Research on Defect Image Enhancement in Ultrasonic TOFD Detection

Abstract

when testing the defect by ultrasonic time of flight diffraction (TOFD), the image signal detected is often reshaped and resulted in inaccuracy of defect measurements because the probe beam has a limited range. This paper proposed an image enhancement method based on synthetic aperture focusing technique (SAFT). A mathematical model of testing image was first established based on the generation process of the image. A method was then designed for detecting defects in near surface blind area based on filtering of through waves. Finally, a synthetic aperture focusing algorithm based on peak capture pretreatment was used to enhance the resolution of the image. By applying the above method to test a crack defect of 15mm, the method was able to accurately judge for crack defect. Also, the measuring accuracy can be improved by 6.4% compared to that of traditional detection method.

Resolution Enhancement in Ultrasonic TOFD Imaging by Combining Sparse Deconvolution and Synthetic Aperture Focusing Technique (Sparse-SAFT)

“…The delay-and-sum (DAS) beamforming algorithms, e.g., synthetic aperture focusing technique (SAFT), are well-known for improving the lateral resolution in ultrasonic imaging [20]. Meanwhile, SAFT is employed to enhance signal-to-noise ratio (SNR) and quantify defects by imaging the ultrasonic signals with low directivity [21][22][23][24][25][26]. Based on the relative position between defect and TOFD probes [27], the lateral resolution of B-scan images is improved to identify defects by using SAFT.…”