Stéphane Lejeunes

Stéphane Lejeunes
French National Centre for Scientific Research | CNRS · LMA UMR7031

PhD Habil

About

85
Publications
10,925
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267
Citations
Introduction
Stéphane Lejeunes currently works at the Laboratory of Mechanics and Acoustics, Aix-Marseille Univ & Centrale Marseille & French National Centre for Scientific Research. Stéphane does research in Scientific Computing, Modeling and Characterization of Materials, Numerical Simulation of Materials and Structures. Its current projects are 'Modeling and Simulation of aging of rubber' & 'Space-Time solvers for multiphysics problems'
Additional affiliations
September 2010 - present
Ecole Centrale de Marseille
Position
  • Part-time Lecturer
Description
  • Lectures: - Thermodynamics of Materials at Finite Strain - Introduction to structural analysis with Abaqus
December 2008 - present
French National Centre for Scientific Research
Position
  • Engineer
November 2006 - August 2008
Ecole Centrale de Marseille
Position
  • Research Assistant
Education
March 2019 - March 2019
Aix-Marseille University
Field of study
October 2002 - March 2006
Aix-Marseille University
Field of study
September 2001 - September 2001
Ecole Centrale Marseille
Field of study

Publications

Publications (85)
Article
This paper gives an intuitive numerical multi-scale method to estimate damping in anisotropic viscoelastic hybrid composite structures using finite element analysis. Different CFRP-R (CFRP with Rubber) architectures, both microstructural and macrostructural, are studied and compared in order to maximize damping but also to minimize rigidity loss. H...
Article
In this study we investigate a stabilized space-time formulation for linear and non-linear elastodynamics. We use Isogeometric Analysis (IGA) in order to benefit from its numerical qualities. We focus on two points: the formulation of stabilized weak-forms in a linear and non-linear context and the interest of using continuous Galerkin schemes in s...
Article
Full-text available
The ITER machine has been classified as a Basic Nuclear Installation French nuclear regulator (INB n ◦ 174), which implies that it will be the first fusion reactor to go through complete French nuclear licencing. The combination of mechanic and electromagnetic phenomena with the heat loads caused by neutron streaming requires a multi-physics approa...
Conference Paper
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Article
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We explore the formulation of nearly incompressible behaviors at finite strain in the context of a hybrid or a mixed energy. Such an energy is a function of both an isochoric deformation and a pressure-like quantity that can be considered as an internal variable. From thermodynamical and physical considerations, new energy functions are developed t...
Conference Paper
Despite some early pioneering attempts in the 1970s and 1980s, space-time methods did not experience the same success as finite-elements combined with discrete time-integration scheme (implicit/explicit finite-differences, Newmark, HHT, etc). Since these years, the software and hardware context has changed and we propose to rediscuss the interest o...
Conference Paper
In this work, we propose to discuss about the interrest of the Isogeometric Analysis as a computational framework for the numerical simulation of rubber structures with a multi-field approach. We show that we can construct stable approximations for hyperelastic problems using the same approach as that used for finite-elements. We also show that the...
Conference Paper
In this work, we propose a constitutive model for the representation of thermal ageing phenomena in a butadiene rubber filled with carbon blacks. This model is based on a thermo-chemo-mechanical framework and takes into account the strong couplings that occur during ageing. This model has been implemented in a multi-fields finite element framework....
Article
This paper focuses on the characterization and the modeling of the behavior of butadiene rubber filled with carbon black that can be subjected to thermal aging phenomena. We consider only anaerobic thermal aging (i.e. we neglect diffusion effects) and we follow both the evolution of the behavior and that of the cross-linked network during aging wit...
Conference Paper
La méthode des éléments finis est aujourd'hui la méthode numérique la plus utilisée en mécanique. Généralement utilisée dans la discrétisation de l'espace, elle est souvent associée à une méthode de type différences finies pour la résolution en temps. Nous nous intéressons dans cette étude à appliquer un schéma de discrétisation en espace et en tem...
Conference Paper
La méthode des éléments finis est aujourd’hui la méthode numérique la plus utilisée en mécanique. Généralement utilisée dans la discrétisation de l’espace, elle est souvent associée à une méthode de type différences finies pour la résolution en temps. Nous nous intéressons dans cette étude à appliquer un schéma de discrétisation en espace et en tem...
Conference Paper
The Helmoltz approach with a volumetric/isochoric splitting is widely used in the literature to describe the nearly incompressible behavior of rubber like materials. Alternatively to this approach it can be interesting to formulate the constitutive equations from the Gibbs approach especially for chemical active materials but this approach is less...
Article
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In this paper we investigate the modeling of chemo-physical evolution due to thermo-mechanical loadings at finite strain in soft materials. In particular we discuss the question of a proper and consistent thermodynamical formulation in the case of nearly incompressible materials. The objective of this phenomenological modeling is to represent the t...
Conference Paper
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In this paper, we focus on the development of isogeometric models to tackle the simulation of elastomers under coupled thermomechanical complex loading and self-heating phenomena.
