On the Modeling of the Unloading Modulus for Metal Sheets

Abstract

The springback phenomenon is defined as the elastic recovery of the residual stresses produced during the forming of a material. An accurate prediction of springback puts high demands on the constitutive modeling. A constitutive model for springback prediction should of course be able to accurately predict the stress state after the forming phase. However, it should also be able to predict the material behavior during the unloading phase. In classical plasticity theory, the unloading of a material after plastic deformation is assumed to be linearly elastic with the stiffness constantly equal to Young’s modulus. However, several experimental investigations have revealed that this is an incorrect assumption.

The main purpose of the present work has been to formulate a constitutive model that can accurately predict the unloading behavior of a sheet metal material. The new model is based on a classical elasticplastic framework, and is totally independent on the choice of yield criterion and hardening evolution law.