



01745nas a2200181   4500008004100000245009400041210006900135260001500204300001100219490000800230520117000238100002401408700001901432700002801451700002601479700002101505856003701526       2022                        eng d00aExperimentally Measuring Rolling and Sliding in Three-Dimensional Dense Granular Packings0 aExperimentally Measuring Rolling and Sliding in ThreeDimensional  c06/18/2022  a0480010 v1293 a<p>We experimentally measure a three-dimensional (3D) granular system&rsquo;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&rsquo; 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&rsquo;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&rsquo; unique and powerful ability to absorb and dissipate energy.</p>1 aBenson, Zackery, A.1 aPeshkov, Anton1 aHalpern, Nicole, Yunger1 aRichardson, Derek, C.1 aLosert, Wolfgang  uhttps://arxiv.org/abs/2108.11975