A parameter investigation of shear-induced coalescence in semidilute PIB–PDMS polymer blends: effects of shear rate, shear stress volume fraction, and viscosity

2006 ◽  
Vol 45 (4) ◽  
pp. 505-512 ◽  
Author(s):  
Sergio Caserta ◽  
Marino Simeone ◽  
Stefano Guido
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Polymer Blends ◽  
Volume Fraction

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

scholarly journals PROCESSING ADDITIVES AND RHEOLOGICAL PROPERTIES OF MOLDED PHENOLIC PLASTICS

2019 ◽  
Vol 14 (1) ◽  
pp. 90-96
Author(s):  
P. V. Surikov ◽  
N. L. Shembel ◽  
A. A. Yurkin ◽  
A. V. Petrogradsky ◽  
V. D. Sevruk ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Phenolic Resin ◽  
Volume Fraction ◽  
Slip Flow ◽  
Capillary Wall ◽  
Flow Curves ◽  
Flow Through ◽  
Capillary Viscosimetry ◽  
Stress Flow

By the method of capillary viscosimetry, the melt flow curves of the molded phenolic resin and its compositions with lubricant, plasticizer and their mixture were obtained. It was shown that the size (diameter) of the capillary channel influences the dependence of the effective shear rate on the shear stress (flow curves) of the studied compositions. Such rheological behavior of the compositions during flow is associated with the effect of sliding along the surface of the capillary wall. According to the Mooney method, the dependences of the effective shear rate at given values of shear stress on the reciprocal of the capillary radius are plotted. The function of the slip velocity on the shear stress on the capillary wall is characterized in terms of the slip coefficient, which relates the shear stress on the capillary wall to the velocity of the composition along it. For the studied compositions, the total flow through the capillary was divided into volume fractions, one of which is associated with a shear flow; the other is determined by the slip effect. It has been shown that the introduction of both a lubricant and a plasticizer into the composition leads to an increase in the fluidity of the compositions. At the same time, adding of lubricant increases the volume fraction of the slip flow. The greatest effect of increasing the fluidity of the composition gives the use of complex modifying additives containing both lubricant and plasticizer.

scholarly journals Aging, Rejuvenation and Thixotropy in Complex Fluids: Time-dependence of the Viscosity at Rest and under Constant Shear Rate or Shear Stress

2008 ◽  
Vol 18 (5) ◽  
pp. 53298-1-53298-13
Author(s):  
Daniel Quemada
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Volume Fraction ◽  
Complex Fluids ◽  
Transient Behaviour ◽  
Volume Fractions ◽  
Constant Shear ◽  
Constant Shear Stress ◽  
Constant Shear Rate ◽  
Viscosity Changes

Abstract Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction ϕc2. For volume fractions less than ϕc2 the viscosity remains finite in the limit t →∞. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress σB, identical to the yield stress σy observed under steady conditions. The divergence of the viscosity for σ≤σB is best defined as aging. However, for σ > σB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress σA(≤σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when σ > σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ >> σB. Finally, the model’s predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

Morphology and rheology of PP/POE blends in high shear stress field

2017 ◽  
Vol 31 (9) ◽  
pp. 1263-1280 ◽  
Author(s):  
Jiru Ying ◽  
Xiaolin Xie ◽  
Shaoxian Peng ◽  
Huamin Zhou ◽  
Dequn Li
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Stress Field ◽  
Polymer Blends ◽  
Morphological Evolution ◽  
High Shear Rate ◽  
Dispersed Phase ◽  
High Shear ◽  
High Shear Stress ◽  
Shear Stress Field

Polypropylene (PP)/polyolefin elastomer (POE; ethylene–octene copolymer) blends with varying weight percentages of POE were prepared in a twin-screw extruder and molded through high shear rate injection-molding process. The morphologies and rheology of the PP/POE blends were systematically investigated based on rheological data and experimental analysis. The results indicate that the polymer blends of plastic and rubber in a high shear stress field result in a multilayered microstructure, which can be divided into skin, transitional, shear, and core layers according to the morphology of the dispersed phase. The morphology formation of the dispersed phase depends on the shear field and temperature field in the processing. Morphological evolution of the dispersed POE phases in PP matrix was described and quantified. A dragging ellipsoid model and capillary number were employed to describe the morphological evolution of the dispersed phase, and the morphological parameters were obtained. The results show that the dragging ellipsoid model is well suited to explain the morphological evolution of the dispersed phase in polymer blends molded under high shear rate.

