Ricochet of deforming projectiles from deforming plates

Ricochet means rebound of a striker from the impacted surface (or penetration into a medium along a curved trajectory emerging through the impacted surface with a residual velocity). Changes in direction, velocity and rotational motion of the penetrator are due to several mechanisms. These include release of stored elastic impact energy; influence of surfaces, material interfaces and impact deformations in the target on the magnitude and direction of the resisting force during impact; resistance to motion due to drag and friction. The subject is of interest due to the need to establish safety zones and to design containment structures to guard against failure of rapidly moving machine parts, to protect outer components of space vehicles from the energetic debris spray resulting from oblique hypervelocity impact and to reconstruct bullet trajectories in forensic engineering. This paper contrasts two-dimensional plane strain calculations of ricochet with fully three-dimensional simulations performed with Apollo, a three-dimensional Lagrangian finite element code for impact and explosive loading problems set up exclusively on personal computers and workstations. While some useful information can be extracted from plane strain calculations regarding the early stages of impact, the use of two-dimensional calculations to simulate fully three-dimensional phenomena with long response times (up to the millisecond regime) results in gross overestimation of deflections and is inherently dangerous.