숏 피닝 처리에 의한 고강도 스프링강의 초고주기피로파괴 거동 분석

Abstract

Shot-peening effects on the fatigue behavior of spring steel have been investigated under the high cyclic loading. The strength is en-hanced by the shot-peening treatment, which can be attributed to the effect of surface hardening and residual compressive stress. How-ever, the effect of shot-peening on fatigue behaviors over the very high cycle fatigue (VHCF, Nf < 107) remains unclear. We studied whether those effects can be expected to the VHCF range. Hourglass shape specimens made of spring steel (SPS 8) were prepared for the VHCF test using a cantilever type rotary bending fatigue tester. Specimens were treated with a heat condition, and with a shot-peening after the heat. Subsurface crack initiation occurred in both kinds of specimens in the VHCF range. The compressive residual stress of the skin layer suppressed the growth of the fish-eye region. But it did not preclude a creation of the fish-eye micro fracturing zone during the subsurface fracture initiation. Shot-peening treatment has little effect on the VHCF life values for the subsurface initiation.