Title: Stress concentration in granular matter under complex and narrow confinement

Author (Table Talk): Will Hobson-Rhoades, University of Michigan

Abstract:

The influence of boundaries on force transmission through granular matter is not well understood, but valuable for a variety of engineering applications. In this study, we investigate how various confinement geometries bias the force and contact networks of monocrystalline ruby spheres during uniaxial compression. These confinement geometries take the form of compression platens possessing ridges of various angles, including flat platens for comparison, and smooth cylindrical side walls. We experimentally resolve the particle packing structure and contact network via X-ray tomography and individual particle strains via high energy X-ray diffraction microscopy (HEDM). These experiments were also simulated with Discrete Element Method simulations. Both experimental and numerical results indicate that boundary-induced ordering dominates under narrow confinement, and numerical results suggest that stresses follow a similar ordering, with regularly spaced high-stress particles. As the boundary ridge angle increases, the stress distribution grows heterogeneous in space, with the largest stresses appearing in a region of particles located near central corners of the complex boundaries.