Three-dimensional resin transfer molding: Isothermal process modeling and explicit tracking of moving fronts for thick geometrically complex composites manufacturing applications - part 1

In resin transfer molding (RTM) process modeling, current practices involved in the simulation of resin impregnation through porous media have been generally restricted to two-dimensional formulations based on Darcy's law for flow through thin cavities due to the increased computational demand and stringent stability restrictions of the traditionally employed explicit finite element-control volume (FE-CV) type approaches. The presence of multiple fiber layers in thick composites, or the notion of introducing impermeable inserts inside the fiber bundles to serve as protective armor, causes the resin impregnation to be a three-dimensional flow. This paper describes full three-dimensional simulations based on an explicit FE-CV technique to assess the practicality and suitability of the approach. Though viable, the technique treats the transient mold filling problem as a series of quasi-steady state problems. Additionally, an effective alternate form and discretization of the field variables based on a flux-based finite element representation is presented in conjunction with the above primarily to illustrate the theoretical developments for general situations. For linear situations, they readily revert exactly to the traditional finite element representations. In part 2 of this paper a transient computational methodology based on a pure implicit finite element method for applicability to three-dimensional RTM flow modeling is presented to demonstrate the improved effectiveness of the approach. The objectives of the efforts (part 1 here and part 2 in this issue), besides providing a clear understanding for flow in thick composites under isothermal conditions, are simply to (1) describe and investigate the traditional developments for practical geometrically complex three-dimensional composite sections, (2) describe extensions of our previous efforts and provide effective avenues for handling three-dimensional thick composites, and (3) contrast the two approaches and explore the pros and cons for practical three-dimensional composites process modeling.