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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alloys, because its impact can lead to various forms of corrosion and finally to decrease of the lifetime of the structure/component, see e.g. Jiang et al. (2009), Kunz et al. (2012), Rajasankar and Iyer (2006) or Seitl et al. (2019). The focus of this work is devoted particularly to pitting corrosion, that has been studied extensively in recent years, as can be found for instance in works of Cui et al. (2020), Guo et al. (2022), Hou et al. (2020), Park et al. (2015), Rezanezhad et al. (2020), Shojai et al. (2022), Singh (2015). Presence of a corrosion pit at the surface changes its morphology and causes significant stress concentrations at this location, see Fig. 1. This undesirable effect can be moreover connected to propagation of fatigue cracks because one of the typical loading manners of metal structures is cyclic loading. Therefore, the mutual interaction of a corrosion pit and a fatigue crack is investigated within this work. The motivation for such research can be found for instance in Brennan (2014), DuQuesnay et al. (2003), Jiang et al. (2009), Jiang et al. (2018), Wang et al. (2014) where the impacts of both phenomena are presented.

(a)

(b)

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Fig. 1. Photographs showing examples of the corrosion on own samples: (a) plates; (b) cylindrical S460, S690 and S960 specimens; (c) specimen surface of S690 after fatigue loading.

In this paper, principles of the linear elastic fracture mechanics (LEFM) concept are utilized to assess the fracture behavior of a short fatigue crack in a high-strength steel specimen influenced by presence of a corrosion pit in its vicinity. Classical LEFM concept assumes knowledge of the stress intensity factor (SIF) or stress intensity factor range in the case of cyclic loading that controls the behavior of the crack. SIFs can be determined analytically or numerically, but it holds that numerical techniques are nowadays more popular than analytical ones. Finite element method (FEM) is applied in this work to simulate various configurations. Thus, the effect of selected parameters can be studied and assessed. It is to emphasize that the fatigue crack is modelled as an inclined edge crack in a rectangular bar loaded in tension and thus, I+II mixed-mode conditions are ensured. Moreover, presence of the corrosion tip in the very vicinity of the crack tip influences the crack-tip distribution and therefore, a thorough analysis is performed.

Nomenclature a

Crack length

a th Threshold crack length (when the crack starts to propagate in stable way) Distance of the corrosion pit centre from the fatigue crack const Distance of the corrosion pit edge from the crack at the specimen surface D Corrosion pit depth E Young’s modulus  K I Stress intensity factor range in mode I  K II Stress intensity factor range in mode II C