激光声表面波检测材料表面微缺陷数值研究

采用平面应变的有限元模型数值模拟了激光线源辐照铝板表面激发出的声表面波的时域波形，比较了不同接收位置得到的位移信号的模式组成；同时研究了激光线源辐照区域近场存在表面微缺陷时产生的时域波形。数值结果说明：当激光源靠近表面微缺陷时激发出的声表面波模式中掠面纵波与瑞利波的位移信号均由典型的单极性迅速转变为显著的双极性特征，且瑞利波的峰-峰值将增加两倍左右，位移信号强度的显著变化为利用扫描激光检测材料表面微缺陷提供了理论依据。

Numerical analysis of inspection of micro-surface crack by laser generated surface acoustic waves

Plane strain finite element method has been employed in this paper to simulate the generation of the surface acoustic wave by the line focused pulsed laser irradiation on the aluminates plate. The temporal displacemental signals on the plate surface have been calculated and compared with the waveforms obtained in the numerical model with a surface micro cracks introduced in the near field of the laser source. The numerical results demonstrate that the monopolar displacement signals of surface skimming longitudinal wave (sP) and Rayleigh wave (R) become the obvious bipolar signals, as there exists a surface micro defect in the immediate vicinity of the laser line source; in addition, the peak-to-peak value of the bipolar Rayleigh wave signal is enhanced about two times compared with the initial monopolar one. This dramatic transition can be the basis for the scanning laser line source inspection technique for shallow cracks.