Eddy current testing (ECT) system for the spring steel materials that is able to estimate crack shape was developed. Inspection signal of spring steel material is affected by the permeability distribution about its surface. Then the magnetizer that reduce variability of permeability and the pancake probe that grasps regional states of spring steel material were introduced to the system. It was confirmed thereby that this probe is able to detect depth 50 µm crack with a sufficient S/N ratio. Exciting coil that generates two-way direction eddy current was developed and average depth and outline of cross-sectional shape were estimated by its inspection signals. Then the method of estimating crack shape was developed, which has feature that integrates two results by different direction eddy current. In addition, the validity of the method was confirmed by evaluating relationship between crack shapes and calculated inspection results with finite element method (FEM) analysis.
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