Effect of deformation heating and strain rate sensitivity on flow localization during the torsion testing of 6061 aluminum

Abstract

The effect of deformation heating and strain rate sensitivity on flow localization during the torsion testing of 6061 aluminum was investigated both theoretically and experimentally. From the theoretical viewpoint, a simple analysis of the torsion test was carried out based on the torque equilibrium and one-dimensional heat transfer equations. The problem formulation was discretized to enable numerical solution of the governing equations and prediction of the effect of material properties on the development of deformation and temperature gradients. The analysis was validated by conducting high strain rate experiments on the 6061 alloy at a variety of temperatures. At low temperatures, at which the flow stress and temperature changes due to deformation heating are large and the strain rate sensitivity is low, marked flow localization occurred. The analysis modeled this behavior correctly, indicating that strain concentrations can occur solely as a result of the temperature gradients set up by heat transfer during testing, i.e. in the absence of geometric or deformation defects. At the higher temperatures, at which temperature changes due to deformation heating are small and the rate sensitivity is large, the flow remained nominally uniform until fracture intervened. The numerical simulations of these tests also showed good agreement with the observations.