Abstract
The equivalent magnetic-dipole model is widely used in magnetic flux leakage testing by assuming that some nonzero surface magnetic charges are concentrated in the walls of the breaking flaw, thus the distribution of the magnetic charges in testing structure conceives information about the edge of flaw, which can be utilized to evaluate the size of the breaking flaw by reconstructing the magnetic charges distribution in structures with measured magnetic flux leakage signals. However, the magnetic flux leakage signals above testing structure are usually influenced not only by the magnetic charges concentrating in the flaw walls, but also by which locating in the continuum below the flaw, and the magnetic charges distribution in the continuum layer is totally different from that of flaw layer, which reduces the estimation precision of flaw size. To strip away the magnetic charge influences in continuum layer and achieve high degree of accuracy in reconstructing the magnetic charge distribution around a flaw, increase the estimation precision of flaw size in magnetic flux leakage testing, a two-layer algorithm is proposed in this paper. In this algorithm, a structure with a flaw is divided into two layers according to the difference of the magnetic charge distribution, the layer 1 contains flaw and the layer 2 is the continuum of base materials, the magnetic flux leakage densities above the upper and lower surface of structure are measured. A scheme based on a new initial value regularization method and steepest descent method is proposed to reconstruct the magnetic charges distributing in flaw layer with the measured magnetic flux leakage signals. The simulation result shows that it can reconstruct the magnetic charges in flaw layers precisely; the experimental results show that it can improve the estimation precision of flaw in magnetic flux leakage testing clearly.