Effect of Crack Opening on Distribution of Magnetic Flux Density around Fatigue Cracks

In order to identify the mechanisms of changes in the magnetic flux density distribution around fatigue cracks that occur during crack propagation, JIS SCM440 specimens were fatigue tested, and the relation between crack morphology and magnetic flux density distribution was investigated. Two features were observed: a high intensity area around the crack tip, and a low intensity area around the crack root. The low intensity area grew larger for wide open cracks and disappeared when the crack was closed by external force. It was hence found that the magnetic flux density distribution is strongly affected by the crack opening.