摘要:

An examination is made of the static orientation solutions for a nematic liquid crystal in a pipe, including those involving phase changes near the center of the pipe. It is found that solutions both with and without phase change are possible if the pipe radius is sufficiently large, but that below a critical value of the pipe radius all solutions involve phase change.

ISSN:0148-6055    

DOI:10.1122/1.549286

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

An infinite viscoelastic body with a cyclindrical cavity subjected to cyclic internal pressure is considered. A quasi‐steady state of wave motion with the stress strain effectively periodic is assumed. A show change in amplitude occurs as a result of the slow rise in temperature due to the continuous dissipation of mechanical energy into heat energy. The material properties of the medium are temperature dependent and hence the shape and speed of wave vary with time. Close‐form solutions for the wave motions as well as the energy dissipation are obtained by using the WKB approximation. The temperature rise is calculated from a nonlinear heat equation by means of finite‐difference methods. This paper presents both the stress components and temperature distributions at different times for various frequencies.

ISSN:0148-6055    

DOI:10.1122/1.549287

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

For viscoelastic fluids the use of a “pressure tap” to measure the normal stress on a channel wall can lead to large errors. In previous studies the true normal stress on the wall was theoretically predicted or indirectly measured and compared to the erroneous measurements. Here pressure transducers are flush mounted on a rectangular channel approximating infinite parallel plates so that the true stress on the wall can be measured experimentally. A transducer is recessed to create a hole; the reading thus obtained is compared with the true stress to determine the hole error. Solutions of 0.9, 2, and 3% Polyox (polyethylene oxide,MW=4,000,000) in water were studied. Shear rates reached17,000 sec−1and hole errors up to6000 dynes/cm3were found. In the region of creeping flow, the hole error is equal to −0.16 of the primary normal stress difference. Hole errors have been determined at Reynolds numbers from10−4to103and at the higher values cross zero and become positive, as they are for Newtonian fluids. A mechanism is presented which explains this behavior of viscoelastic fluids over the seven cycle range of Reynolds number.

ISSN:0148-6055    

DOI:10.1122/1.549288

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

Expressions previously derived for the intrinsic error associated with pressure‐tap measurements under the assumption of steady symmetrical flow of a second order fluid are found to be applicable under more general conditions.

ISSN:0148-6055    

DOI:10.1122/1.549289

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

There has been considerable discussion in the literature of the last few years about the material functions which can be measured in steady uniform extensional flows, and the author has recently summarized much of this discussion. Although the initial work in this field focussed attention on uniaxial extensional flow, there is now a growing interest in biaxial extensional flow. Kinematically, biaxial extension is the reverse of uniaxial extension; i.e., the velocity fields for the two flows are identical except that the signs of the components are changed. An implication of this fact is that any constitutive equation of the “simple fluid” type will predict a biaxial extensional viscosity function which can be obtained from the predicted uniaxial extensional viscosity by a simple variable transformation.

ISSN:0148-6055    

DOI:10.1122/1.549314

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

Fully developed steady flow of a highly elastic liquid such as a molten polymer is not possible at low Reynolds number above a critical value of the elastic shear strain (wall shear stress/modulus). The limiting value is 2.6 in a cylindrical die and 0.7 in a slit die. The result is obtained using the linear theory of hydrodynamic stability and assuming that the fluid rheological properties are adequately described by the convected Maxwell model. Agreement with reported melt flow instabilities in extrusion is encouraging.

ISSN:0148-6055    

DOI:10.1122/1.549290

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

In many polymer processing operations like injection molding, the polymer melt flows under the influence of high pressure, sometimes exceeding 20,000 psi. It has been suggested by a number of workers, on the basis of both experimental and theoretical considerations, that the effect of hydrostatic pressure on viscosity cannot be ignored in such instances. However, most of the proposed techniques to determine the effect of pressure on viscosity suffer from limitations especially at high shear rates. The present work proposes a more general and quantitative method for obtaining the effect of pressure on the viscosity of polymer melts from capillary viscometer data. In addition to its applicability over a wide range of practical shear rates, the proposed method employs less restrictive assumptions than previous techniques and contains corrections for the effect of viscous heating. The results obtained for the effect of pressure on the viscosity of polystyrene at 180°C are compared to rheological data obtained by conventional methods. Preliminary results on the pressure coefficient of viscosity appear to be in agreement with predictions based on the W‐L‐F equation.

ISSN:0148-6055    

DOI:10.1122/1.549315

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

Additional data are presented for a bubble inflation technique which was used to develop equal biaxial extensional flow in viscoelastic materials. Biaxial extensional viscosity and elastic properties of a polyisobutylene at 23°C are compared with the predictions of constitutive equations and with experimental results obtained from other instruments. Constant pressure (rather than constant tension) experiments were carried out to the point of bubble bursting. A modified plot involving variables derived from pressure and bursting time is compared with the biaxial viscosity data, and the prospects for using this simpler test are discussed.

ISSN:0148-6055    

DOI:10.1122/1.549291

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

The instability of jets of some non‐Newtonian fluids under the influence of externally controlled disturbances was studied. Dispersion curves were generated over a range of frequencies. Jets of a 0.1% solution of Carbopol in water, a viscoinelastic fluid, showed a breakup pattern similar to that of jets of water. The dispersion curve matched a viscosity intermediate to the zero shear viscosity of the solution and the viscosity that corresponds to the average shear rate in the tube. Subject to external disturbances, jets of Separan solutions showed a remarkably ordered and regular pattern. On jets of 0.1% Separan, sinusoidal wave formation was absent and a ligament‐droplet configuration formed from the outset. On the less elastic 0.05% Separan jets, there is an initial region in which sinusoidal waves grow exponentially; the growth is later arrested and a ligament‐droplet configuration results. In the initial region the growth rates are about equal to the growth rates that a jet of a Newtonian fluid of the same zero shear viscosity would develop. The ligaments that form on jets of Separan are shown to undergo a stretching motion accounting in part for their unusual stability.

ISSN:0148-6055    

DOI:10.1122/1.549292

出版商:The Society of Rheology    

年代:1973

数据来源: AIP

摘要:

Recently Yamamoto proposed a new procedure to determine the relevant material properties for a widely used viscoelastic fluid constitutive relation. The procedure, based on a hypothetical dependence of the memory function on the rate of deformation, is rather complicated and introduces a few approximations. Also, the procedure was not actually applied to a particular set of experimental data. In this paper it is shown how the basic hypothesis of the constitutive equation can be tested quickly and simply, without introducing any approximations, and in fact without directly determining the relevant memory function. This new procedure is applied to one of the standard model materials; the constitutive relation is revealed to be an inadequate formation for this material.

ISSN:0148-6055    

DOI:10.1122/1.549293

出版商:The Society of Rheology    

年代:1973

数据来源: AIP