Showing papers on "Rheometer published in 1979"
TL;DR: In this article, a shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication, which is a Maxwell model modified with a limiting shear stress.
Abstract: A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: Low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature and, in one specific case where direct comparison could be made, good numerical agreement is shown.
304 citations
TL;DR: In this paper, a universal extensional rheometer, which makes it possible to investigate the elongational properties of polymer melts, is described and the operation modes of the apparatus are demonstrated on a polystyrene sample.
Abstract: A new universal extensional rheometer, which makes it possible to investigate the elongational properties of polymer melts, is described. Measurements under a wide variety of constant stretching rates and constant tensile stresses can be undertaken and recoil and relaxation experiments can be performed on a small amount of material. The operation modes of the apparatus are demonstrated on a polystyrene sample. For this polystyrene the viscosity and the recoverable strain in the steady state of elongation were measured over more than three decades of the tensile stress. At small stresses the recoverable strain is proportional to the stress, i.e., the compliance is constant and the viscosity gives a constant value which is three times the zero‐shear viscosity. At higher stresses the recoverable strain seems to level off and the viscosity runs through a maximum which lies 30% above the stress‐independent value.
193 citations
TL;DR: In this paper, the authors use the concept of an average stress tensor to determine a representative stress state in the central part of the sample, which is least influenced by the ends of the apparatus.
Abstract: The simple shear apparatus is one of the few commonly available laboratory apparatus that permits the application of controlled rotations of the principal axes of stress and strain to soil samples. However, because of the boundary conditions in the apparatus the soil sample does not respond as a single element, and this should be reflected in the analysis of test results. In the Cambridge University simple shear apparatus, the sample is surrounded by an array of load cells (contact stress transducers) that measure the complete distribution of boundary stresses throughout a test. For simple shear test results to be presented in terms of useful stress parameters, a procedure for computing the stress state from the load cell measurements is required. Such a procedure is described, making use of the concept of an average stress tensor to determine a representative stress state in the central part of the sample, which is least influenced by the ends of the apparatus. Less complex and expensive apparatus exist that can only measure the average normal and shear stresses applied to the top and bottom horizontal boundaries of the sample. Patterns of soil response have been determined from tests on Leighton Buzzard sand in the more elaborately instrumented Cambridge apparatus, and a method is described for using these patterns to deduce the complete stress state in the less complex apparatus.
81 citations
TL;DR: In this paper, a simple shear device for undrained simple shearing is presented. But the shear stresses are transmitted to the specimen by a horizontally loaded top cap and zero lateral strain during undrained shearing was achieved through an automatic measuring and regulating system.
Abstract: Existing types of direct simple shear devices are discussed and a newly developed apparatus is presented. This apparatus uses a round specimen that is laterally covered by a rubber membrane and placed in a pressure cell in which vertical and horizontal normal stresses are applied as with triaxial test equipment. The shear stresses are transmitted to the specimen by a horizontally loaded top cap. Zero lateral strain during undrained shearing is achieved through an automatic measuring and regulating system. Procedures and results are described for an undrained cyclic simple shear test on sand and an undrained static strain-controlled test on an undisturbed normally consolidated clay.
53 citations
01 Feb 1979
TL;DR: The mini-rotary viscometer (MRV) as discussed by the authors was developed at the request of SAE Fuels and Lubricants Subcommittee 2 and culminates a two-part ASTM Program to define pumpability characteristics of reference oils in engines and assess/develop bench test methods for predicting low temperature engine pumpability.
Abstract: A new viscometer, the mini-rotary viscometer (MRV), has been demonstrated to predict the low temperature pumpability performance of engine oils. This bench test method was developed at the request of SAE Fuels and Lubricants Subcommittee 2 and culminates a two-part ASTM Program to (1) define pumpability characteristics of reference oils in engines and (2) assess/develop bench test methods for predicting low temperature engine pumpability. The MRV is a low shear stress/shear rate viscometer that correlates either with an "average" engine or an individual engine, depending upon the critical rheological requirements of the particular engine or engines, and attains its high degree of correlation by predicting either of two failure modes -- air binding of the pump or insufficient oil flow rate to the oil pump inlet. Thus, the MRV complements the cold cranking simulator, a high shear stress device, in defining the low temperature behavior of straight-grade and multigrade engine oils.
