Effect of friction, backpressure and strain rate sensitivity on material flow during equal channel angular extrusion

FEM analysis was used to study the interactions between die friction, backpressure and strain rate sensitivity during equal channel angular pressing. One of the key findings is that strain rate sensitivity causes strain redistribution, resulting in higher equivalent strains and a substantial component of compression in the workpiece. This compression gives rise to effects such as lift-off of the leading end of the workpiece from the die bottom and improved die fill. Friction has different effects at room and elevated temperatures. While a moderate amount is beneficial at room temperature, friction has a detrimental interaction with strain rate sensitivity at high temperature. Backpressure, though largely beneficial, is shown to have negative effects when combined with friction and a high strain rate sensitivity.