WorldCat Identities

Yvonnet, Julien

Overview
Works: 25 works in 38 publications in 2 languages and 235 library holdings
Roles: Author, Opponent, Thesis advisor, Other, htt
Publication Timeline
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Most widely held works by Julien Yvonnet
Computational Homogenization of Heterogeneous Materials with Finite Elements by Julien Yvonnet( )

12 editions published between 2019 and 2020 in English and held by 205 WorldCat member libraries worldwide

This monograph provides a concise overview of the main theoretical and numerical tools to solve homogenization problems in solids with finite elements. Starting from simple cases (linear thermal case) the problems are progressively complexified to finish with nonlinear problems. The book is not an overview of current research in that field, but a course book, and summarizes established knowledge in this area such that students or researchers who would like to start working on this subject will acquire the basics without any preliminary knowledge about homogenization. More specifically, the book is written with the objective of practical implementation of the methodologies in simple programs such as Matlab. The presentation is kept at a level where no deep mathematics are required
Multi-phase-field modeling of anisotropic crack propagation for polycrystalline materials by Thanh-Tung Nguyen( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

Solving hyperelastic material problems by asymptotic numerical method by Saeid Nezamabadi( )

1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide

A computational mechanics special issue on: data-driven modeling and simulation--theory, methods, and applications by W. K Liu( )

1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide

Méthode asymptotique numérique pour l'étude multi échelle des instabilités dans les matériaux hétérogènes by Saeid Nezamabadi( Book )

2 editions published in 2009 in French and held by 2 WorldCat member libraries worldwide

The multiscale modelling of the heterogeneous materials is a challenge in computational mechanics. In the nonlinear case, the effective properties of heterogeneous materials cannot be obtained by the techniques used for linear media because the superposition principle is no longer valid. Hence, in the context of the finite element method, an alternative to mesh the whole structure, including all heterogeneities, is the use of the multiscale finite element method (FE2). These techniques have many advantages, such as taking into account : large deformations at the micro and macro scales, the nonlinear constitutive behaviors of the material, and microstructure evolution. The nonlinear problems in micro and macro scales are often solved by the classical Newton-Raphson procedures, which are generally suitable for solving nonlinear problems but have difficulties in the presence of instabilities. In this thesis, the combination of the multiscale finite element method (FE2) and the asymptotic numerical method (ANM), called Multiscale-ANM, allows one to obtain a numerical effective technique for dealing with the instability problems in the context of heterogeneous materials. These instabilities can occur at both micro and macro levels. Different classes of material constitutive relation have been implemented within our procedure. To improve the multiscale problem conditioning, a second order homogenization technique was also adapted in the framework of Multiscale-ANM technique. Furthermore, to reduce the computational time, some techniques been proposed in this work
A data-driven computational homogenization method based on neural networks for the nonlinear anisotropic electrical response of graphene/polymer nanocomposites by Xiaoxin Lü( )

1 edition published in 2018 in English and held by 2 WorldCat member libraries worldwide

Etude de la fléxoélectricité de nanosystèmes par le développement d'algorithmes mêlant approche atomistique et mécanique des milieux continus by Gautier Lecoutre( )

2 editions published in 2018 in French and held by 2 WorldCat member libraries worldwide

The flexoelectricity tensor of a material characterizes its ability to polarize under the action of a deformation gradient. The phenomenon is still rarely used though it exists in every material, because the effects are usually very weak. However, for nanoscale systems, flexoelectricity can be largely enhanced because of a possibly much greater gradient. Thus, the aim of this PHD thesis is to build a model that would allow us to compute the characteristic tensors of flexoelectricity in order to design a nanosytem in which huge flexoelectric effects could be used for energy conversion. For that purpose, we have studied the flexion of several semi-conducting Single-Wall Carbon NanoTubes (SWCNT), considered either as continuous cylinders or as a discrete network of carbon atoms. In the continuum point of view, we have applied the principle of virtual powers and classical thermodynamics to systematically obtain the constitutive equations of a semi-conducting, electro-magnetic deformable continuum, including the effects of the deformation, polarization and magnetization gradients. Meanwhile, we have improved an atomistic model with distributed permanent and induced dipoles to simulate the inverse flexoelectric effect on the SWCNTs. Using homogenization hypothesis, we have coupled these two approaches by obtaining the equations binding the atomistic quantities computed in the numerical simulations, with the corresponding macroscopic quantities used in the previously obtained constitutive equations. The first numerical results seem to show a notable variation of the elements of the flexoelectric tensors as a function of the radius and length of the SWCNT
Approches d'homogénéisation numériques incrémentales pour le calcul des structures hétérogènes élasto-plastiques et élasto-visco-plastiques by Trung Hieu Hoang( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