34 citations
TL;DR: In this article, the authors measured the time-dependent flow birefringence on application of a step-shear strain for an 8% polystyrene solution in chlorinated biphenyl.
Abstract: The time‐dependent flow birefringence was measured on application of a step‐shear strain for an 8% polystyrene solution in chlorinated biphenyl. Measurements were performed with an apparatus of coaxial cylinder type at various shear strains γ ranging from 0.913 to 7.56. The amount of birefringence was in agreement with that evaluated from the shear stress with the use of the stress‐optical law. The extinction angle χ was independent of time and satisfied a relation 2 cot 2χ=γ. This result combined with the stress‐optical law indicates that the Lodge‐Meissner relation holds valid for the polystyrene solution, i.e., the first normal stress difference is equal to the shear stress multiplied by the shear strain in the stress relaxation process following an application of step‐shear strain.
25 citations
TL;DR: In this paper, an instrument modification to a capillary extrusion rheometer is described which permits ready measurement of the viscosity-shear rate behavior of concentrated polymer solutions, particularly in the generally inaccessible region of high temperatures with volatile solvents.
Abstract: An instrument modification to a capillary extrusion rheometer is described which permits ready measurement of the viscosity‐shear rate behavior of concentrated polymer solutions, particularly in the generally inaccessible region of high temperatures with volatile solvents. Despite the fundamental rheological and practical commercial importance of defining the viscosity behavior of highly concentrated (e.g., 50–100%) polymer solutions at temperatures well above the solution Tg, few data in this region are available in the literature. This is largely because of the experimental difficulty of making measurements in the concentrated solution region under conditions where significant evaporative solvent losses are likely to occur. Instrumentation and methodology for performing these experiments with relative ease and generally good precision are described, and typical viscosity‐shear rate curves obtained for solutions of polystyrene in ethylbenzene at various concentrations (50–90 wt %) and temperatures (100–2...
23 citations
TL;DR: The impact microviscometer has been modified so that the ball can be rotated after an entrapment is formed This rotation produces an extra circumferential shear stress which is much larger than the radial stress caused by the outward flow.
Abstract: The impact microviscometer has been modified so that the ball can be rotated after an entrapment is formed This rotation produces an extra circumferential shear stress which is much larger than the radial stress caused by the outward flow Three fluids were studied by using this device All displayed non-Newtonian behaviour at high shear stresses and appeared to be tending towards a limiting shear stress with increasing shear rate at pressures from 03 to 2 GPa Data from one of the fluids (polyphenyl ether) were compared with results from a ball on plate traction test and a remarkable correlation was found It seems reasonable to attribute the peak in the traction-slip curve to the ultimate shear stress that the lubricant can support
21 citations
TL;DR: In this article, a computer program has been written which converts torque-speed data obtained from the five "disk-like" spindles of the Brookfield RVT viscometer into shear stress data.
Abstract: A computer program has been written which converts torque-speed data obtained from the five “disk-like” spindles of the Brookfield RVT viscometer into shear stress — shear rate data Experimental results obtained on the same samples from the Brookfield viscometer and commercial rheogoniometers are used to demonstrate the utility of the program
17 citations
TL;DR: In this article, the elastic component (normal stress) is shown to be responsible for the anomalous flow in polystyrene/decalin solutions, and the onset of flow irregularities was found at low shear rates.
Abstract: Polystyrene/decalin solutions exhibit flow irregularities in a cone-and-plate rheometer at theta-conditions. The onset of flow irregularities was found at low shear rates. The elastic component (normal stress) is shown to be responsible for the anomalous flow. The onset of flow irregularities has been predicted from measurements of recoverable strain as a function of shear stress. We suggest that this analysis should be suitable to find the best coating fluid leading to the highest possible speed without exhibiting flow irregularities.
