The project, in collaboration with the Bundesanstalt für Materialforschung und -prüfung (BAM), aims at the development of a new method for determining Kitagawa-Takahashi diagrams (KT-diagrams) in the practical interesting region with less experimental effort. Therefore, the fatigue behaviour of the unalloyed steel S690QL in the normalized and hardened condition is being investigated. Crack-like notches are introduced in the specimen using a laser engraving system. The start of the crack propagation and the crack length measurement are undertaken with a DC potential drop measurement. The fracture surfaces are examined with light and scanning electron microscopy (SEM). Experiments with overloads are used to calibrate the potential drop measurement, as depicted in the picture. More experimental data for constructing KT- diagrams are obtained in crack propagation experiments, the determination of the closure-free threshold for crack propagation, and fatigue tests using the Risitano method to determine the fatigue limit.


  • Determination of short surface cracks with the DC potential drop measurements.
  • Construction of Kitagawa-Takahashi diagrams to predict the cyclic lifetime of pre-cracked specimens and to determine the area of non-propagating cracks.
  • Fatigue tests using the Risitano-method to determine the fatigue limit of S690N and S690QL steels at different stress ratios (R).