In magnetic flux leakage (MFL) testing, the scraggly surface of the objects actually consists of “concave” and “bump” defects, however, MFL inspection mechanism is only explained based on magnetic field leakage in the vicinity of the “concave” defects. In order to richen the MFL theory and improve the detection signal analysis, 3D magnetic flux leakage for three typical shapes of “concave” and “bump” defects (i.e., the conical, spherical and rectangular defects) are investigated by building magnetic dipole models. It was found that “bump” defects generate a total different 3D MFL distribution from the “concave” defects, including x, y and z components of the MFL. Besides, numerical simulations by finite element method are conducted to validate the magnetic dipole models.
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