Proposal of detecting method of plural cracks and their depth by alternating flux leakage testing: 3-D nonlinear eddy current analysis and experiment

Alternating magnetic flux leakage testing is used for the detection of cracks on the surface of steel plates. In this paper, a new technique and precise inspection of how to detect plural cracks and their depth, which are located at very short distances from each other, is proposed. The leakage flux density of the parallel (x) component is used for the distinction of the plural cracks. Moreover, the depth of plural cracks is obtained by changing the exciting frequency and by detecting the perpendicular (z) component of leakage flux. The behavior of leakage flux is examined using three-dimensional edge-based hexahedral finite-element methods and compared with experimentation. The effect of hysteresis on magnetic phenomena is also examined.