编织复合材料在大气环境中热氧老化与强度降解的多尺度结构机理

Thermal oxygen ageing of braided composite in atmospheric environment is a critical factor in material design and practical application. The ageing behavior will influence the braided composite durability significantly. The objective of the project is to reveal the thermal oxygen ageing mechanisms of braided composite at atmospheric environment for designing the higher durable braided composite. In this project, we propose to study the thermal ageing initiation and propagation with the strength degradation of the braided composite in atmospheric environment from constituent materials’ ageing and the ageing evolution in multi-scale structures. We would test the thermal behaviors and degradation of matrix materials for finding ageing mechanisms and strength degradation. Then the effect of fiber orientation on the ageing development and strength degradation of unidirectional composite would be investigated for unveiling interface weakening and failure mechanisms. Furthermore, we would study the thermal ageing mechanisms of the braided composite, including ageing gradient and ageing path in braided fiber tows and preform structure. The in-situ compressive behaviors in the braided composite would be tested with micro- and nano-indention methods. Finally, the influence of ageing conditions and parameters on strength degradation would be analyzed at fiber, matrix, interface, finer tows and braided structure level. The design methodology would be proposed for designing the braided composite under atmospheric thermal ageing conditions. On the basis of elucidating the thermal ageing mechanism and strength degradation of the braided composite, it is expected that the results could be useful for durable braided composite design under long term service in hot atmospheric environment.

编织复合材料在大气环境中热氧老化是材料设计和工程应用面临的重要问题，显著影响复合材料结构件耐久性。项目将从复合材料组份材料老化和老化在复合材料多尺度结构上的演化出发，研究在大气环境中复合材料老化生成、发展规律和强度降解机理：采用热分析方法测试基体材料热老化和降解性质，发现基体材料热老化特征和强度降解规律；表征单向复合材料热老化的方向性效应和强度降解与热老化关系，揭示热老化所致的界面弱化和复合材料失效机理；采用微纳米压痕法测试编织复合材料沿厚度方向由表及里和沿编织纤维束方向的老化后原位压缩性质，探索老化沿纤维束和编织结构路径发展的多尺度几何结构特征；从纤维、基体、界面、纤维束到编织结构逐级揭示强度降解机理，阐明热老化条件对强度降解的影响规律。该项目在表征复合材料大气热老化过程和各向异性特征基础上，揭示复合材料热氧老化强度降解规律，应用于在大气热环境下长期服役时编织复合材料结构件耐久性设计。

编织复合材料在大气环境中热氧老化现象和由此导致的强度降解是编织复合材料使用过程中无法避免的问题，也是编织复合材料零件设计、制造和实际使用中不可或缺的重要因素，编织复合材料在大气环境中热氧老化将显著影响复合材料结构件耐久性。项目研究了碳纤维 / 环氧树脂四步法三维编织复合材料在大气环境中热氧老化过程和强度降解性质，在如下三方面（1）三维编织复合材料热氧老化损伤及低速冲击失效机理、（2）热氧老化所致三维机织复合材料内部裂纹分布和准静态压缩力学性质、（3）三维纺织复合材料热氧老化的冲击强度降解与应变率效应，取得了系统性研究结果。以环氧树脂浇注体、单向复合材料UD为对照，180℃老化0到16天后，原位弹性模量由4.64 GPa下降到4.12 GPa，模量保留率下降了11.26%，这直接证明了热氧老化过程中三维编织复合材料中树脂基体存在刚度降解，进而发现了环氧树脂基体热氧老化特征、强度降解规律和热氧老化裂纹空间分布特征；揭示了热氧老化所致的界面弱化和复合材料失效机理，得到了准静态和冲击加载强度的降解规律；观测得到了编织复合材料大气热氧老化沿厚度方向由表及里的梯度分布，阐明了复合材料细观结构对老化沿纤维束和编织结构路径发展路径的影响；从纤维、基体、界面、纤维束到编织结构逐级解释了强度降解机理。项目研究成果可用于编织复合材料在大气环境中抗老化、耐久性及安全性设计。项目研究成果发表第一标注的期刊论文26篇，其中包括《中国科学.技术科学》等中文论文3篇，项目研究期间共毕业博士生6名（其中留学生1名），硕士生8名。参加5次在国内召开的学术会议。另外由Springer出版专著1本，项目的部分成果获得2021年高等学校科学研究优秀成果奖自然科学奖二等奖。