Effect of Stress Ratio on Change in Residual Stress of Shot-Peened SUS316L Steel during Fatigue Process

Fatigue tests with three different stress ratios were carried out on shot-peened SUS316L steel, and in situ X-ray stress measurements were performed to analyze the behavior of the residual stress change and related factors. The compressive residual stress decreased during tensile loading and increased during compressive loading. The reduced compressive residual stress was caused by the tensile yielding of the core region, whereas the increase in compressive residual stress was caused by the compressive yielding of the core region. This behavior was observed when the yield strength of the surface layer was significantly increased by shot peening, and the compressive yielding of that layer and the resulting relaxation of compressive residual stress were prevented. In this case, the behavior of the residual stress change during cyclic loading was contingent on the stress ratio. It is because the compressive residual stress, which decreased during tensile loading, increased under subsequent compressive loading, and the amount of increase is based on the magnitude of the applied compressive loading.