Analysis of the crack location in notched steel bars with a multiple DC potential drop measurement

Abstract

The direct current potential drop (DCPD) technique is a frequently used method to measure crack propagation in metallic materials. With a single potential probe attached to the specimen, the size of an initiated crack can be estimated. Therefore, this method is used in crack propagation experiments to determine the crack propagation rate. However, with a single potential probe it is difficult to detect small cracks and impossible to determine the location of the initiated crack.In the present study, three potential probes were attached to cyclic loaded notched steel bars. For the case of an initiated single crack, this experimental set-up delivers different potentials depending on the distance of the probe to the initiated crack. A geometric model to determine the position of the initiated crack from the increase of the individual probe signals is presented.The experimental verification of the model has shown that in case of a single crack, the position can be determined clearly, even in the early stages of crack propagation. Moreover, the sensitivity of the potential drop measurement for the detection of an initiated crack is enhanced by this method. In case of multiple crack initiation sites the scatter of the calculated angle can be used as a criterion for crack detection.