17 citations
TL;DR: In this paper, a constitutive equation has been developed to relate surface stresses to the deformational history of an interface, and experimental results indicate that both spread and adsorbed monolayers can exhibit viscoelastic behavior which may be represented by the model.
Abstract: A constitutive equation has been developed to relate surface stresses to the deformational history of an interface. To verify the applicability of the equation to real surface films, experimental studies involving spread and adsorbed monolayers have been conducted using the deep-channel surface rheometer operated both under the conditions of oscillatory and constant floor motion. The results reported here are the first obtained using an oscillatory system.
Experimental results indicate that both spread and adsorbed monolayers can exhibit viscoelastic behavior which may be represented by the model. Furthermore, it has been found that for three long chain, fatty acid films, spread on a pH 6.1 aqueous substrate, surface shear viscosity and surface elasticity increase with film pressure and molecular weight. The observed rheological behavior was found to be strongly pH dependent.
TL;DR: A capillary extrusion rheometer was developed and tested using Newtonian oils of known viscosity and seven endodontic sealers to appear appropriate for comparative assessment of the rheological characteristics of a variety of fluid dental materials.
Abstract: A capillary extrusion rheometer was developed and tested using Newtonian oils of known viscosity and seven endodontic sealers. The described apparatus and technique appear appropriate for comparative assessment of the rheological characteristics of a variety of fluid dental materials.
TL;DR: In this paper, a mathematical expression for calculating shear stresses from torque values observed with the Mooney rheometer is derived, and the numerical values of the conversion factor are given for both small and large rotors.
Abstract: A mathematical expression is derived for calculating shear stresses from torque values observed with the Mooney rheometer. Examination of this expression indicates that some improvement is possible in the rotor design. The numerical values of the conversion factor are given for both small and large rotors. The application of these factors to the observed data give viscosities in agreement with those obtained with other instruments. Low shear viscosities down to 10−3 and in some cases 10−4s−1 are obtained with the Mooney rheometer operated at 0.05 rpm for several minutes.
TL;DR: In this paper, the tangential stress build-up after a sudden imposition of a shear rate and the decay after cessation of steady shear flow have been collected, which is used to further test a constitutive equation already advanced by some of the authors.
Abstract: Some new data in shear flow are presented for two commercial polyisobutylene samples, namely Vistanex LMMH and L 100. In particular beyond a few steady state results, the tangential stress build-up after a sudden imposition of a shear rate and the decay after cessation of steady shear flow have been collected. The data are used to further test a constitutive equation already advanced by some of the authors. The comparison seems to confirm the validity of the proposed model, whose single adjustable parameter is shown to be independent of molecular weight.
TL;DR: In this paper, the observed torque was converted to shear stress with a theoretical factor derived by taking into account both the parallel plate section and the concentric cylinder section, assuming that the edge effect was negligible.
Abstract: The Mooney rheometer has been used universally as a tester for quality control of raw elastomers and compounds. White and Tokita showed that the tester modified to operate at a range of speeds could be used to obtain fundamental viscoelastic properties: steady-state shear stress-shear rate relationship, normal stress effect, and elastic recoil. We have also made effective use of this rheometer to obtain steady-state viscosity as a function of shear rate and complex viscosity as a function of deformation rate. In these investigations, the observed torque was converted to shear stress with a theoretical factor derived by taking into account both the parallel plate section and the concentric cylinder section. It was assumed that the edge effect was negligible. The viscosities calculated in this manner were compared to those obtained with other instruments and reasonably good agreement was obtained. Some time ago, Mooney and Treloar expressed the opinion that the viscosity obtained from the Mooney rh...
TL;DR: In this paper, the authors consider the effect of variable-viscosity behavior on the departure of the predicted shear rate from that used in the conventional interpretation of experimental results.
