The Optimization Of Ultrasonic Sound Field In Solid Locomotive Axle Flaw Inspection Systems

With the upgrade of railway’s speed, the increasing load of trains and the extension of locomotive maintenance distance, it becomes an important work to detect solid axle defect with the method of ultrasonic testing, which can ensure train traffic safety. Therefore it is an important work to choose suitable ultrasonic transducer in the current solid axle flaw detection, which must meet the accuracy of the test. Ultrasonic sound field visualization simulation is the theoretical foundation of probe selection in axle flaw detection.The transducer sound field’s visualization simulation have been completed in this thesis. We discussed the relationship between ultrasonic field and transducer parameters, and the optimal phased array parameters, which is suitable to detect the solid axle openings crack defects, have been elected. At the same time, the coverage rate of sound field and the defect detection rate are well improved.Numerical analysis method is used for studying acoustic field distribution of ultrasonic transducer in this thesis. The method of combination of point source is used for deriving the single crystal transducer acoustic radiation pressure’s formula. Then the axial sound pressure distribution, axis cross-section sound pressure distribution and directivity characterization have been visualization simulated.After we discussed the single crystal rectangular sound radiation pressure distribution, the beam deflection and beam focusing acoustic radiation pressure formulas of linear phased array sound field have been pushed out by the huygens principle. Then this thesis discussed the relationship between geometric parameters of the linear phased and the sound field’s distribution. The relationships among array elements, array length, array width, array pitch, beam deflection angle and sound field’s distribution have been detailedly discussed. With the purpose of reducing the main lobe width, suppressing width side lobe and cutting down the grating lobe amplitude, the optimal transducer size has been selected, which meet the axle detection.Based on the principle of Fresnel approximate, we established a model, which is used for measuring echo sound pressure of a flat hole defect on axis of a single crystal sound. Then we discussed the relationships among flat bottom hole’s size, sound’s size and echo sound pressure. The flaw detection experiments on standard flat-bottomed hole, which verify the correctness of the theoretical analysis.Finally, with the selected phased array probe, we detected the0.5mm opening cracks located in the axle journal and axle shaft, and the results showed that the design meets the requirement of signal-to-noise ratio greater than12dB. The sound field of the linear phased array had been simulation can greatly reduce the transducer design cycle and axle inspection cost, and the selected probe had higher sound field coverage, higher defect detection rate, and meet the application requirement of axle inspection.