Crack initiation life of titanium notched bars under uniaxial and multiaxial fatigue: calibration analysis of the potential drop method and experimental validation

During experimental fatigue tests it may be necessary to monitor the crack initiation instant, that is often referred to a short crack depth. Several methods exist to assess the initiated crack size, the direct current potential drop (DCPD) technique being one of them. In the present contribution, the calibration curves representing the potential drop change as a function of the crack depth are derived from 3D electrical FE analyses. Based on previous experimental observations, two different crack shapes are considered: (i) circumferential and (ii) semi-elliptical surface. In the case of semi-elliptical cracks, the effects of the crack aspect ratio and the location of the potential probes are investigated in detail. In conclusion, the numerically-derived calibration curves are experimentally validated on the basis of measurements carried out on notched specimens fatigue tested under different loadings.