Effect of mean stress and ratcheting strain on the low cycle fatigue behavior of a wrought 316LN stainless steel

This work reports the low cycle fatigue behavior of a wrought 316LN stainless steel under different control modes at room temperature. Under symmetrical strain and stress cycling, the steel exhibits consistent loading-amplitude-dependent cyclic hardening/softening and fatigue life characteristics. Under asymmetrical stress cycling, the steel is significantly hardened due to mean stress, and the fatigue life at the same strain amplitude is significantly reduced due to ratcheting strain. With the increase of mean stress, though the ratcheting strain level is increased, the fatigue life is prolonged. The effect of mean-stress hardening and ratcheting strain on fatigue life is discussed in terms of strain amplitude and micro-crack initiation and propagation. The Smith-Walker-Topper (SWT) model and a newly proposed fatigue life model based on the Coffin-Manson equation were used to predict the fatigue life under mean stress, and the proposed model yields more robust predictions.