基于导波模态分析的高强钢丝腐蚀评估

为提高桥梁缆索损伤声发射监测的精度和可靠度,将小波变换的用于导波模态分析,提出了基于导波模态特征的高强钢丝腐蚀评估方法。通过有限元方法模拟多模态导波在索内单根高强钢丝中的传播过程,采用小波变换对节点振动加速度信号进行模态分析,并与柱波导理论时频曲线对比。通过在不同腐蚀程度高强钢丝上进行导波传播实验,分析了腐蚀损伤对导波模态特征的影响,并根据导波模态的频率分布特征构建评估指标,进行腐蚀评估。结果表明：有限元节点不同方向振动所包含的模态存在差异,数值计算结果与理论值吻合较好。高阶纵向导波频率更高,能量衰减更快,波形在反射过程中迅速消失。随腐蚀程度增加,高频高阶导波衰减严重,导波模态逐渐向低频低阶转移。基于导波模态特征的评估指标随腐蚀程度的增加单调上升,理想情况下,腐蚀率在7.6%以内的高强钢丝腐蚀损伤均可被有效识别。可见小波变换能够有效提取导波模态特征,基于导波模态特征构建评估指标可有效识别腐蚀损伤。

Corrosion evaluation of high strength steel wire based on guided wave modal analysis

In order to improve the accuracy and reliability of acoustic emission monitoring in bridge cable, wavelet transform was used to analyze guided wave modes, the corrosion evaluation method of steel wires based on guided wave modal characteristics was proposed. Firstly, the propagation of multi-mode guided waves in steel wires was simulated by the finite element method and wavelet transform was used to analyze modal characteristics of vibration signals. Finite element results were compared with theoretical time-frequency curves. Then, guided wave propagation experiments were carried out on steel wires with different corrosion degree, and the influence of corrosion on modal characteristics was analyzed. Finally, frequency distribution characteristics of guided wave modes were used to construct evaluation indexes for corrosion evaluation. The results show that there are different modes for vibration in different directions at the finite element node. Numerical results are in good agreement with theoretical values. Higher-order longitudinal guide waves have higher frequency and faster energy attenuation. With the increase of corrosion degree, the attenuation of high-frequency and high-order guided waves is gradually serious, and guided waves mode are gradually transferred to low-frequency and low-order. The evaluation index based on guided wave modal characteristics monotonically increases with the increase of corrosion degree. Ideally, corrosion damage with corrosion rate less than 7.6% can be effectively identified.It is concluded that wavelet transform can effectively extract guided wave modal features, and the evaluation index based on modal features can effectively identify corrosion damage