EVENT DETAILS AND ABSTRACT

Title: Internal Structure of Granular Shear Flows*
Speaker: Jerry Gollub
Speaker Info: Haverford College and University of Pennsylvania
Brief Description:
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Abstract:

The response of granular material to imposed shear is a key to understanding granular dynamics. The internal structure (e.g. ordered or random) of the material can strongly affect the shear response of these materials. In this work, we use a novel imaging technique and sensitive measurement of granular volume and forces to investigate the interior of granular shear flows with a narrow particle size distribution. We find that shearing can trigger crystallization of the material, and an accompanying step compaction event. The velocity profiles vary over more than five orders of magnitude (as a function of position). The internal flow profiles are radically different in the ordered and disordered internal states. Furtheremore, boundary conditions can have a profound influence on the entire packing. We find that continuously sheared flow can exhibit non-unique final states even under identical boundary conditions. In some cases both ordered and disordered states coexist, with the disordered state being metastable. Our experiments raise interesting theoretical questions about how prior history is recorded in the internal structure of granular packings, affecting their instantaneous rheology and long-term evolution in response to shear. *Work done with JC Tsai, and supported by the NSF, Division of Materials Research.