Showing papers on "Rheometer published in 2012"

Understanding the rheology of concrete

Abstract: Part 1 Measuring the rheological behaviour of concrete: Introduction to the rheology of complex fluids Introduction to the rheometry of complex suspensions Concrete rheometers From industrial testing to rheological parameters for concrete The rheology of cement during setting. Part 2 Mix design and the rheological behaviour of concrete: Particle packing and the rheology of concrete Superplasticizers and the rheology of concrete Viscosity-enhancing admixtures and the rheology of concrete Fibre reinforcement and the rheology of concrete. Part 3 Casting and the rheological behaviour of concrete: Modelling the flow of self-compacting concrete Thixotropy: from measurement to casting of concrete Understanding formwork pressure generated by fresh concrete Understanding the pumping of conventional vibrated and self-compacting concrete.

Flocculation of microfibrillated cellulose in shear flow

Abstract: In this work, the rheological properties of microfibrillated cellulose suspensions under stepped flow and constant shear were studied using a combination of rotational dynamic rheometer and digital imaging. During each rheological measurement, the structure of the suspension was monitored through a transparent outer cylinder with a digital camera. This enabled simultaneous analysis of the suspension floc size distribution and traditional rheological characterization. In stepped flow conditions, a good correlation between suspension floc structure and flow curve measurement was found. At constant shear, the suspension structure was dependent on the shear rate and concentration of the suspension. A low shear rate resulted in heterogeneous floc structure, which was also detected by an increase in the ratio of the viscous component to elastic component in the rheological measurement. At low concentrations and 0.5 s−1 shear rate, flow induced a formation of floc cylinders between the rotating cylinder and stationary cup surface.

High Pressure Rheology of Hydrate Slurries Formed from Water-in-Mineral Oil Emulsions

Abstract: Structure I methane hydrates are formed in situ from water-in-mineral oil emulsions in a high pressure rheometer cell. Viscosity is measured as hydrates form, grow, change under flow, and dissociate. Experiments are performed at varying water volume fraction in the original emulsion (0–0.40), temperature (0–6 °C), and initial pressure of methane (750–1500 psig). Hydrate slurries exhibit a sharp increase in viscosity upon hydrate formation, followed by complex behavior dictated by factors including continued hydrate formation, shear alignment, methane depletion/dissolution, aggregate formation, and capillary bridging. Hydrate slurries possess a yield stress and are shear-thinning fluids, which are described by the Cross model. Hydrate slurry viscosity and yield stress increased with increasing water volume fraction. As driving force for hydrate formation decreases (increasing temperature, decreasing pressure), hydrate slurry viscosity increases, suggesting that slower hydrate formation leads to larger and ...

Shear thickening of cornstarch suspensions

Abstract: We study the rheology of cornstarch suspensions, a non-Brownian particle system that exhibits discontinuous shear thickening. Using magnetic resonance imaging (MRI), the local properties of the flow are obtained by the determination of local velocity profiles and concentrations in a Couette cell. For low rotational rates, we observe shear localization characteristic of yield stress fluids. When the overall shear rate is increased, the width of the sheared region increases. The discontinuous shear thickening is found to set in at the end of this shear localization regime when all of the fluid is sheared: the existence of a nonflowing region, thus, seems to prevent or delay shear thickening. Macroscopic observations using different measurement geometries show that the smaller the gap of the shear cell, the lower the shear rate at which shear thickening sets in. We, thus, propose that the discontinuous shear thickening of cornstarch suspensions is a consequence of dilatancy: the system under flow attempts to...

Electrorheology of Graphene Oxide

Abstract: Novel polarizable graphene oxide (GO) particles with oxidized groups on their edge and basal planes were prepared by a modified Hummers method, and their electro-responsive electrorheological (ER) characteristics when dispersed in silicone oil were examined with and without an electric field applied. The fibrillation phenomenon of this GO-based electro-responsive fluid was also observed via an optical microscope under an applied electric field. Both flow curves and dielectric spectra of the ER fluid were measured using a rotational rheometer and a LCR meter, respectively. Its viscoelastic properties of both storage and loss moduli were also examined using a vertical oscillation rheometer equipped with a high voltage generator, finding that the GO-based smart ER system behaves as a viscoelastic material under an applied electric field.

Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour

Abstract: Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing shear rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With shearing, the network separated first into chain-like floc formations and, upon further shear rate increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the shear rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10−3 M and higher.

