Non-Newtonian Constitutive Relationships for Hyperconcentrated Fiber Suspensions

Abstract

Previously developed relationships for the prediction of the effective Newtonian viscosities of collimated, discontinuous fiber suspensions have been recently extended to include non-Newtonian behavior by incorporating the Carreau constitutive relation for the matrix fluid viscosity [9]. A new class of suspensions termed "hyperconcentrated" are defined here and illustrated to be that class for which these relationships are appropriate. The predictions for the influence of strain rate on the primary anisotropic viscosities of these suspensions are also presented. The predictions are compared to Binding's results [12] for a fiber suspension consisting of polypropylene with 25 volume percent glass fibers. Both axial elongational viscosity and shearing viscosity predictions developed for shear thinning polymers show excellent agreement with experimental results over ranges in strain rate of 100 to 102 s-1 and 101 to 103 s-l, respectively. Utilizing the Carreau model to describe the behavior of the matrix fluid, decreases in the range of strain rate where Newtonian behavior dominates the suspension response are predicted for both the elongational and shearing viscosities when compared to the shearing viscosity of the matrix fluid.