The topic of this investigation is the simulation of the high-pressure torsion process with special consideration of different material models under extreme plastic deformations. The Material- Point-Method is a mixed Euler-Lagrangian method, which is well suited for boundary value problems involving large deformations as well as dynamic processes, see [1]. High-pressure torsion is a thermomechanical forming process in which material samples are subjected to extremely high hydrostatic pressure and simultaneous progressive torsional deformation in order to produce a nanocrystalline microstructure with improved mechanical properties such as increased strength and ductility through extreme shear strain, see [2]. Due to the large deformations occurring herein, the material point method is well suited for the analysis and understanding of this process. In the course of the investigations, the material behaviour under different plasticity models is examined and compared. This enables the analysis of stress concentrations at different yield criteria, which allows conclusions to be drawn about the failure mechanisms of microstructured metals. Perspectively, further microstructural phenomena occuring under severe plastic deformation, such as grain refining, should be examined.