Strain localization and damage prediction during sheet metal forming

This work aims to study the strain localization in different sheet metal forming processesby the finite element method using advanced behaviour models. In order to improve the prediction of the formability limit of sheets under forming it is important to consider constitutive models that take into account the degradation of material properties due to large strain localization. For this purpose, an elastic-plastic model has been coupled with the classical damage model of Lemaitre and Chaboche [2, 3]. Two hardening models are considered in an attempt to more accurately reproduce the work-hardening phenomenon at large strains. The first one represents the classical cyclic hardening model of Chaboche-Marquis [3, 4] while the second corresponds to the so-called dislocation-based microstructural model of Teodosiu and Hu [5, 6]. These two models are able to reproduce some transient hardening phenomena at strain path changes – with a better description obtained with the microstructural model. The coupling with damage is carried out within the framework of continuum damage mechanics thanks to the introduction of a scalar variable describing the degradation of the elastic proprieties and consequently softening behaviour when damage occurs. The coupled elastic-plastic damage model is implemented into the Abaqus software using an implicit integration scheme. The resulting code is used for the prediction of forming limit diagrams.