Effects of Uniaxial Stress on Magnetoacoustic Emission and Magnetoacoustic Responses in Steel

Among the several unique phenomena observed during the irreversible domain wall motion in a ferromagnet, the Barkhausen and AE-type effects have been extensively studied due to their sensitivity to the material properties and residual stress state [1,2]. Between these two effects, the former is based on the abrupt motion of domain walls over pinning sites and the latter is based on the progressive rearrangement of domain structure following the magnetization process. A series of acoustic noise events, which occurs almost simultaneously with the magnetic Barkhausen noise, provides a separate methodology with unique capabilities and is the base of the magnetoacoustic emission (MAE) technqiue. The practical application of the ∆E-type effect to NDE residual stress measurement involves measuring ∆F(B)/F, fractional changes in frequency of phase-locked acoustic waves as a function of net magnetic induction, and the method has been called the low-field magnetoacoustic (MAC) technique by some of us [3]