Acoustics Signal Characteristic And Quality Evaluation Of Thick Wall Complex Structure Girth Weld

As an important part of engine, the welding quality of the tail pipe should be ensured when jointing it using the electron beam welding. Because of the bad protection the main weld defects that may emerge in the weld are incomplete penetration, nail-shaped flaws, cold laps and so on. In order to ensure the weld quality, nondestructive testing is indispensable. Electron beam girth weld with great depth, small curvature was detected by using the ultrasonic testing method in this paper.The characteristic of sound field in water and the steel was analyzed by using the geometry acoustics theory, and the sound field condition was tested in water in this paper. According to the theoretical analysis, the testing method of approximate sound field characteristic in steel was proposed, and it was applied to the designing of special probe. The effects of the testing parameters on the scan results were analyzed, the testing parameters include incidence angle, water path, gate, gain, sound beam diameter, probe frequency and so on.According to surface condition of the above structure, ultrasonic propagation rule of curved surface was studied, and the match principle of the acoustical lens materials was discussed also. Both the parameters of manufacturing acoustic lens and the methods of obtaining long focal length field were proposed in this paper.Focusing probe was manufactured according to the parameters obtained through theoretical analysis. The sound field condition in water was tested, and the difference of the focusing probe and flat probe was analyzed. The scanning experiments of the simulation flaws and the actual defects were carried out using the long focal length probe. Based on the above researches, both the theoretical analysis and the formula deduction of sound field characteristic in curved surface workpiece were done using sound ray model. And the parameters of sound field for curved surface workpiece were given. In order to enhance the reliability of ultrasonic testing, the effects of incidence deflection angle and the radius of curvature on the scan result were discussed, and the methods that can eliminate the above influences were presented also.According to the analysis of echo signal, denoising and filtering were preceded...