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Jamming, Shear and Statistics for Granular Materials
Granular materials exhibit a range of striking behavior, with some of the most fascinating phenomena occuring for dense states—dense granular solids and fluids. Under isotropic compression, we find that real granular systems, i.e. collections of frictional particles, jam in ways that are very similar to what is expected for frictionless particles. Jamming refers to the onset of mechanical stability as the density of a system of particles increases past a critical density. In these experiments, we exploit the properties of photoelasticity to experimentally determine all relevant properties, including contact forces, particle movement etc. for systems of disks. For such systems, we also show that granular materials jam under shear at densities well below isotropic jamming. These jammed states are highly anisotropic and fragile under shear reversal, when the fabric, i.e. contact network rearranges. Recent experiments show that the fabric and shear stress play roles that are similar to the order parameter/field for a critical point (where the critical point is not point-J). As time permits, I will also explore experiments that consider diffusion, non-affine motion, penetrator dynamics and rate-dependence in granular shear flows.
Bob Behringer - Duke University Dept. of Physics
Rendez-vous en amphithéâtre Langevin, à l’ESPCI ParisTech