Limitations of the M-K Based Forming Limit Diagrams

Using a rate dependent Taylor type crystal plasticity formulation, the limitations of Marciniak-Kuczynski (M-K) approach to numerically simulate the Forming Limit Diagrams (FLDs) were studied. Three uniaxial stress-strain curves with three different post-necking hardening behaviors were generated using crystal plasticity formulation. These curves were constructed based on the real tension test data available for AA5754 aluminum. In the first one the true stress strain curve continued as saturated after the necking and in the other two the post-necking hardening behaviors experienced slopes larger than zero. The result showed that the stress-strain curves dictated different imperfections for the localized necking hence the FLDs generated by them were different. The predicted FLD resulted from the saturated hardening behavior was closer to the experimental data in the biaxial region.