Research On Double Cross-hole Lamb Wave Tomography Nondestructive Testing Algorithm

Ultrasonic Lamb wave tomography nondestructive testing technology is a more advanced sheet structure defect detection technology, and the detection process is no excessive demands on the operator, it’s convenient, and has a unique advantage in the detection of large sheet, so that it has been widely used in aerospace research, rail transportation and other fields. However, due to the dispersion characteristics of Lamb waves, resulting in the detection process of signal processing complex, data extraction difficult and Lamb wave testing data collection difficulties, limiting its application in the production practice, in order to simplify the process of data acquisition and image reconstruction, the thesis research double cross-hole pitch probe by the structural arrangement of the Lamb wave nondestructive testing using filtered back projection reconstruction algorithm for reconstruction imaging methods have been studied mainly includes the following aspects:Lamb wave dispersion theory, the propagation characteristics and computed tomography in the board’s theory is based on the application of ultrasonic Lamb wave tomography nondestructive testing, in the thesis we describes the basic theory, drawn the frequency dispersion curves of Lamb wave propagation in aluminum, introduced by the process of implementation and specific image reconstruction algorithm.Through three data models of no defects, defects in the center and defects shifted to the positive X axis, we get double cross-hole projection data through calculation as well as modeling and simulation by numerical analysis software of abaqus, then processing the simulation data in the way of empirical mode decomposition, Hilbert transform and extract data.By the rearrangement program about how the double cross-hole projection data can be rearranged to parallel projection, we obtained the rearranged results of the calculation and simulation data.We use the data before and after rearrangement to reconstruct image by algebraic reconstruction technique, and verify the feasibility and correctness of rearrangement program by the reconstruction results; using the rearranged calculation and simulation data to reconstruct image by filtered backprojection reconstruction algorithm, and obtained the defect information consistent with the model from the reconstruction results.The results showe that using the rearrangement program proposed in this thesis to rearrange the three groups simulated double cross-hole projection data with different defect information to parallel beam projection data, and reconstruct image through filtered back projection reconstruction algorithm of different filtering methods for each set of data, although the data fluctuations, and not ideal, still be able to obtain defect information from the reconstruction results, achieved certain results.