Experimental field dependences of the measuring coil signal, proportional to the reversible magnetic permeability, were obtained on an elastically deformed (by bending) plate made of low-carbon steel 20 during its remagnetization along the major hysteresis loop by a U-shaped attached electromagnet (AEM). Additionally, during magnetization, a local area of the plate was subjected to a variable magnetic field using a flat coil placed between the poles of the AEM. The measuring coil, located on the same frame as the bias coil, was in contact with the plate surface. Magnetic property measurements were taken from both sides of the plate in its central part. It was established that the curves measured with the AEM installed on the top and bottom of the deformed plate differ significantly. On the curves measured from the top side of the plate, where the surface experiences maximum compressive stresses, one central peak in the region of the coercive force and two additional infections (peaks) on both sides of it are observed. On the curves measured from the tension side of the plate, additional infections were observed only at low frequencies of the bias field, when the signal from the measuring coil also contained information about the compressed layers of the plates. The fields at which the inflections occur depend both on the applied load (magnitude of stresses) and on the frequency of the bias field generated by the primary transducer coil. The dependence of the average field of the peaks on the load applied to the plate is close to linear.
Stashkov et al. (Mon,) studied this question.