Damage due to Low-Cycle Fatigue of Type 316 Stainless Steel : Fatigue Life under Variable Loading and Influence of Internal Cracks

Abstract

To obtain a reasonable prediction of fatigue life under variable loading, it is important to understand the damaging process. In this study, the damage process of low-cycle fatigue was investigated for Type 316 stainless steel. Fully-reversed axial fatigue tests were conducted in ambient air at room temperature by controlling strain amplitude, which was 6% at the maximum. Two-step strain tests were also conducted in order to assess the effect of loading history on fatigue life. The fatigue life was shown to be not always longer than that estimated using a linear damage accumulation rule. Furthermore, in order to evaluate the effect of initiation and growth of surface cracks on the fatigue life, the surface layer of specimens was removed after the first step. The fatigue life was extended by surface removal, although it was not recovered completely. Many internal cracks were observed on the fractured surface of the surface-removed specimens, and in some cases the specimens were fractured by these internal cracks. It was concluded that the low-cycle fatigue damage of Type 316 stainless steel consisted of three factors: surface cracking, internal cracking, and strain accumulation.