ABSTRACT
First normal stress difference in shear data corresponding to the viscosities shown in Fig. 11.6 are presented in Fig. 11.7. The addition of fibers leads to a considerable increase in the first normal stress difference over the entire shear rate range of measurement: increasing the fiber aspect ratio leads to still higher normal stress values [33]. This increase is significantly larger than the enhancement in the viscosity or, equivalently. the shear stress. As a result. when N 1 data are replotted as a function of the shear stress. lines for the filled fluid lie above the line for the neat polymer [33 ]. This is in contrast to the behavior of particulate suspensions seen in Chap. I 0. Sec. V. where the relative position of the different lines was found to depend on whether data were plotted in terms of the shear
