Proposal of detecting method of outer side crack by alternating flux leakage testing using 3-D nonlinear FEM

It is known that the detection of cracks on the outer side of steel plate is possible using the dc flux leakage testing. If the examined steel plate is thin, the outer side crack may be detected by alternating flux leakage testing. The merit of the alternating flux leakage testing method is that a cheap coil is used for detecting the leakage flux from the crack. In this paper, the inspection method of outer side crack of the steel plate using the alternating flux leakage testing is proposed. The component |Bx| of the leakage flux parallel to the surface of steel is utilized for detecting the crack. The behavior of leakage flux is examined using a three-dimensional edge-based hexahedral FEM (finite element method). It is shown that the outer side crack can be inspected by detecting the parallel (x-) component of leakage flux