Evolving Yield Loci Based on Anisotropic Hardening Curves

The widely accepted concept of isotropic hardening implies that the ratio between a stress for any straight strain path and the reference flow stress remains constant. Measured hardening curves of for instance bake hardening and dual phase steels show however that these ratio are not always constant. To capture this phenomenon in finite element simulations the concept of an evolving yield locus is proposed. A finite difference model for the simulation of axisymmetric sheet forming processes is used to implement this model. Simulation results show that there is a major impact of the yield locus evolution. The reliability of simulation results with isotropic hardening can be significantly improved if the shape of the yield locus is fitted to an average taking all measured data of the hardening curves into account.