Investigation of the Dominating Mechanism of Fatigue Life for Various Alloys with CSSC on R=0 and −1

Most studies on CSSC (cyclic stress-strain curve) have been conducted in the condition of the stress ratio R=−1. There are few reports on the effect of mean stress on CSSC. In this study, the stress-controlled fatigue tests under R=0 and −1 were performed on JIS S25C (AISI 1020), IF steel, A2024-T6, A6061-T6 and Ti-6Al-4V alloys. CSSCs of R=0 and −1 were compared. Creep strain (ratcheting strain) was also measured to investigate dominating mechanism of fatigue life of these alloys. It was found that the effect of mean stress on CSSC was different with each alloy. The dominating mechanism of JIS S25C and IF steel was creep strain. However, the dominating mechanism of A2024-T6 and A6061-T6 was plastic strain amplitude. The dominating mechanism of Ti-6Al-4V alloy was both creep strain and plastic strain amplitude. Thus, fatigue life reduction caused by mean stress in Ti-6Al-4V alloy was remarkably occurred than the other alloys.