为了实现表面V形裂纹的定量检测, 采用有限元的方法研究了激光激发的超声表面波与表面V形裂纹的作用机理, 在反射回波信号中提取了与表面裂纹长度和角度有关的特征信号。分析了裂纹的角度和长度变化对表面波信号的影响, 并对时域信号进行了时频分析, 提出了一种利用反射表面波定量表征表面V形裂纹长度的方法。数值结果表明, 随着裂纹长度的增加, 反射回波的到达时间差也线性增加, 透射表面波对裂纹角度的变化比较敏感。通过反射回波到达的时间差与裂纹长度之间的关系可以快速判断裂纹长度, 并定量表征出相应裂纹的长度。数值结果与理论结果有很高的吻合度, 为表面V形裂纹长度的定量检测提供了一种高效准确的方法。

In order to realize the quantitative detection of surface V-shaped cracks, this paper uses finite element method to study the mechanism of laser-excited ultrasonic surface waves and surface V-shaped cracks. The characteristics related to the length and angle of surface cracks are extracted from the reflected characteristic signal. The influence of the angle and length of the crack on the surface wave signal is analyzed, and the time-frequency analysis of the time-domain signal is carried out, and then a method to quantitatively characterize the length of the surface V-shaped crack using reflected surface wave is proposed. The numerical results show that with the increase of the crack length, the time difference of the reflected echoes also linearly increases, and the transmitted surface wave is more sensitive to the change of the crack angle. Through the relationship between the time difference of the reflected echo arrival and the crack length, the crack length can be quickly judged, and the length of the corresponding crack can be quantitatively characterized. The numerical results are in good agreement with the theoretical results, which provides an efficient and accurate method for the quantitative detection of the length of surface V-shaped cracks.