Study On Permeability Of Reinforcement In Liquid Composites Molding

Composites are popular used in defense industries for their several advantages, including high modulus, high strength, designable, and so on. Along with the development of composites processing technology, LCM ( Liquid Composite Molding)process, as a advanced composites cost-effective manufacturing technology, is suitable for batch production of integral structures of high performance composites, will farther expand the application domain of composites materials. The reinforcement common used in LCM process includes glass, carbon, or Kevlar fibers. Every kind of fibers also can be woven into various fabrics or preforms according to the practical demand. The favorable LCM process requires that the low-viscosity resins fill the mould and permeate the preforms perfectly in a designated time, accordingly produce the high quality composites products. As a result, making an in-depth study of the permeability of fabrics common used in LCM processes and disclosing the mechanism of the resins flow and permeation are of very significance to the application extension of composites materials.In this thesis, some critical issues of LCM processes have been studied. In order to guide the material's selection and the practical production, the influences of major processing and material parameters on mold filling process were investigated with the aid of experiments and computer simulation. Firstly, this paper give a brief introduction about LCM processes, which contains the development situation, processing peculiarity and existing problems, then we deduce the necessity of permeability study. Secondly, the paper reviews the history of permeability research, farther points out their shortages and synthesizes the content and significance of this paper. Follow that, this paper gives a detailed description of the most often used permeability measurements and their theoretical models, which includes the shearing effects theory, the edge effects theory, and so on. One emphasis of this paper is the study of transverse permeability measurement of reinforcement common used in china which was less investigated. The results show that, the volume of fibrils, the structure of fabrics, shearing and the interspace of two different fabrics all together affect the final transverse permeability of performs, but the pressure doesn't affect so much, the results of this research will be important for the development of science-based application of LCM processes.In addition, the molds designed by myself were used to investigate the influence of mold curvature on permeability. The PAM-RTM^TM was employed to simulate mold filling. It is shown that, the filling time reduces along with the radius enlarging, but prolongs as the volume content of fibers increases. By contrast to the practical mold filling, we find that the curvature decreases the permeability, prolongs the filling time, change the course of filling, the pressure profiles during the processing have impact influences on filling time and void formation. It is shown that the experimental results are in good agreement with the simulated ones. The conclusions are invaluable to establish and understand the base theory of LCM process.