Conventional TOFD technique uses the longitudinal diffracted wave to locate and size the flaw. However, owing to the superposition of the lateral wave and the deviation between the welding and the axis of main acoustic beam, there is an insensitive region near the surface, resulting in missing inspection. In order to solve the problem above, an analytic method named as S-wave TOFD is presented based on shear wave diffracted from defect tips. The characteristic of sound propagation in S-wave TOFD method, the detection principle and the method of quantitative calculation are illustrated in detail. Through the experiments of artificial defects detecting, the result shows that the S-wave TOFD method can significantly improve the detection sensitivity and precision for the shallow buried defects for that it can effectively identify the near surface defect with buried depth of about 2 mm and the calculated error of the height and buried depth of defect is less than ± 1 mm.%TOFD检测是通过分析衍射纵波实现缺陷的检测,但由于直通波的"拖尾"和近表面焊缝偏离探头主声束轴等原因,在被检测焊缝表面一定深度范围内形成了检测盲区,导致近表面缺陷检测灵敏度低.针对常规纵波超声TOFD法存在近表面检测盲区的问题,通过分析纵波和横波在试件内的传播特性,提出一种基于衍射横波的TOFD检测新方法,并阐述了该方法缺陷量化分析的方法.利用加工有人工缺陷的试件进行验证,结果表明:衍射横波TOFD法能够有效识别埋深为2 mm的近表面缺陷,缺陷的埋藏深度和高度检测误差均小于±1 mm,提高了TOFD对近表面缺陷的检测灵敏度和精度.
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