The maximum magnetic flux leakage from a crack is obtained when the direction of the magnetic flux is orthogonal to the longitudinal direction of the crack. In magnetic-particle testing with a yoke method, since we usually cannot predict the direction of the crack to be detected, it is necessary to perform the testing at least two times by changing the direction of magnetization. In a rotating magnetic field type magnetizer using three-pole coils (three-phase alternating current), omnidirectional crack can be detected by a single testing. However, directions of the weak magnetic flux density appear at positions far from the center of the magnetizer, and the rotating magnetic field becomes no homogeneous distribution. In this research, it was considered to split each magnetic pole in the magnetizer to generate the uniform rotating magnetic field. The distribution of the rotating magnetic flux density was evaluated with a finite element method analysis, and an optimal disposition angle of the split coil was discussed. In addition, a multi coil magnetizer was developed to generate the uniform rotating magnetic field more widely.

� ��Katsuhiro FUKUOKA (Mem.), Ippei KAWAGOE Because magnetic particle testing (MT) can detect microcracks by a simplified method, it is applied in non-destructive inspections of ferromagnetic materials in various industrial fields. Recently, establishing a technology that quantitatively evaluates crack shapes as well as detects cracks with high-precision has become an important topic in the non-destructive inspection. We consider developing such a quantitative evaluation technique that employs magnetic particle pattern of a crack in MT. In this research, the process of magnetic particle adherence to a crack was observed with a high-speed video camera and the change in the magnetic particle amount was evaluated at each instant. In addition, the technique for evaluating small magnetic flux leakage (MFL) density accurately was discussed with the measurement and the numerical analysis. From these results, the relationship between the MFL density and the magnetic particle amount was evaluated.