Multilevel Material Modeling to Study Plastic Deformation for Sheet-Bulk Metal Forming Under Different Loading Histories

The simulation of polycrystalline materials provides detailed insight into the material characteristic. Sheet-bulk metal forming is a complex process that needs comprehensive information about the formed metallic material. Further, transient hardening and Bauschinger effects make this process even more challenging. In order to accurately predict the forming process and the final shape of the formed part under these circumstances, one needs to consider sophisticated elastoplastic material models. Plastic deformation is based on a microscopic length scale phenomenon that involves the dislocation activities within the microstructure. Therefore, a physically motivated dislocation density-based material model is developed to consider the effect of plastic deformation for polycrystalline materials. However, the resolution of the material at a microscopic length scale quickly leads to limitations regarding computation time and cost. Due to the high geometrical resolution, it is impossible to simulate large geometries and resolve the complex plastic transformation at the micro-level within the entire domain. Therefore, based on insights gained with representative volume element simulations of the microstructure an effective plasticity model is developed as well. The effective material model can be applied in coarse scale simulations. It can also provide an accurate mechanical response under non-proportional loading while considering isotropic, as well as kinematic hardening. Additionally, this effective material model can be easily extended to anisotropic yield functions. Both length-scale models are used to validate the mechanical response of ferritic steels under cyclic loading.