Modeling of magnetic Barkhausen noise in single and dual easy axis systemsin steel

Angular dependent magnetic Barkhausen noise (MBN) signals measured on plate steel, and on the inside and outside surfaces of sections of seam welded a nd spiral welded 2% Mn steel pipe are modeled by considering a system of di pole moments. The relative orientation of dipole moments is fixed within th e material, but their magnitude grows in the presence of an applied field. Growth of the moments is proportional to the magnetic field projected along a particular moment axis. A single easy axis material consists of an isotr opically aligned population of moments, giving the background, upon which i s superimposed a population of moments with relative orientations that resu lt in a net moment within the sample. A dual easy axis system is proposed t o consist of: (i) a second population of moments with orientations resultin g in a net moment with orientation different from that of the first and (ii ) interactions, possibly quadrupolar in nature, that occur between the indi vidual moments of each population. The model is used to explain differences in the angular-dependent MBN signal between the seam welded pipe, with a s ingle easy axis, and the spiral welded pipe, with a dual easy axis. The sou rce of the dual easy axis system in the spiral welded pipe, which is differ ent on the two pipe surfaces, is considered in terms of the asymmetric manu facturing processes, relative to the pipe axis, applied during its producti on. (C) 1999 Elsevier Science B.V. All rights reserved.