Development of an Anisotropic Failure Criterion for Characterising the Influence of Curvature on Forming Limits of Aluminium Sheet Metal Alloys

For characterising formability of sheet metal materials the so called Forming Limit Curve (FLC) due to the ISO 12004-2 standard to predict material potential, subjected to static multi-axial in-plane load conditions has been developed during recent years [1]. Experimental results have shown that forming limits under bending loads cannot be described by the conventional FLC at all. This is due to the fact that the FLC describes first occurrence of membrane in-stability and no material failure in consequence of an inter-crystalline fracture at bending. However, first experimental and simulative approaches concerning the Bending Limit Curve (BLC) describe the material formability under pure bending conditions, such as hemming [2]. Thus, the investigation of bendability of sheet metal alloys is of great impor-tance for the evaluation of process robustness for the production of mechanically joined sheet metal assemblies. Fur-thermore, material cracks due to a dominant bending load can also occur during deep drawing. The so called combined load FLC (cFLC) enables the failure prediction for such load cases under the assumption of an isotropic damage evo-lution at drawing [3]. This contribution focuses on the development of an improved failure criterion based on the cFLC concept to take the influence of curvature and anisotropic damage evolution on failure prediction at deep drawing into account.