Penetration dynamics of a carbonate sand: A synchrotron phase contrast imaging study

Abstract Penetration into granular materials such as carbonate sand is of fundamental importance to granular physics, and impact and civil engineering, but research along this line suffers considerably from the lack of direct experimental observations. Here we investigate such penetration dynamics of carbonate sand using a vertical gas gun implemented with in situ, high-speed, synchrotron-based X-ray phase contrast imaging. The experiments yield the first direct observation on the penetration dynamics (projectile trajectory/velocity) and particle-scale deformation in real or natural granular materials during sphere penetration, at high temporal and spatial resolutions. The particle displacement fields around the projectile are obtained via X-ray digital image correlation, and the ejecta velocity fields, with particle image velocimetry. Effects of the moisture content and container size on the penetration process are discussed. The enhanced cohesion between wet particles results in particle clustering during splash and a smaller amount of ejecta. Therefore, the particle rearrangement is limited and the projectile penetration depth is smaller. A small container size confines the lateral movement of particles and yields a much more pronounced compaction of particles beneath the projectile, which results in a smaller penetration depth as well.