摘要:

Reported data on polystyrene, polyethylene, and polydimethylsiloxanes are contradictory with respect to the shear rate at which the transition from Newtonian to non‐Newtonian flow occurs. Some data implies that the transition occurs at the same lower limiting shear rate and is independent of molecular weight above a critical molecular weight. On the other hand, other data shows that above a critical molecular weight the transition occurs at lower rates of shear as the molecular weight increases. The considerations of Bueche for melt polymer flow confirm the latter type of transition behavior. It is proposed that the discrepancies are due to molecular weight distribution, temperature effects, and methods of obtaining zero shear viscosities. Data are presented to support these views.

ISSN:0148-6055    

DOI:10.1122/1.549017

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

The steady‐state melt viscosity of several plasticised hydrocarbon elastomers is shown to be described by a reduced variable treatment which allows superposition of the viscosity‐shear rate curve for any polymer containing a diluent on the viscosity curve of the pure polymer. The shift factors which accomplish this superposition may in turn be broken up into two factors: (1) a function of the volume concentration of the diluent alone, which represents the loosening of the entanglement network, and (2) a factor representing the effect of the diluent on segmental friction and chain configuration. The latter is shown to be related to the temperature of measurement and the glass transition temperatures of both polymer and diluent. The relationships developed permit predictions of plasticizer efficacy for any diluent/polymer combination from glass transition and density data alone.

ISSN:0148-6055    

DOI:10.1122/1.548994

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

The Williamson empirical equation which fits polystyrene melt viscosity data is derived by considering the melt as a system of elastic springs which are entangling and disentangling. The theory allows one to trace changes in the number of extensible elements and the relaxation time for the rupture of intermolecular links. For uniform molecular weight samples, the number of extensible elements per molecule is proportional to the molecular weight. Widening the molecular weight distribution lowers the number of extensible elements per cc. The thermal relaxation time increase rapidly with increasing molecular weight. The effect of fillers on the number of extensible elements and the relaxation time is complex.

ISSN:0148-6055    

DOI:10.1122/1.548995

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

Viscosity measurements are reported for a variety of systems as a function of shear using a thin film, double‐thermostatted, concentric cylinder viscometer. The basic instrument design and the cylinders which are of unusually narrow clearance and fine machining permit accurate and precise viscosity measurements to be made at homogeneous shear rates up to two millionsec.−1Measurements are reported on a molecular weight series of pure normal paraffin hydrocarbons fromn‐C8H18ton‐C32H66.Viscosities measured at the highest shear agree within a precision of 2% and better with known low shear hydrocarbon viscosities. This result indicates an absence of both heating effects and molecular degradation and reveals Newtonian flow over the entire103shear rate range of the instrument. Similar tests were also performed on several pure cyclic compounds in a test for conformational shifts between rotational isomers which possibly could be induced by a high shear field. The improved high shear concentric cylinder viscometer was also used to double the shear rate range for the established viscosity of standard API Oil 104, which is the most widely studied and the most non‐Newtonian of current non‐Newtonian viscosity standards.

ISSN:0148-6055    

DOI:10.1122/1.549018

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

The problem of determining the orientation distribution function of rigid particles of arbitrary shape is formulated in a general stochastic approach to consider any acting orientation mechanism, stochastic or deterministic. The effect of the various orientation mechanisms on the partial differential equation of the problem is analysed. A particular orientation mechanism acting on rigid ellipsoidal macromolecules in addition to the hydrodynamic and the Brownian effects is considered in Couette flow: a force field in the radial directionx, varying linearly withx. It is shown that the effect of a uniform electric field in the radial direction on polarizable ellipsoidal particles is of this nature. The corresponding steady‐state orientation distribution function is determined to the third order for the case of predominant Brownian influence, and the theory of streaming birefringence of a dilute suspension of rigid ellipsoidal macromolecules in Couette flow is generalised to include the influence of the additional orientation mechanism: the direction of the isocline and the amount of birefringence are calculated to the second order.

