Nonlinear effects in the unsteady flow of viscoelastic fluids

Abstract

It has long been recognized that interesting features of viscoelastic materials can be revealed through study of the response of such materials to unsteady inputs. Indeed, most of the early work dealing with measurement of viscoelastic properties consisted of a study of the response of specimens to imposition of small-amplitude oscillatory stress or strain (1). Though much of the early work dealt with viscoelastic polymer solids, oscillatory testing has been extended to liquids, and there is now an extensive literature on the subject [see, for example, (2–5)]. However, by far the greatest interest to date has been in analyses and experiments which are restricted to a linear relation between input (for example, strain or strain rate) and output (for example, stress). This is the province of linear viscoelasticity, a subject which is now well developed and which has been quite successful for study of solid-like materials. Linear theory is insufficient, however, for characterization of many situations involving flow of liquid-like polymer melts, polymer solutions, and suspensions.