DEPENDENCE OF ACOUSTOELASTIC CONSTANTS ON EXTERNAL MAGNETIC FIELDS

Abstract The dependence of acoustoelastic constants on external magnetic fields is experimentally investigated for JIS-SS41 mild steel specimens. In the case of ferromagnetic materials, the elastic wave velocities at a demagnetized state are slightly smaller than those at a highly magnetized state. This occurs due to the magnetoelastic interaction, which in turn depends on the stress state. In the present study, we measured the propagation velocities of longitudinal and shear waves in steel specimens as functions of uniaxial stress and external magnetic field. We found that in the demagnetized state, the velocity change with stress showed different slopes for compressive and tensile loading. The difference decreased as the specimens were magnetized, approaching its saturation. As for acoustoelastic birefringence, which measures the principal stress difference, the effect of magnetoelastic interactions is relatively weak, while for the longitudinal/shear wave velocity ratio, which is proportional to the sum of principal stresses, this effect may induce considerable errors. Magnetization of steel components is then recommended to improve the accuracy of acoustoelastic stress measurements. A discussion is given for the strength of magnetization required.