Research On Lamb Wave Imaging Technology For Steel Plate Testing Based On Focusing And Time Reversal Method

Steel plate is widely used in military, aerospace, automotive, chemical and other fields Due to its inevitable corrosion, crack and other defects in the process of manufacturing and using. The production quality and service life of the metal plate has an important influence on the safety operation of the equipment.According to the actual needs of the rapid detection and visualization of large area steel plate,based on time reversal imaging principle and the ultrasonic phased array focusing deflection technique, a method for ultrasonic imaging of steel plate Lamb wave based on focusing is studied. On this basis, through the MATLAB signal processing and COMSOL finite element simulation, 2D imaging of the defect of steel plate has been realized, a new method is provided for the visual inspection of metal plate defects. The main contents are as follows:(1) Introduced the ultrasonic detection theory,ultrasonic phased array detection theory and time reversal theory. A new Lamb wave testing imaging theory is proposed: Linear array focusing-time reversal(LAFTR) Lamb wave testing imaging theory. Based on this theory,derived the theoretical model, and gives the technical steps for steel plate in the flaw detection.(2) Based on the LAFTR ultrasound imaging detection method, the relevant parameters of linear array are optimized design by using MATLAB program, such as acoustic source, focusing mode, element number and so on. Then, select optimal array parameters under the experimental conditions, using COMSOL finite element simulation software to simulate and calculate the important factors which can influence the focusing effect and the imaging quality, at the same time, through physical experiments to verify the simulation results(3) Studied some signal processing methods such as wavelet denoising of defect signals and time reversal and so on. For different defect forms such as single defect、 eccentric defects and double defects, using LAFTR ultrasonic detection system to analysis the imaging quality of the steel plate defect. The results show that the lateral resolution of the imaging system is 10 mm. The vertical resolution can be determined by different excitation duration and velocity.