The effect of superimposed high-cycle fatigue on thermo-mechanical fatigue in cast iron

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

doi:10.1016/j.ijfatigue.2016.03.020

Cited by 29 publications

(28 citation statements)

References 17 publications

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“…These observations are in direct accordance with the general unloading modulus behaviour of cast iron mentioned above, i.e. that the only effect caused by the addition of a HCF strain range was a decrease in the negative slope of the linear unloading modulus curve [42,67] (Paper I and III).…”

Section: Low Temperaturessupporting

confidence: 89%

“…Norman et al [42,67] (Paper I and III) confirmed this general fatigue process using the concept of the unloading modulus, following the previously mentioned hypothesis put forth by Hanney and Zambelli [73,74]. It was observed that regardless of cast iron type and cyclic load conditions, including isothermal low-cycle fatigue (LCF), TMF and TMF-HCF, the unloading modulus always decreased linearly with the number of cycles until a consistent critical value was attained.…”

Section: Low Temperaturesmentioning

confidence: 64%

“…At generic cyclic load conditions at room temperature and up to 500 o C, microcracks have been observed to initiate at multiple graphite tips on polished samples of LGI, CGI and SGI, propagating transversally into the matrix [49,[58][59][60][61][62][63][64][65][66], including the work of Norman et al [42,67,68] (Paper I, III and V), as similar to when under monotonic load conditions. An example of a graphite-initiated microcrack caused by thermo-mechanical cycling is shown in Figure 7a.…”

Section: Low Temperaturesmentioning

confidence: 88%

“…The limit between the two temperature regimes is not completely distinct since it is likely to depend on multiple aspects, such as the material and the characteristics of the cyclic mechanical load. Nevertheless, based on a number of studies on SGI [21,42,[53][54][55][56][57], the limit temperature is presumed to be in the range of 500-600 o C in cast iron.…”

Section: Damage Mechanisms Under Cyclic Load Conditionsmentioning

confidence: 99%

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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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Section: Low Temperaturessupporting

confidence: 89%

Section: Low Temperaturesmentioning

confidence: 64%

Section: Low Temperaturesmentioning

confidence: 88%

Section: Damage Mechanisms Under Cyclic Load Conditionsmentioning

confidence: 99%

See 2 more Smart Citations

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

Norman¹

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“…If a fatigue crack forms at an inclusion and begins to propagate depends on the type of inclusion, size of the inclusion, distribution of inclusion and residual stresses present. Discontinuities such as porosities which are quite common in cast-and powder-metallurgy alloys can also work as possible crack initiation points [52][53][54][55][56]. Crack initiation transition from surface to sub-surface/internal pores and inclusions have been reported to occur during giga-cycle fatigue testing [45,57].…”

Section: Fatigue 15mentioning

confidence: 99%

Cracks in superalloys

Saarimäki¹

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Linköping 2018Cover image: An orientation imaging map illustrating the general crack propagation behaviour of a 2160 s dwell-time tested Inconel 718 bar run at 550 ○ C, with a 15 % superimposed overload at the beginning of the dwell-time.During the course of research underlying this thesis, Jonas Saarimäki was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Jonas Saarimäki AbstractGas turbines are widely used in industry for power generation and as a power source at hard to reach locations where other possibilities for electrical power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects.The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD).The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when iii iv an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ-phase boundaries with subsequent oxidation of the δ phase.This thesis comprises two parts. Part I gives an introducti...

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Imposed Thermal Fatigue and Post-Thermal-Cycle Wear Resistance of Biomimetic Gray Cast Iron by Laser Treatment

Sui

Zhou

Zhang

et al. 2017

Metall Mater Trans A

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The effect of superimposed high-cycle fatigue on thermo-mechanical fatigue in cast iron

Cited by 29 publications

References 17 publications

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

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

Cracks in superalloys

Imposed Thermal Fatigue and Post-Thermal-Cycle Wear Resistance of Biomimetic Gray Cast Iron by Laser Treatment

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