Fabric structure and mold curvature effects on preform permeability and mold filling in the RTM process. Part I. Experiments

Liquid composite molding (LCM) processes require the impregnation of a polymeric resin through a porous preform, being composed of glass, carbon, or kevlar fibers. The successful manufacture of composite parts through these methods is dependent on the successful filling of the mold cavity, expelling all air from within. Numerical simulations are being developed to model this process, and are powerful mold design tools. The accuracy of such simulations is strongly dependent on the specification of the preform permeability tensor throughout the mold cavity, being a numerical description of the resistance to resin flow. Changes in preform architecture can easily modify local permeability, and hence the mold filling. Corners in mold cavities are a potential sites for preform deformation, and are the focus of this study. A family of five molds have been studied, containing corner radii from 0.06 to 8.0 in. A detailed flow visualization study has been completed to investigate the influence of mold corner radii on flow front progression and injection pressure. While flow front progression was not significantly affected by different corner radii, injection pressures were found to be greater for the molds with smaller corner radii. Actual composite parts manufactured in the same molds have revealed that the molds are not of constant cavity thickness, as was the original goal. To determine the importance of corner radii on mold filling, it will be necessary to separate the effects of in-plane preform compression from any effect due to corners. To accomplish this goal, the experimental data presented here is being compared with derailed numerical studies, which will be presented in part II of this work. (C) 2000 Elsevier Science Ltd. All rights reserved.