摘要:

Nonlinear effects have been considered in computations of orthogonal rheometer flow and in flow caused by the oscillation of a sphere in an unbounded fluid. Predictions of fluid response, based on a Bird‐Carreau constitutive model, are qualitatively different from those which follow from linear theory. Of particular interest are the corrections to force components in the orthogonal rheometer analysis and the generation of a steady secondary flow in the oscillating sphere problem. Magnitudes of these nonlinear effects are presented for a variety of fluid and flow parameters.

ISSN:0148-6055    

DOI:10.1122/1.549363

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

摘要:

A theoretical and experimental study for measuring meaningful transient normal force in the cone‐and‐plate geometry of the Weissenberg rheogoniometer type apparatus is presented. Meissner's modifications (J. Appl. Polym. Sci.,16, 2877 (1972)) are adapted to our Weissenberg rheogoniometer. The apparatus is stiffened and the closed loop feedback system is replaced by an open loop cantilever spring to extend the capability of the Weissenberg rheogoniometer to ascertain the transient normal force measurement. Due to these modifications, the transient gap variation in the instrument is limited to less than 1 μ which causes negligible effect on the normal stress measurement response. However, depending on the geometrical factors of the apparatus, the characteristic response time of the normal force measuring system in some cases, might not be small in comparison to the characteristic time of the testing fluid. The factors influencing the characteristic response time of the normal force measuring system are determined and a criterion is established which should be met to minimize the influence of the instrument response on the rheological measurements of the test fluid. Time constants as functions of geometrical and experimental factors associated with gap separation velocity for two Newtonian incompressible liquids are measured and compared with the calculated values. The theory is qualitatively in agreement with the experimental findings, yet for some cases disagreements of up to 43% between the measured and calculated time constants are observed. The dominant effect of gap angle is also confirmed.

ISSN:0148-6055    

DOI:10.1122/1.549388

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

摘要:

Some numerical calculations of the distribution function for bead positions in a linear‐locked‐spring dumbbell are presented together with stresses for transient (start‐of‐shearing) flows. Based upon the idea that this distribution function is sharply peaked in these and other results obtained previously, an approximate constitutive equation of novel form is deduced. The results of stress calculations from the approximate constitutive equations are then compared to those from the numerical work. Some further results for another spring law similar in form to the Langevin spring are also given for comparison. It is concluded that constitutive equations of the type presented are useful for certain classes of flows.

ISSN:0148-6055    

DOI:10.1122/1.549364

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

摘要:

A new technique to measure normal stresses in dilute polymer solutions is described. The apparatus developed for this method essentially consists of two closely spaced disks in relative rotation. Fluid is slowly introduced at the center of the disks so that there is a small radial flow superposed on the circumferential motion, and the normal stresses induced in the circumferential direction are detected by measuring the retardation of the radial flow. From such measurements, a fluid relaxation time can be found for each sample and data with dilute Polyox solutions indicate some agreement with predictions from the molecular theory of Rouse.

ISSN:0148-6055    

DOI:10.1122/1.549365

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

摘要:

A solution is presented to the boundary value problem for the transient development of the velocity profile in a viscoelastic fluid subjected to the sudden onset of shearing in an idealized viscometer. A differential Oldroyd type of constitutive equation is used to describe the mechanical behavior of the fluid. The results indicate that the elastic nature of the fluid significantly increases the length of time required for the steady‐state velocity profile to be established. A solution is also presented for the drainage of a viscoelastic fluid off a vertical plate. The predicted initial elastic overshoot or rapid drainage of the fluid is in qualitative agreement with reported experimental results.

ISSN:0148-6055    

DOI:10.1122/1.549366

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

摘要:

Experimental data on the volume changes accompanying simple tension of peroxide vulcanizates of natural gum rubber, as first reported by Penn inTrans. Soc. Rheol.,14, 509 (1970), are further interpreted within the framework of the theory of a hyperelastic material. Motivated by the formal connection between a hyperelastic material and a nonlinear viscoelastic fluid (Trans. Soc. Rheol.,9, 27 (1965)), and a mathematical result on the decomposition of the scalar potential of that fluid (Z. Angew. Math. Phys.23, 780 (1972)), the interpretation of Penn's data leads to an explicit construction of a strain‐energy function for rubbery materials:W(I1,I2,I3)=C1(I1−3)+C2(I2−3)+H̄(I1,I2)(I3−1)+18K(I3−1)2.

ISSN:0148-6055    

DOI:10.1122/1.549389

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

摘要:

Extremely dilute solutions of certain high molecular weight polymers are known to exhibit anomalous momentum and heat transfer properties such as drag reduction. In order to study the possible connection between these phenomena and the viscoelasticity of the polymer solutions, a Generalized Convected Maxwell model is used to examine transient shear behavior, propagation of simple shear waves, and elongational flow. Unlike previous investigations where a simple Convected Maxwell equation was used, the more complete generalized model predicts that the effects of polymer additives on transient shear disturbances and simple shear‐wave propagation are negligible. This observation is confirmed by experimental measurements. For elongational flow, however, the generalized model predicts that the viscoelastic effect of the polymer will introduce unusually high levels of stress even at very low polymer concentrations, provided the flow time and stretching rate are sufficiently high. As a result, elongational flow is a simple deformation that may be important in formulating explanations for the unusual behavior that has been observed in dilute solutions.

ISSN:0148-6055    

DOI:10.1122/1.549367

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549390

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549391

出版商:The Society of Rheology    

年代:1975

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549392

出版商:The Society of Rheology    

年代:1975

数据来源: AIP