Projectile penetration into sand: Relative density of sand and projectile nose shape and mass

Compacted granular materials, like sand, have a tendency to dilate and expand under shear loading. Such tendency of dilation is beneficial to inhibit projectile penetration. Furthermore, the higher the striking velocity of a given projectile, the higher is the peak strength of the sand sample. Different nose shapes (spherical, flat, hemispherical, conical and ogival) and mass (7 g, 15 g and 20 g) of projectiles were fired into sand samples of relative densities ranging from medium dense to very dense state (60%, 75% and 90%). Results showed that the pointed ogival head projectile had the lowest ballistic limit, whereas the blunt flat head projectile required the highest ballistic energy to defeat the sand block. Despite visible effect of nose shape, the mass of projectile has a larger influence on the amount of absorbed energy. On the other hand, initial compaction of the sand alters the depth of penetration marginally. This is attributed to the projectile impact which compacts the sand as the projectile penetrates through the sand sample. A strong linear correlation between projectile nose shape, mass and ballistic impact energy was established in this study, which allows protective engineers to easily design sand barriers to defeat a range of projectiles. Furthermore, it was found that the energy absorption of sand remains high even when subjected to striking velocities way beyond its ballistic limit. This opens up avenues for sand barriers to be used as sacrificial layer of a composite lightweight protective barrier.