Thermo-mechanical fatigue property and life prediction of vermicular graphite iron

Zhang, M.X.; Pang, J.C.; Yu, Qin; Li, S.X.; Wang, M.; Zhang, Z.F.

doi:10.1016/j.msea.2017.05.035

Cited by 40 publications

(13 citation statements)

References 25 publications

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“…Typically, this growth mode ends with the failure of the specimen at a point when the final crack length is about 1 to 2mm, regardless of cast iron type. Similar fatigue crack growth involving microcrack coalescence has also been reported in the case of thermal fatigue [49,63], as well as for TMF and TMF-HCF tests [65,66]. Thus, regardless of the particular cyclic load condition employed, the fatigue process in cast iron seems to be following a general pattern consisting of a brief crack initiation phase and a subsequent crack propagation phase involving the growth and coalescence of multiple microcracks.…”

Section: Low Temperaturessupporting

confidence: 71%

“…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%

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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: 71%

Section: Low Temperaturesmentioning

confidence: 88%

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

Norman¹

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“…Its strength, plasticity, and toughness are superior to that of gray iron. Its castability, thermal fatigue properties, and heat conductivity are better than those of ductile iron [1,2,3]. Therefore, vermicular graphite cast iron has been widely used in cylinder heads and engine blocks internationally.…”

Section: Introductionmentioning

confidence: 99%

Research on the Oxidation Mechanism of Vermicular Graphite Cast Iron

Guo

Yang

Guo³

et al. 2019

Materials

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The oxidation mechanism of vermicular graphite cast iron was studied. The oxidation reaction starts from graphites and diffused slowly. Graphites in vermicular graphite are interconnected, coral-like clusters, providing the main oxidation core and channel. The worm-like graphites on the surface are mostly oxidized and form oxide affected zones. The oxide films are composed of a loose oxide layer with the phases of Fe3O4, Fe2O3, and FeO, and a dense passivation layer with FeO and Fe2SiO4. After oxidation, pearlites in the vermicular graphite cast iron are decomposed into ferrite and cementite at high temperatures.

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“…And for the notch components especially with high stress concentration factors, the fatigue strength is less dependent on the tensile strength than a smooth specimen (Sonsino, 2007). On the other hand, considering the influencing factors of fatigue strength or life, such as notch, geometry, sample dimension, surface roughness, loading and service environment, researchers have proposed many life prediction methods and models (Jin et al., 2018; Kirane and Bažant, 2016; Wang et al., 2017; Wormsen et al., 2015a, 2015b; Zhang et al., 2017, 2018). Besides, some fatigue assessment guidances can be used to design S–N curves (Haibach, 2003; Sims, 2012).…”

Section: Introductionmentioning

confidence: 99%

A fatigue life prediction method from magnetic pole material to simulation part

Pan

Pang

Xie

et al. 2019

International Journal of Damage Mechanics

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Due to the higher reliability needs of the large moving component motor-generator rotor, the assessment of the service life has drawn more and more attention. After finite element analysis of the rotor, the simulation part which can represent the magnetic pole with the most dangerous position of the rotor was designed to investigate the S–N curves. Compared with the conventional specimen, considering the main influencing factors of fatigue life for simulation part, the comprehensive factor was proposed to establish the fatigue life relationship between magnetic pole material and simulation part. It was found that the calculation method of fatigue notch factor based on the notch sensitivity factor is relatively simple and practical, and there is no significant effect of surface roughness on high and low cycle fatigues for low roughness ( R a is about 1 µm), and the dimension factor changes linearly with the scale factor. Based on those results, a fatigue life prediction method was proposed and validated, and the predicted results were in good agreement with the experimental data. This study will provide a reasonable reference to determine the fatigue life prediction of large moving components.

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Thermo-mechanical fatigue property and life prediction of vermicular graphite iron

Cited by 40 publications

References 25 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

Research on the Oxidation Mechanism of Vermicular Graphite Cast Iron

A fatigue life prediction method from magnetic pole material to simulation part

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