Simulation of softening in high pressure torsion process using continuum damage mechanics model

Abstract

Severe Plastic Deformations (SPD) processes are used for grain refinement without any loss in ductility. Among various SPD processes, High Pressure Torsion (HPT) is extensively used in industries due to generation of high angle grain boundaries and cost effectiveness. Very little work has been reported on the numerical analysis of softening with recovery that might occur in a work-piece undergoing HPT. The present work is an attempt to study the softening behaviour in HPT processed mild steel and aluminium alloy using the Lemaitre’s continuum damage mechanics (CDM) model. This model is implemented in ABAQUS/Explicit through a user defined material model subroutine (VUMAT). A parametric study is carried out to study the effect on softening of various parameters like the compressive load, the friction at the die-workpiece interface, and the height to diameter ratio. Information about the softening with recovery provides an insight into the hardness and microstructure homogeneity in HPT processed work-piece, which is useful in the design of HPT process.