In this work, computational homogenization methods for nonlinear materials with elasto-plastic and elasto-visco-plastic phases are developed, with application to the computation of heterogeneous structures made of these nonlinear materials under cyclic loading. The proposed techniques are based on incremental approaches. In a first part, we develop a methodology to determine the size of an RVE in the nonlinear case for the types of nonlinear behavior mentioned above. For this purpose, a convergence study of the parameters of a semi-analytical incremental constitutive law is carried out. This method allows reducing computational times related to the identification of these parameters and provides a better approximation of the effective constitutive relationship, which can then be used in a structure calculation once identified. In a second part, we propose an incremental computatioal homogenization method in which the originality is to compute directly the effective tangent tensor by superposition of numerical solutions computed by finite elements on an RVE, by taking advantage of the linearization of the problem at each increment. An alternative scheme to classical multilevel finite element techniques (FE2) is then developed, with the advantage of a reduced number of computations to perform on the RVE. The technique is applied to the computation of heterogeneous, nonlinear structures, for anisotropic microstructures or with complex morphologies and for phase with elastoplastic behavior with isotropic and kinematic hardening
Compressive failure of composites: A computational homogenization approach( )

1 edition published in 2015 in English and held by 1 WorldCat member library worldwide

Abstract: This paper revisits the modeling of compressive failure of long fiber composite materials by considering a multiscale finite element approach. It is well known that this failure follows from a fiber microbuckling phenomenon. Fiber microbuckling is governed by both material and geometrical quantities: the elastoplastic shear behavior of the matrix and the fiber misalignment. Although all these parameters are easily accounted by a finite element analysis at the local level, the failure is also influenced by macrostructural quantities. That is why a multilevel finite element model (FE 2) is relevant to describe the compressive failure of composite. Furthermore, fiber local buckling leads to a loss of ellipticity of the macroscopic model, which can be a criterion of failure
Modélisation électro-mécanique multi-échelle des nanocomposites graphène/polymère by Xiaoxin Lu( )

1 edition published in 2017 in French and held by 1 WorldCat member library worldwide

Cette étude porte sur le développement de modèles et de méthodes numériques pour prédire les propriétés électriques et mécaniques des nanocomposites polymères/graphènes.Dans une première partie, un modèle nonlinéaire de conduction électrique prenant en compte l'effet tunnel est introduit pour déterminer la conductivité effective de ces nanocomposites au travers d'une procédure d'homogénéisation numérique. Celle-ci, basée sur une formulation éléments finis a mis en évidence l'influence des paramètres microstructuraux sur la conductivité effective au travers d'une étude statistique.Ensuite, un modèle atomistique de l'interface polymère/graphène a été proposé pour valuer les propriétés de l'interface et de l'interphase. Les champs de contrainte et de déplacement ont été identifiés par une extension de la procédure d'Hardy-Murdoch à partir des simulations de mécanique moléculaire. À l'aide de ces champs, un modèle élastique continue avec des interfaces imparfaites a été identifié et comparé aux résultats des simulations de mécanique moléculaire. Finalement, le modèle atomistique a permis d'identifier un modèle de zone cohésive nonlinéaire pour modéliser la décohésion à l'interface polymère/graphène. Une procédure d'homogénéisation numérique par la méthode des éléments finis a été introduite pour estimer les propriétés mécaniques effectives dans le cadre des transformations finies. Les microstructures déformées ont été utilisées dans le modèle électrocinétique pour déterminer l'impact de la décohésion interfaciale sur la conductivité effective
Méthode des éléments finis augmentés pour la rupture quasi-fragile : application aux composites tissés à matrice céramique by Simon Essongue-Boussougou( )

1 edition published in 2017 in French and held by 1 WorldCat member library worldwide

Le calcul de la durée de vie des Composites tissés à Matrice Céramique (CMC) nécessite de déterminer l'évolution de la densité de fissures dans le matériau(pouvant atteindre 10 mm-1). Afin de les représenter finement on se propose de travailler à l'échelle mésoscopique. Les méthodes de type Embedded Finite Element (EFEM) nous ont paru être les plus adaptées au problème. Elles permettent une représentation discrète des fissures sans introduire de degrés de liberté additionnels.Notre choix s'est porté sur une EFEM s'affranchissant d'itérations élémentaires et appelée Augmented Finite Element Method (AFEM). Une variante d'AFEM, palliant des lacunes de la méthode originale, a été développée. Nous avons démontré que,sous certaines conditions, AFEM et la méthode des éléments finis classique (FEM) étaient équivalentes. Nous avons ensuite comparé la précision d'AFEM et de FEM pour représenter des discontinuités fortes et faibles. Les travaux de thèse se concluent par des exemples d'application de la méthode aux CMC
Phase field modeling of cracks in quasi-brittle and elastoplastic micro-structured materials : topology optimization, 3D printed materials and image-based models by Pengfei Li( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