Conference Paper
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In this contribution, we investigate the potential and the interest of the isogeometric analysis in the context of weakly compressible materials at large strains submitted to thermomechanical loading. Classical finite element models and isogeometric models are compared in term of accuracy, robustness and numerical efficiency. The application target...
Article
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This work focuses on the characterization and the modelling of the complex dynamical behavior of a bu- tadiene rubber filled with carbon black. This material is used in helicopter rotors and submitted to severe operating conditions. In particular the effects of the environmental temperature, of the amplitudes and frequencies of cyclic loading are s...
Article
This paper focuses on the modeling of thermo-chemo-mechanical behaviors of soft materials (polymer, rubber, etc.) at large strains within a rigorous thermodynamical framework. We consider thermo-viscoelastic materials involving chemical reactions that are described by a kinetic approach. Preliminary numerical tests are considered to prove the capab...
Conference Paper
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On présente dans cette communication l'extension du modèle de Delattre [1] au cas des sol-licitations multi-axiales ainsi que son application pour la simulation d'essais de compression/cisaillement sur paliers lamifiés élastomère-métal. Le modèle est basé sur une approche purement phénoménologique en grandes transformations qui permet à la fois de...
Presentation
Full-text available
Lecture slides on Constitutive modeling at Finite Strains given at Ecole Centrale Marseille
Article
A phenomenological hyperviscoelastic model is proposed. This model describes the multiaxial amplitude- and frequency-dependent behavior of the material. Moreover, thanks to the definition of new internal variables, the model is able to take into account the Payne effect. The experimental results of a characterization campaign performed on a butadie...
Conference Paper
Full-text available
A constitutive modelling of the behaviour of a filled rubber is proposed in order to describe its dynamical properties under large strain on a wide range of amplitudes and several frequencies. The model is able to take into account several phenomena experimentally observed such as the Payne effect. The model is then implemented in two FEM codes and...
Article
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This paper presents a continuum damage model based on two mechanisms: decohesion between fillers and matrix at a micro-scale followed by a crack nucleation at a macro-scale. That scenario was developed considering SEM observations and an original experimental procedure based on simple shear and tension specimens. Damage accumulation is related to f...
Chapter
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In this paper, we give a global overview of the latest advances in computational mechanics code design. We give a brief historical perspective of the evolution of finite element code design since the introduction of object-oriented programming in the 90’s. Then, we try to outline the structure of future computational tools. Besides classical archit...
Conference Paper
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Caractérisation et modélisation d'un élastomère dissipatif : applica-tion au pré-dimensionnement de pièces lamifiées élastomère-métal Résumé — Dans cette communication, on présente des essais de caractérisation réalisés sur un caoutchouc chargé. A partir de ces résultats, nous proposons un nouveau modèle de comportement capable de traduire les effe...
Conference Paper
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Dans cette communication, nous présentons une architecture de code dévolue au traitement de problèmes couplés (faiblement ou fortement). Ce travail intègre une réflexion sur la représentation par des objets, de champs physiques et sur une vision globale de construction de formulation éléments finis couplés intégrant le matériau. Cette architecture,...
Conference Paper
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Résumé — Dans cette communication, nous présentons une architecture de code dévolues au traitement de problèmes couplés (faiblement ou fortement). Ce travail intègre une réflexion sur représentation de champs physiques et sur une vision globale de construction de formulation éléments finis couplés intégrant la modélisation du comportement. Nous ill...
Conference Paper
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Résumé — Nous présentons dans cette communication un nouveau modèle de comportement couplé pour les élastomères chargés et dissipatifs qui prend en compte une forme d'évolution chimique du ma-tériau. Cette évolution est activé sous sollicitations thermo-mécaniques et impacte fortement le compor-tement du matériau. Une implémentation éléments-finis...
Conference Paper
Rubber parts are strongly sensitive to thermal effects and to the state of cure of the material which can evolve during utilisation. We propose a finite strain thermochemo- mechanical model to represent the phenomena related to this coupling. This model is based on the thermodynamics of irreversible processes and on the multiplicative decomposition...
Article
Full-text available
The dynamic behavior of filled rubber has been intensively studied during the last 20 years and a large number of finite strain models have been developed. However, many industrial applications involve small vibrations superimposed on large static preloads. In this specific case, the dynamic problem can be treated as a small amplitude problem near...
Article
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This paper presents a campaign of experimental tests performed on a silicone elastomer filled with silica particles. These tests were conducted under controlled temperatures (ranging from −55 °C to +70 °C) and under uniaxial tension and in shearing modes. In these two classes of tests, the specimens were subjected to cyclic loading at various defor...
