超长碳纳米管及其复合结构力学性能的实验研究

Carbon nanotubes (CNTs at micro scale) are ultra-strong materials known at present. However, the performance of CNT fibers and bundles or composite materials is thus far less than that of a single CNT. The emergence of ultra-long CNTs (over the millimeters) provides a new way to explore such deteriorated mechanism. The project will first focus on the research of the mechanical measurement methods and systems to the sample which has a large slenderness ratio (radial at nano scale and the length over the millimeters) based on SEM and optical microscopy and solve the key problems of large field of view in imaging, sample visualization in testing and manipulating, and load sensing independent of the microscopic images. Then, the elastic-plastic parameters and fracture properties of ultra-long carbon tube and its fiber bundles will be measured directly to reveal the mechanism of interwall and intertube sliding and load transferring, and explore the influences of geometry and defects on the mechanical properties of ultra-long CNTs and their composite structures. Secondly, the deformation processes of reinforcing phase and matrix phase will be measured in-situ for nano-reinforced composites, and the interface stress transfer, bonding and fracture behaviors will also be analyzed. Finally, the testing system will be employed to measure the fatigue properties of ultra-long CNTs and their composite structures at room temperature, and the mechanical properties at elevated temperature will also be studied in this project.

碳纳米管(长度微米量级)是目前已知的超强一维材料，但由其制成的纳米纤维或纳米增强复合材料的力学性能和其自身的力学性能相比差距较大。而超长碳纳米管（毫米量级）的出现为探索这一劣化机理提供了新途径。课题首先针对超长碳纳米管所具有的巨大长细比(径向纳米尺度，长度超过毫米)，发展SEM和光学显微环境下的力学测量方法和系统，解决测量中的大视场、试样可视化、以及不依赖显微图像的载荷测量等关键问题。然后，通过直接测量超长碳管及其纤维束，获得其弹塑性参数与断裂性能，进而揭示纤维束中管间/管壁间的滑移与载荷传递机理，探索几何结构和缺陷对超长碳纳米管及其复合结构力学性能的影响；其次，针对纳米增强复合材料，原位测量增强相和基体相的变形过程、分析界面应力传递、粘结与断裂行为。最后，应用研制的检测系统，完成超长碳纳米管及其复合结构室温下疲劳性能测量；通过施加环境温度，研究其在温度升高时弹性、塑性与断裂力学性能。

超长碳纳米管/束的制备为人们进一步增强一维纳米材料及其复合结构的力学性能提供了新的途径。但是，超长碳纳米管/束巨大的比表面积、长细比等对其力学性能的测量提出了新的挑战。本项目开展了新测量技术和系统研制，并对超长碳纳米管及其复合结构的力学性能进行了系统研究，并取得了如下主要的创新研究成果：1）研制了适合光学和扫描显微平台的具有不同加热环境的微纳米尺度材料测量系统，解决了SEM和OM环境中微小尺度试件在1000摄氏度范围的高温力学性能测量问题，可实现长度从亚微米到毫米量级材料的原位力学性能测量。2）通过对超长一维结构的可视化处理，首次实现了大于10e6细长比的超长碳纳米管/束的原位实时单调和循环加载实验，获得了超长碳纳米管的模量、强度等基本力学参数，以及超长碳纳米管的高温拉伸与疲劳性能；结合理论和数值模拟，揭示了其具有超强力学性能的机理，以及超长碳纳米管的弯曲、残余应力、温度等对其强度的影响机制。3）首次完成了毫米级纳米管中管壁间滑移阻力的测量，揭示了其管壁间摩擦、超润滑和载荷传递机制，给出了这些性质和碳纳米管的几何参数与结构、手性、表面共度等特性的关系。4）完成了含缺陷超长碳纳米管的拉伸断裂实验及数值模拟，揭示了辐照缺陷的产生机制及其对超长碳纳米管强韧性的影响，建立了碳纳米管强度与缺陷尺寸之间的定量关系，给出了断裂力学理论在纳米尺度的适用性以及适用下限。5）首次应用水平超取向碳纳米管研发了一种纳米管薄膜胶带，并通过其黏附界面强度的高温实验，发现其从室温至1000摄氏度可提供理想的范德华界面接触，生高达1.1N/μg 的比粘合强度。6）建立了小变形条件下动态物体的扫描成像方程，成功地恢复了由于物体动态变形造成的图像畸变，提出了扫描数字图像相关方法，可以应用SEM畸变显微图像直接计算物体的位移、应变、速度和应变率参数。