Prediction of fatigue crack initial stage based on a multiscale damage criterion

In this paper a multiscale damage criterion for fatigue crack initial stage prediction is introduced. A damage evolution rule based on strain energy density is modified to incorporate crystal plasticity at the microscale (local). A damage tensor that indicates the local damage state is derived using optimization theory. Damage information is passed from local to grain level, bridging microscale and mesoscale in the form of a damage vector via averaging techniques. Finally, the damage evolution rule for a meso representative volume element (RVE), which contains several grains, is calculated through the Kreisselmeier–Steinhauser (KS) function, which can produce an envelope function for multiobjective optimization. The weighted averaging method is also used to obtain the corresponding damage evolution direction for the meso RVE. A critical damage value is derived in this paper to complete the damage criterion for fatigue life prediction. Simulation results and comparison with experimental data are presented.