Effect of thermal oxidation on cyclic tensile damage behavior of CNT-ZnO/carbon fiber reinforced epoxy composites: An in-situ synchrotron radiation CT study

Carbon fiber reinforced polymer (CFRP) composites are widely used in aerospace and other high-end equipment fields. However, they are prone to damage accumulation under the coupled effect of thermal-oxidative environments and cyclic loading. Currently, in-situ three-dimensional damage studies on CNT-ZnO synergistically modified composites under this coupled condition remain limited. In this work, CNT-ZnO/CFRP composites were fabricated via the VARTM process. The samples were subjected to thermal oxidation treatments at room temperature, 120°C, and 180°C, respectively. In-situ X-ray CT cyclic tensile tests combined with SEM characterization were performed to systematically investigate the effect of thermal-oxidative aging temperature on the cyclic tensile damage behavior of the composites. The results show that at room temperature, CNT-ZnO effectively inhibits the initiation and propagation of micro-damage in the composites under cyclic loading through crack bridging and interfacial strengthening mechanisms. Thermal oxidation at 120°C causes preliminary matrix degradation and weakening of interfacial properties, reduces the damage initiation threshold, significantly advances the occurrence of various damages, and weakens the strengthening effect of the modified system. High-temperature thermal oxidation at 180°C leads to severe damage to the matrix crosslinking structure and complete interfacial failure. Large-scale oxidation defects exist in the initial state of the material, the damage evolution process during cyclic loading is greatly advanced, and the effect of the modified system diminished drastically.