Start of shear flow in granular matter

One key practical question for granular matter is under what conditions grains will start to flow. We investigate how individual particles move, and what forces are needed at the start of shear flow of granular matter in a Couette geometry. We find that the forces and flow profiles depend on the his...

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Bibliographic Details
Published in:Bulletin of the American Physical Society 2004-03, Vol.49 (1)
Main Authors: Losert, Wolfgang, Stambaugh, Justin, Toiya, Masahiro
Format: Article
Language:English
Online Access:Get full text
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Summary:One key practical question for granular matter is under what conditions grains will start to flow. We investigate how individual particles move, and what forces are needed at the start of shear flow of granular matter in a Couette geometry. We find that the forces and flow profiles depend on the history of prior shear. When the direction of shear is reversed, particles far from the shear surface are (for the first 5-10 particle diameters of shear) less resistant to flow even though they are in a denser configuration and exhibit a wider shear band. This can be understood as a macroscopic manifestation of the anisotropy of the contact network of sheared granular matter. During the reversal of shear the contact network breaks and reforms with a different anisotropic structure. To determine the microscopic signatures of this structural anisotropy, we probe the arrangement of grains using confocal microscopy. Potential applications to geophysical phenomena include triggering of large geostrophic flows (e.g., rock avalanches). Their location shows some correlation with the history and azimuth of prior shear.
ISSN:0003-0503