The chaotic dynamics of jamming

Abstract

Granular materials are collections of discrete, macroscopic particles characterized by relatively straightforward interactions. Despite their apparent simplicity, these systems exhibit a number of intriguing phenomena, including the jamming transition, in which a disordered collection of grains becomes rigid when its density exceeds a critical value. Many aspects of this transition have been explored, but an explanation of the underlying dynamical mechanisms for the transition remains elusive. Here, applying nonlinear dynamical techniques to simulated two-dimensional Couette shear cells, we reveal the mechanisms of jamming and find that they conflict with the prevailing picture of growing cooperative regions. In addition, at the density corresponding to random close packing, we find a dynamical transition from chaotic to non-chaotic states accompanied by diverging dynamical length- and timescales. Furthermore, we find that the dominant cooperative dynamical modes are strongly correlated with particle rearrangements and become increasingly unstable before stress jumps, providing a way to predict the times and locations of these striking stress-release events in our simulations. © 2013 Macmillan Publishers Limited. All rights reserved.