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

During the tests with the CC-specimen, the maximum stress intensity factor K max predefined in the testing software FAM Control is kept constant at a level of 700 Nmm 3/2 in order to receive a cyclic stress intensity factor of Δ K = 20 MPam 0.5 with an R -ratio of 0.1. When testing the CC-specimens, no bulging was observed and the crack grows straight in the middle of the specimen and is not deflected due to the preformed material. In Fig. 6, it can be seen that some differences in the crack growth rate can be observed especially on the first 0.5 mm of crack length a . These differences also occur within the same specimen, e.g. in the CC-specimen at position A (blue dots). In order to exclude any notch effects, the crack growth rate is investigated only after a crack length variation Δ a of 1 mm and compared to the aforementioned comparative value of the crack growth rate of 2.02E−05 mm/cycle. After 1 mm crack growth, a constant crack growth rate is achieved, which lies within a range of 1.36E−05 mm/cycle to 1.98E−05 mm/cycle for the three different positions of the clinched joints. There is a tendency for the crack to grow more slowly when it is close to the clinched joint, especially at position C. After all, the ratio of crack growth rates is up to almost 1.5 between the base material and the material affected by the clinched joint. Furthermore, the crack growth rate may be considered too far away from the clinched joint to be able to describe the properties directly around this joint. Therefore, the influence of the different joint positions on the crack growth rate needs to be further investigated. For this purpose, another specimen geometry is planned in which the crack grows towards the clinched joint and not away from the clinched joint area as before.

Fig. 6. Comparison of the crack growth rate of different clinched joint positions and the base material.

5. Conclusions A novel CC-specimen was developed to experimentally determine fracture mechanical parameters in the area of clinched joints. After determining the necessary geometry factor function and the calibration function numerically the experimental investigations with the C-shape specimen could be examined. It can be stated that fracture mechanical investigations of preformed metal sheets using the novel CC-specimens are possible and that no bulging during the experiments has been observed. The crack grows straight in the middle of the specimen and is not deflected. Nevertheless, the influence of the different joint positions according to the crack growth rate have to be investigated in more detail. In the future, another kind of specimen has to be used to measure directly at the location of the clinched joint.