# Experimental and Numerical Study of Vacuum Resin Infusion for Thin-Walled Composite Parts
## 1 Introduction
In article [41], a flow front control system was developed using a real-time assessment of the permeability/porosity ratio on the base information obtained by the visualization system monitored the porous panel infusion. This approach substantially used the metamodel of the radial basis function (RBF), obtained as a result of training by Moldex 3D simulation module. The responses of this artificial neural network are used to predict the position of the front of the future flow by entering the injection pressure, the current position of the flow front and the calculated permeability/porosity ratio. By carrying out optimization based on a metamodel, the injection pressure value is obtained, which must be implemented at each stage. The most advanced fully functional optimization systems belonging to the fourth kind include a process simulation module (forward problem solver) and optimizer, which carries out the multiple calls of the forward problem according to some optimization strategy, and forms the optimum solutions set in the objective space. The structure, organization and logic of the prototype of such optimization systems are described with the necessary completeness in an innovative work [37], which uses the FE/CV modeling method, and the results of such a system were published in [12]. The most important part of this paper is aimed at the problem of the dry spots' formation, detection and evolution during infusion. It considers in detail conditions and evidence of dry spots formation at its surrounding by the inner and outer flow fronts. On the base of the numerous fulfilled simulations, the authors formulate the very useful recommendations that can be used in a practice. The dry spot detection algorithm, which is explained in [12], requires significant computational efforts, therefore it is not very efficient, especially for the parts of complex 3D geometry. Moreover, the proposed technique includes the rebuilding of FE mesh in the vicinity of the flow front to supply the necessary accuracy of its configuration [37]. Concluding our analysis of the considered works, it should be noted that the most important problem of the dry spots formation in the infusible preform was not solved with the necessary accuracy and reliability, which is due to the difficulties in reconstructing the movement of the resin front. The reason for this is the extremely high computational complexity of solving the problem of the resin dynamics in a porous medium at moving boundaries, as well as the insufficient accuracy of the widely used FE/CV method, which makes strict requirements for the design of cells of a control volume. Therefore, the main purpose of the present work is the development of a system for diagnosing and reliably predicting the occurrence of incompletely saturated and dry places at the VARTM. This system should provide the reconstruction of the motion of the resin front in preforms of complex 3D geometry, identification of the dry spot formation and effectively simulate the resin infusion dynamics to work as the forward problem solver that will be repeatedly called by the optimization module. This paper is organized as follows. First, we present some results of two experimental studies with large Carbon Fiber Reinforced Plastic (CFRP) panels during vacuum infusion, where resin front advancement and dry spots formation were monitored in time. The next part contains the problem statement where we formulate the resin infusion model as the coupled two-phase (air/resin) media dynamics problem, where the phase field equation is accepted as the ruling one. In order to simplify the verification of the new modeling approach, we neglect the heat transfer, the thermal-kinetics, the wetting compaction and the change of the part's dimension effects during filling and post-filling stages.