Feasibility of optical coherence elastography measurements of shear wave propagation in homogeneous tissue equivalent phantoms

Abstract: In this work, we explored the potential of measuring shear wave propagation using optical coherence elastography (OCE) based on a swept-source optical coherence tomography (OCT) system. Shear waves were generated using a 20 MHz piezoelectric transducer (circular element 8.5 mm diameter) transmitting sine-wave bursts of 400 μs, synchronized with the OCT swept source wavelength sweep. The acoustic radiation force (ARF) was applied to two gelatin phantoms (differing in gelatin concentration by weight, 8% vs. 14%). Differential OCT phase maps, measured with and without the ARF, demonstrate microscopic displacement generated by shear wave propagation in these phantoms of different stiffness. We present preliminary results of OCT derived shear wave propagation velocity and modulus, and compare these results to rheometer measurements. The results demonstrate the feasibility of shear wave OCE (SW-OCE) for high-resolution microscopic homogeneous tissue mechanical property characterization.

Polymer degradation of dilute solutions in turbulent drag reducing flows in a cylindrical double gap rheometer device

Abstract: The drag reduction by high molecular weight polymer additives in a turbulent flow is an important phenomenon that has received the attention of a number of researchers. However, the efficiency of those additives is not constant. Turbulence is also responsible for breaking the polymer molecules, decreasing their ability to reduce drag. This degradation phenomenon has recently received its deserved attention in the literature and investigations that take into account the effect of concentration, molecular weight, Reynolds number, and temperature can be found, although these parameters have not yet been explored in very wide ranges. In the present work we investigate this degradation phenomenon for aqueous solutions of two different polymers: Polyacrylamide (PAM) and Polyethylene oxide (PEO), in a cylindrical double gap rheometer device. The dependence of degradation on molecular weight, concentration, temperature, and Reynolds number is analysed for a wide range of these parameters. Our main results are displayed in terms of drag reduction ( DR ). All tests are performed to compute DR for a long period of time including the values obtained from the very beginning of the process. It is shown that DR increases with time until achieving a maximum value before starting to decrease as a consequence of degradation. We also display the results using a relative drag reduction quantity, DR ′, defined as the ratio of the current drag reduction to the maximum one obtained for a non-degraded solution. We propose an alternative decay function that relates DR ′ as a function of the Reynolds number, concentration, molecular weight, and temperature.

Magneto Mechanical Properties of Iron Based MR Fluids

Abstract: The main aim of this article is to prepare MR fluids, composed of iron particles and analyse their flow behaviour in terms of the internal structure, stability and magneto rheological properties. MR fluids are prepared using silicone oil (OKs) mixed with iron powder. To reduce sedimentation, grease is added as stabilizers. The size of the particles is observed by Optical microscope and flow properties are examined by rheometer. Sedimentation is measured by simple observation of changes in boundary position between clear and turbid part of MR fluid placed into glass tube. The various additive percentages can also influence the MR fluid’s performances.

Simple shear is not so simple! Kinematics and shear senses in Newtonian viscous simple shear zones

Abstract: This work develops an analytical model of shear senses within an inclined ductile simple shear zone with parallel rigid boundaries and incompressible Newtonian viscous rheology. Taking account of gravity that tends to drive the material downdip and a possible pressure gradient that drives it upward along the shear zone, it is shown that (i) contradictory shear senses develop within two sub-zones even as a result of a single simple shear deformation; (ii) the highest velocity and least shear strain develop along the contact between the two sub-zones of reverse shear; (iii) for a uniform shear sense of the boundaries, a zone of reverse shear may develop within the top of the shear zone if the pressure gradient dominates the gravity component; otherwise it forms near the bottom boundary; (iv-a) a ‘pivot’ defined by the intersection between the velocity profile and the initial marker position distinguishes two sub-zones of opposite movement directions ( not shear sense); (iv-b) a pivot inside any non-horizontal shear zone indicates a part of the zone that extrudes while the other subducts simultaneously; (v) the same shear sense develops: (v-a) when under a uniform shear of the boundaries, the shear zone remains horizontal and the pressure gradient vanishes; or alternatively (v-b) if the shear zone is inclined but the gravity component counterbalances the pressure gradient. Zones with shear sense reversal need to be reinterpreted since a pro-sheared sub-zone can retro-shear if the flow parameters change their magnitudes even though the same shear sense along the boundaries is maintained.

