Showing papers on "Rheometer published in 1987"

Tests of the interface between sand and steel in the simple shear apparatus

Abstract: The simple shear apparatus is used for tests on the interface between soil and other construction materials. A comparison was made of its advantages and disadvantages, as well as of the test results for sand-steel interfaces, with respect to three other types of interface testing apparatuses: the direct shear, the annular shear and the ring torsion types. A simple shear apparatus is less sophisticated than a ring torsion apparatus mainly in the non-uniformity of the stress distributions, but it can be used with much less technical difficulty. Good agreement was observed between the results from the three types on the correlations between the coefficient of friction and the roughness of the steel surface. The sliding displacement measured in simple shear tests showed good agreement with the observation in the ring torsion type of apparatus, but the tangential displacement in the direct shear test was larger, possibly because it included the displacement due to the strain in the sand mass inside the shear b...

On the extensional viscosity of mobile polymer solutions

Abstract: We describe experimental results on the extensional viscosity of mobile polymer solutions obtained from two instruments, the first being a commercial Spin Line Rheometer and the second a custom-built lubricated-die Converging Flow Rheometer. The interpretation of data in terms of Trouton ratios is facilitated by a simple analysis for the Generalized Newtonian Fluid model.

Direct measurement of static yield properties of cohesive suspensions

Abstract: A technique of yield stress investigation based upon the combined use of two devices (an applied stress rheometer and an instrument for measuring the propagation velocity of small amplitude, torsional shear waves) is described. Investigations into the low shear rate rheological properties of illitic suspensions are reported for shear rates, typically, in the range 10−4— 10−1 s−1 under applied stresses in the range 0.01 — 10 Nm−2 and involving shear strains between 10−1 and 10−4. Results are presented which demonstrate that the technique does not invoke the excessive structural disruption of material associated with applied shear rate based methods (direct and otherwise) and the widely encountered problem of wall slip at the surface of rotational measuring devices is avoided using miniature vane geometries. Results are compared with those obtained using smooth-walled cyclindrical measuring devices in both applied stress and applied shear rate instruments. Yield measurements are considered in relation to the structural properties of the undisturbed material state and shear moduli obtained by studying the propagation of small amplitude (10−5 rad), high frequency (~ 300 Hz) torsional shear waves through the test materials are reported. Experimental techniques and instrument modifications to permit these measurements are described.

Shear rheometry of fluids with a yield stress

Abstract: This work is concerned with the measurement of viscometric material functions of greases, which are fluids with a yield stress. Rheometers working under controlled stress or under kinematically controlled conditions have been used in plane and cone geometry. Viscometric functions and the problems encountered in measurements are examined simultaneously. It is shown how fracture and slippage at boundng surfaces alter the measurements of the bulk properties and how they can be controlled. Fractures limit the amplitude of deformation; hence the rate of the deformation and duration of measurements. Slippage is a limiting factor at low rates of deformation, but it can be suppressed. Within the range defined by these two limiting factors, viscometric properties have been measured: elastic properties, yield values, and start up, steady and unsteady viscometric material functions similar to those for melted polymers have been found.

Wall and interfacial shear stress in stratified flow in a horizontal pipe

Abstract: Experimental values are presented for the wall and interfacial shear stresses in stratified gas-liquid flow in a pipe. The wall and Reynolds shear stresses were measured using a hot-film anemometry technique. The interfacial shear stress was determined using two methods: from a momentum balance, using the wall shear stresses and void fraction measurements, and from an extrapolation of the Reynolds shear profile at the gas-liquid interface. The predicted interfacial shear stress data were approximated by the formula relating the interfacial friction factor with the void fraction and gas and liquid Reynolds numbers, and were compared with other reported data.

