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Brian Utter

Diffusion and elastic energy measurements in dense granular shear flows

Abstract: We present experiments on granular shear in a 2D Couette geometry. The system consists of photoelastic disks, allowing us to observe the behavior of stresses and kinematic properties at the particle scale. In particular, we study particle diffusion and stored elastic energy, with the goal of generalizing the concept of a granular temperature to dense granular flows. We find particle motion to be diffusive at small time scales with a diffusivity proportional to local shear rate. Diffusivities along the direction of flow are measured to be larger than those perpendicular to the shear band. At larger scales, effects due to particle size and coordinated motion are observed. We find that in dense granular flows the anisotropic stress network induces an anisotropy in the particle diffusivity which is not observed at larger shear rates. Elastic energy storage in the grains is measured as a key factor in determining the thermodynamic analog to temperature in dense systems, where velocity fluctuations form an incomplete picture.