High Temperature Mechanical Response and Failure Analysis of 3D Five-Directional Braided Composites with Different Braiding Angles.

Three-dimensional (3D) five-directional braided composites are extensively applied in aeronautics and national defense due to their integrity and structural superiorities. In this paper, 3D five-directional braided carbon/epoxy composites were manufactured, and the high temperature mechanical response and failure mechanisms of composites with braiding angles of 21° and 32° were studied. The out-of-plane compression tests of composites with different braiding angles were conducted at temperatures ranging from 25 °C to 180 °C. Then compression stress-strain curves, compression mechanical response, and failure modes of composites at high temperatures were analyzed and compared. The results show that compression stress-strain curves linearly increased at the initial stage and dropped at various degrees at different temperatures for composites with different braiding angles. The temperature and braiding angle were both important parameters affecting out-of-plane compression properties of 3D five-directional braided composites. Mechanical properties decreased with increasing temperature for both 21° and 32° specimens. Moreover, composites with a small braiding angle possessed higher properties at each temperature point. The morphologies manifested that the failures were a symmetric ±45° shear crack for 21° specimens and a thorough 45° shear crack for 32° specimens, and a 45° fracture weakened with increasing temperature.