Effects of applied stress on the magnetic properties of high permeability silicon-iron

It is well known that magnetic properties of Goss-oriented silicon-iron are dependent upon external mechanical stress. This paper describes some of the recent work carried out in the UK on the effects of high compressive stress, combined longitudinal and transverse stresses, and also the effects of elevated temperature on the power loss and magnetostriction of silicon-iron. Results show that,when compressive stress greater than about 15 MPa is applied along the rolling direction the power loss generally is double the zero stress level, the permeability drops linearly, and the B-H loop becomes constricted. The loss does not rise so rapidly in higher permeability material, but the magnetostriction reaches a higher final level. These effects are explained using a simple domain model. Measurements of magnetostriction under combined longitudinal and transverse stress before and after coating removal are shown. At elevated temperature,the effect of stress is found to be more pronounced, and the benefit of the coating on high permeability material is reduced. The extent to which stress may degrade the performance of laminated cores is discussed, and it is hinted that perhaps the effects of stress might only partly account for the building loss in high permeability cores.