Non-affine Dynamics of a Sheared Athermal System with Pins

We use molecular dynamics simulations to study a two-dimensional athermal, bidisperse system with purely repulsive harmonic interactions. Energy is dissipated via interactions depending on relative velocity. The system additionally includes fixed degrees of freedom in the form of miniscule particles, ‘pins,’ located on a square lattice. Via the motion of rough top and bottom walls composed of frozen particles, we shear the system at a constant rate. During shearing, we adhere to one of two approaches: either maintaining constant pressure or constant packing fraction. For constant pressure shearing, implemented via a top wall which is able to move vertically, we observe a vertical pressure gradient for higher pin densities.

We study local non-affine dynamics of the sheared system in a steady state, primarily focusing on D²_min , a per-particle metric of non-affine motion. Notably, we find that for quasi-static shearing at a constant packing fraction, the occurrences of local non-affine events tend to be concentrated closer to the pins. The probability density at a certain distance from the nearest pin for the occurrence of non-affine events is independent of pin density for short distances from the pins.