Effect of compressibility on the hypervelocity penetration

We further consider the effect of rod strength by employing the compressible penetration model to study the effect of compressibility on hypervelocity penetration.Meanwhile, we define different instances of penetration efficiency in various modified models and compare these penetration efficiencies to identify the effects of different factors in the compressible model. To systematically discuss the effect of compressibility in different metallic rod-target combinations, we construct three cases, i.e., the penetrations by the more compressible rod into the less compressible target, rod into the analogously compressible target, and the less compressible rod into the more compressible target. The effects of volumetric strain, internal energy, and strength on the penetration efficiency are analyzed simultaneously. It indicates that the compressibility of the rod and target increases the pressure at the rod/target interface. The more compressible rod/target has larger volumetric strain and higher internal energy. Both the larger volumetric strain and higher strength enhance the penetration or anti-penetration ability. On the other hand, the higher internal energy weakens the penetration or anti-penetration ability. The two trends conflict, but the volumetric strain dominates in the variation of the penetration efficiency, which would not approach the hydrodynamic limit if the rod and target are not analogously compressible. However, if the compressibility of the rod and target is analogous, it has little effect on the penetration efficiency.

Spherical cavity-expansion model for penetration of reinforced-concrete targets

The feature of reinforcing bars is introduced into dynamic cavity-expansion theory. Based on the elastic-plastic response penetration model of plain (i.e., unreinforced) concrete (Forrestal and Tzou, 1997), a dynamic spherical cavity-expansion penetration model for reinforced-concrete targets is developed with consideration of the circumferential restriction effect derived from reinforcing bars in the crushed region. The theoretical solution and simplified calculation formula for the cavity radial stress in incompressible and compressible reinforced concrete are obtained by introducing a reinforcement ratio as the volume fraction of rebars in the concrete target. A damping function is presented to describe the restriction effect of a single layer of reinforcing bars on the surrounding concrete, thus establishing a model to calculate the penetration resistance of multilayer reinforced-concrete targets. Compared with test data for the penetration depth, this model considering the circumferential restriction effect produces better results compared with the existing theory.