A Crystal-Plasticity-Based Damage Model Incorporating Material Length-Scale

Abstract

A crystal-plasticity-based damage model that incorporates material length-scale through use of the slip-plane lattice incompatibility is developed with attention to the physical basis for the evolution of damage in a “bulk” shear deformation and without resort to ad hoc measures of shear deformation. To incorporate the physics of the shear damage process recently found by Kweon et al. (2010, “Experimental Characterization of Damage Processes in Aluminum AA2024-O,” ASME J. Eng. Mater. Technol., 132(3), p. 031008), the development of tensile hydrostatic stress in grains due to grain-to-grain interaction, two existing theories, crystal plasticity, and the void growth equation by Cocks and Ashby (1982, “On Creep Fracture by Void Growth,” Prog. Mater. Sci., 27(3–4), pp. 189–244) is combined to make the model in this study. The effect of the void volume increase onto the constitutive behavior is incorporated by adding the deformation gradient due to the void volume growth into a multiplicatively decomposed kinematics map. Simulations with the proposed model reveal the physics of shear and reproduce the accelerated damage in the shear deformation in lab experiments and industrial processes: the gradient of hydrostatic stress along with the development of macroscopic normal stress (hydrostatic stress) components amplifies the development of the local hydrostatic stress in grains under tensile hydrostatic stress.