Dual scale flow during vacuum infusion of compositesexperiments and modelling

Laburpena

Vacuum-assisted resin infusion has emerged in recent years as one of the most promising techniques to manufacture fiber-reinforced polymer-matrix composites. This open mold process uses vacuum as the driving force to infiltrate resin through a bagged fiber preform, leading to reduced tooling costs, as compared with the traditional closed mold process (resin transfer molding). In addition, large components can be produced with this technique. However, manufacturing defect-free components by means of vacuum-assisted resin infusion is not guaranteed due to complexity of the infiltration process and to the intricacies associated with the presence of a flexible bag. In addition, the final thickness of components manufactured by this process is not constant due to both the flexible bag and to the stress partition between the fiber bed and the fluid, leading to a greater thickness near the inlet port than near the vent. This thesis is a contribution to understand the phenomena that control vacuum-assisted resin infusion at the mesoscopic and microscopic scales. The mesoscopic behavior was studied by means of an experimental set-up allows the use of a distribution medium on top of the fiber preform to account for in-plane and through-the thickness infiltration. Fluid pressure was measured by means of pressure gages at different locations and the evolution of the out-of-plane displacement of the vacuum bag (due to changes in the fabric compaction) was continuously measured by means of the digital image correlation. In addition, infusion at the microscale was analyzed by means of \textit{in situ} infiltration experiments carried out in the synchrotron beam to study the mechanisms of microfluid flow and void transport within a fiber tow by means of synchrotron X-ray computer tomography using an apparatus designed and built for this purpose. This information was used to develop a level set based model to simulate fluid flow and fabric compaction during vacuum-assisted infusion. Fluid infusion through the fiber preform was modeled using Darcy's equations for the fluid flow through a porous media. The stress partition between the fluid and the fiber bed was included by means of Terzaghi's effective stress theory. These equation are only valid in the infused region and both regions (dry and wet) were separated by introducing a level set function in the partial differential equation which is defined at any given time as the distance to the flow front. Finally, the model predictions were validated against the experimental results.