Sıvı kompozit kalıplama yöntemlerinde akışın ve malzeme özelliklerinin deneysel ve sayısal incelenmesi

Liquid Composite Molding (LCM) processes are widely used for manufacturing Fiber Reinforced Plastic Composites (FRPCs), and most common of these processes are Resin Transfer Molding (RTM) and Vacuum Infusion (VI). In these processes, parts are manufactured by placing a preform of glass or carbon fibers in a mold and impregnating the preform by a thermoset resin. To ensure the part is completely filled without any dry spots and to achieve this in a repeatable manner with predictable flow patterns and cycle times, a good understanding of resin flow through the porous medium is crucial and requires the knowledge of fabric permeability (i.e., inverse of resistance to flow). Thickness distribution in VI varies spatially and with time due to varying resin pressure (thus, compaction pressure) in the mold. In this context, this thesis investigates (i) characterization of the fabric permeability in the presence of rigid inclusions such as microcapsules or fillers and (ii) monitoring and modeling the thickness variation in VI typically consisting of two stages. In the first filling stage, thickness variation increases due to pressure gradient within the mold; and in the second post-filling stage, the excess resin is removed out of the mold to reduce the thickness and the variation in it. In some cases, a second solid phase, generally in the form of granular particles, may be introduced to FRPCs, to ease the handling of preform, to improve mechanical, thermal and electrical properties, or to functionalize with self-healing capsules (to introduce self-healing capability) or with hollow microspheres (to improve the buoyancy or to decrease the overall weight). The effect of rigid spherical inclusions on the permeability of textile fabrics was investigated by using glass beads as model inclusions. Glass beads with a range of diameters (40 to 800 μm) and volume fractions (2.5 to 10%) were sieved between layers of woven E-glass fabric targeting a constant fiber volume fraction of 40%. Experimental characterization of permeability was followed by X-ray microtomography to reveal the underlying relationship between permeability and microstructural features including pore size distribution, pore shape anisotropy and spatial bead distribution. Furthermore, permeability of the X-ray samples was estimated using Computational Fluid Dynamics simulations and with a Kozeny model taking into account the porosity and the specific surface of samples, and compared with the experimental permeability results. Thickness variation in VI and its minimization is usually dealt with a trial and error based approach. This study offers an alternative approach to overcome this drawback of VI process, by integrating thickness monitoring and resin flow modeling in a flexible mold. A Structured Light Scanning system was verified for its suitability of monitoring thickness during VI and was used for full field thickness monitoring in experiments. A Control Volume Finite Element Method (CVFEM) solver, capable of coupling resin flow, fabric compaction and permeability, was implemented. Two different scenarios were studied experimentally and numerically. Full field thickness, resin pressure at some locations and mass of the infused resin were recorded during filling and post-filling stages of experiments; and simulations were performed with corresponding process parameters. Thickness monitoring system was able to capture the instantaneous thickness distribution of the specimen as well as its evolution during the experiments. Thickness variation within the specimen reached its maximum at the end of mold-filling due to the high resin pressure at the inlet (thus low compaction pressure) compared to vacuum pressure at the exit. The thickness variation was reduced in the post-filling stage by removing the excessive resin and almost equalizing resin pressure. Simulations resulted in a reasonably close estimation of fill time and infused resin mass. Evolution of pressure was simulated successfully as well as the resulting thickness distribution. The thickness variation increased in filling stage and the effects of post-filling actions were in agreement with the experimental results.