Conference Paper
Filled rubber exhibits a complex behavior involving strong coupling of thermo-chemomechanical phenomena. In this paper, we introduce a nearly incompressible rheological model in finite strains which takes into account the thermo-chemo-mechanical couplings. For the mechanical part, this model is based on a visco-elasticity law. The thermal part take...
Conference Paper
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Résumé — Nous proposons une interface graphique, open-source, complètement intégrée à Abaqus qui permet de mettre en oeuvre rapidement et facilement les problèmes de localisation associés aux méthodes classiques d'homogénéisation. Partant d'un maillage de la microstructure, l'ajout de degrés de liberté supplémentaires permet de piloter simplement l...
Conference Paper
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Résumé — Dans cette communication, on présente un formalisme adapté à la linéarisation de comporte-ments autour d'un état pré-chargé et en grandes transformations. Ce formalisme générique est appliqué dans le cas d'un élastomère viscoélastique soumis à de petites vibrations avec pré-chargement statique. Par rapport aux approches existantes il perme...
Article
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The present work is concerned with the numerical integration of finite viscoelastic or viscoplastic models. A numerical integration scheme based on the definition of a flow direction and a flow amplitude as in elastoplasticity is proposed. The most original feature of this approach resides in a local correction of the direction and amplitude with a...
Article
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This paper presents an extension of the numerical reduction method, which has been proposed in Lejeunes etal. (Arch Appl Mech, 76:311–326, 2006), for modeling curved laminated structures of revolution such as for instance rubber bearings. This method based on high-order finite elements is developed in the context of nearly incompressible hyperelast...
Article
In this paper, a numerical integration scheme of the evolution laws for viscohyperelastic models is proposed. The starting points of the method are the exponential mapping (Reese et al., 1998) and the radial return (Weber et al., 1990; Simo, 1988). The originality of this work lies in the substitution of a differential tensorial system by a scalar...
Article
Full-text available
In this paper, a numerical integration scheme of the evolution laws for viscohyperelastic models is proposed. The starting points of the method are the exponential mapping (Reese et al., 1998) and the radial return (Weber et al., 1990; Simo, 1988). The originality of this work lies in the substitution of a differential tensorial system by a scalar...
Conference Paper
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This paper presents a hyper-vico-plastic constitutive model with damage, which is based both on the gener-alization of rheological models to finite strain and on a micro-physically motivated statistical approach. An experimental campaign of fatigue was realized and has allowed to study the fatigue behavior with respect to amplitude and frequency of...
Conference Paper
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Résumé : Ce papier présente une généralisation statistique de modèles rhéologiques étendus au cadre des grandes déformations afin de modéliser la réponse à des sollicitations complexes d'élastomères chargés. Cette méthode permet le passage d'un modèle rhéologique présentant un nombre fini de branches rhéologiques en parallèle, de type Maxwell par e...
Conference Paper
On presente, dans cette communication, l'application des travaux de thèse de S. Lejeunes à savoir des éléments finis réduits permettant de modéliser des structures lamifiées élastomère-métal qui sont largement utilisés dans les ensembles dynamiques d'hélicoptères (systèmes rotors et suspensions). Cette technique, visant à prédire le comportement et...
Conference Paper
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Résumé — Ce papier présente un modèle hyper-visco-plastique endommageable basé sur la gé-néralisation aux grandes déformations des modèles rhéologiques et sur une approche statistique, microphysiquement motivée. Une campagne d'essais permet de suivre le comportement du maté-riau à différents niveaux de fatigue. Un modèle d'endommagement de fatigue,...
Conference Paper
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Résumé — On propose dans cette communication un schéma numérique d'intégration de lois d'évolutions visco-hyperélastiques s'inspirant à la fois des méthodes par retour en exponentiel [5] et des méthodes par retour radial [8, 7]. L'originalité de ce schéma repose à la fois sur la substitution d'un système différentiel tensoriel, traduisant les lois...
Article
In this paper we present a model reduction technique, to find the equilibrium state at finite strain of tridimensional structures which have, invariant properties in a direction. Based on finite-elements formulation, this technique consists in the projection of the unknows fields on a polynomial basis in the purpose to reduce the problem dimension....
Conference Paper
Full-text available
In the aim of modeling the dissipative behavior of a filled silicon rubber we developed in (Boukamel et al. 2005) a statistical and microphysicaly- motivated hyper-visco-plastic model allowing loadings with a wide frequencies range. In particular the dependence of the behavior upon the frequency and amplitude of loading can be well obtained with a...
Article
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On propose, dans ce papier, une technique pour résoudre les problèmes d’équilibre de structures tridimensionnelles possédant des propriétés d’invariance selon une direction et dont le comportement présente des non-linéarités géométriques et matérielles. Basée sur une formulation en éléments finis, elle consiste à projeter sur une base polynomiale,...