A Comparison of Half and Quarter Space Penetration into Granular Media

Abstract

In this study, two experimental techniques are compared for the purpose of visualizing projectile penetration at speeds ranging between 60 and 150 m/s into granular media. The two techniques are half space penetration into a transparent synthetic soil surrogate and quarter space penetration of an opaque natural sand and transparent soil surrogate against an observation window. In both techniques a pneumatic projectile accelerator was employed to launch the projectiles, and high-speed imagery was employed to visualize the penetration events unintrusively. Transparency in transparent targets was achieved by saturating angular fused quartz with a refractive index matched pore fluid made of sucrose. Comparison of both techniques suggests that their results are complimentary. In particular, the terminal depth of penetration is not significantly inhibited by shooting in quarter space. Additionally, both techniques permitted visualizing distinct dilation zones ahead and around penetration. Each technique offers a number of distinct advantages. In particular, half space penetration reduces the possibility of projectile diversion and is much safer, whereas quarter space penetration allows for visualizing penetration into opaque targets at a finer scale than that achieved in half space penetration.