Contact breaking in packings of frictional disks

We employ discrete element modeling simulations of the geometrical asperity or "bumpy particle" model to study the nonlinear vibrational response of jammed packings of frictional disks. We first calculate the eigenmodes of the dynamical matrix for each bumpy-particle packing. We then perturb the packing by a given velocity along a single and multiple eigenmodes of the dynamical matrix, run the simulations at constant total energy, and measure the Fourier transform of the translational and rotational velocities of the particles. For small velocity perturbations, contacts do not break, and the peaks in the power spectrum occur at frequencies that match the eigenfrequencies of the dynamical matrix. We determine the characteristic temperature T_c above which the interparticle contact network breaks, and compare the density of vibrational modes from dynamical matrix to the power spectrum for T > T_c. We show that perturbing along eigenmodes with primarily translational velocities gives rise to qualitatively different behavior of the vibrational response compared to that after perturbing along eigenmodes with primarily rotational content.