Finite cavity expansion method for near-surface effects and layering during Earth penetration

Abstract A finite spherical cavity expansion technique is developed to simulate the loading on projectiles penetrating geologic media. Damaged Mohr–Coulomb plasticity models and a general pressure-dependent damaged plasticity model are used with incompressible kinematics to approximate a wide range of targets. The finite cavity expansion approximation together with directional sampling reasonably captures near-surface and layering effects without resort to ad hoc or empirical correction factors. The Mohr–Coulomb models are integrated exactly to provide a very efficient loading algorithm for use with conventional implicit or explicit finite element structural analysis. The more general constitutive model requires numerical integration and leads to a more computationally intensive procedure. However, subcycling is easily implemented with the numerical integration and thus an efficient loading method is readily achieved even for large complex simulations using explicit finite element analysis. The utility of the finite cavity expansion approach is demonstrated by comparison of simulations to measured test data from projectiles penetrating rock and soil targets.