Observation of magnetic flux density distribution around fatigue crack and application to non-destructive evaluation of stress intensity factor

Abstract

In order to develop a new technique to evaluate fatigue damage non-destructively based on magnetic information, changes in the magnetic flux density around fatigue cracks during their propagation process were observed. The correlation between the change behavior of the distribution of the magnetic flux density and the stress intensity factor was examined. Four-point bending fatigue tests were carried out under six different conditions on JIS SCM440 steel specimens with an artificial slit. Magnetic flux density distributions near the fatigue crack tips were observed using a newly developed apparatus consisting of an MI sensor (Magneto-Impedance sensor) and an x-y stage. It was found that the distribution of magnetic flux density moved with crack propagation. A strong correlation between the movements of the magnetic flux density distribution and stress intensity factor was recognized, regardless of the loading conditions, maximum load or stress ratio. The results suggest that non-destructive evaluation of the stress intensity factor of fatigue cracks would be possible using this relationship. © 2011 Published by Elsevier Ltd.