为了研究线源脉冲激光激发的超声波在带涂层金属板表面裂纹检测方面的应用, 采用有限元模拟的方法, 分别建立了含有裂纹的带镍涂层和不带镍涂层金属板模型, 并模拟出激光激发出的瑞利波以及瑞利波的传播过程。通过对接收点处的波形进行理论分析, 得出了涂层厚度、裂纹深度与瑞利波时频域信号的关系。结果表明,瑞利波波速随着涂层厚度h的不同而不断变化; 当表面存在裂纹时, 不带涂层模型的反射瑞利波与剪切瑞利波的到达时间差Δt与裂纹深度hc成线性关系, 带涂层模型的Δt与hc以涂层厚度为分界点成分段线性关系。此研究结果为实际测量带涂层金属板的表面裂纹深度提供了参考。

In order to study the application of ultrasonic wave induced by line-source pulse laser on surface crack detection of the coated metal plate, finite element simulation method was used to establish the model of metal plate with cracks with and without nickel coating. Rayleigh wave excited by laser and the propagation process of Rayleigh wave were simulated. Through theoretical analysis of waveform at the receiving point, the relationship of coating thickness, crack depth and Rayleigh wave time-frequency domain signal was obtained. The numerical results show that Rayleigh wave velocity varies with the thickness of coating thickness h. When there are cracks on the surface, the arriving time difference Δt between reflection Rayleigh wave and shear Rayleigh wave of the model without coating has linear relationship with crack depth hc. Δt of the model with coating has linear relationship with crack depth hc at different segmentations. The numerical results provide reference for actual measurement of the surface crack depth of metal sheets with coating.