Vacuum-Assisted Resin Transfer Molding (VARTM) processes are becoming promising technologies in the manufacturing of primary composite structures in the aircraft industry as well as infrastructure. A great deal of work still needs to be done on efforts to reduce the costly trial-and-error methods of VARTM processing that are currently in practice today. A computer simulation model of the VARTM process would provide a cost-effective tool in the manufacturing of composites utilizing this technique. Therefore, the objective of this research was to modify an existing three-dimensional, Resin Film Infusion (RFI)/Resin Transfer Molding (RTM) model to include VARTM simulation capabilities and to verify this model with the fabrication of aircraft structural composites. An additional objective was to use the VARTM model as a process analysis tool, where this tool would enable the user to configure the best process for manufacturing quality composites. Experimental verification of the model was performed by processing several flat composite panels. The parameters verified included flow front patterns and infiltration times. The flow front patterns were determined to be qualitatively accurate, while the simulated infiltration times over predicted experimental times by 8 to 10%. Capillary and gravitational forces were incorporated into the existing RFI/RTM model in order to simulate VARTM processing physics more accurately. The theoretical capillary pressure showed the capability to reduce the simulated infiltration times by as great as 6%. The gravity, on the other hand, was found to be negligible for all cases. Finally, the VARTM model was used as a process analysis tool. This enabled the user to determine such important process constraints as the location and type of injection ports and the permeability and location of the high-permeable media. A process for a three-stiffener composite panel was proposed. This configuration evolved from the variation of the process constraints in the modeling of several different composite panels. The configuration was proposed by considering such factors as: infiltration time, the number of vacuum ports, and possible areas of void entrapment. / Ph. D.

Vacuum assisted resin transfer molding (VARTM) is a low cost resin infusion process being developed for the manufacture of composite structures. VARTM is being evaluated for the manufacture of primary aircraft structures, including foam sandwich composite materials. One of the benefits of VARTM is the ability to resin infiltrate large or complex shaped components. However, trial and error process development of these types of composite structures can prove costly and ineffective. Therefore, process modeling of the associated flow details and infiltration times can aide in manufacturing design and optimization. The purpose of this research was to develop a process using VARTM to resin infiltrate stitched and unstitched dry carbon fiber preforms with polymethacrylimide foam cores to produce composite sandwich structures. The infiltration process was then used to experimentally verify a three-dimensional finite element model for VARTM injection of stitched sandwich structures. Using the processes developed for the resin infiltration of stitched foam core preforms, visualization experiments were performed to verify the finite element model. The flow front progression as a function of time and the total infiltration time were recorded and compared with model predictions. Four preform configurations were examined in which foam thickness and stitch row spacing were varied. For the preform with 12.7 mm thick foam core and 12.7 mm stitch row spacing, model prediction and experimental data agreed within 5%. The 12.7 mm thick foam core preform with 6.35 mm row spacing experimental and model predicted data agreed within 8%. However, for the 12.7 mm thick foam core preform with 25.4 mm row spacing, the model overpredicted infiltration times by more 20%. The final case was the 25.4 mm thick foam core preform with 12.7 mm row spacing. In this case, the model overpredicted infiltration times by more than 50%. This indicates that the model did not accurately describe flow through the needle perforations in the foam core and could be addressed by changing the mesh elements connecting the two face sheets. / Master of Science