PSI - Issue 42

Lucie Malíková et al. / Procedia Structural Integrity 42 (2022) 1082–1089 Lucie Malíková et al. / Structural Integrity Procedia 00 (2022) 000–000

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4.3. Dependence of the fatigue parameter  K eq on the size of the nearby corrosion pit

When the influence of the various corrosion pit sizes shall be taken into account, it can be concluded that:  With increasing size of the corrosion pit, its influence on the dependences grows as well. Whereas a very small corrosion pit has nearly no effect on the  K eq values (Fig. 3), a larger corrosion pit affects the obtained results for cracks with lengths of up to 2 mm (depending on the crack angle).  The larger is the corrosion pit, the smaller are the ESIFR values for all configurations. It means, that the corrosion pit acts positively on the small crack fatigue propagation (more or less, in dependence on other parameters). Taking into account the whole discussion above and assuming a given threshold stress intensity factor range  K th = 9 MPa·m 1/2 (see e.g. Blasón Gonzáles et al. (2022) or de Jesus et al. (2012)) corresponding to a typical value for HSS material, it can be expected that:  The fatigue crack influenced by a very small corrosion pit (2 P = 0.5 mm) – or let’s say without any corrosion pit – starts to propagate in the stabile manner when a th ≈ 0.25 to 0.35 mm depending on the crack inclination angle.  With increasing size of the corrosion pit also the threshold crack length increase and it achieves the values about 0.45 to 0.52 mm when the corrosion pit is 2 mm large and even 0.6 to 1.2 mm when the length of the corrosion pit is 4 mm.  Assuming the most positive configuration (corrosion pit of 4 mm length and crack inclination angle (  = -45°), then the existence of the corrosion pit causes that the length when the crack starts to propagate in the stable way increase ca. 3.4 (from 0.35 to 1.2 mm) which is certainly of great benefit.  Similar considerations can be made for any selected configuration that were investigated. 5. Conclusions Mutual interaction between a corrosion pit and a short fatigue crack in HSS specimen has been investigated. I+II mixed mode conditions were modelled both via an arbitrary inclination of the crack with respect to the tensile loading and also the presence of the corrosion pit that affects the crack-tip stress field in the same way. Dependence of the equivalent threshold stress intensity factor range on various parameters was studied and discussed in detail. Finally, it was shown that corrosion pit generally decreases the possibility of the crack to propagate – in other words, when a large enough corrosion pit exists near the tip of a short crack, the threshold crack length necessary for its stable propagation increases. Note that the results presented are a part of a complex (numerical + experimental) analysis on corroded HSS specimens. The presented calibration curves of stress intensity factor ranges are recommended for practical applications (input data) in civil engineering structural analysis under combination of corrosion and fatigue load, see Janas et al. (2020), Kala (2019), Kala (2021), Kala et al. (2019), Krejsa et al. (2018), etc. Acknowledgements Financial supports from the Czech Science Foundation (project No. 21-14886S - Influence of material properties of high strength steels on durability of engineering structures and bridges) and from the Faculty of Civil Engineering, Brno University of Technology (project No. FAST-S-22-7881) are gratefully acknowledged. References ANSYS, 2022. www.ansys.com. Blasón Gonzáles S., Werner T., Kruse, J., Madia, M., Miarka, P., Seitl, S., Benedetti, M., 2022. Determination of fatigue crack growth in the near threshold regime using small-scale specimens. Theoretical and Applied Fracture Mechanics 118, paper 103224. Brennan, F. P., 2014. A framework for variable amplitude corrosion fatigue materials tests for offshore wind steel support structures. Fatigue and Fracture of Engineering Materials and Structures 37(7), 717–721. 4.4. Discussion of the results with regard to the given value of the threshold stress intensity factor range  K th