The objective of this thesis is to develop numerical modeling and simulation techniques to describe the damage in quasi-brittle and elastoplastic composites, which can be obtained by additive manufacturing processes like 3D-printing. We develop phase field methods to fracture and propose several extensions and applications to composites. First, after validating available elastoplastic phase field models on experimental results, we extend these models to interfacial damage, which is central in composites. In a second part, we develop design methodologies for composite microstructures to increase the resistance to cracking, for quasi-brittle and elastoplastic composites. For this purpose, we combine the phase field method and topology optimization (SIMP and BESO techniques). Then, models are proposed to describe cracking in polymer-glass fiber composites obtained by 3D printing, and which are characterized by a strong anisotropy. For this purpose, we develop an original anisotropic elastoplastic phase field model for the macro scale. Finally, experimental images obtained by X-Ray micro tomography are used to model the complex cracking process at the microscale of the composites
Simulation multi-échelle des procédés de fabrication basée sur la plasticité cristalline by Komi Dodzi Badji Soho( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

In this thesis, two coupling methods are proposed for the multiscale simulation of forming processes. In the first part, a simplified procedure (indirect coupling) is adopted to couple the finite element codes (Abaqus and LAM3) with a polycrystalline selfconsistent model based on the large strain elastoplastic behavior of single crystals. This simplified procedure consists in linking the polycrystalline model with the FE analysis by extracting the history of the increment of macroscopic strain and stress, obtained from a preliminary FE simulation with a phenomenological law, and then using it as loading path prescribed to the polycrystalline model. This method is applied to multiscale simulation of skin-pass processes. By following on the loading path extracted at the halfthickness of the sheet, we can predict the evolution of some physical parameters associated with the plasticity model, in particular the crystallographic texture, the morphological texture and hardening. In the second part on this thesis, a small strain version of the elastoplastic polycristalline self-consistent model is coupled to the Abaqus FE code via the user material subroutine UMAT. This coupling (called direct coupling) consists in using crystal plasticity theory as constitutive law at each integration point of the FE mesh. The polycristal is represented by a set of N single crystals. Each time the FE code needs information on the mechanical behavior at the integration points considered, the full polycrystalline constitutive model is called. In order to validate this coupling, simulations of simple mechanical tests have been conducted. The results of this coupling have been validated through comparison with reference models. Unlike phenomenological models, this coupling provides not only information on the overall macroscopic response of the structure, but also important information related to its microstructure
Fracture modeling in clay materials under hydric shrinkageModélisation de fissure dans les matériaux argileux sous retrait hydrique : numerical models, comparisons with experiments and stochastic aspects by Darith-Anthony Hun( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

This thesis is focused on the modeling of crack propagation in random heterogeneous materials or induced by desiccation. A stochastic approach to the modeling of brittle fracture in random media is first proposed. Monte Carlo simulations are specifically conducted to explore microstructural configurations and to subsequently build and identify a mesoscopic phase-field model. In this framework, the stochastic elastic coefficients are defined as fields of apparent properties, obtained under two types of boundary conditions, while the fracture parameters are assumed deterministic and are identified by solving an inverse problem. The methodology allows stochastic simulations of crack propagation to be performed without requiring a fine-grid discretization at the resolution of the heterogeneities.In a second part, we propose a modeling framework combining numerical simulations and physical experiments for the analysis of crack propagation induced by desiccation. Clay drying is specifically investigated on samples filled with rigid inclusions, with the aim of controlling variability on crack initiation and propagation. A finite-strain phase-field model is formulated for shrinkage deformations induced by hydric effects. The experimental analysis is performed by using a digital image correlation technique on a set of configurations with different numbers of inclusions. The deformation fields and crack paths thus obtained are analyzed and allow for the identification of model parameters. A discussion highlighting the advantages and limitations of the framework is finally proposed
Multiscale modeling of materials with mesostructure gradients by Minh Vuong Le( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

