplitude load sequences was discussed.(4) By combining the carburizing and the WPC process, it is possible to generate a high compressive residual stress near the near the surface, maintaining a deep layer of compressive residual stress formed by the carburizing The notched specimens modified by combined show a significantly higher fatigue strength compared to those modified by only carburizing.