Experimentally Measuring Rolling and Sliding in Three-Dimensional Dense Granular Packings
Nicole Yunger Halpern (IPST/NIST/QuICS) with graduate student Zackery A. Benson and UMD colleagues Derek C. Richardson (Astronomy), and Wolfgang Losert (IPST/Physics), published an article titled “Experimentally Measuring Rolling and Sliding in Three-Dimensional Dense Granular Packings“ in Physical Review Letters, July 18.
The team experimentally measured a three-dimensional (3D) granular system’s reversibility under cyclic compression. They imaged the grains using a refractive-index-matched fluid, then analyzed the images using the artificial intelligence of variational autoencoders. These techniques allowed them to track all the grains’ translations and 3D rotations with accuracy sufficient to infer sliding and rolling displacements. Their observations reveal unique roles played by 3D rotational motions in granular flows. They found that rotations and contact-point motion dominate the dynamics in the bulk, far from the perturbation’s source.