The Effect of Negative Stress Triaxialities on Ductile Damage and Fracture Behavior in Metal Sheets

Abstract

The paper deals with an anisotropic continuum damage and fracture model and a series of biaxial experiments with focus on negative stress triaxialities. The continuum model is based on the assumption that different damage mechanisms are present and have to be taken into account depending on stress triaxiality and Lode parameter. Therefore, modeling of onset and evaluation of damage are based on a stress-state-dependent damage condition and a stress-state-dependent damage rule. To identify the corresponding parameters biaxial experiments with specimens taken from aluminum sheets have been performed and results of corresponding numerical simulations are discussed in detail. The experimental behavior has been analyzed with a digital image correlation system to compare the strain fields with those obtained by numerical simulations. In addition, fracture modes are detected by scanning electron microscopy. Based on the experimental and numerical results a stress-state-dependent cut-off value for negative stress triaxialities is proposed.