Research on Near Surface Dead Zone Reduction of TOFD Based on Mode-converted Theory

doi:10.3901/JME.2017.16.120

Abstract

Abstract: 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.

Key words: flaw localization, mode-converted waves, near surface dead zone, time of flight diffraction

CLC Number:

TG156

DING Ning, JIN Shijie, ZHANG Donghui, KANG Da, ZHANG Shuxiao, LEI Mingkai, LIU Lili, LIN Li. Research on Near Surface Dead Zone Reduction of TOFD Based on Mode-converted Theory[J]. Journal of Mechanical Engineering, 2017, 53(16): 120-124.

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