Strain-gradient modelling of grain size effects on fatigue of CoCr alloy

A strain-gradient crystal plasticity framework based on physical dislocation mechanisms is developed for simulation of the experimentally observed grain size effect on the low cycle fatigue of a CoCr alloy. Finite-element models of the measured microstructure are presented for both as-received and heat-treated CoCr material, with significantly different grain sizes. Candidate crystallographic slip-based parameters are implemented for prediction of fatigue crack initiation. The measured beneficial effects of fine grain size on both cyclic stress–strain response and crack initiation life are predicted. The build-up of geometrically necessary dislocations as a result of strain-gradients, leading to grain-size-dependent material hardening, is shown to play a key role.