Evolution of plastic deformation behavior upon strain-path changes in an A6022-T4 Al alloy sheet

The plastic deformation behavior under various strain-path changes in an A6022-T4 Al alloy sheet was studied, focusing on the evolution of the direction of the plastic strain rate theta and the stress ratio qi after abrupt strain-path changes. A cruciform specimen was used to measure the evolution of the plastic deformation behavior after abrupt strain-path change experimentally. Before the strain-path change, the deformation was represented well by the associated flow rule with the Yld2000-2d yield function and isotropic hardening assumption. After the abrupt-path change, the deformation temporarily deviated from the associated flow rule, and it could be represented again by the associated flow rule after the plastic work increased roughly 4.0 MJ.m(-3), which corresponded to the strain increment of approximately 0.024 under uniaxial tension in the rolling direction. The transitions of theta and phi as a function of plastic work showed that both theta and phi tend to converge to certain values regardless of the strain path if the final strain-path angles are identical. It was also found that the relationships between phi and theta temporarily deviate from the associated flow rule immediately after the abrupt-path changes because phi cannot follow the rapid change of theta. Crystal plasticity finite-element simulations reproduced the qualitative tendencies observed in the experiments, but the deviations from the associated flow rule were much more pronounced. Parametric studies showed that phi tends to converge to different values depending on the strain rate sensitivity, whereas theta tends to converge to a same value irrespective of the rate sensitivity exponent. The rate sensitivity exponent m = 0.044 gave the best fits with the experimental results in terms of the evolution of both theta and phi under an abrupt-change path, although the rate sensitivity exponent determined from macroscopic strass-strain curves were m = 0.002.

Automated summary

The study investigated the plastic deformation behavior of an A6022-T4 aluminum alloy sheet under various strain-path changes through experiments and numerical simulations. The results showed that plastic deformation temporarily deviates from the associated flow rule after abrupt-path changes but can be represented by the rule again with an increase in plastic work. Additionally, it was found that both the plastic strain rate direction θ and stress ratio qi tend to converge to certain values regardless of the strain path.