Search

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.

The source of the magnetic easy axis in oil and gas pipeline steel has been investigated. The magnetic anisotropy was characterized by using an angular magnetic Barkhausen noise technique. X-ray pole figure analysis, microstructural examination and high and low temperature annealing treatments were used to examine the texture, microstructure and residual stress. The results showed that plastic deformation and residual stress were the origin of the observed magnetic easy axis.

The stress distribution around a 50% blind-hole pit in a steel pipe with a 9 mm wall was investigated utilizing high-resolution magnetic Barkhausen noise (MBN) measurements. A magnetic disk read-head was employed as the pick up coil in the MBN probe. A stress concentration factor of approximately 2 at the defect edge perpendicular to the direction of applied stress was obtained and approximately -0.6 at the edge parallel to the same. Experimental data were in agreement with the analytical data from Airy's stress function method.

A new model based on irreversible motion of domain walls is developed to represent the angular dependence of the magnetic Barkhausen noise (MBN) signal as a function of the magnetic easy axis. An energy expression, involving isotropic parameter beta, irreversible motion parameter alpha and angle theta, is derived to express the angular dependence of the signal. The energy equation is suitable for all sweep field amplitudes in which the MBN spectrum is generated.

The use of a sacrificial carbon surface layer deposited on the target surfaceto protect it from sputtering during a high dose heavy ion implantation processwas investigated. The results showed that the carbon layer effectively shieldedthe target from sputtering damage. However, as the implantation energy was increased, a significant degree of carbon mixing was observed at the C/Cu interface.

Research is presented into the influence of manufacturing on magnetic easy axis in steel.