Acquisition Of Ultrasonic TOFD Testing Signals And Defect Identification Method Research

As an accurate and rapid testing method, TOFD has advantages on weld defects testing for thick plate, especially on crack defects. It has been widely concerned. In order to use this method testing weld at working field, it is necessary to develop a system that its structure is convenient and its testing processing is simple. At the same time, the system can recognize defects quickly.According to the theory of TOFD, the ultrasonic testing system with defects recognition process was developed in this paper, which depended on the secondary explored of ultrasonic card, the designed scan equipment and the programmed system software. In order to evaluate the system, a specimen with man-made defects was designed and manufactured to estimate the system.Through the testing experiment, the system had been proved that it was easily operating, smoothly running and accurately defect sizing. A red copper specimen with man-made defects was designed and manufactured for detecting the coarse crystalline materials. After discussed the testing result affected by the distance between probes, the selection of testing surface and the coarse crystal, the optimal TOFD testing parameters for red copper was found, further more the red copper weld was detected by the system and the result was satisfactory.To improve the ability of defects recognition and extracting the weak defects from the testing signals, different D scan images were processed with the EMD method. Both maximal and minimal points were added to each side of the A scanning signal to solve the edge effect during the process. The processing results indicated that the accuracy of defects recognition was improved and near surface 2mm defect could be found for the estimated specimen, and the extracting results on weak defects for red copper were also satisfying.According to the testing results by the developed ultrasonic TOFD testing system in this paper, the image of D scan is clear, the testing processing can be implemented easily,the detecting results are apt to be stored, and the defects in weld can be recognized accurately. At the same time, the recognition ability on defects for coarse crystalline materials can be improved by EMD processing method. So the system is suitable for weld detection and it can be widely used as a pocket-type detecting system.