Microstructure based fatigue behavior prediction model for AA 7075-T651 Al Alloy with emphasis on the role played by pre-fractured particles in crack initiation

A 3D microstructure-based model was established to quantify the distribution of accumulated plastic strain as a fatigue damage indicator in 7075-T651 alloy, using crystal plasticity finite element method (CPFEM). It was found that the cross-sectional size of pre-fractured particles significantly influences the stress intensity factor at the micro-notch front, as well as the resolved shear stresses (RSS) on the slip systems and the accumulated plastic strain nearby, thereby governing crack initiation. Larger the cross-sectional size of a pre-fractured particle the easier crack initiation at the particle. It also revealed that the larger the Schmid factor of the grain with a pre-fractured particle in surface, the more fatigue damage accumulated, i.e., the easier crack initiation occurred at the particle. However, the grain orientation effect might come second to the effect of the cross-sectional area of the particle on crack initiation.