Network constitutive equation with internal viscosity: application to stress jump prediction

A stress jump, defined as the instantaneous gain or loss of stress on start up or cessation of a deformation, has been predicted by various models and has relatively recently been experimentally observed. In this paper, the in ternal viscosity idea is incorporated into the transient network model. Via appropriate approximations, we obtain a closed constitutive equation where the total stress equals the sum of an elastic contribution and a viscous c ontribution. As the latter is rate dependent, the model predicts a stress j ump and we consider data on shear flow in this contribution. We successfull y compare the model predictions with the stress jump measurements of Liang and Mackay [C.H. Liang, M.E. Mackay, J. Rheol. 37 (1993) 149]. The model yi elds good quantitative predictions of the steady, transient and dynamic mat erial functions. (C) 2000 Elsevier Science B.V. All rights reserved.