Evaluation of two constitutive modeling approaches for finite element simulation of ballistic impact of varying thickness monolithic aluminum plates by steel spheres

A comparison of material models for numerical simulations of ballistic impact is performed to study a physics motivated model’s efficacy in overcoming the limitations of traditional empirical models in accurately capturing dynamic deformation and failure mechanisms. The ballistic impact of Aluminum 7085-T711 alloy plates struck by hardened steel projectiles has been modeled using Johnson-Cook (JC) and an Internal State Variable (ISV) constitutive model, DMG, embedded in Abaqus Explicit and EPIC finite element simulations. Both constitutive models show good quantitative agreement with experimental perforation velocity and residual projectile velocity characteristics over the range of plate thicknesses tested. For thin plates, both experiments and numerical calculations show transition from large plastic deformation to lower energy perforation modes (localized fracture) for increasing impact velocity. The ISV model tends to accurately predict the shear-plug dominated perforation modes for all target thicknesses and impact velocities, while the JC model inaccurately predicts target fragmentation at impact velocities significantly greater than a given plate’s ballistic limit. ISV model results show that void nucleation is more influential on damage evolution and fracture than void growth for Al 7085-T711 under ballistic impact loads, however each contributes to the fracture mechanism.