Masserey B, Aebi L, Mazza E
Institute of Mechanical Systems, ETH Zurich, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland.
Ultrasonics. 2006 Dec 22;44 Suppl 1:e957-61. doi: 10.1016/j.ultras.2006.05.059. Epub 2006 Jun 5.
The characterization of surface cracks on complex geometries using surface waves is investigated numerically and experimentally. The specimen geometry is implemented in a finite difference code by approximation of the contour using a Cartesian grid. In the experiments the out-of-plane surface displacement is measured by means of a heterodyne laser interferometer. Good agreement is shown by comparison of the calculated out-of-plane displacement with experimental results for both cracked and non-cracked specimens. The crack depth is measured down to a size of 0.7 times the surface wavelength using a time delay approach. The many Rayleigh pulses propagating after the crack can be separated from the other modes by a filtering procedure based on the surface wave propagation velocity. Only a detailed analysis of the scattering phenomenon using the simulation allows an identification of the transmitted pulse required for crack depth measurement. Application of the method to a specimen with a real fatigue crack shows a systematical error possibly due to the inclined crack profile.
利用表面波对复杂几何形状表面裂纹进行表征的研究，采用了数值模拟和实验方法。通过使用笛卡尔网格对轮廓进行近似，将试样几何形状在有限差分代码中实现。在实验中，利用外差激光干涉仪测量面外表面位移。通过将计算得到的面外位移与裂纹和无裂纹试样的实验结果进行比较，显示出良好的一致性。使用时间延迟方法可测量至表面波长0.7倍大小的裂纹深度。裂纹后传播的许多瑞利脉冲可通过基于表面波传播速度的滤波程序与其他模式分离。只有使用模拟对散射现象进行详细分析，才能识别出裂纹深度测量所需的透射脉冲。将该方法应用于具有实际疲劳裂纹的试样时，显示出可能由于裂纹轮廓倾斜而产生的系统误差。