Abstract: We consider theoretically the problem of the shear rate in a cone-and-plate rheometer, giving particular attention to the effect of variable-viscosity behaviour on the departure of the predicted shear rate from that used in the conventional interpretation of experimental results. It is concluded that this departure is much greater for shear-thinning fluids than for Newtonian constant-viscosity fluids. It is also shown that edge effects are significantly enhanced by variable-viscosity behaviour. However, the predicted departure from the constant shear-rate normally assumed is still insignificant for gap angles usually employed in cone-and plate rheometers (≤ 4°). Some consideration is also given toLodge's proposed method of normal-stress measurement which uses a truncated cone-and-plate assembly. It is concluded that the assumptions required to interpret the experimental results are valid to a sufficient degree of approximation. These assumptions concern the smooth transition from torsional flow to cone-and-plate flow near the abrupt change in geometry. Finally, we discuss edge effects in the re-entrant cone situation suggested byCowsley. These are concluded to be significant, pointing to a serious source of experimental error.
TL;DR: In this paper, it is shown that at small eccentricities, the emulsion behaves as a linear viscoelastic fluid and the effect of these variables on emulsion rheology is determined for an eccentric disk rheometer, an instrument in which vorticity and rate of deformation are independent variables.
Abstract: Constitutive behavior of a dilute suspension of drops is affected by drop shape. It is known that this shape is determined by both the rate of deformation and the vorticity of the bulk flow field. The effect of these variables on emulsion rheology is determined for an eccentric-disk rheometer, an instrument in which vorticity and rate of deformation are independent variables. It is shown why, at small eccentricities, the emulsion behaves as a linear viscoelastic fluid. Elastic and viscous moduli are related to emulsion properties. Suggestions are offered for the use of an emulsion model to represent the behavior of other viscoelastic liquids in the regime of nonlinear response.
TL;DR: In this paper, a cone-and-plate rheogoniometer was used to investigate the rheological behavior of aqueous solutions of Separan AP-30 and Polyox WSR-301 in a concentration range of 10-10000 wppm.
Abstract: The rheological behaviour of aqueous solutions of Separan AP-30 and Polyox WSR-301 in a concentration range of 10–10000 wppm is investigated by means of a cone-and-plate rheogoniometer. The relation between the shear stress and the shear rate is for lower shear rates characterized by a timet0, which is concentration dependent. Both polymers show for 4000 s−1 <\(\dot \gamma \) < 10000 s−1 a behaviour similar to that of a Bingham material, characterized by a dynamic viscosityη0 and an “apparent yield stress”τ0, which also depend on the concentration. The inertial forces are measured for water and some other Newtonian liquids. An explanation is given why the theoretical model developed for these forces does not match the experimental values; the shape of the liquid surface is shear rate dependent. To obtain the first normal stress difference, we have to correct for these inertial forces, the surface tension and the buoyancy. The normal forces, measured for Separan AP-30, appear to be a linear function of the shear rate for 350 s−1 <\(\dot \gamma \) < 3300 s−1.
TL;DR: In this article, the relationship between shear stress and shear rate appears to deviate from the expected linear behaviour for Newtonian fluids, and a simple model based on a heat balance describes this behaviour quantitatively.
Abstract: At higher shear rates the relation between shear stress and shear rate appears to deviate from the for Newtonian fluids expected linear behaviour. In cone-and-plate rheogoniometry one of the most important causes of that is the effect of viscous heating. Accurate measurements carried out with a 10 cm diameter cone and plate lead to a semi-logarithmic, linear relationship between temperature increase and time for a Newtonian oil which dynamic viscosity varies approximately linearly with time. A simple model based on a heat balance describes this behaviour quantitatively.
TL;DR: This study describes a new approach to the rheological characterization of fracturing fluids which uses an oscillating or dynamic shear rate rather than a steadyShear rate, which allows the determination of theRheology of highly viscous, cross-linked gels.
