Topology of Three-Dimensionally Braided Fabrics Using Pultruded Rods as Axial Reinforcements

This paper examines the topology of two-step braided fabrics incorporating rigid rods in the axial direction. Fabricated by pultrusion, the 1-mm diameter rods are composed of unidirectional Kevlar fibers and vinylester resin. A modified two-step braiding set-up designed to incorporate the rods is developed. In comparison with conventional three-dimensional fabric composites, using the rods can significantly reduce the level of crimp in both axial and braiding yarns. Crimp-induced problems such as irregular fabric patterns can be effectively improved. The resulting composite geometry parameters are experimentally characterized. According to the micrographs, rods that are placed in an orderly way greatly improve yarn compactness. The braiding yarn paths are modeled by the minimum length criterion. Using this criterion, the braiding processes are simulated, taking into account yarn jamming conditions. The interlacing pattern and the length of the fabric convergence cone are examined. The topology is described in terms of physically measurable parameters, and the effects of yarn size, rod spacing, and pitch length on the resulting fabric geometry are analyzed.