Avalnaches to Flow, Avalanches to Stop

To approach and remain in steady-state, yield stress fluids experience avalanches of plastic rearrangements. These avalanches during flow encode memory of the flow conditions which govern the stress relaxation and final residual of the yield stress fluid. We use large-scale simulations of soft jammed particles to disentangle the role of stored elasticity and the emerging plastic avalanches during stress relaxation to understand the build-up of residual stress [2]. We identify plastic events by the change in locally stiffer (icosahedrally-packed) regions. Our simulations provide evidence of a power-law distribution of inter-times between plastic events which underpin a power-law decay in the stress relaxation, suggesting that avalanches are present as the yield stress recovers its rigidity. The number of icosahedrally-packed regions increase and rearrange over time as the system recovers mechanical equilibrium. Our results suggest that the recovery of rigidity may be related to a percolation of these locally stiffer regions which controls the residual stress build-up. We discuss these results in the context of elastoplastic models and recent experiments [1].

[1] Vinutha, HA et al., “Memory of shear flow in soft jammed materials”, PNAS Nexus 3 (2024): 441

[2] Bayer, L., Vinutha, HA, and Del Gado, E., in preparation (2025)