The flat piece of metal is subjected to a tensile test. Von-Mises plasticitity is assumed. Because of symmetry, only the upper part is modelled. An updated Lagrange large deformation analysis is used.
Quadratic 9-noded elements are used in the FE-analysis. We show a plots for the plastic strain parameter kappa (which measures the build up of plastic strains), and the velocity in lateral direction. It is clear that an instability shows up. The instability is caused by the combined action of plasticity and large deformations.
Here is the Inputfile.