614 Evaluation of defect FG sensor and inverse analysis by singular value decomposition

Abstract

Non-destructive evaluation of defect for ferromagnetic structural material SS400 was performed by magnetic flux leakage technique using a fluxgate sensor. Changes in magnetic flux densities could be measured around defect at a lift off height of 2mm, however, the size of the defect could not be evaluated. Especially at around adjacent defects which distance was 3mm, changes in magnetic flux densities of each defect were mixed and each defect could not be distinguished. In order to evaluate defect size quantitatively, inverse analyses of singular value decomposition were preformed. By eliminating smaller singular values properly, and by using the relationship between leakage magnetic flux densities and magnetic moment of defects, magnetic moment was calculated from the measured magnetic flux densities and the defect size was successfully reconstructed.