Investigation of the dependence of Barkhausen noise on stress and the angle between the stress and magnetization directions

The dependence of Barkhausen noise amplitude on stress, and on the angle between the stress and magnetization directions, has been investigated in specimens of AISI/SAE 4340, HY-80 and ASTM A-36 steels. In all three materials it was found that the Barkhausen noise amplitude measured with the magnetic field applied at 60° to the stress axis is independent of stress. This result is compared with the theory of elasticity which indicates that under a uniaxial or a pure bending stress, the normal component of a strain in steel is zero along the direction approximately 61° from the direction of the applied stress. It was also found that the Barkhausen noise follows the same angle dependence as that of the normal strain. These findings strongly indicate that the Barkhausen noise amplitude is directly dependent on the normal strain along the direction of the magnetization and not on the shearing strain. An explanation for such a direct normal strain dependence is given based on magnetoelastic energy. Possible application of this finding to quantitative nondestructive stress measurements is also discussed.