Investigation of the rupture in tension and bending of DP980 steel sheet
Résumé
This work is focused on the characterization and numerical prediction of the onset of rupture in bending for a dual phase steel. Indeed, numerical validation of forming processes involving bending over very small radii cannot rely on forming limit curves and demands taking the rupture into account. To reach this goal, the mechanical behavior up to fracture of dual phase DP980 steel sheets was studied by means of experiments and numerical simulations. In a first step, monotonic tensile tests on straight samples up to rupture were performed and a local strain measure was used to assess the fracture strain. Numerical simulation of the tensile test was performed in order to identify parameters specific to four macroscopic rupture criteria. Then, interrupted bending tests over a radius much lower than the sheet thickness were performed and local strains were measured by digital image correlation. Moreover, the bent area was observed by scanning electron microscopy at different stages to detect crack development. In this study, the limit in bending corresponds to the appearance of the first cracks and not to the final splitting in two halves of the specimen. Numerical simulation of the bending test was then performed in order to compare the macroscopic load and local strains with experiments. Finally, critical values of the four macroscopic rupture criteria identified in tension were used to predict onset of rupture in bending.