Potentials and limitations of direct current potential drop for measuring elliptical cracks in round bars

• The DCPD method was applied to monitor crack growth in single-edge-crack round bars. • Different test setups were used to assess DCPD measurability, sensitivity and accuracy. • Beach marking was performed to correlate DCPD signals with experimental crack front. • Numerical FE analyses for DCPD calibration were validated against experimental data. This study investigates potentials and limitations of the Direct Current Potential Drop (DCPD) method for monitoring fatigue crack size in single-edge-crack round bars made of 42CrMo4 steel. Specimens with a semi-elliptical crack-starter notch were tested under axial fatigue loading, with DCPD applied in various configurations to evaluate the impact of current and potential probes positions on measurement’s overall accuracy. Therefore, experimental DCPD calibration data were developed by correlating the measured signals with the corresponding crack fronts identified through beach marking. Eventually, experimental data were compared with calibration curves obtained from electrical FE analyses, where semi-elliptical cracks were modelled using crack fronts best fitted to the beach-marked experimental fronts. The results confirmed the reliability and accuracy of DCPD for monitoring fatigue crack growth in single-edge-crack round bars, provided that the propagating crack’s shape is known a priori. Moreover, the effect of probe positioning was highlighted: current injection near the crack plane with potential probes at the crack symmetry plane improved measurability, while the highest sensitivity was achieved with probes near the crack tip. Both local and remote current injections, with current and potential probes at the crack symmetry plane, provided comparable accuracy, making these setups promising for experimental fracture mechanics testing.