Microscopic Dynamics of Particle Rearrangement and its Correlation with Stick-slip Behavior in Granular Shear

The link between the microscopic dynamics of particles and the macroscale response of granular materials has not been well established. To address this, we investigated the microscopic dynamics and fluctuations in the force network in a granular material subjected to plane shear. A two-dimensional discrete element model of a plane shear test was established, considering both sliding and rolling friction. We found that particle rearrangement originated from the reduction of inter-particle forces in an identifiable region, which we call the greatest reduction (GR) region, defined as a region containing inter-particle forces experiencing the greatest decrease in magnitude in a given time interval. Statistical analysis shows that not only the magnitude of the greatest non-affine deformation in the GR region but also dynamics of neighboring particles in the region are highly correlated with the macroscale shear stress drop. These trends were also observed for various sliding friction coefficients and for simulations containing many particles. However, the quantity and configuration of GR regions had minimal impact on macroscale stress drops. We expect that this study will shed new light on the relationship between microscopic dynamics and force network fluctuations in sheared granular media and contribute to developing a mesoscale elasto-plastic model for these materials.