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Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.


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TL;DR: In this paper, the authors discuss the basic rheological properties of different types of ultra-thin membranes, which can be used to form stable capsules walls and analyze the typical structures of these cross-linked films using Brewster-angle microscopy.
Abstract: The synthesis of microcapsules for technical, cosmetic, and pharmaceutical purposes has attracted much interest in recent years. The design of new capsules requires profound knowledge of their mechanical properties. Rheological studies provide interesting information on intrinsic membrane features and they can also be used to obtain information on bursting processes and shear-induced release of encapsulated compounds. In this article we shall discuss the basic rheological properties of different types of ultra-thin membranes, which can be used to form stable capsules walls. We have also analyzed the typical structures of these cross-linked films using Brewster-angle microscopy. Tiny oil or water droplets, which are surrounded by ultra-thin membranes, form simple types of microcapsules. In addition to the interface shear rheology, we have measured the Young's modulus (elongational modulus) and the Poisson ratio using a modified spinning drop apparatus. The shear-induced deformation and orientation of microcapsules was investigated in optical rheometers (rheoscopes). In the regime of small deformations the results were in fairly good agreement with a theoretical model recently proposed by Barthes-Biesel. Due to the simple synthesis and well-defined structure, microcapsules can also serve as model systems to understand the complicated flow properties of red blood cells (erythrocytes).

57 citations

Journal ArticleDOI
TL;DR: Van der Elst et al. as mentioned in this paper showed that the thickness of a steady shear flow at velocities between 10 A3 and 10 2 cm/s, at very low normal stress (7 kPa), can be suppressed by internal acoustic vibration by auto-acoustic compaction, which results in a velocity-weakening granular flow regime at shear rates four orders of magnitude below those previously associated with the transition out of quasi-static granular flows.
Abstract: JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, B09314, doi:10.1029/2011JB008897, 2012 Auto-acoustic compaction in steady shear flows: Experimental evidence for suppression of shear dilatancy by internal acoustic vibration Nicholas J. van der Elst, 1 Emily E. Brodsky, 1 Pierre-Yves Le Bas, 2 and Paul A. Johnson 2 Received 22 September 2011; revised 9 August 2012; accepted 20 August 2012; published 28 September 2012. [ 1 ] Granular shear flows are intrinsic to many geophysical processes, ranging from landslides and debris flows to earthquake rupture on gouge-filled faults. The rheology of a granular flow depends strongly on the boundary conditions and shear rate. Earthquake rupture involves a transition from quasi-static to rapid shear rates. Understanding the processes controlling the transitional rheology is potentially crucial for understanding the rupture process and the coseismic strength of faults. Here we explore the transition experimentally using a commercial torsional rheometer. We measure the thickness of a steady shear flow at velocities between 10 A3 and 10 2 cm/s, at very low normal stress (7 kPa), and observe that thickness is reduced at intermediate velocities (0.1–10 cm/s) for angular particles, but not for smooth glass beads. The maximum reduction in thickness is on the order of 10% of the active shear zone thickness, and scales with the amplitude of shear-generated acoustic vibration. By examining the response to externally applied vibration, we show that the thinning reflects a feedback between internally generated acoustic vibration and granular rheology. We link this phenomenon to acoustic compaction of a dilated granular medium, and formulate an empirical model for the steady state thickness of a shear-zone in which shear-induced dilatation is balanced by a newly identified mechanism we call auto-acoustic compaction. This mechanism is activated when the acoustic pressure is on the order of the confining pressure, and results in a velocity-weakening granular flow regime at shear rates four orders of magnitude below those previously associated with the transition out of quasi-static granular flow. Although the micromechanics of granular deformation may change with greater normal stress, auto-acoustic compaction should influence the rheology of angular fault gouge at higher stresses, as long as the gouge has nonzero porosity during shear. Citation: van der Elst, N. J., E. E. Brodsky, P.-Y. Le Bas, and P. A. Johnson (2012), Auto-acoustic compaction in steady shear flows: Experimental evidence for suppression of shear dilatancy by internal acoustic vibration, J. Geophys. Res., 117, B09314, doi:10.1029/2011JB008897. 1. Introduction [ 2 ] Frictional sliding processes in geophysics often involve granular shear flows at the sliding interface. This is true for landslides and debris flows, as well as for earthquake rup- tures within granulated damage zones or gouge-filled faults. The frictional strength in these contexts is controlled by the rheology of the granular flow, which has a strong dependence Department of Earth and Planetary Science, Univ. of California, Santa Cruz, California, USA. Geophysics Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA. Corresponding author: Nicholas J. van der Elst, Department of Earth and Planetary Science, 1156 High St., Univ. of California, Santa Cruz, CA 95060, USA. (nvandere@ucsc.edu) ©2012. American Geophysical Union. All Rights Reserved. 0148-0227/12/2011JB008897 on shear rate and boundary conditions [Campbell, 2006; Clement, 1999; Iverson, 1997; Savage, 1984]. [ 3 ] For different shear rates, confining stresses, and pack- ing densities, the description of a granular flow can range from “solid-like” to “gas-like” [Jaeger et al., 1996], albeit with complicated second-order behavior in each regime. The appropriate description for a particular flow is typically determined by the dimensionless inertial number, which compares the magnitude of the grain inertial stresses to the confining stress [Bocquet et al., 2001; Campbell, 2006; Clement, 1999; Iverson, 1997; Lu et al., 2007; Savage, 1984] I ≡ rd g _ 2 p where r is density, d is grain diameter, g _ is the strain rate, and p is the confining (normal) pressure. The shear rate profile in boundary driven flows is commonly observed to decay B09314 1 of 18

57 citations

Journal ArticleDOI
TL;DR: In this article, a rheological investigation has been conducted using a concentric cylinder rheometer on a semi-solid sn-15% Pb alloy at solid fractions between 0.2 and 0.5, and the results show anomalous flow behavior in that, at low shear rates, the shear stress falls with increasing shear rate up to 250 s−1 under steady-state conditions.
Abstract: A rheological investigation has been conducted using a concentric cylinder rheometer on a semi-solid sn-15% Pb alloy at solid fractions between 0.2 and 0.5. The results show anomalous flow behaviour in that, at low shear rates, the shear stress falls with increasing shear rate up to 250 s−1 under steady-state conditions. Possible explanations of this anomalous behaviour are discussed and it is concluded that it is a genuine feature of the bulk slurry and not an experimental artefact. It is further suggested to be a consequence of the rapid breakdown of the internal structure of solid particle clusters within the slurry which occurs at low shear rates.

57 citations

Journal ArticleDOI
F.F. Nazem1
01 Jan 1982-Carbon
TL;DR: In this article, a Couette-flow instrument has been modified for measuring the apparent viscosity of mesophase pitch, circumventing most of the experimental difficulties, and the reliability of this apparatus has been tested by cross checking the observed apparent viscoities with the values measured from two other rheometers, Instron Capillary and Seiscor/Han, for a number of fluids.

57 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of binder properties on torque curves, granule growth kinetics, wet mass consistency and dry granule strength has been investigated in two types of laboratory high shear mixers.

57 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023240
2022487
2021164
2020196
2019201
2018162