Impact of elastic modulus evolution on springback prediction

Abstract

Today, the hardening Yoshida-Uemori model is implemented in the most used FEA stamping codes (Autoform®, Pamstamp®, LS-Dyna®…) with occasionally some variations. This forming material card is requested regularly by the car manufacturers. The Yoshida-Uemori model is a combined hardening model coupled with the elastic evolution modulus which depends on the equivalent plastic strain. According to the experimental tests conducted and their identification protocol, the set of parameters improves the springback prediction compared to the prediction with a purely isotropic hardening model. The numerical analysis shows that the elastic modulus evolution has an influence on springback prediction of the same order as the combined hardening (isotropic and kinematic). The adjusting parameters governing the evolution of the elastic modulus are identified thanks to hysteresis loops conducted between 0.2% of plastic deformation and uniform elongation (Uel). For each loop, there are several ways to define an unloading elastic module: the chord of loop; the slope deducted from the linear regression on unloading path on a range. According to the choice of range, the value differs. What is the impact of these choices on the springback prediction of a stamped part?