The effect of pins on micro- and macroscopic properties of sheared particles near jamming

Jamming, the onset of macroscopic rigidity, occurs in a wide variety of disordered soft/granular systems. Fixing degrees of freedom by adding pinned particles facilitates jamming and tunes microscopic and macroscopic properties near the jamming threshold. For example, it has been shown for a system in mechanical equilibrium that pins dramatically alter the distribution of forces and decrease the elastic moduli [1]. Here, we use LAMMPS molecular dynamics to shear an athermal 2D system of harmonically repulsive particles. Particles and pins are sheared at a constant rate between rough particulate walls. We study the effect of pins on pressure and shear stress vs. shear rate and packing fraction, and analyze transient responses like yield. Microscopically, we study relationships between D²_min, which quantifies a particle’s non-affine deformation, contact number, Z, and locations of pins.

[1] A.L. Zhang, S.A. Ridout, C. Parts, A. Sachdeva, C.S. Bester, K. Vollmayr-Lee, B. C. Utter, T. Brzinski, and A.L. Graves, Phys. Rev. E 106, 034902 (2022)