Calibration of the potential drop method by means of electric FE analyses and experimental validation for a range of crack shapes

In experimental fatigue tests, it may be necessary to identify the onset of crack initiation, which is often defined at a given (short) crack length. Different experimental techniques are available to estimate the initiated crack size, one of which is the direct current potential drop technique. In this paper, the calibration curves reporting the potential drop change as a function of the crack depth have been derived by means of 3D electrical finite element analyses. Driven by previous experimental observations, two different crack shapes have been considered: (i) circumferential and (ii) semi‐elliptical surface cracks. Dealing with circumferential cracks, the effects of the three‐dimensional distribution of the electric current density and the temperature have been investigated. Concerning semi‐elliptical surface cracks, the effects of the crack aspect ratio and the potential probes locations have been analysed. Finally, the obtained calibration curves have been validated against experimental measurements, obtained by fatigue testing notched specimens under a selection of loading conditions.