The Direct Current Potential Drop Method (DCPDM) is widely used for crack detection and crack length measurement in fatigue experiments. Unfortunately, crack length measurements are only possible when a calibration for a specified crack initiation site and potential probe location is available. Investigations by Hartweg and Bär (2019) as well as Nahbein and Bär (2022) on notched round specimens equipped with three potential probes placed in a distance of 120° on the circumference have shown that the crack initiation site can be determined using a simple vector-based model. In this model the normal vector of a plane span by the three potentials is calculated in cylindrical coordinates. In the present work a more detailed investigation of crack initiation and propagation is undertaken to show the possibilities offered by this method. During fatigue tests with the simultaneous measurement of the three potential drops using amplifiers of the control electronics, overloads were introduced in fixed intervals to mark the crack front on the fracture surface. The measurement of both crack depth and fractured area allows a calibration of the potential drop measurement. The calibration was performed on the radius coordinate n of the normal vector using a function suggested by Tiedemann (2016). The multiple potential drop measurement enables an early detection of crack initiation as well as a location of the crack initiation site on the circumference of the specimen. Using the Tiedemann function fitted to the measured data, it is possible to determine the crack length independent of the crack initiation site on the circumference of the specimen.    «

The Direct Current Potential Drop Method (DCPDM) is widely used for crack detection and crack length measurement in fatigue experiments. Unfortunately, crack length measurements are only possible when a calibration for a specified crack initiation site and potential probe location is available. Investigations by Hartweg and Bär (2019) as well as Nahbein and Bär (2022) on notched round specimens equipped with three potential probes placed in a distance of 120° on the circumference have shown that...    »