Timescale divergence at the shear jamming transition

Abstract

We find that in simulations of quasi-statically sheared frictional disks, the shear jamming transition can be characterized by an abrupt jump in the number of force bearing contacts between particles. This mechanical coordination number increases discontinuously from $Z = 0$ to $Z \gtrsim d +1$ at a critical shear value $\gamma_c$, as opposed to a smooth increase in the number of geometric contacts. This is accompanied by a diverging timescale $\tau^*$ that characterizes the time required by the system to attain force balance when subjected to a perturbation. As the global shear $\gamma$ approaches the critical value $\gamma_c$ from below, one observes the divergence of the time taken to relax to a state where all the inter-particle contacts have uniformly zero force. Above $\gamma_{c}$, the system settles into a state characterized by finite forces between particles, with the timescale also increasing as $\gamma \to \gamma_{c}^{+}$. By using two different protocols to generate force balanced configurations, we show that this timescale divergence is a robust feature that accompanies the shear jamming transition.