Modeling the edge effect in liquid composites molding

In Liquid Composite Molding (LCM) processes such as RTM or SRIM, preformed fabrics are preplaced in the mold cavity. The mold is then closed and a Liquid thermoset resin is injected. Since it is difficult to precisely cut the fiber preform to the exact shape of the mold, sometimes a gap exists between the preform and the mold edge. This gap, even small (1 or 2 mm), can create a preferential flow-path for the resin which disrupts the filling of the mold cavity. Such flow perturbation is called the edge effect. With existing numerical simulation models it is possible to simulate an edge effect by locally changing the permeability. However. this is not satisfactory. The ideal case will be a model to predict the edge effect from the geometry of the gap end the porosity of the surrounding material. To respond to this need, this paper presents an analysis of the flow patterns using appropriate flow equations in the open channel and Darcy's law in the porous medium. From this an equivalent porous medium is defined for the channel for which an equivalent permeability tensor can be computed. Two geometric models to predict the edge effect are presented. The first model is derived from the Navier-Stokes equation in the channel. In the second model, the flow is assumed to take place in an equivalent cylindrical channel as in Poiseuille flow. However, these models cannot cover all cases. To evaluate the applicability of these simple models, a parameter called the transverse flow factor is defined. For finite element flow simulation an equation to define the equivalent permeability of the first row of elements encompassing the open channel is given. Finally, experimental as well as simulation results are presented. (C) 1998 Published by Elsevier Science Limited. All rights reserved.