Abstract
In the first part of this paper, some studies about the relationship between degradation and magnetic quantities of ferromagnetic materials are reviewed. These studies show some magnetic quantities like magnetic susceptibility, coercive force and saturated magnetization could be parameters to evaluate degradation effectively. Plastic deformation regions can be detected by a SQUID or a Hall sensor. Then, studies about non-ferromagnetic materials are also reviewed. The first one is the study about the change of the magnetic flux leakage due to mechanical loading. This shows the relationship between plastic deformation and change of magnetic flux leakage. The second one is observation results by magnetic colloid and Magnetic Force Microscope (MFM). Magnetic flux density of the sample was changed depending on load. It is realized that periphery of a crack introduced by a cyclic loading was magnetized and magnetization is caused by martensitic transformation. The last one is the inverse analysis method using Neural Networks to predict distribution of magnetization in a sample from magnetic flux density. The validity of this method is confirmed because the magnetic flux density calculated using the magnetization analyzed inversely coincides to the observation results. The possibility that magnetic physical quantities can be parameters of degradation levels is shown by these studies.
