Thixotropy—a review

Barnes, Howard A.

doi:10.1016/s0377-0257(97)00004-9

Cited by 1,302 publications

(876 citation statements)

References 48 publications

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“…In our case, to evaluate the thixotropy influence on the rheological behavior, we ran standard hysteresis loop tests. These tests are known to be insufficient for fully characterizing thixotropy, but satisfactory when the intent is just to appreciate the influence of thixotropy [49]. We first applied a linear shear-rate ramp (from zero to a maximum value) to our sample, then we decreased the shear-rate while following the same ramp backward.…”

Section: Rheometrymentioning

confidence: 99%

Experimental investigation of the spreading of viscoplastic fluids on inclined planes

Cochard

Ancey

2009

Journal of Non-Newtonian Fluid Mechanics

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a b s t r a c tWe report experimental results related to the dam-break problem for viscoplastic fluids. Using image processing techniques, we were able to accurately reconstruct the free-surface evolution of fixed volumes of fluid suddenly released a plane. We used Carbopol Ultrez 10 as a viscoplastic material; its rheological behavior was closely approximated by a Herschel-Bulkley model for a fairly wide range of shear-rates. Varying the Carbopol concentration allowed us to change the yield stress and bulk viscosity. The yield stress ranged from 78 to 109 Pa, producing Bingham numbers in the 0.07-0.35 range. We investigated the behavior of a 43-kg mass released on a plane, whose inclination ranged from 0 • to 18 • . For each run, we observed that the behavior was nearly the same: at short times, the mass accelerated vigorously on gate opening and very quickly reached a nearly constant velocity. At time t = 1 s, independently of plane inclination and yield stress, the mass reached a near-equilibrium regime, where the front position varied as a power function of time over several decades. We did not observe any run-out phase, during which the mass would have gradually come to a halt. The similarity in the flow behavior made it possible to derive an empirical scaling for the front position in the form x f = t 0.275(sin˛) 1/3 (sin˛) 5/4 , where˛and t denote plane inclination and time, respectively, and which holds for sloping beds (˛> 0).

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Section: Rheometrymentioning

confidence: 99%

Experimental investigation of the spreading of viscoplastic fluids on inclined planes

Cochard

Ancey

2009

Journal of Non-Newtonian Fluid Mechanics

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“…[62]). Barnes [63][64][65] concluded that the presence of a yield stress as reported by some workers for thixotropic materials (but not semisolid alloys) is probably due to the limitations of their experimental apparatus in not being able to measure shear stresses at very low shear rates. Koke and Modigell [66] have used a shear stress controlled rheometer to measure yield stress directly on Sn 15%Pb.…”

Section: Background Rheologymentioning

confidence: 99%

Modelling the Semisolid Processing of Metallic Alloys

Atkinson

2005

ChemInform

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Semi-solid processing of metallic alloys and composites utilises the thixotropic behaviour of materials with non-dendritic microstructure in the semi-solid state. The family of innovative manufacturing methods based on this behaviour has been developing over the last twenty years or so and originates from scientific work at MIT in the early 1970s. Here, a summary is given of:-routes to spheroidal microstructures; types of semi-solid processing; and advantages and disadvantages of these routes.Background rheology and mathematical theories of thixotropy are then covered as precursors to the main focus of the review on transient behaviour of semi-solid alloy slurries and computational modelling. Computational Fluid Dynamics (CFD) can be used to predict die filling. However, some of the reported work has been based on rheological data obtained in steady state experiments, where the semi-solid material has been maintained at a particular shear rate for some time. In reality, in thixoforming, the slurry undergoes a sudden increase in shear rate from rest to 100s -1 or more as it enters the die. This change takes place in less than a second. Hence, measuring the transient rheological response under rapid changes in shear rate is critical to the development of modelling of die filling and successful die design for industrial processing. The modelling can be categorised as one phase or two phase and as finite difference or finite element. Recent work by Alexandrou and co-workers and, separately Modigell and co-workers, has led to the production of maps which, respectively summarise regions of stable/unstable flow and regions of laminar/transient/turbulent fill. These maps are of great potential use for the prediction of appropriate process parameters and avoidance of defects. A novel approach to modelling by Rouff and coworkers involves micro-modelling of the 'active zone' around spheroidal particles.There is little quantitative data on the discrepancies or otherwise between die fill simulations and experimental results (usually obtained through interrupted filling).There are no direct comparisons of the capabilities of various software packages to model the filling of particular geometries accurately. In addition, the modelling depends on rheological data and this is sparse, particularly for the increasingly complex two-phase models. Direct flow visualisation can provide useful insight and avoid the effects of inertia in interrupted filling experiments.

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“…Thixotropy means timedependent fluid behaviour in which the apparent viscosity decreases with time of shearing [12]. The viscosity of fluid usually recovers to initially value when shearing is stopped.…”

Section: Identification Of Thixotropic Propertiesmentioning

confidence: 99%

Rheological Analysis of Semi-Solid A380.0 Aluminium Alloy / Analiza Właściwości Reologicznych Stopu Aluminium A380.0 W Stanie Stało-Ciekłym

Sołek

Szczepanik

2015

Archives of Metallurgy and Materials

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RheologIcal analysIs of semI-solId a380.0 alumInIum alloy AnAlizA włAściwości reologicznych stopu Aluminium A380.0 w stAnie stAło-ciekłym Knowledge of the rheological properties is crucial for the numerical modeling of technological processes. The main objective of this study was to conduct an analysis of the rheological properties of A380.0 (AlSi9Cu3(Fe)) aluminium alloy in the semi-solid state. The results could be used for identification of temperature range of the alloy, where thixoforming processes could be executed. Another purpose of the experimental work could be development of the mathematical models of the alloy apparent viscosity. The significant achievement of this particular study is an application of a viscometer which was specially designed for material tests executed at high temperatures, such as the measurement of liquid or semi-liquid aluminium viscosity. This paper presents the results of a rheological analysis of aluminium alloy.

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Thixotropy—a review

Cited by 1,302 publications

References 48 publications

Experimental investigation of the spreading of viscoplastic fluids on inclined planes

Experimental investigation of the spreading of viscoplastic fluids on inclined planes

Modelling the Semisolid Processing of Metallic Alloys

Rheological Analysis of Semi-Solid A380.0 Aluminium Alloy / Analiza Właściwości Reologicznych Stopu Aluminium A380.0 W Stanie Stało-Ciekłym

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