Abstract
Previous NDE techniques, which utilize materials' magnetic characteristics, depend on magnetization and demagnetization of materials. The process of magnetization and demagnetization costs much and takes time. The evaluation system we propose focuses on the material inherent magnetic characteristics. The system can evaluate the damage of materials by detecting the changes in the inherent magnetic characteristics of materials with the ultra sensitive magnetic flux density meter. Therefore, it requires neither magnetization nor demagnetization of materials. To confirm the effectiveness of the method, we conduct tensile and biaxial fatigue tests on various stainless steels. Measured magnetic flux curves indicate that magnetic flux at the stress concentration part increases before crack propagation. Then, it decreases due to stress release by crack propagation. We confirm that the measured magnetic flux curve depicts local periodical cycles with global increasing tendency.
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