Finite element analysis of high pressure torsion processing

Abstract

Bulk nano-structured materials processed by methods of severe plastic deformation (SPD) have attracted the growing interest of researchers in materials science. The high pressure torsion straining (HPT) process, which involves large shear and compressive plastic deformation, has been the subject of intensive study in recent years due to its capability of producing fully dense samples having an ultrafine grain size. Because the evolution of the microstructures and mechanical properties of plastically deformed materials are directly related to the amount of plastic deformation, the understanding of the phenomenon associated with the strain development is very important. In this process, knowledge of the internal stress and strain distribution is fundamental to the determination of the optimum process conditions for a given material, such as the number of rotations, the rotational speed and the temperature. In this study, the commercial elasto-plastic finite element method (ABAQUS) is applied to obtain a better understanding of the plastic deformation behaviour of the workpiece during the torsion straining process. The simulated geometry (thickness distribution) of the workpiece is compared with previous experiment data obtained using copper specimens with different number of rotations. The thickness of the workpiece decreased with distance from the centre because of the higher compressive plastic stress state in the centre region compared to the outer part during the loading stage and the elastic recovery during unloading.