Characterization of evolving plastic anisotropy and asymmetry of a rare-earth magnesium alloy sheet by means of a non-associated flow rule

Abstract

The superior ductility of rare-earth magnesium alloys over conventional magnesium sheets makes them promising candidates for light-weight structural alloys. However, these alloys possess severe evolving anisotropy and tension-compression asymmetry as a result of activation of different deformation mechanisms (slip or twinning) that is extremely challenging to model numerically. In this study, the constitutive plastic behaviour of a rare-earth magnesium alloy sheet, ZEK100 (O-temper), was considered at room temperature, under quasi-static conditions. A CPB06 yield criterion for hcp materials was employed along with a non-associated flow rule where the yield function and plastic potential were calibrated at different plastic deformation levels to account for evolving anisotropy in proportional loading. The constitutive model was implemented as a user material subroutine (UMAT) into the commercial finite element package, LS-DYNA, along with an interpolation technique to consider the evolving anisotropy of the material. Finally, predictions of the model were compared with the experimental results in terms of flow stresses and plastic flow directions under various proportional loading conditions and along different test directions. It was shown that the predictions of the model were in good agreement with experimental data.