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Microstructural effects and crack closure during near-threshold fatigue crack propagation in a high-strength steel

Ravichandran, KS and Rao, Venkata HC and Dwarakadasa, ES and Nair, Krishnadas CG (1987) Microstructural effects and crack closure during near-threshold fatigue crack propagation in a high-strength steel. In: Metallurgical and Materials Transactions A, 18 (6). pp. 865-876.

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Near threshold fatigue crack growth behavior of a high strength steel under different tempered conditions was investigated. The important aspect of the study is to compare the crack growth behavior in terms of the closure-free component of the threshold stress intensity range, $\Delta K_{th,eff}$ While a systematic variation in the absolute threshold stress intensity range with yield strength was observed, the trend in the intrinsic $\Delta K_{th}$ or $\Delta K_{th,eff}$ exhibited a contrasting behavior. This has been explained as due to the difference in fracture modes during near threshold crack growth at different temper levels. It is shown that in a high strength and high strain hardening microstructure, yielding along crystallographic slip planes is difficult and hence it exhibited a flat transgranular fracture. In a steel with low strain hardening characteristics and relatively low strength, a tendency to crystallographic planar slip is observed consequently resulting in high $\Delta K_{th}$. Occurrence of a predominantly intergranular fracture is shown to reduce intrinsic $\Delta K_{th}$ drastically and increase crack growth rates. Also shown is that crack closure can occur in high strength steels under certain fracture morphologies. A ‘transgranular planar slip’ during the inception of a ‘microstructure sensitive’ crack growth is essential to promote intergranular and faceted fracture. The occurrence of a maximum in the fraction of intergranular fracture during threshold crack growth corresponds to the $\Delta K$ value at which the cyclic plastic zone size becomes equal to the prior austenitic grain size.

Item Type: Journal Article
Publication: Metallurgical and Materials Transactions A
Publisher: Springer
Additional Information: Copyright for this article belongs to Springer.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 07 May 2008
Last Modified: 27 Aug 2008 13:21
URI: http://eprints.iisc.ac.in/id/eprint/13853

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