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Flow Orientation of Short Fibers in Rectangular Channels
MONSANTO RESEARCH CORP ST LOUIS MO
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Fabrication of composites from discontinuous fibers are found to pose many rheological problems, especially when fibers are short and their orientation and distribution have to be controlled by a flow process. The effects of fiber concentration, die-geometry and flow rate on the translational and rotational motions of short fibers in concentrated suspensions are determined from cinematographic studies on model systems subjected to flow through uniform and convergent rectangular channels. Fiber concentration is varied from 60 vol. to as low as 0.05 vol.. The total convergence angle of the channels varies from 0 to 210 degrees the channel thickness is comparable to or smaller than the fiber length. The viscosity of resin used is 55 p. When fiber concentration is higher than 5 vol, a plug- type flow is observed in both uniform and convergent channels. However, the observed velocity of fibers is always smaller than the mean velocity of the flowing suspension. A stagnation region is observed in convergent channels when the convergence angle is larger than 120 degrees. The alignment of fibers in the flow direction exclusively occurs in convergent channels. Flow instabilities, migration of trapped air bubbles, generation of voids, deformation of fibers and flow properties are also observed.
APPROVED FOR PUBLIC RELEASE