The effect of non-linear recovery on springback prediction

Numerical prediction of springback remains one of the major problems in sheet metal forming. The quality of springback prediction for a sheet metal forming process depends on a precise estimation of the stress distribution all over the metal sheet. In particular, the decrease of the unloading elastic modulus (non-linear recovery) with increasing plastic prestrain during stress reversals, observed by several authors, was commonly not taken into account in FE analysis. A model is proposed which takes the elastic modulus evolution with plastic prestrain and the unloading stress into account. Numerical simulations show that this model coupled with a non-linear kinematic hardening model can accurately predict the springback amount.