Comparison study on bending properties and failure of 3D5d and 3D6d carbon/phenolic braided composites at room and elevated temperatures

Three-dimensional five-directional and six-directional braided composites (3D5dBCs and 3D6dBCs) are widely used in aerospace industry for their excellent axial and transverse properties. This work successfully fabricated 3D5dBCs and 3D6dBCs with carbon/phenolic, and compared their bending properties and failure mechanisms at room and high temperatures (RT and HT). The influences of braiding structure and temperature on bending properties and failure mechanisms of 3D5dBCs and 3D6dBCs were analyzed. The load/deflection curves are linear elastic at RT, showing prominent plastic characteristics at HT. From RT to HT, the bending properties decrease, but 3D5dBCs always have higher bending properties than 3D6dBCs. The 3D5dBCs and 3D6dBCs are primarily damaged near the surface at RT; fiber shearing fracture feature becomes apparent and the interior damage worsens at HT. 3D5dBCs exhibit obvious shear failure mode, where the fracture is bent and rough, and the damage patterns are braiding and axial fibers shearing fracture, matrix softening, and interface debonding. 3D6dBCs show transverse sawtooth fracture cracks, and the damage mechanisms are braiding fiber shearing fracture, fifth fiber tearing, sixth fiber shedding and pulling-off, matrix plasticization, and interface debonding.