Evaluation of Constitutive Models for non-proportional Deformation

Abstract

The anisotropic hardening behavior of dual phase (DP780), transformation induced plasticity (TRIP780) and extra deep drawing quality (EDDQ) steel sheets under non-proportional loading paths was investigated. Two step uniaxial tension tests were conducted with the first loading step in the rolling or transverse direction and the second every 15 degree from the first loading direction. The experiments showed that a transient hardening behavior was dominant for DP780 and TRIP780 steels, while stress overshooting and strain hardening stagnation were more prominent for EDDQ steel. The identification and validation of constitutive models were performed using the measured stress-strain curves under strain path changes. The von Mises isotropic and Yld2000-2d non-quadratic anisotropic yield functions combined with a non-linear kinematic hardening model or the homogeneous yield function-based anisotropic hardening (HAH) model were investigated. It was shown that the Yld2000-2d yield function combined with either hardening model, nonlinear kinematic or HAH, leads to better material behavior predictions for both steels than the von Mises isotropic yield function. In addition, the nonlinear kinematic hardening law was able to describe the transient hardening behavior of DP780 very well, but unable to reproduce any stress overshooting observed in EDDQ. In contrast, the HAH model was able to satisfactorily predict the stress overshooting and strain hardening stagnation for EDDQ. However, the transient hardening behavior using the HAH model could not be capture accurately for some reloading directions. Possible modifications of the current HAH model were suggested to improve this drawback