Deformation-induced damage in finitely-strained metal sheets: Large-area damage quantification and mechanical property assessment

Abstract

Reliable identification of damage-induced property changes in formed metal sheets remains challenging because plas-tic deformation alters the mechanical response through several coupled mechanisms. Moreover, pronounced ductile damage evolution occurs predominantly under inhomogeneous states of deformation, e.g., strain localization, which compromises the characterization of potential effects of damage on macroscopic mechanical properties, e.g., elastic stiffness. In this study, damage in dual-phase steel DP800 sheets is isolated from other concurrent mechanisms using a novel “sheet extrusion” process. The flat, finitely-strained sheets exhibit large regions with homogeneous properties, enabling subsequent characterization of damage-induced property changes. Damage in the form of microscopic voids is then characterized by large-area scanning electron microscopy (SEM) measurements, and damage-induced property changes are determined by subsequent characterization tests on specimens extracted from the extruded sheets. It is found that deformation-induced damage does not measurably affect the apparent elastic stiffness or the pre-necking tensile response. In contrast, differences in fracture-related performance quantities, i.e., the remaining ductility and the tensile impact energy, indicate that higher deformation-induced damage promotes earlier macroscopic failure by increasing the likelihood of local void coalescence during subsequent loading.