scholarly journals Theory for the rheology of dense non-Brownian suspensions: divergence of viscosities and– rheology

2019 ◽  
Vol 864 ◽  
pp. 1125-1176 ◽  
Author(s):  
Koshiro Suzuki ◽  
Hisao Hayakawa
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Stress Ratio ◽  
Volume Fraction ◽  
Microscopic Theory ◽  
Critical Behaviour

A systematic microscopic theory for the rheology of dense non-Brownian suspensions characterized by the volume fraction $\unicode[STIX]{x1D711}$ is developed. The theory successfully derives the critical behaviour in the vicinity of the jamming point (volume fraction $\unicode[STIX]{x1D711}_{J}$), for both the pressure $P$ and the shear stress $\unicode[STIX]{x1D70E}_{xy}$, i.e. $P\sim \unicode[STIX]{x1D70E}_{xy}\sim \dot{\unicode[STIX]{x1D6FE}}\unicode[STIX]{x1D702}_{0}\unicode[STIX]{x1D6FF}\unicode[STIX]{x1D711}^{-2}$, where $\dot{\unicode[STIX]{x1D6FE}}$ is the shear rate, $\unicode[STIX]{x1D702}_{0}$ is the shear viscosity of the solvent and $\unicode[STIX]{x1D6FF}\unicode[STIX]{x1D711}=\unicode[STIX]{x1D711}_{J}-\unicode[STIX]{x1D711}>0$ is the distance from the jamming point. It also successfully describes the behaviour of the stress ratio $\unicode[STIX]{x1D707}=\unicode[STIX]{x1D70E}_{xy}/P$ with respect to the viscous number $J=\dot{\unicode[STIX]{x1D6FE}}\unicode[STIX]{x1D702}_{0}/P$.

scholarly journals Analysis and Experimental Study on Rheological Performances of Magnetorheological Fluids

Mechanika ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 31-34
Author(s):  
Chao LIU ◽  
Jianxin XIE ◽  
Dongling CAI
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Shear Stress ◽  
Shear Rate ◽  
Volume Fraction ◽  
Magnetorheological Fluids ◽  
Bingham Model ◽  
Shear Thinning Fluids ◽  
Powder Rheometer ◽  
Constant Shear Rate

Silicone-based Magnetorheological Fluids (MRFs) were prepared with 10% volume fraction of carbonyl iron powder. Rheometer Physica MCR 301 was used to test the rheological performances of MRFs.The experimental results show Bingham model and Casson model could well describe rheological behaviors of MRFs. Shear stress of MRFs increases but apparent viscosity is significantly decreased and tends to be stable with the increase of shear rate in the presence of magnetic field. The results also show that MRFs are shear thinning fluids. The dependence of shear stress on magnetic field was tested under the condition of constant shear rate and increasing magnetic field, shear stress of MRFs increases remarkably.

Investigation on the Rheological Behavior of Polyamide6/Montmorillonite Nanocomposites by Reactive Extrusion

2011 ◽  
Vol 233-235 ◽  
pp. 1998-2001 ◽  
Author(s):  
Ming Zhao ◽  
Xiao Zhong Lu ◽  
Kai Gu ◽  
Xiao Min Sun ◽  
Chang Qing Ji
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Shear Rate ◽  
Rheological Behavior ◽  
Reactive Extrusion ◽  
Shear Thinning ◽  
Experimental Results ◽  
Montmorillonite Nanocomposites

The rheological behavior of PA6/montmorillonite(MMT) by reactive extrusion was investigated using cone-and-plate rheometer. The experimental results indicated that PA6/MMT exhibited shear-thinning behavior. The shear stress of both neat PA6 and PA6/MMT increased with the increase in the shear rate. The reduction of the viscous activation energy with the increase of shear stress reflected PA6/MMT can be processed over a wider temperature.

Are the dynamic response characteristics of brachial artery flow-mediated dilation sensitive to the magnitude of increase in shear stimulus?

