Development of non-destructive fatigue damage evaluation method before crack initiation by using magnetism measurement.

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For development of nondestructive fatigue damage evaluation using magnetic measurement, martensitic volume fraction in fatigue damage process was measured by the ferrite scope, and leakage magnetic flux density caused by martensitic phase was measured by the MI sensor, which was high sensitive magnetic sensor. It was found that the martensitic volume fraction changed corresponding to the plastic strain range. This result shows that the fatigue damage can be estimated from the measurement of martensitic volume fraction. For sensitive detection of the change in martensitic phase, SQUID microscope was developed. Synchrotron radiation ・CT imaging was developed to observe the crack initiation and the propagation behavior of small crack.