Effect of Stress Ratio and Residual Stress on Fatigue Properties of S45C Steel Treated by Fine Particle Peening

Abstract

The difference of the effects of residual stress and stress ratio on fatigue properties of S45C steel was examined. Two types of specimens were prepared, one is polished to mirror finish (P series) and the other is treated by fine particle peening (FPP series). The residual stress of the specimens was measured by X-ray diffraction residual stress measurement system. The surface roughness of the specimens was measured by a laser microscope. FPP series exhibited higher compressive residual stress and higher arithmetic average roughness than those of the P series specimens. Fatigue test were performed under axial loading and with different stress ratio of R =-1 and 0. Equivalent stress amplitude calculated by Smith-Watson-Topper (SWT) method was used to correct for the effect of stress ratio. Fatigue lives of the P series and FPP series were comparable because of the generation of compressive residual stress and increase of surface roughness. In the case of P series specimen, there were difference in fatigue lives between stress ratio R = -1 and 0. Modified SWT equation was proposed with considering the effect of residual stress.