Numerical Simulation And Image Processing Of Ultrasonic Phased Array Detection For Planar Defects In T-joint

T-joint has been widely used in engineering field,Nondestructive Testing(NDT)technology is an important method to ensure the production quality and service safety of T-joint welded components.Conventional A-type ultrasound has some problems in detecting T-joint welding quality,such as low detection efficiency,difficulty in identifying defects and poor recording performance.In this paper,ultrasonic phased array is used to detect the planar defects in T-joint.The influence of transducer parameters on phased array sound field is studied by numerical simulation.On this basis,the process of phased array beam interacting with planar defects in T-joint is simulated,and the test specimen containing artificial defects is measured.Combined with digital image processing technology,the method of defects recognition in phased array detection image is studied,and the quantitative information of defects is extracted.The influence of transducer parameters on phased array sound field is studied.Firstly,a two-dimensional model of phased array sound field simulation is established,and simulation parameters such as incentive load,mesh size and computation time step are determined,then the validity of the numerical simulation model is verified by studying the interaction process between phased array acoustic beam and hole defects.On this basis,the influence of array number,array frequency,array center distance and array width on ultrasonic phased array sound field is studied.The results show that the transducer parameters have great influence on the focus size and sound pressure of phased array sound field.In the actual detection,appropriate transducer parameters should be selected according to the characteristics of the parts to be tested,the simulation results provide theoretical instructions for the optimization of detection process.The aluminum alloy specimen with artificial defects is designed and manufactured,and the artificial defects are similar to planar defects in T-joint.According to the size of the specimen and the sound field simulation results of the transducer,the transducer parameters used in the test are determined.Then the numerical simulation model is established,and the interaction process of ultrasonic phased array beam with planar defects in T-joint is simulated,as a guidance to determine the detection process.The results show that: by controlling the focusing effect of phased array acoustic beam,the accessibility of acoustic beam and the angle between acoustic beam and planar defects,defects in T-joint specimen can be effectively detected,such as lack of penetration of weld root,toe crack and groove not fused.For the noise problem in ultrasonic phased array image,image denoising method based on wavelet threshold processing is used to denoise the detected image,and the disadvantages of the traditional threshold and threshold function are improved.The results show that the improved threshold and threshold function improve the quality and signal-to-noise ratio of the image after denoising compared with the traditional wavelet threshold denoising method.For the problem of fuzzy defects boundary in ultrasonic phased array image,the image after denoising is segmented by edge detection method,in order to make edge detection have good self-adaptability,the traditional Canny edge detection operator is improved.The quantitative defects information is extracted from the image segmentation region and compared with the actual defects information.The results show that the quantitative information such as defects tilt angle,defects length and defects depth is basically consistent with the actual defects information.The extracted quantitative information of defects can be used to analyze and evaluate the damage degree of planar defects in T-joint.