激光激发表面波测量表面缺陷深度的数值研究

为了研究声表面波与表面缺陷的作用机理,实现激光超声技术对表面微缺陷定量检测,本文采用有限元法首先分别研究了声表面波与缺陷前沿、缺陷后沿的作用,然后讨论了缺陷宽度的存在对缺陷前沿与声表面波作用的影响,最后通过分析矩形缺陷与声表面波的作用,给出了能定量表征表面缺陷的特征量。研究结果表明:RS波(特征点Q)后的振荡信号(特征点W、E)来源于透射表面波在缺陷后沿所产生的振荡。特征点Q的到达时间随表面缺陷深度或宽度增大都呈现微小的线性增长;特征点W、E的到达时间差随表面缺陷深度的增大呈线性增长,与缺陷宽度的变化无关。最后,根据特征点的到达时间实现了缺陷深度的定量计算。研究结果为表面缺陷的定量检测提供了理论依据。

Numerical study of depth gauging of surface defects using laser-generated surface acoustic waves

In order to realize quantitative detection of the surface-breaking defects by laser ultrasonic technology,the mechanism of the surface acoustic wave and the surface-breaking defects are studied.In this paper,the finite element method is used to study the interaction between the front and rear edge of the surface defects and surface acoustic wave,respectively.Then the influence of the existence of defect width on the front of the defect and the surface acoustic wave is discussed.Finally,the characteristic quantity (oscillation signal) which can quantitatively characterize the surface defect is given by analyzing the rectangular defect interaction with surface acoustic wave.The simulation results show that the oscillation signals (feature points W and E) after RS wave (feature point Q) originate from the oscillations of the transmitted Rayleigh wave at the rear edge of the defect.The arrival time of feature point Q showed a trend of slight increase linearly with the increase of defect depth or width;the arrival time difference of feature points W and E increase linearly with the increase of defect depth,which is independent of the defect width.The depth of the surface defect is quantitatively calculated according to the arrival time of the feature points.The research results will provide a theoretical basis for detecting surface defects.