The penetration of limestone targets by rigid projectiles: Revisited

We reanalyze the results from a set of terminal ballistics tests in which large limestone targets were impacted by similarly shaped rigid projectiles having different sizes. Our first goal is to show that the data in terms of penetration depths as a function of impact velocity can be accounted for by a model in which the limestone's resistance to penetration is constant throughout the penetration process. It turns out that the actual values of this penetration resistance, as derived from the data, decrease with the projectile's size. This is a clear manifestation of a scaling issue in the terminal ballistics of the limestone rock. In order to account for this issue we assume that it is closely related to the size effect in the compressive strengths of rock specimens. Finally, we offer a simple procedure by which one can define a surrogate material model for the targets in numerical simulations, in order to predict the penetration depths in limestone, and possibly other rock targets, under both normal and oblique impacts.