Development of the New Nondestructive Material Degradation Evaluation Method Using the Low Frequency Excitation Magnetic Sensor Under the DC Magnetic Field

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In the fatigue evaluation of an iron-based structural material, the inductance method that uses a pancake-type coil is reported to be effective. This method cannot evaluate the inside fatigue of a specimen because the eddy current does not penetrate into the inside of a specimen through the skin effect. In this method, the accuracy of the fatigue evaluation depends on the surface condition of a specimen. In this study we applied pulsating tension fatigue. We achieved the following results. The detection of pulsating tension fatigue of specimens made of low carbon steel was originally possible by the inductance method which used 10kHz as a excitation frequency. We attempted the improvement of the sensibility using the inductance method excited in the low frequency together with the dc magnetization method that used Nd magnets. This method could evaluate pulsating tension fatigue of a specimen irrespective of the surface condition.