Shearing of Granular Materials

Brian Utter

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Granular flows are ubiquitous in nature and in industry, including processes such as avalanches, draining of silos, and mixing of pharmaceutical powders.  They are also relatively simple in that you can describe the system after an intro physics class (e.g. collisions, friction, and kinetic and potential energy).  Despite this, we still don't have an accurate statistical description of granular systems (like the Navier-Stokes equation for fluids).  In fact, as John showed last week, we can't even properly describe static piles.  I will present results on granular shear flow experiments in which we can measure particle trajectories and forces at the particle scale.  In particular, I'll show diffusivity and stored elastic energy measurements which highlight the importance of the stress network that is unique to dense flows.  I'll describe why current statistical and hydrodynamic models of granular materials are incomplete in light of these results and point to ways in which we should expand current models.

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