FLUID INERTIA IN LARGE-AMPLITUDE OSCILLATORY SHEAR

Homogeneous shearing is required in sliding plate flow experiments wit h one plate fixed and the other oscillating. However,. when fluid iner tia becomes significant, the velocity gradient and the stress will not be uniform. MacDonald et al. (1969) and Schrag (1977) investigated th is effect for a linear viscoelastic fluid. However, Linear viscoelasti city does not describe the behavior of melts in large amplitude oscill atory shear (LAOS). Jeyaseelan et al. (1993) have shown that the Berke ley kinetic network model does accurately describe the LAOS behavior o f polymer melts. In this work, the Berkeley model is solved for LAOS i n sliding plate flow with fluid inertia, by numerical integration of s patially discretized forms of the governing equations. Nonlinear visco elasticity is predicted to aggravate the effects of fluid inertia in L AGS and experiments confirm this. Specifically, fluid inertia amplifie s the first harmonic and produces no even harmonics. Operating limits are presented graphically for minimizing inertial effects in LAGS expe riments.