Characterization of yield stress fluids with concentric cylinder viscometers

Abstract: The methods normally employed for shear rate calculations from concentric cylinder viscometer data generally are not applicable for fluids with a yield stress. In cylindrical systems with large radius ratios, as usually is the case with suspensions, the yield stress induces two possible flow regimes in the annulus. Unless the yield value is exceeded everywhere in the gap only part of the fluid can be sheared while the remaining region behaves like a solid plug. A correct calculation of the shear rate must take into account the presence of a variable effective gap width determined by the extent of the sheared layer. For time-independent yield stress fluids, a two-step procedure, which does not require any specific flow model, is proposed for analysing the experimental torque-speed data. Under the partially sheared condition, the shear rate can be computed exactly, whereas for the fully sheared flow the Krieger and Elrod approximation is satisfactory. The method is assessed by examining both semi-ideal data generated with a Casson fluid with known properties, and experimental data with an industrial suspension. A more complicated problem associated with characterization of time-dependent yield stress fluids is also identified and discussed. An approximate procedure is used to illustrate the dependence of the shear rate on time of shear in constant-speed experiments.

F-actin and microtubule suspensions as indeterminate fluids

Abstract: The viscosity of F-actin and microtubule suspensions has been measured as a function of shear rate with a Weissenberg rheogoniometer. At shear rates of less than 1.0 per second the viscosity of suspensions of these two structural proteins is inversely proportional to shear rate. These results are consistent with previous in vivo measurements of the viscosity of cytoplasm. This power law implies that shear stress is independent of shear rate; that is, shear stress is a constant at all shear rates less than 1.0 per second. Thus the flow profile of these fluids is indeterminate, or nearly so. This flow property may explain several aspects of intracellular motility in living cells. Possible explanations for this flow property are based on a recent model for semidilute suspensions of rigid rods or a classical friction model for liquid crystals.

Polymer melt elongation—methods, results, and recent developments

Abstract: For film blowing of polyethylene it has been shown previously that melt elongation is very powerful for polymer characterization. With two types of rheometers, simple (also called “uniaxial”) elongational tests as well as creep tests can be performed homogeneously. In simple elongation, the melts of branched polyethylene show a remarkable strain hardening. With respect to their advantages and disadvantages, these rheometers complement each other. For multiaxial elongations the various modes of deformation can be performed by means of the rotary clamp technique. With the strain rate components ordered such that 11 ⩾ 22 ≥ 33, the ratio m = 22/11 characterizes the test mode. The Stephenson definition of the elongational viscosities makes use of the linear viscoelastic material equation and proves to be very efficient because the linear shear viscosity (t) (“stressing” viscosity) can act as the reference for the nonlinear behavior in elongation. Results are given for polyisobutylene measured not only in simple, equibiaxial, and planar elongations, but also in new test modes with a change of m during the deformation. This allows one to investigate the consequences of a deformation-induced anisotropy of the rheological behavior.

Rheological behavior of compatible polymer blends. I. Blends of poly(styrene-Co-acrylonitrile) and poly(ε-caprolactone)

Abstract: The rheological behavior of blends of poly(styrene-co-acrylonitrile) (SAN) and poly(e-caprolactone) (PCL) was investigated, using a cone-and-plate rheometer. For the study, blends of various compositions were prepared by melt blending using a twin-screw compounding machine. The rheological properties measured were shear stress (σ12), viscosity (η), and first normal stress difference (N1) as functions of shear rate (γ) in steady shearing flow, and dynamic storage modulus (G′) and loss modulus (G″) as functions of angular frequency (ω) in oscillatory shearing flow, at various temperatures. It has been found that logarithmic plots of N1 versus σ12, and logarithmic plots of G′ versus G″, become virtually independent of temperature but vary regularly with blend composition, and that the zero-shear viscosity of the blends, (ηo)blend, follows the relationship, 1/log(ηo)blend = wA/log η0A + wB/log η0B, where η0A and η0B are the zero-shear viscosities of components A and B, respectively, and wA and wB are the weight fractions of components A and B, respectively. The physical implications of the relationship found are discussed.