Understanding mechanisms at small scales in composite structures is crucial for the design of many applications in engineering, including structures for aircraft engines which allow a reduction of CO2 emissions. The objective of this thesis work is to develop numerical approaches based on the finite element method to describe accurately the thermo-mechanical fields in these complex structures at different scales, at reasonable computations costs.One difficulty in such problems is the lack of scale separation, corresponding to a weak difference between the characteristic dimensions of the heterogeneities and the fluctuation length of the applied loads. Therefore, the classical homogenization methods are poorly accurate near stress concentrations or when global gradient deformation modes such as bending occur.In a first part, we investigate the use of a previously developed method, the filter-based computational homogenization method, and apply it to woven composite structures. The accuracy of the method is tested and a comparison with classical first-order homogenization methods, including with enhanced re-localization process, is conducted.In a second part, an original method is developed in this thesis. The method uses both advantages of computational homogenization and of domain decomposition techniques. The approach, called CMCM (Coarse Mesh Condensation Multiscale) method, is based on several ingredients. The structure is first meshed with a fine mesh, at the scale of heterogeneities. The obtained mesh can be extremely large and lead to intractable computational costs on classical Finite Element solvers. The structure is then decomposed in several subdomains. On each subdomain, preliminary calculations allow constructing a basis of local solutions, which are then condensed on unknown degrees of freedom of a coarse mesh covering the whole structure. The full resolution in the fine mesh is then substituted by solving a problem on the coarse mesh only, allowing computational times saving of several orders of magnitude. The technique is first applied on a linear elastic structure. An error analysis is conducted, and several applications are proposed, including an industrial case comprising a structure with a mesh comprising more than a billion finite elements, or a calculation on a microstructure whose description is provided by micro tomography. CMCM is extended to unstructured and non conforming meshes. The technique is finally extended to other problems, such as thermo-elasticity and nonlinear problems. It is shown that the method allows obtaining a satisfying approximation of the local solution on the fine mesh for large computational costs reduction
Effet des hétérogénéités sur le comportement mécanique du béton à l'échelle mésoscopique : apports de la micro-tomographie à rayons-x in-situ combinée à une modélisation E-FEM by Olga Stamati( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

This doctoral thesis investigates the impact of the meso-scale heterogeneities of concrete (aggregates and macro-pores) on its macroscopic mechanical response. A combined numerical and experimental approach is adopted to study the progressive evolution of the 3D fracturing processes of micro-concrete specimens under uniaxial tension, uniaxial compression and triaxial compression. Part of the originality of this work lies in the exploration of multiple loading paths on concrete samples of realistic composition (including cement, sand, aggregates and water) and in the in-situ nature of the experiments conducted. The experimental campaign is performed inside an x-ray scanner, which allows the internal structure of the material to be non-destructively captured and its evolution from the intact (before loading) until the damaged (after unloading) state to be followed and quantified. The 3D images coming from the x-ray scans are first analysed in order to quantitatively describe the morphology of the meso-structure (aggregates, mortar matrix and macro-pores). A timeseries analysis of the set of 3D images coming from each in-situ test follows, in order to measure the 3D kinematic fields (displacement and strain fields) throughout the experiments. On the numerical side, the identified morphologies coming from the intact x-rays scans are given as an input to a FE meso-model with enhanced discontinuities. The originality of the numerical simulations comes from their 3D nature and the consideration of the actual meso-structure of the micro-concrete specimens, based on the segmentation of the three phases of the material. After a calibration of the model in uniaxial tension, its predictive ability is challenged under different stress paths in compression. An extensive comparison is presented between experimental and numerical observations, in terms of macroscopic responses, displacement fields, fracturing processes and failure patterns. The typical asymmetric behaviour of concrete in tension and compression, as well as the increase of strength and ductility with the increase of confinement are sufficiently captured numerically. Starting from an x-ray scan, it is shown that the model is able to satisfactorily reproduce some of the basic characteristic features of the failure modes observed experimentally for the different loading paths studied. While validating the numerical results and through a combination of numerical and experimental observations, the significant impact of the meso-scale heterogeneities on the local failure mechanisms is revealed. It is shown that, for the studied material, the shape and location of the largest aggregates and macro-pores are essentially driving the fracture patterns under simple tension, simple compression and triaxial compression. The predictive ability of the model strongly suggests that the explicit representation of these heterogeneities is the key feature that allows this predictive power. A further insight into the impact of the meso-structure is obtained by investigating virtual concrete morphologies, generated by modifying the real meso-structures coming from the x-ray scans
Contributions to multiscale modelling of quasi-brittle damage in heterogeneous materials by Thi hai nhu Nguyen( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The objective of thesis is propose modeling methodologies based on multiscale approaches and advanced numerical methods for crack propagation to model the damage in heterogeneous quasi-brittle materials. A first part is devoted to constructing continuous crack propagation models associated to heterogeneous models by identification of a phase field model for crack propagation. A second part aims at constructing directly the numerical response of the homogenized model using a multilevel method based on the phase field method. The techniques developed in the present PhD works can be applied to cementious materials like plaster, concrete or rocks, as well as more periodic heterogeneous materials such as 3D printed lattice structures
Modeling of complex microcracking in cement based materials by combining numerical simulations based on a phase-field method and experimental 3D imaging by Thanh Tung Nguyen( )

