Critical plane approach with two families of microcracks for modelling of unilateral fatigue damage

 New multiaxial fatigue damage model based on the critical plane approach is proposed. Two different physical mechanisms of the fatigue damage development on each potential failure plane (critical plane) are considered. In general, each critical plane contains two families of a parallel microcracks. The proposed model reproduces simultaneously fatigue damage induced anisotropy, the influence of positive and negative mean stresses, unilateral fatigue damage, microcrack closure effect and fatigue behaviour under variable amplitude loading. The expression for the equivalent stress in the damage evolution equation includes the stress intensity for the amplitudes as well as joint invariants for the mean values of the stress tensor and for the vectors associated with the directions of microcracks. The theoretical predictions are compared with experimental data under uniaxial cyclic loading of brass specimens. The influence of positive and negative mean stresses on the fatigue life of brass is investigated.