TY - JOUR T1 - Experimentally Measuring Rolling and Sliding in Three-Dimensional Dense Granular Packings JF - Phys. Rev. Lett. Y1 - 2022 A1 - Zackery A. Benson A1 - Anton Peshkov A1 - Nicole Yunger Halpern A1 - Derek C. Richardson A1 - Wolfgang Losert AB -

We experimentally measure a three-dimensional (3D) granular system’s reversibility under cyclic compression. We image the grains using a refractive-index-matched fluid, then analyze the images using the artificial intelligence of variational autoencoders. These techniques allow us to track all the grains’ translations and 3D rotations with accuracy sufficient to infer sliding and rolling displacements. Our observations reveal unique roles played by 3D rotational motions in granular flows. We find that rotations and contact-point motion dominate the dynamics in the bulk, far from the perturbation’s source. Furthermore, we determine that 3D rotations are irreversible under cyclic compression. Consequently, contact-point sliding, which is dissipative, accumulates throughout the cycle. Using numerical simulations whose accuracy our experiment supports, we discover that much of the dissipation occurs in the bulk, where grains rotate more than they translate. Our observations suggest that the analysis of 3D rotations is needed for understanding granular materials’ unique and powerful ability to absorb and dissipate energy.

VL - 129 U4 - 048001 UR - https://arxiv.org/abs/2108.11975 CP - 4 U5 - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.048001 ER -