Sub-surface granular dynamics in the context of oblique, low-velocity impacts into angular granular media

TL;DR

This study uses 2D discrete simulations with finite element methods to analyze sub-surface granular dynamics during oblique, low-velocity impacts into angular granular media, revealing impact behaviors and grain response mechanisms relevant to space exploration.

Contribution

It introduces a novel simulation approach incorporating angular grain geometry and high-resolution packing analysis to better understand impact dynamics on extraterrestrial terrains.

Findings

Reproduces three impact behavior classes: full-stop, rollout, ricochet.

Identifies a 'skin zone' of perturbed grains during impacts.

Shows higher impact velocity may increase lateral grain perturbation.

Abstract

Oblique, low-velocity impacts onto extraterrestrial terrain are an inevitable occurrence during space exploration. We conduct two-dimensional discrete simulations to model such impacts into a bed of triangular grains. Finite element method provides the basis for simulation, enabling the angular grain geometry. Our findings re-create the three classes of impact behavior previously noted from experiments: full-stop, rollout, and ricochet \citep*{Wright2020}. An application of Set Voronoi tessellation assesses packing fraction at a high resolution, revealing how grains shift relative to each other during an impact event. Calculation of Von Mises strain distributions then reveal how grains shift relative to the overall system, leading to the notion of the 'skin zone'. Intuition would suggest that the region of perturbed grains would grow deeper with higher velocity impacts, results instead show that increasing velocity may actually evoke a change in the grains' dissipative response that boosts lateral perturbation. Finally, we consider as a whole how sub-surface response could link with impactor dynamics to deepen our understanding of oblique, low-velocity impact events and help to improve mission outcomes.