Acoustic emission generated by alternating magnetic field


Stresses born in the solid state may trigger acoustic emission (AE). Stresses are traditionally caused by mechanical forces and/or pressures implemented to the surface of the material. However, inner stresses in solid state may be born due to changing of magnetic field or due to temperature changes especially when cooling down the material, for example in structure changing. It is also well known that elongation of material structures due to rolling may lead to different AE bursts, which may be used for characterization of the structure of material due to cold forming. In the presentation we show in experiments that alternating magnetic field leads to AE burst, which have larger magnitude where the gradient of the changes of magnetic field is larger in absolute value. We also demonstrate correlation of the RMS of AE signals with the direction of the elongation of steel structure. This opens the way to investigate anisotropy in steel sheets. We also investigated the dependence of the measure of acoustic emission on frequency and on different sinus, triangle and rectangle forms in alternating magnetic field. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg
