Modelling of High Strain Rate Failure Under ASB and Microvoiding

High strength, lightweight materials, including notably titanium and aluminium alloys are widely used in aircraft and other structures. When subjected to high strain rate loading involving quasi adiabatic conditions, these materials may be subjected to a thermomechanical instability resulting in a dynamic localization in the form of narrow adiabatic shear bands (ASBs) which cause a premature structural failure. A physics-motivated unified model is presented, based on a specific scale postulate amounting to a global insight into the material response (the representative volume element contains the band, and not the opposite as usually considered) and aiming at reproducing the coupled effects of dynamic plasticity, strain localization and microvoiding in the context of large deformation, high strain rate and high temperature rise. The model is implemented as user material in the engineering finite element computation code LS-DYNA and its performances are evaluated regarding various available experimental results.