The residual velocity of a projectile perforating monolithic and spaced concrete slabs - A simplified approach

A simplified theoretically based approach to simulate a projectile series of perforations of a composite target, composed of several concrete slabs separated by limited air gaps, is presented. The perforation analysis through a certain slab in the composite target calculates the exit residual velocity which is the impact velocity of the next slab. The approach is based on a theoretically based model previously developed by the authors, to solve perforation of a single concrete slab of limited thickness. This model is based on penetration theory into a thick target and accounts for the concrete constitutive relationships. To consider the finite thickness of a single slab, a new parameter denoted as the pseudo-residual velocity (PRV) is defined. The proposed algorithm for assessing the perforation parameters of a single slab is based on the calculated PRV for different slab thicknesses that are smaller than the specific slab thickness under consideration. The procedure is clear, straightforward, and fast. Contrary to many other simplified perforation models, the proposed approach doesn’t require any empirical calibration constant and no shear plug formation is assumed. The present new approach predictions are compared with measured perforation test results of 21 reduced scale projectiles, hitting five different configurations of monolithic and spaced RC 300 mm thick composite targets, and very good correspondence is obtained. A parametric study has been carried out on 400 mm monolithic targets and on 12 different composite targets, made from different arrangements of spaced slabs with different thicknesses of 100, 150, 200, 250, 300 mm. The targets were subjected to a reference projectile impacting at different velocities. In a methodical study the relative response of all target combinations was compared and the minimum residual velocity at the exit of the composite target rear face was determined.