Forming simulation of high-strength steels with direction-specific hardening modelling

The behaviour of mild steels is described very well in todayʹs forming simulation. But advanced high strength steels, especially those exhibiting induced plasticity (TRIP and TWIP steels), may show an anisotropic hardening behaviour that is hardly covered by the commonly used material models. The company MATFEM offers the user material model MF Generalized Yield , which allows for that anisotropic hardening. In order to evaluate the usability of this model for sheet forming simulation, results of real forming experiments were compared to simulation results gained with and without the consideration of anisotropic hardening. Each hardening model was combined with a Hill 48 yield locus. It can be seen that the anisotropic model delivers quite an improvement in some areas, but that this is not true in all areas of the formed part. The punch force prediction is better using the anisotropic model, but still there is no exact match with the experimental results. Overall, the model represents a very interesting concept with high potential, but still some problems. The data acquisition and treatment is very extensive and there are nearly no standardized experiments beyond the uniaxial tensile test to get the needed information about the hardening behaviour of the material. This fact, in combination with insufficient validation of the benefits of the model up to now, inhibits the usage of the model in productive simulation. But for special problems, the model delivers an attractive alternative for further yield locus optimizations.