Browsing by Author "George, Andrew"

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Open Access
Optimization of resin infusion processing for composite materials : simulation and characterization strategies
(2011) George, Andrew; Drechsler, Klaus (Prof. Dr.-Ing.)
Composite materials, especially those made with carbon fiber, have better specific properties than many traditional materials. But despite their promised advantages, industry has been slow to apply composites as they wait to see if an automatable composites manufacturing solution with high properties will become available. Resin infusion processing is being developed in many laboratories in an attempt to find this suitable process. Qualification of an optimized resin infusion process will require significant performance data and accurate manufacturing simulation tools. This is currently hindered by a lack of standardized methods for part characterization, and a lack of understanding of the different flow phenomena that are involved in the simulation of flow processing. This work aims to help meet these needs, so as to allow further implementation of fiber-reinforced composite materials in industry. To improve simulation capabilities, individual modeling systems for each of the following flow phenomena are developed: permeability, compressibility, dynamic viscosity, and dual-scale flow. These models were developed based on relationships previously proposed in the literature, as well as characterization experiments with modern carbon fabrics in this study. A new numerical model is presented in which all the above-mentioned individual models are coupled. This new coupled model is limited to predicting 1-dimensional flow. But it is the first model known to couple all of these phenomena into one solution. The coupled model works well at describing the independent effects and interactions of each of the separate flow phenomenon models. The effects of dual scale flow, as modeled by incorporation of a modeled capillary pressure, proved to be more significant to flow velocity than the viscosity or compressibility for the infusion conditions studied here. The coupled model was compared to benchmark experimental VARI infusions of a variety of modern carbon preforming materials. The change in flow velocity due to fabric selection, relative to a baseline material, exhibited fairly good consistency between experiment and prediction. Further applicability of the coupled model was demonstrated with 3-dimensional point infusion experiments. The permeability in each of the three component directions for 3D flow can be determined from a single point-infusion experiment, independent of any dual scale flow or viscosity effects as they are modeled in the coupled solution. Nevertheless, both in-plane flow and 3-dimensional flow exhibit slower flow velocity then predicted by the model when compared on an absolute basis. It is suspected that this is due to some unknown shear effect. The accurate simulation of resin infusion will require characterization of the permeability for each liquid-fiber combination until these differences, whether from shear or something else, can be explained and modeled. This study also contributes towards the needs of industry by reviewing and optimizing the available measurement methods for fiber content and void content. A demonstration of using the optimized tools for these measurements is made by qualifying different membranes for VAP manufacturing – a promising variant of resin infusion. A demonstration is also made of the correlation between these measurements and resultant shear properties.