PARALLEL SUPERPOSITION OF SMALL-AMPLITUDE AND LARGE-AMPLITUDE OSCILLATIONS UPON STEADY SHEAR-FLOW OF POLYMER FLUIDS

The parallel superposition of small- and large-amplitude oscillations upon steady shear flow of elastic fluids has been considered. Theoretical results, obtained by numerical methods, are based upon the Leonov viscoelastic consititutive equation. Steady-state components, amplitude, and phase angle of oscillatory components of the shear stress, the first and second normal-stress differences as a function of shear rate, deformation amplitude, and frequency have been calculated. These oscillatory components include the first harmonic of the shear stresses and the first and second harmonic of the normal stresses. The experimental results for shear stress components have been found to be in good agreement with theoretical predictions, although there are some deviations for storage modulus at high shear rates.