EXPERIMENTAL INVESTIGATION INTO THE COMPRESSIVE MECHANICAL PROPERTIES OF THREE DIMENSIONAL BRAIDED COMPOSITES

The mechanical properties of three dimensional and four-direction braided composites were investigated by the macroscopic compressive experiments, and the SEM analysis was performed for the fracture surface of specimens to understand the compressive failure mechanism of this kind of composite. The experimental results show that the longitudinal modulus is much larger than the transverse one, and the most important parameter to affect the longitudinal compressive properties of the composites is the braided angle. The mechanism of longitudinal compressive failure of the composites changes with the increase of the braided angles. When the braided angle is smaller, the material behaves as the brittle characteristics. But if the braided angle is larger than a certain critical one, the stress-strain curves of the materials approach nonlinear ones and the ductility of the composites increases, behaving mostly as the characteristics of plastic failure. In addition, the mechanism of transverse compressive failure of the composites is significantly different from the one of longitudinal compression.