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Percussion of granular material by one grain: experiment and model

Presented by: 
J Crassous & D Beladjine & A Valance [Rennes]
Tuesday 6th January 2009 - 10:30 to 10:55
INI Seminar Room 1
We studied experimentally and theoretically the process of erosion of a granular material submitted to the collision of one projected grain. A model experiment consisting of the projection of one bead on a half space filled of a packing of beads has been designed[1]. The effect of the impact is to produce the ejection of many different beads. The kinetics of the ejection process is measured with a rapid camera. The kinetic energy and the orientation of the ejected beads are computed and analysed as a function of the kinetic energy of the impacting bead and of the angle of incidence. We described accurately the full set of experimental observations with a simple model where collisions in the dense packing of spheres are treated as purely binaries[2,3]. In this description, every binary collision splits the momentum in two components, and re-direct their orientations. Momentum is then propagated following a chain of binary collisions. Chains ending with a bead placed on the top surface then allow the ejection of one bead. The successions of collisions and their statistical properties are calculated numerically on 3D packing of spheres. The distribution of the velocities of the ejected spheres, their locus of ejection, and their orientations are well described with this model without the any free parameter. [1] Djaoued Beladjine, Madani Ammi, Luc Oger, and Alexandre Valance Collision process between an incident bead and a three-dimensional granular packing Phys. Rev. E 75, 061305 (2007) [2] Jérôme Crassous, Djaoued Beladjine, and Alexandre Valance, Impact of a Projectile on a Granular Medium Described by a Collision Model, Phys. Rev. Lett. 99, 248001 (2007) [3] Alexandre Valance and Jérôme Crassous, in preparation (2008)
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons