基于变型波的超声TOFD近表面检测新方法

摘要

为了解决传统衍射时差法超声检测技术(TOFD)法对埋藏在近表面的缺陷波无法辨识及近表面区域的测量误差大、深度分辨力差等近表面盲区问题,提出了一种新的近表面检测方法.该方法利用变型波波速较慢的特点,通过计算变型波、直通波及底面反射波,得出了变型波在纵波检测窗口出现的条件,并利用变型波对缺陷进行检测,以减小测量误差并提高检测分辨力,有效地解决了TOFD近表面盲区问题.在10个不同深度的人工缺陷中,对采用基于变型波的检测方法和传统检测方法的实验结果进行了比较和分析,并分别计算了其测量误差及检测分辨力.实验结果表明,该方法能够识别传统方法无法辨识的近表面缺陷,可有效检测到埋藏深度2.0 mm的人工缺陷,同时,该方法具有较高的测量精度和分辨力.%Aiming at the problem of near surface dead zone in ultrasonic time of flight diffraction(TOFD) such as the near surface defect that cannot be distinguished by using conventional methods and low quantitative accuracy and the low resolving power of detection,a new near surface detection method was proposed.The characteristic of distortion wave whose velocity is slow has been used,the condition that transformed wave appears in the windows of lengthways wave detection was obtained by means of calculating transformed wave,through wave and reflected wave of undersurface.To solve the problem of near surface dead zone in ultrasonic TOFD,the defect was detected by transformed wave to reduce the measurement error and to enhance the resolving power of detection.The result of experiment has been compared and analyzed by the measurement error and the resolving power of detection has been calculated by the method based on transformed wave and conventional methods respectively in the ten artificial defects with different buried depth.The results indicate that the method can identify the near surface defect that cannot be distinguished by using conventional methods,and the artificial defect with buried depth of 2.0 mm can be defected effectively.The method has a high quantitative accuracy and a high resolving power.