Jamming and Dynamics of Granular Materials


Robert P. Behringer (Duke University)


This talk will consider the near-jamming behavior of granular systems consisting of frictional particles. We have recently shown that there exists a range of packing fractions for which it is possible to start from zero stress states, and by applying shear strain, traverse a regime of fragile states, ultimately arriving at a jammed state. These results have been obtained by using photoelastic particles, which allow detailed force and contact information, and from several different kinds of experiments. The largest density, phi_J, for which this behavior applies is comparable to the jamming density of frictionless disks, and the lowest density for which this occurs, phi_S, may be tied to the random loose packing density. Shear-jammed states are characterized by anisotropy in various quantities such as the stress stress, the fabric, and in general, the force networks. Shear jamming is of particular interest for granular dynamics, since many slow granular shear flows occur near this regime, and the arrest of flow occurs due to shear jamming, not to isotropic jamming. For example, Couette flow, flows in shear bands, and flows in hoppers may all be influenced by shear jamming.

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