A new material description for sheet metal forming has been developed. The material description exists of the Vegter yield criterion and a physically based hardening rule. In contrast to most former criteria, the Vegter yield criterion is based on measurements of multi-axial yield stress states. The yield criterion is extended with a physically based hardening rule, in which the flow stress depends on the strain and strain rate.
To measure the multi-axial stress states a biaxial test equipment is being designed. The test equipment will be capable of imposing a shear deformation and a plane strain deformation, including combinations of both deformations. To check whether the bi-axial test equipment will give reliable results, a Finite Element model of a part of the test piece and the clamp equipment is constructed.