Abstract: This study describes a new approach to the rheological characterization of fracturing fluids which uses an oscillating or dynamic shear rate rather than a steady shear rate, which allows the determination of the rheology of highly viscous, cross-linked gels. An accurate and reproducible method of determining fluid properties is necessary for both fracturing treatment design in the field and fluid development and optimization in the laboratory. Fracturing fluids of all types can be measured using a dynamic viscometer. Both the elastic storage modulus and the viscous-loss modulus can be measured. These parameters are related to the amount of energy stored elastically and lost through viscous heating, respectively. Both are related to the pumping pressure. In this study, the relationship between steady shear and dynamic viscosity data for several common fracturing fluids will be established. Data for cross-linked fluids will be presented as well as data for sand-laden fluids. 13 references.
TL;DR: The ability to correlate resin elasticity with individual processing requirements in the future could open new channels of communication between resin makers and their customers in terms of elasticity as discussed by the authors, which could lead to compounding for specific processes.
Abstract: Chemical engineers have designed rheometers that measure elasticity as well as viscosity of polymer melts and solutions at high shear rates, continuously and on line. And installation of these instruments at output streams of polymerization reactors, coupled with feedback control loops to control reactor conditions, is paving the way to automated operation for lot-to-lot reproducibility. Ability to correlate resin elasticity with individual processing requirements in the future could open new channels of communication between resin makers and their customers in terms of elasticity. Resins could be specified and designed specifically for such processes as fiber spinning, extrusion, and injection molding. Research on effects of additives, fillers, and coupling agents on viscosity and elasticity may lead to compounding for specific processes. Discovering relationships between melt elasticity and cell development could improve structural foam molding and extrusion. One such rheometer, developed by Chang Dae H...
01 Oct 1979
TL;DR: In this paper, low-dose radiation crosslinking has a greater effect on viscosity at low-shear rates than at high shear rates and form stability of the shaped plastic as it leaves the die can be improved without affecting processing conditions.
Abstract: Low-dose radiation crosslinking has a greater effect on viscosity at low shear rates than at high shear rates. Thus, form stability of the shaped plastic as it leaves the die can be improved without affecting processing conditions. Measurements with a torque rheometer demonstrate dependence of rheological behavior on absorbed radiation dosage.
TL;DR: In this paper, a conicylindrical rheometer suitable for use with disperse systems is described, which has the facility for direct tracing flow curves onx − y coordinates.
Abstract: A conicylindrical rheometer suitable for use with disperse systems is described. The instrument has the facility for direct tracing flow curves onx − y coordinates. Both the end effect and the instrument constant for the rheometer were determined theoretically and confirmed by experiment. Suitability of the instrument for examination of both Newtonian and non-Newtonian fluids is demonstrated.
Journal Article•
TL;DR: In this article, numerical calculations were performed to study the flow of polymeric liquids at the start of rotation of a coaxial cylinder rheometer, where the rheological behavior was represented by a strain-dependent constitutive model of Bernstein, Kearsley, and Zapas (BKZ model) and the stress equation of motion was solved with an electronic computer.
Abstract: Numerical calculations were performed to study the flow of polymeric liquids at the start of rotation of a coaxial cylinder rheometer. The rheological behavior of polymeric liquids was assumed to be represented by a strain-dependent constitutive model of Bernstein, Kearsley, and Zapas (BKZ model) and the stress equation of motion was solved with an electronic computer. The distribution of rate of shear starts from that expected for the steady flow of a Newtonian liquid and approaches the distribution obtained for the steady flow of a power law liquid. The rate of shear at a fixed point varies monotonously at low rates of rotation where the phenomenon of stress-overshoot is not very marked. At high rates of rotation, the rate of shear passes over a maximum or a minimum, respectively, depending on whether the sample is located close to the inner wall or the outer wall. At a certain radius slightly smaller than the average of the inner and outer radii of the cylindrical gap, the rate of shear scarcely depends on time provided that the rotation velocity and the gap width are not too large. The use of coaxial cylinder rheometer to measure time-dependent shear stresses is justified under the same condition.