针对超声衍射时差法（Time of flight diffraction，TOFD）存在的近表面盲区问题，基于波型转换理论，提出盲区抑制方法。根据TOFD平行扫查时变型波变化规律，明确裂纹深度d与变型波声程最短时缺陷偏心距△S之间的理论关系。考虑到△S读数误差较大的问题，引入直通波与变型波声程最短位置点间的垂直距离d'，从而实现近表面盲区抑制。选用中心频率10 MHz、折射角度70°；以及探头中心间距（Probe center spacing，PCS）17.00 mm的TOFD探头对，通过模拟与试验的方法对厚度35.00 mm碳钢试块中深度1.00~6.00 mm的底面开口槽进行平行扫査和定位检测。结果表明，该方法可将近表面盲区抑制到1.00 mm，深度2.00 mm底面开口槽定位误差最大，误差绝对值为0.24 mm。
丁宁
,
金士杰
,
张东辉
,
康达
,
张树潇
,
雷明凯
,
刘丽丽
,
林莉
. 基于波型转换的TOFD近表面盲区抑制研究[J]. 机械工程学报, 2017
, 53(16)
: 120
-124
.
DOI: 10.3901/JME.2017.16.120
To reduce the near surface dead zone in time of flight diffraction(TOFD), one method is proposed based on mode-converted theory. According to the variation of mode-converted waves in parallel scanning of TOFD, the theoretical relationship between flaw depth d and offset distance △S is confirmed. Considering the reading error of △S, the vertical distance d' between lateral wave and mode-converted wave having a shortest ultrasonic path is introduced to achieve the reduction of near surface dead zone. Selecting a pair of TOFD probes with 10 MHz center frequency, 70° refraction angle and 17.00 mm Probe center spacing(PCS), surface breaking notches at bottom, whose depths are from 1.00 mm to 6.00 mm in carbon steel, are inspected in parallel way and located by simulation and experiment. The result shows that near surface dead zone can be suppressed to 1.00 mm, and the biggest absolute located error is 0.24 mm when the notch depth is 2.00 mm.
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