Modeling experiments that simulate fragment attacks on cased munitions

Roberts and Field (1993) have conducted experiments to observe the behavior of a cased high explosive (HE) charge subject to fragment attack at impact velocities below those needed for shock initiation. Two and three-dimensional hydrodynamic calculations have been done to model these experiments. Questions about the degree of confinement of the HE and about the condition of the HE during the impact were addressed. The calculations indicate that the HE was not strongly confined in this experiment, primarily due to the lateral expansion of polycarbonate blocks on the sides of the target during the impact. HE was not ejected from the hole in the casing made by the projectile up to 30 {micro}s after the impact. There are hints from these calculations of how initiation of a homogeneous sample of HE might occur in the experiment. The first involves the reshock of a small amount of HE at {approximately} 20 {micro}s as a result of the impact of the sabot on the target. The second involves the heating of the HE from plastic work during the impact. The maximum temperature rise of the HE (exclusive of the small region that was reshocked) was {approximately} 80 k. However, this is the average temperature of a region the size of a computational cell, and phenomena such as shear bands or cracks could result in higher temperatures on a smaller scale than the cell size. The third involves heating of the HE from contact with the casing material. The maximum temperature rise of the casing material from plastic work is {approximately} 870 k. This temperature occurs at the edge of a plug of casing material sheared off by the projectile. Other parts of the casing are shock heated to higher energies but may not contact the HE.