Abstract
Yield stress fluids display complex dynamics, in particular when driven into the transient regime between the solid and the flowing state. Inspired by creep experiments on dense amorphous materials, we implement mesoscale elasto-plastic descriptions to analyze such transient dynamics in athermal systems. Both our mean-field and space-dependent approaches consistently reproduce the typical experimental strain rate responses to different applied steps in stress. Moreover, they allow us to understand basic processes involved in the strain rate slowing down (creep) and the strain rate acceleration (fluidization) phases. The fluidization time increases in a power-law fashion as the applied external stress approaches a static yield stress. This stress value is related to the stress over-shoot in shear start-up experiments, and it is known to depend on sample preparation and age. By calculating correlations of the accumulated plasticity in the spatially resolved model, we reveal different modes of cooperative motion during the creep dynamics.
Highlights
Yield stress fluids display complex dynamics, in particular when driven into the transient regime between the solid and the flowing state
The implementations we use are suitable for athermal amorphous systems, which constitute a large sub-class of Yield-stress fluids (YSFs), including foams, emulsions, physical gels and granular media [1]; where large Peclet numbers assure that thermal fluctuations are negligible compared with mechanical fluctuations induced by the response to an external driving
The only difference is that the last maximum in Ic(t) appears later and the final stationary correlation pattern is a bit more pronounced for the smaller stress. We used both spatially-resolved and mean-field mesoscopic models to study the creep behavior of athermal amorphous materials with different initial relaxation degrees
Summary
Yield stress fluids display complex dynamics, in particular when driven into the transient regime between the solid and the flowing state. Inspired by creep experiments on dense amorphous materials, we implement mesocale elasto-plastic descriptions to analyze such transient dynamics in athermal systems Both our mean-field and space-dependent approaches consistently reproduce the typical experimental strain rate responses to different applied steps in stress. The response of the system is probed as a function of its initial age Such experiments reveal an intriguing behavior with two salient features: (i) the strain-rate γ (t) in response to a stress larger than the yield stress is strongly non-linear and nonmonotonous, with a so called “S-shaped” dependence of γ (t) [5,6,7], including a nontrivial “primary creep regime” often described by a power law γ ∼ t−μ; (ii) the fluidization time scale τf diverges when approaching the yield stress, yet in a non-universal manner.
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