Strain path changes in Reverse Redrawing of DP Steels

Abstract

There has been a longtime and steady interest for the influence of strain path changes on the forming and formability of metallic sheets. First from an experimental point of view, leading to a classification of strain path changes according to their severity, related to the microstructural changes at the grain scale and stress stagnation or even decrease at the macroscopic scale. And secondly, from a modeling point of view, with the development of dedicated constitutive equations to represent various behaviors ranging from strain path reversal to abrupt (or orthogonal) strain path change. However, apart from path reversal, there is still a need, out of validation's sake, to design forming tests at the laboratory scale that are sensitive to strain path changes, and particularly to orthogonal ones. Reverse redrawing of cylindrical cups is considered in this study. Indeed, during the second stage, strain path changes are expected to occur and the load prediction and the residual stresses should be dependent on the mechanical model. Though the study is purely numerical in a first step, a dual phase steel DP 980 is considered, and its sensitivity to strain path change made of tension followed by simple shear is first checked. The occurrence of strain paths occurring during the two stages of reverse redrawing are then investigated numerically and a comparison of two indicators is performed.