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Pre-avalanche structural rearrangements in granular packing

Thursday 8th January 2009 - 11:30 to 11:45
INI Seminar Room 1
It has long been known that, under increasing inclination, a granular medium displays a transition from a solid like (static regime) to a fluid like (flow regime) phase. A complete understanding of this transition seems yet unavailable. However, predicting this transition is important for geophysics, numerous industrial applications, and for understanding the dynamics of granular materials and the unjamming transition.An important question is whether reliable precursors can be found when approaching the critical angle. The main finding reported in previous studies is that the density of surface rearrangements gradually increases when increasing the inclination angle. For small angles (~10), events are rare and occur randomly on the surface while, close to the critical angle (~25), quasi-periodic rearrangements involving larger and larger numbers of grains were observed. Our experimental work consists in studying the dynamics of a 3D granular packing constituted by glass beads contained in a rectangular box which is inclined up to the threshold of instability. With an image processing technique and tracking methods, we obtain the number of surface rearrangements and we follow the trajectories of grains as a function of the angle inclination. When the angle increases, four types of events are observed. Weak rearrangements take place at random on the surface for small angles (
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons