Transient inhomogeneous flow patterns in supercooled liquids under shear

Abstract

Supercooled liquids and other soft glassy systems show characteristic spatial inhomogeneities in their local dynamical properties. Using detailed molecular dynamics simulations, we find that for sufficiently low temperatures and sufficiently high shear rates supercooled liquids also show transient inhomogeneous flow patterns (shear banding) in the start-up of steady shear flow, similar to what has already been observed for many other soft glassy systems. We verify that the onset of transient shear banding coincides quite well with the appearance of a stress overshoot for temperatures in the supercooled regime. We find that the slower bands adapt less well to the imposed deformation and therefore accumulate higher shear stresses compared to the fast bands at comparable local shear rates. Our results also indicate that the shear rates of the fast and slow bands are adjusted such that the local dissipation rate is approximately the same in both bands.

Non-Newtonian flow effects in supercooled water

“…The stress-strain curves display nonmonotonic behavior that is typical of viscoelastic fluids, as has been observed in a variety of systems, both experimentally as well as in simulations [26][27][28][29][30][31][32]. At the early stages of the flow process, the stress increases linearly with strain, typifying a solid-like elastic response characterized by a modulus that is independent of the deformation rate.…”

On the yielding of a point-defect-rich model crystal under shear: insights from molecular dynamics simulations

“…Another evidence for this hypothesis is provided by the fact that the maximum in the stress vs. strain curves does not disappear at low shear rates where τ s τ h . Eventually we note that the above mentioned features are in striking contrast to non-Newtonian fluids (such as supercooled liquids 60,61,71 , ferrofluids 72 , polymers 73 , mixtures of ferrofluids and liquid crystals 74 , to name a few) where only diffusion of the particles is responsible for the stress relaxation, and the maximum in the stress vs. strain response disappears at low shear rates, i.e. where τ s is comparable to structural relaxation times.…”

Effect of Sodium Chloride on Internal Quasi-Liquid Layers in Ice Ih

“…Figure a displays its behavior for the three considered salinities as a function of the shear strain, defined as γ ≡ Δ y / L z , with Δ y the relative displacement of the grains in the y -direction and L z the size of the bicrystal in the z direction. The stress–strain curves are qualitatively the same for all cases and resemble the typical behavior of viscoelastic systems. − The initial response is elastic in nature, with the shear stress increasing linearly with the strain. In this regime the displacement of the upper grain is small, giving rise to elastic shear deformations of the crystal grains but without evoking any sliding at the GB region.…”