The effect of force fitting on the magnetic properties of iron-cobalt alloy ring samples

Ring samples of annealed iron-27% cobalt (Fe-27 Co) and iron-cobalt-2% vanadium (FeCo-2V) alloys were subjected to a number of force fitted conditions where the maximum tensile and compressive hoop stresses were varied from 0 to 50 MPa. Various dc and 400 Hz ac magnetic characteristics were determined at each stress level. The dc and 400 Hz ac characteristics of both alloys changed in the force fitted condition, with the compressive hoop stress having more of an effect than the tensile hoop stress on most of the magnetic properties. The most drastic changes were observed in the 400 Hz exciting characteristics at 2.0 T in the FeCo-2V alloy, where the unstressed value of 111 VA/kg was increased to 1700 VA/kg at a calculated maximum compressive hoop stress of -49 MPa. The Fe-27 Co alloy, although having poorer exciting characteristics at the same induction level, changed from 880 VA/kg to 1500 VA/kg at -50 MPa, the conclusion being that the Fe-27 Co alloy is less stress sensitive than the magnetically superior FeCo-2V.