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Showing papers on "Rheometer published in 2001"


Journal ArticleDOI
TL;DR: In this paper, the authors examined the dependence of the transient diameter profile and the time to breakup on the molecular weight, and compared the observations with simple theories for breakup of slender viscoelastic filaments.
Abstract: We study the elasto-capillary self-thinning and ultimate breakup of three polystyrene-based ideal elastic fluids by measuring the evolution in the filament diameter as slender viscoelastic threads neck and eventually break. We examine the dependence of the transient diameter profile and the time to breakup on the molecular weight, and compare the observations with simple theories for breakup of slender viscoelastic filaments. The evolution of the transient diameter profile predicted by a multimode FENE-P model quantitatively matches the data provided the initial stresses in the filament are taken into account. Finally, we show how the transient uniaxial extensional viscosity of a dilute polymer solution can be estimated from the evolution in the diameter of the necking filament. The resulting “apparent extensional viscosity” profiles are compared with similar results obtained from a filament stretching rheometer. Both transient profiles approach the same value for the steady state extensional viscosity, which increases with molecular weight in agreement with the Rouse–Zimm theory. The apparent discrepancy in the growth rate of the two transient curves can be quantitatively explained by examining the effective stretch rate in each configuration. Filament thinning studies and filament stretching experiments thus form complementary experiments that lead to consistent measures of the transient extensional viscosity of a given test fluid.

506 citations


Journal ArticleDOI
TL;DR: In this article, the influence of wall slip on the shear yield stress and modulus of cement paste was investigated using a rotational rheometer with smooth-walled concentric cylinders and a vane.

222 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of viscoelasticity on the jet break up of a series of non-shear-thinning fluids is quantified using an opposed-nozzle rheometer.
Abstract: Experimental studies attempting to ascertain the influence of viscoelasticity on the atomization of polymer solution are often hindered by the inability to decouple the effect of shear thinning from the effect of extensional hardening. Here, the influence of viscoelasticity on the jet break up of a series of non-shear-thinning viscoelastic fluids is quantified. Previous characterization using an opposed-nozzle rheometer identified the critical extensional rates for strain hardening of these model fluids. The strain hardening fluids exhibit a beads-on-string structure with reduction or elimination of satellite drops. Capillary instabilities grow on the filaments connecting the spheres and eventually break the filaments up into a string of very small drops about one order of magnitude smaller than the satellite drops formed by a Newtonian fluid with the same shear viscosity, surface tension, and density. These results confirm that strain hardening is the key rheological property in jet break up and that the critical extensional rate of a fluid is pertinent in determining the final characteristics of break up. Results suggest that the opposed-nozzle rheometer does probe extensional behavior in the range of extensional rates that are relevant to jet break up, providing a tool to roughly predict jet break up.

194 citations


Journal ArticleDOI
TL;DR: In this paper, a filament-stretching extensional rheometer at Monash University and similar rheometers have been designed and built in other laboratories are compared to help validate the basic technique, a collaborative program was undertaken to compare results from several instruments.
Abstract: Following development of a filament-stretching extensional rheometer at Monash University, similar rheometers have been designed and built in other laboratories. To help validate the basic technique, a collaborative program was undertaken to compare results from several instruments. First, three test fluids prepared at the University of California at Berkeley were characterized in steady and transient shear flows there and at the Massachusetts Institute of Technology (M.I.T.), and then tested in extensional rheometers at M.I.T., Monash and the University of Toronto. Each fluid is a constant-viscosity solution of narrow-molecular-weight-distribution polystyrene dissolved in oligomeric polystyrene. The solute molecular weights are 2.0, 6.5, and 20 million g/mol, and the polymer concentration in each fluid is 0.05 wt. %. From linear viscoelastic measurements, the Zimm relaxation times of the fluids are found to be 3.7, 31, and 150 s, respectively. The scaling of relaxation times with molecular weight indicat...

