The resistance law in spacecraft-regolith interaction

The impact of an object onto a granular bed is a ubiquitous phenomenon in nature, the scale of which ranges from a man walking on a beach all the way to an asteroid crashing into a planet. Accordingly, impact with granular media has long been investigated, and is being actively pursued at present in terms of experiments and simulations, which have significantly contributed to industry, agriculture and also granular physics. However, due to the fluid-solid like dual nature of granular material under impact, the knowledges about its underlying physical mechanisms are still limited. One mystery that remains is the grain-scale origin of the drag force exerting on an intruder in a granular medium.

Force chains excited by intruders of different shapes impacting on granular medium.

We study the stopping force felt by an intruder impacting onto a granular medium. Variations in the shape of the intruder can influence the penetration depth by changing the inertial drag. We find this observed correlation can be explained by associating the velocity-dependent inertial drag to the energy dissipation that occurs through intermittent collisions of force-chain-like clusters, the mean behavior of which can be statistically described. In consequence, the stopping force can be captured through a proposed collisional model with good accuracy, and the observed impact dynamics data can be reproduced quantitatively.

Related paper: Cheng, B., Yu, Y., & Baoyin, H. Collision-based understanding of the force law in granular impact dynamics, Physical Review E, 2018, https://doi.org/10.1103/PhysRevE.98.012901