The AC magnetostriction of 3.25-percent grain-oriented silicon-iron under combined longitudinal and normal compressive stress

The ac magnetostriction of transformer sheet has been measured with longitudinal compression up to 2000 lbf/in²(13 800 kN.m^-2). Longitudinal stress causes a sudden increase in magnetostriction, while normal stress smooths out the steplike change. Si-Fe sheet from three different manufacturers is shown to have widely varying stress sensitivities, which are due entirely to differences in the insulating coatings on the laminations. Application of a glass coating greatly reduces the stress sensitivity, such that longitudinal stresses over 1100 lbf/in²(7600 kN.m^-2) are needed to produce any increase in magnetostriction. Both longitudinal and normal compression change the domain structure from simple 180-degree walls to a more complicated structure where most of the magnetization is at 90 degrees to the rolling direction. This stress structure is conducive to high positive magnetostriction.