Distinction and Evaluation of Adjacent Parallel Surface Cracks Based on Magnetic Flux Leakage

The magnetic dipole model for two adjacent parallel cracks with rectangular shape was established. The relation between the magnetic flux leakage signals caused by two adjacent parallel cracks with rectangular shape on a ferromagnetic material surface and the crack-to-crack distance was clarified. The depth of the smaller crack can be evaluated by considering an effect that the amplitude of leakage flux decreases as the depth ratio of two cracks and the crack-to-crack distance increase. A method based on the analysis of the vector locus consisting of tangential and normal components of the magnetic flux leakage signals was proposed as an alternative to analyzing the waveform. Some experimental results show that the evaluated crack depth is in good agreement with the actual one.