Reversible component ΔBr of the stress-induced change in magnetization as a function of magnetic field strength and stress amplitude

Abstract

The reversible component ΔBr of the stress-induced change in the magnetic flux density in polycrystalline iron and nickel was studied during cyclic stressing as a function of the magnetic field strength H and the stress amplitude σ. The frequency of the stressing was 25 Hz. Test specimens were magnetized with a magnetic field parallel to the stress axis. In iron the reversible change ΔBr has three different stages A, B and C as a function of the applied magnetic field strength H. In demagnetized state in the beginning of stage A the change ΔBr in the magnetic flux density is zero and, as the magnetic field strength H increases, ΔBr increases and reaches a maximum at a magnetic field strength H1 corresponding to the knee point of the initial hysteresis curve of the test material. In stage B the reversible component ΔBr decreases and reaches a minimum value at a magnetic field strength H2 corresponding to the onset of magnetic saturation. At the magnetic saturation the change δBr in the magnetic flux density remains low. In nickel ΔBr has only two stages A and B. In stage A the reversible component ΔBr increases and in stage B the component ΔBr decreases as a function of H. The differences in ΔBr in iron and in nickel are explained on the basis of the different magnetocrystalline anisotropy energies in these two materials. The observed nonlinear behaviour of the change in magnetization as a function of stress amplitude is explained on the basis of plastic deformation.