Novel approach to enhancement of ultrasonic TOFD B-scan image for measurement of weld crack

In order to accurately measure crack in an aluminium weld component, ultrasonic time of flight diffraction (TOFD) B-scan (cross-section scan) image with poor resolution is processed. A preprocessing method combines clutter repression and amplitude processing is proposed. A synthetic aperture focusing technique (SAFT) model is developed and by which the image is reconstructed. This work shows the principle and practical implementation of image enhancement by presenting the algorithms and the resultant images. The results show the time resolution of the image is improved following data acquisition by repressing the clutter and minimising the duration of ultrasonic impulse, and the lateral resolution of the image is enhanced by removing the redundant parabolic image by SAFT. In the ultimately processed image, the buried depth and lateral location of EMD slot tip can be identified within an error of 0.2 mm, and real fatigue crack tip can be measured within an error of 0.5 mm.