Stress concentration in three-dimensional granular matter under various confinement geometries

There are still many aspects of the transmission of forces through the disordered contact network of a frictional granular material that we do not fully understand. 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 a smooth cylindrical container and compression platens possessing ridges of various angles, including flat platens for comparison. We experimentally resolve the particle packing structure and contact network via X-ray tomography and individual particle strains via X-ray diffraction. These experiments were also simulated with Discrete Element Method simulations. Both experimental and numerical results indicate that the average individual particle strain distribution remains constant regardless of confinement geometry. The locations of high-stress particles within the contact network were then examined across the different platen ridge geometries.