2008 ◽  
Vol 105 (1) ◽  
pp. 282-292 ◽  
Author(s):  
K. E. Pyke ◽  
J. A. Hartnett ◽  
M. E. Tschakovsky
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Dynamic Response ◽  
Phase I ◽  
Brachial Artery ◽  
Flow Mediated Dilation ◽  
Final Phase ◽  
Stimulus Magnitude ◽  
Brachial Artery Diameter ◽  
Response Characteristics

The purpose of this study was to determine the dynamic characteristics of brachial artery dilation in response to step increases in shear stress [flow-mediated dilation (FMD)]. Brachial artery diameter (BAD) and mean blood velocity (MBV) (Doppler ultrasound) were obtained in 15 healthy subjects. Step increases in MBV at two shear stimulus magnitudes were investigated: large (L; maximal MBV attainable), and small (S; MBV at 50% of the large step). Increase in shear rate (estimate of shear stress: MBV/BAD) was 76.8 ± 15.6 s−1 for L and 41.4 ± 8.7 s−1 for S. The peak %FMD was 14.5 ± 3.8% for L and 5.7 ± 2.1% for S ( P < 0.001). Both the L (all subjects) and the S step trials (12 of 15 subjects) elicited a biphasic diameter response with a fast initial phase (phase I) followed by a slower final phase. Relative contribution of phase I to total FMD when two phases occurred was not sensitive to shear rate magnitude ( r2 = 0.003, slope P = 0.775). Parameters quantifying the dynamics of the FMD response [time delay (TD), time constant (τ)] were also not sensitive to shear rate magnitude for both phases (phase I: TD r2 = 0.03, slope P = 0.376, τ r2 = 0.04, slope P = 0.261; final phase: TD r2 = 0.07, slope P = 0.169, τ r2 = 0.07, slope P = 0.996). These data support the existence of two distinct mechanisms, or sets of mechanisms, in the human conduit artery FMD response that are proportionally sensitive to shear stimulus magnitude and whose dynamic response is not sensitive to shear stimulus magnitude.

Effect of Shear Surface Boundaries on Stress for Shearing Flow of Dry Metal Powders—An Experimental Study

1987 ◽  
Vol 109 (2) ◽  
pp. 232-237 ◽  
Author(s):  
K. Craig ◽  
R. H. Buckholz ◽  
G. Domoto
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Normal Stress ◽  
Particle Diameter ◽  
Surface Boundary ◽  
Metal Powders ◽  
Shear Surface ◽  
Shear Cell ◽  
Shearing Flow ◽  
Solids Content

This paper studies the rapid simple shearing flow of dry cohesionless metal powders contained between parallel rotating plates. In this study, an annular shear cell test apparatus was used; the dry metal powders are rapidly sheared by rotating one of the shear surfaces while the other shear surface remains fixed. Such a flow geometry is of interest to tribologists working in the area of dry or powder lubrication. The shear stress and normal stress on the stationary surface are measured as a function of the following parameters: shear surface boundary material and roughness, the shear-cell gap thickness, the shear-rate and the fractional solids content. Both the fractional solids content and the gap thickness are kept at prescribed values during stress measurements. In this experiment the metal powder tested is different from the shear transmission surface material; the effect on the measured normal and shear stress data are reported. The results show the dependence of the normal stress and the shear stress on the shear-rate, particle density and particle diameter. Likewise, a significant stress dependence on both the fractional solids content and the shear-cell gap thickness was observed.

scholarly journals Investigation of the Sedimentation Property of Backfill Material on the Basis of Rheological Test: A Case Study of Iron Tailings

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Yong Wang ◽  
Aixiang Wu ◽  
Lianfu Zhang ◽  
Hongjiang Wang ◽  
Fei Jin
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Mass Concentration ◽  
Filling Material ◽  
Quantitative Characterization ◽  
Filling Materials ◽  
Characterization Studies ◽  
Rheological Test ◽  
Sedimentation Property

Sedimentation of filling materials could cause pipe blocking accident in mines. However, few quantitative characterization studies have investigated the sedimentation characteristics of filling materials. In this study, the sedimentation property of iron tailings with a cement-sand ratio of 1 : 4 and mass concentration of 73%∼82% was investigated based on rheology measurements. Results showed that shear stress increased as shear rate rose from 0 s−1to 120 s−1. The shear stress increased as the filling material concentration increased as well. However, when the shear rate was reversed from 120 s−1to 0 s−1, the shear stress presented an increase-constant-decrease change pattern as the mass concentration increases in the rheological curve. Accordingly, the sedimentation performance of iron tailings filling material was divided into three types: intense sedimentation (the ascending rheological curve) in the mass concentration range of 73%∼76%, slight sedimentation (the constant rheological curve) in the mass concentration range of 77%∼79%, and almost no sedimentation (the descending rheological curve) in the mass concentration range of 80%∼82%. The associated mechanism involving slurry mass concentration-rheological curves-sedimentation performance was illustrated. A correlation between the pipeline rheology and filling material sedimentation performance was established, which provides a practical guide to avoid pipeline blocking while transporting the filling material.

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