A crystal plasticity approach for understanding the effect of microstructure and crystallographic texture on mechanisms of low cycle fatigue

This study analyzes the effect of crystallographic orientations on fatigue nucleation in Ti alloys. Uniaxial low cycle fatigue tests were performed on additively manufactured Ti–6Al–4V specimens at various strain amplitudes. Slip system activity and orientations were examined using a crystal plasticity model implemented in the Massively Parallel Object Oriented Simulation Environment (MOOSE). Gumbel distributions of Fatigue Indicator Parameters (FIPs) increase proportionally with strain amplitude, while FIPs strongly correlate with cycles to failure. Interestingly, the contribution of shear on basal and prismatic slip systems is strain-dependent, verified through FIP projections on Inverse Pole Figure (IPF) maps. Our analyses show that evolution of backstress and threshold stress on prismatic slips plays the key role. Incorporating < c + a > pyramidal slips captured tension–compression asymmetry under cyclic loading, enabling accurate representation of slip competition. Finally, idealized microstructures demonstrate design strategies for fatigue-resistant Ti alloys.