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

Abstract: We explore the behavior of a wormlike micellar solution under both steady and large amplitude oscillatory shear (LAOS) in a cone–plate geometry through simultaneous bulk rheometry and localized velocimetric measurements. First, particle image velocimetry is used to show that the shear-banded profiles observed in steady shear are in qualitative agreement with previous results for flow in the cone–plate geometry. Then under LAOS, we observe the onset of shear-banded flow in the fluid as it is progressively deformed into the non-linear regime—this onset closely coincides with the appearance of higher harmonics in the periodic stress signal measured by the rheometer. These harmonics are quantified using the higher-order elastic and viscous Chebyshev coefficients e n and v n , which are shown to grow as the banding behavior becomes more pronounced. The high resolution of the velocimetric imaging system enables spatiotemporal variations in the structure of the banded flow to be observed in great detail. Specifically, we observe that at large strain amplitudes (γ 0 ≥ 1), the fluid exhibits a three-banded velocity profile with a high shear rate band located in-between two lower shear rate bands adjacent to each wall. This band persists over the full cycle of the oscillation, resulting in no phase lag being observed between the appearance of the band and the driving strain amplitude. In addition to the kinematic measurements of shear banding, the methods used to prevent wall slip and edge irregularities are discussed in detail, and these methods are shown to have a measurable effect on the stability boundaries of the shear-banded flow.

Auto‐acoustic compaction in steady shear flows: Experimental evidence for suppression of shear dilatancy by internal acoustic vibration

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

Rheo-PIV of a yield-stress fluid in a capillary with slip at the wall

Abstract: An analysis of the yielding and flow behavior of a model yield-stress fluid, 0.2 wt% Carbopol gel, in a capillary with slip at the wall has been carried out in the present work. For this, a study of the flow kinematics in a capillary rheometer was performed with a two-dimensional particle image velocimetry (PIV) system. Besides, a stress-controlled rotational rheometer with a vane rotor was used as an independent way to measure the yield stress. The results in this work show that in the limit of resolution of the PIV technique, the flow behavior agrees with the existence of a yield stress, but there is a smooth solid–liquid transition in the capillary flow curve, which complicates the determination of the yield stress from rheometrical data. This complication, however, is overcome by using the solely velocity profiles and the measured wall shear stresses, from which the yield-stress value is reliably determined. The main details of the kinematics in the presence of slip were all captured during the experiments, namely, a purely plug flow before yielding, the solid–liquid transition, as well as the behavior under flow, respectively. Finally, it was found that the slip velocity increases in a power-law way with the shear stress.

A novel method for visualising and quantifying through-plane skin layer deformations

Abstract: Skin is a multilayer composite and exhibits highly non-linear, viscoelastic, anisotropic material properties In many consumer product and medical applications (eg during shaving, needle insertion, patient re-positioning), large tissue displacements and deformations are involved; consequently large local strains in the skin tissue can occur Here, we present a novel imaging-based method to study skin deformations and the mechanics of interacting skin layers of full-thickness skin Shear experiments and real-time video recording were combined with digital image correlation and strain field analysis to visualise and quantify skin layer deformations during dynamic mechanical testing A global shear strain of 10% was applied to airbrush-patterned porcine skin (thickness: 12-16mm) using a rotational rheometer The recordings were analysed with ARAMIS image correlation software, and local skin displacement, strain and stiffness profiles through the skin layers determined The results of this pilot study revealed inhomogeneous skin deformation, characterised by a gradual transition from a low (20-50%; epidermis) to high (10-22%; dermis) shear strain regime Shear moduli ranged from 20 to 130kPa The herein presented method will be used for more extended studies on viable human skin, and is considered a valuable foundation for further development of constitutive models which can be used in advanced finite element analyses of skin

New Insight to the Mechanism of the Shear-Induced Macroscopic Alignment of Diblock Copolymer Melts by a Unique and Newly Developed Rheo–SAXS Combination

Abstract: In-situ flow alignment kinetics of a self-assembled lamellar phase polystyrene-block-polyisoprene (PS-b-PI, Mw = 26 500 g/mol, fPS = 51%) diblock copolymer melt has been investigated in detail under mechanical large amplitude oscillatory shear (LAOS) utilizing a unique Rheo–SAXS combination developed in cooperation with the German Electron Synchrotron (DESY) in Hamburg. This marks the first time that the strain and time dependence of the shear-induced macroscopic perpendicular orientation of the lamellar microstructure could be monitored with a time resolution of 10 s per frame. Two mechanical parameters were used to compare the structural evolution and dynamics with the mechanical response of the sample. The mechanical loss modulus G″, which was directly obtained from the in situ Rheo–SAXS experiments performed with a stress controlled rheometer, and the nonlinear parameter I3/1, which was calculated by Fourier-transform-rheology (FT-rheology) from the raw stress data obtained from a strain controlled rh...

