Processing and microstructures of 3D woven-fabric composites incorporating solid rods

This work has two objectives. The first is to examine the processability of incorporating pultruded rods in three-dimensional woven fabrics. A weaving set-up for this purpose has been developed. The secund objective is to characterize the microstructures of the composites and to assess the merits and limitations associated with the rods. Three types of fabric have been made in this study. The first is a 3-axis orthogonal type combining the rods in the axial direction. The second type has a similar structure except that the rods are also used in the widthwise direction. The third is the addition of two off-axis weaving yarns to the first type, resulting in a 5-axis structure. Material processing involves rod pultrusion, fabric formation, and resin impregnation. Both Kevlar and carbon tows have been used in the rods and weaving yarns. A series of specimens with varying bundle size of the weaving yarns have been made. No pressing force was applied during resin transfer molding to preserve the as-formed fabric configuration. According to the micrographs, the rods are essentially free of distortion, while two E;inds of local deformation have been identified in the yarns. Unit cells are selected to describe interior microstructures of the materials. Fiber distribution along each direction and matrix distribution in interbundle and intrabundle spaces have been examined on the basis of measured fabric dimensions. The influence of the pitch length on the distributions of fiber and matrix has been analyzed by assuming constant yam areas. Unique features in processing/microstructure relationships resulting from the presence of the rods have been discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.