An exponential stress function for predicting fatigue strength and life due to mean stresses

An exponential stress function that relates the effect of mean stress on the fatigue strength and life is presented. This stress-based approach is based on the premise that mean stress directly affects the fatigue strength coefficient σ′f, of the Basquin stress–life relation. The severity of damage depends on the relative measure of mean stress to the ultimate tensile strength of the material. Thus, the fatigue strength parameter σ′f, is a function of the ratio of mean stress to the ultimate tensile strength, i.e. σ′f=f(σm/σu). It is shown that a number of previously proposed stress-based damage relations are particular cases of the present approach. The predictive capability of the proposed method is found to be superior to the popular strain-based Smith–Watson–Topper (SWT) approach when tested on some of the published experimental data.