Huang Yuantian, Turner Joseph A, Song Yongfeng, Ni Peijun, Li Xiongbing
School of Traffic and Transportation Engineering, Central South University, Changsha 410075, China.
Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
Ultrasonics. 2019 Sep;98:20-27. doi: 10.1016/j.ultras.2019.05.010. Epub 2019 May 28.
Diffuse ultrasonic backscatter measurements have been shown to enhance the detection capability of sub-wavelength flaws when combined with extreme value statistics. However, for a normal-incidence immersion measurement, a "dead zone" created by the ring-down of the front-wall echo will hide near-surface flaws. In this article, a pulse-echo transverse wave backscatter measurement is used to detect near-surface flaws under high gain. The approach is validated using a magnesium specimen with side-drilled holes. The confidence bounds of the grain noise from this specimen are given by a transverse-to-transverse scattering model, which takes the grain size distribution and the hexagonal crystal symmetry into account. The upper bound is then treated as a time-dependent threshold for the C-scan. Experiments show that the developed method has good performance for detecting sub-wavelength, near-surface flaws, and can suppress both missed detections and false positives.
已表明，将漫射超声背散射测量与极值统计相结合时，可提高亚波长缺陷的检测能力。然而，对于垂直入射浸入式测量，前壁回波的衰减所产生的“盲区”会掩盖近表面缺陷。在本文中，采用脉冲回波横波背散射测量来在高增益下检测近表面缺陷。该方法通过一个带有侧钻孔的镁试样进行了验证。由横向到横向散射模型给出了该试样晶粒噪声的置信界限，该模型考虑了晶粒尺寸分布和六方晶体对称性。然后将上限作为C扫描的时间相关阈值。实验表明，所开发的方法在检测亚波长近表面缺陷方面具有良好性能，并且可以抑制漏检和误报。
