An Ultrasonic TOFD Defect Detection Technique Using Line-focusing Probes

• 1、State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001

Abstract：Defect signals collected using conventional ultrasonic TOFD (time of flight diffraction) method is often weak in amplitude because of the low energy of the defect diffracted sound field. In order to improve testing sensitivity, a new ultrasonic TOFD defect detection method using line-focusing probes is put forward. Based on geometrical acoustics theory, the line focusing wedge is designed according to the desired refraction angle of the spindle acoustic ray and the focus depth. Through the testing of an artificial defects contained block that made of aluminum alloy, the testing sensitivity of the proposed method is studied. Through the testing of several friction stir welding test pieces that made of aluminum alloy, the advantage of the proposed method is verified. The results show that the testing sensitivity of the line-focusing ultrasound TOFD method is higher than the conventional method. In the collected D-scan image using proposed method, the contrast between the defect and background image is sharp, and the image edge can keep well. The new method has the advantages in improving the defect resolution, increasing the defect detection rate and reducing the residual error rate, which contribute to a great application value.

Keywords： welding process and equipment ultrasonic TOFD defect detection testing sensitivity