A surface integrity-informed crystal-plasticity based modelling of fatigue crack initiation in aerospace-grade Ti-6Al-4V

A Crystal Plasticity Finite Element Method (CPFEM)-based approach is developed to predict fatigue crack initiation sites in aerospace-grade Ti-6Al-4V in an as-machined condition. The model integrates an Electron Backscatter Diffraction (EBSD)-reconstructed microstructure, incorporating prior deformation history, residual stress, and milling-induced roughness. The constitutive formulation employs Armstrong-Frederick kinematics with microstructure-sensitive fatigue indicators. Results show that fatigue initiation is highly localised, driven by surface topology, strain accumulation, and crystallographic variations with depth. Basal and prismatic slip systems dominate deformation, with Extreme Value Statistics (EVS) revealing their susceptibility to fatigue crack initiation. The findings highlight that Schmid factor alone does not fully explain fatigue hotspots, as local stress states, grain interactions, and surface-induced geometric constraints also play a critical role in crack initiation.