疲劳环境下金属结构疲劳裂纹柔性涡流阵列在线定量监测关键问题研究

On-line quantitative monitoring of fatigue cracks in metal structures is of great significance for the safety of large-scale equipment,such as aircraft, high-speed train and so on. However, the large-scale equipment usually services in harsh environment, preventing the application of fatigue crack monitoring technology. It is fatigue loadings that lead to the initiation and propagation of fatigue crack, and therefore fatigue environment is the most basic service condition for sensors used for on-line monitoring of fatigue cracks. Under simulated fatigue environment, an flexible eddy current array sensor was applied for on-line monitoring of fatigue cracks, it was found that the collected signal successfully reflected the fatigue crack length. In order to study the nature and mechanism of this phenomenon, this application is proposed. In this project, a semi-analytic forward model of the flexible eddy current array sensor will be developed and be used to study the inherent mechanism how the sensor monitors fatigue cracks in metal structure. The effect of fatigue environment and integration mode on the stress distribution and fatigue crack monitoring capacity of the sensor will be studied to reveal the mechanism how the sensor integrates with metal structure. Finally, the rules and effect of fatigue environment on output characteristics of the sensor will be investigated, and the essential relationship between the monitoring signal of the sensor and the length of structure’s fatigue crack will be established. In theory, this project will reveal how the sensor monitors fatigue crack in metal structures under fatigue environment. In engineering, it can provide a reference for on-line quantitative monitoring of fatigue cracks in metal structures.

金属结构疲劳裂纹的在线定量监测对于保证飞机、高速列车等大型装备的安全运行具有重大意义，然而大型装备的服役环境往往比较恶劣，制约了疲劳裂纹监测技术的应用。疲劳环境是传感器在线监测疲劳裂纹中最基本的服役环境，申请人在模拟疲劳环境下运用柔性涡流阵列传感器开展了疲劳裂纹在线监测试验，发现监测信号与裂纹长度具有良好的对应关系。为了探明该现象的本质和机理，特申请本项目支持。项目通过建立柔性涡流阵列传感器的半解析正向模型，探究传感器监测金属结构疲劳裂纹的内在机理；通过研究疲劳环境、集成方式与传感器结构应力、裂纹监测特性的相互关系，揭示传感器与金属结构的集成机理；最后研究疲劳环境对传感器输出的影响机理和影响规律，进而建立传感器输出与金属结构疲劳裂纹长度的对应关系模型。项目成果将在机理上获得疲劳环境下柔性涡流阵列传感器在线监测金属结构疲劳裂纹的理论解释，在工程上为金属结构疲劳裂纹的在线定量监测提供方法参考。

金属结构疲劳裂纹的在线定量监测对于保证飞机、高速列车等大型装备的安全运行具有重大意义，然而大型装备的服役环境往往比较恶劣，制约了疲劳裂纹监测技术的应用。疲劳裂纹是在疲劳载荷环境的作用下形成的，因此疲劳环境是传感器在线监测疲劳裂纹中最主要的服役环境，项目对疲劳环境下柔性涡流阵列传感器在线定量监测金属结构裂纹的关键问题进行了研究。首先，将被监测结构损伤等效为结构电磁参数的变化，建立了柔性涡流阵列传感器的半解析正向等效模型、响应特性修正模型和基于二维网格的逆向模型，确立了传感器响应与被监测结构等效电导率之间的映射关系，探究了2A12-T4铝合金结构裂纹损伤与等效电导率之间的关联，揭示了传感器监测金属结构裂纹的内在机理，研究了传感器结构参数与工作参数对疲劳裂纹监测特性的影响规律。然后，通过有限元方法对传感器在典型集成方式下的受载情况进行了分析，明确了影响传感器受载的因素及规律；将传感器与金属结构集成，通过试验研究了传感器的失效模式和失效机理；在此基础上，提出了基于弹性保护胶层的集成方案并验证了方案的可行性，研究了集成参数对裂纹监测特性的影响规律。最后，研究了试验件在有、无裂纹条件下静态和动态应力对传感器输出的影响规律，分析了疲劳环境对传感器输出的影响机理；提出将传感器测量通道相对参考通道的等效电导率变化量△C作为裂纹特征量，研究了△C与疲劳裂纹长度之间的对应关系，发现△C变化趋势发生转变的“拐点”是定量识别裂纹长度的关键特征；构建裂纹特征“拐点”的在线提取算法，实现了“拐点”的有效识别，进而实现了裂纹的在线定量监测。项目成果揭示了柔性涡流阵列传感器在疲劳环境下监测疲劳裂纹的内在机理、传感器与金属结构的集成机理，确立了裂纹长度定量识别的方法，为柔性涡流阵列传感器的工程应用提供了重要的方法参考和理论支撑。