157 citations


Journal ArticleDOI
TL;DR: In this article, the role of soil rheology in determining time-dependent stress-strain relationships was highlighted for predicting and analysis of structural changes in soils, and a previously proposed aggregate-pair model was extended to predict compaction under external steady or transient stresses and experimentally determined rheological information for the above models.
Abstract: Tilled agricultural soils are in a constant state of change induced by variations in soil strength due to wetting and drying and compaction by farm implements. Changes in soil structure affect many hydraulic and transport properties; hence their quantification is critical for accurate hydrological and environmental modeling. This study highlights the role of soil rheology in determining time-dependent stress-strain relationships that are essential for prediction and analysis of structural changes in soils. The primary objectives of this study were (i) to extend a previously proposed aggregate-pair model to prediction of compaction under external steady or transient stresses and (ii) to provide experimentally determined rheological information for the above models. Rheological properties of soils and clay minerals were measured with a rotational rheometer with parallel-plate sensors. These measurements, under controlled steady shear stress application, have shown that wet soils have viscoplastic behavior with well-defined yield stress and nearly constant plastic viscosity. In contrast, rapid transient loading (e.g., passage of a tractor) is often too short for complete viscous dissipation of applied stress, resulting in an elastic (recoverable) component of deformation (viscoelastic behavior). Measured viscoelastic properties were expressed by complex viscosity and shear modulus whose components denote viscous energy dissipation, and energy storage (elastic). Results show that for low water contents and fast loading (tractor speed), the elastic component of deformation increases, whereas with higher water contents, viscosity and shear modulus decrease. Steady and oscillatory stress application to an aggregate pair model illustrates potential use of rheological properties towards obtaining predictions of strains in soils.

148 citations


Journal ArticleDOI
TL;DR: In this article, organophilic montmorillonite clay and poly(ethylene oxide) (PEO) nanocomposites were intercalated by a solvent casting method using chloroform as the cosolvent.
Abstract: The organophilic montmorillonite clay and poly(ethylene oxide) (PEO) nanocomposites were intercalated by a solvent casting method using chloroform as the cosolvent. The prepared nanocomposites were characterized by an X-ray diffraction method to examine their microstructure. Rheological properties of both the PEO/clay nanocomposites and the immiscible PEO/clay blends were investigated via a rotational rheometer in steady shear mode with a parallel plate geometry. The shear thinning viscosity data were fitted with the Carreau model, which showed that steady shear viscosity increases with increasing clay loading. The hysteresis phenomenon is observed to be enhanced with clay loading. PEO/clay nanocomposites exhibit higher zero-shear-rate viscosity and sharper shear thinning behaviors than immiscible PEO/clay blends.

146 citations


Journal ArticleDOI
TL;DR: In this paper, a series of experiments on a typical thickener where these artefacts have been successfully eliminated are reported. And the flow-curves obtained show a smooth but steep transition from a very high Newtonian viscosity at low shear stress to a much lower viscousity at high shear stresses.
Abstract: The thickening properties of many commercial thickeners are difficult to measure because of wall slip artefacts. Here we report a series of experiments on a typical thickener where these artefacts have been successfully eliminated. As a result, complete, steady-state flow-curves of aqueous Carbopol 980 (the toxicologically preferred version of the older and more well-known Carbopol 940) dispersions are reported for a range of concentrations of 0.045–1.0 wt%. The vane-and-basket flow geometry was used to avoid slip problems at low shear stress, with the geometry housed in a TA AR1000-N controlled-stress rheometer, whilst a Haake RV2 viscometer with an SV2P and MV2P concentric-cylinder geometries were used at higher shear rates. The flow-curves obtained show a smooth but steep transition from a very high Newtonian viscosity at low shear stress to a much lower viscosity at high shear stress. No real yield stresses were detected, but the higher shear rate results can be fitted to the Herschel-Bulkley model, which assumes an apparent yield stress. The various model parameters are displayed as a function of Carbopol concentration.

145 citations


Journal ArticleDOI
01 Aug 2001
TL;DR: The rheological properties and dispersion stability of magnetorheological fluids consisting of hydrophilic treated carbonyl iron particles dispersed in a water-in-oil emulsion were studied for the first time by the use of a stress-controlled rheometer and sedimentation test.
Abstract: The rheological properties and dispersion stability of magnetorheological (MR) fluids consisting of hydrophilic treated carbonyl iron particles dispersed in a water-in-oil emulsion were studied for the first time by the use of a stress-controlled rheometer and sedimentation test. In order to improve the stability of the MR fluids, carbonyl iron magnetic particles were chemisorbed by Tween 80 and a water-in-oil emulsion was employed as a continuous phase for MR fluids. Attraction between hydrophilic-treated carbonyl iron and water emulsion in continuous phase plays a critical role in greatly improving stability of dense carbonyl iron particles against sedimentation without restricting rheological properties. On application of magnetic fields, the suspensions show a striking increase in viscosity. Since constant stress is generated within the limit of zero shear rate, the plateau in the flow curve corresponds to the Bingham yield stress. Under a low external magnetic field, the yield stress varied as B 3/2 , indicating that local magnetization saturation occurs between the neighboring magnetized particles. The yield stress has an approximately linear relation to the particle volume fraction.

