Affiliations: [a] School of Mechanical Engineering, Beifang University of Nationalities, Yinchuan, Ningxia, China | [b] State Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, Shaanxi, China
Correspondence:
[*]
Corresponding author: Hongmei Li, School of Mechanical Engineering, Beifang University of Nationalities, Yinchuan, China. E-mail:lihongmei@nun.edu.cn
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.
Keywords: Two-layer reconstruction algorithm, flaw evaluation, magnetic charge distribution
