直流バイアスを加えた矩形波交流磁界を使用する球状黒鉛鋳鉄板の裏面欠陥試験法

抄録

  Magnetic leakage flux testing is a non-destructive electromagnetic testing method for ferromagnetic materials. Since an alternating magnetic field is generally used by this method, it is used only for testing the surface of materials due to the influence of skin effects. Shrinkage cavities and opposite side flaws of ferromagnetic materials cannot be tested using this method.

  In this paper, flux leakage testing using square wave current with direct current bias is proposed for detecting opposite side flaws in spheroidal graphite cast iron plates. This testing method was investigated by experiments and 3-D nonlinear electromagnetic field analysis using the finite-element method, taking into account magnetic characteristics with minor loop curve and eddy current inside the spheroidal graphite cast iron plate. The results showed that the testing of opposite side flaws in spheroidal graphite cast iron plates is possible by magnetic flux leakage testing using the alternating magnetic field of square wave current with direct current bias.