Research on High-Precision Evaluation of Crack Dimensions and Profiles Methods for Underwater Structure Based on ACFM Technique

Abstract

AbstractThe conventional alternating current field measurement (ACFM) technique evaluates the crack dimensions by the distance between Bz peaks and the Bx trough. The interaction of the crack length and depth on the characteristic signals is not considered before, which results in the low accuracy evaluation results of crack dimensions and profiles. In the light of the problems above, the 3D simulation model of ACFM is set up in the underwater environment. The influence rules of the crack length and depth on the characteristic signals are analyzed. On this basis, the two-step interpolation crack dimensions evaluation algorithm and the segmentation interpolation crack profiles reconstruction algorithm are presented to achieve high-precision evaluation of crack dimensions and profiles. The underwater ACFM testing system is set up and the crack detection experiments are carried out. The results show that the crack depth does not affect the distance between the peak and trough of the Bz. The crack length that is shorter than 30 mm affects the trough of the Bx. The two-step interpolation algorithm based on the Bx and Bz can achieve high-precision evaluation of the crack length and depth. The maximum errors of the evaluated length and depth are 3.0 and 7.5% respectively. The segmentation interpolation algorithm based on the Bx can achieve high-precision visual reconstruction of the crack profile. The maximum error of the reconstructed profile is 5.7%.