Kimoto K, Ueno S, Hirose S
Department of Mechanical and Environmental Informatics, Graduate School of Information Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, Japan.
Ultrasonics. 2006 Dec;45(1-4):152-64. doi: 10.1016/j.ultras.2006.08.006. Epub 2006 Sep 1.
This paper presents calibration-free crack sizing techniques based on ultrasonic imaging. The techniques are intended for 2D (line) surface-breaking cracks with the size of the incident wavelength or greater. The probing wave mode is the anti-plane shear wave (SH-wave). Two methods are employed for the ultrasonic imaging. One is a synthetic aperture focusing technique (SAFT) and the other is a computed time-reversal focusing technique (TRFT). In this paper, those methods are modified so that crack tips are located directly from measured A-scope waveforms without any calibration experiments. The results are shown as a peak in the ultrasonic image created by the respective methods. Reasonable accuracies of the proposed techniques are demonstrated first for the sizing of slits with known depths. The techniques are applied thereafter to the sizing of fatigue cracks. Since fatigue cracks may not be open without an external load, ultrasonic measurements are taken with and without external loads. The results of the imaging show that the depths of open cracks can be estimated accurately. It is also shown that crack opening (closing) behavior can be deduced by observing appearance (disappearance) of the peak in the images indicating the crack tip.
本文介绍了基于超声成像的免校准裂纹尺寸测量技术。这些技术适用于尺寸为入射波长或更大的二维（线状）表面开口裂纹。探测波模式为反平面剪切波（SH波）。采用两种方法进行超声成像。一种是合成孔径聚焦技术（SAFT），另一种是计算时间反转聚焦技术（TRFT）。在本文中，对这些方法进行了改进，以便直接从测量的A扫描波形确定裂纹尖端位置，而无需任何校准实验。结果以各自方法创建的超声图像中的峰值表示。首先针对已知深度的狭缝尺寸测量，证明了所提技术具有合理的精度。此后，将这些技术应用于疲劳裂纹的尺寸测量。由于疲劳裂纹在无外部载荷时可能不会张开，因此在有和无外部载荷的情况下进行超声测量。成像结果表明，可以准确估计开口裂纹的深度。还表明，通过观察指示裂纹尖端的图像中峰值的出现（消失）情况，可以推断裂纹的张开（闭合）行为。
