摘要:

In a previous paper we presented the interesting theoretical result that in a two‐step torsional or simple shearing deformation where the magnitude of the second step is one‐half the magnitude of the first step, the normal stress response is predicted to be independent of the duration of the first step and equal to the single step response to a deformation of the same magnitude as the second step. Experimental support for this prediction is presented here based on tests run on two greatly different polymeric systems—a 19.3% solution of polyisobutylene in cetane and glassy poly(methyl methacrylate).

ISSN:0148-6055    

DOI:10.1122/1.549565

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

The rheological properties of suspensions of ionic and nonionic styrene‐divinyl‐benzene copolymer particles in polycrylamide aqueous solution have been measured by means of a cone‐and‐plate‐type rheometer. The dynamic viscoelasticity of suspensions of nonionic particles is remarkably nonlinear, and frequency‐dependent curves ofG′andG″show the so‐called second plateau. Moreover, the yield stress is characteristic of steady‐flow properties of these suspensions. Suspensions of ionic particles, on the other hand, behave like Newtonian liquids, and the second plateau and yield stress disappear.G′andG″of suspensions of slightly ionized particles do not depend on strain amplitude, while those of suspensions of highly ionized do. Similar measurements have been carried out on suspensions of mixtures of anionic and cationic particles. A suspension containing almost the same number cationic and anionic particles behaves like suspensions of nonionic particles and manifests the second plateau, yield stress, and nonlinear viscoelasticity. An attempt has been made to relate the rheological properties to the aggregate structure, applying the electrical theory for stability of lyophobic colloids.

ISSN:0148-6055    

DOI:10.1122/1.549566

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

A theory of flowing granular materials with incompressible grains is presented which is similar to one proposed by Goodman and Cowin in 1972. Using a nonlinear version of the theory, boundary‐value problems corresponding to gravity flow in a closed vertical channel and in a channel with a free surface inclined at various angles from the vertical are considered in detail. In analyzing these problems, the dependence of the free energy and viscosity on the volume fraction are specialized to agree with those proposed as a result of recent experimental work. Solutions of these problems demonstrate many of the characteristics normally assumed in other treatments of granular materials. In particular, for vertical flow, when the volume fraction is greater than (less than) the critical volume fraction, a compressive (tensile) force must be exerted on the walls to maintain isochoric flow. Pluglike regions in which the velocity is almost constant develop, and there is a relatively thin shear region near the wall. For the flow with a free surface, as grain size or angle of inclination increases, the solutions tend to two rigid motions separated by a thin shear layer.

ISSN:0148-6055    

DOI:10.1122/1.549601

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

In an experimental study of polyethylene (PE) and poly(methyl methacrylate)(PMMA) blends, complex viscosityη*(ω)=η′−iη″and non‐Newtonian viscosityη(γ̇)were obtained with a Weissenberg rheogoniometer operating in a cone‐and‐plate mode at 160 °C. Blends were prepared by a standardized melt mixing for volume fractions φ fromφ=0(PE)to 1.0 (PMMA) at increments ofΔφ=0.1.The PMMA was more viscous than PE at all conditions of ω andγ̇,their viscosity ratio being 5.9 in the Newtonianη0limit. Scanning electron micrographs were taken of freeze‐fracture planes in all samples prior to testing. A maximum in both η andη′was found nearφ=0.9and an apparent step increase of viscosity level in the vicinity of 0.5–0.6 at all ω andγ̇.The maximum is quantitatively explained in the Newtonian limit by well‐established viscosity predictions for dilute two‐phase emulsions with spherical droplets; this model is equally successful forφ=0.1(the other dilute regime) and, in both cases, valid also within 5–10% for a substantial range of ω‐ andγ̇‐dependent data. The step increase is attributed to phase inversion, but smooth interpolation betweenφ=0.1and 0.9 is found to yield rather good empirical predictions for intermediate compositions without recourse to microstructural information. Rather conventional behavior is seen in comparisons ofη(γ̇)withη′(ω)and|η*|,the latter upholding the Cox‐Merz approximationη=|η*|rather well. Exceptions to these are noted in the intermediate φ range, but only in theη0limit after high‐γ̇testing, and the discrepancies are suspected to arise from microstructural alterations during steady shear.

ISSN:0148-6055    

DOI:10.1122/1.549595

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

Stress relaxation curves of many solids can be normalized and presented in the linear form ofF(0)t/[F(0)−F(t)]=k1+k2t,whereF(t)is the decaying force andk1,k2are constants. The reciprocal ofk2denotes the asymptotic value of the relaxed portion of the initial stress. Since in active biological materials equilibrium conditions in the conventional sense are difficult to determine, the asymptotic values can be used to calculate residual moduli that are representative of the material short‐term rheological characteristics. Similarly, creep curves of solids in which the strainε(t)stabilizes or practically stabilizes with time (e.g., under small loads or in compression) can be presented byt/ε(t)=k1+k2t,where1/k2is the asymptotic strain. It is shown that the relationships between asymptotic moduli, so calculated, and the strain in relaxation or the stress in creep can carry information that is relevant to structural changes that occur during deformation of the material such as development of hydrostatic pressure, internal fracture, and failure.

ISSN:0148-6055    

DOI:10.1122/1.549567

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

The steady state shear and linear viscoelastic properties of both isotropic and liquid crystalline solutions of the rigid chain polymer poly‐p‐phenyleneterephthalamide in sulfuric acid have been determined. Both the primary normal stress coefficient and the linear viscoelastic properties show the same characteristic concentration behavior as does the viscosity. The unique rheological properties of the anisotropic phase can be attributed to the formation of a suspension of highly ordered regions in a matrix of isotropic fluid. The rheological properties were compared against the Bird‐Carreau model and Hand's anisotropic fluid theory. Remarkably good agreement was found between the Bird‐Carreau model and data especially at high shear rates. This suggested that at high shear rates very little difference may exist between anisotropic and isotropic phases. Hand's model was more applicable to solutions which were only slightly anisotropic.

ISSN:0148-6055    

DOI:10.1122/1.549596

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

For some pure elastomers, the strain‐energy function can be expressed as the sum of three identical functions of the principal stretch ratios, that is the strain energy is of the Valanis‐Landel form. Methods of measuring this function are derived and demonstrated. Examples are given of evaluation from extension and compression (biaxial extension) and from torsion of a cylinder. The character of the strain‐energy function about the undeformed state(λ=1)is examined in detail.

ISSN:0148-6055    

DOI:10.1122/1.549568

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549569

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549570

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549597

出版商:The Society of Rheology    

年代:1980

数据来源: AIP