Modeling of filtration process during manufacturing of functionally graded composites with particulate suspensions
Date
2005
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Publisher
University of Delaware
Abstract
Functionally Graded Composites exhibit properties or functions within the material that vary gradually or in a stepwise manner without a recognizable boundary. One technique to manufacture Functionally Graded Polymer Composites is by Liquid Composite Molding process. Liquid molding process is amenable for manufacturing large-scale composite structures. In this process, fiber preforms of glass, Kevlar or carbon fabric are stacked in a closed mold and resin is injected into the mold. Particles may be added to the resin to tailor the properties of the final product. The preforms used are usually fabrics with yarns or bundles of thousand or more micron size fibers woven, stitched or knitted together. This architecture gives rise to a bimodal distribution of pore sizes; the larger pores in between the bundles and smaller ones within the bundles. The filtration process that takes place during infusion alters the flow resistance of the porous media as well and complicates the impregnation process. In this study, a Vacuum Assisted Resin Transfer Molding (VARTM) process based approach is presented that enables functional grading in composites to obtain a desired distribution in properties. ☐ A modeling of the filtration phenomenon is proposed to predict the concentration distribution of particles within dual scale fibrous porous media infused under a constant pressure drop. The approach uses Darcy’s law and accounts for lowering of the permeability value due to the particle entrapment in the available pores. Experiments are conducted and the concentration of the particles in the fabric is measured. The results compare well with the predictions despite many assumptions made in the model. Non-dimensional analysis and parametric study reveals the influence of critical parameters on the filtration efficiency and the final particles concentration gradient. A similar approach is then extended to model the case of filtration in multilayer preforms. After successful experimental validation, the important parameters that drive the particles concentration gradient in the final composite are investigated. ☐ Limitations of the process for applications requiring high particles volume fraction are observed and alternative approach for such applications is proposed.