The Effects of Pins on Force Chains in a Granular System: A Simulation

Granular media are large collections of disordered macroscopic particles interacting via contact forces. We use molecular dynamics simulations to study a two-dimensional, 50:50 binary mixture of discs with radii ratio 1:1.4.Particles experience both harmonically repulsive and velocity-dependent dissipative forces. We freeze the positions of particles at the top and bottom of the simulation cell to serve as rough walls. Via the walls, we shear the system at a constant strain rate . We study how dynamical properties are influenced by the addition of various densities of tiny discs (termed "pins") of radii 0.004 frozen in positions on a square lattice. We explore the role of pins on the force chains at two pressures above the jamming transition. The probability distribution P(F_ij) for the network of forces F_ij between particles i and j is studied for the system as a whole, as well as for layers at various distances to the shearing walls, and to nearby pins.