Multi-regime fatigue failure model based on damage theory

Abstract

The prediction of a spatial fatigue crack development under arbitrary loading conditions is a complex problem. This paper introduces a new approach to predict crack initiation and propagation development based on damage theory. The fatigue degradation of the material within a physically small volume is described by the kinetic equation for damage function. The mechanical properties of the material (elastic moduli) depend on the damage function value. The uniform descriptions of the left and right branches of the full SN-curve allow the introduction of the general numerical procedure for fatigue ranges from HCF to VHCF. At the initial stage, the values of the damage function are calculated based on the elastic or elastic-plastic solution. The damage function is associated with two different mechanisms of fatigue damage accumulations. The first one is due to normal stress and the second one is due to shear. The contribution of each mechanism to damage function development is calculated simultaneously. As soon as the damage function gets the critical value the dominant mechanism is established. Therefore, the proposed multi regime model and numerical procedure are capable to predict crack initiation, spatial crack propagation and dominant crack opening mechanism at different stages of crack growth.