View - Martin Kröger - ETH Zürich

1306 FANG, KRÖGER, AND ÖTTINGER
FIG. 5. Magnitude of the strain p at which the maximum in the stress overshoot occurs as functions of shear
rate for shear stress under startup of steady shear flow predicted by the models and experiment.
reptation represented by a smaller value of d in the MLDS model. This behavior is
also in accordance with the other experimental results Attane et al. 1985; Menezes and
Graessley 1982.
C. Steady shear flow
In Fig. 7 the steady-state values of the shear stress xy and the first normal stress
difference N 1 are plotted as functions of shear rate. Our model and the FCS model
predict a slight decrease of the shear stress over a range of shear rates that extends from
roughly ˙ 0.3 to ˙ 2s 1 , where the MLDS model predicts a slight increase which
is consistent with the experimental data. This new observation of the MLDS model may
be attributed to the fact that we use a relatively small ratio d / s 10 here. Over the
same range of shear rates, all the model predictions for the first normal stress difference
FIG. 6. Relaxation of the shear stress reduced by its value at steady state as a function of time after cessation
of steady shear flow at two shear rates predicted by experiment and the models.