Three Dimensional Particle Rearrangements During Slow Granular Shear Flow In A Split Bottom Geometry

Abstract

We carry out three dimensional imaging of the positions and rearrangements of all particles during slow shear flow of granular matter in a split bottom shear cell geometry. The aim is to gain insights into dense granular flows at the level of individual particle displacements. To image particle motion in three dimensions plastic spheres are used that are immersed in index matching fluid that is fluorescently dyed. This allows for imaging of cross sections with a laser sheet and sensitive camera. Scanning the laser sheet generates a 3D image, from which we reconstruct the position of all particles and their motion in a 3D volume. We find that for low shear rates the flow structure of this fluid immersed granular material are similar to the flow structure of dry granular materials; the radial velocity profiles can be fit with an error function. Our initial focus is on reversible vs irreversible deformations in granular flows. Reversing the shear direction leads to a flow profile that does not exactly mirror the flow profile before reversal, indicating irreversible deformations in the shear zone. Following the motion of individual particles through at least ten oscillations shows that particles in the shear band rearrange. Their mean squared displacement increases subdiffusively with the number of oscillations.

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