Liquid composite molding (LCM) is one of the most effective processes for manufacturing near net-shaped parts from fiber-reinforced polymer composites. The quality of LCM products and the efficiency of the process depend strongly on the wetting of fiber preforms during the mold-filling stage of LCM. Mold-filling simulation is a very effective approach to optimize the LCM process and mold design. Recent studies have shown that the flow modeling for the single-scale fiber preforms (made from random mats) has difficulties in accurately predicting the wetting in the dual-scale fiber preforms (made from woven and stitched fabrics); the latter are characterized by the presence of unsaturated flow created due to two distinct length-scales of pores (i.e., large pores outside the tows and small pores inside the tows) in the same media.

In this study, we first develop a method to evaluate the accuracy of the permeability-measuring devices for LCM, and conduct a series of 1-D mold-filling experiments for different dual-scale fabrics. The volume averaging method is then applied to derive the averaged governing equations for modeling the macroscopic flow through the dual-scale fabrics. The two sets of governing equations are coupled with each other through the sink terms representing the absorptions of mass, energy, and species (degree of resin cure) from the global flow by the local fiber tows. The finite element method (FEM) coupled with the control volume method, also known as the finite element/control volume (FE/CV) method, is employed to solve the governing equations and track the moving boundary signifying the moving liquid-front. The numerical computations are conducted with the help of an in-house developed computer program called PORE-FLOW^©. We develop the flux-corrected transport (FCT) based FEM to stabilize the convection-dominated energy and species equations. A fast methodology is proposed to simulate the dual-scale flow under isothermal conditions, where flow only in the gap region needs to be solved. The local flow inside tows is characterized by a 'lumped' sink function which is calibrated with the help of the micro-flow simulation in a stand-alone unit-cell of the dual-scale fiber mat. Later, to model the dual-scale flow under non-isothermal conditions, we develop a multiscale approach in which a global grid and a local grid are employed to solve the global and local flows, respectively. Validations of the numerical predictions by the multiscale method are made by comparing with the experimental data on unsaturated flow. Contrary to the conventional wisdom, the numerical studies have shown that there are significant differences in temperatures and cures within the gaps and tows of a dual-scale medium. The ratio of pore volumes in the tow and gap regions, thermal conductivity of the tows, and fiber types are identified as important parameters for the temperature and cure distributions. Finally some future directions of the research are outlined.