ABSTRACT
The steady extensional viscosity of fiber suspensions of Figs. i 1.6 and l l .7 is shown in Fig. l 1.8. This material function is very high at low stretch rates, but then it stretch thins considerably, always remaining above the extensional viscosity of the unfilled melt. The Batchelor theory is not expected to apply to these very concentrated suspensions, and, indeed, it predicts stress values that are very different and much higher than those that are observed [31]. Kamal et al. have also measured the steady extensional viscosity of glass-fiber-filled polymer melts [371. Their results are similar to those of Chan et al. except that they observed yield stresses at high concentrations: the yield stress was evident in extensional data but not in the corresponding shear data. When a yield stress is observed in the shear flow of fiber suspensions. its value typically follows a power law in the fiber mass fraction [8.12].