131 citations


Journal ArticleDOI
David Farrar1, John Rose1
TL;DR: The rheological behaviour of poly(methyl methacrylate) bone cements has been characterised during the curing phase using an oscillating parallel plate rheometer and viscoelastic parameters, such as storage modulus, loss modulus and phase angle are obtained.

120 citations


Journal ArticleDOI
TL;DR: In this article, an experimental investigation was undertaken into the shear-thinning behavior of suspensions of non-Brownian rigid fibers in Newtonian fluids, in particular, the influence of shear stress and the fiber concentration is investigated.
Abstract: An experimental investigation is undertaken into the shear-thinning behavior of suspensions of non-Brownian rigid fibers in Newtonian fluids. In particular, the influence of the shear stress and the fiber concentration is investigated. The shear stress is adjusted by varying both the shear rate and the solvent viscosity. In the semidilute concentration regime, where direct mechanical contacts between fibers are rare, the suspension is found to be nearly Newtonian over the stress range investigated. In the concentrated regime, the suspension becomes shear thinning below a certain shear rate. The shear thinning increases with concentration and decreases with solvent viscosity. Although shear-thinning behavior of fiber suspensions has often been reported in the literature, its physical origins are not well understood. Our experiments are interpreted in terms of the formation and breakage of fiber flocs due to the competition between hydrodynamic and colloidal forces. Our interpretation is confirmed by measurements of the adhesive forces between two individual fibers.

118 citations


Journal ArticleDOI
TL;DR: P pH effects were investigated on a Rheometrics RFS-II rheometer and it was found that pH can change the surface charge of the particles, which also affects the rheological behavior.

Journal ArticleDOI
TL;DR: In this paper, the rheological properties of two types of commercial peanut butter have been studied and a mean volume particle diameter of 6.6μm has been determined, the particle diameter distribution was found to be narrow, and the solids volume fraction was estimated to be 0.6.
Abstract: The rheological properties of two types of commercial peanut butter have been studied. Both products are concentrated suspensions, and differ by the presence of additives. The first type, referred to as “100% peanuts,” is an unstabilized suspension consisting of solid peanut particles in peanut oil which is a Newtonian fluid. The second type, referred to as “smooth,” consists of the same suspension stabilized with a vegetable oil and contains other ingredients such as salt and sugar in very small quantities. A mean volume particle diameter of 6.6 μm has been determined, the particle diameter distribution was found to be narrow, and the solids volume fraction was estimated to be 0.6. Slip encountered in rheometry was greatly reduced by gluing sandpaper to the parallel plates of the rheometer. Both samples behaved like plastic materials and apparent yield stresses of 24 Pa and 370 Pa have been determined for the unstabilized and the stabilized suspensions, respectively. No linear domain was found for both suspensions and the non-linearity was confirmed by deformed Lissajous curves and higher odd harmonics in the output signal of small amplitude oscillatory shear experiments. The stabilized suspension behaved more like a solid, the elastic modulus being larger than the loss modulus and almost independent of the frequency. This solid-like behavior is supposedly caused by strong repulsive (steric) forces induced by the stabilizing agent.

Journal ArticleDOI
TL;DR: In this paper, the authors introduce a category of empirical mathematical models that describe the behavior of very shear-thinning structured liquids, which had hitherto been described only at high shear rates or shear stresses using a flow model with a yield stress parameter, e.g., Bingham, Casson or Herschel-Bulkley types.


Journal ArticleDOI
TL;DR: In this article, a rheometer and laser scanning confocal microscopy (LSCM) were used to study the relationship between rheological properties and microstructural characteristics of developed and partially developed wheat flours.
Abstract: Farinography and mixography are two commonly used procedures for evaluating dough properties. These procedures, however, cannot separate hydration and energy input during dough development, both of which are critically important for understanding fundamental rheological properties of dough. A rheometer and laser scanning confocal microscopy (LSCM) were used to study the relationship between rheological properties and microstructural characteristics of developed (by farinograph with both shear and extensional deformations), of partially developed (by rheometer with either shear or extensional deformation), and of nondeveloped (no deformation) dough samples of wheat flours. Rheological data revealed that developed dough had the highest G* (most elastic or strong), followed by doughs partially developed with extensional deformation, and then shear deformation, and finally by nondeveloped dough. The LSCM z-sectioning (scanning of different layers of the sample) and the analysis of amount of protein m...

