Spring-back evaluation of automotive sheets based on isotropic-kinematic hardening laws and non-quadratic anisotropic yield functions

In order to improve the prediction capability of spring-back in the computational analysis of automotive sheet forming processes, the modified Chaboche type combined isotropic-kinematic hardening law was formulated to account for the Bauschinger and transient behavior in Part I. As for the yield stress function, the non-quadratic anisotropic yield potential, Yld2000-2d, was utilized under the plane stress condition. Experimental procedures to obtain the material parameters of the combined hardening law and the yield potential are presented here in Part II for three automotive sheets: AA5754-O, AA6111-T4 and DP-Steel. The modified Chaboche model was confirmed to well represent the measured hardening behavior including the Bauschinger and transient behavior. While the theoretical and numerical formulations of the constitutive law are discussed in Part I, experimental verifications for spring-back of formed parts are further discussed in Part III.