摘要:

The Maxwell orthogonal rheometer was used to measure the limit of linear viscoelastic response (LLVER) as a function of frequency for three linear polyethylenes at 170°C, for six atactic polystyrenes at 170°C, and for Phenoxy A at 212°C. For the elastic component of the stress, linear viscoelastic response was found to exist in all cases up to finite strains of approximately 50%. The viscous component of the stress exhibited linear viscoelastic response up to approximately 100% strain and sometimes as high as 120%, the maximum strain tested. Two constitutive equations (Bird and Carreau's theory with Gordon and Schowalter's generalization and Tanner's network rupture theory) are noted for the dependence they predict of the strain LLVER as a function of frequency. Bird's theory, with Gordon and Schowalter's generalization, predicts that the elastic strain limit times the frequency will be a constant as the frequency is varied; Tanner's theory predicts that the elastic strain limit will be a constant with varying frequency. Data are shown to support Tanner's theory. Although the theories predict similar relations for the viscous strain limit, since no viscous limit is found up to 120% strain, this portion of the theories could not be checked. Plots of the reduced in‐phase modulus,G′(γ)/GL′,and the reduced in‐phase viscosity,η′(γ)/ηL′,versus strain, γ, (GL′andηL′are the modulus and viscosity below the limit) yield very similar curves for all the polymers. This is in agreement with the limited data from MacDonald, Marsh, and Ashare. The reduced in‐phase modulus is constant as the strain is increased up to the elastic LLVER. A gradual decrease then occurs for all of the polymers; at 120% strain, the reduced modulus has decreased between 20 and 30%.

ISSN:0148-6055    

DOI:10.1122/1.549282

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

The requirements of nonnegative stored energy, nonnegative rate of dissipation of energy, and fading memory are used to derive restrictions upon the forms of the isotropic relaxation functions and the complex moduli of the linear theory of viscoelasticity. The results suggest some new means of displaying and interpreting mechanical properties.

ISSN:0148-6055    

DOI:10.1122/1.549265

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549266

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

Measurements of stress growth and stress relaxation after onset and cessation of steady simple shear flow in concentrated polymer solutions were carried out with a Weissenberg rheogoniometer R‐17 having a gap servo system. By using monodisperse polymers and their blends, the effect of molecular weight distribution on those transient phenomena is discussed. The so‐called stress‐overshoot was observed in both experiments of shear and normal stress growths. Ratio of the time of the maximum normal stress difference and that of the maximum shear stress is close to 2 at the limit of low shear rate for both monodisperse and polydisperse polymers. In the range of finite shear rate, the ratio is remarkably dependent on shear rate for polydisperse samples, whereas it is almost independent of shear rate for monodisperse polymers. Shear rate dependence of the ratio of the apparent relaxation time of normal stress difference and that of shear stress in stress relaxation experiments is also found to be remarkably affected by molecular weight distribution. From a comparison between these experiments and theories so far published, it is concluded that these transient phenomena may be explained by assuming that the relaxation spectrum is a function of shear rate at least if the shear rates are not too high. The comparison between theory and experiments is carried out without assuming explicit forms for relaxation spectrum.

ISSN:0148-6055    

DOI:10.1122/1.549267

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

The transient elongational viscosity of dumbbell suspensions is calculated accounting for the effect of an internal viscosity in the dumbbell. The calculations are relative to conditions of sufficiently large stretching rates for the effect of Brownian motions to be neglibible. Large extensions of the dumbbell are considered and the resulting nonlinear elastic behavior is accounted for. Both numerical and approximate analytical solutions are provided.

ISSN:0148-6055    

DOI:10.1122/1.549268

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

Die swell measurements for polystyrene samples of narrow molecular weight distribution and their blends have been made using a capillary viscometer. For the capillaries studied, the swelling ratios were nearly independent ofL/D(length/diameter) but strongly dependent on the distribution of molecular weights. The broader the distribution, the larger the swelling ratio for the same extrusion pressure. The recoverable shear at the wall, which is defined to be half the ratio of the first normal stress difference over the shear stress, was estimated using Graessley's correlation between experimental and Rouse shear compliance. The results were compared to predictions from the theories of Nakajima and Shida, Bagley and Duffey, Graessley et al., and Tanner.

