Improvement of the Crack Resistance of a Carbon/Epoxy Composite at Cryogenic Temperature

The improvement of crack resistance is essential to the application of composites for cryogenic use such as structures storing liquid oxygen or liquid hydrogen. In this study, an effort to improve the crack resistance of a carbon/epoxy composite was made by adding MWNTs (Multi-Walled Carbon Nanotubes) to the resin formulation. Ahead of the investigation of MWNT effect, an epoxy matrix system was developed by mixing two kinds of epoxy resins and adding additives for high toughness at cryogenic temperature. The MWNT-added carbon/epoxy unidirectional prepregs were fabricated by way of a filament winding method with different concentrations of MWNTs (0.2wt% and 0.7wt%). The mechanical tests were performed inside an environmental chamber at room temperature and -150°C. The developed material system has little influence on interlaminar shear strength but resulted in higher fracture toughness at -150°C than those of baseline material. Microcrack densities after thermo-mechanical cycles were measured through an optical microscope.