Linear low density polyethylenes and their blends: Part 3. Extensional flow of LLDPE's

Abstract: The uniaxial extensional flow at 150°C of 11 linear low density polyethylenes (LLDPE) and one low density polyethylene was measured in a Rheometrics Extensional Rheometer. The presence of silicone oil did not affect the results. However, large effects of the molding time were observed. For specimens molded for 14 min, strain hardening was not observed for any gas-phase polymerized LLDPE. As the molding time was increased to 40 min, the strain hardening was quite apparent, the elongational viscosity nearly doubled, the equilibrium plateau vanished, and the maximum strain at break Increased by about 20 percent. Explanation for the molding time effects can be found in the concept of low entanglement density in the virgin gas-phase resins. The entanglement increases with time at temperatures above the melting point. The specimens molded for longer time show strain hardening.

Rheology of polymers containing carbon black

Abstract: In order to elucidate the flow behavior of electrophotographic toner systems, shear stress was measured as a function of shear rate in a cone and plate rheometer for polymer melts containing carbon blacks of surface area 24 and 625 m2/g at several concentrations and temperatures. Polymers included high and low molecular weight polystyrene and poly(butyl methacrylate). The addition of carbon black to the polymers caused a large increase in viscosity, especially at low shear rates and shear stresses. As the concentration of carbon black was increased, the viscosity at low shear rates became unbounded below a value of the shear stress designated the yield stress. The absolute magnitude of the yield stress depended primarily on the concentration and surface area of the carbon black and was independent of the polymer and temperature. Apparently, carbon black forms an independent network within the polymer at low shear rates which precludes flow. In some cases, the viscosity of polymers filled with carbon black was lower than that of the pure polymer. This effect was favored for polystyrene compared to poly(butyl methacrylate) and was facilitated by increasing the molecular weight of polystyrene, reducing the surface area and concentration of carbon black, and by increasing the temperature and shear rate.

Measurement of the viscosity of guar gum solutions to 50,000 s−1 using a parallel plate rheometer

Abstract: It is frequently necessary to measure the viscosity of polymer solutions at high shear rates to obtain data under the conditions encountered in industrial processes. Such measurements are most often made on a capillary viscometer. This paper presents a method of determining solution viscosities at shear rates up to 50,000 s−1 in a rotational rheometer using a parallel plate geometry. The two keys to performing these measurements are very small gaps between the parallel plates (on the order of 50 microns) to eliminate inertial secondary flows, and the ability to increase and decrease the shear rate quickly to minimize viscous heating. A technique for setting and measuring small gaps is presented. Possible sources of error including inertia, axial compliance, and viscous heating are analyzed. A comparison Is made between the viscosity of a 0.7 percent hydroxypropyl guar (HPG) solution measured on the parallel plate rheometer and the viscosity measured in a capillary viscometer. Viscosities of HPG solutions having concentrations of 0.25, 0.50, 1.00, and 1.45 percent are presented over the shear rate range 100 to 50,000 s−1.

Analysis of a Newly Developed Damped-Oscillation Rheometer: Newtonian Liquid

Abstract: The behavior of a newly developed damped-oscillation rheometer was analyzed for Newtonian liquids from both theoretical and experimental points of view. This rheometer consists, essentially, of a cylindrical tube suspended from a torsion wire that is filled with the liquid to be tested. In order to determine the relationship between the rheological parameters of the liquid and the period or the logarithmic damping factor measured by this rheometer, a Newtonian liquid was considered as a first test liquid. Based on various assumptions, the equations of motion for the liquid and the cylindrical tube were solved simultaneously. Numerical solutions and approximate analytical solutions valid for certain ranges of the parameters were obtained. The results are compared with experimental results which we measured using this rheometer.

Extrusion Stresses, Die Swell, and Viscous Heating Effects in Double‐Base Propellants

Abstract: A capillary extrusion rheometer was used to evaluate the flow behavior of mixtures of nitrocellulose (12.2% nitrogen) and nitroglycerine when processed using solvent blends of different strengths. The aim of the work was to quantify the effects on flow behavior of “gelatinization,” that is, the degree of breakdown of the fibrous structure of the nitrocellulose. The flow behavior was measured over a range of extrusion temperatures. The results indicate that the materials behave as Herschel‐Bulkley fluids, that the shear stress decreases as gelatinization increases, and that viscous heating is more apparent in poorly gelatinized doughs. Surface temperatures of the extrudate determined experimentally are compared with computer‐modelled values. Die swell measurements decreased with decreasing degree of gelatinization and with increasing extrusion temperature.

