正交异性钢桥面板疲劳损伤非线性电磁超声导波检测与定量评估

Fatigue damage is the most common failure type in the orthotropic steel deck and is very difficult to discover due to its feature of randomness and locality. Since the linear ultrasonic guided wave is not sensitive to tiny damage and very difficult to separate on the boundary signals, and need compare signals obtained from the pristine condition of a structure with those from the current state to identify damage. That is not suitable for fatigue damage overall process monitoring. This project proposed a kind of non-contact nonlinear electromagnetism ultrasonic guided wave as a tool of the fatigue damage detection. Firstly, the sharp interface model and auxiliary air cells for nonlinear analysis of the interaction between the electromagnetism ultrasonic wave and the fatigue damage were developed. A rapid speed and high precision wavelet spectral element method were proposed to study nonlinear guided wave propagation in the orthotropic steel decks. The relationship between nonlinear characteristic parameter and fatigue damage variable was obtained. Secondly, the point-focusing electromagnetic ultrasonic transducers for SV waves were developed for fatigue damage inspection of orthotropic steel deck. A fully automated baseline-free theory model of fatigue damage localization was established. Thirdly, the wavelet analysis technology was used to decompose the nonlinear guided wave signal, sensor array technology and the nonlinear guided wave time inverse method was combined to improve the ability for damage localization of multiple fatigue damages. By applying these technologies, the quantitative evaluation of damage scale and crack orientation of the fatigue damage region were realized. Finally, the effectiveness and correctness of these methods in the project would be verified through experiment.

疲劳损伤是正交异形钢桥面板最常见的失效形式，隐蔽性高、随机性强、局部化突出。现有的线性超声导波对微小损伤不敏感、边界信号不易分离、大部分依赖无损状态参考信号识别损伤，很难用于疲劳损伤全过程检测。本项目提出一种非接触式的非线性电磁超声导波对其疲劳损伤进行检测。首先，构建一个尖锐界面模型和辅助虚拟单元用于导波与疲劳损伤相互作用的非线性分析，发展一种计算效率高的小波谱有限元方法模拟疲劳损伤非线性导波传播，建立疲劳损伤变量与导波之间的非线性效应模型。然后，提出疲劳损伤非线性导波检测的点聚焦型斜入射SV波电磁超声波相控阵换能器设计方法，创建疲劳损伤非线性电磁超声导波无参考信号检测理论模型。再次，基于小波技术分离导波信号非线性分量，提出传感阵列技术和非线性导波时间反转法相结合增强信号聚焦，识别多疲劳损伤；实现损伤尺寸、裂缝方向和疲劳区域定量评估。最后，通过试验验证本项目提出方法的有效性和正确性。

本项目首先进行了含有宏观缺陷及闭合缺陷的钢板的非线性超声导波传递过程的三维数值模拟，利用步进式扫描识别宏观缺陷及闭合缺陷，局部区域扫描进行初步成像。进行正交异性钢桥面板疲劳加载后非线性导波信号的捕捉以及非线性超声导波传递过程的二维数值模拟，模拟进一步说明了闭合裂纹可使超声导波发生明显的非线性响应。通过COMSOL有限元软件对电磁超声换能器的换能机理进行了仿真分析，探究了换能器参数对横波幅值的影响。利用电磁超声换能器实现非接触式无损检测，研究缺陷深度对回波信号幅值及能量的影响。分别以信号幅值、能量变化来表征缺陷深度对回波信号的影响，以无缺陷钢板检测信号为基础，构建以超声波衰减为基础理论的损伤指标AI值和EI值。为提高电磁超声Lamb波换能器换能效率和抑制多模态杂波为目标，对适用于铁磁性薄钢板的电磁超声Lamb波换能器进行设计，采用正交试验设计方法对电磁超声换能器探头参数进行优化，得到相关参数对检测信号强度的影响规律。提出一种基于等效时间和网格化迭代算法定位损伤位置，该方法可以实现损伤的精准定位。在含有疲劳缺陷的正交异性钢桥面板及其顶板母材试样上对比探究了疲劳对非线性超声导波的影响，在进行正交异性钢桥面板及其顶板母材试样的疲劳加载过程中，总结不同疲劳损伤程度下声速、能量及非线性参数的变化情况，并应用了HHT变换的实验信号处理方法提高了信号的时域分辨能力。将数值子模型技术用于正交异性桥面板焊缝的焊接残余应力的分布特性研究。采用基于连续损伤力学理论的非线性疲劳损伤模型对某在役斜拉桥的正交异性钢桥面板中上顶板与上顶板U肋的连接焊缝进行评估，并基于正交异性桥面疲劳实验对该非线性疲劳损伤模型进行了验证。

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