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University of Chicago MRSEC Irving P. Jaeger DMR-0213745 Granular Jets (IRG1)

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University of Chicago MRSEC Irving P. Jaeger DMR-0213745 Granular Jets (IRG1)

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  1. When a marble or ball bearing is dropped on the ground, it will typically land with a thud. However, when the same object is dropped onto a bed of fine, loose sand there will be a remarkably different response: a broad splash of sand at impact and, after the marble has penetrated deeply into the bed, a tall jet of granular material that shoots up vertically. Such jets are among the most spectacular manifestations of liquid-like behavior in granular materials, curiously resembling similar phenomena in ordinary liquids. Yet they occur in the absence of any cohesion or surface tension. Even more surprisingly, the jet formation depends on the ambient pressure. Experiments at the Chicago MRSEC in collaboration with researchers from the Advanced Photon Source at Argonne National Lab have tracked the birth and evolution of these granular jets using the fastest x-ray-based imaging performed to date (6000 video frames per second) [1]. The measurements provide a new understanding of how granular jets are formed and establish what gives rise to their dependence on ambient gas pressure. It has been suggested that small-scale impact experiments could serve as a model for crater formation and material ejection due to large-scale astrophysical impact. Our findings show that gas plays a major role in the formation of a granular jet, adding a key parameter that may only be present in certain types of astrophysical impacts. University of Chicago MRSECIrving P. Jaeger DMR-0213745Granular Jets (IRG1) The images show granular jets emerging from a bed of fine glass spheres after impact by a heavy steel sphere dropped from above. Results for four different ambient air pressures are given. Note the two-stage jet shape visible at intermediate pressures. [1] Formation of granular jets observed by high-speed X-ray radiography, J. R. Royer, E. I. Corwin, A. Flior*, M. L. Cordero**, M. L. Rivers, P. J. Eng, and H. M. Jaeger, Nature Physics 1 (3), 164-167 (2005). * undergrad; ** Chilean grad student supported by the Chicago-Chile Inter-American Materials Collaboration DMR-0303072

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