Can ACFM measure the through-thickness depth of an inclined crack?
Summary No, ACFM measures the crack path length. If the crack is inclined to the surface this length is greater than the through-thickness penetration. Detail The disturbance in the current flow, and hence the size of the signal, is related to the extra path length, i.e. the length down the crack face. In ferritic steel the skin depth is small compared to the crack depth, so no information can be gained on crack inclination. In thick-skin materials there is an asymmetry in current density either side of an inclined crack that, in principle, could give information on crack inclination (and hence through-thickness depth), but this is very difficult to measure and interpret in practice.
