Subtle changes in magnetic Barkhausen noise before the macroscopic elasticlimit

A mild steel specimen was loaded in tension up to approximate to 0.4% strai n, with Magnetic Barkhausen Noise (MBN) measurements made at increasing str ain levels. In addition, an MBN investigation was performed on a mild steel specimen bent progressively to approximate to 0.2% longitudinal surface st rain. Overall, the parameter termed 'MBNenergy' increased significantly in the elastic, yet remained basically unchanged in the plastic range of defor mation. While still in the elastic range, particular strain levels displaye d abrupt changes in the MBNenergy. Variations in scatter about the average MBNenergy value, as well as distinct modifications in pulse height distribu tions, occurred simultaneously with the abrupt changes in MBNenergy. The no n-uniform stress distribution among grains in the polycrystalline samples i nitiated dislocation formation in some grains before extending to other gra ins. Dislocation strain fields contributed to redistribution of strain with in a grain leading to non-uniform changes in magnetic texture. Results indi cate that the magnetic Barkhausen noise technique can detect microyielding. (C) 2000 Kluwer Academic Publishers.