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概要

The present study has investigated plasticity-induced martensitic phase transformation in fatigue of unnotched SUS304 plates. Martensitic phase transformation occurred in uunotched SUS304 plate specimens fatigued at room temperature in air. Volume fraction Va of a'martensite in the uunotched potion of fatigued s pecimens was measured by ferrite scope. The relations between the maximum value of Vas Va’max, and the number of load cycles N were represented by reverse sigmoidal curves for all the applied stress range Ao levels tested in this study. For the most portion of fatigue life, the value of Vamax remained almost con stant. This value was increased with increase in the value of Ao. The spatial distribution of Va in the specimens varied with N: i.e., continued cycling of stress made a transformation localized near the central portion of specimens where the V? value reached as high as 35-40%. This value is more than doubled com pared to the highest Va value found in the tensile tests of SUS304 at room temperature. Invisible cracks of 200um in length were found in the high Va value region. These results imply that the measurement of Va in fatigued SUS304 components may detect crack initiation sites and may predict residual fatigue life.

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