Comment on: “Rigid and eroding projectile penetration into concrete targets based on an extended cavity expansion model” by Kong et al. Int. J. Impact Eng. (2017)

Rosenberg et al comment on Kong et al's study proposing a rather elaborate scheme to account for the penetration depths of rigid and eroding projectiles into semi-infinite concrete targets. They introduce a hyperbolic yield criterion to describe the plastic deformation of concrete, and an extended cavity expansion model to account for the force on the projectile's nose. This model is based on the assumption that the resisting stress, which the target exerts on the projectile during penetration, depends on its instantaneous velocity (V). This approach has been used by many authors for metallic targets and also for concrete targets. These analyses, for both spherical and cylindrical cavities, resulted in the threshold pressures (Ps and Pc) which are needed to expand these cavities indefinitely. However, the resulting expressions for these threshold pressures did not account for the experimental data, as far as the penetration depths into metallic targets are concerned. Thus, a target inertia term (ρtV2) was added to the resisting force and often a linear term in V was also added.