Particle Motion and Deformation 

You are watching shearing of 369 grains. The grains are colored differently only to distinguish them from each other. The grains are modeled as elastic-plastic, and the space between grains is void area. Shearing is accomplished by fixing the overlapping grains to the left and right boundaries. The left boundary is fixed and the right moves upward resulting in an average shear strain rate of 8x10^4 /s. The initial geometry is constructed periodic in the vertical direction so that material which flows out the top reappears at the bottom and the calculation simulates shear of an infinite periodic slab. Note that deformation is accommodated largely by cylinder rotation and translation, and is localized near the moving wall.

See Caltech's granular shear movies for some similar experimental results.