Simulations of jammed, quasi-statically sheared particles and fixed pins

Jamming, the onset of macroscopic rigidity, is an important propensity of soft/granular systems that is driven by temperature, stress, and packing fraction. It has recently been shown that fixing degrees of freedom by adding pinned particles also drives jamming, tunes properties of the system near the jamming threshold and modifies the interparticle force network topology [1].

We determine properties of a two-dimensional, soft, granular system at different pin densities via molecular dynamics simulations with rough walls to establish constant pressure and shear rate. Macroscopically, we find that the presence of pins decreases the linear elasticity and increases the plasticity of the system. Mesoscopically, transverse velocity is attenuated and circulation patterns are established around pins. Collective behaviors for shearing and compression are approximated by models with Hookian springs. On the microscopic level, non-affine deformations of clusters of particles, quantified using D²_min, are more pronounced around pins and the total number of locations of high D²_min increase with pin density.

[1] P. Wentworth-Nice et al., Soft Matter 16, 5305 (2020); A.L. Zhang et al, Phys. Rev. E 106, 034902 (2022).