ABSTRACT
This paper develops an integrative scheme combining new image acquisition, filtering and enhancement methods specified for orthogonal weld defect detection based on magneto-optical imaging (MOI) technique. For image acquisition, a controllable magnetic system enabling rotation of magnetic angles is invented to accurately collect MO images. Multiple images are acquired, yet few are utilized for further processing in the conventional method based on human subjective preferences, bearing chances that images containing defects are discarded. Therefore, we turn to an automated-filtering system to scrutinize MO images and filter effective images through Bhattacharyya coefficient screening method. This not only elevates efficiency and objectivity but also eliminates missed inspection. For image enhancement, normalization method is used to balance the image intensity, followed by image fusion and edge extraction by a two-dimensional gradient method. Our pre- and post-processing approaches significantly improve accuracy in defect recognition and precision in MO images.
ABSTRACT
This paper examines the characteristics of magneto-optical images of weld defects under alternating magnetic field excitation. Weld defects such as non-penetration, surface cracks and sub-surface cracks were detected by a magneto-optical imaging method. Magneto-optical imaging nondestructive testing experiments under alternating magnetic field excitation were carried out to detect the weld defects. Image processing methods which include contrast enhancement of original image, fused image, contrast enhancement of fused image were applied to extract the defect information of the magneto-optical images. What's more, the difference among the magneto-optical images of weld defects was obtained by contrast analysis. Experimental results show that non-penetration welding images possess significant differences in brightness and darkness, and this difference in cracks is smaller than non-penetrating ones. Under the same excitation conditions, the leakage flux of welds with non-penetration is stronger than that of weld cracks.
