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Stick slip dynamics in a sheared granular system

Friday 9th January 2009 - 10:30 to 10:55
INI Seminar Room 1
We have investigated the response of a granular medium to shear both experimentally and theoretically. The experiments consisted of a granular medium confined to a circular channel and subjected to the shear exerted by an overhead horizontal plate. On the theoretical side we devised a 1-D Langevin equation capable of describing the dynamics. We explored the parameter space and characterised the statistics of the system response by measuring several quantities, in particular: the reaction torque exerted by the medium against the shear (reaction), the plate velocity, the duration and extension of the slip events in the stick slip regime. Here we summarise the main results: (1) Fluctuations of response stress (the torque exerted by the system against the motion of the plate) are Gaussian in the steady sliding regime, but not in the stick slip regime; (2) The dynamics of the plate is quantitatively well described by a Langevin equation in which the reaction force performs Brownian motion; (3) For thin granular beds, the system behaviour strongly depends on the number of grain layers. An asymptotic state is approached at about five layers, where transition between quasi-solid and quasi-liquid behaviour becomes clearly indetifiable.
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons