The role of interstitial gas in determining the impact response of granular beds
James Franck Institute and Department of Physics, The University of Chicago - Chicago, IL 60637, USA
2 Consortium for Advanced Radiation Sources, The University of Chicago - Chicago, IL 60637, USA
Accepted: 6 January 2011
We examine the impact of a solid sphere into a fine-grained granular bed. Using high-speed X-ray radiography we track both the motion of the sphere and local changes in the bed packing fraction. Varying the initial packing density as well as the ambient gas pressure, we find a complete reversal in the effect of interstitial gas on the impact response of the bed: The dynamic coupling between gas and grains allows for easier penetration in initially loose beds but impedes penetration in more densely packed beds. High-speed imaging of the local packing density shows that these seemingly incongruous effects have a common origin in the resistance to bed packing changes caused by interstitial air.
PACS: 83.80.Fg – Granular solids / 45.70.Cc – Static sandpiles; granular compaction / 47.56.+r – Flows through porous media
© EPLA, 2011