Extensional flow of non‐newtonian fluids—A review

Abstract

Extensional flows have been the object of study in several laboratories in recent years. Polymeric systems have been studied in most cases because of their interesting behaviour and also because of the importance of their rheological properties to the plastics engineer. Controlled, steady elongation is more difficult to achieve in the laboratory than the more traditional viscometric flows. Moreover, it is not in general possible to predict the response of a viscoelastic material to steady extension based on knowledge of its viscometric functions. This review begins by presenting some useful expressions describing the kinematics of extensional flows. Then some results of interest from rational mechanics are presented and the behaviour predicted by a number of constitutive equations for viscoelastic fluids are discussed. After presenting the pertinent relations of linear viscoelasticity for extensional flows, experimental methods and results for steady simple extension are reviewed and some possible implications for the processing of molten polymers are discussed.

Elongational flow behavior of viscoelastic liquids: Part I. Modeling of bubble collapse

“…There are two classes of experiments which have been successful in this endeavor, both using very high viscosity polymer melts (qo > lo6 poise) at relatively low rates of strain ( d < 10-1 s-*). While there have been two very good reviews of the literature (Dealy, 1971;Cogswell, 1975), it is instructive to summarize the major results of past experiments in order to put the present work in proper perspective. The rod pulling experiments form the first class.…”

Steady Non-Viscometric Flows of Viscoelastic Liquids

“…The predictions of the Trouton viscosity given by a large number of constitutive equations are summarized in the review article by Dealy (1971). The Lodge model in its simplest form is sufficient to illustrate the kinds of results that are predicted.…”

Dissipation effects in hydrodynamic stability of viscoelastic fluids

“…This is usually modeled as an extensional or elongational flow. Predictions of the stress extension rate behavior of polymer melts vary greatly, depending on the constitutive relation and exact form of the kinematics assumed (see Coleman and No11 1962;Tanner, 1969; Astarita and Nicodemo, 1970;Dealy, 1971; Marrucci and Murch, 1970;Stevenson and Bird, 1971;Stevenson, 1972;and Cogswell, 1972).…”