PSI - Issue 42

Kamila Kozáková et al. / Procedia Structural Integrity 42 (2022) 270–275

275

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K. Koza´kova´ et al. / Structural Integrity Procedia 00 (2019) 000–000

Fig. 9: Polished surface of smooth specimen, SEM

Fig. 10: Fracture surface, smooth specimen, N f = 1 . 1 × 10 8

Fig. 11: Fracture surface, notched specimen, r = 0 . 1 mm, N f = 1 . 2 × 10 6

6. Conclusion

Fatigue tests of smooth and notched specimens of EN AW 7075 aluminum alloy were performed. Considering the evaluation of the results, the notched specimens can be divided into two groups. The specimens of the first group (notch radii 0.1, 0.2, 0.4 mm) were machined by corresponding knife tools and their approximations of results had a similar trend. The second group consists of specimens with greater notches (notch radii 0.8, 1.5, 3 mm) which had the notches machined using a small knife tool. The desired shape of these notches was machined by the movement of the smaller knife tool, which was controlled numerically in the machine tool. Due to these two di ff erent methods of machining, these two groups of specimens had di ff erent fatigue response. On the surfaces of the notches with radii of 0.8, 1.5 and 3 mm, small steps were observed under the microscope, which caused an increase in stress. These micro-notches act as additional stress concentrators and reduce the expected lifetime of components. Especially, the slope of Wo¨hler curves was steeper in the area of gigacycle fatigue. Whereas notches (radii of 0.1, 0.2, 0.4 mm) machined by knives with corresponding knife tools had the expected behavior. The way of notch machining with a small knife tool is common in practice and should be remembered. An inap propriate way of manufacturing a notch can lead to a shortened fatigue lifetime, especially in the area of gigacycle fatigue, where small details are crucial.

Acknowledgement

The authors thank the Czech Science Foundation for the support of the research through project No. 21-14886S.

References

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