It meets some difficulties in the case of ultrasonic phased arrays testing for the nickel-based alloy welded joint, since the ultrasound will propagate with curvilinear paths in this kind anisotropic joint. Thus, it is hard to calculate the phased array time delays properly according to the traditional focusing approach, which is based on the assumption that the sound beam will propagate in straight lines. In order to focus the phased arrays beam in this kind anisotropic joint, we provide a modified focusing approach by combining the ray tracing method and the bisectional searching optimization. With the help of this focusing approach, the curved ray path connecting each element position in phased arrays to the expected focus point in weldments can be determined, so that it can be used to calculate the proper time delay and control the beam focusing in the anisotropic weldment. Furthermore, some experimental examinations are carried out to compare the focusing behaviors between the traditional and the modified focusing approach. It shows that the provided focusing approach is more accurate than the traditional method in the case of inspection on the nickel-based alloy weldments.
Hilbert transformation and improved ellipse localization method is applied in ultrasonic transducer array tomography to detect defect of metal plate.By combining the improved ellipse localization method and time-reversal method,the new ultrasonic tomography algorithm employs smooth Hilbert envelope instead of discrete amplitude to reconstruct defect image.An ultrasonic tomography system with six transducers is built to evaluate the effectiveness of the new ultrasonic tomography algorithm.The S0 mode Lamb wave is excited on special condition,and the mode of received signal is identified by Vigner-Wille distribution.The gray value of image area is defined by envelope of the reflected S0 mode Lamb wave signal from defect boundary.Defect image can be reconstructed by summing gray value of all pixels in the image area.The experimentally reconstructed defect image shows that the new tomography algorithm based on Hilbert transformation is efficient for defect detection in metal plate.
Ultrasonic inspections on nickel-based alloy weldments meets some difficulties due to the curvilinear propagating paths will appear in both anisotropic and inhomogeneons welded joints. Thus, it is difficult to determine the exact location of flaws using the traditional ultrasonic testing method which is based on the assumption that the sound beam will propagate in straight lines. In order to overcome this problem, we provide a new model-based inspection approach to locate the flaws in the nickel-based alloy weldments. Furthermore, some experimental examinations are carried out to compare the locating accuracy between the traditional and the modeled-based approach. It shows that the provided model-based inspection method is more accurate than the traditional method in inspection of the nickel-based alloy weldments.
