Identification of defect size in ferromagnetic steels based on the piezomagnetic field measurement

The goal of this research is to investigate the correlation between the piezomagnetic field and the defect size in ferromagnetic steels. Specimens of 30Cr steels were machined into standard bars with circular holes of different sizes in the centre. Tensile tests were carried out to measure the piezomagnetic field on the surface of the defective specimens. The variations of the piezomagnetic parameters with the tensile loads were studied and two evaluation parameters were defined to characterise the defect area. Analysis results showed that the evaluation parameters vary exponentially with the defect area. Quantitative algorithms were proposed to characterise the correlation between the evaluation parameters and the defect area. The results obtained in this research provide a method to quantitatively identify the defect size in ferromagnetic steels based on the piezomagnetic field measurement.