ABSTRACT
With magnetic methods of testing, a magnetic field is applied to the object under examination and any resulting changes of magnetic flux in the region of interest are observed. Applications are, of course, confined to ferromagnetic materials and include flaw detection, measuring dimensional changes and observing variations in magnetic permeabilities brought about by changes in bulk phenomena such as hardness, grain structure and the presence of additives due to alloying and impurities. Either direct or alternating fields can be applied. However, with alternating fields, account may sometimes times have to be taken of the induction of eddy currents, but this can be minimized by operating at very low frequencies, e.g. up to a few Hz. On the other hand, with some applications, the induction of eddy currents may provide additional useful information.
