Effects of tensile stress on the magnetic properties of grain-oriented silicon-iron laminations

The paper presents the results of an investigation into the effects of tensile stresses on grain-oriented 3 1/4% silicon-iron laminations. Some results are also given for non-oriented 4% silicon iron and for dynamo iron. It is found that tension in the rolling direction of grain-oriented material produces a sharp fall in permeability and an increase of hysteresis loss. However, for a direction at 90° to the rolling direction, tensile stress up to an optimum value of about 1000 lbf/in2 produces a substantial increase of permeability and decrease of loss. It is inferred that the grain-oriented material in its initial state has a residual tensile strain of about 55 × 10¿6 in the rolling direction and a residual compressive strain of about 33 × 10¿6 at 90° to the rolling direction. Ferromagnetic domain patterns have been examined under various conditions of magnetization and tensile stress. The results seem to show that the observable surface patterns are not representative of the internal-domain vector distributions.