Exponential shear: a strong flow

Abstract: The recent development of new types of sliding‐plate rheometers for concentrated polymeric liquids makes it possible to generate a shearing deformation in which the strain is exponential in time. Such a deformation is a strong flow in the sense that the deformation kinematics have a strong tendency to stretch out the molecules of a polymeric liquid. Previous applications of the concept of strong flows have been limited to motions with constant stretch history, that is, deformations where the components of the strain rate tensor are constant with respect to time. For example, steady simple extension is a strong flow that has attracted much attention because of its ability to generate a high level of molecular stretching. However, it is a deformation that is difficult to generate in the laboratory. We make use of both a kinematic criterion for strong flows and one based on the elastic dumbbell model to show that exponential shear is likely to generate a high degree of molecular stretching. In addition, we p...

Drilling fluid shear stress overshoot behavior

Abstract: Shear stress overshoot behavior was studied in four drilling fluid systems and ten bentonite dispersions. These overshoot properties, also described by the American Petroleum Institute as gel strengths, were measured after gelation times of 10 s to 24 h at temperatures of 20–80 °C. Two different rheometers were used to measure overshoot behavior. Gel strength development with time followed a first-order model. Gel development rates at 20 °C varied from 0.005 to 0.01 min−1 for drilling fluid systems and from 0.0004 to 0.02 min−1 for bentonite dispersions. Increasing the gelation temperature for each drilling fluid system caused an increase in the gelling rate constant. Comparison of gel strengths in bentonite dispersions were made using a Fann 35 A viscometer and a Weissenberg Rheogoniometer. Higher gel strength values observed using the Rheogoniometer were believed to be due to differences in instrument spring stiffness and fixture inertia.

Apparatus and method for determining the viscoelasticity of liquids

Abstract: A rheometer for determining the viscoelasticity of a liquid from the mechanical impedance which the liquid presents to an oscillating surface. The incremental power required to maintain a fixed amplitude of oscillation of the surface upon immersion in the liquid is determined. The differential shift in oscillation frequency due to immersion in the liquid is also determined. By relating (i) the incremental oscillation power to mechanical resistance presented by the liquid to the oscillating surface, and (ii) the differential shift in a oscillation frequency to the mechanical reactance presented by the liquid to the oscillating surface, the viscoelasticity of the liquid is determined. Applications include laboratory measurements and process control.

Rheological and extrusion behavior of dispersed multiphase polymeric systems

Abstract: An experimental study of temperature effect and composition effect on the rheological and extrusion properties of several dispersed multiphase polymer melts were investigated, using a cone-and-plate rheometer and a capillary rheometer. The polymeric systems studied included three homopolymers (two polystyrenes and one poly(methyl methacrylate) (PMMA)), a mechanically blended copolymer of polystyrene and PMMA, two graft copolymers (rubber-modified polystyrene and PMMA), and three particulate-filled polystyrene (CaCO3, milled glass fiber, and glass flake). It was found that the principal normal stress difference plotted against shear stress gives rise to a temperature independence for all dispersed multiphase polymeric systems. Composition independent correlations, however, do not exist for the principal normal stress difference. The extrudate swell plotted against shear stress becomes independent of temperature only for the homopolymers and graft copolymers. For the mechanically blended polymers and particulate-filled polymers, the temperature independent correlation does not exist. The reduction in viscosity of the glass fiber- and glass flake-filled polystyrenes is found due to the degradation of the base polymer during mixing.

