From steady flow to rest: percolation and rigidity in flow cessation of jammed suspensions

Under flow, jammed particle suspensions behave like yield stress fluids and display a complex stress relaxation when the flow is stopped. We have studied their stress relaxation upon flow cessation through large-scale computer simulations of soft, repulsive, and poly-disperse particles. Using a Voronoi analysis of the local packing during the stress relaxation, we construct a set of polyhedra to identify which local packing structures underpin the evolution toward mechanical stability. In particular, the time evolution of icosahedrally shaped Voronoi cells can be directly correlated to the stress relaxation in the the model jammed suspension. A time correlation analysis of the polyhedra dynamics upon flow cessation yields information on the characteristic timescales of relaxation within the jammed suspension. With a cluster analysis, we investigate the percolation of different types of polyhedral regions throughout the jammed suspension. Finally, we link the number of regions which maintain their icosahedral packing throughout relaxation to the suspension's residual stress.