1) dent geometry-only MFL signal: in this case all sample regions (dent and background plate) had isotropic magnetic parameters.
2) dent geometry + dent stress MFL signal: for this case all regions of the plate were isotropic except for the right and left dent rim region blocks, which were assigned anisotropic magnetic parameters corresponding to high tension or compression according to the results of the stress FEA modelling. Specifically, blocks in the ‘right’ region (Figure 9) had a strong x-direction anisotropy, tensile at the top and compressive at the bottom. Blocks in the ‘left’ region had a strong y-direction anisotropy, again tensile at the top and compressive at the bottom. Unfortunately, at this point it was not possible to account directly for shear- direction stresses in the central dent rim region, although some qualitative work was done on the influence that these might have.
3) dent stress-only signal: this MFL signal was generated by subtracting the ‘geometry-only’ signal from the geometry+stress signal.