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J. David, P. Filip, A.A. Kharlamov
Back extrusion of Vocadlo-type fluids

Appl. Rheol. 23:4 (2013) 45366 (8 pages)

Back extrusion represents one of the cheapest experimental methods to determine rheological characteristics of studied fluids, and simultaneously minimise their disruption in comparison with conventional rotational rheometers. This method is based on plunging a circular rod into an axisymmetrically located circular cup containing the experimental sample. Formerly this method has, among other uses, been successfully applied to determinations of parameters appearing in power-law, Bingham and Herschel-Bulkley fluids. The aim of this contribution is to present a sufficiently simple user-friendly procedure for determining individual rheological parameters appearing in the Vocadlo model (sometimes called the Robertson-Stiff model) - yield stress, consistency parameter and flow behaviour index.

Cite this publication as follows:
David J, Filip P, Kharlamov A: Back extrusion of Vocadlo-type fluids, Appl. Rheol. 23 (2013) 45366.

J. David, P. Filip
Phenomenological Modelling of Non-Monotonous Shear Viscosity Functions

Appl. Rheol. 14:2 (2004) 82-88

The aim of this paper is to present a new phenomenological rheological model suitable for the description of a wide class of viscoelastic fluids. Classical phenomenological models predict the relation shear viscosity vs. shear rate (or shear stress) for shear-thinning (or thickening) materials exhibiting smooth monotonous passage from the first - upper (lower) - Newtonian plateau to the second - lower (upper) - one. However, present state of non- Newtonian materials used in practice (ranging from aqueous surfactant solutions, bituminous materials, associative polymers, polymer thickeners, lacquers and gels, to some special disperse systems, etc.) evokes the need to describe this - for many materials non-monotonous - relation in the corresponding way, i.e. through the sufficiently simple phenomenological model with a moderate number of parameters. A six-parameter model enabling description of not only monotonous but also non-monotonous course of shear viscosity function against shear rate (stress) is proposed including physical characterisation of the parameters. This model describes not only extreme points (maximum or minimum) but also a possible appearance of intermediate Newtonian plateau or its indication. The meaning and influence of the individual six parameters is documented on the experimental data published in the literature. There is a good agreement of the model proposed with many different experimental data representing different rheological behaviour. The applicability of this model for a wide class of viscoelastic materials is its principal advantage over the hitherto published phenomenological models.

Cite this publication as follows:
David J, Filip P: Phenomenological Modelling of Non-Monotonous Shear Viscosity Functions, Appl. Rheol. 14 (2004) 82.

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