REVIEW OF MODELING AND SIMULATION OF VOID FORMATION IN LIQUID COMPOSITE MOLDING

Liquid composite molding (LCM) processes are being used in manufacturing near-net-shape, geometrically complex composite parts. One of the current obstacles to a larger scale application of these processes is the formation of defects such as voids during resin injection. To reach aeronautic requirements or short injection cycles in the automotive industry, entrapped air in the final part before curing has to remain as low as possible. Air entrapment will depend on the fibrous structure and on the injection parameters, or more precisely on the fluid pressure and the flow front orientation with respect to the fibrous direction. A key parameter for production of structural composite parts is air entrapment, since high void content could lead to mechanical softening, early failure, or part rejection. The quantitative simulation of the void formation is important for proper design and selection of material and processing parameters to minimize such voids in the composite materials. Despite several advancements in voidage predictions via modeling and simulations, the void formation mechanisms in RTM and similar processes are still not fully understood. In this study, a review of current approaches to modeling and simulation of void formation and unsaturated flow in the liquid composite molding process is presented. We examine modeling efforts considering all the mechanisms involved such as void formation and transport, bubble compression, and gas dissolution. In particular, the capillary number is identified as a key parameter for void formation and transport. The influence of voids on the global resin flow is also investigated and a state-of-the-art is presented.