Abstract
In our previous studies, the changes in the magnetic flux density around fatigue cracks during their propagation process were observed, and a good correlation between the changes of the magnetic flux density distribution and stress intensity factor was recognized. This result suggested that non-destructive evaluation of the stress intensity factor of fatigue cracks would be possible using this relationship. In order to clarify the mechanisms of the changes in the magnetic flux density distribution around fatigue cracks, four-point bending fatigue tests for JIS SCM440 specimens were carried out, and the effects of the heat treatments to ease the plastic deformation around a crack tip, as well as the additional fatigue tests after the heat treatment were discussed. From the changes of the magnetic flux density distribution accompanying “the heat treatment” and “the fatigue testing after the heat treatment”, it was considered that the change of the magnetic flux density around the fatigue crack is caused by plastic deformation generated near the fatigue crack tip and accumulated along the crack path.
