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

PM Miklavcic and P Sanchez and E Wright and AC Quillen and H Askari, ICARUS, 385, 115089 (2022).

DOI: 10.1016/j.icarus.2022.115089

Oblique, low-velocity impacts onto non-terrestrial terrain are regular occurrences during space exploration missions. These are not only a necessary component of landing and sampling maneuvers, but can also be used as impact experiments to reveal characteristics of the interacting surfaces. 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 (Wright et al., 2020). 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. We also assess how packing fraction at the point of impact influences different impact behavior types. 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 evoke a change in the grains' dissipative response that dispatches energy predominantly laterally from the impact site instead of deeper into the bed. Finally, we consider how sub- surface response could link with impactor dynamics to deepen our understanding of oblique, low-velocity impact events, one day helping to improve mission outcomes.

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