Fatigue Life Predictions under General Multiaxial Loading Based on Simple Material Properties

A procedure for fatigue life estimation of components and structures under variable amplitude multiaxial loadings based on simple and commonly available material properties is presented. Different aspects of the analysis consisting of load cycle counting method, plasticity model, fatigue damage parameter, and cumulative damage rule are presented. The only needed material properties for the proposed procedure are hardness and monotonic and axial cyclic deformation properties (HB, K, n, K′ and n′). Rainflow cycle counting method is used for identifying number of cycles. Non-proportional cyclic hardening is estimated from monotonic and axial cyclic deformation behaviors. A critical plane approach is used to quantify fatigue damage under variable amplitude multiaxial loading, where only material hardness is used to estimate the fatigue curve, and where the needed deformation response is estimated based on Tanaka's non-proportionality parameter. The commonly used linear damage rule is then used as a cumulative damage rule, to predict fatigue life. This procedure, when compared to experimental results, is shown to yield reasonably accurate predictions under some challenging axial-torsion loading conditions for a medium carbon steel with no non-proportional hardening, and a stainless steel with significant non-proportional hardening.