Effect of fiber preform architecture on wetting at low Reynolds numbers during resin transfer molding.

The effect of fiber roving dimensions, geometry, and distribution on capillary pressure, void formation and elimination, and permeability on the imbibtion of resin was studied. A unidirectional composite was fabricated to model the structural heterogeneity of a fiber preform. The roving dimension has the greatest influence on the capillary pressure. During imbibtion, a resin-air interface is created at the roving perimeter because of the structured nature of the fiber preform. This high-energy interface negatively influences the capillary pressure of the roving. As the roving dimensions increase, the roving behaves as if infinite and is unaffected by variations in the roving distribution. A roving geometry which minimizes the resin-air interface improves the capillary pressure. Local variations in pore dimension results in void formation. The size and volume of voids created is a influenced by the size of the inter-roving spacing. The void volume fraction retained was least for an intermediate inter-roving spacing. Large voids were eliminated by a snap-off process which increases with capillary number. The permeability is reduced by the presence of voids. Wetting of the composite would be enhanced with rovings having a smallest dimension of approximately 15 fiber diameters. This will maximize the capillary pressure. The intermediate size of the inter-roving spacing will allow easier removal of trapped voids and increase the permeability of the composite.Ph.D.Applied SciencesMaterials scienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129807/2/9624706.pd