Understanding thermal alleviation in cold dwell fatigue in titanium alloys

Zheng, Zebang; Stapleton, Adam M.; Fox, Kate; Dunne, Fionn P.E.

doi:10.1016/j.ijplas.2018.07.018

Cited by 44 publications

(33 citation statements)

References 34 publications

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“…Inclusion of the elevated temperature secondary stress hold, Type Z, results in the lowest rate of evolution of macroscopic strain of the three cycles. Therefore, a thermal alleviation effect 41 is observed, with reduced overall creep strain accumulation in Loading Type Z than in Type Y.…”

Section: Resultsmentioning

confidence: 92%

Predicting dwell fatigue life in titanium alloys using modelling and experiment

Joseph

Karamched

et al. 2020

Nat Commun

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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.

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Section: Resultsmentioning

confidence: 92%

Predicting dwell fatigue life in titanium alloys using modelling and experiment

Joseph

Karamched

et al. 2020

Nat Commun

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“…The modelling work permits the investigation of behaviour in virtual microstructures and in representative in-service conditions so that rig spin tests carried out by Rolls-Royce may be interpreted in the context of the full thermomechanical loading of in-service discs. These studies have demonstrated the role of temperature, alpha-beta microstructure, thermal alleviation, and stress state in dwell fatigue [3], and have provided the pathway to dwell-resistant microstructures. Fig.…”

Section: Hexmat Case Study 1 -Dwell Fatigue Modellingmentioning

confidence: 99%

Titanium Research Developments in the United Kingdom

Jackson

2020

MATEC Web Conf.

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The paper presents highlights of the titanium alloy research developments since Ti-2015 (San Diego). The review underlines the strong and collaborative fundamental research conducted at UK universities through strategic government sponsored programmes. The role of advanced characterisation and modelling techniques in order to better understand the effects of deformation, fatigue loading and environment on titanium alloys continues to be world leading. Researchers in the UK are also continuing to develop a range of new alloys, methods of extraction and emerging near net shape processes via casting, powder and wire-fed routes.

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“…It can be seen that grains with c-axis parallel to the loading axis and grains with c-axis nearly perpendicular to the loading axis are present as alternating layers. Such grain combinations were termed as rogue grain combinations by Dunne et al [12] and is known to cause early crack nucleation under dwell fatigue loading conditions. The as-received rods were subjected to three different heat treatments as shown schematically in Fig.…”

Section: Starting Materialsmentioning

confidence: 99%

“…IMI 834 is a near alpha alloy that is used in the low-pressure compressor sections of a gas turbine engine. The rotating components of the gas turbine engine experience loading spectrums similar to that of dwell fatigue and this material is known to show dwell fatigue sensitivity in its normally used bimodal microstructure [12]. A dedicated study comparing the ambient temperature dwell fatigue behavior of different microstructures in IMI 834 is absent in the literature and hence is the focus of the current study.…”

Section: Introductionmentioning

confidence: 99%

Normal and dwell fatigue behavior of a near-alpha titanium alloy - IMI 834

et al. 2020

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Dwell sensitivity of titanium alloys at ambient temperature (~250 C) is a well-known phenomenon, although the question about the exact micromechanical reasons responsible for this still remains open. In this work, the normal and dwell fatigue response of a near-alpha titanium alloy, IMI 834, is studied. Samples with three different microstructures, namely, fully lamellar, fully equiaxed and bimodal, are evaluated for their dwell fatigue behaviors. A reduction in fatigue life by at least an order of magnitude is seen in all the three microstructures. Large plastic strain accumulation (almost equal to the monotonic ductility) was observed during the dwell fatigue loading condition and this is held responsible for this large debit in fatigue life. The normal fatigue lives decreased in the order, bimodal > fully equiaxed > fully lamellar, while the dwell fatigue lives decreased in the order, fully equiaxed > fully lamellar > bimodal. Bimodal microstructure showed a dwell fatigue debit of 17, while fully lamellar and fully equiaxed showed a debit of 9 and 10, respectively.

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Understanding thermal alleviation in cold dwell fatigue in titanium alloys

Cited by 44 publications

References 34 publications

Predicting dwell fatigue life in titanium alloys using modelling and experiment

Predicting dwell fatigue life in titanium alloys using modelling and experiment

Titanium Research Developments in the United Kingdom

Normal and dwell fatigue behavior of a near-alpha titanium alloy - IMI 834

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