| Plate structure is one of the most widely applied structures(such as pressurevessel, boilers)in industry today. The structures suffer from load, impact, shake andcorrosion when the structure in motion. Therefore, It may lead to appear damage inthe plate structure and there maybe exist the risk of people s property and life, sothat, it is necessary to develop nondestructive testing method to guarantee the safetyoperation of plate structure, which has great value for industrial application andscientific research. In this thesis, a composite image method has been developed fornon-destructive testing of plate using liner arrays. The main work include:(1) The theory in frequency tuning which could control lamb wave modal isresearched. Find the relationship between lamb wave modal respond and excitationfrequency and locate the single modal frequency. Based on this, the experimentverification has been done and the result shows that, the frequency tuning canachieve a single lamb waves incentive and has a good agreement with thetheoretical analysis.(2) The lamb wave linear array parameters are optimized. The parameterswhich include element type,element number and the pitch etc is researched bynumerical analysis. The optimal parameters are selected in order to make narrowmain lobe and low side lobe which will ensure the quality of detection.(3)A composite image method is developed. The influence of severalapodization methods to main lobe width and low side lobe height are discussed.Using the polarity technology locate the sound source and according to the result,composite different apodization images which products a composite image. Theexperimental result proves that the composite image has higher resolution and lowernoise compared to single image method and the plate defects are well recognized. |
