近表面缺陷的超声TOFDR和TOFDW检测

针对超声TOFD方法存在近表面检测盲区问题,提出了基于二次波的综合超声衍射反射回波方法(TOFDR)和缺陷W衍射反射方法(TOFDW)的检测模式。分析了TOFDR和TOFDW检测方法的超声传播特性,阐明了2种方法的检测原理,研究了它们的近表面理论检测能力。对于TOFDR检测方法,缺陷越近表面,D扫图像分辨特征越好。对于TOFDW检测方法,总体分辨能力大于TOFDR方法,但对于特别浅的近表面缺陷,声波难以识别,而将这2种检测方法综合应用,通过调整检测工艺参数可对近表面缺陷进行识别。通过对人工缺陷试样的检测,研究了综合2种方法结合条件的新检测模式的信号图像特征以及检测灵敏度,2种检测方法结合产生的D扫图像能很好的发现埋藏深度为1 mm的缺陷。

Ultrasonic TOFDR and TOFDW for Near Surface Defect Detection

Aiming at the problem of near surface dead zones in ultrasonic TOFD technique, a new testing mode combining ultrasound diffraction reflection echo method （TOFDR） with the three-fold reflected wave （TOFDW） based on secondary longitudinal wave was put forward. The ultrasonic transmission characteristics of TOFDR and TOFDW were analyzed, their detection principles were illustrated, and their detection results for near surface defect were studied. As for TOFDR, the closer the defects to the surface, the better the detecting results. The detecting capacity of TOFDW is better than that of TOFDR, but this method cannot detect the defects closest to the surface. The new testing mode combining these two methods can detect the defects closest to the surface. The new testing mode was used to detect specimens with artificial defects. The imaging characteristics and detecting sensitivity of this new testing mode was studied. The results show that this new testing mode can effectively detect the defects 1 mm below the surface.