诸如结构疲劳和微小裂纹等不可见损伤的检测难题是基于导波的主动在线结构健康监测技术工程实用化的主要因素之一。本项目将以机械装备和工程结构中复杂关键构件为研究对象，应用超声导波与结构微-小损伤耦合的线性和非线性效应，对超声导波在复杂构件中传播的非线性效应、微-小损伤的动力学建模与仿真、基于导波模式转换和非线性导波的损伤识别、微弱超声导波信号的特征提取与损伤识别方法、以及试件模拟与试验研究五个方面开展研究。考虑机械装备和工程结构的工况和服役环境，探索将线性和非线性超声导波用于复杂构件不可见损伤识别的理论分析、建模仿真和试验验证问题。以期在结构损伤出现早期实时监测其健康状况，并及时采取必要的维护措施。研究过程将充分重视学科交叉与渗透，在现有申请者课题组研究成果的基础上，研究开发自主创新的理论和技术。本项目的研究对推动基于导波的结构健康监测技术的发展具有重要的理论意义和工程实用价值。

Barely visible damage (BVD), such as fatigue and micro and small crack, detection for complex structures is one of the difficulties in the practical commercial application of ultrasonic based structural health monitoring techniques. The project will investigate the micro and small damage detection for complex and key components of mechanical equipments and large scale structures, which will be based on the linear and nonlinear characteristics of ultrasonic guided waves with the micro and small defects in the components. Five key problems will be studied in the projects, namely, 1) propagation characteristics of nonlinear ultrasonic guided waves in complex structures, 2) dynamics model and simulation of micro and small damages, 3) damage detection methods based on mode conversion and nonlinear characteristics of guided waves, 4) signal processing methods for non-stationary guided wave signals with feeble damage caused signal features, and 5) specimen manufacturing and experimental research. Working condition and experiment of mechanical equipments and large scale structures will also be considered in the project, to explore the theoretical analysis, model and simulation, and experimental verification in BVD detection for complex structures. Purpose of the project is to inspect the structural damage at the early stage for timely detection and repair. Outcomes of the project will lead to novel and practicable technologies for real-time structural health monitoring and integrity assessment with higher accuracy, and will significantly improve operation safety and reduce maintenance costs.