Modeling formation and evolution of voids in unsaturated dual scale preforms in Resin Transfer Molding processes

Resin transfer molding (RTM) is a composite processing technique in which a fiber preform (usually consisting of fiber tows woven or stitched together) is enclosed in a cavity between two or more rigid molds before injecting resin under pressure to fill all empty spaces between the fibers. In this process preforms exhibit dual scale behavior as the pores between the fibers in a fiber tow are much smaller than the spaces between tows, hence the resin impregnates the inter- and intra-tow pores at different rates. In this research this dual scale behavior and void evolution is modeled through a multi scale approach to predict void location and distribution in a manufactured composite. For the simulation work dual scale behavior of the preform is represented by introducing one dimensional slave elements representing the network of fiber tows. This was conducted for a total of five different layups divided between two types of glass fiber preforms. The pressure calculated in the macroscopic model, and the dual scale results are then used as input in a mesoscopic model, in which the domain consists of fiber tows and gaps between them. Capillary effects are taken into account by locally modifying the values of the permeability. The use of a transparent mold with cameras allowed a comparison of dual scale flow and saturation of the tows at the mesoscopic level domain.