Physics Colloquium
Friday, January 23rd, 2004 4 P.M.

Brian Utter

Center for Nonlinear and Complex Studies
Department of Physics
Duke University

Granular Shear Flows: Scientist in a Sandbox

Granular materials are ubiquitous in nature and in industry, from avalanches and beach erosion to the mixing of pharmaceutical powders and the transport of food materials. Surprisingly though, there is little understood about these materials. This is due to the complex behaviors that develop when many particles interact, the strong fluctuations in the force network, and the fact that systems become jammed in metastable configurations.

I will describe experiments on the shearing of granular materials in a system that allows observation of the complicated "force chain" network, in addition to the kinematics at the particle scale. The ultimate goal is the development of a dynamical description like the Navier-Stokes laws for fluids. Particle diffusion and the first elastic energy measurements at the grain scale are made to determine quantities necessary for a statistical description of granular materials. We find the system behaves diffusively, but coupling to the mean flow leads to apparent sub- or super-diffusive behavior. Diffusion measurements also reveal the importance the force network in these dense systems. I will present the first experimental measurements of elastic energy distributions. I will then suggest the next steps necessary to construct a non-equilibrium statistical mechanics for this interesting class of materials.

Refreshments 3:30 P.M. Room E200 Math/Science Center