ISSN:0148-6055    

DOI:10.1122/1.549739

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

Effects of the larger‐to‐smaller particle size ratio α and mixing ratio of the particles on the relative apparent viscosityητof the suspensions were studied using a capillary viscometer. The decrease inητby the addition of a small amount of the smaller particles was remarkable in the low‐shear regime when α was larger than about 2.4 and the diameter ratio of the larger particle to tube was relatively large.

ISSN:0148-6055    

DOI:10.1122/1.549740

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

A rheological equation of state is developed for a semiconcentrated suspension of stiff fibers in a Newtonian solvent with volume fraction φ in the range(D/L)2<φ<(D/L),whereL/Dis the length‐to‐diameter ratio of the fibers. The constitutive equation gives the stress in terms of an integral over a function of the Cauchy strain tensor and the orientation vector for a fiber. An expression is also obtained for the evolution of the fiber orientation. The development is restricted to homogeneous flows. It is found that in start‐up of steady shear or elongational flow the orientation of the fibers and the measurable rheological properties both depend only on the total applied strain. For a fiber number density ofnthe contribution of the fibers to the stress is roughlynL3times that of the solvent when the fibers are randomly oriented, as for example at the beginning of a flow. In the model presented here the viscosity (at steady state) is identical to that of the Newtonian solvent, because of the alignment of the fibers in the planes of shear and the lack of inclusion of fiber thickness in the model.

ISSN:0148-6055    

DOI:10.1122/1.549748

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

Equations governing the transient stretching of thin plane film of isothermal Newtonian fluids were introduced in both Cartesian and cylindrical coordinates. Using the equations in Cartesian form, it was shown that uniform film thickness is maintained only when the film is initially uniform in thickness and the deformation is uniform biaxial extension/contraction independent of position (x,y) describable by a stretch ratee11(t)in thexdirection ande22(t)in theydirection wheretis time. Furthermore, the stretching is free of wrinkling or three‐dimensional buckling when the conditionse11+2e11>0and2e11+e22>0are both satisfied. In the one‐dimensional case of axisymmetrical stretching the governing equations in cylindrical coordinates reduce upon Lagrangian transformation to a single partial differential equation inf(u,t),wherefis the present radial position of fluid element anduis its initial radial position. Numerical solutions of this equation show that deviation of deformation from uniform biaxial stretching affect thickness uniformity only slightly, and when annular dent is given to initial thickness profile the shape of dent profileH(u)remains almost unchanged while in stretching.

ISSN:0148-6055    

DOI:10.1122/1.549749

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

Four assumptions are made in this theory. The logarithmic flow curve, specific viscosity against shear rate, has three linear segments which correspond to first Newtonian, power law, and second Newtonian regions of shear rate. The logarithmic plot of primary normal‐stress difference against shear rate also has three linear segments, in the same regions. Within any shear‐rate region the logarithm of a rheological property depends linearly on the logarithms of all parameters; these include volume fraction and molecular axial ratio. One long and one short characteristic time determine behavior at low and high shear rates, respectively. From these assumptions it is shown that the rheological properties are then so interrelated that many properties can be predicted if a few are known. Detailed theories for dilute solutions, given in a review by Brenner, confirm these relationships. New predictions for semidilute concentrations at high shear rates are derived from the theory of Doi and Edwards, which is also shown to represent Newtonian data at low shear rates from this laboratory better than the earlier equation of Brodnyan. At high shear rates not only the viscosity but also the normal stress become constant; this requires the relative importance of elasticity compared with viscosity to go through a maximum in the power law region.

ISSN:0148-6055    

DOI:10.1122/1.549750

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

The velocity lag between the two discs in the eccentric disc rheometer, inertia effects being ignored, has been studied theoretically. It is shown that the assumptions made in literature, viz. a constant velocity gradient between the discs, violates the momentum balance. Applying the principle of conservation of momentum to a velocity field of the form suggested by Blyler and Kurtz, but in which the velocity gradient is a function of the distancezto the lower disc, one can determine analytically the velocity field for a Newtonian liquid. For a general viscoelastic fluid a solution can only be given under certain restrictions. For the velocity field found the momentum balance is satisfied. The energy dissipated in the sample is supplied by the upper (driven) disc, as it should be. The energy balance, however, is only satisfied to first approximation. The experimental measurements of Davis and Macosko are in good agreement with the present theory. This is not the case with the experimental data given by Payvar and Tanner.

ISSN:0148-6055    

DOI:10.1122/1.549751

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

A recently constructed parallel‐plate rheometer has been used in conjunction with a commercial Materials Test System to obtain fast transient and steady‐state stress responses of a PIB solution in a number of well‐defined shearing experiments. These include alternate applications of oscillation and steady flow, superimposed steady and oscillatory flow, and shear deformation with exponentially increasing rates. This series of new transient tests are made possible via the servocontrol of a programmable function generator. The results reveal complex history‐dependent rheological properties of the test sample. Specifically, the stress overshoot peak observed when shearing resumes after a fixed rest period following large‐amplitude oscillations may be appreciably lower than the reference case where no prior oscillations are imposed. The overshoot peak reduction depends on the amplitude and frequency of the prior oscillatory deformation. Superimposed flow leads to a lower average stress than that exhibited by the control case of steady flow without the simultaneously applied oscillation. Exponential increases of shear rate result in stress histories dictated by shear‐rate variation. The stress level is thus not a unique function of either the total accumulated strain or the instantaneous strain rate.

ISSN:0148-6055    

DOI:10.1122/1.549752

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549779

出版商:The Society of Rheology    

年代:1984

数据来源: AIP