1 Experimental Investigations of the unsaturated flow in Liquid Composite Molding Tonmoy Roy, Charity Dulmes and Krishna. M. Pillai 1 Department of Mechanical Engineering University of Wisconsin- Milwaukee Milwaukee, WI 53201 Phone: (414) 229-6535 Fax: (414) 229-6958 In Liquid Composite Molding (LCM) processes including VARTM and RTM, a thermoset resin is sucked/injected into a mold cavity with a pre-placed preform of fiber mats and allowed to cure to form a hard solid part. Very often, the fiber preform behind the resin front is partially saturated during mold-filling process thus giving rise to the unsaturated flow. The unsaturated flow caused by the dual-scale nature of certain stitched fiber mats is still poorly understood, and this paper will report some recent experimental explorations of the unsaturated flow. The paper will present some of these flow patterns observed in RTM process by conducting a point injection. Color dyes were mixed with the epoxy resin to differentiate it from the glass fibers of the stitched fiber mats. The observed flow patterns clearly demarcate the saturated and unsaturated regions in the preform, and reveal the extent of the unsaturated flow. Micrographs taken from these samples were analyzed using the image processing software, and clear microstructural distinctions were observed between the saturated and unsaturated regions. Later a two-color point injection experiment, where the injection of a green resin is followed by that of a blue resin, clearly show that the flow patterns in woven or stitched (dual-scale) fiber mats is fundamentally different from the random (single-scale) fiber mats. In dual-scale mats, it was clearly seen that the earlier injected resin is absorbed and retained by the tows where as the later injected resin moves to the front after bypassing the saturated tows. This clearly highlights the need for using different governing equations for modeling LCM flows in the dual-scale fiber mats. Keywords: LCM, RTM, preform, unsaturated flow, dual-scale porous media. 1 The author to whom correspondence should be addressed.