Severe Plastic Deformation Processes: Modeling and Workability

Abstract

Research efforts to model severe plastic deformation (SPD) processes and to quantify the workability of materials during such operations are summarized. The majority of research on the modeling of the equal channel angular extrusion (ECAE) process invented by Segal has focused on the kinematics of metal flow under nominally frictionless conditions. Physical (visioplasticity) models suggest that such assumptions yield reasonable estimates of imposed strain over the bulk of the sample. Recent work on the stress state developed during ECAE has shown that a high degree of compression exists in the deformation zone except near the inner corner of the tooling. At this location, tensile stresses which may lead to fracture are generated. Thus, ductile metals can often be deformed through multiple passes in ECAE unless they exhibit flow softening which can lead to flow localization in the form of shear bands. Research on the modeling of the second major SPD process, that of torsion under superimposed compression, a method developed by Bridgman, has been investigated to a less extent primarily because of the mixed displacement-load boundary conditions and the statically indeterminate nature of the operation.