The magnetic field distribution around a crack can be calculated more easily and quickly by using a dipole model than finite element method (FEM). This paper reports the development of numerical analysis software that uses an improved dipole model to analyze the magnetic field around cracks. The preprocessor in this software includes the crack formation software, which can distribute the magnetic charge per unit area, m, on the crack section area. Also the lift-off, measurement area and sensor interval, and magnetization direction can be considered in the preprocessor. Also, the postprocessor presents functions, such as the natural magnetic field distribution and ∂B/∂x, ∂B/∂y, as results. Also, the physical characteristics of the magnetic optical sensor and the Hall sensor are included in the postprocessor, and the magnetic field distribution can be changed to optical intensity and electrical signal distribution. The experiment results, which are obtained by using the magnetic camera on the crack, are compared with analysis results obtained by using the dipole model analysis software.

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Wheels are essential parts of an express train, as they support the train’s weight, but because of the limited time available for testing and repair in the maintenance factory, the 1000 wheels of each high-speed train must be tested within 1 h. Therefore it is essential to develop a new NDT system that is able to (a) detect cracks quickly and (b) provide high crack-detection ability regardless of the state of the materials. In this paper we propose a scan-type magnetic camera to satisfy this need. We use a linearly integrated Hall sensor array (LIHaS) as a magnetic sensor to make high-speed testing possible, and we use a small, yoke-type magnetizer as the magnetic source for the magnetic camera to assure high crack-detection ability. We tested the method by examining the cracks on a sample wheel traveling at 27.5km/h.

The magnetic camera using magnetic lens is proposed to satisfy the demands such as obtaining the distribution of the magnetic flux leakage (DMFL) on the high lift-off, and improving sensitivity. However, DMFL is strongly affected by the magnetization direction. Therefore, the DMFL has low intensity when the crack is not perpendicular to the magnetizing direction. Also, quantitative nondestructive evaluation would be difficult. This paper proposes an improved magnetization method to evaluate a crack quantitatively, regardless of the crack direction. The secondary magnetic source, which is perpendicular to the primary magnetic source, is introduced in the scan type magnetic camera. The intensity of two values of ∂B/∂x (1st differential to the magnetization direction) of the DMFL can be used to evaluate the crack volume. The experimental and the numerical analysis results are considered to verify this phenomenon.