Aaron P. R. Eberle, Donald G. Baird, Peter Wapperom,
Gregorio M. Vélez-García
Using transient shear rheology to determine material parameters in fiber
suspension theory
Journal of Rheology 53, 2009, p. 685-705
Abstract
Fiber suspension theory model parameters for use in the simulation of fiber
orientation in complex flows are, in general, either calculated from theory
or fit to experimentally determined fiber orientation generated in
processing flows. Transient stress growth measurements in startup of shear
flow and flow reversal in the shear rate range, shear rates
1 to 10 s-1,
were performed on a commercially available short glass fiber-filled
polybutylene terephthalate using a novel "donut-shaped" sample in a
cone-and-plate geometry. Predictions using the Folgar-Tucker model for
fiber orientation, with a "slip" factor, combined with the Lipscomb model
for stress, were fit to the transient stresses at the startup of shear
flow. Model parameters determined by fitting at shear rate 6 s-1
allowed for reasonable predictions of the transient stresses in flow
reversal experiments at all the shear rates tested. Furthermore, fiber
orientation model parameters determined by fitting
the transient stresses were compared to the experimentally determined
evolution of fiber orientation in startup of flow. The results suggested
that fitting model predictions to the stress response in well defined
flows could lead to unambiguous model parameters provided the fiber
orientation as a function of time or strain at some shear rate was known.
Keywords
Short glass fiber; model fitting; fiber suspension; transient stresses