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Fatigue of Heavy-Vehicle Engine Materials: Experimental Analysis and Life Estimation
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The heavy-vehicle automotive industry is constantly subjected to higher demands. In particular, new European emission standards are formulated with the intention of improving the environmental friendliness of newly-produced vehicles through reduced exhaust emission. In one way or another, this implies a successive improvement of the engine efficiency, which in turn, inevitably will require a higher combustion pressure and temperature. This is a respectable challenge for future engine constructions, but also for the engineering materials used to embody them. As higher thermal and mechanical loads must be sustained, there is a higher rate of wear, and consequently, a negative effect on the extent of the engine lifetime.

The aim of the present thesis is to confront the expected increase in rate of wear, henceforth referred to as fatigue, by studying the effect on materials typically employed in heavy-vehicle engines, namely cast irons. Foremost, the intention has been to improve the understanding of the physical mechanisms of fatigue in these materials, in order to develop a lifetime estimation method designated to assist the mechanical design of heavy-vehicle engines.

In essence, a large set of thermo-mechanical fatigue (TMF) and combined thermo-mechanical and high-cycle fatigue (TMF-HCF) tests has been conducted at engine load conditions on laboratory specimens of lamellar, compacted and spheroidal graphite irons. In this way, these three different material groups have been experimentally compared and the associated fatigue mechanism has been studied. In particular, a new property related to TMF-HCF conditions has been identified and measured, . Regarding the fatigue mechanism, it has been affirmed to consist of the initiation, propagation and coalescence of numerous microcracks. Based on this, a successful lifetime assessment model was formulated, allowing good estimations of the fatigue life of laboratory specimens subjected to both TMF and TMF-HCF conditions.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 36 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1719
National Category
Mechanical Engineering Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-121031DOI: 10.3384/lic.diva-121031ISBN: 978-91-7519-023-5 (print)OAI: oai:DiVA.org:liu-121031DiVA: diva2:851017
Presentation
2015-09-18, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2015-09-28Bibliographically approved
List of papers
1. Damage evolution in compacted graphite iron during thermomechanical fatigue testing
Open this publication in new window or tab >>Damage evolution in compacted graphite iron during thermomechanical fatigue testing
2016 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 29, no 1-2, 26-33 p.Article in journal (Refereed) Published
Abstract [en]

Thermomechanical fatigue properties of a compacted graphite iron in an out of phase configuration are investigated for different maximum temperatures and mechanical strain ranges. Furthermore, the stressï¿œstrain hysteresis loops are analysed, and, in particular, the unloading modulus, i.e. the elastic modulus measured during specimen unloading, is obtained from each cycle. This material parameter has earlier been explicitly related to the amount of microcracking in cast irons. The results show that the unloading modulus linearly declines with the numbers of cycles in all tests performed. In addition, the rate of change of the unloading modulus is closely related to the number of cycles to failure. Accordingly, it is concluded that microcracks are independently propagated by fatigue until a point of rapid crack linking resulting in ultimate failure. This is supported by microstructural analyses consisting of optical microscope images taken at different stages throughout the life of a specimen.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keyword
Thermomechanical fatigue, Out-of-phase loading, Compacted graphite iron, Microcracking
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-121028 (URN)10.1179/1743133615Y.0000000019 (DOI)000377468800005 ()
Note

Funding agencies: Scania CV AB; Swedish Governmental Agency for Innovation Systems [FFI-2012-03625]; Swedish Foundation for Strategic Research [SM12-0014]; Strategic Faculty Grant AFM (SFO-MAT-LiU) at Linkoping University [2009-00971]

Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2017-12-04Bibliographically approved
2. Thermo-mechanical and superimposed high-cycle fatigue interactions in compacted graphite iron
Open this publication in new window or tab >>Thermo-mechanical and superimposed high-cycle fatigue interactions in compacted graphite iron
2015 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 80, 381-390 p.Article in journal (Refereed) Published
Abstract [en]

The effect of adding a superimposed high-frequent strain load, denoted as a high-cycle fatigue strain component, upon a strain-controlled thermo-mechanical fatigue test has been studied on a compacted graphite iron EN-GJV-400 for different thermo-mechanical fatigue cycles and high-cycle fatigue strain ranges. It is demonstrated that the successive application of an high-cycle fatigue load has a consistent effect on the fatigue life, namely the existence of a constant high-cycle fatigue strain range threshold below which the fatigue life is unaffected but severely reduced when above. This effect on the fatigue life is predicted assuming that microstructurally small cracks are propagated and accelerated according to a Paris law incorporating an experimentally estimated crack opening level.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Cast iron, Thermo-mechanical fatigue, High-cycle fatigue, Fatigue crack growth, Life prediction
National Category
Other Engineering and Technologies Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-121029 (URN)10.1016/j.ijfatigue.2015.06.005 (DOI)000360596500040 ()
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2017-12-04Bibliographically approved
3. The effect of superimposed high-cycle fatigue on thermo-mechanical fatigue in cast iron
Open this publication in new window or tab >>The effect of superimposed high-cycle fatigue on thermo-mechanical fatigue in cast iron
2016 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 88, 121-131 p.Article in journal (Refereed) Published
Abstract [en]

The eect of superimposing a high-cycle fatigue strain load on an out-ofphase thermo-mechanical fatigue test of a lamellar, compacted and spheroidal graphite iron, has been investigated. In particular, dierent total mechanical strain ranges, maximum temperatures and high-cycle fatigue strain ranges have been studied. From this, a new property has been identied, measured and compared, namely the thermo-mechanical and high-cycle fatigue threshold, dened as the high-cycle fatigue strain range at which the life is reduced to half. Using a model developed earlier, the lifetimes and the threshold have been successfully estimated for the lamellar and compacted graphite iron, however underestimated for the spheroidal graphite iron. Nevertheless, an expression of the threshold was deduced from the model, which possibly can estimate its value in other cast irons and its high-cycle fatigue frequency dependence.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Cast iron, Thermo-mechanical fatigue, High-cycle fatigue, Fatigue crack growth, Life prediction
National Category
Mechanical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:liu:diva-121030 (URN)10.1016/j.ijfatigue.2016.03.020 (DOI)000375817000013 ()
Note

Funding agencies: Scania CV AB; Swedish Governmental Agency for Innovation Systems [FFI - 2012 - 03625]; Swedish Foundation for Strategic Research [SM12 - 0014]; Linkoping University [2009 - 00971]

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Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2017-06-20Bibliographically approved

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