Uniaxial stress effects on magnetoacoustic emission

Uniaxial stress was applied to an embrittled HY-80 steel sample as an externally controlled parameter affecting the spectral characteristics of magnetoacoustic emission (MAE). The experimental results were obtained by applying a 20-Hz external AC magnetic field parallel to the uniaxial stress axis. The effect of tensile stress monotonically lessens the MAE activity due to the increase in the area of 180° domain walls. The effect of compressive stress initially increased the amplitude of MAE burst. Between 50 to 75 MPa of compressive stress, the amplitude of the MAE burst was at its maximum, and the MAE burst was asymmetric. The combined effects of the increased area of 90° domain walls, the compressive stress-induced viscosity of 90° domain-wall motion, and the potential barriers at the grain boundaries can explain such an asymmetry in the MAE burst. Further increase in compressive stress, however, caused a reduction both in asymmetry and amplitude in the MAE burst. This is due to a significant reduction in the 90° domain-wall area and the domain-wall motion which is limited to a relatively flat-potential region between the barriers