Respective/combined roles of thermal softening and dynamic recrystallization in adiabatic shear banding initiation

This work aims at evaluating the respective and combined roles of thermal softening and dynamic recrystallization (DRX) in adiabatic shear banding (ASB) initiation. A unified approach able to describe the whole process of deformation including the stage of ASB in the large scale postulate framework is presented. A physics-motivated model for strain hardening/softening describing the consequences of the competition operating between hardening (gliding) and softening due to dynamic recovery (DRC) and DRX mechanisms is proposed. The temperature rise accompanied by thermal softening is deduced from a thermomechanical analysis. Conditions for ASB initiation are derived from the linear perturbation method leading to a criterion which is consistent with the model. The approach is applied to the simple shear loading of a volume element made of Ti-6Al-4 V titanium alloy and a parametric study is conducted. It is shown that for very late DRX onset, ASB initiation is controlled by thermal softening, whereas for very early DRX onset, ASB initiation is (mainly) controlled by DRX softening, as expected. Between these two extreme cases, thermal softening and DRX both play a role in ASB initiation. The former case may be encountered in initially high stored energy materials.