航天结构螺栓连接的导波传播机理与预紧力监测方法研究

Reusable launch vehicle, Responsive space spacecraft and other aerospace structures generally comprise a large number of bolt connections. Accurately monitoring the bolt preload is of great importance for reliability and safety of the aerospace structures. Bolt connections in aerospace structures are generally lap joints connecting thin plates. Ultrasonic guided wave is one of the most promising structural health monitoring techniques for thin-wall structures. However, the physical behavior of guided wave propagation in bolt lap joints is still not fully understood. Besides, the effects of faying surface characteristics on guided wave propagation are still unclear. Hence, the development of health monitoring technology for bolt joints in space structures is greatly limited. To this end, the main purposes of this project are as follows. First, a guided wave interface model is established to describe guided wave propagation and attenuation at contact interfaces. Then, a time-domain spectral element method considering piezoelectric effect is proposed. Based on this, a theoretical guided wave propagation model of bolt lap joints is further established to accurately describe the physical behavior of guided wave propagation. After that, the laws of guided wave energy transfer, mode conversion and phase change are revealed. Besides, the influence mechanisms of the faying surface characteristics on the guided wave propagation are explored. Finally, a bolt preload monitoring method is presented based on the theoretical guided wave propagation model. In addition, monitoring parameters such as guided wave mode, frequency are then optimized to improve the monitoring accuracy. The research above will provides theoretical basis and technical support for the health monitoring of bolted joints in aerospace structures.

可重复使用运载器、快速响应航天器等航天结构中存在大量螺栓连接部，对螺栓预紧力进行准确监测，对于保障航天结构可靠性与安全性具有重要意义。航天结构螺栓连接部一般为薄壁搭接结构，超声导波是最具潜力的薄壁结构健康监测技术之一，然而目前螺栓搭接结构中导波传播物理行为仍未被完全理解，搭接面接触特性对于导波传播影响机制仍不明确，极大限制了螺栓搭接结构导波监测技术的发展。为此本项目拟建立考虑衰减的粗糙接触面导波界面模型，准确描述接触面导波的传播与衰减；结合考虑压电效应的时域谱单元分析方法，构建螺栓搭接结构导波传播模型，以此准确分析螺栓搭接结构中导波传播物理行为；揭示导波模态转换、能量传递与相位变化规律，阐明搭接面接触特性对于导波传播的影响机制；提出基于导波传播模型的螺栓预紧力监测方法，在优化导波模态、频率等参数的基础上，实现螺栓预紧力准确监测，为航天结构螺栓连接的健康监测提供理论基础与使能技术支撑。

航天结构中存在大量连接部位，比如螺栓连接，而这些连接部位在恶劣服役环境下极易发生螺栓松动等连接损伤，随着航天运载器可重复使用、长期贮存等需求的不断提高，对螺栓预紧力进行准确监测，对于保障航天结构可靠性与安全性具有重要意义。利用压电主动传感器可以采用导波、机电阻抗等方法对损伤进行监测，本项目为实现基于压电主动传感器的螺栓预紧力准确监测，开展了航天螺栓连接结构导波传播机理及预紧力评估方法开展研究。项目主要研究内容包括超声导波在螺栓结构中的半解析传播模型、考虑非线性的时域谱单元数值分析方法、螺栓松动高灵敏度检测方法及装置开发等方面。通过上述研究工作，揭示了接触面积对于超声导波传播透射信号及能量的影响机理，提出了基于时间反转的螺栓预紧力监测方法，开发了基于压电主动传感器的集成化监测装置，上述工作显著提高了螺栓预紧力的检测分辨率，有望在航天运载器弹身连接结构、固体火箭发动机连接结构等的损伤监测中开展应用，实现连接结构健康状态的在线监测，提高结构可靠性。