APPLYING EXTENDED FINITE ELEMENT METHOD AND LEVEL SET METHOD IN RESIN TRANSFER MOLDING PROCESS SIMULATIONS

The resin transfer molding (RTM) process is one of manufacturing processes of composite structures. Various industries such as aerospace and automotive have widely used the RTM process in order to manufacture composite structures. The manufacturing procedures are simply divided into 5 steps: 1. Placing fiber preform on a lower mold 2. Closing a upper mold 3. Injecting resin 4. Curing 5. Demolding. The third step, which is injecting resin, should be carefully designed in order to make products without any defects. However, the designing of the stage is often time-consuming and expensive because various variables to control the mold filling exits as injection pressure, number of injection gates and vents, etc. Numerical simulations of the mold filling stage have been used by the solution to reduce the design time and cost. Through numerical simulations, designers can predict whether defects such as air voids exist or not in the mold after filling. In RTM process simulations, the issue is how to treat the moving interface between resin and air. The representative methods to treat the moving interface are distinguished by moving and fixed grid approaches. The moving grid approaches is necessary to re-mesh a computational domain before every time steps. The frequent re-meshing may cause low accuracy of RTM process simulations, especially when the interface shape is complex. Therefore, fixed grid approaches has more popularly used by researchers in RTM process simulations because the re-meshing is unnecessary. The frequently used numerical methods in fixed grid approaches are finite element method with control volume approach, control volume finite element method, and nonconforming finite element method. However, these methods also have some drawbacks: to roughly describe the moving interface and to inaccurately approximate the pressure in regions intersected by the interface. The alternative numerical methods should be considered in order to overcome the drawbacks and increase accuracy of RTM process simulations. The traditional numerical methods do not intuitionally catch interface positions in the elements intersected by the interface. In addition, although the gradient of pressure in elements intersected by the interface is discontinuous, the traditional methods do not reflect the discontinuous character. In our research, extended finite element method combined with level set method was applied to simulate the RTM process. The moving interface was captured by level set method. The pressure calculation was performed by extended finite element method. The whole computational procedures of our approach are shown in Figure 1. Figure 1. Computation procedures The interface of complex shape, by multiple injection gates and complex geometry mold, was well-described in our simulations. The pressure was more accurately approximated by extended finite element method. For verification of our code, our computation results were compared experimental results as well as analytic results. The results proved that our approaches gave high accuracy in RTM process simulations.