基于非线性声学二次谐波的缆索疲劳损伤磁致伸缩导波检测方法研究

The cable's health is relative to the safety of the whole structure of bridge as cable is one of the main bearing parts of cable supported bridges. The difficulty to evaluate the life of the cable is partly due to the accuracy limitation of the non-destructive testing and the lack of effective online inspection of the fatigue micro-damage. The magnetostrictive guided wave method for detecting the fatigue damage of cables using the nonlinear acoustic second harmonic is presented. From the relation between the fatigue damage and the nonlinear acoustic parameters, the three dimensional nonlinear wave equation is established by considering the longitudinal mode guided wave structures and secondary nonlinear stress-strain relationship. The nonlinear acoustic characterization of the cable fatigue damage is obtained, which provides the basis for cable fatigue damage detection. Based on the magnetostrictive guided wave technology, the energy conversion frequency response of the transducers, the tension and temperature compensation algorithm, the signal processing method combining the singular value decomposition and the bispectrum estimation are studied. Additionally, the relationship between the maximum Lyapunov index and the fatigue damage is explored. The project is expected to reveal the laws between the microscopic structure distortion under cyclic loading and the nonlinear acoustic parameters and obtain the fatigue micro-damage detection method and the life evaluation mechanism of bridge cables. The results of this project will rich the nonlinear acoustics in theory. In practice, the project is expected to obtain key nondestructive testing technologies for detecting fatigue damage of cable in service and provide a new approach to evaluate the life and the safety of the bridge cable.

缆索作为缆索承重桥梁的主要承载部件之一，其健康状况直接关系到桥梁整体结构的安全。针对现有方法无法用于在役缆索微观疲劳损伤检测的问题，提出基于非线性声学二次谐波的缆索疲劳损伤磁致伸缩导波检测方法。从疲劳损伤与非线性声学参数之间的联系出发，结合纵向模态导波波结构和二次非线性应力应变关系，建立三维非线性波动模型，得到用于评估疲劳损伤的弹性非线性参数。对磁致伸缩导波的激励和接收的换能频响规律、基于奇异值分解及双谱相结合和基于混沌理论缆索损伤表征提取的信号处理方法、温度和应力变化的补偿算法展开研究。项目将揭示缆索在循环载荷下的微观组织结构畸变与非线性声学表征的关联规律，得到微观疲劳损伤的检测方法与缆索寿命评价机制，最终丰富非线性声学的相关内容；同时，有望突破在役缆索疲劳损伤无损检测关键技术，从而为桥梁缆索的寿命评估和安全评价提供新手段。

索承式桥梁，如斜拉桥、悬索桥等，由于其美观性在城市桥梁建设中得到广泛采用，缆索作为主要的承力部件其完整性直接关系到桥梁的安全，近年来国内外都发生了由于缆索断裂导致的桥梁倒塌事故。由于缆索长期工作在大拉力风吹日晒雨淋等环境下，同时随着我国经济发展，桥梁作为重要的基础设施，车辆的高密度通行疲劳损伤不可避免。缆索的整个寿命周期里（20-30年）微观损伤占98%左右，宏观缺陷仅占2%，为了获得缆索的健康状态，本项目以非线性声学方法实现了缆索的疲劳损伤检测，主要研究内容：.1）研究了缆索疲劳损伤的非线性纵向模态导波检测机理。.建立了缆索疲劳损伤检测模型，获得了疲劳损伤缆索的频散曲线，研究了纵向导波在疲劳损伤缆索中的传播特性及非线性检测机理，确定了用于缆索疲劳损伤检测的特征参数，同时得到了弹性波在螺旋周期结构中的传播规律，扩展了已有的弹塑性动力学。.2）研究了磁致伸缩导波激励和接收换能频响的规律。.研究了传感器特征参数与检测频率的关系，确定了主频率偏移现象产生的原因，得到了磁致伸缩导波激励和接收换能频响的规律，另外得到的疲劳损伤对磁致伸缩导波激励和接收效率的影响。.3）研究了缆索疲劳损伤非线性声学信号处理方法。.利用基于小波变换的非线性声学信号处理方法，提取了用于评估缆索疲劳损伤的缺失频率、换能效率、衰减系数等特征参数，实现了缆索疲劳损伤的检测。.4）研究了工作状态对缆索疲劳损伤非线性声学特征参数的影响。.将索力等效为偏置磁场研究了索力对磁致伸缩导波激励端和接收端换能效率的影响，并通过实验研究了索力参数对缆索疲劳损伤非线性声学特征参数的影响，实现了索力和温度对非线性声学特征参数的补偿。.本项目在原有宏观缺陷检测的基础上，突破在役缆索微观损伤无损检测关键技术，该技术的应用将为桥梁缆索全寿命评估提供可能。另外，项目研究成果将在国家重点研发计划子课题：“桥梁缆索检测类机器人”得到实际应用。