Shear-banding in polyacrylamide solutions revealed via optical coherence tomography velocimetry

Abstract: We used optical coherence tomography velocimetry inside a fluids rheometer to study the rheology of a family of polyacrylamide (PAM) solutions that contain different polymer molecular weights and concentrations, with picolitre probing volumes. The linear velocity profiles obtained from low molecular weight samples, characteristic of Newtonian fluids under shear, become shear-banded when longer polymer chains (molecular weights 5 000 000 and above) are used at sufficiently high concentrations. Upon increasing the concentration further, shear-banding becomes less dominant and significant wall-slip takes place on the two plates of the rheometer. We describe the shear-banding and wall-slip phenomena in our samples in terms of parameters calculated from the velocity profiles, and use our data to suggest a dynamic phase diagram indicating the linear, shear-banding, and wall-slip regimes as functions of PAM molecular weight and concentration.

Rheometry of compression moulded fibre-reinforced polymer composites: Rheology, compressibility, and friction forces with mould surfaces

Abstract: Compression moulded preimpregnated polymer-matrix composites are often porous materials. Rheological studies usually neglect their subsequent compressible complex flow behaviour, together with mouldcomposite friction effects. Therefore the proposed method, including a newly developed compression rheometer, allows the rheology and the compressibility of such materials together with the mould–composite friction phenomena to be characterised without taking into account a priori assumptions on both the rheology of the composite and the form of the friction law. Its validity and usefulness for improving the interpretation of rheological results is demonstrated using a modelling plastic paste and an industrial Sheet Moulding Compound (SMC) during lubricated (or not) compression tests performed at low or high temperatures.

Thixotropy, yielding and ultrasonic Doppler velocimetry in pulp fibre suspensions

Abstract: This paper reports thixotropy in concentrated pulp fibre suspensions and studies their transient flow behaviour using conventional rheometry coupled with a velocimetry technique. Specifically, an ultrasonic Doppler velocimeter is used in conjunction with a rate-controlled rheometer to deduce the local velocity profiles of pulp fibre suspensions. Pulp suspensions are found to exhibit a plateau in their flow curves where a slight increase in the shear stress generates a jump in the corresponding shear rate, implying the occurrence of shear banding. The velocity profiles were found to be discontinuous in the vicinity of the yielding radius where the Herschel–Bulkley model failed to predict the flow. Shear history and the time of rest prior to the measurement were found to play a significant role on the rheology and the local velocity profiles of pulp suspensions.

Study of shear-stiffened elastomers

Abstract: This paper presents a novel shear-stiffened elastomer (SSE) fabricated with a mixture of silicone rubber and silicone oil. A total of four SSE samples were fabricated in this study. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel plate rheometer. The effects of silicone oil composition, strain amplitude and angular frequency were summarized. When raising the angular frequency in the dynamic shear test, the storage modulus of conventional silicone rubber shows a small increasing trend with the frequency. However, if silicone oil is selected to be mixed with silicone rubber, the storage modulus increases dramatically when the frequency and strain are both beyond the critical values. (Some figures may appear in colour only in the online journal)

Synthesis, rheological properties and magnetoviscos effect of Fe2O3/paraffin ferrofluids

Abstract: In this article, synthesis and rheological behavior of Fe2O3 magnetic nanoparticles ferrofluids in paraffin base as well as their magnetoviscos effects have been investigated. In order to prepare the ferrofluids, ball mill and ultrasonic bath were used. Then rheological behavior of the system was studied using a standard rotating rheometer. Oleic acid was used to stabilize ferrofluids. Also the effect of magnetic field on the fluid was studied. It is shown that using magnetic field will cause noticeable increase in viscosity at constant shear rate. This increase in viscosity, however, is limited to a specific rate of magnetic field. Also, a novel correlation for predicting temperature dependency of fluid has been presented.