Visualization of impact cratering in granular media using quarter space penetration tests

Impact cratering has a number of important scientific, military, and civilian applications. In this study, the techniques of quarter space penetration, transparent soil modeling, and high-speed photography are combined to visualize impact cratering of spherical projectiles as they penetrate into different granular media. The shape and size of the cross section of the impact crater were visualized and quantified using these techniques for two granular materials, in both dry and saturated conditions. The crater rate of expansion and the velocity decay were also mapped and used to estimate deceleration rates of the crater expansion. A tool is presented for assessing the shape and size of the crater for the case when the penetrator diverges from the observation window. Shallower craters were observed in angular fused quartz targets in comparison to the rounded sand targets. Similarly, higher viscosity saturating fluids lead to narrower cavities. Besides the open cavity, permanent dilation regions ahead of the projectile were also mapped. The evolution of the crater versus time was used to estimate the deceleration of the rate of expansion of the crater. New Poncelet parameters are also developed for specific testing conditions not available in the literature.