Measurement of Flat Samples With Rough Surfaces by Magnetic Adaptive Testing

Magnetic nondestructive tests of structural degradation of ferromagnetic construction materials must be often carried out on flat samples whose magnetic circuit is artificially closed by an attached soft magnetic yoke. Quality of magnetic contact between the sample surface and faces of the yoke has a strong influence on the measured signal, and especially with unpolished surfaces, it is difficult to be reproduced. The presented experiment suggests a partial solution of the problem via application of nonmagnetic spacers inserted between the sample and the yoke. The spacers distort and decrease the signal, but they also decrease fluctuation of the magnetic contact quality and smooth scatter of the measured data. As the goal of the nondestructive test is not absolute measurement of magnetic parameters of the material, but relative comparison of some convenient magnetic features, which relate to degradation of microstructure of the sample, application of the spacers proves to be not only acceptable, but it is very helpful.