Pure Shear of 2d Granular Mixtures: Experiment

We report on the behavior of particles in an annular planar Couette shear cell. Particles are made of acrylic and constrained in a vertical stack between two concentric cylinders; the top row of particles is sheared by a serrated loading ring. The annular radius of curvature is much larger than the particle length scale, and so the experiment is effectively-2D and allows for arbitrarily large strains. The confining pressure and pile height can be varied independently, and we investigate pile response in this two-parameter space. Particle shapes include binary mixtures of disks, ellipses and spherocylinders as well as U-shaped and chiral particles that can be aligned with or against the shear. When the bottom boundary is smooth, the pile exhibits solid body motion with a frequency that increases with confining pressure and, as predicted by theory, with decreasing pile height. New experiments are looking at rougher boundaries and the effect of small numbers of non-circular particles embedded in a surrounding “sea” of circular particles.