Characterization of edge cracking using a crystal plasticity model with damage evolution

A challenge to the analysis of edge cracking in the aluminum rolling industry lies in the nature of the stress state at the side of the slab. Traditional models for damage evolution are dependent on the state of tensile hydrostatic stress, whereas edge cracking is developed at free surface and in the presence of shear, where hydrostatic stress cannot build up macroscopically. Due to the inability of traditional damage models to capture damage associated with shear, researchers have introduced the phenomenological Lode parameter to model shear damage. These models are generally applied through use of J2 plasticity. In this study, the underlying physics in the shear damage process are explored through the mesoscale process of grain-to-grain interaction. A polycrystal model implemented with finite elements is subjected to different loading conditions. Hydrostatic stress develops within grains via grain interaction, even with an "average" or macroscopic deformation of simple shear. Shear experiments were conducted utilizing the DIC (Digital Image Correlation) technique to measure deformation gradients for various loading scenarios.