The yield stress myth
TL;DR: In this article, the simple Cross model is shown to be a useful empiricism for many non-Newtonian fluids, including those which have hitherto been thought to possess a yield stress.
Abstract: New experimental data obtained from constant stress rheometers are used to show that the yield stress concept is an idealization, and that, given accurate measurements, no yield stress exists. The simple Cross model is shown to be a useful empiricism for many non-Newtonian fluids, including those which have hitherto been thought to possess a yield stress.
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TL;DR: In this paper, the authors give an account of the development of the idea of yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time.
Abstract: 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 (
950 citations
TL;DR: Semisolid metal (SSM) processing is a relatively new technology for metal forming as discussed by the authors, which deals with semisolid slurries, in which non-dendritic solid particles are dispersed in a liquid matrix.
Abstract: Semisolid metal (SSM) processingis a relatively new technology for metal forming. Different from the conventional metal forming technologies which use either solid metals (solid state processing) or liquid metals (casting) as starting materials, SSM processing deals with semisolid slurries, in which non-dendritic solid particles are dispersed in a liquid matrix. Semisolid metal slurries exhibit distinctive rheological characteristics: the steady state behaviour is pseudoplastic (or shear thinning), while the transient state behaviour is thixotropic. All the currently available technologies for SSM processing have been developed based on those unique rheological properties, which in turn originate from their non-dendritic microstructures. Year 2001 marks the 30th anniversary of the concept of SSM processing. Today, SSM processing has established itself as a scientifically sound and commercially viable technology for production of metallic components with high integrity, improved mechanical properti...
813 citations
01 Nov 2011
TL;DR: In this paper, the authors introduce colloid science and rheology, and present an overview of colloid physics and its applications in viscoelastic media. But they do not discuss the role of non-spherical particles.
Abstract: 1. Introduction to colloid science and rheology 2. Hydrodynamic effects 3. Brownian hard spheres 4. Stable colloidal suspensions 5. Non-spherical particles 6. Weakly flocculated suspensions 7. Thixotropy 8. Shear thickening 9. Rheometry of suspensions 10. Suspensions in viscoelastic media 11. Advanced topics.
792 citations
TL;DR: In this paper, a review of the current understanding of the microscopic phenomena believed to control ER and the models used to describe macroscopic behavior is presented, with particular emphasis placed upon comparing model predictions with experimental observations.
Abstract: Electrorheological (ER) suspensions, typically composed of nonconducting or weakly conducting particles dispersed in an insulating liquid, undergo dramatic, reversible changes when exposed to an external electric field. Apparent suspension viscosities can increase several orders of magnitude for electric field strengths of the order of 1 kV mm −1 , with simultaneous ordering of the microstructure into particulate columns. While this electronic control of momentum transport and structure has many applications, development is severely inhibited by a lack of suitable materials and an incomplete understanding of the underlying mechanisms. This review focuses on the current understanding of the microscopic phenomena believed to control ER and the models used to describe macroscopic behavior. Particular emphasis is placed upon comparing model predictions with experimental observations, relating macroscopic behavior to microscopic mechanisms, and demonstrating the utility of mechanistic models for furthering our understanding of electrorheology.
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TL;DR: In this article, the authors derived a flow equation for pseudoplastic flow that is associated with the formation and rupture of structural linkages in both aqueous and nonaqueous media.
1,703 citations
TL;DR: The most common type of non-Newtonian fluid is the pseudoplastic fluid as discussed by the authors, which is characterized by a constant viscosity at very low shear rates, a viscoability which decreases with shear rate at intermediate shear levels, and an apparently constant viscoality at high hear levels.
Abstract: THE most common type of non-Newtonian fluid is the pseudoplastic fluid. The pseudoplastic fluid is characterised by a constant viscosity at very low shear rates, a viscosity which decreases with shear rate at intermediate shear rates, and an apparently constant viscosity at very high shear rates. That is The apparent viscosity defined by then decreases with shear rate from η0 to η∞ and the pseudoplastic fluid exhibits a lower and upper region of Newtonian behaviour. Examples which illustrate the zero shear viscosity and the decreasing viscosity region for pseudoplastic fluids are very common and include almost all polymer melts and solutions. η∞ is generally not well defined. Often the data available only approach the high shear rate limit and η∞ is either determined by extrapolation or is set equal to zero which is a suggested theoretical value. Data which illustrate the three regions of pseudoplastic behaviour are rare and indeed are not quoted in the standard reference texts on rheology. The purpose of this communication is to present such data for a polymer solution and to compare the results to the models which are available for pseudoplastic fluids.
102 citations