Experimental investigation of the effect of fiber-mat architecture on the unsaturated flow in liquid composite molding

In liquid composite molding technologies such as RTM, this study of the inlet-pressure history for the constant flow-rate I-D flow experiment reveals that the measured pressure profile, which droop downwards as in earlier studies on the unsaturated flow, is at a variance with the linear pressure profile predicted by the physics used for state-of-the-art LCM mold filling simulations. The droop along with the error in the inlet-pressure predictions increase with an increase in the fiber-mat compression. The effect of fiber-mat architecture on the droop in the inlet-pressure profiles is studied and significant droops are observed for various stitched mats as compared to the woven mats. This study repudiates the long-held view that mere presence of cylindrical or elliptical tows in the woven or stitched fiber-mats automatically leads to the unsaturated flow characteristic of dual-scale porous media; rather the presence of continuous uninterrupted macrochannels along the flow direction for preferential channel-flow is found to be necessary for the appearance of a drooping inlet-pressure history characteristic of the unsaturated flow.