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Quantifying fatigue overload retardation mechanisms by energy dispersive X-ray diffraction

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)392-410
Number of pages19
JournalJournal of the Mechanics and Physics of Solids
Volume124
Early online date25 Oct 2018
DOIs
DateAccepted/In press - 24 Oct 2018
DateE-pub ahead of print - 25 Oct 2018
DatePublished (current) - 1 Mar 2019

Abstract

The fatigue crack retardation mechanisms operating after an overload event are investigated for a bainitic steel using high spatial resolution energy dispersive synchrotron X-ray diffraction. The elastic crack-tip strain fields are mapped at mid-thickness of compact tension samples at R-ratios of 0.1 and 0.4. The same overload stress intensity factor (KOL = 60 MPa m1/2) is applied in each case with the cracks then propagating under the same applied stress intensity range, ΔKapp = 27 MPa m1/2. The competing retardation mechanisms are directly quantified and separated, with the associated fatigue crack growth (FCG) rates then being predicted according to a 2-parameter Walker-type assessment and validated against those measured. The stress intensity factor associated with the overload residual stress field is calculated using a weight function approach. For R=0.1, shielding from residual stress controls retardation when crack growth through the overload plastic zone, rp OL, is small (specifically <0.6rp OL). For more extensive crack growth, discontinuous crack closure controls the retardation behaviour, with significant load transfer across opposing crack faces being observed at minimum load (for R=0.1). These crack face tractions are associated with the plastic asperity created during overload. The traction forces holding the crack faces open at minimum load are, for the first time, used to directly quantify the associated stress intensity factor, Kmin tract as a function of crack growth. While no crack shielding is expected, nor observed, for R=0.4, the variation in FCG rate after overload is explained by changes in effective R-ratio.

    Research areas

  • Crack opening displacement, Crack-tip shielding, Intrinsic shielding, Linear elastic fracture mechanics (LEFM)

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Documents

  • Full-text PDF (accepted author manuscript)

    Rights statement: This is the author accepted manuscript (AAM). The final published version (version of record) is available online via Elsevier at https://www.sciencedirect.com/science/article/pii/S0022509618308500 . Please refer to any applicable terms of use of the publisher.

    Accepted author manuscript, 5 MB, PDF document

    Embargo ends: 25/10/19

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    Licence: CC BY-NC-ND

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