Peculiarities of electromagnetic-acoustic transformation in the presence of mechanical stresses: III. Internal stresses

Experimental results are presented that demonstrate the behavior of the emf amplitude of double electromagnetic-acoustic transformation (EMAT) in samples of ferromagnets in the presence of internal stresses produced by both heat treatment and tension of samples to stresses exceeding the yield value. It is shown that, regardless of the sign of the saturation magnetostriction and the method for producing internal stresses, the appearance of internal stresses abruptly reduces the EMAT efficiency. A model calculation, which is based on the fact that the magnetoelastic energy associated with internal stresses plays the main role, has shown the same tendency in the dependence of EMAT on stresses as is offered by experimental results.