Crack depth measurements using alternating current potential drop (ACPD) technique on shallow and finite length cracks are prone to errors. The influence of length of notch on depth measurements in stainless steel (SS) was addressed by the authors using an ‘Equivalent Resistive circuit model’ based on the parallel path length available for the current to flow around the defect, in addition to the path available below the defect. In addition to the path length, due to changes in electrical conductivity of the material, the variation in area of cross section needs to be considered. Working in this direction, a modified model is proposed which takes into account the length and area of cross section through which the current flows in the additional path. The proposed model is able to account for the observed variations in the notch depth with length in SS, brass and aluminum having conductivities of 1.41, 18.73 and 31.51 MS/m respectively.
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