FABRICATION AND MICROGEOMETRY OF 2-STEP BRAIDED COMPOSITES INCORPORATING PULTRUDED RODS

The concept of using consolidated rods as axial reinforcements in two- step braided composites has been demonstrated in this paper The compos ite fabrication consists of three major processes: the fabrication of unidirectional rods, I mm in diameter by pultrusion, the formation of three-dimensional preforms by a modified two-step braiding set-up with the rods as axial reinforcements, and the impregnation of resin into the preforms by resin transfer molding, followed by a curing process t o consolidate the composites. In comparison with conventional three-di mensional fabric composites, this approach (I) essentially eliminates both axial and braiding yarn crimp in the composite interior (2) enhan ces fabric consistency, (3) provides fairly rigid fabrics, and (4) fac ilitates resin infiltration in resin transfer molding. The resulting c omposite geometries have been experimentally characterized. The mechan ism of braider slip was found to dominate the resulting interlacing pa ttern. According to the micrographs the rods were placed regularly wit hin the fabrics with satisfactory compactness. As squeezed by the rods , the braiders are thin and close to rectangular. Two families of spec imens with varying take-zip distances and braider sizes have been made and the corresponding pitch length, yarn content, rod gap, braider cr oss-section, and interlacing pattern have been correlated with these v arying parameters. The processing characteristics and the inherent lim itations of this method are discussed in detail. (C) 1997 Elsevier Sci ence Limited.