An account is given of the development of the idea of a yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time. Originally, it was accepted that the yield stress of a solid was essentially the point at which, when the applied stress was increased, the deforming solid first began to show liquid-like behaviour, i.e. continual deformation. In the same way, the yield stress of a structured liquid was originally seen as the point at which, when decreasing the applied stress, solid-like behaviour was first noticed, i.e. no continual deformation. However as time went on, and experimental capabilities increased, it became clear, first for solids and lately for soft solids and structured liquids, that although there is usually a small range of stress over which the mechanical properties change dramatically (an apparent yield stress), these materials nevertheless show slow but continual steady deformation when stressed for a long time below this level, having shown an initial linear elastic response to the applied stress. At the lowest stresses, this creep behaviour for solids, soft solids and structured liquids can be described by a Newtonian-plateau viscosity. As the stress is increased the flow behaviour usually changes into a power-law dependence of steady-state shear rate on shear stress. For structured liquids and soft solids, this behaviour generally gives way to Newtonian behaviour at the highest stresses. For structured liquids this transition from very high (creep) viscosity (>106 Pa.s) to mobile liquid (

The yield stress—a review or ‘παντα ρει’—everything flows?

Yield stress fluids are encountered in a wide range of applications: toothpastes, cements, mortars, foams, muds, mayonnaise, etc. The fundamental character of these fluids is that they are able to flow (i.e., deform indefinitely) only if they are submitted to a stress above some critical value. Otherwise they deform in a finite way like solids. The flow characteristics of such materials are difficult to predict as they involve permanent or transient solid and liquid regions that are generally hard to locate a priori. Here we review the present state of the art as it appears from experimental data for flows of simple (non-thixotropic) yield stress fluids under various conditions, viz., uniform flows in straight channels or rheometrical geometries, complex stationary flows in channels of varying cross-section such as extrusion, expansion, flow through a porous medium, transient flows such as flows around obstacles, spreading, spin-coating, squeeze flow, and elongation. The effects of surface tension, confinement, and secondary flows are also reviewed. We focus especially on experimental work identifying internal flow characteristics that can be compared with numerical predictions. It is shown in particular that: (i) deformations in the solid regime can play a critical role in transient flows; (ii) the yield character is not apparent in the flow field when the boundary conditions impose large deformations; (iii) the yield character is lost in secondary flows.

Yield stress fluid flows: A review of experimental data

https://pureadmin.qub.ac.uk/ws/files/202071352/20200310_Paper_on_Physics_in_DFC_revised_1_.pdf

Extrusion-based additive manufacturing with cement-based materials – Production steps, processes, and their underlying physics: A review

Plug & abandonment of offshore wells: Ensuring long-term well integrity and cost-efficiency

Slot coating is a common method in the manufacture of a wide variety of products It belongs to a class of coating method known as premetered coating: the thickness of the coated liquid layer in principle is set by the flow rate fed to the die and the speed of the substrate moving past, and is independent of other process variables Thus, premetered methods are ideal for high precision coating An important operating limit of slot coating is the minimum thickness that can be coated at a given substrate speed, generally referred to as the low-flow limit The mechanism that defines this limit balances the viscous, capillary and inertial forces in the flow Although most of the liquids coated industrially are polymeric solutions and dispersions that are not Newtonian, previous analyses of the low-flow limit in slot coating dealt only with Newtonian liquids In this paper, the low-flow limit in slot coating of an extensional thickening polymer solution is examined both by theory and by experiment The continuity and momentum equations coupled with an algebraic non-Newtonian constitutive equation that relates stress to the rate-of-strain and relative-rate-of-rotation tensors were solved by the Galerkin/finite element method to model the flows The flows themselves were visualized by video microscopy and the low-flow limit was found by observing, at given substrate speed, the feed rate at which the flow becomes unstable and breaks up Various solutions of low molecular weight polyethylene glycol (PEG) and high molecular weight polyethylene oxide (PEO) in water were used in order to evaluate the effect of mildly viscoelastic behavior on the process At the concentration level of the high molecular weight polymer explored here, the viscoelastic behavior of the solutions could not be accessed by oscillatory tests; the only measurable response to the addition of PEO was the rise of the apparent extensional viscosity

Low-flow limit in slot coating of dilute solutions of high molecular weight polymer

We examine the internal flow of viscoplastic liquids through ducts consisting of an abrupt axisymmetric expansion followed by an abrupt contraction. Steady, inertialess numerical solutions were obtained by solving the conservation equations of mass and momentum via the finite volume method. The viscoplastic behavior of the liquid was modeled by the generalized Newtonian liquid model with a recently proposed viscosity function. Flow visualization experiments were also conducted with Carbopol aqueous solutions at different concentrations. Yield surfaces delimiting yielded and unyielded regions were observed for different combinations of the governing parameters. The unyielded region is located in the large-diameter portion of the channel, near the wall. The size of the unyielded region is shown to be a strong function of the geometrical, rheological, and flow parameters.

Flow of viscoplastic liquids through axisymmetric expansions-contractions

The influence of the solvent type on the rheological properties of Carbopol ® NF 980 dispersions in water and in water/glycerol solutions is investigated. The material formulation, preparation procedure, common experimental challenges and artifact sources are all addressed. Transient and steady-state experiments were performed. For both solvent types, a clearly thixotropic behavior occurs slightly above the yield stress, where the avalanche effect is observed. For larger stresses, thixotropy is always negligible. Among other findings, it is observed that, for a given Carbopol concentration, the dispersion in the more viscous solvent possesses a lower yield stress and moduli, a larger power-law index, and a longer time to reach steady state.

Rheological Characterization of Carbopol® Dispersions in Water and in Water/Glycerol Solutions

Combustion performance of an aluminum melting furnace operating with natural gas and liquid fuel

Heat transfer to non-Newtonian fluids in laminar flow through rectangular ducts

The effect of inertia and rheology parameters on the flow of viscoplastic fluids inside a lid-driven cavity is investigated using a stabilized finite element approximation. The viscoplastic material behavior is described by the model introduced by de Souza Mendes and Dutra [30] – herein called SMD fluid – which is essentially a regularized viscosity function that involves only rheological properties of the material. The incompressible balance equations are coupled with the non-linear SMD model and are approximated by a multi-field Galerkin least-squares method in terms of extra-stress, pressure and velocity. The results obtained confirm the stability features of the multi-field formulation and the appropriateness of the rheological stress regularization introduced by the SMD fluid. The influence of inertia and rheological parameters on the morphology of the material yield surfaces is analyzed and discussed.

Mônica F. Naccache

Papers

Flow of viscoplastic liquids through axisymmetric expansions-contractions

Rheological Characterization of Carbopol® Dispersions in Water and in Water/Glycerol Solutions

Combustion performance of an aluminum melting furnace operating with natural gas and liquid fuel

Heat transfer to non-Newtonian fluids in laminar flow through rectangular ducts

Numerical approximations for flow of viscoplastic fluids in a lid-driven cavity