A cold dwell fatigue crack nucleation criterion for polycrystalline Ti-6242 using grain-level crystal plasticity FE Model

A grain-level fatigue crack nucleation criterion for cold dwell in Ti-6242 alloy is developed in this paper using a rate and size dependent anisotropic elasto-crystal plasticity constitutive model, and validated with experiments. Early crack initiation in Ti-6242 under cold dwell fatigue has been identified to be caused by stress concentrations in a hard grain, induced by load shedding from creep in adjacent soft grains. Accurate prediction of local stress and strain evolution during loading requires a robust representation of morphological and crystallographic features of the microstructure. These are accounted for in the FE model in a statistically equivalent sense. The proposed crack nucleation model is based on the observed similarities between crack evolution at the tip of a crack and a dislocation pileup. The nucleation model is calibrated and validated using data available from acoustic microscopy though real time monitoring of crack evolution in dwell fatigue experiments.