On the tensile properties and failure mechanisms of 3D six-directional braided composites at elevated temperatures

Three-dimensional six-directional (3D6d) braided composites with different braiding angles were prepared, and the influences of temperature and braiding angle on tensile properties and failure mechanisms were studied. The results show that both temperature and braiding angle have significant effects on the tensile properties of 3D6d braided composites. As temperature increases, due to the weakening of the fiber/matrix interface, the stressstrain curve shows a nonlinear upward trend and the tensile properties decrease. As braiding angle increases, the curve declines, and both the tensile strength and modulus diminish. At high temperatures, the damage pattern is mainly braiding fibers multiple shear fracture, fifth fibers tensile fracture, sixth fibers torn, showing expansion outwards, matrix softening and peeling off from the fiber bundles. At 150 degrees C, the composite shows shear fracture, as the braiding angle increases, the shear fracture characteristics along the braiding angle become prominent. At 200 degrees C, the composite distorts and expands outwards overall. The fibers pull-out feature become obvious with increasing the braiding angle.