Ultrasonic TOFD Testing Model for Crack Measurement in Thick Wall Weldment
Ultrasonic TOFD Testing Model for Crack Measurement in Thick Wall Weldment
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发表时间：
2008
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通讯作者：
T. Gang;D. Chi
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作者：
T. Gang;D. Chi
本文研究了利用超声飞行时间绕射(TOFD)B扫描模式进行裂纹检测的正反问题。对于正问题，描述了超声束的传播行为，并用系统效率因子表征了检测系统的机电元件。在此基础上，利用Kirchhoff近似理论建立了裂纹模拟模型。利用该模型对超声TOFD A扫描线进行了仿真，并合成了B扫描前景图像。对于反问题，为了获得焊缝裂纹的横向位置和埋深信息，研究了B扫描图像重建。根据测试过程中探头与裂纹尖端的动态关系，提出了合成孔径聚焦(SAF)图像增强算法。结果表明，仿真数据与实测值吻合较好，所提出的SAF算法可以通过仿真模型进行验证。经过SAF处理后，利用声定向差、频率较低的换能器可获得高分辨率的图像，且测量速度快、精度高。
In this paper, both forward and inverse problem about crack testing by using ultrasonic Time of Flight Diffraction (TOFD) B-scan mode are st udied. For forward problem, the propagation behavior of ultrasonic beam is described, and t he electrical and electromechanical elements of inspective system are cha racterized by system efficiency factor. Based on this, crack simulating model is established by employing Kirchhoff approximation theory. By using the model, ultrasonic TOFD A-scan line is simulated and B-scan foreground image is synthesized. For inverse problem, in order to obtain lateral locatio n and buried depth information of crack in the weld, B-scan image reconst ruction is studied. According to the dynamic relation between the probes and crack tip in th e course of testing, synthetic aperture focusing (SAF) algorithm for image enhancement is developed. The results show that the simulated dada are in better accordance with the measured ones and the presented SAF algorithm can be validated by the simulating model. Proces sed by SAF, high resolution image can be obtained by using transducers with poor sound directivi ty and lower frequency, and measurement can be carried out rapidly with high accuracy.