ISSN:0148-6055    

DOI:10.1122/1.548996

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

Rheological behavior of a filled elastomer consisting of a polyurethane rubber and granular potassium chloride was investigated with both long‐ and short‐term loading producing conditions of torsion, uniaxial tension, and compression. The volumetric response and the thermo‐rheological behavior of the elastomer was also studied. To represent the observed behavior for moderate stresses and strains a linear viscoelastic model was developed. The results of torsion relaxation tests performed on the inert solid propellant are presented for three strain levels over the temperature range −60 to +200°F. The torsion relaxation moduls (at 5 sec for 4.31% initial shear strain) was changed by 2 orders of magnitude for a temperature variation of −60 to +200°F. Prolonged exposure to high temperatures and humidity degraded the rubber‐to‐filler bond so that the predominant relaxation response was that of a polyurethane rubber foam.

ISSN:0148-6055    

DOI:10.1122/1.549019

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

As part of a general study of the behavior of materials with temperature‐dependent properties, simple models of a viscoelastic solid are considered here. Ideal experiments at constant stress and constant rate of deformation are examined. The analysis leads to yield and fracture criteria which in the usual theory are regarded as experimentally determined quantities. Rate of strain and size effects are also deduced and a phenomenon resembling strain hardening can develop. The treatment is independent of, but complementary to, the atomic scale theories of the deformation of solids. The temperature coefficient of viscosity which is introduced into the continuum theory here, is related to the energy of activation for the flow process which is accessible to the atomic scale theory. Knowledge of the temperature field in which motions of the atoms occur could improve the predictions based on dislocation theory.

ISSN:0148-6055    

DOI:10.1122/1.549020

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

A parametric study was made of the stress relaxation of linear polyethylene in air and a stress cracking environment, Igepal. Breaking time is shown to be a function of reduced variables of time, temperature, and molecular weight. Acreleration of tests for failure time can be achieved if the test temperature is raised, since for 0.96 density P.E. over the range of 50–110°C no mechanism change occurs. Stress relaxation measurements are shown to give results similar to the bent strip stress cracking test (ASTM D 1693‐60T). This latter test can also be accelerated 80 times for 0.96 density polyethylene and 1500 times for 0.95 density polyethylene. A slight modification of the test procedure is required to obtain meaningful results. Some effects of strain, thickness, and presoaking are also reported.

ISSN:0148-6055    

DOI:10.1122/1.549021

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

A simple and precise means of measuring internal bond stresses in peel is now available. By the use of a newly designed “bond stress analyzer” the magnitude and positional distribution of internal normal stresses may be measured during peel. The design theory, construction, and operation of the instrument are reviewed in detail. The influence of the angle of peeling upon the cleavage stress distribution is investigated and analyzed. The results, interpreted in terms of present theory of peel adhesion, suggest that the peel test is a valid measure of interfacial adhesion properties only at a peel angle ofw=πrad=180 deg.The detailed form of the cleavage stress function in the region of boundary fracture indicates that cavitation and orientation processes contribute importantly to high peel strengths in elastomeric adhesive interlayers.

ISSN:0148-6055    

DOI:10.1122/1.549022

出版商:The Society of Rheology    

年代:1965

数据来源: AIP

摘要:

Adhesion studies on spherical particles imbedded in elastomers have shown that cohesive failure of the binder phase always precedes dewetting. The latter is a sudden and irreversible process resulting in permanent damage to the system. Cohesive failure manifests itself in the formation of a number of small holes near the surface of the filler particle. The stressσ′causing these holes is well defined and depends only on the elastic modulusEof the binder:σ′=E/2+C.The further propagation of these initial tears depends on the consistency of the boundary layer surrounding the solid inclusion. In case of no modulus gradient or a softer boundary layer, tear propagation leads to the complete separation of the elastomeric binder from the particle. High modulus layers, which are linked to the polymeric matrix by primary chemical bonds, prevent a dewetting. It is shown that the complex response of filled elastomers can be explained in terms of the above results.

ISSN:0148-6055    

DOI:10.1122/1.548997

出版商:The Society of Rheology    

年代:1965

数据来源: AIP