PSI - Issue 54

Naveen Kumar Kanna et al. / Procedia Structural Integrity 54 (2024) 196–203 Author name / Structural Integrity Procedia 00 (2019) 000–000

203

8

0.8

0.60

Tiedemann function R 2 = 0.903

Tiedemann function R 2 = 0.947

0.7

0.55

q = 0.549 r = 0.864

q = 1.057 r = 0.640

0.6

0.50

0.5

0.45

0.4

0.40

0.3

0.35

0.2

0.30

relative crack depth a/t

relative crack width c/w

0.1

0.25

0.0

0.20

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.0

1.1

1.2

1.3

1.4

1.5

1.6

mean Potential P mean

mean Potential P mean

Fig. 9. Relative crack depth and crack width plotted against the mean potential with the fitted Tiedemann equation. The Tiedemann equation shows a better agreement with the measured potential data especially for short fatigue cracks. 4. Conclusions • The use of multiple potential probes does not exhibit significant differences in the measured potential probe values. Hence, an independent measurement of the crack depth a and the crack width c with a specific potential probe is not possible. • To reduce the scatter in the measured potential values a mean value of the three measurements can be used. • The aspect ratio a/c, increases with the crack length without a linear relation with the increasing crack size. • The calibration with the Johnson equation overestimates the crack size of short cracks and underestimates the size of long cracks. • Calculation of crack size with the Tiedemann function gives better results than the Johnson equation, especially for short cracks. References Bär, J., Volpp, T., 2001. Vollautomatische Experimente zur Ermüdungsrissausbreitung. Materialprüfung 43, 242–247. Bär, J., 2020. Crack Detection and Crack Length Measurement with the DC Potential Drop Method–Possibilities, Challenges and New Developments. Applied Sciences 10 (23), p. 8559. DOI: 10.3390/app10238559. Chapetti, M., 2003. Fatigue propagation threshold of short cracks under constant amplitude loading. In International Journal of Fatigue 25 (12), 1319–1326. DOI: 10.1016/S0142-1123(03)00065-3. El Haddad, M. H., Smith, K. N., Topper, T. H., 1979. Fatigue Crack Propagation of Short Cracks. In Journal of Engineering Materials and Technology 101 (1), 42–46. DOI: 10.1115/1.3443647. Johnson, H. H., 1965. Calibrating the Electric Potential Method for Studying Slow Crack Growth, Materials Research and Standards 5, No. 9, 442 445. Kitagawa, H., Takahashi, S., 1976. Applicability of fracture mechanics to very small cracks or the cracks in the early stage. In: Proc. 2nd Intern. Conf. Mech. Behav. Mater., Boston, ASM, Cleveland, Ohio, 627–631. Lambourg, A., Henaff, G., Nadot, Y., Gourdin, S., Pujol d’Andrebo, Q., Pierret, S., 2020. Optimization of the DCPD technique for monitoring the crack propagation from notch root in localized plasticity. Int. J. Fatigue, 130, 105228. DOI: 10.1016/j.ijfatigue.2019.105228. Moreno, B., Zapatero, J., Dominguez, J., 2003. An experimental analysis of fatigue crack growth under random loading. Int. J. Fatigue, 25, 597– 608. DOI: 10.1016/S0142-1123(03)00018-5 Raja, M.K., Mahadevan, S., Rao, B.P.C., Behera, S.P., Jayakumar, T., Raj, B., 2010. Influence of crack length on crack depth measurement by an alternating current potential drop technique. Meas. Sci. Technol, 21, 105702. Schijve, J., 2003. Fatigue of structures and materials in the 20th century and the state of the art, International Journal of Fatigue 25, 679–702. https://doi.org/10.1016/S0142-1123(03)00051-3. Tiedemann, D., 2016. Zweidimensionale Ausbreitung kurzer Risse unter Berücksichtigung bruchmechanischer und kontinuumsmechanischer Aspekte. PhD.-Thesis, Universität der Bundeswehr München.