Chapter 6 - Braided Composite Materials

Abstract

Three-dimensional (3D) braided preforms are very versatile forms of textile reinforcement for composite structures. 3D braids can be produced in a wide range of cross-sectional shapes and these shapes can be varied along their length to form structural details such as tapers, bifurcations, and holes. The presence (or absence) of axial fibers and the angle of the braiding yarns both play an important role in controlling the mechanical properties. Improved longitudinal performance results from increased axial fiber content and decreased braiding angle, but at the expense of transverse properties. The damage resistance and tolerance of 3D braided composites are also significantly better than two-dimensional (2D) tape laminates because of the highly interlinked nature of the 3D architecture; however, the fatigue performance is shown to be worse. The 3D braided composites are provided with high sensitivity to cut edges. The act of machining the specimen edge, and thus, cutting the braiding yarns into discontinuous sections, is found to significantly decrease the tensile and flexural properties of the composite. This indicates the need to produce 3D braided composite components to net-shape, thus, removing any need for machining that will reduce its performance.