Mechanics of Deformation in 3D Granular Materials Using X-ray Measurements*

Granular materials deform in complex ways, including through particle deformation, local particle rearrangements, inter-particle slip, and particle fracture. Discrete and continuum models have been proposed within the engineering and physics communities to capture the effects of these deformation mechanisms on mechanical and dynamical material properties. For instance, local particle rearrangements have been captured in glassy rheology models and shear transformation zone theories, while particle fractures have been captured in the continuum breakage mechanics framework. A major challenge remains the quantitative validation and calibration of these models using in-situ 3D experimental data.

In this talk, I will discuss our experiments combining in-situ X-ray computed tomography (XRCT) and 3D X-ray diffraction (3DXRD) during the deformation of granular materials. The samples we have studied to-date include tens to over 1,000 spherical and angular particles, each ranging in size from 100 to 400 μm, and each typically composed of single-crystal sapphire or quartz. We have subjected samples to a variety of loading conditions, including uniaxial compression and triaxial compression. XRCT measurements performed periodically during loading provide high-resolution 3D images of the evolving structure of granular materials during deformation. 3DXRD measurements provide the location (with several um precision), the orientation (with 0.05^○ precision) and the strain tensor (with 10^-4 resolution) in each of thousands of particles, from which the stress tensor of each particle can be computed. I will present examples of prior work studying local particle rearrangements and inter-particle slip. I will also discuss ongoing and future work on the impact of both structure and forces on ultrasound transmission and the quantitative details of local particle rearrangements.