摘要:

Eleven differential and nine integral rheological models for viscoelastic fluids are tabulated in a uniform notation. Included among these are several very recently published models and three previously unpublished models. Representative experimental data are presented and used in qualitative and quantitative evaluations of the models. Comparisons between the models and the experimental data are summarized in a table where a six‐point rating scheme is used to assess the ability of several models to quantitatively describe seven material functions. The table indicates which models show promise for future work.

ISSN:0148-6055    

DOI:10.1122/1.549057

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

The Ericksen theory of anisotropic fluids is examined with respect to its usefulness for describing the constitutive properties of real fluids. It is found that except in the limit of low shear rates, anisotropic effects may not be observed in simple laminar shearing flows or in helical flows, in both of which the behavior of these materials is indistinguishable from the predictions of the isotropic theory of simple fluids, and such flows do not suffice to determine uniquely all the material functions needed to describe other configurations. In unsteady flows, the theory as presently developed is limited to applications in which the fluid time constant is much smaller than the characteristic time of the flow field, i.e., to flows for which the Deborah number is sufficiently small. In these, the theory of simple fluids again appears to suffice with but the same exception.

ISSN:0148-6055    

DOI:10.1122/1.549045

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

The full range of phenomena occurring in the flow of suspensions remains still unexplored. This paper describes phenomena observed in a neutrally buoyant suspension consisting of a single layer (a monolayer) of rigid spherical particles, flowing through a 220‐cm long rectangular channel of high‐aspect ratio (1:16) with its minor dimension(116in.)1.6 times larger than the particle diameter. The flow was investigated over a range of particle Reynolds numbers between 101 and 407, and of concentrations between 1.7 and 5%. Concentration distributions obtained from a detailed analysis of direct photographic observations show the existence of four consecutive regions as the suspension moves down the channel: (a) an initial region, close to the channel entrance, characterized by essentially uniform particle distribution. (b) A region in which the particles move away from the wall forming a particle‐free layer next to it. The core containing the particles does not have a uniform concentration distribution but exhibits marked concentration peaks at its outer margin. (c) A region in which the core has narrowed, the peaks have merged, and the concentration has become uniform. (d) A region of instability characterized by the onset of waves in the configuration of the core, followed, as the flow progresses downstream, by a breaking up of the core and by the formation of groups of particles separated by axial gaps of suspending liquid. The transitions between these regions are not sharply bounded, each region evolving gradually into the next. The process is accelerated by increases in flow velocity, and decelerated by increases in concentration. The phenomena point to the existence of a hydrodynamic force leading to the formation of the core, and possibly of concentration‐dependent particle interactions opposing such a formation and contributing to the onset of instabilities.

ISSN:0148-6055    

DOI:10.1122/1.549058

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

The dynamic stress‐strain‐time response of a clay in compression is studied using a high‐speed explosive pulse type of apparatus. The rise times of the applied stress pulses are the order of magnitude of 0.2 msec and the entire test durations are approximately 3.0 msec. Compressive loading is obtained with a piston using the high pressure developed by firing a Springfield 30–06 cartridge into a combustion chamber. Measurements include forces at the top and bottom of the test specimen, deformation of the specimen, and acceleration as well as velocity of the upper platen. Dynamic stress‐strain response exhibits an under‐linear type of nonlinearity for a wide range of consistencies (moisture contents) generally encountered in field applications. Effects of moisture content are conveniently handled in terms of a nondimensional dynamic stress‐strength parameter using the static ultimate unconfined compressive strength as a consistency index. The nonlinear effects are represented in terms of a two‐constant hyperbolic stress‐strain relation. The two hyperbolic constants are measures of the initial tangent modulus and the ultimate strength of the clay. These constants are easily obtained as the intercept and slope of the straight line approximation of the experimental data when presented in transformed hyperbolic coordinates. Because of the multiphase nature of clay, the results may be of value in studying the response characteristics of other composite materials.

ISSN:0148-6055    

DOI:10.1122/1.549046

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

The kinetic theory of liquids has been used to derive two crude models which rationalize the establishment of a molecular weight gradient during the capillary extrusion of polydisperse thermoplastic melts. A molecular weight decrease near the polymer/die wall interface is predicted along with a decay in the degree of extrudate swelling with increasing die length, each model giving equations relating decay rate with die dimensions and shear rate. Polyethylene data indicate some shortcomings in the theory, but both models fit experimental extrudate swelling data well, and appreciably better than an empirical equation of exponential decay. Further in keeping with theory, surface sections of broad molecular weight distribution polyethylene extrudates have lower molecular weights than whole extrudates, the magnitude of the effect increasing with increasing die length. No significant molecular effect was found for a fractionated linear polyethylene. The decay in extrudate swelling was also found to be much greater for broad molecular weight polyethylene samples than for the fractionated polymer. It is suggested that molecular fractionation in capillary flow is a significant contributing cause to the difference in die length variation of melt viscosity and melt elasticity.

ISSN:0148-6055    

DOI:10.1122/1.549047

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

It was shown that three material functions are required to relate various phenomena in the capillary flow of polyethylene. The phenomena examined are the entrance pressure loss, laminar flow through a capillary, memory decay in the flow, and extrudate swelling. A unified picture was constructed for the capillary flow and the energy balance was calculated.

ISSN:0148-6055    

DOI:10.1122/1.549048

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

Using a new instrument, the influence of the shear amplitudes0on the dynamic behavior of polymer solutions up to 700% shear was investigated. At amplitudes<∼100% shear, the dynamic viscosityη1remained constant, as required by linear viscoelasticity; however, the shear storage modulusG′decreased considerably. The steady‐state flow curve forms the envelope of curves measured with different amplitudes and frequencies, predominantly in the range of higher rates of shear. The more complete analysis of the results is forthcoming.

ISSN:0148-6055    

DOI:10.1122/1.549049

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549050

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549051

出版商:The Society of Rheology    

年代:1966

数据来源: AIP

摘要:

In order to evaluate the stored energy functionWfor elastomeric materials, at least biaxial experiments must be made. Two of the biaxial testers developed at the Jet Propulsion Laboratory are an inflated cylinder device and a second biaxial sheet tester. Some preliminary experimental results obtained with these two devices at small values of strain invariants are presented for a polyurethane elastomer. These results are analyzed without making the assumption that the elastomer is incompressible, a fact which modifies the analysis of multiaxial or large‐strain behavior. The results from the biaxial sheet tester are consistent with those obtained from an inflated cylinder of the same material, though experimental difficulties prevent a detailed comparison. Nevertheless, both series of experiments show that all three terms,∂W/∂Ii,whereIiare the three strain invariants, depend strongly on the invariants. Moreover,∂W/∂I2is negative, in agreement with theoretical expectations. Thus, the form ofWin the region whereIi<4is very complex.

ISSN:0148-6055    

DOI:10.1122/1.549059

出版商:The Society of Rheology    

年代:1966

数据来源: AIP