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利用有限元法模拟了金属板材中激光激发的声表面波经过缺陷位置时发生散射的瞬态过程,采用线状激光源作为超声导波的激发源.针对三种不同深度的表面缺陷以及三种亚表面缺陷的模型进行了对比计算,结果显示缺陷的深度及位置对声表面波的时域特征存在显著的影响.表面缺陷深度越深将产生较大幅度的表面反射回波,亚表面缺陷的影响将取决于缺陷上顶面距离板材上表面的距离.因此,数值模拟结果表明通过分析激光产生的表面波形可以判定近表面缺陷的尺寸和所处的位置.
The finite element method was used to simulate the transient process of laser-induced surface acoustic wave scattering when passing through the defect position, and the linear laser source was used as the excitation source of ultrasonic guided wave.According to three kinds of surface defects with different depths and three kinds Sub-surface defect model were compared and calculated, the results show that the depth and location of defects on the SAW time domain characteristics have a significant impact.Deep surface defects will have a greater depth of the surface echo, sub-surface defects The effect will depend on the distance of the upper surface of the defect from the upper surface of the plate.Thus, the numerical simulation results show that by analyzing the surface waveforms generated by the laser, the size and the location of the near surface defects can be determined.