A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules

Andriollo, Tito; Thorborg, Jesper; Tiedje, Niels Skat; Hattel, Jesper Henri

doi:10.1088/0965-0393/24/5/055012

Cited by 30 publications

(45 citation statements)

References 48 publications

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“…In the equatorial area, some traces of the superficial destruction of the spheroid structure in the form of parallel shifted graphene layers, were revealed in the radial sectors (Figure c,d). Such a displacement of graphene layers could be caused by the local tangential stress effect on the superficial shield of the graphite nodule, mentioned by Andriollo et al (). This effect was active when the graphite nodule was finally pulled out from the matrix.…”

Section: Resultsmentioning

confidence: 97%

“…Thus, the models of the microstructural determination of damage course in the spheroidal cast iron were extended to a discrete approach. The local stress field at the G/M interface around a graphite spheroid embedded into metal matrix was analyzed and recognized as a factor involved in the material damage (Andriollo, Thorborg, Tiedje, & Hattel, ; Bonora & Ruggiero, ; Di Cocco, Iacoviello, Rossi, & Iacoviello, ; Fukumasu, Pelegrino, Cueva, Souza, & Sinatora, ; Zhang et al, ). Furthermore, the obtained results showed that graphite could not be considered as an isotropic phase.…”

Section: Introductionmentioning

confidence: 99%

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Microscopic approach to micromechanism of damage in spheroidal cast iron

Warmuzek

Polkowska

Gazda

2020

Microscopy Res & Technique

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In this work, the observations of the fracture surface after standard tensile tests of several kinds of spheroidal cast irons, ferritic and austempered ductile irons, have been carried out by means of scanning electron microscopy. The local crack path in the area of graphite (G)/matrix (M) interface has been analyzed as affected by a matrix phase composition and the austempering treatment parameters. The obtained results allowed identifying some determination factors for debonding mode at the G/M interface and their role in a final damage mechanism. Some microstructural details in the microregions composed of graphite and matrix showed that the G-M debonding mode in the separation area of the G/M interface seems to be controlled by macroscopic properties of the alloy and by the morphology of G/M interface. On the other hand, the internal destruction of graphite nodule has been mainly determined by a structure and anisotropy of graphite crystal lattice. K E Y W O R D S characterization, electron microscopy, fracture behavior, iron alloys

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Microscopic approach to micromechanism of damage in spheroidal cast iron

Warmuzek

Polkowska

Gazda

2020

Microscopy Res & Technique

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“…The different DCIs mechanical properties, such as, high values of tensile strength and Young's modulus, among others [7], are some of the reasons that make DCIs very versatile for different engineering fields such as the automotive industry, mining industry, among others [8,9]. To perform the analysis of the mechanical properties, it is necessary to use computational tools, such as the Finite Element Analysis (FEA), which allows for relating the mechanical behavior with the microstructural properties of the DCI [10,11]. In order to obtain adequate results through the FEA, it is necessary to develop models that represent the geometry of the DCI as closely as possible to the real geometries (or to that established by studies concerning nodule sphericity), since models with incorrect approximations, which can show very pronounced or irregular graphite nodules contours, can generate stress concentrators that will lead in practice to an incorrect estimation of the mechanical properties in the FEA simulation.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the models that consider graphite nodules as holes, despise the effects on the mechanical properties of graphite in the microstructure of DCIs. On the other hand, other works have used models where the graphite nodules are not considered as holes, but as ideal spheres of graphite, with the aim of making a thermoelastic formulation of the internal structure of graphite nodules to verify the elastic behavior of a DCI by means of an FEA [10]. At this point, the works that are mentioned above have only used geometric models where nodules are considered as holes or ideal spheres.…”

Section: Introductionmentioning

confidence: 99%

Genetic Algorithm-Based Optimization Methodology of Bézier Curves to Generate a DCI Microscale-Model

et al. 2017

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Abstract:The aim of this article is to develop a methodology that is capable of generating micro-scale models of Ductile Cast Irons, which have the particular characteristic to preserve the smoothness of the graphite nodules contours that are lost by discretization errors when the contours are extracted using image processing. The proposed methodology uses image processing to extract the graphite nodule contours and a genetic algorithm-based optimization strategy to select the optimal degree of the Bézier curve that best approximate each graphite nodule contour. To validate the proposed methodology, a Finite Element Analysis (FEA) was carried out using models that were obtained through three methods: (a) using a fixed Bézier degree for all of the graphite nodule contours, (b) the present methodology, and (c) using a commercial software. The results were compared using the relative error of the equivalent stresses computed by the FEA, where the proposed methodology results were used as a reference. The present paper does not have the aim to define which models are the correct and which are not. However, in this paper, it has been shown that the errors generated in the discretization process should not be ignored when developing geometric models since they can produce relative errors of up to 35.9% when an estimation of the mechanical behavior is carried out.

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“…Regarding SGI, the most common way has been to use a unit-cell approach due to the favourable symmetry of a spheroidal graphite particle [31,105,106,[115][116][117][118][119][120]. In this approach, the RVE is modelled as a cubic or cylindrical cell in which a spherical graphite particle or void is situated.…”

Section: Constitutive Modellingmentioning

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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A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules

Cited by 30 publications

References 48 publications

Microscopic approach to micromechanism of damage in spheroidal cast iron

Microscopic approach to micromechanism of damage in spheroidal cast iron

Genetic Algorithm-Based Optimization Methodology of Bézier Curves to Generate a DCI Microscale-Model

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

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