Mean and residual stress effects on fatigue behavior in a pre-strained corner of stainless steel sheet

Abstract

There are many thin-walled corners in the components of automobiles, machines, and structures. It is essential to elucidate their fatigue properties and influence factors. Parameters for stress–strain behavior of ferritic stainless plane sheet and pre-strained sheet were obtained under tensile, bending, and cyclic bending loads using the Ramberg–Osgood model. The parameters were integrally used as the fundamental characteristics of bending fatigue behavior for obtaining the mean stress and crack initiation stress amplitude from the measured strains in the curved portion of corner specimens. Bending fatigue tests of pre-strained corner specimens were carried out, and the relationships between the crack initiation strain amplitudes and the mean strains were verified. The strain amplitude ratios of the curved inside to outside portion were analyzed. The residual stress and hardness were measured, and work hardening effect on the inside was higher than that on the outside for improving fatigue strength. The fatigue limit of the corner specimen with the radius ratio of 1.3 was 23% higher than the unworked plane sheet. The effects of mean stress and residual stress on the fatigue strength were analyzed using the fatigue limit–static stress relation equations, indicating that the Gerber parabola can be used for fatigue limit predictions in the stress ratio range of R < –0.5 and that the Goodman line can be used after the point of R = –0.5. The SWT function can be used to accurately predict the fatigue lives in various conditions of stress amplitudes combined with static stresses.