Aaron P. R. Eberle, Gregorio M. Vélez-García,
Donald G. Baird, and Peter Wapperom
Fiber orientation kinetics of a concentrated short glass fiber suspension
in startup of simple shear flow
Journal of Non-Newtonian Fluid Mechanics 165 (2010) 110-119
Abstract
The common approach for simulating the evolution of fiber orientation during
flow in concentrated suspensions is to use an empirically modified form of
Jeffery's equation referred to as the Folgar-Tucker (F-T) model. Direct
measurements of fiber orientation were performed in the startup of shear flow
for a 30 wt % short glass fiber-filled polybutylene terephthalate (PBT-30);
a matrix that behaves similar to a Newtonian fluid. Comparison between
predictions based on the F-T model and the experimental fiber orientation
show that the model over predicts the rate of fiber reorientation. Rheological
measurements of the stress growth functions show that the stress overshoot
phenomenon approaches a steady state at a similar strain as the fiber
microstructure, at roughly 50 units. However, fiber orientation measurements
suggest that a steady state is not reached as the fiber orientation continues
to slowly evolve, even up to 200 strain units. The addition of a "slip"
parameter to the F-T model improved the model predictions of the fiber
orientation and rheological stress growth functions.
Keywords
Short glass fiber; fiber orientation; concentrated suspension;
transient rheology