1 edition published in 2015 in English and held by 1 WorldCat member library worldwide

Une approche combinant simulation numérique et expérimentation est développée pour modéliser la microfissuration complexe dans des matériaux hétérogènes cimentaires. Le modèle numérique proposé a permis de prévoir précisément en 3D l'initiation et la propagation des microfissures à l'échelle de la microstructure réelle d'un échantillon soumis à un chargement de compression. Ses prévisions ont été validées par une comparaison directe avec le réseau de fissures réel caractérisé par des techniques d'imagerie 3D. Dans une première partie, nous développons et testons les outils de simulation numérique. Plus précisément, la méthode de champ de phase est appliquée pour simuler la microfissuration dans des milieux fortement hétérogènes et ses avantages pour ce type de modélisation sont discutés. Ensuite, une extension de cette méthode est proposée pour tenir compte d'un endommagement interfacial, notamment aux interfaces inclusion/matrice. Dans une deuxième partie, les méthodes expérimentales utilisées et développées au cours de cette thèse sont décrites. Les procédures utilisées pour obtenir l'évolution du réseau de fissures 3D dans les échantillons à l'aide de microtomographie aux rayons X et d'essais mécaniques in-situ sont présentées. Ensuite, les outils de traitement d'image utilisant la corrélation d'images volumiques, pour extraire les fissures des images en niveaux de gris avec une bonne précision, sont détaillés. Dans une troisième partie, les prévisions du modèle numérique sons comparées avec les données expérimentales d'un matériau modèle en billes de polystyrène expansé intégrées dans une matrice de plâtre dans un premier temps, et, dans un second temps, d'un béton léger plus complexe. Plus précisément, nous utilisons les données expérimentales pour identifier les paramètres microscopiques inconnus par une approche inverse, et utilisons les déplacements expérimentaux déterminés par corrélation d'images volumiques pour définir des conditions limites à appliquer sur les bords de sous-domaines dans l'échantillon pour les simulations. Les comparaisons directes de réseaux de microfissures 3D et de leur évolution montrent une très bonne capacité prédictive du modèle numérique
Sur l'analyse multiéchelle du changement de morphologie du PET sous l'effet de la température ou des sollicitations mécaniques by Yang Hao Gong( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

In this thesis work, we are interested in simulating the evolution of the microstructure of a polymer. In particular, we have studied in the morphology change of polyethylene terephthalate (PET) under different mechanisms. These simulations carried out by the phase field simulation. This method based on the Cahn-Hilliard equation or the Ginzburg-Landau equation. It uses an order parameter to describe the state of material, thermodynamic and kinetic variables. Thus we can describe the microstructure evolution without tracking the interface (which would require complex remeshing) and reproduce the evolution of the crystalline structure within the polymers, for example the growth of spherulites which appear during crystallization induced by temperature. Within the scope the morphology changing by the temperature, the evolution of phase field simulation is performed by the finite difference method and the finite element method. The kinetic coefficient is adjusted in order to fit the experiment data in of the literature. We introduce the multiphase field model (the MPF model) in order to simulate the evolution of several spherulites and to describe the junction of spherulites. The growth and junction of spherulites have been modeled by the finite element method and nicely reproduced in comparing the experimental evolution of isothermal crystallization of a polymer. Comparing these results with the Avrami macroscopic model, an evaluation of the Avrami constant, K (T), was discussed according to the fluctuations of the initial conditions (positions and size of the germs).In the following part, we study the crystallization induced by mechanical deformation. We are interested in the viscoelastic model to simulate the induced crystallization of PET in plane stress. The phase field model coupled to mechanics will be presented. Different viscoelastic behaviors have been considered for each phase. The influence on crystallization and orientation of the deformation, the stress velocity and the contrast between the phases are studied and compared qualitatively with the experimental observations. This is a preliminary study that will have to be continued in order to predict a more realistic morphology
Approche expérimentale de l'homogénéisation numérique by Thibault Dassonville( )

1 edition published in 2020 in French and held by 1 WorldCat member library worldwide

Numerical approach of experimental homogeneisation
 
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Computational Homogenization of Heterogeneous Materials with Finite Elements
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