Material parameter influence on the expression of impulse-induced surface dilation

Abstract

We formulate a method for predicting peak particle forces in a wavefront within a randomly filled 3D granular channel. The wavefronts in our simulation are driven by a sustained impact originating in the bumpy floor of the channel. We show that, when generated in this manner, forces in the driven wavefront within the 3D assembly follow the same power law scaling on material properties and impact velocity as in a 1D chain. A simple scaling of the 1D forces matches results from simulated impact tests we conduct using Soft Sphere Discrete Element method simulations. We then quantify the magnitude of impulse-induced dilation that occurs as a result of varied material properties and gravitational environments, giving an equation that can be used to predict the lofting depth (depth to which particles experience bulk density changes as a result of a laterally propagating wavefront). As predicted by our equation and confirmed with simulated results, dilation is amplified as particle material properties become closer to lunar regolith grains, supporting the hypothesis that impulse-induced surface dilation is the lunar cold spot formation mechanism.