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Thermo-mechanical and superimposed high-cycle fatigue interactions in compacted graphite iron
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
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, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
2015 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 80, p. 381-390Article 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. Vol. 80, p. 381-390
Keywords [en]
Cast iron, Thermo-mechanical fatigue, High-cycle fatigue, Fatigue crack growth, Life prediction
National Category
Other Engineering and Technologies Mechanical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-121029DOI: 10.1016/j.ijfatigue.2015.06.005ISI: 000360596500040OAI: oai:DiVA.org:liu-121029DiVA, id: diva2:850966
Available from: 2015-09-03 Created: 2015-09-03 Last updated: 2018-02-13Bibliographically 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. p. 36
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1719
National Category
Mechanical Engineering Materials Engineering
Identifiers
urn:nbn:se:liu:diva-121031 (URN)10.3384/lic.diva-121031 (DOI)978-91-7519-023-5 (ISBN)
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
2. Fatigue of Heavy-Vehicle Engine Materials: Damage Mechanisms, Laboratory Experiments and Life Estimation
Open this publication in new window or tab >>Fatigue of Heavy-Vehicle Engine Materials: Damage Mechanisms, Laboratory Experiments and Life Estimation
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to increasing demands on sustainability exerted by end-costumers and policy makers, heavyvehicle manufacturers are urged to increase the engine efficiency in order to reduce the exhaust gas emission. However, increasing the efficiency is also associated with an elevated fatigue rate of the materials constituting the engine parts, which consequently reduces the engine service life. The aim of the present thesis is therefore to confront the expected increase by studying the fatigue behaviour and damage mechanisms of the materials typically employed in heavy-vehicle diesel engines. With this knowledge, this work seeks to guide the development of new heavy-vehicle engine materials, as well as to develop improved life estimation methods designated to assist the mechanical design of durable heavy-vehicle engines.

In essence, a large set of thermo-mechanical fatigue (TMF) and combined thermomechanical and high-cycle fatigue (TMF-HCF) tests is conducted at engine load conditions on laboratory specimens of lamellar, compacted and spheroidal graphite iron. In this way, the fatigue performance and associated damage mechanisms are investigated. In particular, a new fatigue property is identified, the TMF-HCF threshold, which quantifies how resistant a material is to superimposed high-cycle fatigue.

The damage mechanism at low temperatures (≲500°C) is confirmed to consist of the initiation, propagation and coalescence of numerous microcracks. Based on this, a successful fatigue life estimation model is formulated, allowing accurate estimations of TMF and TMF-HCF tests on smooth specimens, and TMF tests on notched specimens. In the latter case, the microcrack growth behaviour in non-uniform cyclic stress fields and its implications for life estimation are clarified. At elevated temperatures (≳500°C), surface oxidation is shown to govern the fatigue performance of cast iron grades intended for exhaust manifolds. It is observed that oxide intrusions are induced, from which surface fatigue cracks are initiated. Consequently, an optimal material at these conditions should have a low oxide growth rate and few casting defects at the surface, as these factors are found to stimulate the growth of intrusion.  

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 49
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1894
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-145176 (URN)10.3384/diss.diva-145176 (DOI)9789176853900 (ISBN)
Public defence
2018-03-16, ACAS, Hus A, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
VINNOVASwedish Foundation for Strategic Research
Available from: 2018-02-13 Created: 2018-02-13 Last updated: 2018-02-13Bibliographically approved

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