Measurement of the first normal-stress difference at high shear rates for a polyisobutylene/decalin solution “D2”

Abstract: Reasonable agreement is found between values of the first normal-stress differenceN 1 for samples of “D2”, a polyisobutylene/decalin solution, measured in steady shear flow using three different instruments: a Weissenberg Rheogoniometer (a cone-plate rotational rheometer), a Torsional Balance (plate-plate rotational) Rheometer, and a Stressmeter (a transverse-slot slit-die rheometer). Viscosity values are also in reasonable agreement. Ranges of variables common to at least two rheometers include values of shear stressσ up to 3,700 Pa and shear rate $$\dot \gamma $$ up to 20,700 s−1 near 25 °C. The agreement supports the approximate validity of the semi-empirical “HPBL equation” used to calculateN 1 from Stressmeter data over a range of shear rates up to 20,700 s−1 near 25 °C. Time-temperature superposition behavior exhibited by Stressmeter data at temperatures in the range 21 °C to 111 °C suggest that the range of validity of the Stressmeter method for determiningN 1 approximately may extend up to shear rates of 290,000 s−1 at 111 °C.

A Shear Wave Rheology Sensor

Abstract: A rheology sensor for monitoring the dynamic viscosity of a thermally curing resin is described The complex shear modulus of the resin at 1 MHz is derived from the measured reflection coefficient of shear wave pulses at the resin surface A special transducer-buffer assembly has been developed that operates at high temperature (T = 145°C) and provides a reference calibration signal With this assem- bly, absolute determinations are made throughout the cure cycle of the real and imaginary components of the shear modulus From the latter high-frequency dynamic viscosity is calculated The results are com- pared with data obtained at low shear rates with a 10 Hz torque vis- cometer

Properties and principles of mycelial flow: experiments with a tube rheometer.

Abstract: The flow behavior of a penicillin mash has been investigated with a tube rheometer and compared with rotational viscometer observations. In the low-shear regions plug flow and breakdown of the plug have been studied. For turbulent flow turbulence damping was demonstrated. The Theological development during the fermentation was followed. At low deformation rates the pressure drop increased during the fermentation. In turbulent regions the opposite tendency was observed. The possible underlying flow mechanisms are discussed, and the influence of a number of physical parameters have been investigated.

Adiabatic reactive viscometry for polyurethane reaction injection molding

Abstract: Adiabatic reactive rheometry involves the simultaneous measurement of viscosity and temperature changes during adiabatic polymerization. Using the adiabatic reactor method to relate temperature to fractional conversion results in a useful rheokinetic tool ideally suited for fastreacting reaction injection molding (RIM) systems for which the mold-filling step is nearly adiabatic. In this work, a small laboratory RIM machine is used to mix the reactants and deliver them to a constant stress rheometer retrofitted with a wide-gap Couette geometry and two thermocouples. Measurements on two polyurethane systems are reported. A simple cross-linking system is used to verify the adiabatic rheokinetic method through comparison to a known gel conversion. Subsequent measurements on a phase-separating RIM system show that increases in catalyst level, hard segment content, and initial reactant temperature result in a decreased gel time and an increased gel conversion. The viscosity rise profiles aid our understanding of the onset and development of phase separation. They are also essential for mold-filling models and establishing moldability criteria for these RIM systems.

Flow of K-BKZ fluids between parallel plates rotating about distinct axes: shear thinning and inertial effects

Abstract: It has been shown that for any simple fluid, a flow field of the form u = –Ω[y - g(z)], v = Ω[x – f(z], w = 0, which is appropriate for modeling the flow in a orthogonal rheometer, is dynamically possible. The functions f(z) and g(z) depend on the choice of constitutive equation. In the present paper, these are calculated for a class of K-BKZ fluids which exhibit shear thinning. The results are then used to study the interaction of shear thinning and inertial effects on the flow field in an orthogonal rheometer.

Properties and principles of mycelial flow: a tube rheometer system for fermentation fluids.

Abstract: A tube rheometer system has been constructed for aseptic study of the rheology and fundamental flow properties of mycelial fermentation fluids. The rheometer consists of a U-formed tube circuit starting and ending inside the fermentor. The mash is pumped through the tubes with a lobe rotor pump. The flow is measured by an electromagnetic flow meter. Pressure drops have been measured with a system of differential membrane transducers for different flow rates. The rheometer system was tested with Newtonian and non-Newtonian fluids.