PSI - Issue 28

Levke Wiehler et al. / Procedia Structural Integrity 28 (2020) 925–932 Author name / Structural Integrity Procedia 00 (2019) 000–000

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order to establish a more precise connection between the crack front geometry and the measured potentials depending on the crack length. The multiple potential drop measurement offers new possibilities for the investigation of crack initiation and propagation in fatigue experiments. By integrating the measurements into a test software, a detection and a stop of the experiment in case of crack initiation can be performed with appropriate conditions. The measurements can also provide important information about the shape of the crack front when precracking samples for fracture mechanical tests and thus help to avoid invalid results due to inclined or curved crack fronts. In addition, the use for structural health monitoring is also conceivable. 5. Conclusion Based on the investigations in this work the following conclusions can be drawn:  The multiple potential drop measurement enables an early detection of cracks in notched specimens during fatigue experiments.  The use of quotients of different potentials allows the determination of the crack initiation site.  The method compensates cross-potential fluctuations such as temperature influences.  By analyzing the quotients, reliable statements about the shape of the crack front can be made.  The use of multiple potential drop measurement appears to be a promising method and will be investigated in further experiments. References ASTM E647; 2013. Test Method for Measurement of Fatigue Crack Growth Rates. DOI: 10.1520/E0647-15E01 Bär, J.; Tiedemann, D.; 2017. Experimental investigation of short crack growth at notches in 7475-T761, Structural Integrity Procedia 5, 793-800. DOI: 10.1016/j.prostr.2017.07.171. Campagnolo, A.; Bär, J.; Meneghetti, G.; 2019. Analysis of Crack Geometry and Location in Notched Bars by Means of a Three-Probe Potential Drop Technique, International Journal of Fatigue 124, 167-187. DOI: 10.1016/j.ijfatigue.2019.02.045. Doremus, L.; Nadot, Y.; Henaff, G.; Mary, C.; Pierret, S.; 2015. Calibration of the potential drop method for monitoring small crack growth from surface anomalies – Crack front marking technique and finite element simulations, International Journal of Fatigue 70, 178–185. DOI: 10.1016/j.ijfatigue.2014.09.003. Hartman, G. A.; Johnson, D. A.; 1987. D-C electric-potential method applied to thermal/mechanical fatigue crack growth. Experimental Mechanics 27, 106–112. DOI: 10.1007/BF02318872. Hartweg, M.; Bär, J.; 2019. Analysis of the crack location in notched steel bars with multiple DC potential drop measurement, Procedia Structural Integrity 17, 254-261. DOI: 10.1016/j.prostr.2019.08.034 Johnson, H. H.; 1965. Calibrating the Electric Potential Method for Studying Slow Crack Growth, Materials Research and Standards 5, No. 9, 442– 445. Ritchie, R. O.; Garrett, G. G.; Knott, J. F.; 1971. Crack-growth monitoring: Optimisation of the electrical potential technique using analogue method. In: International Journal of Fracture Mechanics 7, 462–467. Verpoest, I.; Aernoudt, E.; Dedruyttere, A.; 1981. An Improved A.C. Potential Drop Method for Detecting Surface Microcracks during Fatigue Tests of Unnotched Specimens. Fatigue and fracture of Engineering Materials and Structures 3, 203-217.