Effects of the isotropic and anisotropic hardening within each grain on the evolution of the flow stress, the r-value and the deformation texture of tensile tests for AA6016 sheets

Both the isotropic and anisotropic hardening laws implemented in a crystal elastic visco-plastic finite element model (CEPFEM) were tested for the prediction of the flow stress, the r-value and the deformation texture for tensile tests of the AA6016 sheet. The isotropic hardening law provides good predictions of the flow stress anisotropy. The dislocation hardening was found to be dominant in the hardening behavior. By accounting for the strength variety of different dislocation junctions, predictions of the anisotropic hardening law are sensitive to the activity/strength of different dislocation junctions. Both the plastic shear of slip systems and the dominant dislocation junctions are grain orientation dependent. The flow stress level correlates with the strength of particular dislocation junctions. Both hardening models give similar predictions of the r-value and the deformation texture. Although the physics of crystal plasticity is implemented by including the strength difference of different dislocation junctions, the predictions have not significantly improved. This demonstrates that the strength of dislocation junctions is not responsible for explaining the limitation of the isotropic hardening model. Since the latter does not suffer from neglecting the strength variety of different dislocation junctions, the less complicated isotropic hardening model may still be used as such.