FLOW AND VOID CHARACTERIZATION OF STITCHED STRUCTURAL COMPOSITES USING RESIN FILM INFUSION PROCESS (RFIP)

The resin film infusion process (RFIP), which is similar to resin tran sfer molding (RTM), was applied to investigate the possibility of manu facturing high performance stitched composites, With the objective of understanding the resin flow mechanisms and void formation in stitched fibrous preform, two recent technological developments in homogeneous tough resin and bendable stitching fibers were incorporated in produc ing stitched composites with RFIP. These included new lightly crosslin ked thermosets (LXT) that were phenolic or amine based. Second, bendab le carbon stitching reinforcement (T-900) was utilized as a stitching fiber. Flow characteristics were inferred by ultrasonic C-scan analysi s of cured panels. Microscopic studies indicated that voids were distr ibuted along the stitching fiber because of low consolidation pressure in the resin-rich area (stitching fiber region) where the fiber volum e content was lower. In contrast to stitched composites, non-stitched composites contained lower void content and irregular void distributio n because of uniform fiber compaction. Microscopic studies of partiall y resin infused quasi-isotropic stitched composites demonstrated that the resin flows along the stitching fiber region and then infuses into the fibrous preform. These infusion phenomena were the result of anis otropic permeability in the preform. Consequently, anisotropic resin f low in the stitched fibrous preform was found to be related to the het erogeneous textile structure caused by the stitching process.