Experimental and numerical analysis of damage and fracture mechanisms in metal sheets under non-proportional loading paths

New biaxial experiments and corresponding numerical simulations with specimens taken from metal sheets are discussed. Inelastic deformation behavior as well as damage and fracture mechanisms are examined in detail under different biaxial loading conditions with special focus on non-proportional loading paths. In this context, a continuum damage model is presented based on a yield condition and a damage criterion as well as evolution equations for plastic and damage strain rates. The damage criterion takes into account the effect of different processes on the micro-scale depending on the stress state. Experiments with biaxially loaded specimens with newly developed geometries have been performed using proportional and non-proportional loading histories. Strain fields are monitored by digital image correlation technique and fracture surfaces are analyzed with scanning electron microscopy. Numerical simulations of the experiments have been performed and numerical results are compared with available experimental data. In addition, based on the numerical calculations stress distributions in critical specimen’s areas are detected allowing prediction of damage and fracture modes. The results demonstrate the efficiency of the new geometries of the specimens covering a wide range of stress states as well as the effect of the loading paths on damage and fracture behavior in ductile metal sheets.