ISSN:0148-6055    

DOI:10.1122/1.549269

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

In measuring the normal stress exerted by a fluid on a surface it is often convenient to puncture the surface with a ‘small’ hole leading to a larger cavity. An estimate of the stress is then made by measuring the hydrostatic pressure at the bottom of this cavity with a pressure transducer. Such a procedure, expedient though it is in practice, can result in large systematic errors in the estimate of the stress exerted on the surface, as has been shown experimentally by Kaye, Lodge, and Vale. The present paper gives a discussion of these errors based on kinematic considerations. The value of an approach of this kind is that it gives a physical understanding of the source of the error and suggests how such errors may arise even with rather complicated fluids. Three different configurations are examined. In the first example we consider a shear flow past a deep two‐dimensional slot normal to the flow; for the particular case of a second‐order fluid the intrinsic error is a quarter of the primary normal‐stress difference, in agreement with the previous calculation of Tanner and Pipkin. In the second case, the rectilinear motion along a slot aligned with the flow is considered, and the result obtained by Kearsley is recovered. However, the present analysis is applicable to the rectilinear motion of any material along a slot and, accordingly, a new method is suggested by which direct measurements of the secondary normal‐stress difference might be made. The third configuration comprises a shear flow past a circular hole and it is suggested, in this case, that the intrinsic error is approximately a sixth of the difference between the primary and the secondary normal‐stress differences of the material.

ISSN:0148-6055    

DOI:10.1122/1.549270

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

The drainage behavior of a wide variety of non‐Newtonian liquids has been studied under circumstances when “free‐drainage” conditions apply. Experimental values for the time‐variant film thicknesses were obtained while drainage proceeded using a light absorption technique, and an analytic expression relating film thickness to drainage time was derived for fluids described by the Ellis model. Deviations between the experimental and theoretical results are interpreted in light of the Ellis model's inability to describe the elastic properties of the liquids studied.

ISSN:0148-6055    

DOI:10.1122/1.549271

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

The BKZ theory is applied to finite amplitude dynamic motion of polymer solutions. Material parameters are obtained by fitting steady shearing and small amplitude oscillatory data. Predictions ofη′(γ0,ω)/η′(ω)andG′(γ0,ω)/G′(ω)are shown to be quite good. The second normal stress predictions are also in agreement with the currently accepted sign and magnitude.

ISSN:0148-6055    

DOI:10.1122/1.549272

出版商:The Society of Rheology    

年代:1972

数据来源: AIP

摘要:

Pressure profilesπψψ(r)were obtained for several polymer solutions in a cone‐and‐plate device (R=10 in.,ψ0=1.5°) over a shear rate range7–266 sec−1.Measurements were made with a single transducer mounted flush with a movable plate; the transducer could also be lowered to simulate the effect of holes. Normal stress functionsN1=π11−π22andN2=π22−π33were calculated by four different methods, representing varying approximations to the realπψψ(r)distribution. For polyethylene oxide (PEO) in water/glycerin and polystyrene (PS) in Aroclor,N2/N1was found to benegativeand greater in magnitude for the latter system. The function|N2/N1|for PEO appeared nearly constant over most of the shear range, although possibly increasing below30 sec−1.Values for PS did not achieve this asymptotic condition, but were consistent with such behavior. Magnitude of the asymptote for PEO was 0.1–0.2, depending on the method of calculation. Simulated pressure tap holes caused lowerπψψ,leading toN1values reduced by as much as 30% and totally misleadingN2.The holes are thus shown to be responsible for the commonly reported positive values ofN2/N1.

ISSN:0148-6055    

DOI:10.1122/1.549273

出版商:The Society of Rheology    

年代:1972

数据来源: AIP