The Deep Penetration of Concrete Targets by Rigid Rods - Revisited

Abstract

The penetration of rigid long rods into semi-infinite concrete targets is revisited. In particular, we focus on the deceleration of these rods during their penetration, as inferred from the experimental data for penetration depths vs. impact velocities. We find that for a given concrete these decelerations are independent on impact velocity, which enables us to construct a simple relation between the penetration depth and impact velocity. Our model is different from the model which is based on the dynamic cavity expansion analysis to account for the resisting forces on the rod. The cavity expansion model has two terms for the resisting force, a strength term and an inertia term which depends on the velocity of the rod. In the present work we show that there is no physical basis for the inclusion of an inertia term and that the concrete's resisting force depends only on its strength, as with metallic targets. We demonstrate the validity of our approach by comparing its predictions with penetration depths from published data for different concrete and grout targets. We also find an empirical relation between the concrete's resisting stress and its unconfined compressive strength. Several important issues concerning target dimensions and the strength of the rod are discussed. These issues should be carefully considered as they influence the rigid nature of the rod and the semi-infinite condition of the target.