Penetration of granular materials: New experimental techniques

The photon-doppler-velocimeter, (PDV) is a powerful new technique for measuring the resistance of bulk materials to penetration. We have been able to use this device to observe spheres as they impact and penetrate granular materials Projectiles were 14-mm diameter hard steel spheres. Granular materials included dry sand, saturated sand at two densities, and crushed fused quartz saturated with an index-matching oil. It is found that the PDV can follow these 14-mm diameter spheres over a penetration depth of approximate 300 mm. This has enabled us to measure penetration resistance over a range of about 300 to 50 m/s. No special surface treatment of the spheres was necessary. Data are interpreted in terms of Poncelet parameters, but it is found that the strength term is negligible until the projectile has almost stopped.