Rheological properties of short fiber model suspensions

Abstract

International audienceThe rheological behavior of two series of model suspensions containing the same glass fibers in a Newtonian polybutene and in a Boger fluid has also been investigated. The steady-state shear viscosity of both supensions increased with fiber content, but the suspensions in the Boger fluid became shear thinning. Both types of suspension exhibited non-negligible normal stresses. The steady-state viscosity and normal stress difference of the supensions in the polybutene are well predicted by the Lipscomb ~1987! equation coupled with the Folgar–Tucker ~1984! model. Both types of fiber suspensions were shown to exhibit shear and normal stress overshoots in stress growth experiments. Under flow reversal, a shear stress overshoot was observed at a larger deformation compared to the primary overshoot. The reverse overshoot has been attributed to tumbling of fibers that are not totally aligned in the flow direction even after a very long time. When the flow was reversed, the normal stress difference took initially mimimum values ~negative values in the polybutene case! and then depicted a smaller positive overshoot before reaching a steady-state value. The normal stress undershoot has been attributed to a transient fiber-oriented structure. The shape and the magnitude of these overshoots depend on the fiber content, nature of the matrix, and time delay between consecutive experiments

Rheology of concentrated suspensions of non-colloidal rigid fibres

“…Different explanations have been proposed to explain the departure from a Newtonian response. These include arguments that the fibres were not rigid under the imposed conditions (Powell 1991;Sepehr et al 2004) or that the fibres are not force-free. An example of the latter is the assertion that adhesive forces (Mongruel & Cloitre 1999;Chaouche & Koch 2001;Bounoua et al 2016b) can exist between the fibres, even though their size is large compared to typical colloidal scales.…”

Orientierungsverhalten plättchenförmiger Zusatzstoffe in Kunststoffsuspensionen

“…Wie in [9,12] [20,21]. Daher wurde eine Modellerweiterung vorgeschlagen, wobei der Geschwindigkeitsgradient mit einem konstanten Faktor skaliert wird [20,21].…”

“…Daher wurde eine Modellerweiterung vorgeschlagen, wobei der Geschwindigkeitsgradient mit einem konstanten Faktor skaliert wird [20,21]. Dieser Ansatz wird auch als "reduced strain closure" (RSC) bezeichnet.…”

Dissipative particle dynamics simulations for fibre suspensions in newtonian and viscoelastic fluids

“…The results clearly showed that at low shear rates, increasing volume fractions and/or fibre aspect ratios leads to increase the viscosity, whereas at high shear rate the suspension viscosity approach to that of suspending viscoelastic fluids and almost independence of fibre characteristics. More recently, Sepehr et al [16] have done some experiments of fibre suspended into both Newtonian and Boger fluids. The results show that shear-thinning behaviour occurs strongly in Boger solvent but is only lightly observable in Newtonian solvent and the suspension viscosity seems to approach that of the suspending viscoelastic fluid at very high shear rates.…”

“…0045 The fibre-suspended fluids in question are shear thinning, so that the shear viscosity decreases with increasing shear rates. Some modelling effort has been directed to this problem [11][12][13][14][15][16]. Azaier [13] successfully simulated fibre suspensions in polymeric liquids modelled by different models (FENE-P, FENE-GR and Giesekus models), their numerical results showed that the ratio of the suspension viscosity and the solvent viscosity is almost constant over whole range of shear rates even at high shear rates that is not observed in several other experiments done by Chan et al [11], Ganani and Powell [12] and Ramazani et al [15].…”