采用有限元法研究了激光激发的声表面波与表面微缺陷的作用机理,在位移信号中选取出能定量表征缺陷深度的特征量(振荡信号),分析了缺陷深度和宽度对振荡信号的影响。根据表面波与缺陷后沿作用的位移场,解释了振荡信号的来源。数值结果表明,振荡信号(特征点A、B)来源于透射表面波在缺陷后沿所产生的振荡,同一温度下特征点A、B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。根据特征点A、B的到达时间差与缺陷深度之间的关系,结合表面波声速与温度之间的关系,实现了不同温度下缺陷深度的定量计算。

The mechanism of the laser-induced surface acoustic wave interacting with surface-breaking defects is studied by using the finite element method. The characteristic quantity (oscillation signal) quantifying defect depth is selected from the displacement signals and the influences of the defect depth and the width on the oscillation signals are further analyzed. The source of oscillation signals is clarified according to the displacement field occurred in the interaction between the surface acoustic wave and the rear edge of defects. The numerical results show that the oscillation signal with feature points of A and B originates from the oscillation induced at the rear edge of defects by the transmitted surface wave. At the same temperature, the arrival time difference between feature points A and B increases linearly with the defect depth, but is independent of the defect width. According to the relationship between the arrival time difference and the defect depth, the quantitative calculation of defect depths at different temperatures is realized by combining the relationship between the surface wave speed and the temperature.