Evaluation of the Physical and Mechanical Properties of Braided Fabrics and their Composites

This study aims to evaluate the permeability and the basic mechanical properties of braided fabrics intended for hollow composites to be manufactured by resin infusion processes. A simple procedure has been devised to obtain flat specimens for the required permeability and mechanical tests. Permeability measurements have been performed on 2-D biaxially braided glass fabrics at three braiding angles. The change of the braiding angle affects the fiber volume fraction, which in turn affects the permeability. Tension, compression, and shear tests have also been conducted on unidirectional (UD) and braided glass-epoxy composites. From the experimental UD properties, the lamination theory (LT) has been used to predict the properties of angle ply () laminates equivalent to the braided composites tested. From the comparison of the predicted and experimental results, the effects of the fibers’ intertwining and undulation on the mechanical properties have been derived. The undulation of the fibers is responsible for the compression strength reduction, mainly at low braiding angles, but has no effect on the tensile strength. For all angles, the braided composites have a higher modulus than the predicted angle ply laminates. The Iosipescu shear method is not suitable for the characterization of composites containing braided fabrics because of their high shear stiffness and strength.