The lateral wave in ultrasonic TOFD （time of flight diffraction） image has a tail in transit time, which disturbs the detection and evaluation of shallow weld defect. Meanwhile, the lateral wave and back-wall echo t...The lateral wave in ultrasonic TOFD （time of flight diffraction） image has a tail in transit time, which disturbs the detection and evaluation of shallow weld defect. Meanwhile, the lateral wave and back-wall echo that act as background add redundant data in digital image processing. In order to separate defect wave from lateral wave and prepare the way for following image processing, an algorithm of background removal method named as mean-subtraction is developed. Based on this, an improved method by statistic of the energy distribution in the image is proposed. The results show that by choosing proper threshold value according to the axial energy distribution of the image, the background can be removed automatically and the defect section becomes predominant. Meanwhile, diffractive wave of shallow weld defect can be separated from lateral wave effectively.展开更多
Traditional ultrasonic TOFD （ time of flight diffraction） has the major shortcoming of low amplitude of diffractive wave which brings about lack of sensitivity for weld defect detection. Aimed at the technological l...Traditional ultrasonic TOFD （ time of flight diffraction） has the major shortcoming of low amplitude of diffractive wave which brings about lack of sensitivity for weld defect detection. Aimed at the technological limitation, a novel TOFD method is proposed by developing a focusing probe. Through the analyses and calculation of sound field distribution based on geometric acoustics, a cylindrical surface wedge is designed and produced. Artificial defect containing testing piece is made and tested using both traditional and focusing TOFD, and the received signal and image are compared. The result shows that the proposed focusing method can converge the emitted sound energy effectively and improve testing sensitivity greatly. Compared with traditional TOFD tested data, focusing TOFD tested defect wave in A-scan line and defect diffractive stripe in D-scan image can be identified easily.展开更多
基金This project is supported by National High Technique Project (2002AA305402)
文摘The lateral wave in ultrasonic TOFD （time of flight diffraction） image has a tail in transit time, which disturbs the detection and evaluation of shallow weld defect. Meanwhile, the lateral wave and back-wall echo that act as background add redundant data in digital image processing. In order to separate defect wave from lateral wave and prepare the way for following image processing, an algorithm of background removal method named as mean-subtraction is developed. Based on this, an improved method by statistic of the energy distribution in the image is proposed. The results show that by choosing proper threshold value according to the axial energy distribution of the image, the background can be removed automatically and the defect section becomes predominant. Meanwhile, diffractive wave of shallow weld defect can be separated from lateral wave effectively.
基金Supported by the International Cooperation Project （2007DFR70070）, the National Natural Science Foundation of China （51005056, 50775054） and the Research Fund for the Doctoral Program of Higher Education （20102302120045 ）.
文摘Traditional ultrasonic TOFD （ time of flight diffraction） has the major shortcoming of low amplitude of diffractive wave which brings about lack of sensitivity for weld defect detection. Aimed at the technological limitation, a novel TOFD method is proposed by developing a focusing probe. Through the analyses and calculation of sound field distribution based on geometric acoustics, a cylindrical surface wedge is designed and produced. Artificial defect containing testing piece is made and tested using both traditional and focusing TOFD, and the received signal and image are compared. The result shows that the proposed focusing method can converge the emitted sound energy effectively and improve testing sensitivity greatly. Compared with traditional TOFD tested data, focusing TOFD tested defect wave in A-scan line and defect diffractive stripe in D-scan image can be identified easily.
