Thermo-mechanical and superimposed high-cycle fatigue interactions in compacted graphite iron

Norman, Viktor; Skoglund, Peter; Leidermark, Daniel; Moverare, Johan

doi:10.1016/j.ijfatigue.2015.06.005

Cited by 24 publications

(37 citation statements)

References 15 publications

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“…Regarding TMF testing with superimposed HCF, only a handful of experimental studies have been carried out on cast irons including the work of this thesis [37][38][39][44][45][46]. Nevertheless, it has been reported that there is an existence of a consistent HCF strain range, below which the fatigue life is unaffected by the superimposed HCF load, for LGI, CGI and SGI [39,44,46].…”

Section: Crack Initiation and Propagation During Cyclic Loadingmentioning

confidence: 99%

“…Nevertheless, it has been reported that there is an existence of a consistent HCF strain range, below which the fatigue life is unaffected by the superimposed HCF load, for LGI, CGI and SGI [39,44,46]. Regarding the fatigue crack mechanisms, extensive studies have only been conducted on SGI.…”

Section: Crack Initiation and Propagation During Cyclic Loadingmentioning

confidence: 99%

“…Similarly, the model presented by Norman et al [46] (Paper II) was also based on a Paris law, Equation 5, combined with Equation 4 to account for a superimposed HCF load. In contrast to previous models, they interpreted the crack length as an average of the large number of microcracks and the point of failure as the instant when the average microcrack length gets in the same order as the average distance between microcracks.…”

Section: Life Assessmentmentioning

confidence: 99%

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Fatigue of Heavy-Vehicle Engine Materials : Experimental Analysis and Life Estimation

Norman¹

2015

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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.iii

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Section: Crack Initiation and Propagation During Cyclic Loadingmentioning

confidence: 99%

Section: Crack Initiation and Propagation During Cyclic Loadingmentioning

confidence: 99%

Section: Life Assessmentmentioning

confidence: 99%

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Fatigue of Heavy-Vehicle Engine Materials : Experimental Analysis and Life Estimation

Norman¹

2015

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“…However, the repetition of start-up and shutdown of engines can cause high mechanical loading and may lead to localized crack at the engine blocks and heads as a result of thermo-mechanical fatigue [1,2]. From this aspect, researchers have found that Compacted Graphite Iron (CGI) is the best candidate in replacing CI.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of cutting force and surface roughness in high-speed milling of compacted graphite iron

et al. 2017

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Abstract. Compacted Graphite Iron, (CGI) is known to have outstanding mechanical strength and weightto-strength ratio as compared to conventional grey cast iron, (CI). The outstanding characteristics of CGI is due to its graphite particle shape, which is presented as compacted vermicular particle. The graphite is interconnected with random orientation and round edges, which results in higher mechanical strength. Whereas, graphite in the CI consists of a smooth-surfaced flakes that easily propagates cracks which results in weaker and brittle properties as compared to CGI. Owing to its improved properties, CGI is considered as the best candidate material in substituting grey cast iron that has been used in engine block applications for years. However, the smooth implementation of replacing CI with CGI has been hindered due to the poor machinability of CGI especially at high cutting speed. The tool life is decreased by 20 times when comparing CGI with CI under the same cutting condition. This study investigates the effect of using cryogenic cooling and minimum quantity lubrication (MQL) during high-speed milling of CGI (grade 450). Results showed that, the combination of internal cryogenic cooling and enhanced MQL improved the tool life, cutting force and surface quality as compared to the conventional flood coolant strategy during highspeed milling of CGI.

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“…Similarly, the model presented by Norman et al [87] (Paper II) was also based on Paris' law, Equation 5, combined with Equation 4 to account for a superimposed HCF load. In contrast to previous models, the crack length was interpreted as an average of a large number of microcracks and the point of failure as the instant when the average microcrack length gets in the same order as the average distance between microcracks.…”

Section: Fatigue Life Estimationmentioning

confidence: 99%

Fatigue of Heavy-Vehicle Engine Materials: Damage Mechanisms, Laboratory Experiments and Life Estimation

Norman¹

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Due to increasing demands on sustainability exerted by end-costumers and policy makers, heavy-vehicle 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 thermo-mechanical 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 o 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 o 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.iii Populärvetenskaplig sammanfattningMen anledning av ökande krav på hållbarhet från slutkunder och beslutsfattare pressas tillverkare av tunga lastbilar att öka drivlinans verkningsgrad och minska utsläppen av luftföroreningar. För dieselmotorn som är den vanligaste motortypen i tunga lastbilar förväntas i dagsläget det största bidraget till att möta kraven vara att öka motorns verkningsgrad. Högre verkningsgrad innebär lägre bränsleförbrukning, vilket i sin tur står i direkt proportion till mängden utsläppt koldioxid. Denna eftertraktade förbättring åstadkoms generellt genom att öka kompressionsförhållandet, vilket medför en ökning i det maximala förbränningstrycket och temperaturen i förbränningskam-maren. Till följd av detta uppkommer även ett ökat slitage av motorkomponenterna, i tekniska sammahang kallat utma...

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Thermo-mechanical and superimposed high-cycle fatigue interactions in compacted graphite iron

Cited by 24 publications

References 15 publications

Fatigue of Heavy-Vehicle Engine Materials : Experimental Analysis and Life Estimation

Fatigue of Heavy-Vehicle Engine Materials : Experimental Analysis and Life Estimation

Evaluation of cutting force and surface roughness in high-speed milling of compacted graphite iron

Fatigue of Heavy-Vehicle Engine Materials: Damage Mechanisms, Laboratory Experiments and Life Estimation

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