Prediction of the formability limit using damage mechanics

Abstract

Forming limit diagrams (FLD’s) are used to evaluate the workability of metal sheets. These diagrams provide the failure locus at which plastic instability occurs and localized necking develops (commonly designated as the forming limit curve - FLC), and the failure loci at the onset of fracture by tension or by in-plane shear. In this work, the possibility to predict the FLD’s using damage mechanics is presented. Following the approach proposed by Lemaitre [1], the fracture forming limit (FFL) for ductile metals is theoretically derived using the extended Bonora damage model (XBDM). The XBDM is used in numerical simulation with FEM of formability tests (Nakazima and Marciniak) to demonstrate the possibility to account correctly for necking development before fracture. The proposed model prediction was validated with available experimental data for high purity copper.