Shear cessation in the pre-yielding and post-yielding of jammed suspensions

A range of soft materials, for example, foams, emulsions & grains, begin to flow beyond some threshold value of external deformation. This transition from solid-like to liquid-like deformation behavior is known as yielding. Here, we simulate the steady shear startup of a non-Brownian jammed suspension, whose flow curve is described by the Herschel-Bulkley form. The transient behavior of our dense soft solids shows a stress overshoot followed by a steady shear plateau. We perform an iterative series of flow cessation simulations as the strain increases to probe the progression of yielding. We study the time-dependent recovery of the solid-like character in these granular materials by separating the role of the shear rate prior to flow cessation and the jammed structure.

We find that stress relaxation shows two distinct processes or regimes, the relaxation is stretched exponential in the first and power-law or logarithmic, and dominant for higher shear rates, in the second regime. We show the differences in the material microstructure at the onset of shear banding and the steady-state from the stress relaxation behavior and the particle rearrangements. Further, we investigate the role of shear rate and residual stresses on the viscoelastic response of the final jammed solids.