Department of Physics, Engineering Physics & Astronomy

Queen's University
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Department of Physics, Engineering Physics & Astronomy
Department of Physics, Engineering Physics & Astronomy

Craters in Granular Materials

John deBruyn
Western University

Thurs., April 17, 2014
10:30 AM @ Stirling 401

Abstract:

After a brief review of the interesting physics of granular materials, I will discuss experiments on the formation of craters in two- and three-dimensional noncohesive granular materials. Our craters are formed in two ways — by the normal impact of a solid spherical projectile or by the collapse of a pre-existing cavity. In three dimensions, the surfaces of the resulting craters are accurately digitized using laser profilometry, allowing for detailed investigation of the crater shape. In the two-dimensional experiments we obtain the surface profile from high-speed video images of the collapse and visualize the sub-surface flow field by particle image velocimetry. While the observed scaling of crater size with impact energy is (almost) consistent with what would be expected if all of the projectile's kinetic energy was used to excavate the crater, we find that in fact the excavation energy is only 1% of the impact energy of the projectile. The cavity collapse experiments allow a study of the granular flow without the complication of the impact. We study the evolution of the flow as the walls of the cavity collapse and model our results with a modified version of the Saint-Venant equations for shallow water flow. Finally, I will discuss the relevance of this work to the formation of craters by meteor impacts.