Predicting dwell fatigue life in titanium alloys using modelling and experiment

Fatigue is a difficult multi-scale modelling problem nucleating from localised plasticity at the scale of dislocations and microstructure with significant engineering safety implications. Cold dwell fatigue is a phenomenon in titanium where stress holds at moderate temperatures lead to substantial r...

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Bibliographic Details
Published in:Nature communications 2020-11, Vol.11 (1), p.5868-5868, Article 5868
Main Authors: Xu, Yilun, Joseph, Sudha, Karamched, Phani, Fox, Kate, Rugg, David, Dunne, Fionn P. E., Dye, David
Format: Article
Language:English
Subjects:
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Alloys
Cyclic loads
Dislocation
Dislocation density
Electron backscatter diffraction
Fatigue life
Fatigue tests
Grains
Humanities and Social Sciences
Jet engines
Metal fatigue
Modelling
multidisciplinary
Plastic properties
Plasticity
Safety engineering
Science
Science (multidisciplinary)
Spin tests
Threshold stress
Titanium
Titanium alloys
Titanium base alloys
Transmission electron microscopy
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Summary:Fatigue is a difficult multi-scale modelling problem nucleating from localised plasticity at the scale of dislocations and microstructure with significant engineering safety implications. Cold dwell fatigue is a phenomenon in titanium where stress holds at moderate temperatures lead to substantial reductions in cyclic life, and has been implicated in service failures. Using discrete dislocation plasticity modelling complemented by transmission electron microscopy, we successfully predict lifetimes for ‘worst case’ microstructures representative of jet engine spin tests. Fatigue loading above a threshold stress is found to produce slip in soft grains, leading to strong dislocation pile-ups at boundaries with hard grains. Pile-up stresses generated are high enough to nucleate hard grain basal dislocations, as observed experimentally. Reduction of applied cyclic load alongside a temperature excursion during the cycle lead to much lower densities of prism dislocations in soft grains and, sometimes, the elimination of basal dislocations in hard grains altogether. Material fatigue is the most common source behind failures of mechanical structures. Here the authors combine transmission electron microscopy, high-resolution electron backscatter diffraction and discrete dislocation plasticity modeling to study the underlying mechanism of dwell fatigue in titanium alloys.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-020-19470-w