INFLUENCE OF STRESS CONDITION ON INITIATION OF MAGNETOSTRICTION IN GRAIN-ORIENTED SILICON STEEL

It is commonly known that the magnetostriction of grain oriented silicon steel for electric transformers, is strongly influenced by applied stress on the steel as well as coating stress of the steel and is dominated exclusively by the formation of 90-degrees domain walls. A new concept on a condition for the formation of 90-degrees domain wall considers the total elastic energy which consists of both strain elastic energy and magnetoelastic energy in axes of easy magnetization of Goss texture {110} (001). It is proposed that 90-degrees domain wall is formed under the condition that the total elastic energies in the three easy axes of magnetization are related by the expression Ex([100]) < Ey([010]), Ez([001]). This was confirmed by electron microscopy, and calculated in various stress conditions including applied stress to a specimen and coating stress as well. The calculation by this new assumption could satisfactorily explain not only previous magnetostriction results by many researchers in silicon steel, such as the harmful effect of compressive applied stress on magnetostriction which is reduced by higher coating stress, but also an excellent study of magnetostriction under sophisticated complex superimposed longitudinal and transverse stress reported by Moses et al. as well as their study in coating removal and on the effects of increased temperature. In the new concept, strain elastic energy is dominant in the total elastic energy, which results in good agreement with past data on the influence of stress on magnetostriction even under sophisticated complex stress conditions and coating stress as well.