| Cracks are quite harmful to the safety operation of the pressure vessels. It is very important to test the crack quantitatively in high-efficiency and accuracy. Ultrasonic phased array technology has the potential of rapid imaging and sizing of the cracks, and the accuracy is superior than conventional ultrasound testing technology. However, it is quite time-consuming and expensive to design and fabricate the specimens. And the high cost of a phased array equipment is also an adverse factor for carrying out the experimental research. Through the simulation of ultrasonic phased array testing, it can not only provide the simplified testing condition, but also help to understand about the propagation rule and the interaction process with defects of sound waves more clearly. The simulation results is quite helpful for the experimental design, the optimization of parameters and the judgment of defect image, and so on. The simulation can provide a great convenience for scientific research and practical test.In this study, the numerical model of phased array ultrasonic testing using the finite difference method(FDM) was set up. according to the one-dimensional phased array probe. The sizing of crack was carried out, and the influence of defect status and focusing parameters on the testing result were analyzed. The main results are as follows:(1) The calculation formula of time delay under the different beam control conditions were provided according to the basic principle of ultrasonic phased array technology. ZETEC LM-5MHz linear array longitudinal wave probe (the total number of elements is64, exciting32elements each time) was selected in the numerical model of ultrasonic phased array testing. The echo signal of the side drill hole which was5mm in diameter and25mm deep was calculated under the different focusing profiles, and the B scan imaging characteristics were analyzed. The simulation results was contrast, the accuracy of the model calculation result is verified by experiment.(2) The defects were sized using the RATT. and the corresponding calculation formula was given. According to the bottom surface notches in the different states within55mm thick carbon block, the echo signal amplitude-the difference of B scan, and the quantitative accuracy were analyzed to study the effects of defect status(height, width and orientation) on the echo signal. Experiments were carried out for verifying the simulation; The B scan of buried defect (5mm) was carried out by simulation, the result showed that ZETEC LM-5MHZ probe could size of it, and the error was-0.17mm; B scan result of real topography by simulation proved that the ultrasonic phased array could reflect the complexity of crack shape, but due to edge diffraction signal identification more difficult, so it was easy to cause a big error quantitatively.(3) The experimental and simulation B-scans of bottom surface notch were imaged using phased array by steering the beam for an angular range of20°—50°, and it was inferred that operating at30°—40°angles of incidence was optimal for inspection; The influence of the focal position was studied, and the results showed that the echo signal energy could be increased by setting the focal position reasonably, but the influence was very small when the focal position is out of the Near-field. |
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