Assessment With Mechanical Barkhausen Effect of Residual Stress in Grain Oriented Polycrystalline 3% Si-Fe Sheet

Residual stress properties have been studied in grain oriented 3% Si-Fe commercial sheets (grade M140-30S, EN 10107:2005) using mechanical Barkhausen effect (MBE). The MBE is due do abrupt movement of 90 deg magnetic domain walls during mechanical loading. Two types of stress loading have been used at this experiment. The first loading was made with torque motor in order to apply torsion vibrations of the sample. Samples have longer axis oriented within three directions against rolling direction ("a'-0, "b'-45 and "c'-90 deg, respectively). The MBE voltage signal was detected with surrounding pick-up coil. The second loading mode was performed by means of bending the sample glued to the surface of 8 mm thick austenite bar. These glued samples were oriented or parallel (case A) or perpendicular (case B) to rolling direction, respectively. The MBE signal was detected with pick-up coil perpendicular and close to the sample surface. It was revealed that MBE intensity varies in function of applied direction of stress. For torsion vibrating mode the highest level was detected in the case "b'. It is explained by coincidence of external strains axis in this case with main axis of magnetic anisotropy of the sample. When the sample was uniformly strained then evident anisotropy of MBE hysteresis loop against tensile-compression was detected only for the case A. The MBE activity maximums appears for compression range of external stress. This asymmetry means that residual stress of tensile type acts in rolling direction.