Journal ArticleDOI
TL;DR: In this paper, a Meissner-type rheometer was used to measure the extensional flow behavior of high-melt-strength polypropylene under transient extensional flows with constant tensile strain rate.
Abstract: Uniaxial extensional flow behavior was measured for the high-melt-strength polypropylene using a Meissner-type rheometer under transient extensional flow with constant tensile strain rate. The equibiaxial extensional flow behavior of the high-melt-strength polypropylene was measured via the lubricated squeezing flow method under constant strain rate. The high-melt-strength polypropylene consists of polypropylene (PP) as a main component and high-molecular-weight polyethylene (PE) component as a long relaxation time component (see part 1). This system is generally believed to be an immiscible system, at least under the quiescent state. Nevertheless, in part 1, we have found that the high-melt-strength PP with very high-molecular-weight PE shows distinctly different shear flow behaviors from conventional PP, e.g., high elasticity and two-step viscosity at low shear rates and strong and weak strain-dependent nonlinear damping functions characterizing fast and slow relaxation processes. In this study, the tra...

Journal ArticleDOI
TL;DR: The rheo-optical behavior of a viscoelastic solution of a surfactant subjected to transient shear flows is reported and the transient physical characteristics of the liquid are recorded, i.e., the shear stress sigma, the transmitted intensity I(t), and the scattering pattern.
Abstract: The rheo-optical behavior of a viscoelastic solution of a surfactant subjected to transient shear flows is reported. A steplike shear rate is suddenly imposed and we record the transient physical characteristics of the liquid, i.e., the shear stress sigma, the transmitted intensity I(t), and the scattering pattern. At the inception of the flow the shear stress shows an important overshoot followed by damped oscillations which also appear in the intensity profile. Then a sigmoidal relaxation process brings the liquid in its final steady state. During this first phase, the diffusion pattern due to enhanced concentration fluctuations can also be observed. A fine anisotropic layer appears near the moving wall shortly after the inception of the flow, but its width starts to increase significantly well after the end of the relaxation process. When the laser beam travels through this band a diffraction pattern can be observed indicating that it is formed by small subbands, the characteristic width of which is in the order of 100 micro m.

Journal ArticleDOI
TL;DR: In this paper, the trajectories of individual particles on the vorticity (z)-velocity (x) plane were determined through particle tracking, and the particle trajectories were used for gaining qualitative insight into the microscopic particle motion.
Abstract: The shear-induced self-diffusion and rheology of concentrated suspensions of noncolloidal hard spheres have been studied experimentally. The combined results provide an interesting physical picture. The projection of the trajectories of individual particles on the vorticity (z)–velocity (x) plane were determined through particle tracking. The particle trajectories turned out to be very useful for gaining qualitative insight into the microscopic particle motion. However, the technique is less suitable to obtain quantitative information. For a quantitative analysis of the particle displacements we measured the evolution of the ensemble averaged displacements as a function of time. The statistical analysis revealed two diffusion regimes, where 〈ΔzΔz〉 ∼ Δt. For large strain values (Δt>1) long-time self-diffusion was observed. The associated diffusion coefficient ∞ is in excellent agreement with literature data on shear-induced self-diffusion. On very short times (Δt≪1) a novel diffusive regime was discovered, characterized by a diffusion coefficient 0, which is significantly smaller than ∞ and grows monotonically with ϕ. 0 is detected on time scales on which the particle configuration is not changed significantly and thus it must represent the fluctuating motion of particles in the “cage” formed by their nearest neighbors. Finally, the rheology was studied with steady shear and oscillatory rheometry. The dynamic measurements in a controlled stress rheometer revealed that the viscoelastic response of the suspension is determined mainly by the amplitude of deformation. At small strain amplitudes γ0<1, the response is linear and a dynamic viscosity η′ is found, which is in excellent agreement with the high frequency limit η∞′ as reported in literature for colloidal hard sphere suspensions. Around γ0 = 1 the “cage” around a particle is deformed and a shear-induced microstructure is built. This leads to O(a) displacements of the particles and the viscoelastic response becomes strongly nonharmonic. Although the effect persists at large amplitudes, it becomes relatively small for γ0≫1. The microstructure is rearranged immediately after flow reversal and remains unchanged for the larger part of the period of oscillation. As a result a pseudolinear viscoelastic regime is found with a viscosity close to steady shear viscosity. Experiments show a correlation between the time scales controlling the 0/∞ diffusive behavior and the ones controlling the shear-induced changes in particle configuration as probed by the rheological measurements.

Journal ArticleDOI
TL;DR: In this article, the shear flow of a granular material between parallel plates is treated by means of the Boltzmann equation with pseudo-Maxwellian grains, and the moments for reverse reflection boundary conditions are found explicitly.
Abstract: The shear flow of a granular material between parallel plates is treated by means of the Boltzmann equation with pseudo-Maxwellian grains. The moments for reverse reflection boundary conditions are found explicitly. The shearing stress is found to depend quadratically on the shear rate.

Journal ArticleDOI
TL;DR: Behavior of a dilute polymer solution in a random three-dimensional flow with an average shear is studied experimentally and indicates that the polymer molecules are strongly stretched by the random motion of the fluid.
Abstract: Behavior of a dilute polymer solution in a random three-dimensional flow with an average shear is studied experimentally Polymer contribution to the shear stress is found to be more than 2 orders of magnitude higher than in a laminar shear flow The results indicate that the polymer molecules are strongly stretched by the random motion of the fluid

Journal ArticleDOI
Nicolas Reuge, Fabrice Schmidt1, Y. Le Maoult1, Mohamed Rachik, F. Abbé2 
TL;DR: In this paper, the authors describe the optimization of a bubble-inflation rheometer and show that the most sensitive point of the technique is the estimation of the elongation at the bubble pole, deduced from video camera measurements.
Abstract: The biaxial rheological behavior of materials such as elastomers or polymers can be obtained using a bubble-inflation-technique. A circular membrane is clamped at the rim and expanded under gas pressure. The inflation of the circular membrane is recorded using a CCD video camera and the blowing pressure by a pressure sensor. Then, from elongation and curvature radius measurements at the pole of the bubble, one can deduce equibiaxial stress-strain data. This study describes the optimization of a bubble-inflation rheometer. The most sensitive point of the technique is the estimation of the elongation at the bubble pole, deduced from video camera measurements. A direct measurement of the bubble thickness was performed using a magnetic probe in order to validate rheometer results. Such a validation has evidently never been carried out before. Results of quasi-static equibiaxial characterization of elastomers are presented and analyzed.

Journal ArticleDOI
TL;DR: In this article, the influence of various extrusion and drawing parameters on the extensional rheological performance of two polypropylenes is discussed and an attempt was made to estimate the transient extensional viscosity from the Rheotens test.
Abstract: In recent years the “Rheotens” melt strength test has emerged as one of the most important tools for comparing the drawability of polymer melts. This paper examined whether a reliable set of test conditions could be obtained to determine a true and accurate melt strength of a polymer. The influence of various extrusion and drawing parameters on the extensional rheological performance of two polypropylenes are discussed. Using this knowledge an attempt was made to estimate the transient extensional viscosity from the Rheotens test. An analytical Wagner model in the linear region of the Rheotens test was used for the first time to calculate the transient extensional viscosity from the Rheotens test. These results were compared to the transient extensional viscosity obtained from a constant strain rate Rheometrics melt extensional rheometer (RME). The results agree within measurement accuracy with those measured from an RME. Consequently, the viscosity determined from the Rheotens experiment can be used to estimate transient extensional viscosity. The influence of different Rheotens test conditions on transient extensional viscosity are also discussed.

Journal ArticleDOI
TL;DR: In this article, a single phase model is derived for a semi-solid alloy with thixotropic properties, where the microstructure is characterized by a structural parameter, and the model consists of two parts: the equation of state, including a finite yield stress and a rate equation for the structural parameter.

Journal ArticleDOI
TL;DR: In this paper, a high-speed camera was employed in conjunction with cone-and-plate and parallel-disk fixtures of a Rheometric Scientific Advanced Rheometry Expansion System rheometer.
Abstract: The traditional technique for the experimental characterization of the shear stress relaxation modulus by applying a step shear strain was investigated using flow visualization. A high-speed camera was employed in conjunction with cone-and-plate and parallel-disk fixtures of a Rheometric Scientific Advanced Rheometric Expansion System rheometer. In the nonlinear region the true shear strain imposed on a polyethylene melt deviates considerably from the targeted strain. The main source of the deviation is the wall slip of the polymer melt. The presence of wall slip reduces significantly the range of strains for which the strain-dependent relaxation modulus can be determined for the linear polyethylene melt. Errors associated with the control of the motion of the tool which introduces the shear strain are also documented.

