Evaluation of Stress Saturation Effect with a Stress Based Failure Criterion for Sheet Metal Using Numerical Simulations

In order to effectively design sheet metal components using numerical simulations, an accurate means to predict tearing concerns is necessary. Currently, a strain based failure criterion is used to predict this type of failure in the automotive and aerospace industries. However, due to the strain path dependence of the strain based Forming Limit Diagram, accurate prediction is only possible for forming cases which possess a single linear strain path. Alternatively, a stress based failure criterion has been proposed and demonstrated analytically, experimentally in tube forming, and through numerical simulations. In this paper, further support for the stress based failure criterion is provided by demonstrating that the saturation of the stress level during plastic deformation is not the cause of the convergence of various strain based Forming Limit Curves to a single curve in stress space. To demonstrate this, analytical methods have been employed and a stress based failure criterion was used to predict the failure in dome height numerical simulations using a simple yield criterion, von Mises.