Numerical simulation of LCM mold-filling during the manufacture of natural fiber composites

In this paper, a finite element/control volume (FE/CV) method based computer code is adapted to simulate the flow of resin-like liquids in swelling jute fabrics during the manufacture of natural-fiber composites using the liquid composite molding (LCM) technique. A novel treatment of the continuity equation using the rigorous volume-averaging method indicates that the despite liquid absorption and fiber swelling, the form of the continuity equation may remain identical to the traditional form seen for non-absorbing carbon or glass fibers. Such a continuity equation in conjunction with the Darcy's law with a time-varying permeability function is employed to model the resin flow as a fully saturated porous medium flow behind a clearly defined liquid front. Two new methods of estimating the time-varying local permeability and porosity of the wetted fiber mats behind the moving liquid-front are proposed. Later, the two time-dependent permeability models, one based on direct experimental estimation and the other based on indirect estimation using the Kozeny-Carman model, are used to alter permeability in finite elements behind the moving liquid-front during the numerical simulation. Such numerical modeling of the mold-filling process, as applied to the one-dimensional flows with constant flow rate and constant injection-pressure conditions, shows significant improvement over the traditional analytical solution obtained for a constant permeability. A good prediction of the experimentally observed flow-front location and inlet-pressure evolution plots by the two permeability models is observed. Of the two permeability models, the one based on direct estimation of permeability is found to be superior to the one employing the indirect approach. The novel analytical solution developed for the constant flow-rate (one-dimensional flow) case under a time-dependent permeability is shown to perform extremely well while predicting the flow-front location and inlet pressure evolution.