Journal ArticleDOI
TL;DR: In this article, a rotational, compressional, and lubricated squeezing flow rheometer was used to measure the storage and loss modulus of up to 60% glass bead filled polydimethyl siloxane (PDMS) materials.
Abstract: The frequency and time dependent moduli of up to 60% glass bead filled polydimethyl siloxane (PDMS) were studied for four different molecular weight materials with a rotational, compressional, and lubricated squeezing flow rheometer Measurements of the storage and loss modulus taken with a conventional rotational instrument show good qualitative and quantitative agreement with those taken with a newly developed oscillatory compressional rheometer for PDMS of the lowest molecular weight studied, and show trends similar to those reported previously for similar materials The agreement between the two instruments is better for both unfilled and 35% filled material of a higher molecular weight Good agreement was also observed between measurements of the relaxation modulus in lubricated squeezing flow and measurements of the storage modulus with the new compressional device for a high molecular weight PDMS at all filler levels The modulus derived from oscillatory measurements showed good quantitative agreement with that measured in lubricated squeezing flow for identical materials The effect of polymer molecular weight on the relative behavior of the loss and storage modulus with increasing filler content was also studied It was shown that as the polymer molecular weight increases, the ratio of the loss to storage modulus becomes nearly independent of the filler volume fraction over the frequency range studied The effect of an increase in filler amount on the elasticity of the material was shown to depend both on the polymer molecular weight and the frequency, and is explained in terms of the influence of the filler on the Deborah number of the system

Journal ArticleDOI
TL;DR: In this article, two types of viscoelastic scaling models were developed to predict the effects of both CO 2 concentration and pressure on the viscosity of the polymer melts.
Abstract: High-pressure rheological behavior of polymer melts containing dissolved carbon dioxide (CO 2 ) at concentrations up to 6 wt % were investigated using a high-pressure extrusion slit die rheometer. In particular, the steady shear viscosity of poly(methyl methacrylate), polypropylene, low-density polyethylene, and poly(vinylidene fluoride) with dissolved CO 2 were measured for shear rates ranging from 1 to 500 s -1 and under pressure conditions up to 30 MPa. The viscosity of all samples revealed a reduction in the presence of CO 2 with its extent dependent on CO 2 concentration, pressure, and the polymer used. Two types of viscoelastic scaling models were developed to predict the effects of both CO 2 concentration and pressure on the viscosity of the polymer melts. The first approach utilized a set of equations analogous to the Williams-Landel-Ferry equation for melts between the glass-transition temperature (T g ) and T g + 100 °C, whereas the second approach used equations of the Arrhenius form for melts more than 100 °C above T g . The combination of these traditional viscoelastic scaling models with predictions for T g depression by a diluent (Chow model) were used to estimate the observed effects of dissolved CO 2 on polymer melt rheology. In this approach, the only parameters involved are physical properties of the pure polymer melt that are either available in the existing literature or can be measured under atmospheric conditions in the absence of CO 2 . The ability of the proposed scaling models to accurately predict the viscosity of polymer melts with dissolved high-pressure CO 2 were examined for each of the polymer systems.

Journal ArticleDOI
TL;DR: In this article, the extrusion characteristics of alumina pastes involving boehmite gel as a binder are reported and the paste rheology, workability, green strength and sintered properties are studied and reported.

Journal ArticleDOI
TL;DR: New measurements on the creep rheological behaviour of gelatin gels from both traditional mammalian and piscine sources are described and a novel gel viscosity versus concentration state diagram presented.

Journal ArticleDOI
TL;DR: In this paper, a new empirical equation is developed to evaluate rheological parameters of polymer melts in torque rheometers, in which the effects of rotor speed, temperature and apparent filling degree on torque are all considered.

Journal ArticleDOI
TL;DR: In this paper, the stability of magnetorheological (MR) fluids has been studied using a stress-controlled rheometer and sedimentation test, and the steady-shear MR response was independent of the continuous and nano additives.
Abstract: In order to improve the stability of magnetorheological (MR) fluids, viscoelastic medium having 2.2 Pa yield stress has been used as a continuous phase and nanosized CrO2 particles are added too. The rheological properties as well as the dispersion stability of MR fluids have been studied by using a stress-controlled rheometer and sedimentation test. The steady-shear MR response was independent of the continuous and nano additives and the fieldinduced yield stress increased subquadratically with the flux density. Since the constant stress is generated within the limit of zero shear rate, the plateau in the flow curve corresponds to the Bingham yield stress. Under an external field, the yield stress varied as B3/2. The yield stress has an approximately linear relation with the particle volume fraction.