Magnetic Barkhausen noise analysis of stress in steel

When a changing magnetic field is applied to a magnetic material, the domain walls move so domains aligned close to the field direction grow at the expense of those that are less aligned. The movement occurs in a series of sudden jumps leading to magnetic Barkhausen noise (MBN). Analysis of MBN can provide an effective non-destructive testing technique for determining residual stress in steel. MBN measurements on AS1548-7-460R steel under applied stress show a clear asymmetry between compression and tension. MBN features show more sensitivity to compression and undergo a Villari reversal in their stress dependence at about 100 MPa of tension. Measurements are also made on a welded plate of the same material. Away from the weld the results are consistent with the expected compressive stress parallel to the weld direction. At a point near one edge of the weld, the amount and character of the MBN changed sharply, suggesting a concentration of stress.