Effects of transverse compressional stress on magnetic laminations

Toroidal, laminated cores of several important magnetic materials were tested for their magnetic properties at compressional stresses ranging from 0 to 500 pounds per square inch (psi). The compressional stress was applied in a direction perpendicular to the plane of the laminations and perpendicular to the direction of the magnetic field. The materials tested were 3.5 and 6.4-per-cent silicon-iron, 81 and 90-per-cent nickel-iron, and both hydrogen- and air-annealed samples of AEM 4750, 12 Alfenol, and 16 Alfenol. Tests were run at frequencies of zero, 60, and 400 cycles per second (cps). Under the action of an increasing compressional stress, each of the materials having nonzero magnetostriction exhibited a decrease in maximum permeability and remanence, an increase in coercive force, and a maximum flux density which remained virtually unchanged. The a-c magnetization curve was shifted downward, and the a-c hysteresis loops became less rectangular as the compressional stress was increased. Except at very low fields, materials having zero magnetostriction were unaffected magnetically by the transverse compressional stress. The experimental results indicate that magnetic effects of transverse compressional stress are dependent on the magnitude and independent of the sign of the magnetostriction. The results of this paper can be applied in choosing a magnetic material for a particular application where sensitivity to transverse compressional stress is an important design consideration.