Nonlocal microdamage constitutive model for high energy impacts

During highly dynamic and ballistic loading processes, large inelastic deformation associated with high strain rates leads, for a broad class of heterogeneous materials, to degradation and failure by localized damage and fracture. However, as soon as material failure dominates a deformation process, the material increasingly displays strain softening and the finite element predictions of ballistic response are considerably affected by the mesh size. This gives rise to non-physical description of the ballistic behavior and mesh-dependent ballistic limit velocities that may mislead the design of ballistic-resistant materials. This study is concerned with the development and numerical implementation of a novel coupled thermo-hypoelasto-viscoplastic and thermo-viscodamage constitutive model within the laws of thermodynamics in which an intrinsic material length scale parameter is incorporated through the nonlocal gradient-dependent damage approach. It is shown through simulating plugging failure in ballistic penetration of high-strength steel targets by blunt projectiles that the length scale parameter plays the role of a localization limiter allowing one to obtain meaningful values for the ballistic limit velocity independent of the finite element mesh density. Therefore, the proposed nonlocal damage model leads to an improvement in the modeling and numerical simulation of high velocity impact related problems.