Experimental study on the low-temperature compression performance of 3D five-directional braided composites applied to extreme environments

3D five-directional braided (3D5dB) composites with different braiding angles were designed and prepared, and their compressive properties in the longitudinal, out-of-plane and transverse directions were investigated at room temperature (RT) and liquid nitrogen temperature (LNT). The results of the stress-strain curves showed that the composites at LNT exhibited more pronounced brittle fracture failure and increased compressive strength in all directions compared to RT. The longitudinal compression strength decreased with increasing braiding angle, while the opposite effect was observed for transverse and out-of-plane. The effect of LNT on the failure of 3D5dB composites was mainly focused on the interfacial debonding of fibers and matrix, so the mechanical properties can generally be improved by modifying the fibers to increase the interfacial shear strength at low temperatures. 3D5dB composites with high mechanical strength at the temperature of LNT can be potentially used as cryogenic materials for aerospace applications.