Self Magnetic Flux Leakage as a Diagnostic Signal in the Assessment of Active Stress - Analysis of Influence Factors

On the macroscopic scale, mechanical and magnetic properties of ferromagnetics are closely related.Under mechanical stress, ferromagnetics are subject to deformations alongside the changes in magnetization.Stresses and strains lead to changes of interaction forces acting between adjacent atoms and lead to a change in the magnetization distribution in domains, which in turn results in a change of the magnetic properties.Generally, these phenomena are referred to as magnetomechanical effects.As a part of this research study, specimens of P91 steel were tested after being subjected to diverse heat treatment procedures affecting their microstructure.The samples were subjected to periodically pulsed tensile cyclic loads with different values of the active stress induced in the part of the sample used in the measurements.For each of the tested combinations of applied stresses and microstructures, the magnetization changes followed a different pattern although certain similarities were reported, too.The greatest changes in the value of the sample magnetization were registered in the initial load cycles.There were significant differences in the magnetization process between samples with a different microstructure.Potential applications of the self-magnetic flux leakage value to analyses of active stresses in the sample were explored.