Since steel, in general, has a positive magnetostriction coefficient, 180° domains will tend to align their magnetic easy axes closest to, and ultimately rotate it towards, the direction of the applied tensile stress. This increases the magnetic permeability in the tensile stress direction. Conversely, an applied compression will increase the magnetic permeability in a direction transverse to the stress axis. As shown in Figure 9, the dent rim is divided into 3 sectors – left, right and centre. Within each of these sectors there are 4 ‘blocks’ through the thickness. The results from the stress FEA study were used to determine the approximate stress level and direction in each of these blocks. Then, by applying specialized, user-defined magnetization functions in each of these blocks, different magnetic properties were be assigned in each of the orthogonal directions x, y, and z in order to account for local residual stress effects on magnetic behaviour. The exact details of how the local anisotropy is modified to account for stress effects has been presented in earlier papers4,5.