复合材料结构中的超声导波广义多重散射机制与损伤评估研究

Ultrasonic guided wave method is considered to be one of the most promising methods for evaluating the integrity and reliability of composite structures. However, in practical applications, the lack of information limits its performance for structural damage evaluation. Compared to the Born approximation, the generalized multi-scattering theory retains the multi-mode scattering at the object and multiple scattering between the object and other scatterers. These scattered signals capture much information about the structural damage, which could be used for damage quantification. The motivation and objective of this project is to establish a systematic strategy for in-situ monitoring and assessment of composite structures via generalized multi-scattering guided waves. Firstly, the principles of multi-mode scattering and mode conversion at the structural damage and multi-path scattering between several scatterers are investigated. On this basis, signal processing techniques are introduced to the guided wave signals for underlining and interpreting the multi-scattering signals. Furthermore, the paths of the multi-scattering signals are traced so as to help identifying and decoupling the information related to the structural damage. Finally, the strategy for damage detection and evaluation in composites is established, which could form the basis of the structural health monitoring for composites. This project may provide theories and methodologies for the condition assessment, health maintenance and effective management of the on-service composites.

超声导波监测技术被认为是目前最具前景的复合材料服役性能和结构完整性评价手段之一。然而，在实际应用中，导波信息的挖掘不充分显著限制了其对结构损伤的定量表征能力。相比波恩近似，广义多重散射理论保留了大量的散射信号，可显著增加信息量，为损伤的定量表征提供有力支撑。本项目拟从多模态导波在缺陷处的散射与模态转换效应以及导波途经多个异质体的多次散射机理入手，探索损伤引起的结构物理变化与散射信号的特征变化之间的内在关联机制；在此基础上，建立多重散射信号的损伤特征信息表征方法，通过对微弱多重散射成分的锐化和信息解读，充分挖掘其中蕴含的缺陷信号特征；进一步，回溯多重散射成分的传播轨迹，精确识别并解耦缺陷特征信息；最后，建立损伤的精细表达与定量评估方法，拓宽现有导波监测技术的应用广度和诊断精度，为复合材料结构健康监测提供基础理论支撑和解决方案。

导波监测技术是实现复合材料服役性能监测和结构完整性评价的有效手段，然而，信息量的不足导致其难以定量表征损伤的特征。相比波恩近似，广义多重散射理论保留了大量的散射信号，信息量显著增加，可为损伤的定量表征提供充分的信息支撑，是复合材料损伤监测的一个前沿科学问题。课题围绕复合材料的广义多重散射导波损伤监测与评估开展研究，针对多模态导波的散射与模态转换效应以及多个异质体的多次散射机理研究，开发了基于二维和三维谱有限元法的导波传播仿真工具，揭示了各个导波模态对结构损伤的敏感度与模态的波结构特征、频散特性和衰减效应等的关联规律，探索了损伤类型、程度、轮廓等特征变化与各模态导波散射系数矩阵变化的关联机制；在此基础上，针对多重散射信号的损伤特征信息表征问题，利用频散补偿的思想，提出了两种新的宽带导波时频域频散分析方法（即参数化时频变换和频散消除时频变换），实现了多模态、多路径导波信号的高分辨时频表达，为多重散射导波信号的损伤信息分离与特征提取提供了有效的分析工具；进一步，在射线声学理论支撑下，建立多重散射成分的轨迹回溯以及损伤精细表达与定量评估方法，实现了结构损伤的高精度定性诊断与定量表征，为复合材料结构健康监测提供基础理论支撑和解决方案。本课题的研究工作可为在役复合材料结构的状态评估、健康维护和有效管理提供可靠的依据。