Effect of Nose Shape on Long Rod Penetration into Dry Sand

Flat and Ogive-3 nosed mild steel projectiles (10~mm diameter, 100~mm length) were fired at 200~m~s$^{-1}$ into the end face of cylindrically confined dry sand (100~mm diameter, 150~mm length). Projectiles were tracked through the sand using flash radiography and high speed photography. By seeding a horizontal plane of randomly dispersed lead shot ($<$~1.5~mm diameter) across the centre of the cylinder, the induced displacement field was mapped using Digital Speckle Radiography~(DSR). By imaging at successive time intervals, a temporal history of the penetration is generated. DSR reveals a cone of displacement emanating from the impact point in all cases, leaving areas unmoved during the early stages of penetration. The magnitude and extent of the displacement cone is observed to be greater in the flat nosed case. Initial rapid deceleration is seen in both nose cases, relaxing to an approximately steady velocity as the projectile reaches the end of the target. Ogive nosed projectiles suffer less deceleration, and perforate the target with greater speed than the flat nosed projectile. This combined behaviour is attributed to the flat nosed projectile transferring more energy to movement of sand, and hence experiencing more effective drag.