Determining the media composition dependence of low-energy impact cratering characteristics in a dry, granular medium (original) (raw)
Impact cratering depends on projectile-to-grain and grain-to-grain interactions during the very short time of impact. This study investigates the effects of different media composition, namely the ratio between beach sand and silica sand of the impacted medium, on crater diameter and depth. Pure silica sand, pure beach sand, and ratios of 1:2, 1:1 and 2:1 of silica:beach sand were tested, and a plastic ball was dropped from various heights for different media. The recorded crater diameters and depths indicate that impact cratering is a more complex process than previously thought mainly because of the increased randomness in grain-to-grain contacts and force chain distributions produced by mixing different granular materials. It seems that mixtures of smaller grains and larger grains create a quasi-alloy state where smaller grains fill in the gaps between larger grains to increase the number of grain-to-grain contacts and force chains, and hence increase the rigidity of the medium. An equal partitioning of silica sand and beach sand seem to maximize this effect, as the medium with a volume ratio of 1:1 silica:beach sand has the smallest scaling factor for crater diameter. Although the crater depths result did not follow the 1/3 to 1/4 scaling factor proposed by previous studies, the shallower depths with larger compositions of silica sand confirm that crater depth decreases as grain sizes increase. The data also suggest that the quasi-alloy state of mixed medium redirects the energy of the projectile from deeper penetrations instead to wider and shallower displacements of sand.
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