Shear stress from rate-dependent and nonaffine network models for melts in complex shear histories

Analytical expressions of shear stress for arbitrary multi-rate-step flows are presented for a rate-dependent network model and for a nonaffine network model. For both models the linear spectrum is modified to account for large deformations. Predictions of both models are evaluated for the following cases: concave steps, reversed steps, and large amplitude oscillations. Model predictions are compared to experimental results on a polydimethylsiloxane melt. Quantitative agreement is obtained for both models, which justifies the usefulness of the proposed equations for the prediction of shear responses in complex transient shear flows. The performance and limitations of the two models are also discussed in terms of physical considerations. (C) 1996 John Wiley & Sons, Inc.