Effect of Underload Cycles on Oxide-Induced Crack Closure Development in Cr-Mo Low-Alloy Steel

0543626 - ÚFM 2022 RIV CH eng J - Journal Article
Pokorný, Pavel - Vojtek, Tomáš - Jambor, Michal - Náhlík, Luboš - Hutař, Pavel
Effect of Underload Cycles on Oxide-Induced Crack Closure Development in Cr-Mo Low-Alloy Steel.
Materials. Roč. 14, č. 10 (2021), č. článku 2530. E-ISSN 1996-1944
R&D Projects: GA MPO(CZ) FV40034
Institutional support: RVO:68081723
Keywords : high-load-ratio * aluminum-alloy * fatigue * growth * propagation * dependence * stress * underload cycles * crack closure * threshold * fatigue crack growth * oxidation * EA4T steel
OECD category: Audio engineering, reliability analysis
Impact factor: 3.748, year: 2021
Method of publishing: Open access
https://www.mdpi.com/1996-1944/14/10/2530

Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent crack propagation quite significantly. This phenomenon is a consequence of oxide-induced crack closure development during cyclic loading below the threshold. The experimentally described effect of fatigue crack growth retardation was supported by measurement of the width and the thickness of the oxide debris layer using the EDS technique and localized FIB cuts, respectively. Both the retardation effect and the amount of oxide debris were larger for higher number and larger amplitudes of the applied underload cycles. Crack closure measurement revealed a gradual increase of the closure level during underload cycling. Specimens tested in low air humidity, as well as specimens left with the crack open for the same time as that needed for application of the underload cycles, revealed no retardation effect. The results can improve our understanding of environmental effects on fatigue crack propagation and understanding the differences between the results of laboratory testing and the fatigue lives of components in service.
Permanent Link: http://hdl.handle.net/11104/0320816