Investigation of optimum field amplitude for stress dependence of magnetic Barkhausen noise

An investigation of the sensitivity of magnetic Barkhausen noise (MBN) to changes in uniaxial tensile stress applied to mild steel under conditions of low, medium, and high excitation field amplitudes is presented. Field excitation in the lowest range that was tested produced the most sensitive response to change in stress for the squared-voltage-signal output integrated with respect to time ([MBN.sub.energy]). The linear response extended to the highest applied stress of 220 MPa, which was 80% of yield strength. In this field range, the angle-dependent [MBN.sub.energy] and distribution of pulse heights under applied stress conditions was observed to be consistent with previous measurements performed in the medium- to high-field amplitude ranges. However, the number of Barkhausen events was less, and increased linearly with applied stress up to 120 MPa. In contrast, at higher field amplitudes, the initial number of events was greater, but then decreased with increasing applied stress. The results at low field amplitudes are attributed to the additional 180[degree] domain wall activity, accompanied by increased magnetization level, which could be induced by tensile stress. The reduction in number of events at higher stresses and higher excitation field amplitudes, which corresponds to an increase in [MBN.sub.energy] and broadened pulse-height distribution, is associated with increased collective Barkhausen behavior. These results demonstrate that improved sensitivity of Barkhausen signals to changes in stress can be achieved in mild steel if optimized field excitation is used. Index Terms--Magnetic Barkhausen noise, magnetic stress measurement, mild steel, 180[degrees] domain walls, uniaxial tensile stress.