Crystal plasticity model to predict fatigue crack nucleation based on the phase transformation theory

A crystal plasticity model is developed to predict the fatigue crack nucleation of polycrystalline materials, in which the accumulated dislocation dipoles are considered to be the origin of damage. To describe the overall softening behavior under cyclic loading, a slip system-level dislocation density-related damage model is proposed and implemented in the finite element analysis with Voronoi tessellation. The numerical model is applied to calibrate the stress–strain relationship at different cycles before fatigue crack nucleation. The parameters determined from the numerical analysis are substituted into a modified phase transformation model to predict the critical fatigue crack nucleation cycle. Comparing with the experimental results of Sn–3.0Ag–0.5Cu (SAC305) alloy and P91 steel, the proposed method can describe the constitutive behavior and predict the fatigue crack nucleation accurately.