Matrix cracking of carbon fibre reinforced polymer composites at super cold temperatures, such as liquid hydrogen temperature, is a major issue for lightweight fuel storage, because the microcracks induced by the high thermal residual stresses in the matrix can cause fuel leaks and degrade the structural integrity of the storage vessel. Herein, we report a new method of toughening carbon fibre composites using nanomaterials of low-thermal expansion, i.e., nano-silica (nSiO₂) and nano-cupric oxide (nCuO), at cryogenic liquid nitrogen temperature (~196 °C). In addition to their low coefficients of thermal expansion, these two nanoparticles are sufficiently small to avoid the filtering effect of carbon fibres during resin infusion process. The surfaces of nCuO are functionalized by a polydopamine coating to enhance their bonding with the epoxy resin and the cross-linking density of the epoxy resin. Results from tension and fracture toughness tests of an epoxy modified with these nanoparticles reveal that PDA-coated nCuO are more effective than their un-coated counterpart and nSiO₂ in increasing the mechanical and fracture properties of epoxy nanocomposites at both room and cryogenic temperatures, tripling the fracture toughness values. More importantly, PDA-coated nCuO demonstrate significant improvements in the initiation and propagation fracture toughness of angle-ply carbon fibre composite ([±35°]₈) by 113% and 46% respectively at the cryogenic temperature. The underlying toughening mechanisms are identified using scanning electron microscope as being fiber peel-off, debonding, and striation in the matrix. These exceptional improvements stem from the higher interfacial residual thermal stress at cryogenic temperature due to their low thermal expansion properties, which in turn promotes crack branching that increases the energy dissipation of the matrix.

碳纤维增强聚合物复合材料在超低温（如液氢温度）下的基体开裂是轻质燃料储存的主要问题，因为基体中高热残余应力引起的微裂纹会导致燃料泄漏并降低结构完整性的存储容器。在此，我们报告了一种使用低热膨胀纳米材料，即纳米二氧化硅 (nSiO ₂) 和纳米氧化铜 (nCuO)，在低温液氮温度 (~196 °C)。除了它们的低热膨胀系数外，这两种纳米粒子足够小，可以避免树脂灌注过程中碳纤维的过滤作用。nCuO 的表面通过聚多巴胺涂层功能化，以增强它们与环氧树脂的结合和环氧树脂的交联密度。用这些纳米粒子改性的环氧树脂的拉伸和断裂韧性测试结果表明，PDA 涂层的 nCuO 比未涂层的对应物和 nSiO ₂更有效提高环氧树脂纳米复合材料在室温和低温下的机械和断裂性能，使断裂韧性值增加三倍。更重要的是，PDA 涂层的 nCuO 在低温下显着提高了角层碳纤维复合材料 ([±35°] ₈ )的起始和传播断裂韧性，分别提高了 113% 和 46%。使用扫描电子显微镜识别出潜在的增韧机制是纤维剥离、脱粘和基质中的条纹。这些特殊的改进源于低温下较高的界面残余热应力，因为它们的热膨胀特性较低，这反过来又促进了裂纹分支，从而增加了基体的能量耗散。