基于交流电磁场的水下结构物裂纹尺寸及剖面高精度评估方法

High-precision evaluation method of crack dimension and profile for underwater structures based on ACFM technique

传统交流电磁场检测(ACFM)技术依靠特征信号Bz峰值间距和Bx波谷评估裂纹尺寸,未考虑裂纹长度和深度对特征信号交互影响,造成裂纹尺寸及剖面评估精度不足。针对这些问题,建立海水环境ACFM三维仿真模型,深入分析裂纹长度和深度对特征信号的影响规律,在此基础上提出两步插值裂纹尺寸评估算法和分割插值裂纹剖面重构算法,搭建水下ACFM试验系统并开展不同尺寸裂纹检测试验。结果表明裂纹深度变化对特征信号Bz峰谷间距不产生影响,长度小于30 mm的裂纹长度对特征信号Bx波谷影响较大;基于特征信号Bx和Bz两步插值算法可实现裂纹长度和深度的高精度评估,长度和深度评估最大误差分别为3.0%和7.5%;基于特征信号Bx分割插值算法可实现裂纹剖面高精度可视化重构,重构最大误差为5.7%。

The conventional alternating current field measurement(ACFM)technique is used to evaluate the crack dimension by the distance between Bz peaks and the Bx trough.The interaction of the crack length and depth on the characteristic signals has not been considered in this method,which results in low accuracy evaluation results on the crack dimension and profile.In the light of the problems above,the 3D simulation model of ACFM was set up in the underwater environment.The influence laws of the crack length and depth on the characteristic signals were analyzed.On this basis,the two-step interpolation crack dimension evaluation algorithm and the segmentation interpolation crack profile reconstruction algorithm were presented to achieve high-precision evaluations on the crack dimension and profile.The underwater ACFM testing system was set up and the crack detection experiments were 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 significantly affects the trough of the Bx.The two-step interpolation algorithm based on the Bx and Bz can achieve high-precision evaluations on 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,and the maximum error of the reconstructed profile is 5.7%.