Abstract
Modelling of the mechanical response of the materials using computer simulation is very useful tool to optimize their mechanical properties. It is especially important for ultrafine-grained (UFG) materials obtained using severe plastic deformation (SPD) techniques. Those materials are characterized by high strength however their application on an industrial scale is limited, first of all because of poor ductility. Proper understanding of the deformation and strengthening mechanisms that govern the mechanical response of UFG materials can be the way to propose the guidelines to improve their ductility. Application of the Finite Element Method (FEM) for calculations and modelling of the mechanical response of UFG materials needs properly built rheological models. In the case of heavily deformed microstructures that are mostly characterized by high inhomogeneity of microstructure and mechanical properties, existing flow stress models need to be modified and justified to the new conditions. The present study shows some modelling results of the mechanical behaviour of specimens subjected to severe plastic deformation using MaxStrain system. Different grades of steels were examined and their mechanical response was simulated using modified Khan-Huang-Liang (KHL) flow stress model that was implemented into Abaqus Explicit code via user subroutine VUMAT. An effect of various deformation conditions was discussed with respect to the microstructure evolution and its influence on final mechanical properties. The methodology, using Considére criterion to assess the plastic instability in a tensile test, was also implemented into FEM code. The comparison of the measured and calculated results shows that presented approach can be successfully applied to the evaluation of the ductility of various materials with different levels of microstructure refinement.