Deceleration of Projectiles in Sand

Deceleration of projectiles has been measured for hemispherical and conical nose shapes penetrating granular media. Targets were beds of~Ottawa sand and Eglin sand.~The velocity range extended up to 600 m/s. Projectiles were rigid metals. Deceleration was measured by conventional time-of-arrival screens plus several innovative techniques: embedded EM coils, embedded optical fibers, and a photonic Doppler velocimeter (PDV), which observed the rear surface of the penetrator. Experimental parameters that were varied included velocity (from 300 to 600 m/s), sand density, and scale (from 5 mm to 25 mm). In this paper we will compare these various measurement techniques and we will show how the cavity geometry (cavitation and crushed veins of sand) and retarding stress $(MdV/dt)/A$vary with velocity, scale, and density.