Development of a three-dimensional microstructure sensitive crystal plasticity model for aluminum

A dislocation density based crystal plasticity finite element model (CPFEM) has been developed in which different dislocation densities evolve on all octahedral slip systems in aluminum. Based upon the kinematics of crystal deformation and dislocation interaction laws, dislocation generation and annihilation are modeled. Dislocation densities evolve in form of closed loops and are tracked as state variables in the model, leading to spatially inhomogeneous dislocation densities that show patterning in the dislocation structures. A generalized Taylor equation is used as the hardening law in which hardening coefficients are based on the reactions between dislocations on co-planar and non-planar slip systems. The hardening coefficients for reactions involving latent slip systems are determined using 3D discrete dislocation dynamics. The model is validated using distinct hardening behavior of {100} and {111} single crystals of aluminum. The phenomenon of overshooting in aluminum is predicted using the model. Effect of collinear interactions of dislocations is shown to enhance the overshooting behavior.Evolution of crystallographic texture during plane strain deformation of polycrystalline aluminum is predicted. The crystallographic texture shows characteristic texture components observed in the "rolling texture" in the experiments reported in the literature. Description of dislocation densities is presented in form of pole figures along with evolution of crystallographic texture which shows increasing heterogeneity in microstructure with increasing deformation.Simulations of plane strain deformation on bicrystals are performed which predict rotations of crystallites during deformation and orientation spread at the final stage of deformation reasonably well as compared with the experimental observation. Similar studies are done for more complex grain topology in 2D columnar multicrystals. Overall, the model predicts heterogeneous evolution of accumulated plastic strain which is found to be consistent with the accumulated dislocation density, shear strain, dislocation density evolution rate and the Taylor factor in the corresponding grains.