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Damage evolution in compacted graphite iron during thermomechanical fatigue testing
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Scania CV AB, Materials Technology, Södertälje, Sweden.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
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. Vol. 29, no 1-2, 26-33 p.
Keyword [en]
Thermomechanical fatigue, Out-of-phase loading, Compacted graphite iron, Microcracking
National Category
Other Materials Engineering
URN: urn:nbn:se:liu:diva-121028DOI: 10.1179/1743133615Y.0000000019ISI: 000377468800005OAI: diva2:850964

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: 2016-07-06Bibliographically approved
In thesis
1. Fatigue of Heavy-Vehicle Engine Materials: Experimental Analysis and Life Estimation
Open this publication in new window or tab >>Fatigue of Heavy-Vehicle Engine Materials: Experimental Analysis and Life Estimation
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.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1719
National Category
Mechanical Engineering Materials Engineering
urn:nbn:se:liu:diva-121031 (URN)10.3384/lic.diva-121031 (DOI)978-91-7519-023-5 (print) (ISBN)
2015-09-18, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2015-09-28Bibliographically approved

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