Investigation on Features of Alternating Electromagnetic Field for Perpendicular and Parallel Cracks Detection

摘要

Alternating current field measurement is based on alternating electromagnetic field disturbed by cracks, which is sensitive to detect the crack being parallel to the magnetization direction. In this paper, the alternating electromagnetic fields distribution around both parallel and perpendicular cracks in steel and aluminium are analysed by 3D FEM and experimental methods. In the simulation, the perpendicular and parallel cracks could be detected out distinctly in steel and only the parallel crack could be detected out distinctly in aluminium. Furthermore, frequency analysis indicates that when detecting parallel and perpendicular cracks with the same probe, the excitation frequency has a signification influence in amplitude and sensitivity of magnetic signals. Finally, the experiment is carried out to verify the conclusion. The experiment reveals that with probe passing the parallel and perpendicular cracks, the magnetic fields induced by perturbation current and leakage magnetic field exist simultaneously in different weighting and sensitivity. The tendency of frequency variation in the experiment is in accord with simulation result. The optimal excitation frequency of perpendicular and parallel cracks detection is 1000Hz.