PSI - Issue 42

D. Weiß et al. / Procedia Structural Integrity 42 (2022) 879–885

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Author name / Structural Integrity Procedia 00 (2019) 000–000

Fig. 3. (a) Specimen geometry; (b) Comparison of the geometry factor function of the CC-specimen and the extended Mini-CT-specimen.

3.2. Calibration function In addition to the geometry factor function, a calibration function for the direct current potential drop method is required for measuring the crack length a during the test. With this method, a constant electric current I is passed into the specimen and the potential drop U is measured. As the crack grows, the ohmic resistance increases due to the reduction of the specimen cross-section. A calibration function describes the relationship between the potential drop U and the crack length a and is determined numerically using a finite element program, Richard and Sander (2016). Because of the low sheet thickness of only 1.5 mm, the holes for the solder pins, where the current is injected and the potential drop is measured, are placed on the front face according to the extended Mini-CT specimen, Weiß et al. (2021). The experimental setup and the numerically determined calibration function in comparison with the extended Mini-CT specimen are illustrated in Fig. 4. It can be seen that the calibration functions differ from each other.

Fig. 4. (a) Test setup; (b) Comparison of the calibration function of the CC-specimen and the extended Mini-CT-specimen.