Ratcheting and fatigue behavior of a copper alloy under uniaxial cyclic loading with mean stress

Stress-control fatigue tests have been conducted on a copper alloy at room temperature with and without mean stress. Ratcheting strain was measured to failure under four sets of stress amplitude and mean stress. The ratcheting strain versus cycle curve is similar to the conventional creep curve under static load consisting of primary, steady-state and tertiary stages. The steady-state rate and ratcheting strain at failure increase with mean stress for a given stress amplitude and with stress amplitude for a given mean stress. Ratcheting strain increases as the stress rate decreases. The S–N curve approach and mean stress models of Smith–Watson–Topper and Walker yielded good correlation of fatigue lives in the life range of 10²–10⁵ cycles.